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LINUX
IN A NUTSHELL
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Sixth Edition
LINUX
IN A NUTSHELL
Ellen Siever, Stephen Figgins, Robert Love,
and Arnold Robbins
Beijing • Cambridge • Farnham • Köln • Sebastopol • Taipei • Tokyo
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Linux in a Nutshell, Sixth Edition
by Ellen Siever, Stephen Figgins, Robert Love, and Arnold Robbins
Copyright © 2009 Ellen Siever, Stephen Figgins, and Robert Love. All rights reserved.
Printed in the United States of America.
Publishedby O’ReillyMedia,Inc.,1005GravensteinHighwayNorth, Sebastopol,CA95472.
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Printing History:
January 1997: First Edition.
February 1999: Second Edition.
August 2000: Third Edition.
June 2003: Fourth Edition.
July 2005: Fifth Edition.
September 2009: Sixth Edition.
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While every precaution has been taken in the preparation of this book, the publisher and
authors assume no responsibility for errors or omissions, or for damages resulting from the
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ISBN: 978-0-596-15448-6
[M]
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v
Chapter 1
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Excitement of Linux 2
Distribution and Support 3
Commands on Linux 3
What This Book Offers 4
Sources and Licenses 6
Beginner’s Guide 7
Communication 7
Comparisons 8
File Management 8
Media 9
Printing 9
Programming 9
Program Maintenance 10
Searching 10
Shell Programming 11
Storage 11
System Status 11
Text Processing 12
Miscellaneous 13
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vi | Table of Contents
2. System and Network Administration Overview . . . . . . . . . . . . . . . . . 14
Common Commands 14
Clocks 14
Daemons 14
Hardware 15
Host Information 15
Installation 16
Mail 16
Managing Filesystems 16
Managing the Kernel 17
Networking 18
Printing 18
Security and System Integrity 18
Starting and Stopping the System 19
System Activity and Process Management 19
Users 20
Miscellaneous 20
Overview of Networking 21
TCP/IP Administration 21
NFS and NIS Administration 22
Overview of TCP/IP 22
IP Addresses 23
Gateways and Routing 25
Name Service 26
Configuring TCP/IP 27
Troubleshooting TCP/IP 28
Overview of Firewalls and Masquerading 28
Overview of NFS 29
Administering NFS 30
Daemons 30
Exporting Filesystems 30
Mounting Filesystems 30
Overview of NIS 31
Servers 31
Domains 31
NIS Maps 31
Map Manipulation Utilities 31
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Table of Contents | vii
Administering NIS 32
Setting Up an NIS Server 32
Setting Up an NIS Client 32
NIS User Accounts 32
RPC and XDR 32
3. Linux Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Alphabetical Summary of Commands 34
4. Boot Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
The Boot Process 505
LILO: The Linux Loader 506
The LILO Configuration File 507
The lilo Command 514
lilo Command Options 515
LILO Boot Errors 516
GRUB: The Grand Unified Bootloader 516
Installing GRUB 518
The GRUB Configuration File 521
Using the Menu Interface 523
The GRUB Shell 523
GRUB Commands 525
Command-Line and Global Menu Commands 526
Command-Line and Menu-Entry Commands 530
Dual-Booting Linux and Windows 2000/XP/Vista 536
Boot-Time Kernel Options 539
initrd: Using a RAM Disk 541
5. Package Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
Yum: Yellowdog Updater Modified 545
The yum Command 545
yum Command Summary 547
Plugins and yum-utils 551
The Red Hat Package Manager 552
RPM Package Concepts 552
The rpm Command 553
RPM Examples 563
The rpmbuild Command 564
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viii | Table of Contents
The Debian Package Manager 565
Files 565
Package Priorities 566
Package and Selection States 567
Package Flags 567
Scripts 568
Debian Package Manager Command Summary 569
6. The Bash Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
Overview of Features 597
Invoking the Shell 597
Options 598
Arguments 599
Syntax 599
Special Files 599
Filename Metacharacters 599
Quoting 600
Command Forms 602
Redirection Forms 602
Coprocesses 604
Functions 605
Variables 606
Variable Substitution 606
Built-in Shell Variables 607
Other Shell Variables 609
Arrays 611
Special Prompt Strings 612
Arithmetic Expressions 613
Operators 613
Examples 613
Command History 614
Line-Edit Mode 614
The fc Command 614
Programmable Completion 615
Job Control 617
Command Execution 618
Restricted Shells 619
Built-in Commands 619
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Table of Contents | ix
7. Pattern Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
Filenames Versus Patterns 654
Metacharacters 655
Search Patterns 655
Replacement Patterns 656
Metacharacters, Listed by Program 657
Examples of Searching 658
Examples of Searching and Replacing 659
8. The Emacs Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661
Conceptual Overview 661
Modes 661
Buffer and Window 662
Point and Mark 662
Kill and Yank 662
Notes on the Tables 662
Absolutely Essential Commands 663
Command-Line Syntax 663
Summary of Commands by Group 663
File-Handling Commands 663
Cursor-Movement Commands 664
Deletion Commands 664
Paragraphs and Regions 665
Stopping and Undoing Commands 665
Transposition Commands 665
Search Commands 665
Capitalization Commands 666
Word-Abbreviation Commands 666
Buffer-Manipulation Commands 666
Window Commands 666
Special Shell Characters 667
Indentation Commands 667
Centering Commands 668
Macro Commands 668
Detail Information Help Commands 668
Help Commands 669
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x | Table of Contents
Summary of Commands by Key 669
Control-Key Sequences 669
Meta-Key Sequences 671
Summary of Commands by Name 672
9. The vi, ex, and vim Editors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677
Conceptual Overview 677
Command-Line Syntax 678
Command-Line Options 678
Review of vi Operations 681
Command Mode 681
Insert Mode 681
Syntax of vi Commands 681
Status-Line Commands 683
vi Commands 683
Movement Commands 683
Insert Commands 686
Edit Commands 687
Saving and Exiting 688
Accessing Multiple Files 689
Window Commands 689
Interacting with the System 690
Macros 691
Miscellaneous Commands 691
vi Configuration 692
The :set Command 692
Options Used by :set 692
Sample .exrc File 696
ex Basics 696
Syntax of ex Commands 696
Addresses 696
Address Symbols 697
Options 697
Alphabetical Summary of ex Commands 697
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Table of Contents | xi
10. The sed Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
Conceptual Overview 711
Typical Uses of sed 711
sed Operation 712
Command-Line Syntax 712
Standard Options 712
GNU sed Options 713
Syntax of sed Commands 713
Pattern Addressing 714
Pattern Addressing Examples 714
GNU sed Regular Expression Extensions 715
Group Summary of sed Commands 715
Basic Editing 716
Line Information 716
Input/Output Processing 716
Yanking and Putting 716
Branching Commands 717
Multiline Input Processing 717
Alphabetical Summary of sed Commands 717
11. The gawk Programming Language . . . . . . . . . . . . . . . . . . . . . . . . . . 726
Conceptual Overview 726
Command-Line Syntax 727
Standard Options 728
Important gawk Options 728
Patterns and Procedures 729
Patterns 729
Procedures 730
Simple Pattern-Procedure Examples 730
Built-in Variables 731
Operators 732
Variable and Array Assignment 732
Escape sequences 733
Octal and Hexadecimal Constants in gawk 734
User-Defined Functions 734
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xii | Table of Contents
gawk-Specific Features 735
Coprocesses and Sockets 735
Profiling 735
File Inclusion 736
Internationalization 736
Implementation Limits 737
Group Listing of awk Functions and Commands 737
Alphabetical Summary of awk Functions and Commands 738
Output Redirections 746
printf Formats 746
12. Source Code Management: AnOverview . . . . . . . . . . . . . . . . . . . . . 749
Introduction and Terminology 749
Usage Models 751
Source Code Management Systems 752
Other Source Code Management Systems 753
13. The Subversion Version Control System . . . . . . . . . . . . . . . . . . . . . . . 755
Conceptual Overview 755
Basic Version-Control Operations 755
Key Features 756
Special File Properties 757
Obtaining Subversion 759
Using Subversion: A Quick Tour 759
The Subversion Command Line Client: svn 761
Common svn Options 761
svn Subcommands 766
Repository Administration: svnadmin 794
Common svnadmin Options 794
Common svnadmin Subcommands 795
Examining the Repository: svnlook 799
svnlook Options 799
svnlook Subcommands 800
Providing Remote Access: svnserve 803
svnserve Options 804
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Table of Contents | xiii
14. The Git Version Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
Conceptual Overview 805
Git Repository Format 806
Referring to Commits 806
Using Git: A Quick Tour 808
Before You Start 808
Example: The Linux Kernel Repository 809
Creating and Sharing a New Repository 810
The Git Command Line Client: git 811
The git Command 811
Accessing Git’s Online Help 812
git Subcommands 812
15. Virtualization Command-LineTools . . . . . . . . . . . . . . . . . . . . . . . . . . 837
Conceptual Overview 838
System Requirements 838
Virtualization Technology 839
Network Concepts 839
libvirt Tools and Terminology 839
Basic Virtualization Operations 840
Creating Virtual Systems 840
Managing Virtual Systems 841
Graphic and Console Interfaces 842
Configuring Networks 842
MAC Addresses 844
Making Changes to Virtual Machines 844
Creating and Manipulating Disk Image Files 844
Xen 845
Paravirtualization and Architecture 846
Xen Networking 846
Xen Commands 846
KVM 849
QEMU 849
Ubuntu Builder Scripts 850
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xiv | Table of Contents
libvirt and Red Hat Virtual Machine Manager 850
XML Configuration Files 850
Connection URIs 850
Connection URI Examples 850
Remote GUI control 851
IP Forwarding and libvirt Networking 851
libvirt and Virtual Machine Manager Commands 852
VMware ESX 3.5 862
ESX Management Client 862
Virtual Center 862
VMware Networking 863
Shared Disks 863
Snapshots 863
VMware Tools 864
ESX Server Commands 864
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
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xv
This is the Title of the Book, eMatter Edition
Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
Chapter 2
Preface
This is a book about Linux, a freely available clone of the Unix operating system
whose uses range from embedded systems and personal data assistants (PDAs) to
corporate servers, web servers, and massive clusters that perform some of the
world’s most difficult computations.
Whether you are using Linux for personal software projects, for a small office or
home office (the so-called SOHO environment), to provide services to a small
group of colleagues, or to administer a site responsible for millions of email and
web connections each day, you need quick access to information on a wide range
of tools. This book covers all aspects of administering and making effective use of
Linux systems. Among its topics are booting, package management, and revision
control. But foremost in Linux in a Nutshell are the immeasurable utilities and
commands that make Linux one of the most powerful and flexible systems
available.
In addition to the tools and features written specifically for it, Linux has inherited
many from the Free Software Foundation’s GNU project, the Berkeley Software
Distribution (BSD), the X Window System, and contributions from major corpo-
rations as well as the companies that created the major Linux distributions. More
recent projects extend Linux in exciting ways, some through changes to the kernel
and some through libraries and applications that radically change the user’s
experience.
This book is a quick reference for the basic commands and features of the Linux
operating system. As with other books in O’Reilly’s “In a Nutshell” series, this
book is geared toward users who know what they want to do and have some idea
how to do it, but can’t always remember the correct command or option. The
sixth edition has been examined from start to end and checked against the most
common Linux distributions (Debian, Ubuntu, Fedora, and SUSE) so that it
reflects the most useful and popular commands.
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xvi | Preface
This is the Title of the Book, eMatter Edition
Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
Organization of This Book
This book is a reference to the most important commands and utilities available
on Linux systems.
Chapter 1, Introduction, explains Linux’s strengths and the key aspects of working
with Linux, and lays out the scope of this book.
Chapter 2, System and Network Administration Overview, introduces TCP/IP
networking and the Linux commands used for system administration and
network management.
Chapter 3, Linux Commands, is the core of the book, a reference listing of
hundreds of the most important shell commands available on Linux.
Chapter 4, Boot Methods, covers the commands used to control booting on Linux,
particularly LILO and GRUB.
Chapter 5, Package Management, explains the apt series of commands that
manage updating and installation on Debian, and the RPM system and yum used
by Red Hat/Fedora, Novell/SUSE, and several other distributions of Linux.
Chapter 6, The Bash Shell, documents Bash, the default command-line interpreter
on Linux.
Chapter 7, Pattern Matching, introduces regular expressions and explains how
different tools interpret these powerful tools for searching and text processing.
Chapter 8, The Emacs Editor, provides reference information on Emacs, a text
editor and full-featured development environment.
Chapter 9, The vi, ex, and vim Editors, describes the classic vi editor that is the
most popular text-manipulation tool on Linux.
Chapter 10, The sed Editor, describes this “stream editor” that is useful for
processing files in standardized ways.
Chapter 11, The gawk Programming Language, documents another valuable tool
for processing text files, the GNU version of awk that is the default on Linux
systems.
Chapter 12, Source Code Management: An Overview, provides the background for
understanding Subversion and Git, which are valuable tools for tracking changes
to files and projects, and are discussed in the following two chapters.
Chapter 13, The Subversion Version Control System, provides a description of a
popular source code management and version-control tool.
Chapter 14, The Git Version Control System, describes a distributed version
control system with many advanced features including the ability to access project
history even when not connected to a central server.
Chapter 15, Virtualization Command-Line Tools, describes virtualization on
Linux, which allows multiple virtual servers to run on a single physical server.
Tools covered include Xen, KVM, the libvirt API, and the VMware command-line
interface.
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Preface | xvii
This is the Title of the Book, eMatter Edition
Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
Other Resources
This book doesn’t tell you how to install and get up to speed on a Linux system. For
that, you’ll probably want O’Reilly’s Running Linux, by Matthias Kalle Dahlheimer
and Matt Welsh, an in-depth guide suitable for all major distributions. For
networking information, check out Linux Network Administrator’s Guide by Tony
Bautts et al. (O’Reilly). If you’re new to Linux/Unix concepts, O’Reilly’s Learning
the Unix Operating System, by Jerry Peek et al., provides introductory information. In
addition to these and other Linux titles, O’Reilly’s wide range of Unix, X, web-
related, and scripting and programming language titles may also be of interest.
Online Documentation
The Internet is full of information about Linux. One of the best resources is the
Linux Documentation Project at http://www.tldp.org (or one of the dozens of
mirror sites around the world), which has numerous short guides called
HOWTOs, along with some full manuals. For online information about the GNU
utilities covered in this book, consult http://www.gnu.org (also widely mirrored).
The Free Software Foundation, which is in charge of the GNU project, publishes
its documentation in a number of hardcopy and online books about various tools.
Each distribution maintains its own website, and contains documentation for the
software it provides as well as guides to maintaining your system under that
distribution.
Websites
As befits a hot phenomenon, Linux is the central subject of several websites and a
frequent topic of discussion on others. Some sites offer original content; others
just have links to articles posted elsewhere and threaded discussions (which can
be a useful service). Among the sites frequented by Linux users are:
http://lwn.net
Linux Weekly News, a site with weekly in-depth articles and frequent news
updates
http://www.linuxgazette.net
Linux Gazette, a site published monthly with articles and tips in many languages
http://www.linuxquestions.org
A very popular source for technical guidance, including a growing wiki (site
maintained by user contributions) at http://wiki.linuxquestions.org
http://linuxsecurity.com
Linux Security, a collection of security-related news
http://linuxinsider.com
Linux Insider, a news feed
http://linuxtoday.com
Linux Today, another news feed
http://slashdot.org
Slashdot, a famous discussion list
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xviii | Preface
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Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
Linux Journal and Linux Magazine
Linux Journal and Linux Magazine are monthly magazines for the Linux commu-
nity, written and published by a number of Linux activists. These magazines are two
of the oldest among many monthly print and online magazines devoted to Linux.
With both print editions and websites, they offer articles ranging from questions and
answers for novices to kernel programming internals. Linux Journal, at http://www.
linuxjournal.com, is the older magazine. Linux Magazine is at http://www.linux-mag.
com.
Usenet Newsgroups
Most people can receive Usenet news at work or through their ISPs. While this
communications technology has lost ground in the past several years to web-based
threaded discussions, it is still a valuable source of help and community connec-
tions on many topics. The following Linux-related newsgroups are popular:
comp.os.linux.announce
A moderated newsgroup containing announcements of new software, distribu-
tions, bug reports, and goings-on in the Linux community. All Linux users
should read this group. Submissions may be mailed tocola@stump.algebra.com.
comp.os.linux.development.apps
Guidance for using features of Linux for application development, and for
understanding the effects of the operating system on user-space programs.
comp.os.linux.development.system
Discussions about developing the Linux kernel and the system itself.
comp.os.linux.networking
Discussions relating to networking with Linux.
comp.os.linux.x
Help on getting the X graphical window system to work. This list used to see
some of the highest traffic of any Linux group back when distributions had
more trouble setting up graphics automatically. This is no longer the case,
thanks to the increasing sophistication of autodetection and configuration
software.
There are also several newsgroups devoted to Linux in languages other than
English, as well as newsgroups and online forums for the different distributions.
Online Linux Support
There are many ways of obtaining help online, where volunteers from around the
world offer expertise and services to assist users with questions and problems.
Thefreenode IRC service is an Internet relay chat network devoted to so-called
“peer-directed” projects, particularly those involving free software. Some of its
channels are designed to provide online Linux support services.
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Preface | xix
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Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
Internet relay chat is a network service that allows you to talk interactively on the
Internet to other users. IRC networks support multiple channels where different
groups of people type their thoughts. Whatever you type in a channel is seen by
all other users of that channel.
There are a number of active channels on the freenode IRC network, where you will
find users 24 hours a day, 7 days a week who are willing and able to help you solve
any Linux problems you may have, or just chat. You can use this service by
installing an IRC client (some distributions install them by default), connecting to
server name irc.freenode.org:6667, and joining a channel focusing on Linux, such as:
#linpeople
General help and discussion
#debian
Help for Debian distribution
#gentoo
Help for Gentoo distribution
#redhat
Help for Red Hat distribution
#suse
Help for SUSE distribution
And so on. Please be sure to read up on the rules of chat etiquette before chatting.
In particular, the participants in these groups tend to expect people to read docu-
mentation and do some experimentation before asking for help with a problem.
Some IRC clients include Xchat, Konqueror, and KVirc. Note that these are all
graphical programs and as such are not described in this book.
Linux User Groups
Many Linux User Groups around the world offer direct support to users. Typi-
cally, Linux User Groups engage in such activities as installation days, talks and
seminars, demonstration nights, and purely social events. Linux User Groups are
a great way of meeting other Linux users in your area. There are a number of
published lists of Linux User Groups. Linux Online (http://www.linux.org) has a
list of Linux user groups organized by country at http://www.linux.org/groups.
Using Code Examples
This book is here to help you get your job done. In general, you may use the code
in this book in your programs and documentation. You do not need to contact
O’Reilly for permission unless you’re reproducing a significant portion of the
code. For example, writing a program that uses several chunks of code from this
book does not require permission. Selling or distributing a CD-ROM of examples
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Copyright © 2009 O’Reilly & Associates, Inc. All rights reserved.
from O’Reilly books does require permission. Answering a question by citing this
book and quoting example code does not require permission. Incorporating a
significant amount of example code from this book into your product’s documen-
tation does require permission.
We appreciate, but do not require, attribution. An attribution usually includes the
title, author, publisher, and ISBN. For example: “Linux in a Nutshell, Sixth
Edition, by Ellen Siever, Stephen Figgins, Robert Love, and Arnold Robbins. Copy-
right 2009 Ellen Siever, Stephen Figgins, and Robert Love, 978-0-596-15448-6.”
If you feel your use of code examples falls outside fair use or the permission given
above, feel free to contact the publisher at permissions@oreilly.com.
Conventions
This desktop quick reference follows certain typographic conventions:
Bold
Used for commands, programs, and options. All terms shown in bold are
typed literally.
Italic
Used to show arguments and variables that should be replaced with user-
supplied values. Italic is also used to introduce new terms, indicate filenames
and directories, and to highlight comments in examples.
Constant width
Used to show the contents of files or the output from commands.
Constant width bold
Used in examples to show commands or other text that should be typed liter-
ally by the user.
Constant width italic
Used in examples to show text that should be replaced with user-supplied
values.
$ Used in some examples as the bash shell prompt ( $ ).
[ ]
Surround optional elements in a description of syntax. (The brackets them-
selves should never be typed.) Note that many commands show the argument
[files]. If a filename is omitted, standard input (e.g., the keyboard) is
assumed. End with an end-of-file character.
EOF
Indicates the end-of-file character (normally Ctrl-D).
| Used in syntax descriptions to separate items for which only one alternative
may be chosen at a time.
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Preface | xxi
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This icon indicates a note, which is an important aside to its nearby
text.
This icon indicates a warning.
A final word about syntax. In many cases, the space between an option and its
argument can be omitted. In other cases, the spacing (or lack of spacing) must be
followed strictly. For example, -wn (no intervening space) might be interpreted
differently from -w n. It’s important to notice the spacing used in option syntax.
How to Contact Us
We have tested and verified all of the information in this book to the best of our
ability, but you may find that features have changed (or even that we have made
mistakes!). Please let us know about any errors you find, as well as your sugges-
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Acknowledgments
This sixth edition of Linux in a Nutshell is the result of the cooperative efforts of
many people. Many thanks to Avery Pennarun for writing the Git chapter. Thanks
also to Simon St.Laurent and Andy Oram for their editorial skills. For technical
review, thanks go to Greg Goddard, Leam Hall, Forrest Humphrey, Josh More,
and Dave Pawson.
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1
Chapter 1Introduction
1
Introduction
It is hard to chart the rise of Linux without risking the appearance of exaggera-
tion and hyperbole. During the past few years alone, Linux has grown from a
student/hacker playground to an upstart challenger in the server market to a well-
respected system taking its rightful place in educational and corporate networks.
Many serious analysts claim that its trajectory has just begun, and that it will
eventually become the world’s most widespread operating system.
Linux was first developed by Linus Torvalds at the University of Helsinki in
Finland. From his current location in Silicon Valley, Linus continues to centrally
coordinate improvements. The Linux kernel continues to develop under the dedi-
cated cultivation of a host of other programmers and hackers all over the world,
joined by members of programming teams at major computer companies, all
connected through the Internet.
By “kernel,” we mean the core of the operating system itself, not the applications
(such as the compiler, shells, and so forth) that run on it. Today, the term “Linux”
is often used to mean a software environment with a Linux kernel, along with a
large set of applications and other software components. In this larger meaning,
many people prefer the term GNU/Linux, which acknowledges the central role
played by tools from the Free Software Foundation’s GNU project as comple-
ments to the development of the Linux kernel.
Linux systems cannot be technically referred to as a “version of Unix,” as they
have not undergone the required tests and licensing. * However, Linux offers all
the common programming interfaces of standard Unix systems, and, as you can
see from this book, all the common Unix utilities have been reimplemented on
Linux. It is a powerful, robust, fully usable system.
*Before an operating system can be called “Unix,” it must be branded by The Open Group.
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2 | Chapter1: Introduction
The historical impact of Linux goes beyond its role as a challenge to all versions of
Unix as well as Microsoft Windows, particularly on servers. Linux’s success has
also inspired countless other free software or open source (defined at http://
opensource.org) projects, including Samba, GNOME, and a mind-boggling collec-
tion of innovative projects that you can browse at numerous sites like SourceForge
(http://sourceforge.net) and Freshmeat (http://freshmeat.net). As both a platform
for other developers and a development model, Linux gave a tremendous boost to
the GNU project and has also become a popular platform for Java development.
In short, Linux is a focal point in the most exciting and productive free-software
movement ever seen.
If you haven’t obtained Linux yet, or have it but don’t know exactly how to get
started using it, see “Other Resources” on page xvii.
The Excitement of Linux
Linux is, first of all, free software: anyone can download the source from the
Internet or buy it on a low-cost CD-ROM. But Linux is becoming well known
because it’s more than just free software—it’s unusually good software. You can
get more from your hardware with Linux and be assured of fewer crashes; even its
security is better than many commercial alternatives.
Linux first appeared in organizations as ad hoc installations by hackers running
modest web servers or development systems at universities and research institu-
tions, but it now extends deeply into corporations around the world. People
deploying Linux for mission-critical systems tend to talk about its ample practical
advantages, such as the ability to deliver a lot of bang for the buck and the ease of
deploying other powerful tools on Linux, such as Apache, Samba, and Java envi-
ronments. They also cite Linux’s ability to grow and sprout new features of
interest to large numbers of users. But these advantages can be traced back to the
concept of software freedom, which is the root of the broad wave of innovation
driving Linux.
As free software, Linux revives the grand creativity and the community of sharing
that Unix was long known for. The unprecedented flexibility and openness of
Unix—which newcomers usually found confusing and frustrating, but eventually
found they couldn’t live without—continually inspired extensions, new tools, and
experiments in computer science that sometimes ended up in mainstream
commercial computer systems.
Many programmers fondly remember the days when AT&T provided universities
with Unix source code at no charge and the University of Berkeley started distrib-
uting its version in any manner that allowed people to get it. For these older
hackers, Linux brings back the spirit of working together—all the more so
because the Internet is now so widespread. And for the many who are too young
to remember the first round of open systems or whose prior experience has been
constricted by trying to explore and adapt proprietary operating systems, now is
the time to discover the wonders of freely distributable source code and infinitely
adaptable interfaces.
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Commands on Linux | 3
Introduction
The economic power behind Linux’s popularity is its support for an enormous
range of hardware. People who are accustomed to Microsoft Windows are often
amazed at how much faster their hardware appears to work with Linux—it makes
efficient use of its resources.
For the first several years after its appearance, users were attracted to Linux for a
variety of financial and political reasons, but soon they discovered an unexpected
benefit: Linux works better than many commercial systems. With the Samba file
and print server, for instance, Linux provides stable Windows-based networking
to a large number of end-user PCs. With the Apache web server, it provides more
of the useful features web administrators want than competing products do.
Embedded versions of the Linux kernel are growing in use because, although they
are larger than the most stripped-down operating systems, they deliver a range of
powerful features within a remarkably small footprint.
Opinions still differ on how suitable Linux is as a general-purpose desktop
system. But the tremendous advances in usability and stability of the desktop soft-
ware and its applications are undisputed. Soon (if not today), one will find Linux in
many offices and other end-user environments. Meanwhile, the strides made by
Linux in everyday computing tasks are reflected in the many new commands found
in this edition.
Distribution and Support
Because of the vast number and variety of tools beyond the kernel required for
a functional computing environment, building a Linux installation from scratch
is quite complex. Over the years, therefore, commercial and noncommercial pack-
ages called distributions have emerged. The first distribution consisted of approximately
50 diskettes, at least one of which would usually turn out to be bad and have to be
replaced. Since then, CD and DVD drives, as well as high-speed Internet connec-
tions, have become widespread and sharing Linux has become much easier.
After getting Linux, the average user is concerned next with support. While online
newsgroups and forums offer quick responses and meet the needs of many
intrepid users, you can also buy support from the vendors of the major distribu-
tions and a number of independent experts. Linux is supported at least as well as
commercial software. When you buy a distribution from a vendor, you typically
are entitled to a period of free support as well.
Intel’s x86 family and other compatible chips are still by far the most common
hardware running Linux, but Linux is also now commercially available on a
number of other hardware systems, notably the PowerPC, the Intel Itanium
processor, and Sun Microsystems’ SPARC.
Commands on Linux
Linux commands are not the same as standard Unix ones. Most of the commands
are provided by the GNU project run by the Free Software Foundation (FSF).
GNU means “GNU’s Not Unix”—the first word of the phrase is expanded with
infinite recursion.
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4 | Chapter1: Introduction
Benefiting from years of experience with standard Unix utilities and advances in
computer science, programmers on the GNU project have managed to create
versions of standard tools that have more features, run faster and more efficiently,
and lack the bugs and inconsistencies that persist in the original standard versions.
While GNU provided the programming utilities and standard commands such as
grep, many of the system and network administration tools on Linux came from
the Berkeley Software Distribution (BSD). In addition, some people wrote tools
that specifically allow Linux to deal with special issues such as filesystems. This
book documents the standard Unix commands that are commonly available on
most Linux distributions.
The third type of software most commonly run on Linux is the X Window
System, ported by the XFree86 and X.org projects to standard Intel chips. This
book does not discuss the X Window System; see the O’Reilly book Running
Linux, by Matthias Kalle Dalheimer and Matt Welsh, for an introduction to X.
What This Book Offers
Originally based on the classic O’Reilly quick reference, Unix in a Nutshell, this
book has been expanded to include much information that is specific to Linux.
These enhancements include chapters on:
• Package managers (which make it easy to install, update, and remove related
software files)
• Boot methods
• The Subversion and Git version control systems
• Virtualization
The book also contains dozens of Linux-specific commands, along with tried-and-
true Unix commands that have been supporting users for decades (though they
continue to sprout new options).
This book does not cover the graphical tools contained in most distributions of
Linux. Many of these, to be sure, are quite useful and can form the basis of
everyday work. Examples of these tools include OpenOffice (Sun Microsystems’
free, open source version of the StarOffice suite), Evolution (a mail, calendar, and
office productivity tool from Novell), Firefox and Thunderbird (a browser and
mail program from Mozilla), and the GIMP (a graphic image-manipulation
program and provider of a powerful library used by the GNOME project). But
they are not Linux-specific, and their graphical models do not fit well into the
format of this book.
While you probably log in to one of the graphical desktop environments such as
GNOME or KDE and do much of your work with the graphical applications, the
core of Linux use is the text manipulation and administration done from the
command line, within scripts, or using text editors such as vi and Emacs. Linux
remains largely a command-driven system, and this book continues to focus on
this level of usage; for many tasks, the command line is the most efficient and flex-
ible tool. In your day-to-day work, you’ll likely find yourself moving back and
forth between graphical programs and the commands listed in this book.
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What This Book Offers | 5
Introduction
Every distribution of Linux is slightly different. There are variations in directory
structure, choice of standard utilities, and software versions, but you’ll find that
the commands we document are the ones you use most of the time, and that they
work the same on all distributions. Note, though, that some commands are only
available with certain devices or configurations, or have alternatives that may be
preferred in your environment. Basic commands, programming utilities, system
administration, and network administration are all covered. However, some areas
were so big that we had to leave them out. The many applications that depend on
the X Window System didn’t make the cut. Nor did the many useful program-
ming languages—such as Java, Perl, and Python—with which users can vastly
expand the capabilities of their systems. XML isn’t covered here, either. These
subjects would stretch the book out of its binding.
Linux in a Nutshell doesn’t teach you Linux—it is, after all, a quick reference—
but novices as well as highly experienced users will find it of great value. When
you have some idea of what command you want but aren’t sure just how it works
or what combinations of options give you the exact output required, this book is
the place to turn. It can also be an eye-opener, making you aware of options that
you never knew about before.
Once you’ve installed Linux, the first thing you need to do is get to know the
common utilities run from the shell prompt. If you know absolutely nothing
about Unix, we recommend you read a basic guide (introductory chapters in the
O’Reilly books Learning Red Hat Enterprise Linux and Fedora, by Bill McCarty,
and Running Linux, mentioned previously, can get you started). This chapter and
Chapter 2 offer a context for understanding different kinds of commands
(including commands for programming, system administration, and network
administration). Chapter 3 is the central focus of the book, containing about one
half its bulk.
The shorter chapters immediately following Chapter 3 help you get your system
set up. Since most users do not want to completely abandon other operating
systems (whether a Microsoft Windows system or some Unix flavor), many users
opt for a dual-boot system, with Linux residing on the same computer as other
operating systems. Users can then boot to the system they need for a particular
job. Chapter 4 describes the commonly used booting options on Intel systems,
including LILO (Linux Loader) and GRUB (the GRand Unified Bootloader).
Chapter 5 covers the Red Hat package manager (rpm)—which is supported by
many distributions, including Red Hat Enterprise Linux, Fedora, SUSE, and
Mandriva—and the Debian package-management system, which is used by such
distributions as Ubuntu, Knoppix, and Gnoppix. It also describes some of the
frontend package-management tools that simplify package management and auto-
matically resolve dependencies. These tools include yum for rpm-based systems
and aptitude and synaptic for Debian-based systems. Package managers are
useful for installing and updating software; they make sure you have all the files
you need in the proper versions.
All commands are interpreted by the shell. The shell is simply a program that
accepts commands from the user and executes them. Different shells sometimes
use slightly different syntax to mean the same thing. Under Linux, the standard
shell is bash. Others, such as the ksh Korn shell, the tcsh enhanced C shell, and
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6 | Chapter1: Introduction
zsh, are available. Chapter 6 provides thorough coverage of bash; you may decide
to read this chapter after you’ve used Linux for a while, because it mostly covers
powerful, advanced features that you’ll want when you’re a steady user. Chapter 7
covers pattern matching, which is used by the Linux text-editing utilities for
searching based on a pattern rather than an explicit string.
To get any real work done, you’ll have to learn some big, comprehensive utilities,
notably an editor and some scripting tools. Two major editors are used on Linux:
vi and Emacs. Emacs is covered in Chapter 8, and vi is discussed in Chapter 9.
Chapter 9 also describes vim, an extended version of vi, commonly found on
Linux systems. Chapters 10 and 11 cover two classic Unix tools for manipulating
text files on a line-by-line basis: sed and gawk (the GNU version of the tradi-
tional awk). O’Reilly offers separate books about these topics that you may find
valuable, as they are not known for being intuitive upon first use. (Emacs does
have an excellent built-in tutorial, though; to invoke it, press Ctrl-h followed by t
for “tutorial.”)
The Subversion and Git version control systems manage files so you can retrieve
old versions and maintain different versions simultaneously. Originally used by
programmers, who have complicated requirements for building and maintaining
applications, these tools have turned out to be valuable for anyone who main-
tains files of any type, particularly when coordinating a team of people. Version
control systems have become a distribution channel for thousands of free soft-
ware projects. Chapter 12 offers a brief overview of version control, including
basic terms and concepts. Chapter 13 presents Subversion commands, and
Chapter 14 presents Git commands.
Chapter 15 covers virtualization and examines several virtualization systems such
as Xen and VMWare and their command-line tools.
Our goal in producing this book is to provide convenience, and that means keeping
the book (relatively) small. It certainly doesn’t have everything the manual pages
have, but you’ll find that it has what you need 95 percent of the time. See the man
command in Chapter 3 for information on reading the manpages. They can also be
read with the info command, the GNU hypertext documentation reader, also
documented in Chapter 3.
Sources and Licenses
Some distributions contain the source code for Linux; it is also easily available for
download at http://www.kernel.org and elsewhere. Source code is similarly avail-
able for all the utilities on Linux (unless your vendor offers a commercial
application or library as a special enhancement). You may never bother looking at
the source code, but it’s key to Linux’s strength. Under the Linux license, the
source code has to be provided or made available by the vendor, and it permits
those who are competent at such things to fix bugs, provide advice about the
system’s functioning, and submit improvements that benefit everyone. The license
is the GNU project’s well-known General Public License, also known as the GPL
or “copyleft,” invented and popularized by the Free Software Foundation (FSF).
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Beginner’s Guide | 7
Introduction
The FSF, founded by Richard Stallman, is a phenomenon that many people might
believe to be impossible if it did not exist. (The same goes for Linux, in fact—20
years ago, who would have imagined a robust operating system developed by
collaborators over the Internet and made freely redistributable?) One of the most
popular editors on Unix, GNU Emacs, comes from the FSF. So do gcc and g++
(C and C++ compilers), which for a while set the standard in the industry for
optimization and the creation of fast code. One of the most ambitious projects
within GNU is the GNOME desktop, which encompasses several useful general-
purpose libraries and applications that use these libraries to provide consistent
behavior and interoperability.
Dedicated to the sharing of software, the FSF provides all its code and documen-
tation on the Internet and allows anyone with a whim for enhancements to alter
the source code. One of its projects is the Debian distribution of Linux.
To prevent hoarding, the FSF requires that the source code for all enhancements
be distributed under the same GPL that it uses. This encourages individuals or
companies to make improvements and share them with others. The only thing
someone cannot do is add enhancements, withhold the source code, and then sell
the product as proprietary software. Doing so would be taking advantage of the
FSF and users of the GPL. You can find the text of the GPL in any software
covered by that license, or online at http://www.gnu.org/copyleft/gpl.html.
As we said earlier, many Linux tools come from BSD instead of GNU. BSD is also
free software. The license is significantly different, but that probably doesn’t
concern you as a user. The effect of the difference is that companies are permitted
to incorporate the software into their proprietary products, a practice that is
severely limited by the GNU license.
Beginner’s Guide
If you’re just beginning to work on a Linux system, the abundance of commands
might prove daunting. To help orient you, the following lists present a sampling
of commands on various topics.
Communication
Command Action
dig Query DNS server.
ftp File Transfer Protocol.
login Sign on.
rsync Transfer files, particularly across a network.
scp Securely copy files to remote system.
sftp Secure file transfer program.
ssh Run shell or single command on remote system (secure).
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8 | Chapter1: Introduction
Comparisons
File Management
Command Action
cmp Compare two files, byte by byte.
comm Compare items in two sorted files.
diff Compare two files, line by line.
diff3 Compare three files.
sdiff Compare and interactively merge two files.
Command Action
cat Concatenate files or display them.
chattr Change attributes on an ext2 file.
chgrp Change group of files.
chmod Change access modes on files.
chown Change ownership of files.
chsh Change login shell.
cp Copy files.
csplit Split a file into pieces with a specific size or at specific locations.
dd Copy files in raw disk form.
file Determine a file’s type.
head Show the first few lines of a file.
hexdump Display files in hexadecimal format.
less Display files by screenful, forward and backward.
ln Create filename aliases.
ls List files and directories.
md5sum Compute MD5 checksum.
merge Merge changes from different files.
mkdir Create a directory.
more Display files by screenful, forward only.
mv Move or rename files or directories.
newgrp Change current group.
od Display files in octal format.
pwd Print working directory.
rm Remove files.
rmdir Remove directories.
sha1sum Compute SHA1 checksum
shred Securely delete files.
split Split files evenly.
tac Print lines of a file in reverse order.
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Beginner’s Guide | 9
Introduction
Media
Printing
Programming
tail Show the last few lines of a file.
tailf Follow the growth of a logfile.
touch Update file timestamps and create the file if it doesn’t exist.
wc Count lines, words, and characters.
Command Action
cdparanoia Rip a CD while providing extra features.
cdrdao Copy a CD.
eject Eject a removable disk or tape.
genisoimage Generate a binary image from a directory tree.
icedax Rip a CD or DVD to create a computer-friendly WAV format.
readom Read or write a data CD or DVD.
volname Provide the volume name of a CD-ROM.
wodim Record to a CD or DVD.
Command Action
lpq Show status of print jobs.
lpr Send to the printer.
lprm Remove print job.
lpstat Get printer status.
pr Format and paginate for printing.
Command Action
ar Create and update library files.
as Generate object file.
bison Generate parsing tables.
cpp Preprocess C code.
flex Lexical analyzer.
g++ GNU C++ compiler.
gcc GNU C compiler.
ld Link editor.
ldd Print shared library dependencies.
m4 Macro processor.
Command Action
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10 | Chapter1: Introduction
Program Maintenance
Searching
make Create programs.
ranlib Regenerate archive symbol table.
rpcgen Translate RPC to C code.
yacc Generate parsing tables.
Command Action
ctags Generate symbol list for use with thevi editor.
etags Generate symbol list for use with the Emacs editor.
gdb GNU debugger.
git Scalable, distributed revision control system.
gprof Display object file’s profile data.
make Maintain, update, and regenerate related programs and files.
nm Display object file’s symbol table.
objcopy Copy and translate object files.
objdump Display information about object files.
patch Apply patches to source code.
pmap Print the memory map of a process.
size Print the size of an object file in bytes.
strace Trace system calls and signals.
strip Strip symbols from an object file.
svn Subversion revision control system.
Command Action
apropos Search manpages for topic.
egrep Extended version ofgrep.
fgrep Search files for literal words.
find Search the system for files by name and take a range of possible actions.
grep Search files for text patterns.
locate Search a preexisting database to show where files are on the system.
look Search file for string at the beginning of lines.
strings Search binary files for text patterns.
updatedb Update thelocate database.
whereis Find command.
which Print pathname of a command.
Command Action
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Beginner’s Guide | 11
Introduction
Shell Programming
Storage
System Status
Command Action
basename Remove leading directory components from a path.
echo Repeat command-line arguments on the output.
envsubst Substitute the value of environment variables into strings.
expr Perform arithmetic and comparisons.
mktemp Generate temporary filename and create the file.
printf Format and print command-line arguments.
sleep Pause during processing.
test Test a condition.
Command Action
bunzip2 Expand compressed.bz2 files.
bzip2 Compress files to free up space.
cpio Create and unpack file archives.
gunzip Expand compressed (.gz and.Z) files.
gzip Compress files to free up space.
tar Copy files to or restore files from an archive medium.
zcat Display contents of compressed files.
zforce Forcegzip files to have.gz extension.
Command Action
at Execute commands later.
atq Show jobs queued byat.
atrm Remove job queued byat.
crontab Automate commands.
date Display or set date.
df Show free disk space.
du Show disk usage.
env Show environment variables.
finger Display information about users.
free Show free and used memory.
hostname Display the system’s hostname.
kill Terminate a running command.
printenv Show environment variables.
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12 | Chapter1: Introduction
Text Processing
ps Show processes.
quota Display disk usage and limits.
stat Display file or filesystem status.
stty Set or display terminal settings.
top Display tasks currently running.
tty Display filename of the terminal connected to standard input.
uname Display system information.
uptime Show how long the system has been running.
vmstat Show virtual memory statistics.
who Show who is logged in.
Command Action
col Process control characters.
cut Select columns for display.
emacs Work environment with powerful text-editing capabilities.
ex Line editor underlyingvi.
expand Convert tabs to spaces.
fmt Produce roughly uniform line lengths.
fold Break lines.
gawk Process lines or records one by one.
groff Formattroff input.
gs Display PostScript or PDF file.
ispell Interactively check spelling.
join Merge different columns into a database.
paste Merge columns or switch order.
rev Print lines in reverse.
sed Noninteractive text editor.
sort Sort or merge files.
tr Translate (redefine) characters.
unexpand Convert spaces to tabs.
uniq Find repeated or unique lines in a file.
vi Visual text editor.
vim Enhanced version ofvi.
Command Action
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Beginner’s Guide | 13
Introduction
Miscellaneous
Command Action
bc Arbitrary precision calculator.
cal Display calendar.
clear Clear the screen.
info Get command information from the GNU hypertext reader.
man Get information on a command.
nice Reduce a job’s priority.
nohup Launch a command that will continue to run after logging out.
openvt Run a program on the next available virtual terminal.
passwd Set your login password.
script Produce a transcript of your login session.
su Become a different user, often the superuser.
sudo Execute an authorized command as root or another user.
tee Simultaneously store output in file and send to screen.
time Time the execution of a command.
wall Send a message to all terminals.
whoami Print the current user id.
xargs Process many arguments in manageable portions.
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14
Chapter 2Sys Admin Overview
2
System and Network
Administration Overview
Common Commands
Following are lists of commonly used system administration commands.
Clocks
Daemons
Command Action
hwclock Manage hardware clock.
rdate Get time from network time server.
Command Action
apmd Advanced Power Management daemon.
atd Queue commands for later execution.
bootpd Internet Boot Protocol daemon.
cupsd Printer daemon.
ftpd File Transfer Protocol daemon.
imapd IMAP mailbox server daemon.
klogd Managesyslogd.
mountd NFS mount request server.
named Internet domain nameserver.
nfsd NFS daemon.
pppd Maintain Point-to-Point Protocol (PPP) network connections.
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Common Commands | 15
Sys Admin
Overview
Hardware
Host Information
rdistd Remote file distribution server.
rexecd Remote execution server.
rlogind rlogin server.
routed Routing daemon.
rpc.rusersd Remote users server.
rpc.statd NFS status daemon.
rshd Remote shell server.
rsyslogd Alternate system logging daemon.
rwhod Remote who server.
sshd Secure shell daemon.
syslogd System logging daemon.
xinetd Extended Internet services daemon. Starts other services as needed.
ypbind NIS binder process.
yppasswdd NIS password modification server.
ypserv NIS server process.
Command Action
agetty Start user session at terminal.
arp Manage the ARP cache.
fdisk Maintain disk partitions.
hdparm Get and set hard drive parameters.
kbdrate Manage the keyboard’s repeat rate.
ramsize Print information about RAM disk.
setkeycodes Change keyboard scancode-to-keycode mappings.
slattach Attach serial lines as network interfaces.
Command Action
arch Print machine architecture.
dig Query Internet domain nameservers.
domainname Print NIS domain name.
free Print memory usage.
host Print host and zone information.
hostname Print or set hostname.
uname Print host information.
Command Action
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16 | Chapter2: System and Network Administration Overview
Installation
Mail
Managing Filesystems
To Unix systems, a filesystem is a device (such as a partition) that is formatted to
store files. Filesystems can be found on hard drives, floppies, CD-ROMs, USB
drives, or other storage media that permit random access.
The exact format and means by which the files are stored are not important; the
system provides a common interface for all filesystem types that it recognizes. By
default, almost all modern distributions of Linux use a journaling filesystem.
When the kernel interacts with a journalling filesystem, writes to disk are first
written to a log or journal before they are written to disk. This slows down writes
to the filesystem, but reduces the risk of data corruption in the event of a power
outage. It also speeds up reboots after a system unexpectedly loses power.
Most current Linux distributions default to the Third Extended (ext3) Filesystem.
The ext3 filesystem was developed primarily for Linux and supports 256-character
filenames and 4-terabyte maximum filesystem size. This ext3 filesystem is essentially
a Second Extended (ext2) filesystem with an added journal. Since it is in all other
ways identical to the ext2 system, it is both forward- and backward-compatible with
ext2—all ext2 utilities work with ext3 filesystems.
Although not covered in this edition of Linux in a Nutshell, Linux supports other
open source journaling filesystems including: IBM’s Journaled Filesystem (JFS),
SGI’s Extensible Filesystem (XFS), and the Naming System Venture’s Reiser File-
system (ReiserFS). In some situations these can be faster than ext3. Some Linux
distributions use these alternative filesystems by default. Other common filesys-
tems include the FAT and VFAT filesystems, which allow files on partitions and
floppies of Microsoft Windows systems to be accessed under Linux, and the ISO
9660 filesystem used by CD-ROMs.
Command Action
cpio Copy files to and from archives.
install Copy files into locations providing user access and set permissions.
rdist Distribute files to remote systems.
tar Copy files to or restore files from an archive medium.
Command Action
formail Convert input to mail format.
mailq Print a summary of the mail queue.
makemap Updatesendmail’s database maps.
newaliases Rebuildsendmail’s alias database.
rmail Handleuucp mail.
sendmail Send and receive mail.
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Common Commands | 17
Sys Admin
Overview
Managing the Kernel
Command Action
debugfs Debug ext2 filesystem.
dosfsck Check and repair a DOS or VFAT filesystem.
dump Back up data from a filesystem.
dumpe2fs Print information about superblock and blocks group.
e2fsck Check and repair an ext2 filesystem.
e2image Store disaster-recovery data for an ext2 filesystem.
e2label Label an ext2 filesystem.
edquota Edit filesystem quotas withvim.
fdformat Format floppy disk.
fsck Another name fore2fsck.
fsck.ext2 Check and repair an ext2 filesystem.
mke2fs Make a new ext2 filesystem.
mkfs Make a new filesystem.
mkfs.ext2 Another name formke2fs.
mkfs.ext3 Yet another name formke2fs.
mklost+found Makelost+found directory.
mkraid Set up a RAID device.
mkswap Designate swapspace.
mount Mount a filesystem.
quotacheck Audit stored quota information.
quotaon Enforce quotas.
quotaoff Do not enforce quotas.
quotastats Display kernel quota statistics.
rdev Describe or change values for root filesystem.
repquota Display quota summary.
resize2fs Enlarge or shrink an ext2 filesystem.
restore Restore data from adump to a filesystem.
rootflags List or set flags to use in mounting root filesystem.
setquota Edit filesystem quotas.
showmount List exported directories on a remote host.
swapoff Cease using device for swapping.
swapon Begin using device for swapping.
sync Write filesystem buffers to disk.
tune2fs Manage an ext2 filesystem.
umount Unmount a filesystem.
warnquota Mail disk usage warnings to users.
Command Action
depmod Create module dependency listing.
lsmod List kernel modules.
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18 | Chapter2: System and Network Administration Overview
Networking
Printing
Security and System Integrity
modinfo Print kernel module information.
modprobe Load and remove a module and its dependent modules.
sysctl Examine or modify kernel parameters at runtime.
Command Action
ifconfig Manage network interfaces.
iptables Administer firewall facilities (2.4 kernel).
named Translate between domain names and IP addresses.
nameif Assign names to network devices.
netstat Print network status.
nfsstat Print statistics for NFS and RPC.
nsupdate Submit dynamic DNS update requests.
portmap Map daemons to ports (renamedrpcbind).
rarp Manage RARP table.
rndc Send commands to a BIND nameserver.
route Manage routing tables.
routed Dynamically keep routing tables up to date.
rpcbind Map daemons to ports (replacesportmap).
rpcinfo Report RPC information.
traceroute Trace network route to remote host.
Command Action
accept Tell printer daemon to accept jobs.
lpadmin Configure printer and class queues.
lpinfo Show available printers and drivers.
lpmove Move a print job to a different queue.
reject Tell printer daemon to reject jobs.
tunelp Tune the printer parameters.
Command Action
badblocks Search for bad blocks.
chroot Change root directory.
Command Action
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Common Commands | 19
Sys Admin
Overview
Starting and Stopping the System
The job of booting and rebooting a machine falls to a special program called init.
Init is responsible for finishing the boot process once the kernel is done loading,
launching the services necessary to run the computer. Init is also responsible for
stopping services when needed and for shutting down or rebooting the computer
when instructed.
For decades, the software handling these duties was called SysVinit, or System V init.
Modern Linux distributions have begun switching to a replacement called Upstart
(a less common replacement, init-ng, we will not discuss). The traditional model,
facilitated by SysVinit, divides potential system states into multiple runlevels, each
with a distinct purpose. Runlevel 3, for example, indicates a standard booted
system; runlevel 6 indicates a reboot. When entering a runlevel N, SysVinit runs
all of the commands in the directory /etc/rcN.d. In this manner, the scripts in /etc/
rc3.d handle a system’s booting while those in /etc/rc6.d handle a reboot. Various
commands (see accompanying table) allow a system administrator to force the
system into a given runlevel. The file /etc/inittab specifies what runlevel is entered
on boot, as well as configuration for the system’s tty’s.
Upstart replaces this functionality with a more general mechanism for the stop-
ping, starting, and monitoring of services. Upstart operates asynchronously and is
a much more powerful system than SysVinit. Thankfully, however, it is backward
compatible with SysVinit and most distributions use it in a way in which much of
the preceding paragraph remains accurate. Indeed, most modern Linux distribu-
tions have moved to Upstart but still manage runlevels via SysVinit-style scripts in
/etc/rcN.d.
The biggest change with Upstart is with configuration. Instead of an inittab, Upstart
maintains a directory of configuration scripts, /etc/event.d. Files within this direc-
tory describe how Upstart should handle tty’s and SysVinit-style runlevels: /etc/
event.d/ttyN configures ttyN while /etc/event.d/rcN configures runlevel N.
System Activity and Process Management
A number of additional commands in Chapter 3 are particularly useful in control-
ling processes, including kill, killall, pidof, ps, and who.
Command Action
chkconfig Manage which services run in a runlevel.
ctrlaltdel Shut down and then soft reboot system.
halt Stop or shut down system.
initctl Manage the Upstart init daemon.
reboot Shut down and then hard reboot system.
runlevel Print system runlevel.
shutdown Shut down system.
telinit Change the current runlevel.
uptime Display uptimes of local machines.
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20 | Chapter2: System and Network Administration Overview
Users
Miscellaneous
Command Action
fuser Identify processes using file or filesystem.
renice Change the priority of running processes.
top Show most CPU-intensive processes.
vmstat Print virtual-memory statistics and process statistics.
Command Action
chpasswd Change multiple passwords.
groupadd Add a new group.
groupdel Delete a group.
groupmod Modify groups.
grpck Check the integrity of group system files.
grpconv Convert group file to shadow group file.
lastlog Generate report of last user login times.
newusers Add new users in a batch.
pwck Check the integrity of password system files.
pwconv Convert password file to shadow passwords.
rusers Printwho-style information on remote machines.
rwall Print a message to remote users.
useradd Add a new user.
userdel Delete a user and that user’s home directory.
usermod Modify a user’s information.
w List logged-in users.
wall Write to all users.
whoami Show how you are currently logged in.
Command Action
anacron Schedule commands for periodic execution.
atrun Schedule commands for later execution.
cron Schedule commands for specific times.
dmesg Print bootup messages after the system is up.
ldconfig Update library links and do caching.
logger Send messages to the system logger.
logrotate Compress and rotate system logs.
run-parts Run all scripts in a directory.
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Overview of Networking | 21
Sys Admin
Overview
Overview of Networking
Networks connect computers so that the different systems can share information.
For users and system administrators, Unix systems have traditionally provided a
set of simple but valuable network services that let you check whether systems are
running, refer to files residing on remote systems, communicate via electronic
mail, and so on.
For most commands to work over a network, one system must be continuously
running a server process in the background, silently waiting to handle the user’s
request. This kind of process is called a daemon. Common examples, on which you
rely for the most basic functions of your Linux system, are named (which trans-
lates between numeric IP addresses and more human-readable alphanumeric
names), cupsd (which sends documents to a printer, possibly over a network).
Most Unix networking commands are based on Internet protocols, standardized
ways of communicating across a network on hierarchical layers. The protocols
range from addressing and packet routing at a relatively low layer to finding users
and executing user commands at a higher layer.
The basic user commands that most systems support over Internet protocols are
generally called TCP/IP commands, named after the two most common proto-
cols. You can use all of these commands to communicate with other Unix systems
in addition to Linux systems. Many can also be used to communicate with non-
Unix systems, almost all systems support TCP/IP.
This section also covers NFS and NIS—which allow for transparent file and infor-
mation sharing across networks—and sendmail.
TCP/IP Administration
Command Action
arp Manipulate address resolution protocol tables.
dig Query domain nameservers.
ftpd Server for file transfers.
host Print host and zone information.
ip NetworkconfigurationtoolwithCiscoIOS-likesyntax.Replacesifconfig,route,and
arp on some systems.
ifconfig Configure network interface parameters.
named Translate between domain names and IP addresses.
netstat Print network status.
ping Check that a remote host is online and responding.
pppd Create PPP serial connection.
quagga Routing daemon.
rdate Notify time server that date has changed.
route Manage routing tables.
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22 | Chapter2: System and Network Administration Overview
NFS and NIS Administration
Overview of TCP/IP
TCP/IP is a suite of communications protocols that define how different types of
computers talk to one another. It’s named for its foundational protocols, the
Transmission Control Protocol and the Internet Protocol. The Internet Protocol
provides logical addressing as data moves between hosts: it splits data into
packets, which are then forwarded to machines via the network. The Transmis-
sion Control Protocol ensures that the packets in a message are reassembled in the
correct order at their final destination and that any missing datagrams are re-sent
until they are correctly received. Other protocols provided as part of TCP/IP
include:
Address Resolution Protocol (ARP)
Translates between Internet and local hardware addresses (Ethernet, etc.).
routed Dynamically keep routing tables up to date.
slattach Attach serial lines as network interfaces.
sshd Server for secure shell connections.
tcpdump Write network packet information to screen or file.
telnetd Server for Telnet sessions from remote hosts.
tftpd Server for restricted set of file transfers.
zebra Routing daemon.
Command Action
domainname Set or display name of current NIS domain.
makedbm Rebuild NIS databases.
rpcbind DARPA port to RPC program number mapper.
portmap The old name forrpcbind.
rpcinfo Report RPC information.
ypbind Connect to NIS server.
ypcat Print values in NIS database.
ypinit Build new NIS databases.
ypmatch Print value of one or more NIS keys.
yppasswd Change user password in NIS database.
yppasswdd Update NIS database in response toyppasswd.
yppoll Determine version of NIS map at NIS server.
yppush Propagate NIS map.
ypserv NIS server daemon.
ypset Pointypbind at a specific server.
yptest Check NIS configuration.
ypwhich Display name of NIS server or map master.
ypxfr Transfer NIS database from server to local host.
Command Action
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Overview of TCP/IP | 23
Sys Admin
Overview
Internet Control Message Protocol (ICMP)
Error-message and control protocol.
Point-to-Point Protocol (PPP)
Enables TCP/IP (and other protocols) to be carried across both synchronous
and asynchronous point-to-point serial links.
Reverse Address Resolution Protocol (RARP)
Translates between local hardware and Internet addresses (opposite of ARP).
Simple Mail Transport Protocol (SMTP)
Used by sendmail to send mail via TCP/IP.
Simple Network Management Protocol (SNMP)
Performs distributed network management functions via TCP/IP.
User Datagram Protocol (UDP)
Transfers data without first making a persistent connection between two
systems the way TCP does. Sometimes called unreliable transport.
TCP/IP is covered in depth in the three-volume set Internetworking with TCP/IP
(Prentice Hall). The commands in this chapter and the next are described in more
detail in TCP/IP Network Administration and Linux Network Administrator’s
Guide, both published by O’Reilly.
In the architecture of TCP/IP protocols, data is passed down the stack (toward the
Network Access Layer) when it is sent to the network, and up the stack when it is
received from the network (see Figure 2-1).
IP Addresses
The IP (Internet protocol) address is a binary number that differentiates your
machine from all others on the network. Each machine on the Internet must have
a unique IP address. The most common form of IP address used currently (IPv4)
uses a 32-bit binary address. An IPv4 address contains two parts: a network part
and a host part. The number of address bits used to identify the network and host
differ according to the class of the address. There are three main address classes:
A, B, and C (see Figure 2-2). The leftmost bits indicate what class each address is.
Figure 2-1 . Layers in the TCP/IP protocol architecture
consists of applications and
processes that use the network.
provides end-to-end data
delivery services.
defines the datagram and handles
the routing of data.
consists of routines for accessing
physical networks.
Application Layer
Host-to-Host Transport Layer
Internet Layer
Network Access Layer 1
2
3
4
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24 | Chapter2: System and Network Administration Overview
A standard called Classless Inter-Domain Routing (CIDR, or supernetting)
extends the class system’s idea of using initial bits to identify where packets
should be routed. Under CIDR, a new domain can be created with any number of
fixed leftmost bits (not just a multiple of eight). A CIDR address looks like a
regular IPv4 address followed by a slash and a number indicating the number of
network bits. For example: 192.168.32.1/24 or 128.66.128.1/17. Virtually all
Internet gateway hosts now use CIDR.
IPv6, a newer standard, changes the method of addressing and increases the
number of fields. An IPv6 address is 128 bits. Part of an IPv6 address is based on
the Media Access Control (MAC) address of the network interface. The MAC
address is unique for each network interface. When written, it is usually divided
into eight 16-bit hexadecimal blocks separated by colons. For example:
FE80:0000:0000:0000:0202:B3FF:FE1E:8329
To shorten this, leading zeros may be skipped, and any one set of consecutive
zeros can be replaced with double colons. For example, the above address can be
reduced to:
FE80::202:B3FF:FE1E:8329
Figure 2-2 . IP address structure
8 network bits
26
0
104 0 19
24 host bits
Class A
16 network bits
128
1
66 12 1
16 host bits
0
Class B
24 network bits
192
1
178 16 1
8 host bits
1
Class C
0
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Overview of TCP/IP | 25
Sys Admin
Overview
When IPv4 and IPv6 networks are mixed, the IPv4 address can be packed into the
lower four bytes, yielding an address like 0:0:0:0:0:0:192.168.1.2, or ::192.168.1.2,
or even ::C0A8:102.
Because improvements in IPv4, including CIDR, have relieved much of the pres-
sure to migrate to IPv6, organizations have been slow to adopt IPv6. Some use it
experimentally, but communication between organizations using IPv6 internally is
still usually encapsulated inside IPv4 datagrams, and it will be a while before IPv6
becomes common.
If you wish to connect to the Internet, contact an Internet Service Provider (ISP).
For most users, an ISP dynamically assigns an IP address to their systems. If you
wish to always have the same address, have them assign you a static network
address or range of addresses. If you are not connecting to an outside network,
you can choose your own network address as long as it conforms to the IP address
syntax. You should use the special reserved addresses provided in RFC 1597,
which lists IP network numbers for private networks that don’t have to be regis-
tered with the IANA (Internet Assigned Numbers Authority). An IP address is
different from an Ethernet address, which is assigned by the manufacturer of the
physical Ethernet card.
Gateways and Routing
Gateways are hosts responsible for exchanging routing information and forwarding
data from one network to another. Each portion of a network that is under a sepa-
rate local administration is called an autonomous system (AS). Autonomous systems
connect to each other via exterior gateways. An AS also may contain its own
system of networks, linked via interior gateways.
Gateway protocols
Gateway protocols include:
EGP (Exterior Gateway Protocol)
BGP (Border Gateway Protocol)
Protocols for exterior gateways to exchange information
RIP (Routing Information Protocol)
Interior gateway protocol; most popular for LANs
Hello Protocol
OSPF (Open Shortest Path First)
Interior gateway protocols
Routing daemons
While most networks will use a dedicated router as a gateway, routing daemons
like quagga and GNU Zebra, can be run on a host to make it function as a
gateway. Thes replace the older gated daemon. Only one of them can run on a host at
any given time. They allow a host to function as both an exterior and interior
gateway and simplify routing configuration by combining the protocols RIP,
Hello, BGP, EGP, and OSPF into a single package. We do not cover quagga or
GNU Zebra in this book.
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26 | Chapter2: System and Network Administration Overview
routed, a network routing daemon that uses RIP, allows a host to function only as
an interior gateway, and manages the Internet routing tables. For more details on
routed, see Chapter 3.
Routing tables
Routing tables provide information needed to route packets to their destinations.
This information includes destination network, gateway to use, route status, and
number of packets transmitted. Routing tables can be displayed with the netstat
command.
Name Service
Each host on a network has a name that points to information about that host.
Hostnames can be assigned to any device that has an IP address. A name service
translates the hostnames (which are easy for people to remember) to IP addresses
(the numbers the computer deals with).
DNS and BIND
The Domain Name System (DNS) is a distributed database of information about
hosts on a network. Its structure is similar to that of the Unix filesystem—an
inverted tree, with the root at the top. The branches of the tree are called domains
(or subdomains) and correspond to IP addresses. The most popular implementa-
tion of DNS is the BIND (Berkeley Internet Name Domain) software.
DNS works as a client/server application. The resolver is the client, the software
that asks questions about host information. The nameserver is the process that
answers the questions. The server side of BIND is the named daemon. You can
interactively query nameservers for host information with the dig and host
commands. See Chapter 3 for more details on named, dig, and host.
The nameserver of a domain is responsible for keeping (and providing on request)
the names of the machines in its domain. Other nameservers on the network
forward requests for these machines to this nameserver.
Domain names
The full domain name is the sequence of names from the current domain back to
the root, with a period separating the names. For instance, oreilly.com indicates
the domain oreilly (for O’Reilly Media, Inc.), which is under the domain com (for
commercial). One machine under this domain is www.oreilly.com. Top-level
domains include:
aero
Air-transport industry
biz
Commercial organizations
com
Commercial organizations
coop
Cooperatives
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Overview of TCP/IP | 27
Sys Admin
Overview
edu
United States educational organizations
gov
United States government organizations
info
Informative sites
int
International organizations
mil
United States military departments
museum
Museums
name
Names of individuals
net
Commercial Internet organizations, usually Internet service providers
org
Miscellaneous organizations
pro
Professionals, including accountants, lawyers, and physicians
Countries also have their own two-letter top-level domains based on two-letter
country codes. For example, the web server for the British Broadcasting System
(BBC) in the United Kingdom has the following domain name: www.bbc.co.uk.
Some domains (e.g., edu, gov, and mil) are sponsored by organizations that
restrict their use; others (e.g., com, info, net, and org) are unrestricted. One special
domain, arpa, is used for technical infrastructure purposes. The Internet Corporation
for Assigned Names and Numbers (ICANN) oversees top-level domains and
provides contact information for sponsored domains.
Configuring TCP/IP
Certain commands are normally run in the system’s startup files to enable a
system to connect to a network. These commands can also be run interactively.
Network interfaces
The network interface represents the way that the networking software uses the
hardware: the driver, the IP address, and so forth. To configure a network inter-
face, use the ip command. This command replaces the older ifconfig command. It
has a Cisco IOS-like command syntax that will be familiar to many network
administrators. With ip, you can assign an address to a network interface, setting
the netmask, broadcast address, and IP address at boot time. You can also set
network interface parameters, including the use of ARP, the use of driver-dependent
debugging code, the use of one-packet mode, and the address of the correspon-
dent on the other end of a point-to-point link. For more information on ip, see
Chapter 3.
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28 | Chapter2: System and Network Administration Overview
Serial-line communication
There are two protocols for serial-line communication: Serial Line IP (SLIP) and
Point-to-Point Protocol (PPP). These protocols let computers transfer information
using the serial port instead of a network card, and a serial cable instead of an
Ethernet cable. SLIP is rarely used anymore, having been replaced by PPP.
PPP was intended to remedy some of SLIP’s failings; it can hold packets from
non-Internet protocols, it implements client authorization and error detection/
correction, and it dynamically configures each network protocol that passes
through it. Under Linux, PPP exists as a driver in the kernel and as the daemon
pppd. For more information on pppd, see Chapter 3.
Troubleshooting TCP/IP
The following commands can be used to troubleshoot TCP/IP. For more details
on these commands, see Chapter 3:
dig
Query the DNS name service.
ifconfig
Provide information about the basic configuration of the network interface.
ifup and ifdown
On many systems used to start or stop a network interface.
iwconfig, iwlist, and wlancfg
Tools commonly used to configure a wireless network interface.
nc
Read and write data across a network connection.
netstat
Display network status.
ping
Indicate whether a remote host can be reached.
route
Allows you to read and set default gateway information, as well as static
routes.
tcpdump
Dump network packet information to the screen or to file.
traceroute
Trace route taken by packets to reach network host.
Overview of Firewalls and Masquerading
A firewall is a secure computer that sits between an internal network and an
external network (i.e., the Internet). It is configured with a set of rules that it uses
to determine what traffic is allowed to pass and what traffic is barred. While a
firewall is generally intended to protect the network from malicious or even acci-
dentally harmful traffic from the outside, it can also be configured to monitor
traffic leaving the network. As the sole entry point into the system, the firewall
makes it easier to construct defenses and monitor activity.
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Overview of NFS | 29
Sys Admin
Overview
The firewall can also be set up to present a single IP address to the outside world,
even though multiple IP addresses may be used internally. This is known as
masquerading. Masquerading can act as additional protection, hiding the very
existence of a network. It also saves the trouble and expense of obtaining multiple
IP addresses.
IP firewalling and masquerading are implemented with netfilter, also known as
iptables. Tthe facilities provided by netfilter are designed to be extensible; if there
is some function missing from the implementation, you can add it.
The packet filtering facilities provide built-in rule sets. Each network packet is
checked against each rule in the rule set until the packet either matches a rule or is
not matched by any rule. These sets of rules are called chains. These chains are
organized into tables that separate filtering functions from masquerading and
packet mangling functions. If a match is found, the counters on that rule are
incremented and any target for that rule is applied. A target might accept, reject,
or masquerade a packet, or even pass it along to another chain for processing.
Details on the chains provided in iptables can be found in Chapter 3.
In addition to these chains, you can create your own user-defined chains. You
might want a special chain for your PPP interfaces or for packets from a particular
site. To call a user-defined chain, you just make it the target for a match.
It is possible to make it through a chain without matching any rules that have a
target. If no rule matches the packet in a user-defined chain, control returns to the
chain from which it was called, and the next rule in that chain is checked. If no
rule matches the packet in a built-in chain, a default policy for that chain is used.
The default policy can be any of the special targets that determine what is done
with a packet. The valid targets are detailed in Chapter 3.
You use the iptables command to define the rules. Once you have the rules
defined you can use iptables-save to create a file with all the rule definitions, and
iptables-restore to restore those definitions when you reboot.
For more information on the kinds of decisions you need to make and the consid-
erations that go into defining the rules, see a general book on firewalls such as
Building Internet Firewalls (O’Reilly) by Elizabeth D. Zwicky et al. For more details
on iptables, consult the Linux Network Administrator’s Guide (O’Reilly) by Tony
Bautts et al., Linux iptables Pocket Reference (O’Reilly) by Gregor N. Purdy, or one
of the relevant HOWTOs, such as the “Packet Filtering HOWTO.” These
HOWTOs and a number of tutorials are available on the Netfilter website at http://
www.netfilter.org/.
Overview of NFS
The Network File System (NFS) is a distributed filesystem that allows users to
mount remote filesystems as if they were local. NFS uses a client/server model in
which a server exports directories to be shared and clients mount the directories
to access the files in them. NFS eliminates the need to keep copies of files on
several machines by letting the clients all share a single copy of a file on the server.
NFS is an RPC-based application-level protocol. For more information on the
architecture of network protocols, see “Overview of TCP/IP” on page 22.
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30 | Chapter2: System and Network Administration Overview
Administering NFS
To set up NFS clients and servers, you must start the NFS daemons on the servers,
export filesystems from the NFS servers, and mount the filesystems on the clients.
The /etc/exports file is the NFS server configuration file; it controls which files and
directories are exported and which kinds of access are allowed. Names and
addresses for clients that should be allowed or denied access to NFS are kept in
the /etc/hosts.allow and /etc/hosts.deny files.
Daemons
NFS server daemons, called nfsd daemons, run on the server and accept RPC calls
from clients. NFS servers also run the mountd daemon to handle mount requests.
On the client, caching and buffering are handled by biod, the block I/O daemon.
The rpcbind daemon maps RPC program numbers to the appropriate TCP/IP
port numbers. If the rpcbind daemon is not running properly, NFS will not work
either. On older systems rpcbind is named portmap.
Exporting Filesystems
To set up an NFS server, first check that all the hosts that will mount your file-
system can reach your host. Next, edit the /etc/exports file on the server. Each
entry in this file indicates the name of a directory to be exported, domain names
of machines that will have access to that particular mount point, and any options
specific to that machine. A typical entry looks like:
/projects hostname1(rw) hostname2(ro)
If you are running mountd, the files will be exported as allowed by the permis-
sions in /etc/exports. See the exports manpage for all available export options.
Mounting Filesystems
To enable an NFS client, mount a remote filesystem after NFS is started, either by
using the mount command or by specifying default remote filesystems in /etc/
fstab. For example:
#mount servername:/projects /mnt/nfs/projects
A mount request calls the server’s mountd daemon, which checks the access
permissions of the client and returns a pointer to a filesystem. Once a directory is
mounted, it remains attached to the local filesystem until it is unmounted with the
umount command or until the local system is rebooted.
Usually, only a privileged user can mount filesystems with NFS. However, you
can enable users to mount and unmount selected filesystems using the mount and
unmount commands ifthe user option is set in /etc/fstab. This can reduce traffic
by having filesystems mounted only when needed. To enable user mounting,
create an entry in /etc/fstab for each filesystem to be mounted. You can verify file-
systems that have been mounted by using the mount or showmount commands.
Or, you can read the contents of the /etc/mtab file.
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Overview of NIS | 31
Sys Admin
Overview
Overview of NIS
The Network Information System (NIS) refers to the service formerly known as
Sun Yellow Pages (YP). It is used to make configuration information consistent on
all machines in a network. It does this by designating a single host as the master of
all the system administration files and databases and distributing this information
to all other hosts on the network. The information is compiled into databases
called maps. NIS is built on the RPC protocol.
Another version of NIS, NIS+, adds encryption and strong authentication to NIS.
NIS+ is a proprietary standard created by Sun Microsystems. This chapter
discusses standard NIS, which is supported by most Linux systems. There are
currently two NIS servers freely available for Linux, yps and ypserv. We describe
ypserv in this book.
Servers
In NIS, there are two types of servers: master servers and slave servers. Master
servers are responsible for maintaining the maps and distributing them to the
slave servers. The files are then available locally to requesting processes.
Domains
An NIS domain is a group of hosts that use the same set of maps. The maps are
contained in a subdirectory of /var/yp having the same name as the domain. The
machines in a domain share password, host, and group file information. NIS
domain names are set with the domainname command.
NIS Maps
NIS stores information in database files called maps. Each map consists of a pair
of dbm database files, one containing a directory of keys (a bitmap of indices) and
the other containing data values. The non-ASCII structure of dbm files necessi-
tates using NIS tools such as yppush to move maps between machines.
The file /var/yp/YP_MAP_X_LATE contains a complete listing of active NIS maps,
as well as NIS aliases for NIS maps. All maps must be listed in this file in order for
NIS to serve them.
Map Manipulation Utilities
The following utilities are used to administer NIS maps:
makedbm
Make dbm files. Modify only ypserv’s map and any nondefault maps.
ypinit
Build and install NIS databases. Manipulate maps when NIS is being initial-
ized. Should not be used when NIS is already running.
yppush
Transfer updated maps from the master server.
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32 | Chapter2: System and Network Administration Overview
Administering NIS
NIS is enabled by setting up NIS servers and NIS clients. The descriptions given
here describe NIS setup using ypserv, which does not support a master/slave
server configuration. All NIS commands depend on the RPC rpcbind program, so
make sure it is installed and running before setting up NIS.
Setting Up an NIS Server
Setting up an NIS server involves the following steps:
1. Set a domain name for NIS using domainname.
2. Edit the ypMakefile, which identifies which databases to build and what
sources to use in building them.
3. Copy the ypMakefile to /var/yp/Makefile.
4. Run make from the /var/yp directory, which builds the databases and initial-
izes the server.
5. Start ypserv, the NIS server daemon.
Setting Up an NIS Client
Setting up an NIS client involves only the following steps:
1. Set the domain name for NIS using domainname, which should be the same
name used by the NIS server.
2. Run ypbind.
NIS User Accounts
NIS networks have two kinds of user accounts: distributed and local. Distributed
accounts must be administered from the master machine; they provide informa-
tion that is uniform on each machine in an NIS domain. Changes made to
distributed accounts are distributed via NIS maps. Local accounts are adminis-
tered from the local computer; they provide account information unique to a
specific machine. They are not affected by NIS maps, and changes made to local
accounts do not affect NIS. When NIS is installed, preexisting accounts default to
local accounts.
RPC and XDR
RPC (remote procedure call) is the session protocol used by both NFS and NIS. It
allows a host to make a procedure call that appears to be local but is really
executed remotely on another machine on the network. RPC is implemented as a
library of procedures, plus a network standard for ordering bytes and data struc-
tures called XDR (eXternal Data Representation).
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Chapter 3Linux Commands
3
Linux Commands
This chapter presents the Linux user, programmer, and system administration
commands. These are entered into a shell at the console or on a virtual terminal
on a graphical desktop.
Each entry is labeled with the command name on the outer edge of the page. The
syntax line is followed by a brief description and a list of available options. Many
commands come with examples at the end of the entry. If you need only a quick
reminder or suggestion about a command, you can skip directly to the examples.
Typographic conventions for describing command syntax are listed in the preface.
For help in locating commands, see the index at the back of this book.
We’ve tried to be as thorough as possible in listing options. The basic command
information and most options should be correct; however, there are many Linux
distributions and many versions of commands. New options are added, and occa-
sionally old options are dropped. You may, therefore, find some differences
between the options you find described here and the ones on your system. When
there seems to be a discrepancy, check the manpage. For most commands, you
can also use the option --help to get a brief usage message. (Even when it isn’t a
valid option, it will usually result in an “invalid option” error along with the usage
message.)
Traditionally, commands take single-letter options preceded by a single hyphen,
such as -d. A more recent convention allows long options preceded by two
hyphens, such as --debug. Often, a feature can be invoked through either the old
style or the new style of options.
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Alphabetical Summary of Commands
accept accept [option]queue
System administration command. Instruct printing system to
accept jobs for the specified print queue or queues. Depending on
queue settings, the system may prompt for a password.
Option
-E Force encrypted connection.
-hhost [port]
Connect to specified server.
-Uusername
Use alternate username when connecting to server.
access access [mode] [filename]
Check whether a file is available for the action specified with the
mode argument: r for read, w for write, x for execute. Used mostly
in scripting, access works better than test because it uses a direct
system call rather than looking at the file permissions, which can
be misleading when a filesystem is mounted read-only.
Options
--help
Display help message, then quit.
--version
Display version, then quit.
aclocal aclocal [options]
GNU autoconf tool. Place m4 macro definitions needed by auto-
conf into a single file. The aclocal command first scans for macro
definitions in m4 files in its default directory (/usr/share/aclocal on
some systems) and in the file acinclude.m4. It next scans for macros
used in the configure.in file. It generates an aclocal.m4 file that
contains definitions of all m4 macros required by autoconf.
Options
--acdir=dir
Look for macro files in directory dir instead of the default
directory.
--help
Print help message, then exit.
-I dir
Additionally, search directory dir for m4 macro definitions.
--output=file
Save output to file instead of aclocal.m4.
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acpi
--print-ac-dir
Print the name of the directory to be searched for m4 files,
then exit.
--verbose
Print names of files being processed.
--version
Print version number, then exit.
aconnect aconnect [options] [sender] [receiver]
aconnect [options]
Like its GUI relative alsa-patch-bay, aconnect connects ports in
MIDI hardware and software to route events, similar to running
patch cables between different mixers and synthesizers in an all-
hardware audio system. aconnect is part of the ALSA (Advanced
Linux Sound Architecture) system.
Options
-d, --disconnect
Undo the connection described.
-e, --exclusive
The connection being created must be exclusive: the sender
and receiver ports may not connect to any other port.
-i, --input
List all input (sender) ports. This flag is used without any
other arguments or flags.
-o, --output
List all output (receiver) ports. This flag is used without any
other arguments or flags.
-r, --real queue-name
All events processed through this connection get new time-
stamps from the named real-time queue. The receiving port
must have access to, and use, the real-time queue.
-t, --tick queue-name
All events processed through this connection get new time-
stamps from the specified tick queue.
-x, --remove-all
Cancel all connections. This flag is used without any other
arguments or flags.
acpi acpi [options]
Displays information about the ACPI (Advanced Configuration and
Power Interface) system, based on the /proc/acpi file. Most kernels
after 2.4 support ACPI hardware, and in both hardware and soft-
ware, ACPI is gradually replacing the older APM (Advanced Power
Management) system. Some operating systems, including SUSE, ship
a combined ACPI/APM power interface called powersaved. Most,
however, require either ACPI or APM software.
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acpid
Note that some ACPI systems have special events that are not avail-
able on others. For example, some laptops have events related to
their docking stations and keyboard lights that are not used on
nondocking or unlighted laptops. On all systems, the /proc/acpi
directory must be present for acpi commands to work.
Options
--a, --ac-adapter
Show whether the AC adapter is connected.
-A, --without-ac-adapter
Do not show information about the AC adapter.
b, --battery
Display battery information.
-B, --without-battery
Do not display battery information.
-c, --celcius
Use degrees Celsius as the temperature unit. This is the default
unit.
-d, --directory path
Use the specified path to ACPI information. The default is /proc/
acpi.
-f, --fahrenheit
Use degrees Fahrenheit as the temperature unit.
-h, --help
Display help information.
-k, --kelvin
Use degrees Kelvin as the temperature unit.
-s, --show-empty
Display information even on devices that are not available or
not installed, such as empty slots for extra batteries.
-S, --hide-empty
Do not display information on devices that are not opera-
tional or not installed.
-t, --thermal
Display temperature information.
-T, --without-thermal
Do not display temperature information.
-v, --version
Display version information.
-V, --everything
Show all information on every device.
acpid acpid [options]
Daemon that informs user-space programs about ACPI (Advanced
Configuration and Power Interface) events, such as battery warnings,
power-supply changes, and laptop lid closings. As ACPI hardware
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addr2line
replaces older APM (Advanced Power Management) hardware,
acpid replaces apmd. Like other daemons, this application iscontrolled
primarily through a configuration file that determines which events
merit action, and what those actions are.
Options
-c directory, --confdir=directory
Set the directory used for configuration files. The default
directory is /etc/acpi/events. All files in this directory, except
those beginning with a period (.), are parsed as configuration
files. Typically, a single file is used for each ACPI event to be
acted upon.
In the configuration files, blank lines and those beginning with
# are ignored. Other lines are expected to consist of a regular
expression and a command to be executed when an ACPI
event matches the expression.
-d, --debug
Debug mode: run the daemon in the foreground and send all
log output to stderr and stdout, rather than a logfile.
-e filename, --eventfile=filename
Set the file used to find events. Normally this is /proc/acpi/
event.
-g group, --socketgroup=group
Set the group ownership of the socket to which acpid
publishes events. This allows you to restrict which users on
the system can access ACPI event information.
-l filename, --logfile=filename
Set the logfile location. Normally, it is /var/log/acpid.
-m mode, --socketmode=mode
Set the permission mode of the socket. Normally, it is 666,
with the sticky bit off.
-s filename, --socketfile=filename
Set the file used to define the socket. Normally, this is /var/
run/acpid.socket.
-S, --nosocket
Tells acpid not to open a socket at all. Overrides all other
socket options.
-v, --version
Print version information and quit.
-h, --help
Print help message and quit.
addr2line addr2line [options] [addresses]
Translate hexadecimal program addresses into filenames and line
numbers for the executable given with the -e option, or a.out if -e is
not specified. If addresses are given on the command line, display
the filename and line number for each address. Otherwise, read the
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agetty
addresses from standard input and display the results on standard
output (useful for use in a pipe). addr2line prints two question
marks (??) if it cannot determine a filename, and 0 if it cannot
determine the line number. addr2line is used for debugging.
Options
-b bfdname, --target=bfdname
Set the binary file format using its binary file descriptor name,
bfdname. Use the -h option for a list of supported formats for
your system.
-C, --demangle[=style]
Decode (demangle) low-level symbol names into usernames.
See the -h help output for a list of styles supported by your
compiler.
-e file, --exe=file
Specify the filename of the executable to use. The default file-
name is a.out.
-f, --functions
Display function names in addition to filenames and line
numbers.
-h, --help
Display help information and exit.
-s, --basenames
Strip directories off filenames and show only the basenames.
agetty agetty [options]portbaudrate [term]
System administration command. agetty opens a tty port, prompts
for login, and invokes the login command with the user’s name as
an argument. While reading the name, agetty attempts to adapt the
system to the speed and type of device being used. agetty is usually
invoked by init using parameters specified in the /etc/inittab file, or
in newer distributions of linux by an upstart event using parame-
ters given in /etc/event.d/tty[1–6] files. On some systems this
command may also be invoked as getty or replaced by an alternative
command like mingetty. (See discussion of upstart in Chapter 2.)
You must specify a port, which agetty will search for in the /dev
directory. You may use -, in which case agetty reads from standard
input. You must also specify baudrate, which may be a comma-
separated list of rates through which agetty will step. Optionally,
you may specify the term, which is used to override the TERM
environment variable.
Options
-8 Disable parity detection and assume tty is 8-bit clean.
-f file
Specify the use of file instead of /etc/issue upon connection to
terminal. It is overridden by -i.
-h Specify hardware, not software, flow control.
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alsactl
-H hostname
Write login hostname into the utmp file. By default, no login
host is specified.
-I string
Specify string to be sent to the tty or modem.
-i Suppress printing of /etc/issue before printing the login prompt.
-l program
Specify the use of program instead of /bin/login.
-L Do not require carrier detect; operate locally only. Use this
when connecting terminals.
-m Attempt to guess the appropriate baud rate.
-n Don’t prompt for a login name.
-t timeout
Specify that agetty should exit if the open on the line succeeds
and there is no response to the login prompt in timeout
seconds.
-U Enable uppercase-only terminal detection. This will turn on
some upper- to lowercase conversions if the login name is
given in all capitals.
-w Wait for carriage return or linefeed before sending login
prompt. Use when sending an initialization string.
alsactl alsactl [options] [command] [card]
Control advanced configuration settings for sound cards using the
ALSA (Advanced Linux Sound Architecture) system. Driver
settings are written to and loaded from configuration files. The
card can be specified as a card number, id, or device. If no card is
specified, the configuration for all cards is saved or loaded. The
default configuration file is /etc/asound.state.
Commands
init
Attempt to initialize all sound cards to a default state.
restore
Load the driver information from the configuration file.
store
Save the current driver information to the configuration file.
Options
-d, --debug
Debug mode: increased information output to the console.
-E var=value, --env var=value
Set an environment variable. Useful for init or to override
ALSA_CONFIG_PATH.
-f file, --file=file
Specify the use of file instead of /etc/asound.state as a configu-
ration file.
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alsamixer
-F, --force
Force the restoration of settings; used with restore. This is the
default.
-g, --ignore
With store and restore, do not display errors and do not set
error exit codes.
-h, --help
Display help message and quit.
-i file, --initfile=file
Specify the configuration file for init. The default is /usr/share/
alsa/init/00main.
-p, --pedantic
Ignore mismatched control settings; used with restore.
-r file, --runstate=file
Save restore and init errors to the specified file, appending
new errors to the end of the file (unless -R is specified).
-R, --remove
Remove the runstate file first, before running the restore or
init.
-v, --version
Display version information and quit.
alsamixer alsamixer [options]
An ALSA mixer with an ncurses interface, for use with ALSA
soundcard drivers. alsamixer supports multiple sound cards with
multiple drivers. Use ESC or Alt-Q to exit.
Options
-c cardnum
Specify the number or id of the soundcard to use, if there are
multiple cards. Card numbers start from 0 (the default).
-Ddeviceid
Specify the id of the mixer device to control.
-g Toggle use of color or monochrome in the alsamixer window.
-h, --help
Display brief usage message and exit.
-s Minimize the mixer window.
-V mode
Select the starting view mode. The possible modes are play-
back, capture, or all.
amidi amidi [options]
Read and write raw MIDI files (.syx format, without timing infor-
mation) to ALSA ports. For standard MIDI (.mid) files, use aplaymidi
and arecordmidi.
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amixer
Options
-a, --active-sensing
Record and send active-sensing (FEh) bytes in MIDI
commands. By default, these bytes are ignored.
-d, --dump
Output received data directly to the screen as hexadecimal
bytes.
-h, --help
Display help information and quit.
-l, --list-devices
List all hardware MIDI ports.
-L, --list-rawmidis
List all RawMIDI definitions. Useful for debugging configura-
tion files.
-p, --port=name
Use the specified port. This overrides the port set in the
configuration file. If neither this flag nor the configuration file
sets a port, the default is port 0 on device 0, which may or may
not exist.
-r, --receive=filename
Write data from the port specified with the -p or --port flag to
the file named here, which is a raw file, and should end in .syx.
Unless you use the -a option, the data does not include Active
Sensing (FEh) bytes.
-s, --send=filename
Send the file to the port specified with the -p or --port flag.
Use raw (.syx) MIDI files only.
-S, --send-hex="hex-numbers..."
Send a string of hexadecimal numbers to the port specified
with the -p or --port flag.
-t, --timeout=n
Stop listening after n seconds of receiving no data.
-V, --version
Display version information and quit.
amixer amixer [options] [command]
Command-line ALSA mixer. For an ncurses interface, use alsamixer.
amixer displays or changes the current mixer settings for the
current sound card and sound device. To display all mixer settings,
use with no flags or commands.
Commands
contents
List card controls and their contents.
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amixer
controls
Display a complete list of card controls. These controls can
be set with the cset command, in contrast to simple mixer
controls, which use set or sset.
cget [control]
Display the contents of the specified card control.
cset [control] [parameter]
Set the card control to the value specified in the parameter.
Card controls may be identified by iface, name, index, device,
subdevice, or numid. The parameter is normally a number or
percentage value. For example, the command amixer -c 1 cset
numid=16 50% sets the 16th element of the first sound card
to 50%.
get, sget [control]
Display the current values for the specified simple mixer control.
help
Display help message and quit.
info
Display information about the current card or the card speci-
fied with the -c flag.
scontents
Display a complete list of simple mixer controls and their
contents.
scontrols
Display a list of simple mixer controls. Simple mixer controls
can be set with the set or sset commands, in contrast to card
controls, which use the cset command.
set, sset [control] [parameter]
Set one of the controls listed by scontrols. You can specify the
volume with a percentage from 0% to 100%, or a specific
hardware value. Append + or – to the number to increase or
decrease the volume by that amount. To set recording and
muting values, use the parameters cap (meaning capture, or
record), nocap, mute, unmute, or toggle. To specify individual
channels, use the parameters front, rear, center, or woofer.
For example, the command amixer -c 1 sset Line,0 100%
unmute sets Line 0 on the first sound card to 100% and
unmutes it.
Options
-c n
The number of the card to adjust.
-D devicename
Specify the name of the device. By default, the name is default.
-h Display help information and quit.
-q Quiet mode: do not show the results of changes made.
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aplay
-s, --stdin
Read command lines from standard input and execute
sequentially.
anacron anacron [options] [job]
System administration command. Normally started in a system
startup file. Execute commands periodically. By default, anacron
reads a list of jobs from a configuration file, /etc/anacrontab. The
file consists of shell variables to use when running commands,
followed by a list of tasks to run. Each task specifies how often in
days it should be run, a delay in minutes to wait before running the
task, a unique job identifier used to store a timestamp, and the
shell command to execute. Timestamps for the last run of each task
are stored in the /var/spool/anacron file. For each task, anacron
compares the stored timestamp against the current time. If the
command has not been executed within the specified frequency,
the command is run. Upon completion, anacron records the new
date in the timestamp file. Limit anacron to a specified task by
providing the task’s unique job identifier on the command line.
The anacron command is often used to support the cron daemon
on systems that do not run continuously.
Options
-d Run in foreground rather than as a background process. Send
messages to standard error.
-f Run tasks ignoring timestamps.
-h Print help message, then exit.
-n Run tasks now, ignoring delay specifications.
-q Suppress messages to standard error when using the -d option.
-s Execute tasks serially. Do not start new task until previous
task is completed.
-S directory
Store timestamps in directory instead of /var/spool/anacron.
-t file
Read tasks from file instead of from /etc/anacrontab.
-T Test validity of configuration file. Can be used with -t.
-u Update timestamps for tasks, but don’t run them.
-V Print version number, then exit.
aplay aplay [options] [file]
Play sound files using the ALSA sound system. The related arecord
records sound files.
Options
-c, --channels=n
Use n channels: 1 for mono, 2 for stereo.
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aplaymidi
-d, --duration=n
Set an interrupt for n seconds after playback begins.
-D, --device=devicename
Select a PCM device by name.
-f, --format=format
Specify the sample format. The sample formats available will
depend on hardware. For CD and DAT output, use the cd and
dat shortcuts, which set the sample rate, format, and channel
numbers all at once.
-h, --help
Print help message, then exit.
-l, --list-devices
List available sound cards and digital audio devices.
-L, --list-pcms
List all PCM (pulse-coded modulation, or digital audio)
devices that have been defined. PCMs may be defined in the
.asoundrc file.
-q, --quiet
Run quietly. Do not display messages.
-r, --rate=n
Set the sample rate in Hertz. The default is 8000 Hertz.
-s, --sleep-min=n
Set the minimum number of ticks to sleep. The default is not
to sleep.
-t, --file-type=type
Name the file type used. Files may be voc, wav, raw, or au.
--version
Print version and quit.
aplaymidi aplaymidi [options] [file]
Play MIDI files using the ALSA sound system; output is to ALSA
sequencer ports.
Options
-d, --delay=n
Delay n seconds at the end of a file to allow for reverberation
of the final notes.
-h, --help
Print help message, then exit.
-V, --version
Print version and quit.
-l, --list
List output ports available.
-p, --port=client:port
Specify the port to which the MIDI file will be sent. If no port
is specified, the file will be sent to port 0.
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apmd
apmd apmd [options]
System administration command. apmd handles events reported by
the Advanced Power Management BIOS driver. The driver reports
on battery level and requests to enter sleep or suspend mode. apmd
will log any reports it gets via syslogd and take steps to make sure
that basic sleep and suspend requests are handled gracefully. You
can fine-tune the behavior of apmd by editing the apmd_proxy
script, which apmd runs when it receives an event. Note that the
APM hardware standard has been replaced by the ACPI (Advanced
Configuration and Power Interface) standard, and apmd by acpid.
Options
-c n, --check n
Set the number of seconds to wait for an event before
rechecking the power level. Default is to wait indefinitely.
Setting this causes the battery levels to be checked more
frequently.
-p n, --percentage n
Log information whenever the power changes by n percent.
The default is 5. Values greater than 100 will disable logging
of power changes.
-P command, --proxy command
Specify the apmd_proxy command to run when APM driver
events are reported. This is generally a shell script. The
command will be invoked with parameters indicating what
kind of event was received. The parameters are listed in the
next section.
-T [n], --proxy-timeout [n]
Set time-out for proxy to n seconds. Without this option apmd
will wait indefinitely for the proxy to finish. Default value of n
is 30 seconds.
-v, --verbose
Verbose mode; all events are logged.
-V, --version
Print version and exit.
-w n, --warn n
Log a warning at ALERT level when the battery charge drops
below n percent. The default is 10. Negative values disable
low-battery-level warnings.
-W, --wall
Use wall to alert all users of a low battery status.
-q, --quiet
Disable low-battery-level warnings.
-?, --help
Print help summary and exit.
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apropos
Parameters
The apmd proxy script is invoked with the following parameters:
start
Invoked when the daemon starts.
stop
Invoked when the daemon stops.
standby [ system | user ]
Invoked when the daemon receives a standby request. The
second parameter indicates whether the request was made by
the system or by the user. Standby mode powers off the
monitor and disks, but the system continues to run and use
power.
suspend [ system | user ]
Invoked when the daemon receives a suspend request. The
second parameter indicates whether the request was made by
the system or by the user. Suspend, also known as “hiber-
nate,” effectively powers the system down but has a quicker
recovery than a normal boot process.
resume [ suspend | standby | critical ]
Invoked when the system resumes normal operation. The
second parameter indicates the mode the system was in before
resuming. critical suspends indicate an emergency shutdown.
After a critical suspend, the system may be unstable, and you
can use the resume command to help you recover from the
suspension.
change power
Invoked when system power is changed from AC to battery or
from battery to AC.
change battery
Invoked when the APM BIOS driver reports that the battery is
low.
change capability
Invoked when the APM BIOS driver reports that some hard-
ware that affects its capability has been added or removed.
apropos aproposstring...
Search the short manual page descriptions in the whatis database
for occurrences of each string and display the result on standard
output. Similar to whatis, except that it searches for strings instead
of words. Equivalent to man -k.
apt apt
The Advanced Package Tool, the Debian package management
system. A freely available packaging system for software distribu-
tion and installation. For detailed information on apt and its
commands, see Chapter 5.
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ar
ar arkey [args] [posname] [count]archive [files]
Maintain a group of files that are combined into a file archive. Used
most commonly to create and update static library files, as used by
the link editor (ld). Compiler frontends often call ar automatically.
Only one key letter may be used, but each can be combined with
additional args (with no separations between). posname is the name
of a file in archive. When moving or replacing files, you can specify
that they be placed before or after posname. ar has largely been
superseded by tar and bzip2.
Keys
d Delete files from archive.
m Move files to end of archive.
p Print files in archive.
q Append files to archive.
r Replace files in archive.
t List the contents of archive or list the named files.
x Extract contents from archive or only the named files.
Arguments
a Use with r or m key to place files in the archive after posname.
b Same as a, but before posname.
c Create archive silently.
f Truncate long filenames.
i Same as b.
l For backward compatibility; meaningless in Linux.
N Use count parameter. Where multiple entries with the same
name are found, use the count instance.
o Preserve original timestamps.
P Use full pathname. Useful for non-POSIX-compliant archives.
s Force regeneration of archive symbol table (useful after running
strip).
S Do not regenerate symbol table.
u Use with r to replace only files that have changed since being
put in archive.
v Verbose; print a description of actions taken.
V Print version number.
Example
Replace mylib.a with object files from the current directory:
ar r mylib.a `ls *.o`
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arch
arch arch
Print machine architecture type to standard output. Equivalent to
uname -m.
arecord arecord [options] [filename]
Records sound using ALSA. Accepts the same arguments and options
as aplay.
arecordmidi arecord [options] [filename]
Records midi files using ALSA. You must specify the port using the
-p flag.
Options
-b, --bmp=n
Set the tempo value to n beats per minute. The default is 120.
-f, --fps=n
Set timing (SMPTE resolution) to n frames per second. The
value is normally 24, 25, 29.97 (NTSC dropframe), or 30.
-h, --help
Display help message.
-i, --timesig=numerator:denominator
Set the time signature for the file and the metronome, speci-
fied as the numerator and the denominator separated by a
colon. The denominator must be a power of 2. Defaults to 4:4.
-l, --list
List available ports.
-m, --metronome=client:port
Play a metronome signal on the specified sequencer port.
-p, --port=host:port
Set the sequencer host and port used. The default host is the
local host, and the default port is port 0.
-s, --split-channels
For each channel of input, create a separate track in the MIDI
output file.
-t, --ticks=n
Set the frequency with which timestamps, or ticks, are used in
the file. For MIDI files using musical tempo, timestamps are
set in ticks per beat (default 384), while those with SMPTE
timing use ticks per frame (default 40).
-v, --version
Display version number.
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arp
arp arp [options]
TCP/IP command. Clear, add to, or dump the kernel’s Address
Resolution Protocol (ARP) cache (/proc/net/arp). ARP is used to
translate protocol addresses to hardware interface addresses. Modi-
fying your ARP cache can change which interfaces handle specific
requests. ARP cache entries may be marked with the following
flags: C (complete), M (permanent), and P (publish). While arp
can create a proxy for a single system, subnet proxies are now
handled by the arp kernel module, arp(7). See the “Linux
Advanced Routing & Traffic Control HOWTO” for details.
Options
host option arguments may be given as either a hostname or an IP
address. With the -D option, they may also be given as a hardware
interface address (e.g., eth0, eth1).
-a [hosts], --all [hosts]
Display entries in alternate (BSD) style for hosts or, if none are
specified, all entries.
-d host [pub], --delete host [pub]
Remove the specified host’s entry. To delete a proxy entry, add
the pub argument and specify the interface associated with the
proxy using -i.
-D, --use-device
Use the hardware address associated with the specified inter-
face. This may be used with -s when creating a proxy entry.
-e Display entries in default (Linux) style.
-f file, --file file
Read entries from file and add them.
-H type, --hw-type type, -t type
Search for type entries when examining the ARP cache. type is
usually ether (Ethernet), which is the default, but may be
ax25 (AX.25 packet radio), arcnet (ARCnet), pronet
(PROnet), or netrom (NET/ROM).
-i interface, --device interface
Select an interface. If you are dumping the ARP cache, this
option will cause the command to display only the entries
using that interface. When setting entries, this will cause the
interface to be associated with that entry. If you do not use
this option when setting an entry, the kernel will guess.
-n, --numeric
Display host IP addresses instead of their domain names.
-s host hardware-address [netmask mask] [pub], --set host hardware-
address [netmask mask] [pub]
Add a permanent entry for host at hardware-address. A
hardware-address for type ether hardware is 6 hexadecimal
bytes, colon-separated. The pub argument can be used to set
the publish flag, creating a proxy entry.
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as
-v, --verbose
Verbose mode.
Examples
Display entry for host eris:
arp -a eris
Set a permanent cache entry for host illuminati, whose hardware
address you know:
arp -s illuminati 00:05:23:73:e6:cf
Set an ARP proxy for host fnord using the eth0 interface’s hard-
ware address:
arp -Ds fnord eth0 pub
Remove the fnord ARP proxy:
arp -i eth0 -d fnord pub
as as [options]files
Generate an object file from each specified assembly-language
source file. Object files have the same root name as source files but
replace the .s suffix with .o. There may be some additional system-
specific options.
Options
-- [ | files]
Read input files from standard input, or from files if the pipe is
used.
-a[cdhlmns][=file]
With only the -a option, list source code, assembler listing,
and symbol table. The other options specify additional things
to list or omit:
-ac Omit false conditionals.
-ad Omit debugging directives.
-ah Include the high-level source code, if available.
-al Include an assembly listing.
-am Include macro expansions.
-an Suppress forms processing.
-as Include a symbol listing.
=file
Set the listing filename to file.
--defsym symbol=value
Define the symbol to have the value value, which must be an
integer.
-f Skip whitespace and comment preprocessing.
--fatal-warnings
Treat warnings as errors.
--gstabs
Generate debugging information in stabs format.
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at
--gdwarf2
Generate DWARF2 debugging information.
-o objfile
Place output in object file objfile (default is file.o).
--statistics
Print information on how much time and space assembler
uses.
-v Display the version number of the assembler.
-I path
Include path when searching for .include directives.
-J Don’t warn about signed overflow.
-R Combine both data and text in text section.
-W Don’t show warnings.
-Z Generate object file even if there are errors.
at at [options]time [date]
Execute commands at a specified time and optional date. The
commands are read from standard input or from a file. (See also
batch.) End input with EOF. time can be formed either as a
numeric hour (with optional minutes and modifiers) or as a keyword.
It can contain an optional date, formed as a month and date, a day
of the week, or a special keyword (today or tomorrow). An incre-
ment can also be specified.
The at command can always be issued by a privileged user. Other
users must be listed in the file /etc/at.allow if it exists; otherwise,
they must not be listed in /etc/at.deny. If neither file exists, only a
privileged user can issue the command.
Options
-c job [job...]
Display the specified jobs on the standard output. This option
does not take a time specification.
-d job [job...]
Delete the specified jobs. Same as atrm.
-f file
Read job from file, not from standard input.
-l Report all jobs that are scheduled for the invoking user. Same
as atq.
-m Mail user when job has completed, regardless of whether
output was created.
-q letter
Place job in queue denoted by letter, where letter is any single
letter from a-z or A-Z. Default queue is a. (The batch queue
defaults to b.) Higher-lettered queues run at a lower priority.
-V Display the version number.
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at
Time
hh:[mm] [modifiers]
Hours can have one digit or two (a 24-hour clock is assumed
by default); optional minutes can be given as one or two
digits; the colon can be omitted if the format is h, hh, or hhmm
(e.g., valid times are 5, 5:30, 0530, 19:45). If modifier am or
pm is added, time is based on a 12-hour clock.
midnight | noon | teatime | now
Use any one of these keywords in place of a numeric time.
teatime translates to 4:00 p.m.; now must be followed by an
increment (described in a moment).
Date
month num[, year]
month is one of the 12 months, spelled out or abbreviated to
its first three letters; num is the calendar date of the month;
year is the four-digit year. If the given month occurs before the
current month, at schedules that month next year.
day
One of the seven days of the week, spelled out or abbreviated
to its first three letters.
today | tomorrow
Indicate the current day or the next day. If date is omitted, at
schedules today when the specified time occurs later than the
current time; otherwise, at schedules tomorrow.
Increment
Supply a numeric increment if you want to specify an execution time
or day relative to the current time. The number should precede any
of the keywords minute, hour, day, week, month, or year (or their
plural forms). The keyword next can be used as a synonym of + 1.
Examples
In typical usage, you run at and input commands that you want
executed at a particular time, followed by EOF.
$at 1:00 am tomorrow
at>./total_up > output
at>mail joe < output
at><EOT> Entered by pressing Ctrl-D
job 1 at 2003-03-19 01:00
The two commands could also be placed in a file and submitted as
follows:
$at 1:00 am tomorrow < scriptfile
More examples of syntax follow. Note that the first two commands
here are equivalent:
$at 1945 December 9
$at 7:45pm Dec 9
$at 3 am Saturday
$at now + 5 hours
$at noon next day
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autoconf
atd atdoptions
System administration command. Normally started in a system
startup file. Execute jobs queued by the at command.
Options
-b n
Wait at least n seconds after beginning one job before begin-
ning the next job. Default is 60.
-d Print error messages to standard error instead of using syslog.
-l average
When system load average is higher than average, wait to
begin a new job. Default is 0.8.
-n Don’t fork. Run in foreground.
-s Process queue once, then exit.
atq atq [options]
List the user’s pending jobs, unless the user is a privileged user; in
that case, list everybody’s jobs. Same as at -l, and related to batch
and atrm.
Options
-q queue
Query only the specified queue and ignore all other queues.
-V Print the version number.
atrm atrm [option]job [job...]
Delete jobs that have been queued for future execution. Same as at
-d.
Option
-V Print the version number and then exit.
autoconf autoconf [options] [template_file]
Generate a configuration script from m4 macros defined in
template_file, if given, or in a configure.ac or configure.in file in the
current working directory. The generated script is almost invari-
ably called configure.
Options
-d, --debug
Don’t remove temporary files.
-f, --force
Replace files generated previously by autoconf.
-h, --help
Print help message, then exit.
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autoheader
-i, --initialization
When tracing calls with the -t option, report calls made during
initialization.
-o file, --output=file
Save output to file.
-t macro, --trace=macro
Report the list of calls to macro.
-v, --verbose
Verbosely print information about the progress of autoconf.
-B dir, --prepend-include=dir
Prepend directory dir to the search path.
-I dir, --include=dir
Append directory dir to the search path.
-V, --version
Print version number, then exit.
-W category, --warnings=category
Print any warnings related to category. Accepted categories are:
cross
Cross compilation.
obsolete
Obsolete constructs.
syntax
Questionable syntax.
all
All warnings.
no-category
Turn off warnings for category.
none
Turn off all warnings.
error
Treat warnings as errors.
autoheader autoheader [options] [template_file]
GNU autoheader tool. Generate a template file of C #define state-
ments from m4 macros defined in template_file, if given, or in a
configure.ac or configure.in file in the current working directory.
The generated template file is almost invariably called config.h.in.
Options
-d, --debug
Don’t remove temporary files.
-f, --force
Replace files generated previously by autoheader.
-h, --help
Print help message, then exit.
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automake
-o file, --output=file
Save output to file.
-v, --verbose
Verbosely print information about the progress of autoheader.
-B dir, --prepend-include=dir
Prepend directory dir to the search path.
-I dir, --include=dir
Append directory dir to the search path.
-V, --version
Print version number, then exit.
-W category, --warnings=category
Print any warnings related to category. Accepted categories
are:
obsolete
Obsolete constructs.
all
All warnings.
no-category
Turn off warnings for category.
none
Turn off all warnings.
error
Treat warnings as errors.
automake automake [options] [template_file]
GNU automake tool. Create GNU standards-compliant Makefile.in
files from Makefile.am template files and can be used to ensure
that projects contain all the files and install options required to be
standards-compliant. Note that versions 1.4 and 1.6 differ enough
that many distributions include an automake14 package for back-
ward compatibility.
Options
-a, --add-missing
Add any missing files that automake requires to the directory
by creating symbolic links to automake’s default versions.
-c, --copy
Used with the -a option. Copy missing files instead of creating
symbolic links.
--cygnus
Specifies project has a Cygnus-style source tree.
-f, --force-missing
Used with the -a option. Replace required files even if a local
copy already exists.
--foreign
Treat project as a non-GNU project. Check only for elements
required for proper operation.
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autoreconf
--gnu
Treat project as a GNU project with the GNU project
structure.
--gnits
A stricter version of --gnu, performing more checks to comply
with GNU project structure rules.
--help
Print help message, then exit.
-i, --ignore-deps
Disable automatic dependency tracking.
--libdir=dir
Used with the -a option. Search in directory dir for default
files.
--no-force
Update only Makefile.in files that have updated dependents.
-v, --verbose
List files being read or created by automake.
--version
Print version number, then exit.
-Werror
Treat warnings as errors.
autoreconf autoreconf [options]
GNU autoreconf tool. Update configure scripts by running auto-
conf, autoheader, aclocal, automake, and libtoolize in specified
directories and subdirectories. This command is seldom invoked
manually. It is usually called automatically from other autoconf
tools.
Options
-d, --debug
Don’t remove temporary files.
-f, --force
Remake all configure scripts, even when newer than their
template files.
-h, --help
Print help message, then exit.
-i, --install
Add any default files missing from package by copying
versions included with autoconf and automake.
-s, --symlink
Used with the -i option. Create symbolic links to default files
instead of copying them.
-v, --verbose
Verbosely print information about the progress of autoreconf.
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autoscan
-I dir, --include=dir
Search in directory dir for input files.
-V, --version
Print version number, then exit.
-W category, --warnings=category
Print any warnings related to category. Accepted categories are:
cross
Cross compilation.
obsolete
Obsolete constructs.
syntax
Questionable syntax.
all
All warnings.
no-category
Turn off warnings for category.
none
Turn off all warnings.
error
Treat warnings as errors.
autoscan autoscan [options] [directory]
GNU autoscan tool. Create or maintain a preliminary configure.ac
file named configure.scan based on source files in specified direc-
tory, or current directory if none given. If a configure.ac file already
exists, autoconf will check it for completeness and print sugges-
tions for correcting any problems it finds.
Options
-d, --debug
Don’t remove temporary files.
-h, --help
Print help message, then exit.
-v, --verbose
Verbosely print information about the progress of autoscan.
-I dir, --include=dir
Search in directory dir for input files. Use multiple times to
add multiple directories.
-B dir, --prepend-include=dir
Search dir for input files before searching in other directories.
Use multiple times to add multiple directories.
-V, --version
Print version number, then exit.
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autoupdate
autoupdate autoupdate [options] [file]
GNU autoupdate tool. Update the configure template file file, or
configure.ac if no file is specified. This command is seldom invoked
manually. It is usually called automatically from other autoconf
tools.
Options
-d, --debug
Don’t remove temporary files.
-f, --force
Remake all configure scripts, even when newer than their
template files.
-h, --help
Print help message, then exit.
-v, --verbose
Verbosely print information about the progress of autoupdate.
-I dir, --include=dir
Search in directory dir for input files.
-V, --version
Print version number, then exit.
badblocks badblocks [options]deviceblock-count
System administration command. Search device for bad blocks.
You must specify the number of blocks on the device (block-count).
e2fsck and mke2fs will invoke badblocks automatically when
given the -c option.
Options
-b blocksize
Expect blocksize-byte blocks.
-c blocksize
Test blocksize-byte blocks at a time. Default is 16.
-e number
Abort test after finding specified number of blocks.
-f Force a read/write or nondestructive write test on a mounted
device. Use only when /etc/mtab incorrectly reports a device as
mounted.
-i file
Skip test of known bad blocks listed in file.
-n Perform a nondestructive test by writing to each block and
then reading back from it while preserving data.
-o file
Direct output to file.
-p number
Repeat search of device until no new bad blocks have been
found in number passes. Default is 0.
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basename
-s Show block numbers as they are checked.
-t pattern
Test blocks by reading and writing the specified pattern. You
may specify pattern as a positive integer or as the word
random. If you specify multiple patterns, badblocks tests all
blocks with one pattern, and then tests all blocks again with
the next pattern. Read-only mode accepts only one pattern. It
does not accept random.
-v Verbose mode.
-w Test by writing to each block and then reading back from it.
This option will destroy data. Don’t use it on devices that
contain filesystems.
base64 base64 [option] [file]
Use base64 encoding to encode or decode the specified file and
print the results to standard output. With no file or with a dash (-),
read the data from standard input.
Options
-d, --decode
Decode the data.
--help
Print help message and exit.
-i, --ignore-garbage
When decoding, ignore nonalphabetic characters except
newline.
--version
Print version information and exit.
-w cols, --wrap=cols
When encoding, wrap lines after cols characters. The default is
76, while 0 disables line wrap.
basename basenamename [suffix]
basenameoption
Remove leading directory components from a path. If suffix is
given, remove that also. The result is printed to standard output.
This is useful mostly in a script when you need to work with a file-
name but can’t predict its full path in every instance.
Options
--help
Print help message and then exit.
--version
Print the version number and then exit.
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bash
Examples
$basename /usr/lib/libm.a
libm.a
$basename /usr/lib/libm.a .a
libm
bash bash [options] [file [arguments]]
sh [options] [file [arguments]]
Standard Linux shell, a command interpreter into which all other
commands are entered. For more information, see Chapter 6.
batch batch
Execute commands entered on standard input. Commands are run
when the system load permits (when the load average falls below 0.8).
Very similar to at, but takes no parameters on the command line.
See at for details.
bc bc [options] [files]
bc is a language (and compiler) whose syntax resembles that of C,
but with unlimited-precision arithmetic. bc consists of identifiers,
keywords, and symbols, which are briefly described in the
following entries. Examples are given at the end.
Interactively perform arbitrary-precision arithmetic or convert
numbers from one base to another. Input can be taken from files or
read from the standard input. To exit, type quit or EOF.
Options
-h, --help
Print help message and exit.
-i, --interactive
Interactive mode.
-l, --mathlib
Make functions from the math library available.
-s, --standard
Ignore all extensions, and process exactly as in POSIX.
-w, --warn
When extensions to POSIX bc are used, print a warning.
-q, --quiet
Do not display welcome message.
-v, --version
Print version number.
Identifiers
An identifier is a series of one or more characters. It must begin
with a lowercase letter but may also contain digits and under-
scores. No uppercase letters are allowed. Identifiers are used as
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bc
names for variables, arrays, and functions. Variables normally store
arbitrary-precision numbers. Within the same program you may
name a variable, an array, and a function using the same letter. The
following identifiers would not conflict:
x Variable x.
x[i]
Element i of array x. i can range from 0 to 2047 and can also
be an expression.
x(y,z)
Call function x with parameters y and z.
Input-output keywords
ibase, obase, scale, and last store a value. Typing them on a line by
themselves displays their current value. You can also change their
values through assignment. The letters A–F are treated as digits
whose values are 10–15.
ibase = n
Numbers that are input (e.g., typed) are read as base n (default
is 10).
obase = n
Numbers that are displayed are in base n (default is 10). Note:
once ibase has been changed from 10, use A to restore ibase
or obase to decimal.
scale = n
Display computations using n decimal places (default is 0,
meaning that results are truncated to integers). scale is normally
used only for base-10 computations.
last
Value of last printed number.
Statement keywords
A semicolon or a newline separates one statement from another.
Curly braces are needed when grouping multiple statements:
if (rel-expr) {statements} [else {statements}]
Do one or more statements if relational expression rel-expr is
true. Otherwise, do nothing, or if else (an extension) is speci-
fied, do alternative statements. For example:
if (x= =y) {i = i + 1} else {i = i - 1}
while (rel-expr) {statements}
Repeat one or more statements while rel-expr is true. For
example:
while (i>0) {p = p*n; q = a/b; i = i-1}
for (expr1; rel-expr; expr2) {statements}
Similar to while. For example, to print the first 10 multiples of
5, you could type:
for (i=1; i<=10; i++) i*5
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bc
GNU bc does not require three arguments to for. A missing
argument 1 or 3 means that those expressions will never be
evaluated. A missing argument 2 evaluates to the value 1.
break
Terminate a while or for statement.
print list
GNU extension. It provides an alternate means of output. list
consists of a series of comma-separated strings and expres-
sions; print displays these entities in the order of the list. It
does not print a newline when it terminates. Expressions are
evaluated, printed, and assigned to the special variable last.
Strings (which may contain special characters—i.e., characters
beginning with \) are simply printed. Special characters can be:
a Alert or bell
b Backspace
f Form feed
n Newline
r Carriage return
q Double quote
t Tab
\ Backslash
continue
GNU extension. When within a for statement, jump to the
next iteration.
halt
GNU extension. Cause the bc processor to quit when
executed.
quit
GNU extension. Cause the bc processor to quit whether line is
executed or not.
limits
GNU extension. Print the limits enforced by the local version
of bc.
Function keywords
define f(args) {
Begin the definition of function f having the arguments args.
The arguments are separated by commas. Statements follow
on successive lines. End with }.
auto x, y
Set up x and y as variables local to a function definition,
initialized to 0 and meaningless outside the function. Must
appear first.
return(expr)
Pass the value of expression expr back to the program. Return
0 if (expr) is left off. Used in function definitions.
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bc
sqrt(expr)
Compute the square root of expression expr.
length(expr)
Compute how many significant digits are in expr.
scale(expr)
Same as length, but count only digits to the right of the
decimal point.
read()
GNU extension. Read a number from standard input. Return
value is the number read, converted via the value of ibase.
Math library functions
These are available when bc is invoked with -l. Library functions
set scale to 20:
s(angle)
Compute the sine of angle, a constant or expression in
radians.
c(angle)
Compute the cosine of angle, a constant or expression in
radians.
a(n)
Compute the arctangent of n, returning an angle in radians.
e(expr)
Compute e to the power of expr.
l(expr)
Compute the natural log of expr.
j(n, x)
Compute the Bessel function of integer order n.
Operators
These consist of operators and other symbols. Operators can be
arithmetic, unary, assignment, or relational:
arithmetic
+ - * / % ^
unary
- ++ --
assignment
=+ =- =* =/ =% =^ =
relational
< <= > >= = = !=
Other symbols
/* */
Enclose comments.
() Control the evaluation of expressions (change precedence).
Can also be used around assignment statements to force the
result to print.
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bison
{ } Use to group statements.
[ ] Indicate array index.
"text"
Use as a statement to print text.
Examples
Note in these examples that when you type some quantity (a
number or expression), it is evaluated and printed, but assignment
statements produce no display.
ibase = 8 Octal input
20 Evaluate this octal number
16 Terminal displays decimal value
obase = 2 Display output in base 2 instead of base 10
20 Octal input
10000 Terminal now displays binary value
ibase = A Restore base-10 input
scale = 3 Truncate results to 3 decimal places
8/7 Evaluate a division
1.001001000 Oops! Forgot to reset output base to 10
obase = 10 Input is decimal now, so A isn’t needed
8/7
1.142 Terminal displays result (truncated)
The following lines show the use of functions:
define p(r,n){ Function p uses two arguments
auto v v is a local variable
v = r^n r raised to the n power
return(v)} Value returned
scale = 5
x = p(2.5,2) x = 2.5 ^ 2
x Print value of x
6.25
length(x) Number of digits
3
scale(x) Number of places right of decimal point
2
bison bison [options]file
Given a file containing context-free grammar, convert into tables
for subsequent parsing while sending output to file.c. To a large
extent, this utility is compatible with yacc, and is in fact named for
it. All input files should use the suffix .y; output files will use the
original prefix. All long options (those preceded by --) may instead
be preceded by +.
Options
-b prefix, --file-prefix=prefix
Use prefix for all output files.
-d, --defines
Generate file.h, producing #define statements that relate
bison’s token codes to the token names declared by the user.
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bzip2
-r, --raw
Use bison token numbers, not yacc-compatible translations,
in file.h.
-k, --token-table
Include token names and values of YYNTOKENS, YYNNTS,
YYNRULES, and YYNSTATES in file.c.
-l, --no-lines
Exclude #line constructs from code produced in file.c. (Use
after debugging is complete.)
-n, --no-parser
Suppress parser code in output, allowing only declarations.
Assemble all translations into a switch statement body and
print it to file.act.
-o file, --output-file=file
Output to file.
-p prefix, --name-prefix=prefix
Substitute prefix for yy in all external symbols.
-t, --debug
Compile runtime debugging code.
-v, --verbose
Verbose mode. Print diagnostics and notes about parsing
tables to file.output.
-V, --version
Display version number.
-y, --yacc, --fixed-output-files
Duplicate yacc’s conventions for naming output files.
bzcmp bzcmp [options]file1 file2
Apply cmp to the data from files in the bzip2 format without
requiring on-disk decompression. See bzip2 and cmp for usage.
bzdiff bzdiff [options]file1 file2
Apply diff to data from files in the bzip2 format without requiring
on-disk decompression. See bzip2 and diff for usage.
bzgrep bzgrep [options]pattern [file...]
Apply grep to data from files in the bzip2 format without requiring
on-disk decompression. See bzip2 and grep for usage.
bzip2 bzip2 [options]filenames
bunzip2 [options]filenames
bzcat [option]filenames
bzip2recoverfilename
File compression and decompression utility similar to gzip, but
uses a different algorithm and encoding method to get better
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bzip2
compression. bzip2 replaces each file in filenames with a compressed
version of the file and with a .bz2 extension appended. bunzip2
decompresses each file compressed by bzip2 (ignoring other files,
except to print a warning). bzcat decompresses all specified files to
standard output, and bzip2recover is used to try to recover data
from damaged files.
Additional related commands include bzcmp, which compares the
contents of bzipped files; bzdiff, which creates diff (difference) files
from a pair of bzip files; bzgrep, to search them; and the bzless and
bzmore commands, which apply the more and less commands to
bzip output, as bzcat does with the cat command. See cat, cmp,
diff, and grep for information on how to use those commands.
Options
-- End of options; treat all subsequent arguments as filenames.
-dig
Set block size to dig × 100 KB when compressing, where dig
is a single digit from 1 to 9. For gzip compatibility, you can
use --fast as an alias for -1 and --best for -9, but they have little
effect on the compression speed.
-c, --stdout
Compress or decompress to standard output.
-d, --decompress
Force decompression even if invoked by bzip2 or bzcat.
-f, --force
Force overwrite of output files. Default is not to overwrite.
Also forces breaking of hard links to files.
-k, --keep
Keep input files; don’t delete them.
-L, --license, -V, --version
Print license and version information, and exit.
-q, --quiet
Print only critical messages.
-s, --small
Use less memory, at the expense of speed.
-t, --test
Check the integrity of the files, but don’t actually compress them.
-v, --verbose
Verbose mode. Show the compression ratio for each file
processed. Add more -vs to increase the verbosity.
-z, --compress
Force compression, even if invoked as bunzip2 or bzcat.
Examples
To produce two files: fileone.txt.bz2 and filetwo.ppt.bz2, while
deleting the two original files:
bzip2 fileone.tzt filetwo.ppt
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c++filt
To produce a single compressed file, output.bz2, which can be
decompressed to reconstitute the original fileone.txt and filetwo.txt:
bzip2 -c fileone.txt filetwo.txt > output.bz2
The tar command, combined with the -j or --bzip2 option, creates
the output file nutshell.tar.bz2:
tar -cjf nutshell.tar.bz2 /home/username/nutshell
bzless bzless [options]file
Applies less to datafiles in the bzip2 format without requiring on-
disk decompression. See bzip2 and less for usage.
bzmore bzmore [options]file
Applies more to datafiles in the bzip2 format without requiring on-
disk decompression. See bzip2 and more for usage.
c++ c++ [options]files
See g++.
c++filt c++filt [options] [symbol]
Decode the specified C++ or Java function name symbol, or read
and decode symbols from standard input if no symbol is given.
This command reverses the name mangling used by C++ and Java
compilers to support function overloading, multiple functions that
share the same name.
Options
-_, --strip-underscores
Remove initial underscores from symbol names.
--help
Print usage information, then exit.
-j, --java
Print names using Java syntax.
-n, --no-strip-underscores
Preserve initial underscores on symbol names.
-s format, --format=format
Expect symbols to have been coded in the specified format.
Format may be one of the following:
arm
C++ Annotated Reference Manual.
edg
EDG (Intel) compiler.
gnu
Gnu compiler (the default).
gnu-new-abi
Gnu compiler with the new application binary interface
(for gcc 3.x.)
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cal
hp
HP compiler.
lucid
Lucid compiler.
--version
Print version number, then exit.
cal cal [options] [[[day]month]year]
Print a 12-month calendar (beginning with January) for the given
year, or a one-month calendar of the given month and year. With a
day specified as well, print the calendar for that month and year,
with the day highlighted. month ranges from 1 to 12. year ranges
from 1 to 9999. With no arguments, print a calendar for the
current month.
Options
-3 Display the previous, current and next month.
-j Display Julian dates (days numbered 1 to 365, starting from
January 1).
-m Display Monday as the first day of the week (the default is
Sunday).
-y Display entire year.
Examples
cal 12 2006
cal 2006 > year_file
cat cat [options] [files]
Read (concatenate) one or more files and print them on standard
output. Read standard input if no files are specified or if - is speci-
fied as one of the files; input ends with EOF. You can use the >
operator to combine several files into a new file, or >> to append
files to an existing file. When appending to an existing file, use
Ctrl-D, the end-of-file symbol, to end the session.
Options
-A, --show-all
Same as -vET.
-b, --number-nonblank
Number all nonblank output lines, starting with 1.
-e Same as -vE.
-E, --show-ends
Print $ at the end of each line.
-n, --number
Number all output lines, starting with 1.
-s, --squeeze-blank
Squeeze down multiple blank lines to one blank line.
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cdparanoia
-t Same as -vT.
-T, --show-tabs
Print TAB characters as ^I.
-u Ignored; kept for Unix compatibility.
-v, --show-nonprinting
Display control and nonprinting characters, with the excep-
tion of LINEFEED and TAB.
Examples
cat ch1 Display a file
cat ch1 ch2 ch3 > all Combine files
cat note5 >> notes Append to a file
cat > temp1 Create file at terminal. To exit, enter EOF
Ctrl-D).
cat > temp2 << STOP Create file at terminal. To exit, enter STOP.
cc cc [options]files
See gcc.
cdda2wav cdda2wav [options] [files]
Convert Compact Disc Digital Audio (CDDA) to the WAV format.
This process is often called “ripping” a CD-ROM and is generally
performed before using an encoder to convert the file to a
compressed music format, such as OGG or MP3.
cdda2wav is now generally a symbolic link to icedax.
cdparanoia cdparanoia [options]span [outfile]
cdparanoia records Compact Disc audio files as WAV, AIFF, AIFF-C,
or raw format files. It uses additional data-verification and sound-
improvement algorithms to make the process more reliable and is
used by a number of graphical recording programs as a backend.
The output is written to outfile if specified; otherwise it is written
to one of cdda.wav, cdda.aifc, or cdda.raw depending on the
output-format option given.
The command takes one argument, span, which describes how
much of the CD to record. It uses numbers followed by bracketed
times to designate track numbers and time within them. For
example, the string 1[2:23]-2[5] indicates a recording from the
two-minute and twenty-three-second mark of the first track up to
the fifth second of the second track. The time format is demar-
cated by colons, hours:minutes:seconds:.sectors, with the last item,
sectors, preceded by a decimal point (a sector is 1/75 of a second).
It’s best to put this argument within quotes.
If you use the -B option, the span argument is not required.
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cdparanoia
Options
-a, --output-aifc
Output in AIFF-C format.
-A, --analyze-drive
Analyze and log drive caching, timing and reading. Implies-vQL.
-B, --batch
Split output into multiple files, one per track. Each file begins
with the track number. This is the most commonly used flag
for this command.
-C, --force-cdrom-big-endian
Force cdparanoia to treat the drive as a big-endian device.
-c, --force-cdrom-little-endian
Force cdparanoia to treat the drive as a little-endian device.
-d, --force-cdrom-device devicename
Specify a device name to use instead of the first readable CD-ROM
available.
-e, --stderr-progress
Send all progress messages to standard error instead of standard
output; used by wrapper scripts.
-f, --output-aiff
Output in AIFF format. The default format is WAV.
-h, --help
Display options and syntax.
-l, --log-summary [file]
Write results to file if specified, otherwise to cdparanoia.log.
-L, --log-debug [file]
Write device autosensing and debugging output to file if speci-
fied, otherwise to cdparanoia.log.
-p, --output-raw
Output headerless raw data.
-R, --output-raw-big-endian
Output raw data in big-endian byte order.
-r, --output-raw-little-endian
Output raw data in little-endian byte order.
-Q, --query
Display CD-ROM table of contents and quit.
-q, --quiet
Quiet mode.
-S, --force-read-speed n
Set the read speed to n on drives that support it. This is useful
if you have a slow hard disk or not much RAM.
-s, --search-for-drive
Search for a drive, even if /dev/cdrom exists.
-V, --version
Print version information and quit.
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cdrdao
-v, --verbose
Verbose mode.
-w, --output-wav
Output in WAV format. This is the default.
-X, --abort-on-skip
If a read fails and must be skipped, skip the entire track and
delete any partially completed output file.
-z, --never-skip[=retries]
If a read fails (for example, due to a scratch in the disc), keep
trying. If you specify a number, cdparanoia will try that
number of times. If you do not, cdparanoia will retry until it
succeeds. The default number of attempts is 20.
Progress symbols
The output during operation of cdparanoia includes both smiley
faces and more standard progress symbols. They are:
:-) Operation proceeding normally.
:-| Operation proceeding normally, but with jitter during reads.
:-/ Read drift.
8-| Repeated read problems in the same place.
:-O SCSI/ATAPI transport error (hardware problem not related to
the disc itself).
:-( Scratch detected.
;-( Unable to correct a problem.
8-X Aborted read due to uncorrectable error.
:^D Finished.
Blank space in the progress indicator means that no corrections
were necessary.
- Jitter correction was required.
+ Read errors.
! Errors even after correction; repeated read errors.
e Corrected transport errors.
V An uncorrected error or a skipped read.
cdrdao cdrdaocommand [options]toc-file
Write all content specified in description file toc-file to a CD-R disk
drive in one step. This is called disk-at-once (DAO) mode, as
opposed to the more commonly used track-at-once (TAO) mode.
DAO mode allows you to change the length of gaps between tracks
and define data to be written in these gaps (like hidden bonus
tracks or track intros). The toc file can be created by hand or gener-
ated from an existing CD using cdrdao’s read-toc command. A cue
file, as generated by other audio programs, can be used instead of a
toc file. The file format for toc files is discussed at length in the
cdrdao manpage.
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cdrdao
Commands
The first argument must be a command. Note that not all options
are available for all commands. Run cdrdao command -h to see the
options that apply to a particular command.
blank
Blank a CD-RW. The default is to do minimal blanking; use
--blank-mode to change to full blanking.
copy
Copy the CD. If you use a single drive, you will be prompted
to insert a CD-R after reading. An image file is created unless
you use the --on-the-fly flag and two CD drives.
discid
Display CDDB information.
disk-info
Display information about the CD-R currently in the drive.
drive-info
Display information about the drive.
msinfo
Display multisession information. Useful mostly for wrapper
scripts.
read-cd
Read from a CD and create a disk image and toc file that will
allow creation of duplicates. Use --datafile to specify a filename.
read-cddb
Check a CDDB server for data about the CD represented by a
given toc file; then write that data to the toc file as CD-TEXT
data.
read-test
Check the validity of the audio files described in the toc file.
read-toc
Create a toc file from an audio CD.
scanbus
Scan the system bus for devices.
show-data
Print out the data that will be written to the CD-R. Useful for
checking byte order.
show-toc
Print a summary of the CD to be created.
simulate
A dry run: do everything except write the CD. Equivalent to
write --simulate.
toc-info
Display a summary of the toc file.
toc-size
Display the total toc blocksize.
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cdrdao
unlock
Unlock the recorder after a failure. Run this command if you
cannot eject the CD after using cdrdao.
write
Write the CD.
Options
--blank-mode mode
Set the blanking mode to full or minimal. The default is
minimal.
--buffers n
Set the number of buffers. Since each buffer holds 1 second of
data, this is equivalent to setting the number of seconds of data
to be buffered. The default is 32; set to a higher number if
your read source is unreliable or is slower than the CD-R. The
minumum is 10.
--cddb-servers server,server
Enter hosts for servers. Servers may include ports, paths, and
proxies; you can list multiple servers separated by spaces or
commas.
--cddb-timeout s
Set the timeout for CDDB server connections to s seconds.
--cddb-directory localpath
CDDB data that is fetched will be saved in the directory
localpath.
--datafile filename
When used with the read-toc command, this option specifies
the datafile placed in the toc file. When used with read-cd and
copy, it specifies the name of the image file created.
--device bus,id,logicalunit
Set the SCSI address of the CD-R using the bus number, ID
number, and logical-unit number.
--driver driver-id:option-flags
Force cdrdao to use the driver you choose with the driver
options named, instead of the driver it autodetects.
--eject
Eject the disc when done.
--force
Override warnings and perform the action anyway.
--keep
On exit, keep any temporary WAV files created.
--keepimage
Keep the image file created during the copy process. Used only
with the copy command.
--multi
Record as a multisession disc.
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cdrdao
-n Do not wait 10 seconds before writing the disc.
--on-the-fly
Do not create an image file: pipe data directly from source to
CD-R.
--overburn
If you are using a disc with more storage space than cdrdao
detects, use this option to keep writing even when cdrdao thinks
you’re out of space.
--paranoia-mode n
Specify the amount of error correction in the CD read, where n
is a value from 0 to 3. 0 is none; 3 is full. Set error correction
to a lower number to increase read speed. The default is 3.
--read-raw
Used only with the read-cd command. Write raw data to the
image file.
--reload
Allow the drive to be opened before writing, without inter-
rupting the process. Used with simulation runs.
--save
Save current options to the settings file $HOME/.cdrdao.
--session n
Used only with the read-toc and read-cd commands when
working with multisession CDs. Specify the number of the
session to be processed.
--source-device bus,id,logicalunit
Used only with the copy command and two drives. Set the
SCSI address of the source device.
--source-driver driver-id:option-flags
Used only with the copy command. Set the source device
driver and flags.
--speed value
Set the write speed to value. The default is the highest available
speed; use a lower value if higher values give poor results.
--swap
Swap byte order for all samples.
-v verbose-level
Set the amount of information printed to the screen. 0, 1, and
2 are fine for most users; greater numbers are useful for
debugging.
--with-cddb
Use CDDB to fetch information about the disc and save it as
CD-TEXT data. Used with the copy, read-toc, and read-cd
commands.
Examples
To find devices on the system:
cdrdao scanbus
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cfdisk
To copy from a CD device (at 1,1,0) to a CD-R device (at 1,0,0):
cdrdao copy --source 1,1,0 --device 1,0,0 --buffers 64
cdrecord cdrecord [options]track1,track2...
Record data or audio compact discs. This program normally
requires root access. cdrecord is now generally a symbolic link to
wodim.
cfdisk cfdisk [options] [device]
System administration command. Partition a hard disk using a full-
screen display. Normally, device will be /dev/hda, /dev/hdb, /dev/
sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on; the default is the first
device on the system. See also fdisk.
Options
-a Use an arrow on the left side to highlight the currently selected
partition, instead of reverse video.
-c cylinders
Specify the number of cylinders to use to format the specified
device.
-g Ignore driver-provided geometry; guess one instead.
-h heads
Specify the number of heads to use to format the specified
device.
-s sectors
Specify the number of sectors per track to use to format the
specified device.
-v Print version number and exit.
-z Do not read the partition table; partition from scratch.
-P format
Display the partition table in format, which must be r (raw
data), s (sector order), or t (table format). See the manpage for
the meaning of the fields in the raw format, which shows what
will be written by cfdisk for each partition. The sector format
shows information about the sectors used by each partition.
The table format shows the starting and ending head, sector,
and cylinder for each partition.
Commands
up arrow, down arrow
Move among partitions.
left arrow, right arrow
Move among commands at the bottom of the screen.
Enter key
Select currently highlighted command or value.
b Toggle flag indicating whether selected partition is bootable.
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chage
d Delete partition (allow other partitions to use its space).
g Alter the disk’s geometry. Prompt for what to change: cylinders,
heads, or sectors (c, h, or s, respectively).
h Help.
m Attempt to ensure maximum usage of disk space in the
partition.
n Create a new partition. Prompt for more information.
p Print the partition table to the screen or a file. Possible formats
are the same as for the -P option.
q Quit without saving information.
t Prompt for a new filesystem type, and change to that type.
u Change the partition-size units. The choice of units rotates
from megabytes to sectors to cylinders and back.
W Save information. Must be uppercase, to prevent accidental
writing.
chage chage [options]user
Change information about user password expirations. If run with
no option flags, chage prompts for values to be entered; you may
also use option flags to change or view information. Requires a
shadow password file. An unprivileged user can only run chage
with the -l option.
Options
-d lastday, --lastday=lastday
Date of last password change. This may be expressed as a date
in YYYY-MM-DD format, or as the number of days between
January 1, 1970 and the last password change.
-E expiredate, --expiredate=expiredate
Set the date when the account will be locked. This is not a
date for password expiration, but for account expiration. It
may be expressed in YYYY-MM-DD format or as a number of
days since January 1, 1970.
-I inactivedays, --inactive=inactivedays
If a password expires and the user does not log in for this
number of days, the account will be locked and the user must
contact a system administrator before logging in. Set to 0 to
disable the feature.
-l, --list
This flag is used without any others and causes chage to
display the current password expiration attributes for the user.
-m mindays, --mindays=mindays
Specify the minimum number of days between password
changes. Default is zero, meaning that the user may change
the password at any time.
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chattr
-M maxdays, --maxdays=maxdays
Maximum number of days between password changes.
-W warndays, --warndays=warndays
The number of days before password expiration that a user
will be warned to change passwords.
chattr chattr [options]mode files
Modify file attributes. Specific to Linux Second and Third
Extended Filesystems (ext2 and ext3). Like symbolic chmod, chattr
specifies attributes with +, -, and = but it operates on extended file
attributes (see the upcoming section “Attributes”). mode is in the
form opcode attribute. See also lsattr.
Options
-R Modify directories and their contents recursively.
-f Suppress most error messages.
-V Verbose; print modes of attributes after changing them.
-v version
Set the file’s version.
Opcodes
+ Add attribute.
- Remove attribute.
= Assign attributes (removing unspecified attributes).
Attributes
A Don’t update access time on modify.
a Append only for writing. Can be set or cleared only by a privi-
leged user.
c Compressed.
D Write changes synchronously to disk.
d No dump.
H The file’s blocks are stored in units of the filesystem block-
size, not of sectors. The file is or was at one time larger than 2
TB.
I A directory is indexed using hashed trees.
i Immutable. Can be set or cleared only by a privileged user. A
file marked as immutable cannot be deleted, renamed, modi-
fied, or linked to until the setting has been cleared.
j Journalled file. This is useful only in cases where you are using
an ext3 filesystem mounted with the data="ordered" or
data="writeback" attributes. The data="journal" option for
the filesystem causes this operation to be performed for all
files in the system and makes this option irrelevant.
S Synchronous updates.
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chfn
s Secure deletion. The contents are zeroed on deletion, and the
file cannot be undeleted or recovered in any way.
u Undeletable. This causes a file to be saved even after it has
been deleted, so that a user can undelete it later.
Example
chattr +a myfile As superuser
chfn chfn [options] [username]
Change the information that is stored in /etc/passwd and displayed
to the finger query. With no options, chfn enters interactive mode
and prompts for changes. To blank a field, enter the keyword none.
Only a privileged user can change information for another user. For
regular users, chfn prompts for the user’s password before making
the change.
Options
-f name, --full-namename
Specify new full name.
-h homephone, --home-phonehomephone
Specify new home phone number.
-o office, --officeoffice
Specify new office number.
-p officephone, --office-phoneofficephone
Specify new office phone number.
-u, --help
Print help message and then exit.
-v, --version
Print version information and then exit.
Example
chfn -f "Ellen Siever" ellen
chgrp chgrp [options]newgroupfiles
Change the group of one or more files to newgroup. newgroup is
either a group ID number or a group name located in /etc/group.
Only the owner of a file or a privileged user may change the group.
Options
-c, --changes
Print information about files that are changed.
--dereference
Change the group of the file pointed to by a symbolic link, not
the group of the symbolic link. This is the default behavior.
-f, --silent, --quiet
Do not print error messages about files that cannot be changed.
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chkconfig
-h, --no-dereference
Change the group of the symbolic link.
-H Used with -R. If a command-line argument is a symbolic link
to a directory, traverse the directory.
--help
Print help message and then exit.
-L Used with -R. Traverse every symbolic link that points to a
directory.
--no-preserve-root
Do not treat / as special. This is the default behavior.
-P Used with -R. Do not traverse any symbolic links. This is the
default behavior.
--preserve-root
Do not operate recursively on /.
-R, --recursive
Traverse subdirectories recursively, applying changes.
--reference=filename
Change the group to that associated with filename. In this case,
newgroup is not specified.
-v, --verbose
Verbosely describe ownership changes.
--version
Print version information and then exit.
chkconfig chkconfig [options] [service [flag]]
System administration command. Manipulate symbolic links in the
/etc/rc.d/rc[0–6].d directories. chkconfig manages which services
will run in a specified runlevel. Valid flags are on, off, reset or
resetpriorities to reset the service to default on/off or priorities
given in its initialization script in /etc/rc.d/init.d. This command is
available in Fedora and RedHat-style distributions, including SUSE
and SUSE-based distributions. To specify defaults in a standard
initialization script, add a comment line to the script beginning
with chkconfig: followed by the runlevels in which the service
should run, and the start and kill priority numbers to assign—e.g.,
chkconfig: 2345 85 15. To override defaults specified in init files,
you can create a file with the same service name in /etc/chkconfig.d.
Place a chkconfig line in this override file. This allows you to safely
customize package maintained services.
Options
--add service
Create a start or kill symbolic link in every runlevel for the
specified service according to default behavior specified in
the service’s initialization script.
--del service
Remove entries for specified service from all runlevels.
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chmod
--level numbers
Specify by number the runlevels to change. Provide numbers as
a numeric string: e.g., 016 for levels 0, 1, and 6. Use this to
override specified defaults.
--list [service]
Print whether the specified service is on or off in each level. If no
service is specified, print runlevel information for all services
managed by chkconfig.
--override service
If service is configured according to defaults in /etc/rc.d/init.d
and an override file exists in /etc/chkconfig.d, reconfigure
service to match the override settings.
chmod chmod [options]modefiles
chmod [options] --reference=filenamefiles
Change the access mode (permissions) of one or more files. Only
the owner of a file or a privileged user may change the mode. mode
can be numeric or an expression in the form of who opcode permis-
sion. who is optional (if omitted, the default is a); choose only one
opcode. Separate multiple modes by commas.
Options
-c, --changes
Print information about files that are changed.
-f, --silent, --quiet
Do not notify user of files that chmod cannot change.
--help
Print help message and then exit.
--no-preserve-root
Do not treat / as special. This is the default behavior.
--preserve-root
Do not operate recursively on /.
-R, --recursive
Traverse subdirectories recursively, applying changes.
--reference=filename
Change permissions to match those associated with filename.
-v, --verbose
Print information about each file, whether changed or not.
--version
Print version information and then exit.
Who
u User.
g Group.
o Other.
a All (default).
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chmod
Opcode
+ Add permission.
- Remove permission.
= Assign permission (and remove permission of the unspecified
fields).
Permissions
r Read.
w Write.
x Execute.
X Execute if file is a directory or already has execute permission
for some user.
s Set user (or group) ID.
t Sticky bit; used on directories to prevent removal of files by
nonowners.
u User’s present permission.
g Group’s present permission.
o Other’s present permission.
Alternatively, specify permissions by a three-digit octal number. The
first digit designates owner permission; the second, group permis-
sion; and the third, other’s permission. Permissions are calculated
by adding the following octal values:
4 Read.
2 Write.
1 Execute.
Note that a fourth digit may precede this sequence. This digit
assigns the following modes:
4 Set user ID on execution to grant permissions to process based
on the file’s owner, not on permissions of the user who
created the process.
2 Set group ID on execution to grant permissions to process
based on the file’s group, not on permissions of the user who
created the process.
1 Set sticky bit.
Examples
Add execute-by-user permission to file:
chmod u+xfile
Either of the following assigns read/write/execute permission by
owner (7), read/execute permission by group (5), and execute-only
permission by others (1) to file:
chmod 751file
chmod u=rwx,g=rx,o=xfile
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chown
Any one of the following assigns read-only permission to file for
everyone:
chmod =rfile
chmod 444file
chmod a-wx,a+rfile
The following makes the executable setuid, assigns read/write/
execute permission by owner, and assigns read/execute permission
by group and others:
chmod 4755file
chown chown [options]newownerfiles
chown [options]--reference=filenamefiles
Change the ownership of one or more files to newowner. newowner
is either a user ID number or a login name located in /etc/passwd.
chown also accepts users in the form newowner:newgroup or
newowner.newgroup. The last two forms change the group owner-
ship as well. If no owner is specified, the owner is unchanged. With
a period or colon but no group, the group is changed to that of the
new owner. Only the current owner of a file or a privileged user
may change the owner.
Options
-c, --changes
Print information about files that are changed.
--dereference
Follow symbolic links.
-f, --silent, --quiet
Do not print error messages about files that cannot be
changed.
--from=currown:currgroup
Only change owner and/or group if the current owner and
group match those specified in --from. If currown or currgroup
is omitted, a match is not required for that attribute.
-h, --no-dereference
Change the ownership of each symbolic link (on systems that
allow it), rather than the referenced file.
-v, --verbose
Print information about all files that chown attempts to change,
whether or not they are actually changed.
-R, --recursive
Traverse subdirectories recursively, applying changes.
-H With -R, traverse symbolic link to a directory.
-L With -R, traverse every symbolic link that leads to a directory.
-P With -R, do not traverse any symbolic links. This is the
default.
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chrt
--reference=filename
Change owner to the owner of filename instead of specifying a
new owner explicitly.
--help
Print help message and then exit.
--version
Print version information and then exit.
chpasswd chpasswd [options]
System administration command. Change user passwords in a batch.
chpasswd accepts input in the form of one username:password pair
per line. Unless the -e option is specified, password is encrypted
before being stored. This command doesn’t use PAM. It updates
the /etc/passwd and /etc/shadow files.
Option
-e, --encrypted
Passwords given are already encrypted.
-m, --md5
Use MD5 Encryption
chroot chrootnewroot [command]
System administration command. Change root directory for
command or, if none is specified, for a new copy of the user’s shell.
This command or shell is executed relative to the new root. The
meaning of any initial / in pathnames is changed to newroot for a
command and any of its children. In addition, the initial working
directory is newroot. This command is restricted to privileged
users.
chrt chrt [options] [prio] [pid |command ...]
Set or retrieve the real-time scheduling properties of a given
process, or run a new process with the given real-time scheduling
properties.
Options
-b, --batch
Use the batch scheduling policy.
-f, --fifo
Use the FIFO (first-in, first-out) scheduling policy.
-h, --help
Display usage information and then exit.
-m, --max
Show the minimum and maximum valid scheduling priorities.
-o, --other
Use the normal (called “other”) scheduling policy.
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chsh
-p, --pid
Operate on the given, existing PID and do not execute a new
command.
-r, --rr
Use the round-robin scheduling policy.
-v, --version
Display version information and then exit.
chsh chsh [options] [username]
Change your login shell, either interactively or on the command
line. Warn if shell does not exist in the file /etc/shells. Specify the
full path to the shell. chsh prompts for your password. Only a priv-
ileged user can change another user’s shell.
Options
-l, --list-shells
Print valid shells, as listed in /etc/shells, and then exit.
-s shell, --shell shell
Specify new login shell.
-u, --help
Print help message and then exit.
-v, --version
Print version information and then exit.
Example
chsh -s /bin/tcsh
chvt chvtN
Switch to virtual terminal N (that is, switch to /dev/ttyN). If you
have not created /dev/ttyN, it is created when you run this
command. There are keyboard shortcuts for this functionality as
well. From a graphical desktop, you can press Ctrl-Alt-F1 through
F12 to switch to different virtual terminals. In text mode, you can
skip the Ctrl key and just use Alt-F1 through F12. To switch back
to graphical mode, use Alt-F7.
cksum cksum [files]
Compute a cyclic redundancy check (CRC) checksum for all files;
this is used to ensure that a file was not corrupted during transfer.
Read from standard input if the character - is given or no files are
given. Display the resulting checksum, the number of bytes in the
file, and (unless reading from standard input) the filename. Also
see md5sum and sha1sum.
clear clear
Clear the terminal display. Equivalent to pressing Ctrl-L.
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col
cmp cmp [options]file1file2 [skip1 [skip2]]
Compare file1 with file2. Use standard input if file1 is - or missing.
This command is normally used for comparing binary files,
although files can be of any type. (See also diff.) skip1 and skip2 are
optional offsets in the files at which the comparison is to start.
Options
-i num, --ignore-initial=num
Ignore the first num bytes of input. num can be given as
num1:num2 to skip a different number of bytes in file1 and
file2.
-l, --verbose
Print offsets and codes of all differing bytes.
-s, --quiet, --silent
Work silently; print nothing, return an exit code:
0 Files are identical.
1 Files are different.
2 Files are inaccessible.
Example
Print a message if two files are the same (exit code is 0):
cmp -s old new && echo 'no changes'
col col [options]
A postprocessing filter that handles reverse linefeeds and escape
characters, allowing output from tbl or nroff to appear in reasonable
form on a terminal.
Options
-b Ignore backspace characters; helpful when printing manpages.
-f Process half-line vertical motions, but not reverse line motion.
(Normally, half-line input motion is displayed on the next full
line.)
-l n
Buffer at least n lines in memory. The default buffer size is 128
lines.
-p Do not filter out unrecognized control sequences, but pass
them through.
-x Normally, col saves printing time by converting sequences of
spaces to tabs. Use -x to suppress this conversion.
Examples
Run myfile through tbl and nroff, then capture output on screen by
filtering through col and more:
tbl myfile | nroff | col | more
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colcrt
Save manpage output for the ls command in out.print, stripping
out backspaces (which would otherwise appear as ^H):
man ls | col -b > out.print
colcrt colcrt [options] [files]
A postprocessing filter that handles reverse linefeeds and escape
characters, allowing output from tbl or nroff to appear in reasonable
form on a terminal. Put half-line characters (e.g., subscripts or
superscripts) and underlining (changed to dashes) on a new line
between output lines.
Options
- Do not underline.
-2 Double space by printing all half-lines to make subscripts and
superscripts visible.
colrm colrm [start [stop]]
Remove specified columns from a file, where a column is a single
character in a line. Read from standard input and write to standard
output. Columns are numbered starting with 1. Begin deleting
columns at (including) the start column, and stop at (including) the
stop column; if stop is not given, delete all columns to the end.
Entering a tab increments the column count to the next multiple of
either the start or stop column; entering a backspace decrements it
by 1.
Example
colrm 3 5 < test1 > test2
column column [options] [files]
Format input from one or more files into columns, filling rows first.
Read from standard input if no files are specified.
Options
-c num
Format output into num columns.
-s char
Delimit table columns with char. Meaningful only with -t.
-t Format input into a table. Delimit with whitespace, unless an
alternate delimiter has been provided with -s.
-x Fill columns before filling rows.
comm comm [options]file1file2
Compare lines common to the sorted files file1 and file2. Output is
in three columns, from left to right: lines unique to file1, lines
unique to file2, and lines common to both files. comm is similar to
diff in that both commands compare two files. But comm can also
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cp
be used like uniq; comm selects duplicate or unique lines between
two sorted files, whereas uniq selects duplicate or unique lines
within the same sorted file.
Options
-num
Suppress printing of column num. Multiple columns may be
specified and should not be space-separated.
--help
Print help message and exit.
--version
Print version information and exit.
Example
Compare two lists of top-10 movies, and display items that appear
in both lists:
comm -12 siskel_top10 ebert_top10
cp cp [options]file1file2
cp [options]files directory
Copy file1 to file2, or copy one or more files to the same names
under directory. If the destination is an existing file, the file is over-
written; if the destination is an existing directory, the file is copied
into the directory (the directory is not overwritten).
Options
-a, --archive
Preserve attributes of original files where possible. The same
as -dpr.
-b, --backup[=control]
Back up files to be overwritten. As -b, takes no argument.
For --backup, control specifies the type of backup and can
also be set with the environment variable VERSION-
CONTROL. The default is existing. Valid arguments are:
t, numbered
Always make numbered backups.
nil, existing
Make numbered backups of files that already have them;
otherwise, make simple backups.
never, simple
Always make simple backups.
none, off
Never make backups, even if --backup is specified.
-c The same as --preserve=context.
--copy-contents
Copy contents of special files when recursive.
-d The same as --no-dereference --preserve=links.
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cp
-f, --force
Remove an existing file in the destination if it can’t be opened.
See also --remove-destination.
-H Follow command-line symbolic links in the source.
-i, --interactive
Prompt before overwriting destination files. On most systems,
this flag is turned off by default except for the root user, who
is normally prompted before overwriting files.
-l, --link
Make hard links, not copies, of nondirectories.
-L, --dereference
Always follow symbolic links.
--no-preserve[=attribs]
Do not preserve the specified attributes. See --preserve for the
list of possible attributes.
-p The same as --preserve=mode,ownership,timestamps.
--preserve[=attribs]
Preserve the specified attributes. By default, preserve owner-
ship, permissions, and timestamps. Other possible attributes
include context, links, all.
-P, --no-dereference
Never follow symbolic links.
--parents
Preserve intermediate directories in source. The last argument
must be the name of an existing directory. For example, the
command:
cp --parents jphekman/book/ch1 newdir
copies the file jphekman/book/ch1 to the file newdir/jphekman/
book/ch1, creating intermediate directories as necessary.
-r, -R, --recursive
Copy directories recursively.
--remove-destination
Remove existing destination files without attempting to open
them. See also --force.
-s, --symbolic-link
Make symbolic links instead of copying. Source filenames
must be absolute.
-S backup-suffix, --suffix=backup-suffix
Set suffix to be appended to backup files. This may also be set
with the SIMPLE_BACKUP_SUFFIX environment variable.
The default is ~. You need to explicitly include a period if you
want one before the suffix (for example, specify .bak, not bak).
--sparse=[always|auto|never]
Handle files that have “holes” (are defined as a certain size but
have less data). always creates a sparse file, auto creates one if
the input file is sparse (the default), and never creates a non-
sparse file without holes.
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cpio
--strip-trailing-slashes
Remove trailing slashes from each source file argument.
-u, --update
Do not copy a file to an existing destination with the same or
newer modification time.
-v, --verbose
Before copying, print the name of each file.
-x, --one-file-system
Stay on the current filesystem.
Example
Copy the contents of the guest directory recursively into the /archives
/guest/ directory, and display a message for each file copied:
cd/archives&& cp -av/home/guest guest
cpio cpiomode [options]
Copy file archives from or to tape or disk, or to another location on
the local machine. Each of the three modes -i, -o, or -p accepts
different options.
Mode
-i, --extract [options] [patterns]
Copy in (extract) from an archive files whose names match
selected patterns. Each pattern can include Bourne shell file-
name metacharacters. (Patterns should be quoted or escaped so
that they are interpreted by cpio, not by the shell.) If pattern is
omitted, all files are copied in. Existing files are not overwritten
by older versions from the archive unless -u is specified.
-o, --create [options]
Copy out to an archive a list of files whose names are given on
the standard input.
-p, --pass-through [options] directory
Copy (pass) files to another directory on the same system.
Destination pathnames are interpreted relative to the named
directory.
Comparison of valid options
Single-character options available to the -i, -o, and -p modes are
shown here (the - is omitted for clarity):
i: bcdf mnrtsuv B SVCEHMR IF
o: 0a c vABL VC HM O F
p: 0a d lm uv L V R
Options
-0, --null
Expect list of filenames to be terminated with null, not
newline. This allows files with a newline in their names to be
included.
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cpio
-a, --reset-access-time
Reset access times of input files after reading them.
-A, --append
Append files to an existing archive, which must be a disk file.
Specify this archive with -O or -F.
-b, --swap
Swap bytes and half-words to convert between big-endian and
little-endian 32-bit integers.
-B Block input or output using 5120 bytes per record (default is
512 bytes per record).
--block-size=size
Set input or output size to size × 512 bytes.
-c Read or write header information as ASCII characters, which
is useful when source and destination machines are different
types.
-C n, --io-size=n
Like -B, but block size can be any positive integer n.
-d, --make-directories
Create directories as needed.
-E file, --pattern-file=file
Extract from the archives filenames that match patterns in file.
-f, --nonmatching
Reverse the sense of copying; copy all files except those that
match patterns.
-F file, --file=file
Use file as the archive, not stdin or stdout. file can reside on
another machine, if given in the form [user@]hostname:file
(where user@ is optional).
--force-local
Assume that file (provided by -F, -I, or -O) is a local file, even
if it contains a colon (:) indicating a remote file.
-H type, --format=type
Use type format. Default for copy-out is bin; default for copy-
in is autodetection of the format. Valid formats (all caps also
accepted) are:
bin
Binary.
odc
Old (POSIX.1) portable format.
newc
New (SVR4) portable format.
crc
New (SVR4) portable format with checksum added.
tar
Tar.
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cpio
ustar
POSIX.1 tar (also recognizes GNU tar archives).
hpodc
HP-UX portable format.
-I file
Read file as an input archive. May be on a remote machine
(see -F).
-k Ignored. For compatibility with other versions of cpio.
-l, --link
Link files instead of copying.
-L, --dereference
Follow symbolic links.
-m, --preserve-modification-time
Retain previous file modification time.
-M msg, --message=msg
Print msg when switching media, as a prompt before switching
to new media. Use variable %d in the message as a numeric ID
for the next medium. -M is valid only with -I or -O.
-n, --numeric-uid-gid
When verbosely listing contents, show user ID and group ID
numerically.
--no-absolute-filenames
Create all copied-in files relative to the current directory.
--no-preserve-owner
Make all copied files owned by yourself, instead of the owner
of the original. Can be used only if you are a privileged user.
Valid in copy-in and pass-through modes.
-O file
Archive the output to file, which may be a file on another
machine (see -F).
--only-verify-crc
For a CRC-format archive, verify the CRC of each file; don’t
actually copy the files in.
--quiet
Don’t print the number of blocks copied.
-r, --rename
Rename files interactively.
-R [user][:group], --owner [user][:group]
Reassign file ownership and group information to the user’s
login ID (privileged users only).
--rsh-command=cmd
Use the specified command to communicate with remote systems.
-s, --swap-bytes
Swap bytes of each two-byte half-word.
-S, --swap-half-words
Swap half-words of each four-byte word.
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cpp
--sparse
For copy-out and copy-pass, write files that have large blocks
of zeros as sparse files.
-t, --list
Print a table of contents of the input (create no files). When used
with the -v option, resembles output of ls -l.
--to-stdout
In copy-in mode, extract files to standard output.
-u, --unconditional
Unconditional copy; old files can overwrite new ones.
-v, --verbose
Print a list of filenames processed.
-V, --dot
Print a dot for each file read or written (this shows cpio at
work without cluttering the screen).
--version
Print version number and then exit.
Examples
Generate a list of files whose names end in .old using find; use the
list as input to cpio:
find . -name "*.old" | cpio -ocBv > /dev/rst8
Restore from a tape drive all files whose names contain save
(subdirectories are created if needed):
cpio -icdv "*save*" < /dev/rst8
Move a directory tree:
find . -depth | cpio -padm /mydir
cpp cpp [options] [ifile [ofile]]
GNU C language preprocessor. cpp is normally invoked as the first
pass of any C compilation by the gcc command. The output of cpp
is a form acceptable as input to the next pass of the C compiler.
The ifile and ofile options are, respectively, the input and output for
the preprocessor; they default to standard input and standard
output.
Options
-$ Do not allow $ in identifiers.
-ansi
Use 1990 ISO C standard. This is equivalent to -std=c89.
-dD
Similar to -dM, but exclude predefined macros and include
results of preprocessing.
-dM
Suppress normal output. Print series of #defines that create
the macros used in the source file.
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cpp
-dN
Similar to -dD, but don’t print macro expansions.
-dI
Print #include directives in addition to other output.
-fpreprocessed
Treat file as already preprocessed. Skip most processing direc-
tives, remove all comments, and tokenize file.
-ftabstop=width
Set distance between tabstops so columns will be reported
correctly in warnings and errors. Default is 8.
-fno-show-column
Omit column numbers in warnings and errors.
-gcc
Define _ _GNUC_ _, _ _GNUC_MINOR_ _, and _ _GNUC_
PATCHLEVEL_ _ macros.
--help
Print usage message and exit.
-idirafter dir
Search dir for header files when a header file is not found in
any of the included directories.
-imacros file
Process macros in file before processing main files.
-include file
Process file before main file.
-iprefix prefix
When adding directories with -iwithprefix, prepend prefix to
the directory’s name.
-isystem dir
Search dir for header files after searching directories specified
with -I but before searching standard system directories.
-iwithprefix dir
Append dir to the list of directories to be searched when a
header file cannot be found in the main include path. If -iprefix
has been set, prepend that prefix to the directory’s name.
-iwithprefixbefore dir
Insert dir at the beginning of the list of directories to be
searched when a header file cannot be found in the main
include path. If -iprefix has been set, prepend that prefix to
the directory’s name.
-lang-c, -lang-c++, -lang-objc, -lang-objc++
Expect the source to be in C, C++, Objective C, or Objective
C++, respectively.
-lint
Display all lint commands in comments as #pragma lint
command.
-nostdinc
Search only specified, not standard, directories for header files.
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cpp
-nostdinc++
Suppress searching of directories believed to contain C++-
specific header files.
-o file
Write output to file. (Same as specifying a second filename in
the command line.)
-pedantic
Warn verbosely.
-pedantic-errors
Produce a fatal error in every case in which -pedantic would
have produced a warning.
-std=standard
Specify C standard of input file. Accepted values are:
iso9899:1990, c89
1990 ISO C standard.
iso9899:199409
1994 amendment to the 1990 ISO C standard.
iso9899:1999, c99, iso9899:199x, c9x
1999 revised ISO C standard.
gnu89
1990 C Standard with gnu extensions. The default value.
gnu99, gnu9x
1999 revised ISO C standard with gnu extensions.
-traditional
Behave like traditional C, not ANSI.
-trigraphs
Convert special three-letter sequences, meant to represent
missing characters on some terminals, into the single character
they represent.
-undef
Suppress definition of all nonstandard macros.
-v Verbose mode.
-version
Print version number, then process file.
--version
Print version number, then exit.
-w Don’t print warnings.
-x language
Specify the language of the input file. language may be c, c++,
objective-c, or assembler-with-cpp. By default, language is
deduced from the filename extension. If the extension
is unrecognized, the default is c.
-A name[=def]
Assert name with value def as if defined by #assert. To turn
off standard assertions, use -A-.
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cpp
-A -name[=def]
Cancel assertion name with value def.
-C Retain all comments except those found on cpp directive lines.
By default, cpp strips C-style comments.
-Dname[=def]
Define name with value def as if by a #define. If no =def is
given, name is defined with value 1. -D has lower precedence
than -U.
-E Preprocess the source files, but do not compile. Print result to
standard output. This option is usually passed from gcc.
-H Print pathnames of included files, one per line, on standard
error.
-Idir
Search in directory dir for #include files whose names do not
begin with / before looking in directories on standard list.
#include files whose names are enclosed in double quotes and
do not begin with / will be searched for first in the current
directory, then in directories named on -I options, and last in
directories on the standard list.
-I- Split includes. Search directories specified by -I options
preceding this one for header files included with quotes
(#include "file.h") but not for header files included with angle
brackets (#include <file.h>). Search directories specified by -I
options following this one for all header files.
-M [-MG]
Suppress normal output. Print a rule for make that describes
the main source file’s dependencies. If -MG is specified,
assume that missing header files are actually generated files,
and look for them in the source file’s directory.
-MF file
Print rules generated by -M or -MM to file.
-MD file
Similar to -M, but output to file; also compile the source.
-MM
Similar to -M, but describe only those files included as a result
of #include "file".
-MMD file
Similar to -MD, but describe only the user’s header files.
-MQ target
Similar to -MT, but quote any characters that are special to
make.
-MT target
Specify the target to use when generating a rule for make. By
default, the target is based on the name of the main input file.
-P Preprocess input without producing line-control information
used by next pass of the C compiler.
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cpp
-Uname
Remove any initial definition of name, where name is a
reserved symbol predefined by the preprocessor, or a name
defined on a -D option. Names predefined by cpp are unix
and i386 (for Intel systems).
-Wall
Warn both on nested comments and trigraphs.
-Wcomment, -Wcomments
Warn when encountering the beginning of a nested comment.
-Wtraditional
Warn when encountering constructs that are interpreted
differently in ANSI than in traditional C.
-Wtrigraphs
Warn when encountering trigraphs, which are three-letter
sequences meant to represent missing characters on some
terminals.
Special names
cpp understands various special names, some of which are:
_ _DATE_ _
Current date (e.g., Jan 10 2003).
_ _FILE_ _
Current filename (as a C string).
_ _LINE_ _
Current source line number (as a decimal integer).
_ _TIME_ _
Current time (e.g., 12:00:00).
These special names can be used anywhere, including in macros,
just like any other defined names. cpp’s understanding of the line
number and filename may be changed using a #line directive.
Directives
All cpp directive lines start with # in column 1. Any number of
blanks and tabs is allowed between the # and the directive. The
directives are:
#assert name (string)
Define a question called name, with an answer of string. Asser-
tions can be tested with #if directives. The predefined
assertions for #system, #cpu,and #machine can be used for
architecture-dependent changes.
#unassert name
Remove assertion for question name.
#define name token-string
Define a macro called name, with a value of token-string.
Subsequent instances of name are replaced with token-string.
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cpp
#define name( arg, ... , arg ) token-string
This allows substitution of a macro with arguments. token-
string will be substituted for name in the input file. Each call to
name in the source file includes arguments that are plugged
into the corresponding args in token-string.
#undef name
Remove definition of the macro name. No additional tokens
are permitted on the directive line after name.
#ident string
Put string into the comment section of an object file.
#include "filename", #include<filename>
Include contents of filename at this point in the program. No
additional tokens are permitted on the directive line after the
final " or >.
#line integer-constant "filename"
Cause cpp to generate line-control information for the next
pass of the C compiler. The compiler behaves as if integer-
constant is the line number of the next line of source code and
filename (if present) is the name of the input file. No addi-
tional tokens are permitted on the directive line after the
optional filename.
#endif
End a section of lines begun by a test directive (#if, #ifdef, or
#ifndef). No additional tokens are permitted on the directive
line.
#ifdef name
Lines following this directive and up to matching #endif or
next #else or #elif will appear in the output if name is
currently defined. No additional tokens are permitted on the
directive line after name.
#ifndef name
Lines following this directive and up to matching #endif or
next #else or #elif will appear in the output if name is not
currently defined. No additional tokens are permitted on the
directive line after name.
#if constant-expression
Lines following this directive and up to matching #endif or
next #else or #elif will appear in the output if constant-
expression evaluates to nonzero.
#elif constant-expression
An arbitrary number of #elif directives are allowed between
an #if, #ifdef, or #ifndef directive and an #else or #endif
directive. The lines following the #elif and up to the next
#else, #elif, or #endif directive will appear in the output if
the preceding test directive and all intervening #elif directives
evaluate to zero, and the constant-expression evaluates to
nonzero. If constant-expression evaluates to nonzero, all
succeeding #elif and #else directives will be ignored.
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crond
#else
Lines following this directive and up to the matching #endif
will appear in the output if the preceding test directive evalu-
ates to zero, and all intervening #elif directives evaluate to
zero. No additional tokens are permitted on the directive line.
#error
Report fatal errors.
#warning
Report warnings, but then continue processing.
crond crond [options]
System administration command. Normally started in a system
startup file. Execute commands at scheduled times, as specified in
users’ files in /var/spool/cron. Each file shares its name with the user
who owns it. The files are controlled via the command crontab.
The crond command will also read commands from the /etc/crontab
file and from the /etc/cron.d/ directory. See anacron for scheduling
events on systems that are frequently rebooted or powered off,
such as notebook computers.
Options
-m command
User command to send mail instead of sendmail.
-n Run the command in the foreground.
-p Remove security restrictions on crontab file permissions.
crontab crontab [options] [file]
View, install, or uninstall your current crontab file. A privileged
user can run crontab for another user by supplying -u user. A
crontab file is a list of commands, one per line, that will execute
automatically at a given time. Numbers are supplied before each
command to specify the execution time. The numbers appear in
five fields, as follows:
Minute 0-59
Hour 0-23
Day of month 1-31
Month 1-12
Jan, Feb, Mar, ...
Day of week 0-6, with 0 = Sunday
Sun, Mon, Tue, ...
Use a comma between multiple values, a hyphen to indicate a
range, an asterisk to indicate all possible values, and a slash (/) to
indicate a repeating range. For example, assuming these crontab
entries:
59 3 * * 5 find / -print |backup_program
0 0 1,15 * * echo "Timesheets due" | mailuser
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csplit
the first command backs up the system files every Friday at 3:59 a.m.,
and the second command mails a reminder on the 1st and 15th of
each month.
The superuser can always issue the crontab command. Other users
must be listed in the file /etc/cron.allow if it exists; otherwise, they
must not be listed in /etc/cron.deny. If neither file exists, only the
superuser can issue the command.
Options
The -e, -l, and -r options are not valid if any files are specified.
-e Edit the user’s current crontab file (or create one).
-l Display the user’s crontab file on standard output.
-r Delete the user’s crontab file.
-u user
Indicate which user’s crontab file will be acted upon.
csplit csplit [options]filearguments
Separate file into context-based sections and place sections in files
named xx00 through xxn (n < 100), breaking file at each pattern
specified in arguments. The byte count for each section is written to
standard output. See also split.
Options
- Read from standard input.
-b format, --suffix-format=format
Use sprintf format instead of %02d for the suffix.
-f prefix, --prefix=prefix
Name new files prefix00 through prefixn (default is xx00
through xxn).
-k, --keep-files
Keep newly created files even when an error occurs (which
would normally remove these files). This is useful when you
need to specify an arbitrarily large repeat argument, {n}, and
you don’t want an out-of-range error to cause removal of the
new files.
-n num, --digits=num
Use output filenames with numbers num digits long. The
default is 2.
-s, -q, --silent, --quiet
Suppress display of character counts.
-z, --elide-empty-files
Do not create empty output files. However, number as if those
files had been created.
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ctags
Arguments
Any one or a combination of the following expressions may be
specified as arguments. Arguments containing blanks or other
special characters should be surrounded by single quotes.
/expr/[offset]
Create file from the current line up to the line containing the
regular expression expr. offset should be of the form +n or -n,
where n is the number of lines below or above expr.
%expr%[offset]
Same as /expr/, except no file is created for lines before a line
containing expr.
num
Create file from current line up to (but not including) line
number num. When followed by a repeat count (number
inside { }), put the next num lines of input into another output
file.
{n}
Repeat argument n times. May follow any of the preceding
arguments. Files are split at instances of expr or in blocks of
num lines. If * is given instead of n, repeat argument until
input is exhausted.
Examples
Create up to 20 chapter files from the file novel:
csplit -k -f chap. novel '/CHAPTER/' '{20}'
Create up to 100 address files (xx00 through xx99), each four lines
long, from a database named address_list:
csplit -k address_list 4 {99}
ctags ctags [options]files
Create a list of function and macro names defined in a program-
ming source file. More than one file may be specified. ctags
understands many programming languages, including C, C++,
FORTRAN, Java, Perl, Python, flex, yacc, and bison. The output
list (named tags by default) contains lines of the form:
name file context
where name is the function or macro name, file is the source file in
which name is defined, and context is a search pattern that shows
the line of code containing name. After the list of tags is created,
you can invoke vi on any file and type:
:set tags=tagsfile
:tagname
This switches the vi editor to the source file associated with the
name listed in tagsfile (which you specify with -t).
etags produces an equivalent file for tags to be used with Emacs.
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cupsd
Options
-a Append tag output to existing list of tags.
-e Create tag files for use with emacs.
-h extensionlist
Interpret files with filename extensions specified in extension-
list as header files. The default list is “.h.H.hh.hpp.hxx.h++.
inc.def”. To indicate that files without extensions should be
treated as header files, insert an additional period in the list
beforeanother period or at the end of the list, or use just a
period by itself. To use this option multiple times and have the
specified lists ANDed together, use a plus sign as the first
character in the list. To restore the default, use the word
“default”.
-n Use numeric ex commands to locate tags. Same as --excmd=
number.
-o file, -f file, --output=file
Write to file.
--packages-only
Include tag entries for members of structure-like constructs.
-R Recursively read files in subdirectories of the directory given
on the command line.
-u Don’t sort tag entries.
-x Produce a tabular listing of each function, and its line number,
source file, and context.
-B Search for tags backward through files.
-I tokenlist
Specify a list of tokens to be specially handled. If tokenlist is
given as a file, use ex pattern commands to locate tags. Same
as --excmd=pattern.
-N Use ex pattern commands to locate tags. Same as --excmd=
pattern.
-S, --ignore-indentation
Normally ctags uses indentation to parse the tag file; this
option tells ctags to rely on indentation less.
-T, --typedefs-and-c++
Include tag entries for typedefs, structs, enums, unions, and
C++ member functions.
-V, --version
Print the version number and exit.
cupsd cupsdoptions
System administration command. Start the print scheduler for the
Common UNIX Printing System.
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cut
Options
-c file
Use specified configuration file instead of /etc/cups/cupsd.conf.
-f Run scheduler in foreground.
-F Run scheduler in foreground but detach it from the control-
ling terminal and current directory. Sometimes used when
running cupsd from init.
cut cutoptions [files]
Cut out selected columns or fields from one or more files. With no
file, or if file is -, read from standard input. In the following
options, list is a sequence of integers. Use a comma between values,
and a hyphen to specify a range (e.g., 1-10,15,20 or 50-). See also
paste and join.
Options
-b list, --bytes list
Specify list of positions; only bytes in these positions will be
printed.
-c list, --characters list
Cut the column positions identified in list. Column numbers
start with 1.
-d c, --delimiter c
Use with -f to specify field delimiter as character c (default is
tab); special characters (e.g., a space) must be quoted.
-f list, --fields list
Cut the fields identified in list.
-n Don’t split multibyte characters. Use with -b.
-s, --only-delimited
Use with -f to suppress lines without delimiters.
--output-delimiter=string
Use string as the output delimiter. By default, the output
delimiter is the same as the input delimiter.
--help
Print help message and exit.
--version
Print version information and exit.
Examples
Extract usernames and real names from /etc/passwd:
cut -d: -f1,5 /etc/passwd
Find out who is logged on, but list only login names:
who | cut -d" " -f1
Cut characters in the fourth column of file, and paste them back as
the first column in the same file:
cut -c4 file | paste - file
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date
date date [options] [+format] [date]
Print the current date and time. You may specify a display format,
which can consist of literal text strings (blanks must be quoted) as
well as field descriptors, whose values are described in the
following entries (the listing shows some logical groupings). A priv-
ileged user can change the system’s date and time.
Options
+format
Display current date in a nonstandard format. For example:
$date +"%A %j %n%k %p"
Friday 051
23 PM
The default is %a %b %e %T %Z %Y (e.g., Fri Feb 20
22:59:43 EST 2009).
-d date, --date date
Display date, which should be in quotes and may be in the
format d days or m months d days, to print a date in the
future. Specify ago to print a date in the past. You may include
formatting (see the following section).
-f datefile, --file=datefile
Like -d, but printed once for each line of datefile.
-r file, --reference=file
Display the time file was last modified.
-R, --rfc-2822
Display the date and time in RFC 2822 format.
--rfc-3339=timespec
Display the date and time in RFC 3339 format. The value of
timespec can be one of date, seconds, or ns (nanoseconds) to
get the desired degree of precision.
--help
Print help message and exit.
--version
Print version information and exit.
-s date, --set=date
Set the date.
-u, --utc, --universal
Set the date to Coordinated Universal Time, not local time.
Format
The exact result of many of these codes is locale-specific and
depends upon your language setting, particularly the LANG envi-
ronment variable. See locale.
%%
Literal %.
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date
- (hyphen)
Do not pad fields (default: pad fields with zeros).
_ (underscore)
Pad fields with space (default: zeros).
^ Use uppercase if possible.
# Use the opposite case if possible.
%a Abbreviated weekday.
%A Full weekday.
%b Abbreviated month name.
%B Full month name.
%c Country-specific date and time format.
%C Century; like %Y but show only the two-digit century (e.g.,
show 20, not 2009).
%d Day of month (01–31).
%D Date in %m/%d/%y format.
%e Day of month padded with spaces.
%h Same as %b.
%H Hour in 24-hour format (00–23).
%I Hour in 12-hour format (01–12).
%j Julian day of year (001–366).
%k Hour in 24-hour format, without leading zeros (0–23).
%l Hour in 12-hour format, without leading zeros (1–12).
%m Month of year (01–12).
%MMinutes (00–59).
%n Insert a new line.
%N Nanoseconds (000000000–999999999).
%p String to indicate a.m. or p.m.
%P Like %p but lowercase.
%r Time in %I:%M:%S %p (12-hour) format.
%R Time in %H:%M (24-hour) format.
%s Seconds since “the Epoch,” which is 1970-01-01 00:00:00
UTC (a nonstandard extension).
%S Seconds (00–59).
%t Insert a tab.
%T Time in %H:%M:%S format.
%u Day of the week (1–7, Monday = 1).
%U Week number in year (00–53); start week on Sunday.
%V Week number in year (01–52); start week on Monday.
%w Day of week (0–6, Sunday = 0).
%WWeek number in year (00–53); start week on Monday.
%x Country-specific date format.
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dd
%XCountry-specific time format.
%YFour-digit year (e.g., 2006).
%yLast two digits of year (00–99).
%zRFC 822-style numeric time zone.
%ZTime-zone name.
Strings for setting date
Strings for setting the date may be numeric or nonnumeric.
Numeric strings consist of time, day, and year in the format
MMDDhhmm[[CC]YY][.ss]. Nonnumeric strings may include
month strings, time zones, a.m., and p.m.
time
A two-digit hour and two-digit minute (hhmm); hh uses 24-
hour format.
day
A two-digit month and two-digit day of month (MMDD);
default is current day and month.
year
The year specified as either the full four-digit century and year
or just the two-digit year; the default is the current year.
Examples
Set the date to July 1 (0701), 4 a.m. (0400), 2009 (09):
date 0701040009
The command:
date +"Hello%t Date is %D %n%t Time is %T"
produces a formatted date as follows:
Hello Date is 02/20/09
Time is 17:53:39
dd ddoptions
Make a copy of an input file (if) using the specified conditions, and
send the results to the output file (or standard output if of is not
specified). Any number of options can be supplied, although if and
of are the most common and are usually specified first. Because dd
can handle arbitrary block sizes, it is useful when converting
between raw physical devices.
Options
bs=n
Set input (ibs) and output (obs) block size to n bytes; this
option overrides ibs and obs set separately.
cbs=n
Set the size of the conversion buffer (logical record length) to n
bytes. Use only if the conversion format is ascii, ebcdic, ibm,
block, or unblock.
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dd
conv=format
Convert the input according to one or more (comma-separated)
formats listed next. The first five formats are mutually exclusive.
ascii
EBCDIC to ASCII.
ebcdic
ASCII to EBCDIC.
ibm
ASCII to EBCDIC with IBM conventions.
block
Variable-length records (i.e., those terminated by a
newline) to fixed-length records.
unblock
Fixed-length records to variable-length records.
excl
Fail if the output file already exists.
fdatasync
Physically write the output file before finishing.
fsync
Physically write both the output file and the metadata
before finishing.
lcase
Uppercase to lowercase.
nocreate
Do not create an output file.
noerror
Continue processing after read errors.
notrunc
Don’t truncate output file.
swab
Swap each pair of input bytes.
sync
Pad input blocks to ibs with trailing zeros.
ucase
Lowercase to uppercase.
count=n
Copy only n input blocks.
ibs=n
Set input block size to n bytes (default is 512).
if=file
Read input from file (default is standard input).
obs=n
Set output block size to n bytes (default is 512).
of=file
Write output to file (default is standard output).
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debugfs
seek=n
Skip n output-sized blocks from start of output file.
skip=n
Skip n input-sized blocks from start of input file.
--help
Print help message and then exit.
--version
Print the version number and then exit.
You can multiply size values (n) by a factor of 1024, 512, or 2 by
appending the letter k, b, or w, respectively. You can use the letter
x as a multiplication operator between two numbers.
Examples
Convert an input file to all lowercase:
dd if=caps_file of=small_file conv=lcase
Retrieve variable-length data and write it as fixed-length to out:
[data_retrieval_cmd]| dd of=out conv=sync,block
deallocvt deallocvtN
Deallocate and destroy the unused virtual console /dev/ttyN.
Multiple consoles may be named with additional spaces and integers:
deallocvt 1 4 deallocates the /dev/tty1 and /dev/tty4 consoles.
Consoles are considered unused if they are not in the foreground,
have no open processes, and have no selected text. The command
does not destroy consoles that are still active.
debugfs debugfs [[option]device]
System administration command. Provide direct access to data
structure of an ext2 or ext3 filesystem in order to debug problems
with the device. device is the special file corresponding to the device
containing the filesystem (e.g., /dev/hda3). debugfs may be used on
a mounted filesystem device.
Option
-b blocksize
Use the specified blocksize for the filesystem.
-c Catastrophic mode. Open the filesystem in read-only mode;
do not read the inode and group bitmaps initially.
-f file
Read commands from file. Exit when done executing
commands.
-i Specify filesystem device is an ext2 image file created by
e2image.
-s block
Read the superblock from the specified block.
-w Open the filesystem in read-write mode.
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debugfs
-R request
Execute the given request (see list below), then exit.
-V Print version number, then exit.
Requests
bmapfile logicalblock
Given the logicalblock of inode file, print the corresponding
physical block.
cat file
Dump the contents of an inode to standard output.
cd directory
Change the current working directory to directory.
chroot directory
Change the root directory to be the specified inode.
close
Close the currently open filesystem.
clri file
Clear the contents of the inode corresponding to file.
dump [-p] file out_file
Dump the contents of inode file to out_file. Change owner-
ship and permissions of out_file to match file if -p is specified.
expand_dir directory
Expand directory.
feature [[-]feature]
Set filesystem feature listed on the command line, then print
current feature settings. Use - to clear a feature.
find_free_block [[n] goal]
Find and allocate first n free blocks starting from goal (if
specified).
find_free_inode [dir [mode]]
Find a free inode and allocate it.
freeb block [n]
Free n blocks beginning from block. Default is 1 block.
freei file
Free the inode corresponding to file.
help
Print a list of commands understood by debugfs.
icheck block
Do block-to-inode translation.
imapfile
Print the location of the inode data structure for file.
init_filesys device blocksize
Create an ext2 filesystem on device.
kill_file file
Remove file and deallocate its blocks.
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debugfs
lcd directory
Change current working directory on native filesystem.
ln source_file dest_file
Create a link.
logdump [-acs] [-bblock] [-iinode] [-fjournal_file] [out_file]
Print the ext3 journal contents to screen or to the specified
out_file. Prints the superblock journal by default. Specify other
journal information by block or inode. You can also specify a
journal_file containing journal data. Use -a to print the
contents of descriptor blocks. Use -b to print records referring
to a specified block. Use -c to print the hexadecimal and ASCII
contents of blocks referenced by the logdump.
ls [-l] [-d] [-p] [pathname]
Emulate the ls command. Use -l for verbose format and -d to
list deleted entries. Use -p for output that can be more easily
parsed by scripts.
modify_inode file
Modify the contents of the inode corresponding to file.
mkdir directory
Make directory.
mknod file [p|[[c|b] major minor]]
Create a special device file.
ncheck inode
Do inode-to-name translation.
open [-b blocksize] [-c] [-e] [-f] [-i] [-w] [-s block] device
Open a filesystem. The -f option forces the filesystem to open
disregarding any unknown or incompatible features that
would otherwise prevent it from opening. The -e option
causes the filesystem to be opened in exclusive mode. The
remaining options are identical to the command-line options
for debugfs.
pwd
Print the current working directory.
quit
Quit debugfs.
rdump directory dest_directory
Recursively dump directory and its contents to dest_directory
on the native filesystem.
rm file
Remove file.
rmdir directory
Remove directory.
setb block [n]
Mark n blocks as allocated, beginning from block. Default is 1
block.
set_block_group number field value
Set descripter field to value for the block group specified by
number.
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depmod
seti file
Mark in use the inode corresponding to file.
set_super_value [-l] field value
Set superblock field to value. Use -l to print a list of valid
fields.
show_super_stats [-h]
List the contents of the superblock and block group descrip-
tors. Use -h to list only the superblock contents.
stat file
Dump the contents of the inode corresponding to file.
testb block [n]
Print whether each of n blocks is in use, beginning with block.
By default, just check the specified block.
testi file
Test whether the inode corresponding to file is marked as
allocated.
undel <inode>[pathname]
Undelete (mark as used) the specified inode. You must include
the angle brackets. Optionally link the recovered inode with
pathname. If undeleting multiple inodes, linking may not be
safe. Use a separate pass to link the pathname after all inodes
have been undeleted. Always run e2fsck after undeleting
inodes.
unlink file
Remove a link.
write source_file file
Create a file in the filesystem named file, and copy the
contents of source_file into the destination file.
depmod depmod [options]modules
System administration command. Create a dependency file for the
modules given on the command line. This dependency file can be
used by modprobe to automatically load the relevant modules. The
normal use of depmod is to include the line /sbin/depmod -a in
one of the files in /etc/rc.d so that the correct module dependencies
will be available after booting the system.
Options
-a, --all
Create dependencies for all modules listed in /etc/modules.
conf.
-A, --quick
Check timestamps and only update the dependency file if
anything has changed.
-b dir, --basedir dir
Specify a base directory to use instead of /lib/modules.
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devdump
-C file, --config file
Use the specified configuration file instead of /etc/modules.dep.
May also be set using the MODULECONF environment
variable.
-e, --errsyms
Print a list of all unresolved symbols.
-F file, --kernelsyms file
Use the specified kernel symbol file to build dependencies.
Usually this is either a copy of a system’s System.map file or
the output of /proc/ksyms.
-h, --help
Print help message, then exit.
-n, --dry-run, --show
Write dependency file to standard output instead of writing to
module directory.
-q, --quiet
Don’t display error messages about missing symbols.
-r, --root
Allow root to load modules not owned by root.
-s, --syslog
Write error messages to the syslog daemon instead of to stan-
dard error.
-v Print a list of all processed modules.
-V, --version
Print version number.
Files
/etc/modules.dep, /etc/depmod.d
Information about modules: which ones depend on others,
and which directories correspond to particular types of modules.
/sbin/insmod, /sbin/rmmod
Programs that depmod relies on.
devdump devdumpisoimage
Interactively display the contents of the device or filesystem image
isoimage. devdump displays the first 256 bytes of the first 2048-
byte sector and waits for commands. The prompt shows the extent
number (zone) and offset within the extent, and the contents
display at the top of the screen.
Commands
+ Search forward for the next instance of the search string.
a Search backward within the image.
b Search forward within the image.
f Prompt for a new search string.
g Prompt for a new starting block and go there.
q Exit.
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df
df df[options] [name]
Report the amount of free disk space available on all mounted file-
systems or on the given name. (df cannot report on unmounted
filesystems.) Disk space is shown in 1 KB blocks (default) or 512-
byte blocks if the environment variable POSIXLY_CORRECT is set.
name can be a device name (e.g., /dev/hd*), the directory name of a
mounting point (e.g., /usr), or a directory name (in which case df
reports on the entire filesystem in which that directory is
mounted).
Options
-a, --all
Include empty filesystems (those with 0 blocks).
-Bn, --block-size=n
Show space as n-byte blocks.
-h, --human-readable
Print sizes in a format friendly to human readers (e.g., 1.9 MB
instead of 1967156).
-H, --si
Like -h, but show as power of 1000 rather than 1024.
-i, --inodes
Report free, used, and percent-used inodes.
-k Print sizes in kilobytes.
-l, --local
Show local filesystems only.
-m, --megabytes
Print sizes in megabytes.
--no-sync
Show results without invoking sync first (i.e., without flushing
the buffers). This is the default.
-P, --portability
Use POSIX output format (i.e., print information about each
filesystem on exactly one line).
--sync
Invoke sync (flush buffers) before getting and showing sizes.
-t type, --type=type
Show only filesystems of the specified type.
-T, --print-type
Print the type of each filesystem in addition to the sizes.
-x type, --exclude-type=type
Show only filesystems that are not of type type.
--help
Print help message and then exit.
--version
Print the version and then exit.
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diff
diff diff [options]file1 file2
Compare two text files. diff reports lines that differ between file1
and file2. Output consists of lines of context from each file, with
file1 text flagged by a < symbol and file2 text by a > symbol.
Context lines are preceded by the ed command (a, c, or d) that
would be used to convert file1 to file2. If one of the files is -, stan-
dard input is read. If one of the files is a directory, diff locates the
filename in that directory corresponding to the other argument (e.g.,
diff my_dir junk is the same as diff my_dir/junk junk). If both
arguments are directories, diff reports lines that differ between all
pairs of files having equivalent names (e.g., olddir/program and
newdir/program); in addition, diff lists filenames unique to one
directory, as well as subdirectories common to both. See also cmp.
Options
-n For context and unified diff, print n lines of context. Same as
specifying a number with -C or -U.
-a, --text
Treat all files as text files. Useful for checking to see if binary
files are identical.
-b, --ignore-space-change
Ignore repeating blanks and end-of-line blanks; treat succes-
sive blanks as one.
-B, --ignore-blank-lines
Ignore blank lines in files.
-c Context diff: print three lines surrounding each changed line.
-C n, --context[=n]
Context diff: print n lines surrounding each changed line. The
default context is three lines.
-d, --minimal
Ignore segments of numerous changes and output a smaller
set of changes.
-D symbol, --ifdef=symbol
When handling C files, create an output file that contains all
the contents of both input files, including #ifdef and #ifndef
directives that reflect the directives in both files.
-e, --ed
Produce a script of commands (a, c, d) to recreate file2 from
file1 using the ed editor.
-F regexp, --show-function-line[=regexp]
For context and unified diff, show the most recent line
containing regexp before each block of changed lines.
-H, --speed-large-files
Speed output of large files by scanning for scattered small
changes; long stretches with many changes may not show up.
--help
Print brief usage message.
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diff
--horizon-lines=n
In an attempt to find a more compact listing, keep n lines on
both sides of the changed lines when performing the
comparison.
-i, --ignore-case
Ignore case in text comparison. Uppercase and lowercase are
considered the same.
-I regexp, --ignore-matching-lines=regexp
Ignore lines in files that match the regular expression regexp.
-l, --paginate
Paginate output by passing it to pr.
-L label, --label=label
For context and unified diff, print label in place of the file-
name being compared. The first such option applies to the
first filename and the second option to the second filename.
--left-column
For two-column output (-y), show only left column of common
lines.
-n, --rcs
Produce output in RCS diff format.
-N, --new-file
Treat nonexistent files as empty.
-p, --show-c-function
When handling files in C or C-like languages such as Java,
show the function containing each block of changed lines.
Assumes -c, but can also be used with a unified diff.
-P, --unidirectional-new-file
If two directories are being compared and the first lacks a file
that is in the second, pretend that an empty file of that name
exists in the first directory.
-q, --brief
Output only whether files differ.
-r, --recursive
Compare subdirectories recursively.
-s, --report-identical-files
Indicate when files do not differ.
-S filename, --starting-file=filename
For directory comparisons, begin with the file filename, skipping
files that come earlier in the standard list order.
--suppress-common-lines
For two-column output (-y), do not show common lines.
-t, --expand-tabs
Produce output with tabs expanded to spaces.
-T, --initial-tab
Insert initial tabs into output to line up tabs properly.
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diff3
-u Unified diff: print old and new versions of lines in a single
block, with 3 lines surrounding each block of changed lines.
-U n, --unified[=n]
Unified diff: print old and new versions of lines in a single
block, with n lines surrounding each block of changed lines.
The default context is 3 lines. With the -U form, n must be
given.
-v, --version
Print version number of this version of diff.
-w, --ignore-all-space
Ignore all whitespace in files for comparisons.
-W n, --width=n
For two-column output (-y), produce columns with a maximum
width of n characters. Default is 130.
-x regexp, --exclude=regexp
Do not compare files in a directory whose basenames match
regexp.
-X filename, --exclude-from=filename
Do not compare files in a directory whose basenames match
patterns described in the file filename.
-y, --side-by-side
Produce two-column output.
diff3 diff3 [options]file1file2 file3
Compare three files and report the differences. No more than one
of the files may be given as - (indicating that it is to be read from
standard input). The output is displayed with the following codes:
= = = =
All three files differ.
= = = =1
file1 is different.
= = = =2
file2 is different.
= = = =3
file3 is different.
diff3 is also designed to merge changes in two differing files based
on a common ancestor file (i.e., when two people have made their
own set of changes to the same file). diff3 can find changes
between the ancestor and one of the newer files and generate
output that adds those differences to the other new file. Unmerged
changes occur where both of the newer files differ from each other
and at least one of them differs from the ancestor. Changes from
the ancestor that are the same in both of the newer files are called
merged changes. If all three files differ in the same place, it is called an
overlapping change.
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dig
This scheme is used on the command line, with the ancestor being
file2, the second filename. Comparison is made between file2 and
file3, with those differences then applied to file1.
Options
-3, --easy-only
Create an ed script to incorporate into file1 unmerged,
nonoverlapping differences between file1 and file3.
-a, --text
Treat files as text.
-A, --show-all
Create an ed script to incorporate all changes, showing
conflicts in bracketed format.
-e, --ed
Create an ed script to incorporate into file1 all unmerged
differences between file2 and file3.
-E, --show-overlap
Create an ed script to incorporate unmerged changes, showing
conflicts in bracketed format.
--help
Print usage information and exit.
-i Append the w (save) and q (quit) commands to ed script
output.
-L label, --label=label
Use label to replace filename in output.
-m, --merge
Create file with changes merged (not an ed script).
-T, --initial-tab
To line tabs up properly in output, begin lines with a tab
instead of two spaces.
-v, --version
Print version information and then exit.
-x, --overlap-only
Create an ed script to incorporate into file1 all differences
where all three files differ (overlapping changes).
-X Same as -x, but show only overlapping changes in bracketed
format as with -E.
dig dig [@server] [options] [name] [type] [class] [query-options]
dig @servernametype
dig -h
TCP/IP command. The dig command is used to query DNS
servers; it is more flexible than the deprecated nslookup command.
When invoked with just the -h option, it displays a list of options
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dig
for the command. If you use it without any options or arguments,
it will search for the root server. The standard arguments are:
server
The server to query. If no server is supplied, dig will check the
nameservers listed in /etc/resolv.conf. The address may be an
IPv4 dotted address or an IPv6 colon-delimited address. It may
also be a hostname, which dig will resolve (through the
nameservers in /etc/resolv.conf).
name
The domain name to look up.
type
The type of query to perform, such as A, ANY, MX, SIG, and
so forth. The default is A, but you may use any valid BIND9
query type.
Options
You may use the following option flags with dig:
-b address
Set the source IP address for the query.
-c class
Set the class of query. The default value is IN (internet), but
you can choose HS for Hesiod or CH for CHAOSNET.
-f filename
Operate in batch mode, performing the queries in the file you
specify.
-k filename
Specify a TSIG keyfile; used for signed transactions. You can
also use the -y key, although this is less secure.
-p portnumber
Choose the port number for the query. The default value is the
standard DNS port, 53.
-q name
Specify domain name to query. Sometimes this is needed to
distinguish the domain name from other options.
-t type
Set the type of query, as with the query argument. The default
value is A, but you may use any valid BIND9 query.
-x addr
Use the -x flag for reverse lookups, specifying an IPv4 or IPv6
address. You do not need the name, class, or type arguments if
you use the -x flag.
-y keyname: keyvalue
Enter the actual key name and value when conducting a
signed transaction. Because the key and value can be seen in
the output of ps, this is not recommended for use on multiuser
systems; use -k instead.
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dir
Query options
There are a large number of query options for dig. Each query
option is preceded by +, and many have an opposite version
beginning with no. For example, the tcp flag is passed as +tcp, and
negated with +notcp. Because there are so many options, only a
few are discussed here. For greater detail, see the dig manpage.
+tcp, +notcp
Use (or do not use) the TCP protocol instead of the default
UDP.
+domain=searchdomain
Perform a search in the domain specified; this is equivalent to
using the +search option and having “searchdomain” as the sole
entry in the search list or domain directive of /etc/resolv.conf.
+search, +nosearch
Use (or do not use) the search list provided in /etc/resolv.conf.
The default is not to use the search list.
+time=t
Timeout for queries, in seconds. The default is 5, and the
minimum is 1.
+tries=n
The number of times to retry UDP queries. The default is 3,
and the minimum is 1.
Examples
Query the mail exchange record for example.com:
dig mx example.com
Ask a specific nameserver to resolve a domain:
dig @ns.example.com smtp.example.com
Perform a reverse look up on an IP address:
dig -x 208.201.239.37
dir dir [options] [file]
List directory contents. dir is equivalent to the command ls -C -b
(list files in columns, sorted vertically, special characters escaped),
and it takes the same arguments as ls. This is an alternate invoca-
tion of the ls command and is provided for the convenience of
those converting from Microsoft Windows and the DOS shell.
dircolors dircolors [options] [file]
Set the color options for the ls command. dircolors outputs shell
commands which, when evaluated, update the LS_COLORS envi-
ronment variable. If you specify a file, dircolors reads it to
determine which colors to use. Otherwise, it uses a default set of
colors. If the shell is not specified, dircolors checks the SHELL
environment variable.
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doexec
Options
The program takes three options in addition to the standard --help
and --version flags:
-b, --sh, --bourne-shell
Use the Bourne shell syntax when setting the LS_COLORS
variable.
-c, --csh, --c-shell
Use csh (C shell) syntax when setting the LS_COLORS
variable.
-p, --print-database
Display the default colors. You can copy this information into
a file and change it to suit your preferences, and then run the
program with the file as its argument to set the colors to your
new values.
Example
Set LS_COLORS using the default color database:
eval `dircolors`
dirname dirnamepathname
Print pathname, excluding the last level. Useful for stripping the
actual filename from a pathname. If there are no slashes (no direc-
tory levels) in pathname, dirname prints . to indicate the current
directory. See also basename.
dmesg dmesg [options]
System administration command. Display the system control
messages from the kernel ring buffer. This buffer stores all
messages since the last system boot, or the most recent ones if the
buffer has been filled.
Options
-c Clear buffer after printing messages.
-nlevel
Set the level of system message that will display on console.
-sbuffersize
Specify buffersize of kernel ring buffer. This is useful if you
have changed the kernel default.
doexec doexec/path/to/command [argv[0]] ... [argv[n]]
Execute the specified command with the specified options and
arguments. Differs from the normal exec command in that argv[0]
may be completely arbitrary, and in that it passes all options to the
executable being run.
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domainname
domainname domainname [name]
NFS/NIS command. Set or display name of current NIS domain.
With no argument, domainname displays the name of the current
NIS domain. Only a privileged user can set the domain name by
giving an argument; this is usually done in a startup script.
dosfsck dosfsck [options]device
fsck.msdos [options]device
System administration command. Similar to fsck, but specifically
intended for MS-DOS filesystems. When checking an MS-DOS file-
system, fsck calls this command. Normally dosfsck stores all
changes in memory, then writes them when checks are complete.
Options
-a Automatically repair the system; do not prompt the user.
-d file
Drop the named file from the file allocation table. Force
checking, even if kernel has already marked the filesystem as
valid. dosfsck will normally exit without checking if the
system appears to be clean.
-f Save unused cluster chains to files.
-l List pathnames of files being processed.
-r Repair the system, prompting user for advice.
-t Mark unreadable clusters as bad.
-u file
Attempt to undelete the named file.
-v Verbose mode.
-w Write changes to disk immediately.
-y When queried, answer “yes.”
-A Filesystem is an Atari version of MS-DOS.
-V Repeat test to verify all errors have been corrected.
du du [options] [directories]
Print disk usage (as the number of 1 KB blocks used by each named
directory and its subdirectories; default is the current directory).
Options
-0, --null
End output lines with null, not newline.
-a, --all
Print disk usage for all files, not just subdirectories.
--apparent-size
Print the apparent sizes, not disk usage.
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du
-b, --bytes
Print sizes in bytes.
-B bytes, --block-size=bytes
Use the specified number of bytes for the blocksize.
-c, --total
In addition to normal output, print grand total of all arguments.
-D, --dereference-args
Follow symbolic links, but only if they are command-line
arguments.
--exclude=pattern
Exclude files that match pattern.
-h, --human-readable
Print sizes in human-readable format.
-H, --si
Like -h, but show as power of 1000 rather than 1024. -H also
produces a warning.
--help
Print help message and then exit.
-k, --kilobytes
Print sizes in kilobytes (this is the default).
-l, --count-links
Count the size of all files, whether or not they have already
appeared (i.e., via a hard link).
-L, --dereference
Follow symbolic links.
-m Print sizes in megabytes.
--max-depth=num
Report sizes for directories only down to num levels below the
starting point (which is level 0).
-P, --no-dereference
Do not follow symbolic links (the default).
-s, --summarize
Print only the grand total for each named directory.
-S, --separate-dirs
Do not include the sizes of subdirectories when totaling the
size of parent directories.
--time[=word]
Print the last-modification time. With word, show the time as
one of the following, not as modification time: atime, access,
use, ctime, or status.
--time-style=style
Show times using the specified style. Possible values are: full-iso,
long-iso, iso, +format (interpreted as in date). Used with --time.
--version
Print the version and then exit.
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dump
-x, --one-file-system
Display usage of files in current filesystem only.
-X file, --exclude-from=file
Exclude files that match any pattern in file.
dump dump [options]files
System administration command. This simple backup utility
accesses ext2 and ext3 file devices directly, quickly backing up files
without affecting file access times. files may be specified as a mount
point or as a list of files and directories to back up. While you can
use this on a mounted system, dump may write corrupted informa-
tion to the backup when the kernel has written only part of its
cached information. Dump maintains a record of which files it has
saved in /etc/dumpdates, and will perform incremental backups
after creating an initial full backup. Use the restore command to
restore a dump backup.
Options
-a Write until end-of-media. Default behavior when writing to
tape drives.
-A file
Create a table of contents for the archive in the specified file.
-bblocksize
Block size in kilobytes to use in dumped records. By default, it
is 10, or 32 when dumping to a tape with a density greater
than 6250 bpi.
-Bblocks
Specify number of blocks to write per volume.
-c Treat target as a 1700-foot-long cartridge tape drive with 8000
bpi. Override end-of-media detection.
-d density
Specify tape density.
-D file
Write dump information to file instead of /etc/dumpdates.
-E file
Exclude inodes specified in file.
-f files
Write backup volumes to the specified files or devices. Use - to
write to standard output. Separate multiple files with a
comma. Use host:file or user@host:file to write to a networked
host using either the rmt program or the program specified by
the RMT environment variable.
-F script
Run script at the end of each volume other than the last. dump
will pass the current device and volume number to the script.
The script should return 0 to continue, 1 to prompt for a new
tape, or any other exit value to abort the dump. The script will
run with the processes real user and group ID.
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dump
-i inodes
Specify a comma-separated list of inodes to skip.
-I n
Ignore the first n read errors. dump ignores 32 read errors by
default. Specify 0 to ignore all errors. You may need to do this
when dumping a mounted filesystem.
-j[level]
Compress each block using the bzlib library at the specified
compression level. By default dump uses level 2 compression.
-k Use Kerberos authentication when writing to a remote system.
-L label
Write the specified volume label into the dump header.
-m Save only metadata when backing up changed but not modi-
fied files.
-M Create a multivolume backup. Treat any filename provided
with -f as a prefix.
-n Use wall to notify members of group operator when
prompting for information.
-q Abort the backup instead of prompting for information when
operator input is required.
-Q file
Create Quick Access information in the specified file for use
by restore.
-s n
Write only n feet of tape in a single volume. Prompt for a new
tape upon reaching this limit.
-S Calculate and print the amount of space required to perform
the backup, then exit.
-T date
Only back up files changed or modified since date. This over-
rides the time given in /etc/dumpdates.
-u Update /etc/dumpdates after completing the backup.
-v Print verbose information about the dump.
-W Generate a report on the backup status of all filesystems based
on information in /etc/dumpdates and /etc/fstab.
-w Generate a report of filesystems that need to be backed up.
Only report on filesystems listed in /etc/fstab and /etc/mtab
that need to be backed up.
-y Compress each block using the lzo library.
-z[level]
Compress each block using the zlib library. If provided, use
the specified compression level. The default is 2.
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dumpe2fs
dumpe2fs dumpe2fsdevice
System administration command. Print ext2/ext3 information
about device’s superblock and blocks group.
Options
-b List blocks marked as bad.
-f Force display of filesystems with unknown feature flags.
-h Display superblock information only.
-i Specify device is an image file created by e2image.
-o superblock=superblock
Specify location of the superblock.
-o blocksize=blocksize
Specify blocksize to use when examining filesystem.
-x Print block numbers in hexadecimal.
-V Print version number and exit.
dumpiso dumpiso [ options ] [ file ]
Listen on selected channels and dump IEEE 1394 packets received
into the specified file, or to standard output if file is not specified.
The current number of packets is written to standard error.
Options
-c nums, --channels=nums
Set channels to listen to, as a single number or a range.
Channel numbers can be from 0 to 63, and the option can be
specified multiple times to add new channels each time.
Without this option, dumpiso defaults to all channels.
-h, --help
Print usage information and exit.
-p port, --port=port
Specify the IEEE 1394 port to receive on; only required if there
is more than one on your system. The default is 0.
dumpkeys dumpkeys [options]
Print information about the keyboard driver’s translation tables to
standard output. Further information is available in the manual
pages under keymaps(5).
Options
-1, --separate-lines
Print one line for each modifier/keycode pair, and prefix plain
to each unmodified keycode.
-ccharset, --charset=charset
Specify character set with which to interpret character code
values. The default character set is iso-8859-1. Use --help for
the list of valid character sets.
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e2fsck
--compose-only
Print compose key combinations only. Requires compose key
support in the kernel.
-f, --full-table
Output in canonical, not short, form: for each key, print a row
with modifier combinations divided into columns.
--funcs-only
Print function-key string definitions only; do not print key
bindings or string definitions.
-h, --help
Print help message and the version.
-i, --short-info
Print in short-info format, including information about accept-
able keycode keywords in the keytable files; the number of
actions that can be bound to a key; a list of the ranges of action
codes (the values to the right of a key definition); and the
number of function keys that the kernel supports.
--keys-only
Print key bindings only; do not print string definitions.
-l, --long-info
Print the same information as in --short-info, plus a list of the
supported action symbols and their numeric values.
-n, --numeric
Print action code values in hexadecimal notation; do not
attempt to convert them to symbolic notation.
dvdrecord dvdrecord [options]track1,track2...
Record data to a DVD recorder. dvdrecord is generally a symbolic
link to wodim. See wodim for more information.
e2fsck e2fsck [options]device
fsck.ext2 [options]device
System administration command. Checks and repairs a disk, as
does fsck, but specifically designed for ext2 (Linux Second
Extended) and ext3 (Third Extended, a journaling version of ext2)
filesystems. fsck actually uses this command when checking ext2
and ext3 filesystems. Most often used after a sudden shutdown,
such as from a power outage, or when damage to the disk is
suspected.
Options
-b superblock
Use superblock instead of the default superblock.
-B size
Expect to find the superblock at size; if it’s not there, exit.
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e2image
-c Find bad blocks using the badblocks command. Specify this
option twice to perform the scan with a nondestructive read-
write test.
-C filedescriptor
Write completion information to the specified filedescriptor. If
0, print a completion bar.
-d Debugging mode.
-D Optimize directories by reindexing, sorting, and compressing
them where possible.
-f Force checking, even if kernel has already marked the file-
system as valid. e2fsck will normally exit without checking if
the system appears to be clean.
-F Flush buffer caches before checking.
-j file
Use the specified external journal file.
-k Preserve all previously marked bad blocks when using the -c
option.
-l file
Consult file for a list of bad blocks, in addition to checking for
others.
-L file
Consult file for list of bad blocks instead of checking file-
system for them.
-n Ensure that no changes are made to the filesystem. When
queried, answer “no.”
-p “Preen.” Repair all bad blocks noninteractively.
-s Byte-swap the filesystem if necessary to standard (little-
endian) byte-order.
-S Byte-swap the filesystem.
-t Display timing statistics.
-v Verbose.
-y When queried, answer “yes.”
e2image e2image [option]device file
System administration command. Store disaster recovery data for
ext2 filesystem on device to image file file. Weekly filesystem
images can be an important part of a disaster recovery plan.
Option
-r Create a raw image file that can be checked and debugged
using filesystem utilities such as e2fsck or debugfs. Raw
images are created as sparse files. Either compress the image
file before moving it, or use the --sparse=always option when
copying it with cp.
-I Restore filesystem metadata in image to device. Note you will
lose any changes to the filesystem since your image was created.
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edquota
e2label e2labeldevice [label]
System administration command. Display the filesystem label on
an ext2 filesystem device. Change filesystem label to label if
specified.
echo echo [options] [string]
Send (echo) the input string to standard output. This is the /bin/
echo command. echo also exists as a command built into bash.
You may have to specify the full path to run /bin/echo instead of
the shell built-in command. The following character sequences
have special meaning:
\a Alert (bell).
\b Backspace.
\c Suppress trailing newline.
\f Form feed.
\n Newline.
\r Carriage return.
\t Horizontal tab.
\v Vertical tab.
\\ Literal backslash.
\nnn
The octal character whose ASCII code is nnn.
Options
-e Enable character sequences with special meaning. (In some
versions, this option is not required in order to make the
sequences work.)
-E Disable character sequences with special meaning.
-n Suppress printing of newline after text.
--help
Print help message and exit.
--version
Print version information and exit.
Examples
/bin/echo "testing printer" | lp
/bin/echo "TITLE" > file ; cat doc1 doc2 >> file
/bin/echo "Warning: ringing bell \a"
edquota edquota [options] [name]
System administration command. Edit filesystem quotas using a
text editor. When edits are complete, edquota writes the new infor-
mation to the binary quota files. Uses the editor specified in the
EDITOR environment variable, or vi by default.
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egrep
Options
-ffilesystem
Only apply changes to the specified filesystem.
-Fformat
Specify filesystem quota format to use. See quota for a list of
accepted values.
-g Edit group quotas.
-pprototype
Apply the same settings as used for the specified user or
group: prototype.
-r Edit quotas on remote systems.
-t Edit grace times for block and inode quotas.
-T Edit grace times for individual user or group name.
-u Edit user quotas. (This is the default.)
egrep egrep [options] [regexp] [files]
Search one or more files for lines that match an extended regular
expression regexp. egrep doesn’t support the regular expressions \(,
\), \n, \<, \>, \{, or \}, but it does support the other expressions, as
well as the extended set +, ?, |, and (). Remember to enclose these
characters in quotes. Regular expressions are described in
Chapter 7. Exit status is 0 if any lines match, 1 if none match, and
2 for errors.
See grep for the list of available options. Also see fgrep.
Examples
Search for occurrences of Victor or Victoria in file:
egrep 'Victor(ia)*'file
egrep '(Victor|Victoria)'file
Find and print strings such as old.doc1 or new.doc2 in files, and
include their line numbers:
egrep -n '(old|new)\.doc?'files
eject eject [options] [device]
Eject removable media such as a CD, DVD, floppy, or tape. You
may name the device by its /dev or /mnt filename. The /dev and /mnt
prefixes are optional for any items in the /dev and /mnt directories.
If no device is named, it is assumed that “cdrom” should be
ejected.
Options
The eject command takes the following option flags:
-a, --auto on|1|off|0
Set the auto-eject mode to on or off (equivalent to 1 or 0,
respectively). If auto-eject mode is on, the device is ejected
when closed or unmounted.
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eject
-c slotnumber, --changerslot slotnumber
If using a CD-ROM changer, select a CD from one of the slots.
Slot numbers start with 0, and the CD-ROM drive must not be
playing music or mounted to read data.
-d, --default
List the default device name rather than doing anything.
-f, --floppy
Use floppy commands to eject the drive. Normally, the system
tries all methods (CD-ROM, SCSI, floppy, tape) to eject.
-h, --help
Display help information.
-m, --no-unmount
Do not try to unmount the device.
-n, --noop
Do not perform any actions; merely display the actions that
would be performed.
-p, --proc
Use the mounted files listed in /proc/mounts rather than in /etc/
mtab.
-q, --tape
Use tape commands to eject the drive. Normally, the system
tries all methods (CD-ROM, SCSI, floppy, tape) to eject.
-r, --cdrom
Use CD-ROM commands to eject the drive. Normally, the
system tries all methods (CD-ROM, SCSI, floppy, tape) to
eject.
-s, --scsi
Use SCSI commands to eject the drive. Normally, the system
tries all methods (CD-ROM, SCSI, floppy, tape) to eject.
-t, --trayclose
Close the CD-ROM drive. Not all drives respond to this
option.
-T, --traytoggle
Close the CD-ROM drive if it’s open and eject the CD if it’s
closed. Not all drives respond to this option.
-v, --verbose
Verbose mode: display additional information about actions.
-V, --version
Display version information and exit.
-x speed, --cdspeed speed
Set the speed multiplier for the CD-ROM to an integer,
usually a power of 2. Not all devices support this option.
Setting the speed to 0 indicates that the drive should operate
at its maximum speed.
-X, --listspeed
Detect and list all available speeds that can be specified with -x.
Not all devices support this option.
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elvtune
elvtune elvtune [options]devices
System administration command. Set the latency in the elevator
algorithm used to schedule I/O activities for the specified block
devices. If no options are given, print the current settings for
devices.
Options
-b n
Set the maximum coalescing factor allowed on writes when
reads are pending to n.
-h Print help message, then exit.
-r n
Set the maximum read latency (basically, the number of
sectors to read before writes are allowed) to n. The default is
8192.
-v Print version number, then exit.
-w n
Set the maximum write latency (sectors to write before
allowing a read) to n. The default is 16,384.
emacs emacs [options] [files]
A text editor and all-purpose work environment. For more infor-
mation, see Chapter 8.
enable enable -E [destination]
Enable printers or printer classes. Part of the CUPS system. More
often invoked as accept.
env env [option] [variable=value ... ] [command]
Display the current environment or, if an environment variable is
specified, set it to a new value and display the modified environ-
ment. If command is specified, execute it under the modified
environment.
Options
-, -i, --ignore-environment
Ignore current environment entirely.
-u name, --unset name
Unset the specified variable.
--help
Print help message and then exit.
--version
Print version information and then exit.
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etags
envsubst envsubst [options] [shell-format]
Substitutes environment variables in a shell string or script. When
used with no options, copies stdin to stdout, replacing any environ-
ment variable string, such as $VARIABLE or ${VARIABLE}, with
the appropriate environment variable value. So, “My editor is
$EDITOR” would be converted to “My editor is /usr/bin/emacs.”
Specifying a shell format limits the substitutions to those variables
referenced in the shell format.
Options
-h, --help
Print help message and then exit.
-v, --variables
Display the variables referenced in the shell format, and then
exit.
-V, --version
Print version information and then exit.
etags etags [options]files
Create a list of function and macro names defined in a program-
ming source file. etags generates tags for use by emacs. (ctags
produces an equivalent tags file for use with vi.) More than one file
may be specified. etags understands many programming languages,
including C, C++, FORTRAN, Java, Perl, Python, flex, yacc, and
bison. The output list (named TAGS by default) contains lines of
the form:
name file context
where name is the function or macro name, file is the source file in
which name is defined, and context is a search pattern that shows
the line of code containing name. After the list of tags is created,
you can invoke Emacs on any file and type:
M-x visit-tags-table
You will be prompted for the name of the tag table; the default is
TAGS. To switch to the source file associated with the name listed
in tagsfile, type:
M-x find-tag
You will be prompted for the tag you would like Emacs to search
for.
Options
-a, --append
Append tag output to existing list of tags.
-d, --defines
Include tag entries for C preprocessor definitions.
-i file, --include=file
Add a note to the tags file that file should be consulted in
addition to the normal input file.
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ex
-l language, --language=language
Consider the files that follow this option to be written in
language. Use the -h option for a list of languages and their
default filename extensions.
-o file, --output=file
Write to file.
-r regexp, --regex=regexp
Include a tag for each line that matches regexp in the files
following this option.
-C, --c++
Expect .c and .h files to contain C++, not C, code.
-D, --no-defines
Do not include tag entries for C preprocessor definitions.
-H, -h, --help
Print usage information.
-R, --noregex
Do not include tags based on regular-expression matching for
the files that follow this option.
-S, --ignore-indentation
Normally, etags uses indentation to parse the tag file; this
option tells it to rely on it less.
-V, --version
Print the version number.
ex ex [options]file
An interactive command-based editor. For more information, see
Chapter 9.
expand expand [options] [files]
Convert tabs in given files (or standard input, if the file is given as -)
to the appropriate number of spaces; write results to standard
output.
Options
--help
Print help message and then exit.
-i, --initial
Convert tabs only at the beginning of lines.
-tabs, -t tabs, --tabs tabs
tabs is a comma-separated list of integers that specify tab
stops. With one integer, the tab stops are set to every integer
spaces. By default, tab stops are eight spaces apart. With -t
and --tabs, the list may be separated by whitespace instead of
commas.
--version
Print version information and then exit.
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expr
expr exprarg1operatorarg2 [operatorarg3 ... ]
Evaluate arguments as expressions and print the results to stan-
dard output. Arguments and operators must be separated by
spaces. In most cases, an argument is an integer, typed literally or
represented by a shell variable. There are three types of operators:
arithmetic, relational, and logical, as well as keyword expressions.
Exit status for expr is 0 (expression is nonzero and nonnull), 1
(expression is 0 or null), 2 (expression is invalid), or 3 (an error
occurred).
Arithmetic operators
Use these to produce mathematical expressions whose results are
printed:
+ Add arg2 to arg1.
- Subtract arg2 from arg1.
* Multiply the arguments.
/ Divide arg1 by arg2.
% Take the remainder when arg1 is divided by arg2.
Addition and subtraction are evaluated last, unless they are
grouped inside parentheses. The symbols *, (, and ) have meaning
to the shell, so they must be escaped (preceded by a backslash or
enclosed in single quotes).
Relational operators
Use these to compare two arguments. Arguments can also be
words, in which case comparisons are defined by the locale. If the
comparison statement is true, the result is 1; if false, the result is 0.
Symbols > and < must be escaped.
=, ==
Are the arguments equal?
!= Are the arguments different?
> Is arg1 greater than arg2?
>= Is arg1 greater than or equal to arg2?
< Is arg1 less than arg2?
<= Is arg1 less than or equal to arg2?
Logical operators
Use these to compare two arguments. Depending on the values, the
result can be arg1 (or some portion of it), arg2, or 0. Symbols | and
& must be escaped.
| Logical OR; if arg1 has a nonzero (and nonnull) value, the
result is arg1; otherwise, the result is arg2.
& Logical AND; if both arg1 and arg2 have a nonzero (and
nonnull) value, the result is arg1; otherwise, the result is 0.
: Like grep; arg2 is a pattern to search for in arg1. arg2 must be
a regular expression. If part of the arg2 pattern is enclosed in \(\)
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expr
(escaped parentheses), the result is the portion of arg1 that
matches; otherwise, the result is simply the number of charac-
ters that match. By default, a pattern match always applies to
the beginning of the first argument (the search string implic-
itly begins with a ^). Start the search string with .* to match
other parts of the string.
Keywords
index string character-list
Return the first position in string that matches the first
possible character listed in character-list. Continue through
character-list until a match is found, or return 0.
length string
Return the length of string.
match string regex
Same as string : regex.
+token
Treat token as a string, even if it would normally be a keyword
or an operator.
substr string start length
Return a section of string, beginning with start, with a
maximum length of length characters. Return null when given
a negative or nonnumeric start or length.
Examples
Division happens first; result is 10:
expr 5 + 10 / 2
Addition happens first; result is 7 (truncated from 7.5):
expr \( 5 + 10 \) / 2
Add 1 to variable i. This is how variables are incremented in shell
scripts:
i=`expr $i + 1`
Print 1 (true) if variable a is the string “hello”:
expr $a = hello
Print 1 (true) if b plus 5 equals 10 or more:
expr $b + 5 \>= 10
Find the 5th, 6th, and 7th letters of the word character:
expr substr character 5 3
In the examples that follow, variable p is the string "version.100" .
This command prints the number of characters in p:
expr $p : '.*' Result is 11
Match all characters and print them:
expr $p : '\(.*\)' Result is "version.100"
Print the number of lowercase letters at the beginning of p:
expr $p : '[a-z]*' Result is 7
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fc-cache
Match the lowercase letters at the beginning of p:
expr $p : '\([a-z]*\)' Result is ""version""
Truncate $x if it contains five or more characters; if not, just print
$x. (Logical OR uses the second argument when the first one is 0
or null, i.e., when the match fails.)
expr $x : '\(.....\)' \| $x
In a shell script, rename files to their first five letters:
mv $x `expr $x : '\(.....\)' \| $x`
(To avoid overwriting files with similar names, use mv -i.)
factor factor [options]n
Calculate and display the prime factors of number n, which must
be a positive integer. If n is not specified, numbers are read from
standard input, separated by commas, spaces, or tabs.
Options
--help
Display help information.
--version
Display version information.
Example:
user@systemname:~>factor 60
60: 2, 2, 3 5
false false
A null command that returns an unsuccessful (nonzero) exit status.
Normally used in bash scripts. See also true.
fc-cache fc-cache [options] [dirs]
Create font information caches for fontconfig system, enabling
applications that use fontconfig to load fonts more rapidly. If no
directory is specified, the current font configuration directories are
used. Only fonts readable by FreeType are cached.
Options
-f, --force
Regenerate cache files, even if they seem to be up to date.
-s, --system-only
Scan directories of fonts for the whole system, not the fonts in
the user’s home directory.
-v, --verbose
Verbose mode: display status information during operation.
-V, --version
Display version information.
-?, --help
Display help information.
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fc-list
fc-list fc-list [options] [pattern] [element]
Part of the fontconfig system. Lists available fonts and font styles.
The first argument limits listed fonts to those matching the pattern,
and the second displays the listed font attribute or element. To set
the element argument without setting a pattern, use the : character
to match all fonts. For example, fc-list : family displays all avail-
able fonts, with their font family information.
Options
-v, --verbose
Verbose mode: display status information during operation.
-?, --help
Display help message
-V, --version
Display version information and quit.
fdisk fdisk [options] [device]
System administration command. fdisk displays information about
disk partitions, creates and deletes disk partitions, and changes the
active partition. It is possible to assign a different operating system
to each of the four possible primary partitions, though only one
partition is active at any given time. You can also divide a physical
partition into several logical partitions. The minimum recom-
mended size for a Linux system partition is 40 MB. Normally, each
device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/
hdd, and so on. An interactive, menu-driven mode is also available.
Note that this command can be destructive if used improperly.
Options
-b sectorsize
Set the size of individual disk sectors. May be 512, 1024, or
2048. Most systems now recognize sector sizes, so this is not
necessary.
-l List partition tables and exit.
-u Report partition sizes in sectors instead of cylinders.
-s partition
Display the size of partition, unless it is a DOS partition.
-v Print version number, then exit.
-C cylinders
Specify the number of cylinders on the disk.
-H heads
Specify the number of heads per cylinder.
-S sectors
Specify sectors per track for partitioning.
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file
Commands
a Toggle a bootable flag on current partition.
b Edit disklabel of a BSD partition.
c Toggle DOS compatibility flag.
d Delete current partition.
l List all partition types.
m Main menu.
n Create a new partition; prompt for more information.
o Create an empty DOS partition table.
p Print a list of all partitions and information about each.
q Quit; do not save.
t Replace the type of the current partition.
u Modify the display/entry units, which must be cylinders or
sectors.
v Verify: check for errors, and display a summary of the number
of unallocated sectors.
w Save changes and exit.
x Switch to expert commands.
fgconsole fgconsole
Print the number of the current virtual console. For example, if you
are using /dev/tty1, the command would return 1.
fgrep fgrep [options]string [files]
Search one or more files for lines that match the specified text
string. Exit status is 0 if any lines match, 1 if not, and 2 for errors.
fgrep is faster than normal grep searches, but less flexible: it can
only find fixed text, not regular expressions.
See grep for the list of available options. Also see egrep.
Examples
Print lines in file that don’t contain any spaces:
fgrep -v ' 'file
Print lines in file that contain the words in the file spell_list:
fgrep -f spell_listfile
file file [options]files
Classify the named files according to the type of data they contain.
file checks the magic file (usually /usr/share/magic) to identify some
file types. If the file type cannot be determined, it is shown as
“data.” file does its best to identify the file type, but it is some-
times incorrect. See also the strings command to search for
printable strings in nontext files.
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file
Options
-b, --brief
Brief mode; do not prepend filenames to output lines.
-c, --checking-printout
Check the format of the magic file (the files argument is
invalid with -c). Usually used with -m.
-f file, --files-from file
Read the names of files to be checked from file.
-h, --no-dereference
Do not follow symbolic links. The default unless the environ-
ment variable POSIXLY_CORRECT is defined.
--help
Print help message and exit.
-i, --mime
Print mime strings rather than the traditional strings.
-L, --dereference
Follow symbolic links. By default, symbolic links are not
followed.
-m file, --magic-file file
Search for file types in file instead of /usr/share/magic, where
file can be either a single file or a colon-separated list of files.
--mime-type, --mime-encoding
Like -i, but print only the mime type or the mime encoding.
-n, --no-buffer
Flush standard output after checking a file.
-N, --no-pad
Do not pad filenames to align in the output.
-s, --special-files
Check files that are block or character special files in addition
to checking ordinary files.
-v, --version
Print the version.
-z, --uncompress
Attempt checking of compressed files.
Many file types are understood. The output lists each filename,
followed by a brief classification such as:
ascii text
c program text
c-shell commands
data
empty
iAPX 386 executable
directory
[nt]roff, tbl, or eqn input text
shell commands
symbolic link topath
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find
Examples
List all files that are deemed to be troff/nroff input:
file * | grep roff
Print the file type of the status file:
file status
status: ASCII English text
Print the file type of the status file in mime format:
file status
status: text/plain charset=us-ascii
find find [pathnames] [conditions]
An extremely useful command for finding particular groups of files
(numerous examples follow this description). find descends the
directory tree beginning at each pathname and locates files that
meet the specified conditions. The default pathname is the current
directory. The most useful conditions include -name and -type (for
general use), -exec and -size (for advanced use), and -mtime and -user
(for administrators).
Conditions may be grouped by enclosing them in \( \) (escaped
parentheses), negated with !, given as alternatives by separating
them with -o, or repeated (adding restrictions to the match; usually
only for -name, -type, or -perm). Note that “modification” refers to
editing of a file’s contents, whereas “change” means a modifica-
tion, or permission or ownership changes. In other words, -ctime is
more inclusive than -atime or -mtime.
Conditions and actions
-amin +n| -n| n
Find files last accessed more than n (+n), less than n (-n), or
exactly n minutes ago.
-anewer file
Find files that were accessed after file waslast modified.
Affected by -H or -L when after them on the command line.
-atime +n| -n| n
Find files that were last accessed more than n (+n), less than n
(-n), or exactly n days ago. Note that find changes the access
time of directories supplied as pathnames.
-cmin +n| -n| n
Find files last changed more than n (+n), less than n (-n), or
exactly n minutes ago.
-cnewer file
Find files that were changed after they were last modified.
Affected by -H or -L when after them on the command line.
-ctime +n| -n| n
Find files that were changed more than n (+n), less than n (-n),
or exactly n days ago. A change is anything that changes the
directory entry for the file, such as a chmod.
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find
-daystart
Calculate times from the start of the day today, not 24 hours
ago. Only affects tests that come after it on the command line.
-delete
Delete files. Automatically turns on -depth.
-depth
Descend the directory tree, skipping directories and working
on actual files first, and then the parent directories. Useful
when files reside in unwritable directories (e.g., when using
find with cpio).
-empty
Continue if file is empty. Applies to regular files and
directories.
-exec command{ } \ ;
Run the Linux command, from the starting directory on each
file matched by find (provided command executes successfully
on that file—i.e., returns a 0 exit status). When command
runs, the argument { } substitutes the current file. Follow the
entire sequence with an escaped semicolon (\;). In some shells,
the braces may need to be escaped as well.
-false
Return false for each file encountered.
-fstype type
Match files only on type filesystems. Acceptable types include
minix, ext, ext2, xia, msdos, umsdos, vfat, proc, nfs,
iso9660, hpfs, sysv, smb, and ncpfs.
-gid num
Find files with numeric group ID of num.
-group gname
Find files belonging to group gname. gname can be a group
name or a group ID number.
-ilname pattern
A case-insensitive version of -lname.
-iname pattern
A case-insensitive version of -name.
-inum n
Find files whose inode number is n.
-ipath pattern
A case-insensitive version of -path.
-iregex pattern
A case-insensitive version of -regex.
-links n
Find files having n links.
-lname pattern
Search for files that are symbolic links, pointing to files named
pattern. pattern can include shell metacharacters and does not
treat / or . specially. The match is case-insensitive.
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find
-maxdepth num
Do not descend more than num levels of directories.
-mindepth num
Begin applying tests and actions only at levels deeper than
num levels.
-mmin +n| -n| n
Find files last modified more than n (+n), less than n (-n), or
exactly n minutes ago.
-mount, -xdev
Search only for files that reside on the same filesystem as path-
name. -xdev is for compatibility with other versions of find.
-mtime +n| -n| n
Find files that were last modified more than n (+n), less than n
(-n), or exactly n days ago. A modification is a change to a
file’s data.
-name pattern
Find files whose names match pattern. Filename metacharac-
ters may be used but should be escaped or quoted.
-newer file
Find files that were modified more recently than file; similar to
-mtime. With -H or -L, if file is a symbolic link, use the modi-
fication time of the file the link points to.
-nogroup
The file’s group ID does not correspond to any group.
-noleaf
Normally, find assumes that each directory has at least two
hard links that should be ignored (a hard link for its name and
one for “.”—i.e., two fewer “real” directories than its hard
link count indicates). -noleaf turns off this assumption, a
useful practice when find runs on non-Unix-style filesystems.
This forces find to examine all entries, assuming that some
might prove to be directories into which it must descend (a
time-waster on Unix).
-nouser
The file’s user ID does not correspond to any user.
-ok command { }\;
Same as -exec, but prompts user to respond with y or Y before
command is executed.
-path pattern
Find files whose names match pattern. Expect full pathnames
relative to the starting pathname (i.e., do not treat / or .
specially).
-perm nnn
Find files whose permission flags (e.g., rwx) match octal
number nnn exactly (e.g., 664 matches -rw-rw-r--). Use a
minus sign before nnn to make a “wildcard” match of any
unspecified octal digit (e.g., -perm -600 matches -rw-******,
where * can be any mode).
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find
-print
Print the matching files and directories, using their full path-
names. Return true. This is the default behavior.
-regex pattern
Like -path, but uses Emacs-style regular expressions instead of
the shell-like globbing used in -name and -path.
-regextypepattern
Use an alternative regular expression syntax for -regex and
-iregex. The possible types are Emacs (the default), posix-
awk, posix-basic, posix-egrep, and posix-extended.
-size n[u]
Find files containing n blocks. If u, is specified, measure size in
one of the following units: b (512-byte blocks), c (bytes), k
(kilobytes), G (gigabytes), M (megabytes), or w (two-byte
words).
-true
Return true for each file encountered.
-type c
Findfiles whose type is c. c can be b (block special file), c
(character special file), d (directory), p (fifo or named pipe), l
(symbolic link), s (socket), or f (plain file).
-user user
Find files belonging to user (name or numeric ID).
Examples
List all files (and subdirectories) in your home directory:
find $HOME -print
List all files named chapter1 in the /work directory:
find /work -name chapter1
List all files beginning with memo owned by ann:
find /work -name 'memo*' -user ann -print
Search the filesystem (begin at root) for manpage directories:
find / -type d -name 'man*' -print
Search the current directory, look for filenames that don’t begin
with a capital letter, and send them to the printer:
find . \! -name '[A-Z]*' -exec lpr { }\;
Find and compress files whose names don’t end with .gz:
gzip `find . \! -name '*.gz' -print`
Remove all empty files on the system (prompting first):
find / -size 0 -ok rm { } \;
Search the system for files that were modified within the last two
days (good candidates for backing up):
find / -mtime -2 -print
Recursively grep for a pattern down a directory tree:
find /book -print | xargs grep '[Nn]utshell'
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flex
If the files kt1 and kt2 exist in the current directory, their names
can be printed with the command:
$find . -name 'kt[0-9]'
./kt1
./kt2
Since the command prints these names with an initial ./ path, you
need to specify the ./ when using the -path option:
$find . -path './kt[0-9]'
./kt1
./kt2
The -regex option uses a complete pathname, like -path, but treats
the following argument as a regular expression rather than a glob
pattern (although in this case the result is the same):
$find . -regex './kt[0-9]'
./kt1
./kt2
flex flex [options] [file]
flex (Fast Lexical Analyzer Generator) is a faster variant of lex. It
generates a lexical analysis program (named lex.yy.c) based on the
regular expressions and C statements contained in one or more
input files. See also bison, yacc, and the O’Reilly book lex & yacc.
Options
-b Generate backup information to lex.backup.
-d Debug mode.
-f Use a faster scanner. The result is larger but faster.
-h Help summary.
-i Scan case-insensitively.
-l Maximum lex compatibility.
-o file
Write output to file instead of lex.yy.c.
-p Print performance report.
-s Exit if the scanner encounters input that does not match any
of its rules.
-t Print to standard output. (By default, flex prints to lex.yy.c.)
-v Print a summary of statistics.
-w Suppress warning messages.
-B Generate batch (noninteractive) scanner.
-F Use the fast scanner table representation. This option is
usually as fast as -f and often generates smaller data (although
for some data sets, it generates larger data).
-I Generate an interactive scanner (default).
-L Suppress #line directives in lex.yy.c.
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fmt
-P prefix
Change default yy prefix to prefix for all globally visible vari-
able and function names.
-V Print version number.
-7 Generate a 7-bit scanner.
-8 Generate an 8-bit scanner (default).
-+ Generate a C++ scanner class.
-C Compress scanner tables but do not use equivalence classes.
-Ca
Align tables for memory access and computation. This creates
larger tables but gives faster performance.
-Ce
Construct equivalence classes. This creates smaller tables and
sacrifices little performance (default).
-Cf
Generate full scanner tables, not compressed.
-CF
Generate faster scanner tables, like -F.
-Cm
Construct metaequivalence classes (default).
-Cr
Bypass use of the standard I/O library; use read() system calls
instead.
fmt fmt [options] [files]
Convert text to specified width by filling lines and removing
newlines. Concatenate files on the command line, or read text from
standard input if - (or no file) is specified. By default, preserve
blank lines, spacing, and indentation. fmt attempts to break lines at
the end of sentences and to avoid breaking lines after a sentence’s
first word or before its last.
Options
-c, --crown-margin
Crown margin mode. Do not change indentation of each para-
graph’s first two lines. Use the second line’s indentation as the
default for subsequent lines.
-p prefix, --prefix=prefix
Format only lines beginning with prefix.
-s, --split-only
Suppress line-joining.
-t, --tagged-paragraph
Tagged paragraph mode. Same as crown mode when the
indentations of the first and second lines differ. If the indenta-
tion is the same, treat the first line as its own separate
paragraph.
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formail
-u, --uniform-spacing
Reduce spacing to a maximum of one space between words
and two between sentences.
-w width, --width=width
Set output width to width. The default is 75.
--help
Print help message and exit.
--version
Print version information and exit.
fold fold [option] [files]
Break the lines of the named files so that they are no wider than the
specified width. fold breaks lines exactly at the specified width,
even in the middle of a word. Reads from standard input when
given - as a file. By default, fold cuts at 80 columns; tab counts as
multiple columns, and a backspace as negative one.
Options
-b, --bytes
Count bytes instead of columns, making tab, backspace, and
return characters count as one byte instead of altering the
column count, as in the default behavior.
-c, --characters
Count characters, not columns. Similar to counting by bytes.
-s, --spaces
Break at spaces only, if possible.
-w, --width width, -width
Set the maximum line width to width. The flags -w 6, --width
6, and -6 all set the maximum width to six columns.
formail formail [options]
Filter standard input into mailbox format. Useful for splitting mail
digests or passing the contents of a mail file to another program,
such as a spam filter, for additional processing. If no sender is
apparent, provide the sender foo@bar. By default, escape bogus
From lines with >.
Options
+skip
Do not split first skip messages.
-total
Stop after splitting total messages.
-a headerfield
Append headerfield to header, unless it already exists. If
headerfield is Message-ID or Resent-Message-ID with no
contents, generate a unique message ID.
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formail
-A headerfield
Append headerfield whether or not it already exists.
-b Do not escape bogus From lines.
-B Assume that input is in BABYL rmail format.
-c When header fields are more than one line long, concatenate
the lines.
-d Do not assume that input must be in strict mailbox format.
This option disables recognition of the Content-Length field
so you can split digests or use nonstandard mailbox formats.
-D maxlen idcache
Remember old message IDs (in idcache, which will grow no
larger than approximately maxlen). When splitting, refuse to
output duplicate messages. Otherwise, return true on discov-
ering a duplicate. With -r, look at the sender’s mail address
instead of the message ID.
-e Allow messages to begin one immediately after the other; do
not require empty space between them.
-f Do not edit non-mailbox-format lines. By default, formail
prepends From to such lines.
-i headerfield
Like -A, but rename each existing headerfield to Old-header-
field, unless it is empty.
-I headerfield
Like -i, but also remove existing similar fields. If there is only a
field name but no content, delete the field.
-k For use only with -r. Keep the body as well as the fields speci-
fied by -r.
-lfolder
Generate a log summary in procmail format. You can then use
mailstat to summarize the logs.
-m minfields
Require formail to find at least minfields consecutive headers
before recognizing the beginning of a new message. Default is 2.
-n[max]
Allow simultaneous formail processes to run. Specify max to
set the number of simultaneous processes allowed.
-p prefix
Set off quoted lines with prefix instead of >.
-q Do not display write errors, duplicate messages, or
mismatched Content-Length fields. This is the default; use -q-
to turn it off and display the messages.
-r Throw away all existing fields, retaining only X-Loop, and
generate autoreply header instead. You can preserve particular
fields with the -i option.
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fsck
-R oldfield newfield
Change all fields named oldfield to newfield.
-s[progname]
Must be the last option; everything following -s is assumed to
be its arguments. Divide input to separate mail messages, and
pipe them to the program specified or concatenate them to
standard output (by default).
-t Assume sender’s return address to be valid. (By default,
formail favors machine-generated addresses.)
-u headerfield
Delete all but the first occurrence of headerfield.
-U headerfield
Delete all but the last occurrence of headerfield.
-x headerfield
Display the contents of headerfield; to always display on a single
line, use with -c.
-X headerfield
Like -x, but also display the field name.
-Y Format in traditional Berkeley style (i.e., ignore Content-
Length fields).
-z When necessary, add a space between field names and
contents. Remove (“zap”) empty fields.
free free [options]
Display statistics about memory usage: total free, used, physical,
swap, shared, and buffers used by the kernel.
Options
-b Calculate memory in bytes.
-k Default. Calculate memory in kilobytes.
-m Calculate memory in megabytes.
-o Do not display “buffer adjusted” line. The -o switch disables
the display “-/+ buffers” line that shows buffer memory
subtracted from the amount of memory used and added to the
amount of free memory.
-s time
Check memory usage every time seconds.
-t Display all totals on one line at the bottom of output.
-V Display version information.
fsck fsck [options] [filesystem]...
System administration command. Call the filesystem checker for
the appropriate system type to check and repair unmounted filesys-
tems. If a filesystem is consistent, the number of files, number of
blocks used, and number of blocks free are reported. If a filesystem
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ftp
is inconsistent, fsck prompts before each correction is attempted.
fsck’s exit code can be interpreted as the sum of all conditions that
apply:
0 No errors found.
1 Errors were found and corrected.
2 Reboot suggested.
4 Errors were found but not corrected.
8 fsck encountered an operational error.
16 fsck was called incorrectly.
32 fsck canceled by user request.
128
A shared library error was detected.
Options
-- Pass all subsequent options to filesystem-specific checker. All
options that fsck doesn’t recognize will also be passed.
-s Serial mode. Check one filesystem at a time.
-tfstype
Specify the filesystem type. Do not check filesystems of any
other type. Multiple filesystem types to check can be specified
in a comma-separated list.
-A Check all filesystems listed in /etc/fstab. The root filesystem is
checked first.
-C[fd]
Display completion (progress) bar. Optionally specify a file-
descriptor to receive the progress. (Useful for a GUI frontend.)
-M Don’t check mounted filesystems. Returns a 0 exit code for
mounted system.
-N Suppress normal execution; just display what would be done.
-P Meaningful only with -A: check root filesystem in parallel with
other systems. This option is potentially dangerous.
-R Meaningful only with -A: check all filesystems listed in /etc/
fstab except the root filesystem.
-T Suppress printing of title.
-V Verbose mode.
ftp ftp [options] [hostname]
Transfer files to and from remote network site hostname. ftp
prompts the user for a command. The commands are listed after
the options. Some of the commands are toggles, meaning they turn
on a feature when it is off and vice versa. Note that some versions
may have different options.
Options
-d Enable debugging.
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ftp
-g Disable filename globbing.
-i Turn off interactive prompting.
-n No autologin upon initial connection.
-v Verbose. Show all responses from remote server.
Commands
![command [args]]
Invoke an interactive shell on the local machine. If arguments
are given, the first is taken as a command to execute directly,
with the rest of the arguments as that command’s arguments.
$macro-name [args]
Execute the macro macro-name that was defined with the
macdef command. Arguments are passed to the macro
unglobbed.
account [passwd]
Supply a supplemental password that will be required by a
remote system for access to resources once a login has been
successfully completed. If no argument is given, prompt the
user for an account password in a nonechoing mode.
append local-file [remote-file]
Append a local file to a file on the remote machine. If remote-
file is not given, the local filename is used after being altered
by any ntrans or nmap setting. File transfer uses the current
settings for type, format, mode, and structure.
ascii
Set the file transfer type to network ASCII (default).
bell
Sound a bell after each file transfer command is completed.
binary, image
Set file transfer type to support binary image transfer.
bye, quit
Terminate FTP session and then exit ftp.
case
Toggle remote-computer filename case mapping during mget.
The default is off. When case is on, files on the remote
machine with all-uppercase names are copied to the local
machine with all-lowercase names.
cd remote-directory
Change working directory on remote machine to remote-
directory.
cdup
Change working directory on remote machine to its parent
directory.
chmod [mode] [remote-file]
Change file permissions of remote-file. If options are omitted,
the command prompts for them.
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ftp
close, disconnect
Terminate FTP session and return to command interpreter.
cr
Toggle carriage-return stripping during ASCII-type file retrieval.
delete remote-file
Delete file remote-file on remote machine.
debug [debug-value]
Toggle debugging mode. If debug-value is specified, it is used
to set the debugging level.
dir [remote-directory] [local-file]
Print a listing of the contents in the directory remote-directory
and, optionally, place the output in local-file. If no directory is
specified, the current working directory on the remote
machine is used. If no local file is specified or - is given instead
of the filename, output comes to the terminal.
form format
Set the file transfer form to format. Default format is file.
getremote-file [local-file], recv remote-file [local-file]
Retrieve remote-file and store it on the local machine. If local-file
is not specified, the file is given the same name as on the
remote machine, subject to alteration by the current case,
ntrans, and nmap settings. If local-file is -, the output comes
to the terminal.
glob
Toggle filename expansion for mdelete, mget, and mput. If
globbing is turned off, the filename arguments are taken liter-
ally and not expanded.
hash
Toggle hash sign (#) printing for each data block transferred.
help [command], ? [command]
Print help information for command. With no argument, ftp
prints a list of commands.
idle [seconds]
Get/set idle timer on remote machine. seconds specifies the
length of the idle timer; if omitted, the current idle timer is
displayed.
lcd [directory]
Change working directory on local machine. If directory is not
specified, the user’s home directory is used.
ls [remote-directory] [local-file]
Print listing of contents of directory on remote machine, in a
format chosen by the remote machine. If remote-directory is
not specified, current working directory is used.
macdef macro-name
Define a macro. Subsequent lines are stored as the macro
macro-name; a null line terminates macro input mode. When $i
is included in the macro, loop through arguments, substituting
the current argument for $i on each pass. Escape $ with \.
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ftp
mdelete [remote-files]
Delete the remote-files on the remote machine.
mdir remote-files local-file
Like dir, except multiple remote files may be specified.
mget remote-files
Expand the wildcard expression remote-files on the remote
machine and do a get for each filename thus produced.
mkdir directory-name
Make a directory on the remote machine.
mls remote-files local-file
Like nlist, except multiple remote files may be specified, and
the local file must be specified.
mode [mode-name]
Set file transfer mode to mode-name. Default mode is stream.
modtime file-name
Show last modification time of the file on the remote machine.
mput local-files
Expand wildcards in local-files given as arguments and do a
put for each file in the resulting list.
newer remote-file [local-file]
Get the remote file if it is newer than the local file.
nlist [remote-directory] [local-file]
Print list of files in a directory on the remote machine to local-
file (or to the screen if local-file is not specified). If remote-
directory is unspecified, the current working directory is used.
nmap [inpattern outpattern]
Set or unset the filename mapping mechanism. The mapping
follows the pattern set by inpattern, a template for incoming
filenames, and outpattern, which determines the resulting
mapped filename. The sequences $1 through $9 are treated as
variables; for example, the inpattern $1.$2, along with the
input file readme.txt, would set $1 to readme and $2 to txt.
An outpattern of $1.data would result in an output file of
readme.data. $0 corresponds to the complete filename.
[string1, string2] is replaced by string1 unless that string is
null, in which case it’s replaced by string2.
ntrans [inchars [outchars ]]
Set or unset filename character translation. Characters in a
filename matching a character in inchars are replaced with the
corresponding character in outchars. If no arguments are spec-
ified, the filename mapping mechanism is unset. If arguments
are specified:
• Characters in remote filenames are translated during
mput and put commands issued without a specified
remote target filename.
• Characters in local filenames are translated during mget
and get commands issued without a specified local target
filename.
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ftp
open host [port]
Establish a connection to the specified host FTP server. An
optional port number may be supplied, in which case ftp
attempts to contact an FTP server at that port.
prompt
Toggle interactive prompting.
proxy ftp-command
Execute an FTP command on a secondary control connection
(i.e., send commands to two separate remote hosts simulta-
neously to allow the transfer of files between the two servers).
put local-file [remote-file], send local-file [remote-file]
Store a local file on the remote machine. If remote-file is not
specified, the local filename is used after processing according
to any ntrans or nmap settings in naming the remote file. File
transfer uses the current settings for type, file, structure, and
transfer mode.
pwd
Print name of the current working directory on the remote
machine.
quote arg1 arg2...
Send the arguments specified, verbatim, to the remote FTP
server.
reget remote-file [local-file]
Retrieve a file (like get), but restart at the end of local-file.
Useful for restarting a dropped transfer.
remotehelp [command-name]
Request help from the remote FTP server. If command-name is
specified, remote help for that command is returned.
remotestatus [filename]
Show status of the remote machine or, if filename is specified,
of filename on remote machine.
rename [from] [to]
Rename file from on remote machine to to.
reset
Clear reply queue.
restart marker
Restart the transfer of a file from a particular byte count.
rmdir directory-name
Delete a directory on the remote machine.
runique
Toggle storing of files on the local system with unique file-
names. When this option is on, rename files as .1 or .2, and so
on, as appropriate, to preserve unique filenames, and report
each such action. Default value is off.
sendport
Toggle the use of PORT commands.
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ftpd
site [command]
Run a site-specific command on the remote machine.
size filename
Return size of filename on remote machine.
status
Show current status of ftp.
struct [struct-name]
Set the file transfer structure to struct-name. By default, stream
structure is used.
sunique
Toggle storing of files on remote machine under unique
filenames.
system
Show type of operating system running on remote machine.
tenex
Set file transfer type to that needed to talk to TENEX machines.
trace
Toggle packet tracing.
type [type-name]
Set file transfer type to type-name. If no type is specified, the
current type is printed. The default type is network ASCII.
umask [mask]
Set user file-creation mode mask on the remote site. If mask is
omitted, the current value of the mask is printed.
user username [password] [account]
Identify yourself to the remote FTP server. ftp prompts the
user for the password (if not specified and the server requires
it) and the account field.
verbose
Toggle verbose mode.
ftpd in.ftpd [options]
TCP/IP command. Internet File Transfer Protocol server. The server
uses the TCP protocol and listens at the port specified in the ftp
service specification. ftpd is usually started by xinetd and must
have an entry in xinetd’s configuration file, /etc/xinetd.conf. It can
also be run in standalone mode using the -p option. There are
several FTP daemons available. On many Linux distributions, the
default is the Kerberos-supporting DARPA version, which we docu-
ment here.
Options
-a Require authentication via ftp AUTH. Allow anonymous users
as well, if configured to do so.
-A Require authentication via ftp AUTH, but allow only users
who are authorized to connect without a password. Allow
anonymous users as well, if configured to do so.
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fuser
-C Require local credentials for nonanonymous users. Prompt for
a password unless the user forwards credentials during
authentication.
-d, -v
Write debugging information to syslogd.
-l Log each FTP session in syslogd.
-p port
Use port as the FTP control port instead of reading the appro-
priate port from /etc/services. This option will launch ftpd in
standalone mode.
-q Use PID files to record the process IDs of running daemons.
This is the default. These files are needed to determine the
current number of users.
-r file
Read Kerberos configuration from file instead of /etc/krb5.conf.
-s file
Read Kerberos V4 authentication information from file instead
of /etc/srvtab.
-t n
Set default inactivity timeout period to n seconds. (The default
is 15 minutes.)
-T n
Allow ftp clients to request a different timeout period of up to
n seconds. (The default is 2 hours.)
-u umask
Set the default umask to umask.
-U file
Read the list of users denied remote access from file instead of
/etc/ftpusers.
-w format
Specify the format for the remote hostname passed to login.
Use one of the following formats:
ip
Pass the IP address.
n[,[no]striplocal]
Pass hostnames less than n characters in length, and IP
addresses for longer hostsnames. Set n to 0 to use the
system default. The striplocal portion of the option deter-
mines whether or not to strip local domains from
hostnames. The default is to strip them.
fuser fuser [options] [files |filesystems]
Identifies and outputs the process IDs of processes that are using
the files or local filesystems. Each process ID is followed by a letter
code: c if process is using file as the current directory; e if execut-
able; f if an open file; F if open file for writing; m if a shared library;
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gawk
and r if the root directory. Any user with permission to read /dev/
kmem and /dev/mem can use fuser, but only a privileged user can
terminate another user’s process. fuser does not work on remote
(NFS) files.
If more than one group of files is specified, the options may be
respecified for each additional group of files. A lone dash (-)
cancels the options currently in force, and the new set of options
applies to the next group of files. Like a number of other adminis-
trator commands, fuser is usually installed to the /sbin directory.
You may need to add that directory to your path or execute the
command as /sbin/fuser.
Options
- Return all options to defaults.
-signal
Send signal instead of SIGKILL.
-a Display information on all specified files, even if they are not
being accessed by any processes.
-i Request user confirmation to kill a process. Ignored if -k is not
also specified.
-k Send SIGKILL signal to each process.
-l List signal names.
-m Expect files to exist on a mounted filesystem; include all files
accessing that filesystem.
-n space
Set the namespace checked for usage. Acceptable values are
file for files, udp for local UPD ports, and tcp for local TCP
ports.
-s Silent.
-u User login name, in parentheses, also follows process ID.
-v Verbose.
-V Display version information.
g++ g++[options]files
Invoke gcc with the options necessary to make it recognize C++.
g++ recognizes all the file extensions gcc does, in addition to C++
source files (.C, .cc, or .cxx files) and C++ preprocessed files (.ii
files). See also gcc.
gawk gawk [options] 'script' [var=value...] [files]
gawk [options] -fscriptfile [var=value...] [files]
The GNU version of awk, a program that does pattern matching,
record processing, and other forms of text manipulation. For more
information, see Chapter 11.
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gcc
gcc gcc [options]files
GNU Compiler Collection. gcc, formerly known as the GNU C
Compiler, compiles multiple languages (C, C++, Objective-C, Ada,
FORTRAN, and Java) to machine code. Here we document its use
to compile C, C++, or Objective-C code. gcc compiles one or more
programming source files; for example, C source files (file.c),
assembler source files (file.s), or preprocessed C source files (file.i).
If the file suffix is not recognizable, assume that the file is an object
file or library. gcc normally invokes the C preprocessor, compiles
the process code to assemble language code, assembles it, and then
links it with the link editor. This process can be stopped at one of
these stages using the -c, -S, or -E option. The steps may also differ
depending on the language being compiled. By default, output is
placed in a.out. In some cases, gcc generates an object file having a .o
suffix and a corresponding root name.
Preprocessor and linker options given on the gcc command line are
passed on to these tools when they are run. These options are
briefly described here, but some are more fully described under
entries for cpp, as, and ld. The options that follow are divided into
general, preprocessor, linker, and warning options. gcc accepts many
system-specific options not covered here.
gcc is the GNU form of cc; on most Linux systems, the command
cc will invoke gcc. The command g++ will invoke gcc with the
appropriate options for interpreting C++.
General options
-a Provide profile information for basic blocks.
-aux-info file
Print prototyped declarations and information on their origins
to file.
-ansi
Enforce full ANSI conformance.
-b machine
Compile for use on machine type.
-c Create linkable object file for each source file, but do not call
linker.
-dumpmachine
Print compiler’s default target machine, then exit.
-dumpspecs
Print built-in specification strings, then exit.
-dumpversion
Print version number, then exit.
-foption
Set the specified compiler option. Many of these control
debugging, optimization of code, and special language
options. Use the --help -v options for a full listing.
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gcc
-g Include debugging information for use with gdb.
-glevel
Provide the given level of debugging information. level must be
1, 2, or 3, with 1 providing the least amount of information.
The default is 2.
--help
Print most common basic options, then exit. When used with
option -v, print options for all of gcc’s subprocesses. For
options specific to a target, use --target-help.
-moption
Set the specified machine specific option. Use the --target-help
option for a full listing.
-o file
Specify output file as file. Default is a.out.
-p Provide profile information for use with prof.
-pass-exit-codes
On error, return highest error code as the exit code, instead of
1.
-pedantic
Warn verbosely.
-pedantic-errors
Generate an error in every case in which -pedantic would have
produced a warning.
-pg
Provide profile information for use with gprof.
-print-file-name=file
Print the full path to the library specified by filename file, then
exit. This is the library gcc would use for linking.
-print-search-dirs
Print installation directory and the default list of directories
gcc will search to find programs and libraries, then exit.
-pipe
Transfer information between stages of compiler by pipes
instead of temporary files.
-save-temps
Save temporary files in the current directory when compiling.
-std=standard
Specify C standard of input file. Accepted values are:
iso9899:1990, c89
1990 ISO C standard (C89).
iso9899:199409
1994 amendment to the 1990 ISO C standard.
iso9899:1999, c99, iso9899:199x, c9x
1999 revised ISO C standard (C99).
gnu89
1990 C Standard with GNU extensions (the default
value).
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gcc
gnu99, gnu9x
1999 revised ISO C standard with GNU extensions.
c++98
1998 ISO C++ standard plus amendments.
gnu++98
1998 ISO C++ standard plus amendments and GNU
extensions.
-time
Print statistics on the execution of each subprocess.
-v Verbose mode. Print subprocess commands to standard error
as they are executed. Include gcc version number and prepro-
cessor version number. To generate the same output without
executing commands, use the option -###.
-w Suppress warnings.
-x language
Expect input file to be written in language, which may be c,
objective-c, c-header, c++, ada, f77, ratfor, assembler, java,
cpp-output, c++-cpp-output, objc-cpp-output, f77-cpp-
output, assembler-with-cpp, or ada. If none is specified as
language, guess the language by filename extension.
-Bpath
Specify the path directory in which the compiler files are
located.
-E
Preprocess the source files, but do not compile. Print result to
standard output. This option is useful to meaningfully pass
some cpp options that would otherwise break gcc, such as -C,
-M, or -P.
-Idir
Include dir in list of directories to search for include files. If dir
is -, search those directories specified by -I before the -I- only
when #include "file" is specified, not #include <file>.
-Ldir
Search dir in addition to standard directories.
-O[level]
Optimize. level should be 1, 2, 3, or 0 (the default is 1). 0
turns off optimization; 3 optimizes the most.
-S Compile source files into assembler code, but do not
assemble.
-V version
Attempt to run gcc version version.
-Wa,options
Pass options to the assembler. Multiple options are separated
by commas.
-Wl,options
Pass options to the linker. Multiple options are separated by
commas.
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gcc
-Wp,options
Pass options to the preprocessor. Multiple options are sepa-
rated by commas.
-Xlinker options
Pass options to the linker. A linker option with an argument
requires two -Xlinkers, the first specifying the option and the
second specifying the argument. Similar to -Wl.
Preprocessor options
gcc will pass the following options to the preprocessor:
-$ Do not allow $ in identifiers.
-dD, -dI, -dM, -dN
Suppress normal output; print preprocessor instructions
instead. See cpp for details.
-idirafter dir
Search dir for header files when a header file is not found in
any of the included directories.
-imacros file
Process macros in file before processing main files.
-include file
Process file before main file.
-iprefix prefix
When adding directories with -iwithprefix, prepend prefix to
the directory’s name.
-isystem dir
Search dir for header files after searching directories specified
with -I but before searching standard system directories.
-iwithprefix dir
Append dir to the list of directories to be searched when a header
file cannot be found in the main include path. If -iprefix has
been set, prepend that prefix to the directory’s name.
-iwithprefixbefore dir
Insert dir at the beginning of the list of directories to be
searched when a header file cannot be found in the main
include path. If -iprefix has been set, prepend that prefix to
the directory’s name.
-nostdinc
Search only specified, not standard, directories for header files.
-nostdinc++
Suppress searching of directories believed to contain C++-
specific header files.
-trigraphs
Convert special three-letter sequences, meant to represent
missing characters on some terminals, into the single char-
acter they represent.
-undef
Suppress definition of all nonstandard macros.
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gcc
-A name[=def]
Assert name with value def as if defined by #assert. To turn
off standard assertions, use -A-.
-A -name[=def]
Cancel assertion name with value def.
-C Retain all comments except those found on cpp directive lines.
By default, the preprocessor strips C-style comments.
-Dname[=def]
Define name with value def as if by #define. If no =def is
given, name is defined with value 1. -D has lower precedence
than -U.
-H Print pathnames of included files, one per line, on standard
error.
-M, -MG, -MF, -MD, -MMD, -MQ, -MT
Suppress normal output and print Makefile rules describing
file dependencies. Print a rule for make that describes the
main source file’s dependencies. If -MG is specified, assume
that missing header files are actually generated files, and look
for them in the source file’s directory. Most of these options
imply -E. See cpp for further details.
-Uname
Remove definition of symbol name.
Linker options
gcc will pass the following options to the linker:
-llib
Link to lib.
-nostartfiles
Force linker to ignore standard system startup files.
-nostdlib
Suppress linking to standard library files.
-s Remove all symbol table and relocation information from the
executable.
-shared
Create a shareable object.
-shared-libgcc
Link to a shared version of libgcc if available.
-static
Suppress linking to shared libraries.
-static-libgcc
Link to a static version of libgcc if available.
-u symbol
Force the linker to search libraries for a definition of symbol
and to link to the libraries found.
Warning options
-pedantic
Warn verbosely.
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gcc
-pedantic-errors
Produce a fatal error in every case in which -pedantic would
have produced a warning.
-w Don’t print warnings.
-W Warn more verbosely than normal.
-Waggregate-return
Warn if any functions that return structures or unions are
defined or called.
-Wall
Enable -W, -Wchar-subscripts, -Wcomment, -Wformat,
-Wimplicit, -Wmain, -Wmissing-braces, -Wparentheses,
-Wreturn-type, -Wsequence-point, -Wswitch, -Wtemplate-
debugging, -Wtrigraphs, -Wuninitialized, -Wunknown-
pragmas, -Wstrict-aliasing, and -Wunused.
-Wcast-align
Warn when encountering instances in which pointers are cast
to types that increase the required alignment of the target from
its original definition.
-Wcast-qual
Warn when encountering instances in which pointers are cast
to types that lack the type qualifier with which the pointer was
originally defined.
-Wchar-subscripts
Warn when encountering arrays with subscripts of type char.
-Wcomment
Warn when encountering the beginning of a nested comment.
-Wconversion
Warn in particular cases of type conversions.
-Werror
Exit at the first error.
-Wformat
Warn about inappropriately formatted printfs and scanfs.
-Wimplicit
Warn when encountering implicit function or parameter
declarations.
-Winline
Warn about illegal inline functions.
-Wmain
Warn about malformed main functions.
-Wmissing-braces
Enable more verbose warnings about omitted braces.
-Wmissing-declarations
Warn if a global function is defined without a previous
declaration.
-Wmissing-prototypes
Warn when encountering global function definitions without
previous prototype declarations.
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gcc
-Wnested-externs
Warn if an extern declaration is encountered within a function.
-Wno-import
Don’t warn about use of #import.
-Wparentheses
Enable more verbose warnings about omitted parentheses.
-Wpointer-arith
Warn when encountering code that attempts to determine the
size of a function or void.
-Wredundant-decls
Warn if anything is declared more than once in the same
scope.
-Wreturn-type
Warn about violations of sequence point rules defined in the
C standard.
-Wreturn-type
Warn about functions defined without return types or with
improper return types.
-Wshadow
Warn when a local variable shadows another local variable.
-Wstrict-prototypes
Insist that argument types be specified in function declarations
and definitions.
-Wswitch
Warn about switches that skip the index for one of their
enumerated types.
-Wtraditional
Warn when encountering code that produces different results
in ANSI C and traditional C.
-Wtrigraphs
Warn when encountering trigraphs.
-Wuninitialized
Warn when encountering uninitialized automatic variables.
-Wundef
Warn when encountering a nonmacro identifier in an #if
directive.
-Wunknown-pragmas
Warn when encountering a #pragma directive not understood
by gcc.
-Wunused
Warn about unused variables, functions, labels, and parameters.
Pragma directives
#pragma interface [header-file]
Used in header files to force object files to provide definition
information via references instead of including it locally in
each file. C++-specific.
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gdb
#pragma implementation [header-file]
Used in main input files to force generation of full output from
header-file (or, if it is not specified, from the header file with
the same basename as the file containing the pragma direc-
tive). This information will be globally visible. Normally the
specified header file contains a #pragma interface directive.
gdb gdb [options] [program [core|pid]]
GDB (GNU DeBugger) allows you to step through the execution of
a program in order to find the point at which it breaks. It fully
supports C and C++, and provides partial support for FORTRAN,
Java, Chill, assembly, and Modula-2. The program to be debugged
is normally specified on the command line; you can also specify a
core or, if you want to investigate a running program, a process ID.
Options
-b bps
Set line speed of serial device used by GDB to bps.
-batch
Exit after executing all the commands specified in .gdbinit and
-x files. Print no startup messages.
-c file, -core=file
Consult file for information provided by a core dump.
-cd=directory
Use directory as gdb’s working directory.
-d directory, -directory=directory
Include directory in path that is searched for source files.
-e file, -exec=file
Use file as an executable to be read in conjunction with source
code. May be used in conjunction with -s to read the symbol
table from the executable.
-f, -fullname
Show full filename and line number for each stack frame.
-h, -help
Print help message, then exit.
-n, -nx
Ignore .gdbinit file.
-q, -quiet
Suppress introductory and copyright messages.
-s file, -symbols=file
Consult file for symbol table. With -e, also uses file as the
executable.
-tty=device
Set standard in and standard out to device.
-write
Allow gdb to write into executables and core files.
-x file, -command=file
Read gdb commands from file.
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gdb
Common commands
These are just some of the more common gdb commands; there are
too many to list them all.
bt
Print the current location within the program and a stack trace
showing how the current location was reached. (where does
the same thing.)
break
Set a breakpoint in the program.
cd
Change the current working directory.
clear
Delete the breakpoint where you just stopped.
commands
List commands to be executed when a breakpoint is hit.
c Continue execution from a breakpoint.
delete
Delete a breakpoint or a watchpoint; also used in conjunction
with other commands.
display
Cause variables or expressions to be displayed when program
stops.
down
Move down one stack frame to make another function the
current one.
frame
Select a frame for the next continue command.
info
Show a variety of information about the program. For
instance, info breakpoints shows all outstanding breakpoints
and watchpoints.
jump
Start execution at another point in the source file.
kill
Abort the process running under gdb’s control.
list
List the contents of the source file corresponding to the
program being executed.
next
Execute the next source line, executing a function in its entirety.
print
Print the value of a variable or expression.
ptype
Show the contents of a datatype, such as a structure or C++ class.
pwd
Show the current working directory.
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genisoimage
quit
Exit gdb.
reverse-search
Search backward for a regular expression in the source file.
run
Execute the program.
search
Search for a regular expression in the source file.
set variable
Assign a value to a variable.
signal
Send a signal to the running process.
step
Execute the next source line, stepping into a function if
necessary.
undisplay
Reverse the effect of the display command; keep expressions
from being displayed.
until
Finish the current loop.
up
Move up one stack frame to make another function the
current one.
watch
Set a watchpoint (i.e., a data breakpoint) in the program.
whatis
Print the type of a variable or function.
genisoimage genisoimage [ options ] [-o filename ] pathspec ...
Generate an ISO9660/Joliet/HFS hybrid filesystem for writing a
CD with a program such as wodim. (HFS is the native Macintosh
Hierarchical File System.) genisoimage takes a snapshot of a direc-
tory tree and generates a binary image that corresponds to an
ISO9660 or HFS filesystem when it is written to a block device.
Each specified pathspec describes the path of a directory tree to be
copied into the ISO9660 filesystem; if multiple paths are specified,
the files in all the paths are merged to form the image.
Options
-abstract file
Specify the abstract filename. Overrides an ABST=file entry in
.genisoimagerc.
-allow-leading-dots, -idots
Allow ISO9660 filenames to start with a period instead of
replacing it with an underscore. Violates the ISO9660
standard.
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genisoimage
-allow-lowercase
Allow ISO9660 filenames to be lowercase. Violates the
ISO9660 standard.
-allow-multidot
Allow more than one dot in ISO9660 filenames. Violates the
ISO9660 standard.
-A id, -appid id
Specify a text string id that describes the application to be
written into the volume header.
-b image
Specify the path and filename of the boot image to be used for
making a bootable CD based on the El Torito specification.
-biblio file
Specify bibliographic filename. Overrides a BIBL=file entry in
.genisoimagerc.
-boot-info-table
Specify that a 56-byte table with information on the CD layout
is to be patched in at offset 8 of the boot file. If specified, the
table is patched into the source boot file, so make a copy if the
file isn’t recreatable.
-boot-load-seg addr
Specify the load segment address of the boot image for a no-
emulation El Torito CD.
-boot-load-size size
Specify the number of virtual 512-byte sectors to load in no-
emulation mode. The default is to load the entire boot file.
The number may need to be a multiple of 4 to prevent prob-
lems with some BIOSes.
-c catalog
Specify the path, relative to the source pathspec, and the file-
name of the boot catalog for an El Torito bootable CD.
Required for making an El Torito bootable CD.
-C last-start,next-start
Required for creating a CDExtra or a second or higher-level
session for a multisession CD. last-start is the first sector
number in the last session on the disk, and next-start is the
first sector number for the new session. Use the command:
wodim -msinfo
to get the values. Use -C with -M to create an image that is a
continuation of the previous session; without -M, create an
image for a second session on a CDExtra (a multisession CD
with audio data in the first session and an ISO9660 filesystem
image in the second).
-[no-]cache-inodes
Cache [do not cache] inode and device numbers to find hard
links to files. The default on Linux is to cache. Use -no-cache-
inodes for filesystems that do not have unique inode numbers.
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genisoimage
-check-oldnames
Check all filenames imported from old sessions for
genisoimage compliance with ISO9660 file-naming rules. If
not specified, check only those files with names longer than 31
characters.
-check-session file
Check all old sessions for genisoimage compliance with
ISO9660 file-naming rules. This option is the equivalent of:
-Mfile -C 0,0 -check-oldnames
where file is the pathname or SCSI device specifier that would
be specified with -M.
-copyright file
Specify the name of the file that contains the copyright infor-
mation. Overrides a COPY=file entry in .genisoimagerc.
-d Omit trailing period from files that do not have one. Violates
the ISO9660 standard, but works on many systems.
-D Do not use deep directory relocation. Violates the ISO9660
standard, but works on many systems.
-dir-mode mode
Specify the mode for directories used to create the image.
Automatically enables the Rock Ridge extensions.
-eltorito-alt-boot
Start with a new set of El Torito boot parameters. Allows putting
more than one El Torito boot image on a CD (maximum is 63).
-exclude-list file
Check filenames against the globs contained in the specified
file and exclude any that match.
-f Follow symbolic links when generating the filesystem.
-file-mode mode
Specify the mode for files used to create the image. Automati-
cally enables the Rock Ridge extensions.
-force-rr
Do not use automatic Rock Ridge detection for the previous
session.
-G image
Specify the path and filename of the generic boot image for
making a generic bootable CD.
-gid gid
Set the group ID to gid for the source files. Automatically
enables the Rock Ridge extensions.
-graft-points
Allow the use of graft points for filenames, which permits
paths to be grafted at locations other than the root direc-
tory. -graft-points checks all filenames for graft points and
divides the filename at the first unescaped equals sign (=).
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genisoimage
-gui
Switch the behavior for a GUI. Currently, the only effect is to
make the output more verbose.
-hard-disk-boot
Specify that the boot image to be used to create an El Torito
bootable CD is a hard disk image that must begin with a
master boot record containing a single partition.
-hidden glob
Set the hidden (existence) ISO9660 directory attribute for
paths or filenames matching the shell-style pattern glob. To
match a directory, the path must not end with a trailing /. May
be specified more than once.
-hidden-list file
Specify a file containing a list of globs that are to be hidden
with -hidden.
-hide glob
Find paths or files that match the shell-style pattern glob and
hide them from being seen on the ISO9660 or Rock Ridge
directory. The files are still included in the image file. If the
pattern matches a directory, the contents of the directory are
hidden. To match a directory, the path must not end with a
trailing /. See also the -hide-joliet option and the file
README.hide. May be specified more than once.
-hide-joliet glob
Hide paths or files that match the shell-style pattern glob so
they will not be seen in the Joliet directory. If the pattern
matches a directory, the contents of the directory are hidden.
To match a directory, the path must not end with a trailing /.
Usually used with -hide. See also the README.hide file. May
be specified more than once.
-hide-joliet-list file
Specify a file containing a list of globs to be hidden with -hide-
joliet.
-hide-joliet-trans-tbl
Hide the TRANS.TBL files from the Joliet tree.
-hide-list file
Specify a file containing a list of globs to be hidden with -hide.
-hide-rr-moved
Rename the directory RR_MOVED to .rr_moved to hide it as
much as possible from the Rock Ridge directory tree. Use the -D
option to omit the file entirely.
-input-charset charset
Specify the character set for characters used in local filenames.
Specify help in place of a charset for a list of valid character sets.
-iso-level level
Set the ISO9660 conformance level. Possible values are:
1 Filenames are restricted to 8.3 characters, and files may
have only one section.
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genisoimage
2 Files may have only one section.
3 No restrictions.
4 genisoimage maps level 4 to ISO-9660:1999 (ISO9660
version 2).
-J Generate Joliet directory records in addition to regular
ISO9660 filenames.
-jcharset charset
The equivalent of -input-charset -J.
-l Allow full 31-character filenames instead of restricting them to
the MS-DOS-compatible 8.3 format.
-log-file file
Send all messages to the specified logfile.
-m glob
Exclude files matching the shell-style pattern glob. May be
specified multiple times.
-M path, -dev device
Specify the path to an existing ISO9660 image to be merged.
path (or the device given with -dev) can also be a SCSI device
specified in the same syntax as wodim’s dev= parameter. May
be used only with -C.
-max-iso9660-filenames
Allow up to 37 characters in ISO9660 filenames. Forces -N.
Violates the ISO9660 standard.
-N Omit version numbers from ISO9660 filenames. Violates the
ISO9660 standard. Use with caution.
-new-dir-mode mode
Specify the four-digit chmod-style mode to use for new direc-
tories in the image. The default is 0555.
-nobak, -no-bak
Do not include backup files on the ISO9660 filesystem.
-no-boot
Mark the El Torito CD to be created as not bootable.
-no-emul-boot
Specify that the boot image for creating an El Torito bootable
CD is a no-emulation image.
-no-iso-translate
Do not translate the # and ~ characters. Violates the ISO9660
standard.
-no-rr
Do not use Rock Ridge attributes from previous sessions.
-o file
Specify the filename of the output ISO9660 filesystem image.
-output-charset charset
Specify the output character set for Rock Ridge filenames. The
default is the input character set.
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genisoimage
-p prepid
Specify a text string of up to 128 characters describing the
preparer of the CD. Overrides a PREP= parameter set in the file
.genisoimagerc.
-publisher pubid
Specify a text string of up to 128 characters describing the
publisher of the CD to be written to the volume header. Over-
rides a PUBL= parameter set in .genisoimagerc.
-[no -]pad
Pad [do not pad] the ISO9660 filesystem by 150 sectors (300 KB).
If used with -B, force the first boot partition to start on a
sector number that is a multiple of 16. The default is -pad.
-path-list file
Specify a file that contains a list of pathspec directories and
filenames to add to the ISO9660 filesystem. Note that at least
one pathspec must be given on the command line. If file is -,
read from standard input.
-print-size
Print estimated filesystem size and exit.
-quiet
Run in quiet mode; do not display progress output.
-r Like -R, but set UID and GID to zero, set all file read bits to
write, and turn off all file write bits. If any execute bit is set for a
file, set all execute bits; if any search bit is set for a directory, set
all search bits; if any special mode bits are set, clear them.
-R Generate SUSP (System Use Sharing Protocol) and Rock Ridge
records using the Rock Ridge protocol.
-relaxed-filenames
Allow ISO9660 filenames to include seven-digit ASCII charac-
ters except lowercase characters. Violates the ISO9660 standard.
-sort file
Sort file locations according to the rules in the specified file,
which contains pairs of filenames and weights, with one space
or tab between them. A higher weight puts the file closer to
the beginning of the media.
-sysid id
Specify the system ID of up to 32 characters. Overrides a
SYSI= parameter set in the file .genisoimagerc.
-T Generate the file TRANS.TBL in each directory for estab-
lishing the correct filenames on non-Rock Ridge-capable systems.
-table-name table
Use table as the translation table name instead of TRANS.TBL.
Implies -T. For a multisession image, the table name must be
the same as the previous session.
-U Allow untranslated filenames. Violates the ISO9660 standard.
Forces the following options: -d, -l, -N, -allow-leading-dots,
-relaxed-filenames, -allow-lowercase, -allow-multidot, -no-
iso-translate. Use with extreme caution.
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genisoimage
-ucs-level num
Set the Unicode conformance level to the specified number,
which can be between 1 and 3 (default is 3).
-use-fileversion
Use file version numbers from the filesystem. The version
number is a string from 1 to 32767. The default is to set a
version of 1.
-v Run in verbose mode. Specify twice to run even more
verbosely.
-V volid
Specify the volume ID (volume name or label) of up to 32
characters to be written to the master block. Overrides a
VOLI= parameter specified in the file .genisoimagerc.
-volset id
Specify the volume set ID of up to 128 characters. Overrides a
VOLS= parameter specified in .genisoimagerc.
-volset-seqno num
Set the volume set sequence number to num. Must be speci-
fied after -volset-size.
-volset-size num
Set the volume set size (the number of CDs in a set) to num.
Must be specified before -volset-seqno.
HFS options
-apple
Create an ISO9660 CD with Apple’s extensions.
-auto file
Set file as the Autostart file to make the HFS CD use the
QuickTime 2.0 Autostart feature. file must be the name of an
application or document at the top level of the CD and must
be less than 12 characters long.
-boot-hfs-file file
Install file as the driver file that may make the CD bootable on
a Macintosh.
-cluster-size size
Specify the size in bytes of a cluster or allocation units of PC
Exchange files. Implies --exchange (see --format onpage 173).
-hfs
Create a hybrid ISO9660/HFS CD. Use with -map, -magic,
and/or the various --HFS options (see manpage).
-hfs-bless folder
“Bless” the specified directory (folder), given as the full path-
name as genisoimage sees it. This is usually the System Folder
and is used in creating HFS bootable CDs. The pathname
must be in quotes if it contains spaces.
-hfs-creator creator
Set the four-character default creator for all files.
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genisoimage
-hfs-type type
Set the four-character default type for all files.
-hfs-unlock
Leave the HFS volume unlocked so other applications can
modify it. The default is to lock the volume.
-hfs-volid id
Specify the volume name for the HFS partition. This name is
assigned to the CD on a Macintosh and replaces the ID set
with the -V option.
-hide-hfs glob
Hide files or directories matching the shell-style pattern glob
from the HFS volume, although they still exist in the ISO9660
and/or Joliet directory. May be specified multiple times.
-hide-hfs-list file
The specified file contains a list of globs to be hidden.
-input-hfs-charset charset
Specify the input character set used for HFS filenames when
used with the -mac-name option. The default is cp10000 (Mac
Roman).
-mac-name
Use the HFS filename as the starting point for the ISO9660,
Joliet, and Rock Ridge filenames.
-magic file
Use the specified magic file to set a file’s creator and type
information based on the file’s magic number, which is usually
the first few bytes of the file. The magic file contains entries
consisting of four tab-separated columns specifying the byte
offset, type, test, and a message.
-map file
Use the specified mapping file to set a file’s creator and type
information based on the filename extension. Only files that
are not known Apple or Unix file types need to be mapped.
The mapping file consists of five-column entries specifying the
extension, file translation, creator, type, and a comment.
Creator and type are both four-letter strings.
-no-desktop
Do not create empty Desktop files. The default is to create
such files.
-output-hfs-charset charset
Specify the output character set used for HFS filenames.
Defaults to the input character set.
-part
Generate an HFS partition table. The default is not to generate
the table.
-probe
Search the contents of files for known Apple or Unix file types.
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gpg
--format
Look for Macintosh files of the specified file format type. The
valid formats are cap (Apple/Unix File System (AUFS) CAP
files), netatalk, double, ethershare, ushare, exchange, sgi,
xinet, macbin, single, dave, sfm, osx-double, and osx-hfs.
getent getent [options]database key
Search the specified database for the specified key. The database may
be any one of passwd, group, hosts, services, protocols, or networks.
Options
-sCONFIG, --service=CONFIG
Specify the service configuration to be used. See nsswitch.
conf(5) for information about name-service switching.
-?, --help
Display a help message.
--usage
Display a very short syntax synopsis.
-V, --version
Print version information and quit.
getkeycodes getkeycodes
Print the kernel’s scancode-to-keycode mapping table.
gpasswd gpasswd [options]group
Administer /etc/group and /etc/gshadow entries. May only be used
by an administrator. When used with a group name only, prompts
for new group password. Defaults such as minimum and maximum
group id values are specified in /etc/login.defs.
Options
-a Add a new group.
-Ausers
Add administrative members.
-d Delete a group.
-Musers
Add group members.
-R Disable access to the group. Also prevent creation of a new
group with the same name.
-r Remove the password entirely.
gpg gpg [options] command [options]
The GNU Privacy Guard application allows you to encrypt and
decrypt information, create public and private encryption keys,
and use or verify digital signatures. GPG is based on the use of a
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gpg
pair of keys, one public and one private (or “secret”). Data
encrypted with one key can only be decrypted with the other. To
encrypt a message to you, someone would use your public key to
create a message that could only be unlocked with your private
key. To sign information, you would lock it with your private key,
allowing anyone to verify that it came from you by unlocking it
with your public key.
GPG has dozens of additional options that fine-tune its available
options. For a complete list, plus a guide to careful use of encryp-
tion and a deeper explanation of how public-key encryption works,
visit www.gnupg.org.
Key commands
--check-sigs[keyname]
Lists keys and signatures like --list-sigs, but also verifies the
signatures.
--delete-key keyname
Delete the specified key from the keyring.
--delete-secret-key keyname
Delete the named secret key from the secret and public
keyring.
--delete-secret-and-public-key keyname
Delete the secret (if any) and then the public key for the speci-
fied name.
--desig-revoke keyname
Create a revocation certificate for a key pair and designate
authority to issue it to someone else. This allows the user to
permit someone else to revoke the key, if necessary.
--edit-key [keyname]
Edit key options using a menu-driven tool. Key options are too
numerous to list here, but include everything from trust
settings to images attached to keys for user identification
purposes.
--export [keyname]
Output the specified key or, if no key is named, the entire
keyring. Use the --output flag to send the key information to a
file, and --armor to make the key mailable as ASCII text.
--export-secret-keys [keyname]
Outputs the specified secret key or keys. Operation is the
same as --export, except with secret keys. This is a security
risk and should be used with caution.
--export-secret-subkeys [keyname]
Outputs the specified secret subkeys. Operation is the same as
--export, except with secret keys. This is a security risk and
should be used with caution.
--fingerprint [keyname]
List keys and their fingerprints for keys named, or all keys if
no name is specified. If repeated, shows fingerprints of
secondary keys.
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gpg
--gen-key
Generate a new pair of keys, prompting for several preferences
and a passphrase. For most purposes, the default answers to
the questions about algorithm and key length are fine.
--gen-revoke keyname
Create a revocation certificate for a key pair. A revocation
certificate is designed to assure all parties that the key pair is
no longer valid and should be discarded.
--keyserver keyserver
Specifies the name of the keyserver holding the key.
--list-keys [keyname]
List keys with the specified name, or all keys if no name is
specified.
--list-public-keys [keyname]
List public keys with the specified name, or all public keys if
no name is specified.
--list-secret-keys [keyname]
List secret keys with the specified name, or all secret keys if no
name is specified.
--list-sigs [keyname]
List keys as --list-keys does, but also list the signatures.
--gen-revoke keyname
Delete the secret key (if any) and then the public key for the
specified name.
--import file
Read keys from a file and add them to your keyring. This is
most often used with public keys that are sent by email, but
can also be used to move private keys from one system to
another. Combined with the --merge-only option, adds only
new signatures, subkeys, and user IDs, not keys.
--lsign-key keyname
Sign a public key, but mark it as nonexportable.
--recv-keys keyname
Download and import keys from a keyserver. The key name
here should be the key ID as known to the keyserver, and you
must specify the server with the --keyserver option.
--refresh-keys [keyname]
Check the keyserver for updates to keys already in the keyring.
You can specify which keys to check for updates using the key
IDs known to the server, and you must specify the server with
the --keyserver option.
--search-keys [keyname]
Search the names of keys on the keyserver. Specify the
keyserver with --keyserver.
--send-keys [keyname]
Send one or more keys to a keyserver. Specify the keyserver
with --keyserver.
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gpg
--sign-key keyname
Sign a public key using your private key. Often used to send
the public key to a third party. This is the same as selecting
“sign” from the --edit-key menu.
Signature commands
-b, --detach-sign
Create a signature that is not attached to anything.
--clearsign
Create a signature in cleartext.
-s, --sign
Create a signature. May be combined with --encrypt and/or
--symmetric.
--verify [detached-signature] [signed-file]
Verify the signature attached to a file. If the signature and data
are in the same file, only one file needs to be specified. For
detached signatures, the first file should be the .sig or .asc
signature file, and the second the datafile. If you wish to use
stdin instead of a file for the nonattached data, you must
specify a single dash (-) as the second filename.
--verify-files [files]
Verify one or more files entered on the command line or to
stdin. Signatures must be part of the files submitted, and files
sent to stdin should be one file per line. This is designed to
check many files at once.
Encryption commands
-e, --encrypt
Encrypt data. May be used with --sign to create signed,
encrypted data.
--encrypt-files [files]
Encrypt files one after another, either at the command line or
sent to stdin one per line.
-c, --symmetric
Encrypt using a symmetric cipher. The cipher is encrypted
using the CAST5 algorithm unless you specify otherwise using
the --cipher-algo flag.
--store
Create a PGP message packet (RFC 1991). This does not
encrypt data; it just puts it into the right packet format.
Decryption commands
-d, --decrypt [file]
Decrypt a file. If no file is specified, stdin is decrypted.
Decrypted data is sent to stdout or to the file specified with
the --output flag. If the encrypted data is signed, the signature
is also verified.
--decrypt-files [files]
Decrypt files one after another, either at the command line or
sent to stdin one per line.
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gpgsplit
Other commands
--check-trustdb
Check the list of keys with defined trust levels to see if they
have expired or been revoked.
--export-ownertrust
Create a backup of the trust values for keys.
--h, --help
Display a help message.
--import-ownertrust [file]
Import trust values from a file or stdin. Overwrites existing
values.
--list-packets
Display packet sequence for an encrypted message. Used for
debugging.
--update-trustdb
Update the database of trusted keys. For each key that has no
defined level of trust, --update-trustdb prompts for an esti-
mate of how much the key’s owner can be trusted to certify
other keys. This builds a web of more-trusted and less-trusted
keys by which the overall security of a given key can be
estimated.
--version
Display version information and quit.
--warranty
Display warranty information. There is no warranty.
gpgsplit gpgsplit [options] [files]
Split an OpenPGP-format message into individual packets. If no
file is specified, the message is read from stdin. The split packets
are written as individual files.
Options
-h, -?, --help
Display a short help message.
--no-split
Write to stdout instead of splitting the packets into individual
files.
-pstring, --prefix string
Begin each filename with the specified string.
--secret-to-public
Convert any secret keys in the message to public keys.
--uncompress
Uncompress any compressed packets.
-v, --verbose
Verbose mode. More informative.
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gpgv
gpgv gpgv [options] [detached-signature] [signed-files]
Check the signature of one or more OpenPGP-signed files. This is
similar in operation to gpg --verify but uses a different keyring,
~/.gnupg/trustedkeys.gpg by default. Also, gpgv assumes that the
keyring is trusted, and it cannot edit or update it. By contrast, gpg
--verify can go to a keyserver to verify signatures that are not in the
local keyring, and offers various levels of trust. In both cases, you
can use a detached signature file
Options
-h, -?, --help
Display a short help message.
--ignore-time-conflict
Use this flag to ignore incorrect dates on signatures. An incor-
rect date can be a sign of fraud, but is often just a result of an
incorrectly set clock.
--keyring file
Use the specified file as a keyring, in addition to the default
~/.gnupg/trustedkeys.gpg.
--homedir dir
Use the specified directory as the GPG home directory, instead
of the default (set in the GNUPGHOME variable, or, if that is
unset, ~/.gnupg).
--logger-fd FD
Send log output to the specified file descriptor. By default, log
output goes to stderr. Use of file descriptors is described in the
DETAILS section of the GPG documentation.
-q, --quiet
Minimal output.
--status-fd FD
Send special status messages to the specified file descriptor.
-v, --verbose
Verbose mode. More informative.
gpm gpm [options]
System administration command. Provide a mouse server and cut-
and-paste utility for use on the Linux console. gpm acts like a
daemon, responding to both mouse events and client input. If no
clients are connected to the active console, gpm provides cut-and-
paste services.
Options
-2 Force two buttons. If there is a middle button, it is treated as
the right button.
-3 Force three buttons. With a three-button mouse, the left
button makes a selection, the right button extends the selec-
tion, and the middle button pastes it. Using this option with a
two-button mouse results in being unable to paste.
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gpm
-a accel
Set the acceleration for a single motion longer than the delta
specified with the -d option.
-A [limit]
Start up with pasting disabled for security. If specified, limit
gives the time in seconds during which a selection can be
pasted. If too much time has passed, the paste is not allowed.
-b baud
Specify the baud rate.
-B seq
Set a three-digit button sequence, mapping the left, middle,
and right buttons to buttons 1, 2, and 3. The default is 123.
The sequence 321 is useful if you are left-handed, or 132 for a
two-button mouse.
-d delta
Set the delta value for use with -a. When a mouse motion
event is longer than the specified delta, use accel as a multi-
plier. delta must be 2 or greater.
-D Debugging mode. When set, gpm does not put itself into the
background, and it logs messages to standard error instead of
syslog.
-g num
For a glidepoint device, specify the button to be emulated by a
tap. num must be 1, 2, or 3 and refers to the button number
before any remapping is done by the -B option. Applies to
mman and ps2 protocol decoding.
-h Print a help message and exit.
-i interval
Specify the upper time limit, in milliseconds, between mouse
clicks for the clicks to be considered a double or triple click.
-k Kill a running gpm. For use with a bus mouse to kill gpm
before running X. See also -R.
-l charset
Specify the inword() lookup table, which determines which
characters can appear in a word. charset is a list of characters.
The list can include only printable characters. Specify a range
with -, and use \ to escape the following character or to specify
an octal character.
-m filename
Specify the mouse file to open. The default is /dev/mouse.
-M Enable the use of more than one mouse. Options appearing
before -M apply to the first mouse; those appearing after it
apply to the second mouse. Forces the use of -R.
-o extra-options
Specify a comma-separated list of additional mouse-specific
options. See the gpm info page for a description of the mouse
types and the possible options.
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gpm
-p Keep the pointer visible while text is being selected. The
default is not to show the pointer.
-r num
Specify the responsiveness. A higher number causes the cursor
to move faster.
-R name
Act as a repeater and pass any mouse data received while in
graphical mode to the fifo /dev/gpmdata in the protocol speci-
fied by name (default is msc). In addition to certain protocol
types available with -t, you can specify raw to repeat the data
with no protocol translation.
-s num
Specify the sample rate for the mouse device.
-S [commands]
Enable special-command processing (see the next section).
Custom commands can be specified as a colon-separated list to
associate commands with the left button, middle button, and
right button. If a command is omitted, it defaults to sending a
signal to init.
-t type
Specify the mouse protocol type. Use -t help for a list of types;
those marked with an asterisk (*) can be used with -R.
-v Print version information and exit.
-V [increment]
Make gpm more or less verbose by the specified increment.
The default verbosity level is 5, and the default increment is 1.
A larger value of increment causes more messages to be logged.
The increment can be negative, but must be specified with no
space (e.g., -V-3).
Special commands
Special commands, activated with the -S option, are associated
with each mouse button. You can also use -S to customize the
commands. To execute a special command, triple-click the left and
right buttons (hold down one of the buttons and triple-click the
other). A message appears on the console, and the speaker beeps
twice. At this point, release the buttons and press the desired
button within three seconds to activate the associated special
command. The default special commands are:
Left button
Reboot by signaling init.
Middle button
Shut down the system with /sbin/shutdown -h now.
Right button
Reboot with /sbin/shutdown -r now.
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gprof
gprof gprof [options] [object_file]
Display the profile data for an object file. The file’s symbol table is
compared with the call graph profile file gmon.out (previously
created by compiling with gcc -pg). Many of gprof’s options take a
symbol-specification argument, or symspec, to limit the option to
specified files or functions. The symspec may be a filename, a func-
tion, or a line number. It can also be given as filename:function or
filename:linenumber to specify a function or line number in a
specific file. gprof expects filenames to contain a period and func-
tions to not contain a period.
Options
-a, --no-static
Do not display statically declared functions. Since their infor-
mation might still be relevant, append it to the information
about the functions loaded immediately before.
-b, --brief
Do not display information about each field in the profile.
-c, --static-call-graph
Consult the object file’s text area to attempt to determine the
program’s static call graph. Display static-only parents and
children with call counts of 0.
--demangle[=style], --no-demangle
Specify whether C++ symbols should be demangled or not.
They are demangled by default. If profiling a program built by a
different compiler, you may need to specify the mangling style.
--function-ordering
Print suggested function order based on profiling data.
--file-ordering file
Print suggested link line order for .o files based on profiling
data. Read function name to object file mappings from file.
This file can be created using the nm command.
-i, --file-info
Print summary information on datafiles, then exit.
-k from to
Remove arcs between the routines from and to.
-m n, --min-count[=n]
Don’t print count statistics for symbols executed less than n
times.
-n[symspec], --time[=symspec]
Propagate time statistics in call graph analysis.
-p[symspec], --flat-profile[=symspec]
Print profile statistics.
-q[symspec], --graph[=symspec]
Print call graph analysis.
-s, --sum
Summarize profile information in the file gmon.sum.
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grep
-v, --version
Print version and exit.
-w n, --width=n
Print function index formatted to width n.
-x, --all-lines
When printing annotated source, annotate every line in a basic
block, not just the beginning.
-y, --separate-files
Print annotated-source output to separate files instead of stan-
dard output. The annotated source for each source file is
printed to filename-ann.
-z, --display-unused-functions
Include zero-usage calls.
-A[symspec], --annotated-source[=symspec]
Print annotated source code.
-C[symspec], --exec-counts[=symspec]
Print statistics on the number of times each function is called.
When used with option -l, count basic-block execution.
-F routine
Print only information about routine. Do not include time
spent in other routines.
-I dirs, --directory-path=dirs
Set directory path to search for source files. The dirs argument
may be given as a colon-separated list of directories.
-J[symspec], --no-annotated-source[=symspec]
Don’t print annotated source code.
-L, --print-path
Print the path information when printing filenames.
-N[symspec], --no-time[=symspec]
Don’t propagate time statistics in call graph analysis.
-P[symspec], --no-flat-profile[=symspec]
Don’t print profile statistics.
-Q[symspec], --no-graph[=symspec]
Don’t print call graph analysis.
-T, --traditional
Print output in BSD style.
-Z[symspec], --no-exec-counts[=symspec]
Don’t print statistics on the number of times each function is
called.
grep grep [options]pattern [files]
Search one or more files for lines that match a regular expression
pattern. Regular expressions are described in Chapter 7. Exit status
is 0 if any lines match, 1 if none match, and 2 for errors. See also
egrep and fgrep.
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grep
Options
-a, --text
Don’t suppress output lines with binary data; treat as text.
-A num, --after-context=num
Print num lines of text that occur after the matching line.
-b, --byte-offset
Print the byte offset within the input file before each line of
output.
-B num, --before-context=num
Print num lines of text that occur before the matching line.
-c, --count
Print only a count of matched lines. With -v or --revert-match,
count nonmatching lines.
-C[num], --context[=num], -num
Print num lines of leading and trailing context. Default context
is 2 lines.
-d action, --directories=action
Define an action for processing directories. Possible actions
are:
read
Read directories like ordinary files (default).
skip
Skip directories.
recurse
Recursively read all files under each directory. Same as -r.
-Daction, --directories=action
Define an action for processing an input file that is a device,
FIFO, or socket. Possible actions are read (default) and skip,
as in -d.
-e pattern, --regexp=pattern
Search for pattern. Same as specifying a pattern as an argu-
ment, but useful in protecting patterns beginning with -.
-E, -extended-regexp
Act like egrep, recognizing extended regular expressions such
as (UN|POS)IX to find UNIX and POSIX.
-f file, --file=file
Take a list of patterns from file, one per line.
-F, --fixed-strings
Act like fgrep, recognizing only fixed strings instead of regular
expressions. Useful when searching for characters that grep
normally recognizes as metacharacters.
-G, --basic-regexp
Expect the regular expressions traditionally recognized by
grep (the default).
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grep
-h, --no-filename
Print matched lines but not filenames (inverse of -l) when
multiple files are searched.
-H, --with-filename
Display, before each line found, the name of the file
containing the line. This is done by default if multiple files are
submitted to a single grep command.
-i, --ignore-case
Ignore uppercase and lowercase distinctions.
-l, --files-with-matches
Print the names of files with matches but not individual
matched lines. Scanning per file stops on the first match.
-L, --files-without-match
Print only the names of files with no matches. Scanning per
file stops on the first match.
-mnum, --max-count=num
Stop looking after num matches are found.
--mmap
Try to use memory mapping (mmap) to read input in order to
save time.
-n, --line-number
Print lines and their line numbers.
-q, --quiet, --silent
Suppress normal output in favor of quiet mode; scanning
stops on the first match.
-r, --recursive
Recursively read all files under each directory. Same as -d
recurse.
-s, --no-messages
Suppress error messages about nonexistent or unreadable files.
-v, --invert-match
Print all lines that don’t match pattern.
-V, --version
Print the version number and then exit.
-w, --word-regexp
Match on whole words only. Words are divided by characters
that are not letters, digits, or underscores.
-x, --line-regexp
Print lines only if pattern matches the entire line.
-Z, --null
When displaying filenames, follow each with a zero byte
instead of a colon.
Examples
List the number of users who use tcsh:
grep -c /bin/tcsh /etc/passwd
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groff
List header files that have at least one #include directive:
grep -l '^#include' /usr/include/*
List files that don’t contain pattern:
grep –cpatternfiles | grep :0
groff groff [options] [files]
troff [options] [files]
Frontend to the groff document-formatting system, which
normally runs troff along with a postprocessor appropriate for the
selected output device. Options without arguments can be grouped
after a single dash (-). A filename of - denotes standard input.
Options
-a Generate an ASCII approximation of the typeset output.
-b Print a backtrace.
-C Enable compatibility mode.
-dcs, -dname=s
Define the character c or string name to be the string s.
-e Preprocess with eqn, the equation formatter.
-E Don’t print any error messages.
-ffam
Use fam as the default font family.
-Fdir
Search dir for subdirectories with DESC and font files before
searching the default directory /usr/lib/groff/font.
-h, --help
Print a help message.
-i Read standard input after all files have been processed.
-l Send the output to a print spooler (as specified by the print
command in the device description file).
-Larg
Pass arg to the spooler. Each argument should be passed with
a separate -L option.
-mname
Read the macro file tmac.name.
-Mdir
Search directory dir for macro files before searching the default
directory /usr/lib/groff/tmac.
-nnum
Set the first page number to num.
-N Don’t allow newlines with eqn delimiters; equivalent to eqn’s
-N option.
-olist
Output only pages specified in list, a comma-separated list of
page ranges.
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groff
-p Preprocess with pic.
-Parg
Pass arg to the postprocessor. Each argument should be
passed with a separate -P option.
-rcn, -name=n
Set the number register c or name to n. c is a single character,
and n is any troff numeric expression.
-R Preprocess with refer.
-s Preprocess with soelim.
-S Use safer mode (that is, pass the -S option to pic and use the
-msafer macros with troff).
-t Preprocess with tbl.
-Tdev
Prepare output for device dev; the default is ps.
-v, --version
Make groff and programs run by it print out their version
numbers.
-V Print the pipeline on stdout instead of executing it.
-wname
Enable warning name. You can specify multiple -w options.
See the troff manpage for a list of warnings.
-Wname
Disable warning name. You can specify multiple -W options.
See the troff manpage for a list of warnings.
-z Suppress troff output (except error messages).
-Z Do not postprocess troff output. Normally groff automati-
cally runs the appropriate postprocessor.
Devices
ascii
Typewriter-like device.
dvi
T E X DVI format.
html
HTML output.
latin1
Typewriter-like devices using the ISO Latin-1 character set.
lj4
HP LaserJet4-compatible (or other PCL5-compatible) printer.
ps PostScript.
utf8
Unicode (ISO 10646) character set with UTF-8 encoding.
X75
75-dpi X11 previewer.
X100
100-dpi X11 previewer.
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groupadd
Environment variables
GROFF_COMMAND_PREFIX
If set to X, groff runs Xtroff instead of troff.
GROFF_FONT_PATH
Colon-separated list of directories to search for the devname
directory.
GROFF_TMAC_PATH
Colon-separated list of directories to search for the macro
files.
GROFF_TMPDIR
If set, temporary files are created in this directory; otherwise,
they are created in TMPDIR (if set) or /tmp (if TMPDIR is not
set).
GROFF_TYPESETTER
Default device.
PATH
Search path for commands that groff executes.
groupadd groupadd [options]group
System administration command. Create a new user group.
Options
-f, --force
This option is useful for scripts. When specified the command
will exit without error if the group being added already exists.
If a gid requested with -g already exists and the -o option has
not been specified, assign a different gid as if -g had not been
specified. This option is not available on all distributions.
-g gid, --gidgid
Assign numerical group ID. (By default, the first available
number above 500 is used.) The value must be unique, unless
the -o option is used.
-Kkey=value, --key key=value
Override defaults in /etc/login.defs.
-o Accept a nonunique gid with the -g option.
-pstring, --passwordstring
Set the password for the group. string must already be
encrypted appropriately for the system.
-r, --system
Add a system account. Assign the first available number lower
than 499.
--usage
Display a very short list of acceptable options for the
command.
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groupdel
groupdel groupdelgroup
System administration command. Remove group from system
account files. You may still need to find and change permissions on
files that belong to the removed group.
groupmod groupmod [options]group
System administration command. Modify group information for
group.
Options
-g gid, --gidgid
Assign numerical group ID. (By default, the first available
unreserved number is used. Many distributions reserve the
first 500 IDs for system groups, some the first 1000.) The value
must be unique, unless the -o option is used.
-n name
Change the group name to name.
-o Override. Accept a nonunique gid.
-pstring, --passwordstring
Set the initial password for the group. string must already be
encrypted appropriately for the system.
groups groups [options] [users]
Show the groups that each user belongs to (default user is the
owner of the current group). Groups are listed in /etc/passwd and
/etc/group.
Options
--help
Print help message.
--version
Print version information.
grpck grpck [option] [files]
System administration command. Remove corrupt or duplicate
entries in the /etc/group and /etc/gshadow files. Generate warnings
for other errors found. grpck will prompt for a “yes” or “no” before
deleting entries. If the user replies “no,” the program will exit. If
run in a read-only mode, the reply to all prompts is “no.” Alternate
group and gshadow files can be checked. If other errors are found,
the user will be encouraged to run the groupmod command.
Option
-r Read-only mode.
-s Sort entries by GID.
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gs
Exit codes
0 Success.
1 Syntax error.
2 One or more bad group entries found.
3 Could not open group files.
4 Could not lock group files.
5 Could not write group files.
grpconv grpconv
grpunconv
System administration command. Like pwconv, the grpconv
command creates a shadowed group file to keep your encrypted
group passwords safe from password-cracking programs. grpconv
creates the /etc/gshadow file based on your existing /etc/groups file
and replaces your encrypted password entries with x. If you add
new entries to the /etc/groups file, you can run grpconv again to
transfer the new information to /etc/gshadow. It will ignore entries
that already have a password of x and convert those that do not.
grpunconv restores the encrypted passwords to your /etc/groups file
and removes the /etc/gshadow file.
gs gs [options] [files]
GhostScript, an interpreter for Adobe Systems’ PostScript and PDF
(Portable Document Format) languages. Used for document
processing. With - in place of files, standard input is used.
Options
-- filename arg1 ...
Take the next argument as a filename, but use all remaining
arguments to define ARGUMENTS in userdict (not system-
dict) as an array of those strings before running the file.
-Dname=token, -dname=token
Define a name in systemdict with the given definition. The
token must be exactly one token (as defined by the token
operator) and must not contain any whitespace.
-Dname, -dname
Define a name in systemdict with a null value.
-gnumber1xnumber2
Specify width and height of device; intended for systems like
the X Window System.
-Idirectories
Add a list of directories at the head of the search path for
library files.
-q Quiet startup.
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gunzip
-rnumber, -rnumber1xnumber2
Specify X and Y resolutions (for the benefit of devices, such as
printers, that support multiple X and Y resolutions). If only
one number is given, it is used for both X and Y resolutions.
-Sname=string, -sname=string
Define a name in systemdict with a given string as value.
Special names
-dDISKFONTS
Cause individual character outlines to be loaded from the disk
the first time they are encountered.
-dNOBIND
Disable the bind operator. Useful only for debugging.
-dNOCACHE
Disable character caching. Useful only for debugging.
-dNODISPLAY
Suppress the normal initialization of the output device. May
be useful when debugging.
-dNOPAUSE
Disable the prompt and pause at the end of each page.
-dNOPLATFONTS
Disable the use of fonts supplied by the underlying platform
(e.g., the X Window System).
-dSAFER
Disable the deletefile and renamefile operators, and the ability
to open files in any mode other than read-only.
-dWRITESYSTEMDICT
Leave systemdict writable.
-sDEVICE=device
Select an alternate initial output device.
-sOUTPUTFILE=filename
Select an alternate output file (or pipe) for the initial output
device.
gunzip gunzip [options] [files]
Uncompress files compressed by gzip. See gzip for a list of options.
gzexe gzexe [option] [files]
Compress executables. When run, these files automatically uncom-
press, thus trading time for space. gzexe creates backup files with a
tilde at the end (filename~). These backup files can be deleted once
you are sure the compression has worked properly.
Option
-d Decompress files.
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gzip
gzip gzip [options] [files]
gunzip [options] [files]
zcat [options] [files]
Compress specified files (or data read from standard input) with
Lempel-Ziv coding (LZ77). Rename compressed file to filename.gz;
keep ownership modes and access/modification times. Ignore
symbolic links. Uncompress with gunzip, which takes all of gzip’s
options except those specified. zcat is identical to gunzip -c and
takes the options -fhLV, described here. Files compressed with the
compress command can be decompressed using these commands.
Options
-n, --fast, --best
Regulate the speed of compression using the specified digit n,
where -1 or --fast indicates the fastest compression method
(less compression), and -9 or --best indicates the slowest
compression method (most compression). The default
compression level is -6.
-c, --stdout, --to-stdout
Print output to standard output, and do not change input files.
-d, --decompress, --uncompress
Same as gunzip.
-f, --force
Force compression. gzip normally prompts for permission to
continue when the file has multiple links, its .gz version
already exists, or it is reading compressed data to or from a
terminal.
-h, --help
Display a help screen and then exit.
-l, --list
Expects to be given compressed files as arguments. Files may
be compressed by any of the following methods: gzip, deflate,
compress, lzh, or pack. For each file, list uncompressed and
compressed sizes (the former is always -1 for files compressed
by programs other than gzip), compression ratio, and uncom-
pressed name. With -v, also print compression method, the
32-bit CRC of the uncompressed data, and the timestamp.
With -N, look inside the file for the uncompressed name and
timestamp.
-L, --license
Display the gzip license and quit.
-n, --no-name
When compressing, do not save the original filename and
timestamp by default. When decompressing, do not restore
the original filename if present, and do not restore the original
timestamp if present. This option is the default when
decompressing.
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halt
-N, --name
Default. Save original name and timestamp. When decom-
pressing, restore original name and timestamp.
-q, --quiet
Print no warnings.
-r, --recursive
When given a directory as an argument, recursively compress
or decompress files within it.
-S suffix, --suffix suffix
Append .suffix. Default is gz. A null suffix while decom-
pressing causes gunzip to attempt to decompress all specified
files, regardless of suffix.
-t, --test
Test compressed file integrity.
-v, --verbose
Print name and percent size reduction for each file.
-V, --version
Display the version number and compilation options.
halt halt [options]
System administration command: turns off the computer. Inserts a
note in the file /var/log/wtmp; if the system is in runlevel 0 or 6,
stops all processes; otherwise, calls shutdown -h.
Options
-d Suppress writing to /var/log/wtmp.
-f Call halt even when shutdown -nf would normally be called
(i.e., force a call to halt, even when not in runlevel 0 or 6).
-h Place hard drives in standby mode before halt or power off.
-i Shut down network interfaces before halt.
-n No sync before reboot or halt.
-p Perform power-off when halting system.
hdparm hdparm [options] [device]
System administration command. Read or set the hard drive para-
meters. This command can be used to tune hard drive
performance. It is primarily used with IDE drives, but some can be
used with SCSI drives as well.
Options
The hdparm command accepts many option flags, including some
that can result in filesystem corruption if misused. Flags can be
used to set or get a parameter. To get a parameter, just pass the flag
without a value. To set a parameter, follow the flag with a space
and the appropriate value.
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hdparm
-a [n]
Get or set the number of sectors to read ahead in the disk. The
default is 8 sectors (4 KB); a larger value is more efficient for
large, sequential reads, and a smaller value is better for small,
random reads. Many IDE drives include this functionality in
the drive itself, so this feature is not always necessary.
-A Enable or disable the IDE read-ahead feature. Usually on by
default.
-b [n]
Get or set the bus state for the drive.
-B Set the Advanced Power Management (APM) data if the drive
supports it.
-c [n]
Get or set 32-bit I/O values for IDE drives. Acceptable values
are 0 (32-bit support off), 1 (32-bit support on), and 3 (on,
but only with a sync sequence).
-C Check the power status of the drive. This will tell you
unknown, active/idle, standby, or sleeping. Use -S, -y, -Y, and
-Z to set the power status.
-d [n]
Get or set the using_dma flag for the drive, which may be 0
(not using DMA) or 1 (using DMA).
-D Enable or disable defect-handling features that are controlled
by the hard drive itself.
-E n
Set CD-ROM read speed to n times normal audio playback
speed. Not normally necessary.
-f Flush and sync the buffer cache on exit.
-F Flush write cache buffer on-drive.
-g Query and display drive size and geometry information, such
as number of cylinders, heads, and sectors.
-h Display a short help message.
-i Display the drive identification information obtained at boot
time. If the drive has changed since boot, this information may
not be current.
-I Display more detailed identification information for the drive.
--Istdin
Read identify data from standard input.
--Istdout
Write identify data to standard output.
-k [n]
Get or set the keep_settings_over_reset variable. Valid
settings are 0 and 1, and a value of 1 will keep the -dmu
options when rebooting (soft reset only).
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hdparm
-K [n]
Get or set the keep_features_over_reset variable. Valid
settings are 0 and 1, and a value of 1 will keep settings for the
flags -APSWXZ over a soft reset.
-L n
Set the door lock flag for the drive. Used for Syquest, ZIP, and
JAZ drives.
-m [n]
Get or set the number of sectors used for multiple sector count
reading. A value of 0 disables the feature, and values of 2, 4, 8,
16, and 32 are common. Drives that try to support this feature
and fail may suffer corruption and data loss.
-M [n]
Get or set the level for Automatic Acousting Management
(AAM) features. Newer drives support this feature, which can
slow down head movements to reduce hard disk noise. Values
range from 128 (quiet, but slow) to 254 (fast, but loud). Some
drives support only 128 and 254, while others support
multiple levels between the extremes. At the time of writing,
this feature was still considered experimental and not recom-
mended for production use.
-n [n]
Set to 0 or 1 to disable or enable, respectively, the “ignore
write errors” flag. This can cause massive data loss if used
incorrectly, and is for development purposes only.
-N [n]
Get or set visible number of sectors. Without a parameter this
will display the current maximum sectors and the hardware
limit for the disk. The invisible sectors form the Host
Protected Area (HPA) commonly used to hold diagnostic soft-
ware or the original copy of the operating system. Changing
this value will usually result in data loss.
-p n
Tune the IDE interface to use PIO mode n, usually an integer
between 0 and 5. Incorrect values can result in massive data
loss. Support for the PIO mode-setting feature varies between
IDE chips, so tuning it is not for the faint of heart.
-P n
Set the internal prefetch sector count. Not all drives support
the feature.
-q Suppress output for the flag after this one, unless it is the -i, -v,
-t, or -T flag.
-Q [n]
Set the depth of tagged queues. 0 disables tagged queues. This
is supported only on specific drives, and only for kernels 2.5.x
and later.
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hdparm
-r [n]
Get or set the flag for read-only on the device. A value of 1
marks the device as read-only.
-R This option should be used by experts only. It registers an IDE
interface. See the -U option for further details.
-S n
Set the amount of time a disk is inactive before it spins down
and goes into standby mode. Settings from 1 to 240 represent
chunks of five seconds (for timeout values between 5 seconds
and 20 minutes); values from 241 to 251 are increments of 30
minutes (for 30 minutes to 5.5 hours). A value of 252 sets the
timeout to 21 minutes, 253 to the vendor default, and 255 to
20 minutes and 15 seconds.
-t Time device reads to determine performance.
-T Time cache reads to determine performance.
-u [n]
Get or set the interrupt-unmask value for the drive. A value of
1 lets the drive unmask other interrupts and can improve
performance; when used with older kernels and hardware, it
can cause data loss.
-U Unregister an IDE interface. Use this feature and the -R feature
only with hot-swappable hardware, such as very high-end
servers and some laptops. It can damage or hang other
systems, and should be used with caution.
-v Display all appropriate settings for device except -i. This is the
same as the default behavior with no flags.
-w Reset the device. Use as a last resort only; may cause data loss.
-W Enable or disable the write-cache feature for the drive. The
default varies among drive manufacturers.
-x Sets tristate. Use only for hot-swappable devices. See the -R
and -U entries.
-X n
Set the IDE transfer mode. Possible values include 34 (multi-
word DMA mode2 transfers) and 66 (UltraDMA mode2
transfers), or any PIO mode number plus 8. This option is
suggested for experts only, and is useful only with newer
EIDE/IDE/ATA2 drives. Often used in combination with -d.
-y Put the IDE drive into standby (spin-down) mode, saving
power.
-Y Put the IDE drive into sleep mode.
-z Force the kernel to reread the partition table.
-Z Disable automatic powersaving on some drives, which can
prevent them from idling or spinning down at inconvenient
moments. This will increase the electrical power consumption
of your system.
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head
head head [options] [files]
Print the first few lines (default is 10) of one or more files to stan-
dard output. If files is missing or -, read from standard input. With
more than one file, print a header for each file showing the
filename.
Options
-c num[b|k|m], --bytes num[b|k|m]
Print first num bytes or, if num is followed by b, k, or m, first
num 512-byte blocks, 1-kilobyte blocks, or 1-megabyte blocks.
--help
Display help and then exit.
-n num, --lines num, -num
Print first num lines. Default is 10.
-q, --quiet, --silent
Quiet mode; never print headers giving filenames.
-v, --verbose
Print filename headers, even for only one file.
--version
Output version information and then exit.
Examples
Display the first 20 lines of phone_list:
head -20 phone_list
Display the first 10 phone numbers having a 202 area code:
grep '(202)' phone_list | head
hexdump hexdump [options]file
Display specified file or input in hexadecimal, octal, decimal, or
ASCII format. Option flags are used to specify the display format.
Options
-b Use a one-byte octal display; show the input offset in hexadec-
imal, followed by 16 three-column octal data bytes, filled with
zeroes and separated by spaces.
-c Use a one-byte character display; show the input offset in
hexadecimal, followed by 16 three-column entries, filled with
zeroes and separated by spaces.
-C Canonical mode. Display hexadecimal offset, two sets of eight
columns of hexadecimal bytes, then a | followed by the ASCII
representation of those same bytes.
-d Use a two-byte decimal display. The input offset is again in
hexadecimal, but the display has only eight entries per line, of
five columns each, containing two bytes of unsigned decimal
format.
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host
-e format_string
Choose a format string to be used to transform the output
data. Format strings consist of:
Iteration count
The iteration count is optional. It determines the number
of times to use the transformation string. The number is
followed by a slash (/) to distinguish it from the byte
count.
Byte count
The number of bytes to be interpreted by the conversion
string, preceded by a slash character to distinguish it from
the iteration count. The byte count is optional.
Format characters
The actual format characters are required. They are
surrounded by quotation marks and are interpreted as
fprintf (see printf) formatting strings, although the *, h, l,
n, p, and q options will not work as expected. Format
string usage is discussed at greater length in the hexdump
manpage.
-f filename
Choose a file that contains several format strings, separated by
newlines; the # character marks a line as a comment.
-n length
Limit the number of bytes of input to be interpreted.
-o Two-byte octal display; show a hexadecimal offset followed by
eight five-column data entries of two bytes each, in octal format.
-s offset
Skip to specified offset. The offset number is assumed to be
decimal unless it starts with 0x or 0X (hexadecimal), or 0
(octal). Numbers may also be designated in megabytes, kilo-
bytes, or half-kilobytes with the addition of m, k, or b at the
end of the number.
-v Display all input data, even if it is the same as the previous
line. Normally, a duplicate line is replaced by an asterisk (*).
-x Display data in a two-byte hexadecimal format. The offset is in
hexadecimal, and is followed by eight space-separated entries,
each of which contains four-column, two-byte chunks of data
in hexadecimal format.
host host [options]name [server]
System administration command. Print information about hosts or
zones in DNS. Hosts may be IP addresses or hostnames; host
converts IP addresses to hostnames by default and appends the
local domain to hosts without a trailing dot. Default servers are
determined in /etc/resolv.conf. For more information about hosts
and zones, read Chapters 1 and 2 of Paul Albitz’s and Cricket Liu’s
DNS and BIND (O’Reilly).
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hostid
Options
-a Same as -t ANY.
-c class
Search for specified resource record class (IN, CH, CHAOS,
HS, HESIOD, or ANY). Default is IN.
-d Verbose output. Same as -v.
-l List mode. This also performs a zone transfer for the named
zone. Same as -t AXFR.
-n Perform reverse lookups for IPv6 addresses using IP6.INT
domain and “nibble” labels instead of IP6.ARPA and binary
labels.
-r Do not ask contacted server to query other servers, but require
only the information that it has cached.
-s Stop querying nameservers upon receiving a SERVFAIL response.
-t type
Look for type entries in the resource record. type may be any
recognized query type, such as A, AXFR, CNAME, NS, SOA,
SIG, or ANY. If name is a hostname, host will look for A
records by default. If name is an IPv4 or IPv6 address, it will
look for PTR records.
-v Verbose. Include all fields from resource record, even time-to-
live and class, as well as “additional information” and
“authoritative nameservers” (provided by the remote
nameserver).
-w Never give up on queried server.
-C Display SOA records from all authoritative nameservers for
the specified zone.
-N n
Consider names with fewer than n dots in them to be relative.
Search for them in the domains listed in the search and
domain directives of /etc/resolv.conf. The default is usually 1.
-R n
Retry query a maximum of n times. The default is 1.
-T Use TCP instead of UDP to query nameserver. This is implied
in queries that require TCP, such as AXFR requests.
-W n
Wait a maximum of n seconds for reply.
hostid hostid
Print the ID number in hexadecimal of the current host.
hostname hostname [option] [nameofhost]
Set or display name of current host system. A privileged user can
set the hostname with the nameofhost argument.
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hunspell
Options
-a, --alias
Display the alias name of the host (if used).
-d, --domain
Display DNS domain name.
-f, --fqdn, --long
Display fully qualified domain name.
-F file, --file file
Consult file for hostname.
-h, --help
Display a help message and then exit.
-i, --ip-address
Display the IP address(es) of the host.
-s, --short
Trim domain information from the display output.
-v, --verbose
Verbose mode.
-V, --version
Display version information and then exit.
-y, --yp, --nis
Display the NIS domain name. A privileged user can set a new
NIS domain name with nameofhost.
htdigest htdigest [-c]filename realm username
Create or update user authentication files used by the Apache web
server. The -c option is used if you wish to create the file, and will
overwrite any existing files rather than update them. The three
arguments are the file you wish to use as the authentication file, the
realm name to which the user belongs, and the username you will
update in the password file. You will be prompted for a password
when you run the command.
The Apache manual contains information about authentication
mechanisms, including more detail about using htdigest and the
ways in which you can control access to the resources served by
Apache.
hunspell hunspell [options] [files]
A spell checker modeled after ispell. With no files specified,
hunspell reads from standard input. See ispell for details of the
available options and commands. Commands are single-character
and case-insensitive; use them to tell hunspell what to do with a
misspelled word.
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hwclock
hwclock hwclock [option]
System administration command. Read or set the hardware clock.
This command maintains change information in /etc/adjtime,
which can be used to adjust the clock based on how much it drifts
over time. hwclock replaces the clock command. The single-letter
options are included for compatibility with the older command.
Options
You may specify only one of the following options:
-a, --adjust
Adjust the hardware clock based on information in /etc/
adjtime and set the system clock to the new time.
--getepoch
Print the kernel’s hardware clock epoch value, then exit.
-r, --show
Print the current time stored in the hardware clock.
-s, --hctosys
Set the system time in accordance with the hardware clock.
--setepoch, --epoch=year
Set the hardware clock’s epoch to year.
--set --date=date
Set the hardware clock to the specified date, a string appro-
priate for use with the date command.
-v, --version
Print version and exit.
-w, --systohc
Set the hardware clock in accordance with the system time.
The following may be used with the above options:
--debug
Print information about what hwclock is doing.
--localtime
The hardware clock is stored in local time.
--noadjfile
Disable /etc/adjtime facilities.
--test
Do not actually change anything. This is good for checking
syntax.
-u, --utc
The hardware clock is stored in Universal Coordinated Time.
icedax icedax [options] [output.wav]
Retrieve audio tracks in CDDA (Compact Disc Digital Audio)
format and convert to WAV format. icedax stands for InCrEdible
Digital Audio eXtractor. The manpage has full details as well as
hints on the options and on usage.
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icedax
Options
Some of the following options use sectors as a unit of measure-
ment. Each sector of data on a CD represents approximately 1/75
second of play time.
-an, --divider n
Set the sample rate to a value equal to 44100/n samples per
second. The -R option, used by itself, lists the possible values.
-Adrivename, --auxdevice drivename
Specify a different drive for ioctl purposes.
-bn, --bits-per-sample n
Set the quality of samples to n bits per sample per channel.
Possible values are 8, 12, and 16.
-B, --bulk, --alltracks
Copy each track into its own file. This is the most commonly
used flag.
-c channel, --channels channel
Set stereo instructions. Set channel to 1 for mono; 2 for
stereo; or s for stereo, but swapped left-to-right. You can
also use -s (--stereo) to record in stereo and -m (--mono) to
record in mono.
-C byteorder, --cdrom-endianness byteorder
Set the byte order, or “endianness” of the input data. You may
set the order to little, big, or guess. This is useful when your
CD-ROM drive uses an unexpected or unusual byte order for
your platform.
--cddbp-server=servername
Set the name of the CD lookup server used. The default server
is freedb.freedb.org.
--cddbp-port=portnumber
Select the port on which to access the CD lookup server. The
servers at freedb.org use cddbp on port 8880, and http on port 80.
-dduration, --duration
Set the number of seconds duration, or follow with f to set the
duration in frames (sectors). Set duration to zero to record an
entire track.
-Ddevicename, --device devicename
Specify the device. The device must work with the -I (--interface)
settings.
-e, --echo
Copy output to an audio output device. Use -K (--sound-
device) to set the device (usually /dev/dsp).
-E byteorder, --output-endianness byteorder
Set the byte order or “endianness” of the output data. As with
-C, you may set the order to little, big, or guess.
-g, --gui
Format all text output for easy parsing by GUI frontends.
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icedax
-h, --help
Print usage information and exit.
-H, --no-infofile
Do not copy any info or CDDB files, only the audio files.
-in, --index n
Set the start index to n when recording.
-Iifname, --interface ifname
Specify the type of interface, generic_scsi or cooked_ioctl. It’s
usually safest to use generic_scsi.
-J, --info-only
Use this option by itself to display information about the disc,
but do nothing else.
-Kdevice, --sound-devicedevice
Set the sound device to use with -e.
-ln, --buffers-in-ringn
Use a ring of n buffers.
-L n, --cddb n
icedax looks up CD information online, if possible. This
option determines what happens when there are multiple
entries identifying the CD. If the mode is 0, the user is
prompted to select an entry.If the mode is 1, the application
uses the first entry returned.
-M n, --md5 n
Create MD5 checksums for the first n bytes of each track
copied.
-nn, --sectors-per-request n
Read n sectors in each request.
-N, --no-write
For debugging purposes, this option suppresses writing an
output file.
-on, --offset n
Start recording n sectors before the beginning of the first track.
-Oformat, --output-format=format
Choose the output file format. Normal file options are wav,
aiff, aifc, au, and sun. You can also use cdr and raw for header-
less files dumped into recording devices.
-pn, --set-pitch n
Adjust the pitch by n percent when copying data to an audio
device.
-Pn, --set-overlap n
Use n sectors of overlap for jitter correction. Very fast systems
with absolutely perfect drives and unscratched CDs can set
this to 0.
--paranoia
Read and interpret the CD using the paranoia library instead
of the icedax code.
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iconv
-q, --quiet
Quiet mode; the program sends no data to the screen.
-rn, --rate n
Set the sample rate in samples per second. To get a list of
possible values, use the -R option by itself.
-R, --dump-rates
Output a list of possible sample rates and dividers. This
option is typically used with no other option flags or
arguments.
-Sn, --speed n
Specify the speed at which your system will read the CD-
ROM. Set the value to the multiple of normal playback speed
given as your CD-ROM drive speed (4, 16, 32, and so forth).
Setting the speed lower than the maximum can prevent errors
in some cases.
-tm[+n], --track m[+n]
Set start track to n. Optionally, use + and a second track
number for the end track: 1+10 copies tracks one through ten.
-vlist, --verbose-level list
Specify CD information to display in a comma-separated list.
The options are: for no information, use disable; for all infor-
mation, use all. Specify toc for the table of contents, summary
for a summary of recording parameters, indices for index
offsets, catalog for the media catalog number (MCN), trackid
for track IDs, sectors for the table of contents in start sector
notation, and titles for title information, if available.
--version
Display version and quit.
-w, --wait
Wait for a signal before recording anything.
-x, --max
Set recording quality (and amount of hard disk usage) to
maximum.
iconv iconv [options]files
Convert the contents of one or more files from one character
encoding to another and write the results to standard output. Use -l
to print a list of possible encodings.
Options
-c Omit invalid output characters.
-f code1, --from-code=code1
Convert input characters from the code1 encoding.
-?, --help
Print help message and exit.
-l, --list
Print a list of valid encodings to standard output.
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id
-o file, --output=file
Write the converted output to file instead of standard output.
-s, --silent
Operate silently; don’t print warning messages.
-t code2, --to-code=code2
Convert input characters to the code2 encoding.
--usage
Print a brief usage message showing only the command syntax
and then exit.
-V, --version
Print version information and exit.
--verbose
Operate verbosely; print progress messages.
id id [options] [username]
Display information about yourself or another user: user ID, group
ID, effective user ID and group ID if relevant, and additional group IDs.
Options
-g, --group
Print effective group ID only.
-G, --groups
Print supplementary groups only.
-n, --name
With -u, -g, or -G, print user or group name, not number.
-r, --real
With -u, -g, or -G, print real, not effective, user ID or group
ID.
-u, --user
Print user ID only.
-Z, --context
Print security context of the current user.
--help
Print help message and then exit.
--version
Print version information.
ifconfig ifconfig [interface]
ifconfig [interfaceaddress_familyparametersaddresses]
TCP/IP command. Assign an address to a network interface and/or
configure network interface parameters. ifconfig is typically used at
boot time to define the network address of each interface on a
machine. It may be used at a later time to redefine an interface’s
address or other parameters. Without arguments, ifconfig displays
the current configuration for a network interface. With the single
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ifconfig
option -a and no other arguments, it will display all current inter-
faces. Used with a single interface argument, ifconfig displays that
particular interface’s current configuration. Note that interfaces are
usually numbered starting at zero: eth0, eth1, eth2, and so forth.
Wireless network interfaces may begin with ath0 or wlan0. On
some systems the ifconfig command is deprecated in favor of the ip
command.
Arguments
interface
String of the form name unit: for example, en0.
address_family
Since an interface may receive transmissions in differing proto-
cols, each of which may require separate naming schemes, you
can specify the address_family to change the interpretation of
the remaining parameters. You may specify inet (for TCP/IP, the
default), ax25 (AX.25 Packet Radio), ddp (Appletalk Phase 2),
or ipx (Novell).
parameters
The following parameters may be set with ifconfig:
add address/prefixlength
Add an IPv6 address and prefix length.
address address
Assign the specified IP address to the interface.
allmulti/-allmulti
Enable/disable sending of incoming frames to the kernel’s
network layer.
arp/-arp
Enable/disable use of the Address Resolution Protocol in
mapping between network-level addresses and link-level
addresses.
broadcast/-broadcast [address]
(inet only) Set or clear the address to use to represent
broadcasts to the network. Default is the address with a
host part of all ones (i.e., x.y.z.255 for a class C network).
debug/-debug
Enable/disable driver-dependent debugging code.
del address/prefixlength
Delete an IPv6 address and prefix length.
down
Mark an interface “down” (unresponsive).
hw class address
Set the interface’s hardware class and address. class may
be ether (Ethernet), ax25 (AX.25 Packet Radio), or
ARCnet.
io_addr addr
I/O memory start address for device.
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ifconfig
irq addr
Set the device’s interrupt line.
metric n
Set routing metric of the interface to n. Default is 0.
mem_start addr
Shared memory start address for device.
media type
Set media type. Common values are 10base2, 10baseT,
and AUI. If auto is specified, ifconfig will attempt to
autosense the media type.
mtu n
Set the interface’s Maximum Transfer Unit (MTU).
multicast
Set the multicast flag.
netmask mask
(inet only) Specify how much of the address to reserve for
subdividing networks into subnetworks. mask can be
specified as a single hexadecimal number with a leading
0x, with a dot notation Internet address, or with a
pseudo-network name listed in the network table /etc/
networks.
pointopoint/-pointopoint [address]
Enable/disable point-to-point interfacing, so that the
connection between the two machines is dedicated.
promisc/-promisc
Enable/disable promiscuous mode. Promiscuous mode
allows the device to receive all packets on the network.
txqueuelen n
Specify the transmit queue length.
tunnel addr
Create an IPv6-in-IPv4 (SIT) device, tunneling to IPv4
address addr.
up
Mark an interface “up” (ready to send and receive).
addresses
Each address is either a hostname present in the hostname
database (/etc/hosts), or an Internet address expressed in the
Internet standard dot notation.
Examples
To list all interfaces:
ifconfig -a
To add a second IP address to wlan0:
ifconfig wlan0:1 192.168.2.41 netmask 255.255.255.0
To change the hardware address (MAC address) assigned to eth0
(useful when setting up a router for a DSL or cable modem):
ifconfig eth0 hw ether 01:02:03:04:05:06
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info
imapd imapd [options]
TCP/IP command. The Interactive Mail Access Protocol (IMAP)
server daemon. imapd is often invoked by xinetd and listens on
port 143 for requests from IMAP clients. IMAP allows mail
programs to access remote mailboxes as if they were local. IMAP is
a richer protocol than POP because it allows a client to retrieve
message-level information from a server mailbox instead of the
entire mailbox. IMAP can be used for online and offline reading.
The popular Pine mail client contains support for IMAP. There are
several versions of imapd available. Here we document the Cyrus
IMAP server with its most common command options.
Options
-C file
Read configuration options from file instead of /etc/imapd.
conf.
-s Encrypt data using the Secure Socket Layer (SSL).
-T n
Wait n seconds for a new connection before closing the
process. The default is 60.
-U n
Reuse process for new connections no more than n times.
inetd inetd [options] [configuration_file]
TCP/IP command. The Internet services daemon. This is an older
daemon usually replaced with xinetd. See xinetd.
info info [options] [topics]
GNU hypertext reader. Display online documentation previously
built from Texinfo input. Info files are arranged in a hierarchy and
can contain menus for subtopics. When entered without options,
the command displays the top-level info file (usually /usr/local/info/
dir or /usr/local/share/dir). When topics are specified, find a
subtopic by choosing the first topic from the menu in the top-level
info file, the next topic from the new menu specified by the first
topic, and so on. The initial display can also be controlled by the -f
and -n options. If a specified topic has no info file but does have a
manpage, info displays the manpage; if there is neither, the top-
level info file is displayed.
Options
-d directories, --directory directories
Search directories, a colon-separated list, for info files. If this
option is not specified, use the INFOPATH environment
variable or the default directory (usually /usr/local/info or /usr/
share/info).
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init
--dribble file
Store each keystroke in file, which can be used in a future
session with the --restore option to return to this place in info.
-f file, --file file
Display specified info file.
--help
Display brief help message and exit.
--index-searchstring
Display node pointed to by index entry string.
-kstring, --aproposstring
Search all info topics for string and display the results.
-n node, --node node
Display specified node in the info file.
-o file, --output file
Copy output to file instead of displaying it on the screen.
-O, --show-options, --usage
Display the node with the command-line options.
--restore file
When starting, execute keystrokes stored in file.
--subnodes
Display subtopics.
--version
Display version.
--vi-keys
Use vi-like key bindings.
init init
System administration command. The init daemon is the parent of
all processes on Linux. Traditionally Linux has used a System V
Unix style boot process (SysVinit) that calls this daemon at system
startup. The SysVinit daemon starts or stops other programmings
depending on run level. Newer Linux distributions use a more flex-
ible process called Upstart, but for backward compatibility many
still group processes into run levels. For a System V init process use
the telinit program to change run levels. For Upstart use initctl to
communicate with the init daemon. For more information, see the
section “Starting and Stopping the System” on page 19.
initctl initctl [options]command
System administration command. initctl sends commands to the
Upstart init daemon. Use it to monitor jobs or events, call jobs
directly, or send custom events to the daemon.
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insmod
Options
--show-ids
Show unique process id (pid) as well as the job id.
--by-id
Parameter passed to command is a job id.
--no-wait
When using start, stop, or emit, exit immediately instead of
waiting for the request to finish.
--quiet
Only show errors when running the given command.
Commands
These generally apply to upstart jobs. Jobs are usually defined in
files located in the /etc/event.d directory. Most commands will
accept multiple job names given in a space separated list.
emit event [arguments]
Emit a custom event to which init should respond. Event argu-
ments may be passed in a comma separated list. If any job
status changes as a result of the event, print each change.
events
Monitor system events.
list [pattern]
Print a list of all known jobs. If an optional shell style matching
pattern is given, only those jobs matching the pattern will be
shown.
log-priority priority
Change init message logging priority to one of debug, info,
message, warn, error, or fatal.
start job...
Start and print job status changes to screen.
status job...
Print status. The job name, goal (to start or stop) and the
current status of the job are shown, along with any associated
pids.
stop job...
Stop and print job status changes to screen.
jobs
Monitor job changes, printing changes to the screen.
version
Print version of running init daemon.
insmod insmodfilename [module-options]
System administration command. Load the module filename into
the kernel. Simpler but less flexible than the modprobe command.
Error messages from insmod may be vague, because the kernel
performs module operations internally and therefore sends error
information to the kernel log instead of standard output; see dmesg.
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install
install install [options] [source]destination
System administration command. Used primarily in Makefiles to
update files. install copies files into user-specified directories.
Similar to cp, but attempts to set permission modes, owner, and
group. The source may be a file or directory, or a list of files and
directories. The destination should be a single file or directory.
Options
-b, --backup[=control]
Back up any existing files. When using the long version of the
command, the optional control parameter controls the kind of
backup. When no control is specified, install will attempt to
read the control value from the VERSION_CONTROL envi-
ronment variable. Accepted values are:
none, off
Never make backups.
numbered, t
Make numbered backups.
existing, nil
Match existing backups, numbered or simple.
simple, never
Always make simple backups.
-C Do not overwrite file when the target exists and is identical to
the new file. Preserve original timestamp.
-d, --directory
Create any missing directories.
-D Create leading components of destination except the last, then
copy source to destination.
-g group, --group group
Set group ID of new file to group (privileged users only).
--help
Print help information and exit.
-m mode, --mode mode
Set permissions of new file to mode (octal or symbolic). By
default, the mode is 0755.
-o [owner], --owner[=owner]
Set ownership to owner or, if unspecified, to root (privileged
users only).
-p, --preserve-timestamps
Preserve access and modification times on source files and
directories.
-P, --preserve-context
Preserve SELinux security context.
-s, --strip
Strip symbol tables.
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ip
-S suffix, --suffix=suffix
Use suffix instead of the default backup suffix, usually ~.
-t directory, --target-directory directory
Copy SOURCE arguments into the specified directory.
-T, --no-target-directory
Treat destination as a normal file.
-v, --verbose
Print name of each directory as it is created.
--version
Print version, then exit.
ionice ionice [ options ] [ program [ arg ]]
Set the I/O scheduling class and priority for a program. The three
possible scheduling classes are idle, best effort, and real time. The
default is best effort. With no arguments or just -p, query the
current class and priority for the process. Without -p, the program
is run with the specified parameters.
Options
-cn
Set the scheduling class, where n is 1 for real time, 2 for best
effort, and 3 for idle.
-h Print help information and exit.
-n n
Define the scheduling class data for classes that accept it. For
real time and best effort, n can be in the range 0–7.
-p pid
Specify the process id of a running program to be changed.
ip ip [ options ] object command [ arguments ]
ip [ object [ command ]] help
System administration command. Show and manipulate network
devices and routing. This command is a part of the iproute2 utili-
ties for controlling TCP and UDP IP networking and traffic control.
It’s meant to replace the ifconfig, route, and arp commands among
others. On some distributions these utilities may be deprecated in
favor of ip.
ip’s subcommand syntax is very similar to the Cisco’s IOS syntax
used on many Cisco routers and switches. The ip command can be
used to configure tunnels, load balancing and other traffic shaping.
For brevity, we won’t cover all of its features here. For more in-
depth coverage, we recommend iproute2’s Linux Foundation web
pages at: http://www.linuxfoundation.org/en/Net:Iproute2.
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ip
Options
-s, --stats, --statistics
Print statistics or time values. Use multiple times to increase
the verbosity of output even more.
-fprotocol_family, --family protocol_family
Specify the protocol_family to use for the commands given.
This may be inet, inet6, or link. The protocol_family link may
be used to indicate no protocol is involved. The ip command
also accepts shortcut options of -4, -6, and -0 for families inet,
inet6, and link.
-o, --oneline
Format output as one line, replacing linefeeds with the ‘\’
character. This is useful when piping output of ip to another
command.
-r, --resolve
Resolve IP addresses to host names. The default is to use IP
addresses.
Commands
We will only cover commands for address, link, neighbor and route
objects, and the syntax of the help command. These are the
commands that replace ifconfig, arp, and route. (In IPv4 the
neighbor table is known as the arp table.) Most objects and
commands have a long name (or two) as well as one or more abbre-
viations. For example, the object address can be given as address,
addr, or a. The commands show and list are interchangeable and
can be abbreviated as sh, s, li, or l. Here we show the most
commonly used form in examples and documentation:
help
List command syntax, including applicable arguments. The
syntax is given in a form similar to BNF grammar notation.
addr add address[/netmask] arguments
Add a new protocol address to a device. The format of the
address depends on the protocol (inet or inet6). A netmask
may be given in CIDR notation. If no netmask is given, a mask
of /32 is assumed.
addr del address[/netmask] [arguments]
Remove a protocol address.
addr show [arguments]
Print current addresses.
link set device_name [arguments]
Define or change settings on a network device.
link show [device_name]
Print current settings for network devices.
neigh add address [arguments]
Add a new entry to the neighbor table for the IPv4 or IPv6
address.
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ip
neigh chg address [arguments]
Change an existing entry in the neighbor table.
neigh del address [arguments]
Mark as invalid then remove an entry from the neighbor table
when released from all clients.
neigh list [address] [arguments]
Add a new entry or change an existing one in the neighbor
table.
neigh repl address [arguments]
Add a new entry or change an existing one in the neighbor
table.
neigh flush arguments
Flush the specified entries from neighbors table. This command
requires an argument, either an address, address prefix, dev,
nud, or unused argument.
route add address [arguments]
Add a new entry to the routing table.
route chg address [arguments]
Change an existing entry in the routing table.
route del address [arguments]
Remove an entry from the routing.
route list [arguments]
Show current routing table entries. Use arguments to limit the
entries shown.
route repl address [arguments]
Add a new entry or change an existing one in the routing
table.
Common arguments
The following are common arguments for the above commands:
address address[/netmask]
Set a link layer address (i.e., MAC address) for a network
device.
arp on, arp off
Set the arp flag of a network device on or off.
brd address
Set the broadcast address. Addresses for address objects may
also be given as the symbols + or – meaning to set all the host
bits of the broadcast address to 1 or 0. When used with a link
object, this argument sets the link layer broadcast address
instead.
dev name
The name of the network device to which the command
applies (e.g., lo or eth0.) For link object commands you can
omit dev and just pass the name as the first argument.
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ip
down, up
Change the state of a network device, disabling or enabling it
(or limit shown devices to those with the specified state).
dynamic on, dynamic off
Set the dynamic flag of a network device on or off.
label name
Assign a label string of name to an address.
local address
The IPv4 or IPv6 address to use with addr object commands.
For these commands you can omit local and just pass the
address as the first argument.
lladdr address
Set a link layer address for a neighbors table entry.
mtu n
Set the maximum transfer unit (MTU) for a network device to n.
multicast on, multicast off
Set the multicast flag of a network device on or off.
nud state
Set the neighbor unreachability detection (nud) state of a
neighbor entry. State values include:
noarp
Mark the entry as valid and not to be checked. It may be
removed when it expires.
permanent
Like noarp, but a permanent entry can only be removed
by an administrator.
reachable
Mark the entry as valid until its reachability timeout
expires.
stale
Mark a new or changed entry as valid, but suspicious.
The kernel will check stale entries at the first
transmission.
promisc on, promisc off
Turn promiscuous mode on or off for a network device.
proto protocol
Set the routing protocol. The protocol identifies how a route
was entered. If you are manually entering a route, the appro-
priate value for protocol should be static. If not specified the
protocol defaults to boot.
scope value
Set the valid scope of an address or route entry. Valid values
include global, site, link, and host. If used with the show
command, only addresses of the given scope will be shown.
src address
The preferred IPv4 or IPv6 source address for a routing table
entry.
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ipcrm
to address
The IPv4 or IPv6 address or address prefix for a neighbor table
or routing table entry. For neigh and route object commands
you can omit the to and pass the address as the first argu-
ment. For route object commands you may also use the special
address default, which is equivalent to an address of 0/0 or /0.
tos key
An 8-bit hexadecimal number or the IPv4 or IPv6 address or
address prefix for a neighbor table or routing table entry. For
neigh and route object commands you can omit the to and
pass the address as the first argument.
txqlen n
Set the transmit queue length of a network device to n.
unused
When given with neigh show, show only unused entries.
via address
The address of the nexthop router (e.g., the Ipv4 or IPv6
address of the gateway). Used with route commands.
Examples
Show all configured network cards:
# ip link show
Bring down eth0:
# ip link set eth0 down
Add an IP address to device eth0 and label it “internal”:
# ip addr add 192.186.0.32/24 brd + dev eth0 label internal
Show current routing table entries for device eth1:
# ip route list dev eth1
Add a router table entry for a private network on eth1 with gateway
via 192.168.0.254:
# ip route add 10.0.0.1/8 via 192.168.0.254 dev eth1
Put eth0 into promiscuous mode in order to sniff traffic:
# ip link set eth0 promisc on
Add a permanent entry to the neighbors table (arp table) for eth1:
# ip neigh add 10.0.0.5 lladdr 52:54:00:32:5e:20 dev eth1
nud permanent
ipcrm ipcrm [options]
System administration command. Remove interprocess communica-
tion (IPC) message queues, shared memory segments, or semaphore
arrays. These may be specified either by numeric identifier or by
key, using the following options.
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ipcs
Options
-m identifier, -M key
Remove specified shared memory segment and its associated
data structures after the last detach is performed.
-q identifier, -Q key
Remove specified message queue and its associated data
structures.
-s identifier, -S key
Remove specified semaphore array and its associated data
structures.
ipcs ipcs [options]
System administration command. Print report on interprocess
communication (IPC) message queues, shared memory segments,
and semaphore arrays for which the current process has read
access. Options can be used to specify the type of resources to
report on and the output format of the report.
Options
Resource specification options:
-a Report on all IPC facilities: shared memory segments, message
queues, and semaphore arrays. This is the default.
-m Report on shared memory segments.
-q Report on message queues.
-s Report on semaphore arrays.
Output format options:
-c Print creator and owner user IDs for IPC facilities.
-l Print resource maximum and minimum limits.
-p Print creator and last operation process identifiers.
-t Print attach, detach, and change times for shared memory
segments; last operation and change times for semaphore
arrays; and send, receive, and change times for message queues.
-u Print summary of current resource usage.
Other options:
-h Print help message, then exit.
-i identifier
Used in combination with the -m, -q, or -s options. Report
only on the resource specified by numeric identifier.
iptables iptablescommand [options]
System administration command. Configure netfilter filtering rules
for kernels 2.4 and later. Rules for iptables consist of some
matching criteria and a target, a result to be applied if the packet
matches the criteria. The rules are organized into chains. You can
use these rules to build a firewall, masquerade your local area
network, or just reject certain kinds of network connections.
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iptables
There are three built-in tables for iptables: one for network filtering
(filter), one for Network Address Translation (nat), and the last for
specialized packet alterations (mangle). Firewall rules are orga-
nized into chains, ordered checklists of rules that the kernel works
through looking for matches. The filter table has three built-in
chains: INPUT, OUTPUT, and FORWARD. The INPUT and
OUTPUT chains handle packets originating from or destined for
the host system. The FORWARD chain handles packets just
passing through the host system. The nat table also has three built-
in chains: PREROUTING, POSTROUTING, and OUTPUT.
mangle has only two chains: PREROUTING and OUTPUT.
netfilter checks packets entering the system. After applying any
PREROUTING rules, it passes them to the INPUT chain, or to the
FORWARD chain if the packet is just passing through. Upon
leaving, the system packets are passed to the OUTPUT chain and
then on to any POSTROUTING rules. Each of these chains has a
default target (a policy) in case no match is found. User-defined
chains can also be created and used as targets for packets but do
not have default policies. If no match can be found in a user-
defined chain, the packet is returned to the chain from which it was
called and tested against the next rule in that chain.
iptables changes only the rules in the running kernel. When the
system is powered off, all changes are lost. You can use the iptables-
save command to make a script you can run with iptables-restore to
restore your firewall settings. Such a script is often called at bootup.
Many distributions have an iptables initialization script that uses
the output from iptables-save.
Commands
iptables is almost always invoked with one of the following
commands:
-A chain rules, --append chain rules
Append new rules to chain.
-D chain rules, --delete chain rules
Delete rules from chain. Rules can be specified by their ordinal
number in the chain as well as by a general rule description.
-E old-chain new-chain, --rename-chain old-chain new-chain
Rename old-chain to new-chain.
-F [chain], --flush [chain]
Remove all rules from chain, or from all chains if chain is not
specified.
-I chain number rules, --insert chain number rules
Insert rules into chain at the ordinal position given by number.
-L [chain], --list [chain]
List the rules in chain, or all chains if chain is not specified.
-N chain, --new-chain chain
Create a new chain. The chain’s name must be unique. This is
how user-defined chains are created.
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iptables
-P chain target, --policy chain target
Set the default policy for a built-in chain; the target itself
cannot be a chain.
-R chain number rule, --replace chain number rule
Replace a rule in chain. The rule to be replaced is specified by
its ordinal number.
-X [chain], --delete-chain [chain]
Delete the specified user-defined chain, or all user-defined
chains if chain is not specified.
-Z [chain], --zero [chain]
Zero the packet and byte counters in chain. If no chain is spec-
ified, all chains will be reset. When used without specifying a
chain and combined with the -L command, list the current
counter values before they are reset.
Targets
A target may be the name of a chain or one of the following special
values:
ACCEPT
Let the packet through.
DROP
Drop the packet.
QUEUE
Send packets to the user space for processing.
RETURN
Stop traversing the current chain and return to the point in the
previous chain from which this one was called. If RETURN is
the target of a rule in a built-in chain, the built-in chain’s
default policy is applied.
Rule specification parameters
These options are used to create rules for use with the preceding
commands. Rules consist of some matching criteria and usually a
target to jump to (-j) if the match is made. Many of the parameters
for these matching rules can be expressed as a negative with an
exclamation point (!) meaning “not.” Those rules will match every-
thing except the given parameter.
-c packets bytes, --set-counters packets bytes
Initialize packet and byte counters to the specified values.
-d [!] address[/mask] [!] [port], --destination [!] address[/mask]
[port]
Match packets from the destination address. The address may
be supplied as a hostname, a network name, or an IP address.
The optional mask is the netmask to use and may be supplied
either in the traditional form (e.g., /255.255.255.0) or in the
modern form (e.g., /24).
[!] -f, [!]--fragment
The rule applies only to the second or further fragments of a
fragmented packet.
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iptables
-i [!] name[+], --in-interface name[+]
Match packets being received from interface name. name is the
network interface used by your system (e.g., eth0 or ppp0). A
+ can be used as a wildcard, so ppp+ would match any inter-
face name beginning with ppp.
-j target, --jump target
Jump to a special target or a user-defined chain. If this option
is not specified for a rule, matching the rule only increases the
rule’s counters, and the packet is tested against the next rule.
-o [!] name[+], --out-interface name[+]
Match packets being sent from interface name. See the
description of -i for the syntax for name.
-p [!] name, --protocol [!] name
Match packets of protocol name. The value of name can be
given as a name or number, as found in the file /etc/protocols.
The most common values are tcp, udp, icmp, or the special
value all. The number 0 is equivalent to all, and this is the
default value when this option is not used. If there are
extended matching rules associated with the specified
protocol, they will be loaded automatically. You need not use
the -m option to load them.
-s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port]
Match packets with the source address. See the description of -d
for the syntax of this option.
Options
-h [icmp], --help [icmp]
Print help message. If icmp is specified, a list of valid ICMP
type names will be printed. -h can also be used with the -m
option to get help on an extension module.
--line-numbers
Used with the -L command. Add the line number to the begin-
ning of each rule in a listing, indicating its position in the
chain.
-m module, --match module
Explicitly load matching rule extensions associated with
module. See the next section.
--modprobe=command
Use specified command to load any necessary kernel modules
while adding or inserting rules into a chain.
-n, --numeric
Print all IP address and port numbers in numeric form. By
default, text names are displayed when possible.
-t name, --table name
Apply rules to the specified table. Rules apply to the filter
table by default.
-v, --verbose
Verbose mode.
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iptables
-x, --exact
Expand all numbers in a listing (-L). Display the exact value of
the packet and byte counters instead of rounded figures.
Match extensions
Several modules extend the matching capabilities of netfilter rules.
Using the -p option will cause iptables to load associated modules
implicitly. Others need to be loaded explicitly with the -m or --match
options. Here we document those modules used most frequently.
icmp
Loaded when -p icmp is the only protocol specified:
--icmp-type [!] type
Match the specified ICMP type. type may be a numeric
ICMP type or one of the ICMP type names shown by the
command iptables -p icmp -h.
multiport
Loaded explicitly with the -m option. The multiport exten-
sions match sets of source or destination ports. These rules
can be used only in conjunction with -p tcp and -p udp. Up to
15 ports can be specified in a comma-separated list:
--source-port [ports]
Match the given source ports.
--destination-port [ports]
Match the given destination ports.
--port [ports]
Match if the packet has the same source and destination
port and that port is one of the given ports.
state
Loaded explicitly with the -m option. This module matches
the connection state of a packet:
--state states
Match the packet if it has one of the states in the comma-
separated list states. Valid states are INVALID, ESTAB-
LISHED, NEW, and RELATED.
tcp
Loaded when -p tcp is the only protocol specified:
--source-port [!] [port][:port], --sport [!] [port][:port]
Match the specified source ports. Using the colon speci-
fies an inclusive range of services to match. If the first
port is omitted, 0 is the default. If the second port is
omitted, 65535 is the default. You can also use a dash
instead of a colon to specify the range.
--destination-port [!] [port][:port], --dport [!] [port][:port]
Match the specified destination ports. The syntax is the
same as for --source-port.
--mss n[:n]
Match if TCP SYN or SYN/ACK packets have the speci-
fied MSS value or fall within the specified range. Use this
to control the maximum packet size for a connection.
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iptables
[!] --syn
Match packets with the SYN bit set and the ACK and FIN
bits cleared. These are packets that request TCP connec-
tions; blocking them prevents incoming connections.
Shorthand for --tcp-flags SYN,RST,ACK SYN.
--tcp-flags [!] mask comp
Match the packets with the TCP flags specified by mask
and comp. mask is a comma-separated list of flags that
should be examined. comp is a comma-separated list of
flags that must be set for the rule to match. Valid flags are
SYN, ACK, FIN, RST, URG, PSH, ALL, and NONE.
--tcp-option [!] n
Match if TCP option is set.
udp
Loaded when -p udp is the only protocol specified:
--source-port [!] [port][:port], --sport [!] [port][:port]
Match the specified source ports. The syntax is the same
as for the --source-port option of the TCP extension.
--destination-port [!] [port][:port], --dport [!] [port][:port]
Match the specified destination ports. The syntax is the
same as for the --source-port option of the TCP extension.
Target extensions
Extension targets are optional additional targets supported by sepa-
rate kernel modules. They have their own associated options. We
cover the most frequently used target extensions below.
DNAT
Modify the destination address of the packet and all future
packets in the current connection. DNAT is valid only as a
part of the POSTROUTING chain in the nat table:
--to-destination address[-address][port-port]
Specify the new destination address or range of addresses.
The arguments for this option are the same as the --to-
source argument for the SNAT extension target.
LOG
Log the packet’s information in the system log:
--log-level level
Set the syslog level by name or number (as defined by
syslog.conf).
--log-prefix prefix
Begin each log entry with the string prefix. The prefix
string may be up to 30 characters long.
--log-tcp-sequence
Log the TCP sequence numbers. This is a security risk if
your log is readable by users.
--log-tcp-options
Log options from the TCP packet header.
--log-ip-options
Log options from the IP packet header.
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iptables-restore
MASQUERADE
Masquerade the packet so it appears that it originated from
the current system. Reverse packets from masqueraded connec-
tions are unmasqueraded automatically. This is a legal target
only for chains in the nat table that handle incoming packets
and should be used only with dynamic IP addresses (like dial-
up.) For static addresses use DNAT:
--to-ports port[-port]
Specify the port or range of ports to use when masquer-
ading. This option is valid only if a tcp or udp protocol
has been specified with the -p option. If this option is not
used, the masqueraded packet’s port will not be changed.
REJECT
Drop the packet and, if appropriate, send an ICMP message
back to the sender indicating the packet was dropped. If the
packet was an ICMP error message, an unknown ICMP type,
or a nonhead fragment, or if too many ICMP messages have
already been sent to this address, no message is sent:
--reject-with type
Send specified ICMP message type. Valid values are
icmp-net-unreachable, icmp-host-unreachable, icmp-port-
unreachable, or icmp-proto-unreachable. If the packet
was an ICMP ping packet, type may also be echo-reply.
SNAT
Modify the source address of the packet and all future packets
in the current connection. SNAT is valid only as a part of the
POSTROUTING chain in the nat table:
--to-source address[-address][port-port]
Specify the new source address or range of addresses. If a
tcp or udp protocol has been specified with the -p option,
source ports may also be specified. If none is specified,
map the new source to the same port if possible. If not,
map ports below 512 to other ports below 512, those
between 512 and 1024 to other ports below 1024, and
ports above 1024 to other ports above 1024.
Examples
To reject all incoming ICMP traffic on eth0:
iptables -A INPUT -p ICMP -i eth0 -j REJECT
iptables-restore iptables-restore [options]
System administration command. Restore firewall rules from infor-
mation provided on standard input. iptables-restore takes
commands generated by iptables-save and uses them to restore the
firewall rules for each chain. This is often used by initialization
scripts to restore firewall settings on boot.
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isoinfo
Options
-c, --counters
Restore packet and byte counter values.
-n, --noflush
Don’t delete previous table contents.
iptables-save iptables-save [options]
System administration command. Print the IP firewall rules
currently stored in the kernel to stdout. Output may be redirected
to a file that can later be used by iptables-restore to restore the
firewall.
Options
-c, --counters
Save packet and byte counter values.
-t name, --table name
Print data from the specified table only.
isodump isodumpisoimage
Interactively display the contents of the ISO9660 image isoimage.
Used to verify the integrity of the directory inside the image.
isodump displays the first portion of the root directory and waits
for commands. The prompt shows the extent number (zone) and
offset within the extent, and the contents display at the top of the
screen.
Commands
+ Search forward for the next instance of the search string.
a Search backward within the image.
b Search forward within the image.
f Prompt for a new search string.
g Prompt for a new starting block and go there.
q Exit.
isoinfo isoinfo [options]
Display information about ISO9660 images. You can use isoinfo to
list the contents of an image, extract a file, or generate a find-like
file list. The -i option is required to specify the image to examine.
Options
-d Print information from the primary volume descriptor (PVD)
of the ISO9660 image, including information about Rock
Ridge and Joliet extensions if they are present.
dev=target
Set the SCSI target for the drive.
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isosize
-f Generate output similar to the output of a find . -print
command. Do not use with -l.
-h Print help information and exit.
-i isoimage
Specify the path for the ISO9660 image to examine.
-j charset
Convert any Joliet filenames to the specified character set.
-J Extract filename information from any Joliet extensions.
-l Generate output similar to the output of an ls -lR command.
Do not use with -f.
-N sector
To help examine single-session CD files that are to be written
to a multisession CD. Specify the sector number at which the
ISO9660 image is to be written when sent to the CD writer.
-p Display path table information.
-R Extract permission, filename, and ownership information from
any Rock Ridge extensions.
-T sector
To help examine multisession images that have already been
burned to a multisession CD. Use the specified sector number
as the start of the session to display.
-x path
Extract the file at the specified path to standard output.
isosize isosize [option] iso9660-img-file
Display the length of an ISO9660 filesystem contained in the speci-
fied file. The image file can be a normal file or a block device such
as /dev/sr0. With no options, the length is displayed in bytes. Only
one of the two options can be specified.
Options
-d num
Display the size in bytes divided by num.
-x Display thenumber of blocks and the block size (although the
output refers to blocks as sectors).
isovfy isovfyisoimage
Verify the integrity of the specified ISO9660 image and write the
results to standard output.
ispell ispell [options] [files]
Compare the words of one or more named files with the system
dictionary. Display unrecognized words at the top of the screen,
accompanied by possible correct spellings, and allow editing via a
series of single-character commands that are case-insensitive.
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ispell
Options
-b Back up original file in filename.bak.
-B Count two correctly spelled words without a space between
them as a spelling error.
-C Count two correctly spelled words without a space between
them as a legitimate compound word.
-d file
Search file instead of standard dictionary file.
-H File is in HTML/XML format.
-L number
Show number lines of context.
-m Suggest combinations of known roots and affixes, even if the
result is not known. For example, “generous” and “ly” are
known, so “generously” would be suggested as a word, even if
it were not in the dictionary.
-M List interactive commands at bottom of screen.
-n Expect nroff or troff input file.
-N Suppress printing of interactive commands.
-p file
Search file instead of personal dictionary file.
-P Do not guess new words using known roots and affixes. The
opposite of -m.
-S Sort suggested replacements by likelihood that they are correct.
-t Expect T E X or L A T E X input file.
-T type
Expect all files to be formatted by type.
-V Use hat notation (^L) to display control characters, and M- to
display characters with the high bit set.
-w chars
Consider chars to be legal, in addition to a–z and A–Z.
-W n
Never consider words that are n characters or fewer to be
misspelled.
-x Do not back up original file.
Interactive commands
? Display help screen.
space
Accept the word in this instance.
number
Replace with suggested word that corresponds to number.
!command
Invoke shell and execute command in it. Prompt before
exiting.
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join
a Accept word as correctly spelled, but do not add it to personal
dictionary.
i Accept word and add it (with any current capitalization) to
personal dictionary.
l Search system dictionary for words.
q Exit without saving.
r Replace word.
u Accept word and add lowercase version of it to personal
dictionary.
x Skip to the next file, saving changes.
^L Redraw screen.
^ZSuspend ispell.
join join [options]file1 file2
Join lines of two sorted files by matching on a common field. If either
file1 or file2 is -, read from standard input. Often used to merge data
stored in text-based file formats such as comma-separated-value
formatted spreadsheets.
Options
-1 fieldnum1
The join field in file1 is fieldnum1. Default is the first field.
-2 fieldnum2
The join field in file2 is fieldnum2. Default is the first field.
-a filenum
Print a line for each unpairable line in file filenum, in addition
to the normal output.
--check-order, --nocheck-order
Check or do not check that the files are correctly sorted on the
join fields.
-e string
Replace missing input fields with string.
-i, --ignore-case
Ignore case differences when comparing fields.
-o fieldlist
Order the output fields according to fieldlist, where each entry
in the list is in the form filenum.fieldnum. Entries are sepa-
rated by commas or blanks.
-t char
Specifies the field-separator character (default is whitespace).
-v filenum
Print only unpairable lines from file filenum.
--help
Print help message and then exit.
--version
Print the version number and then exit.
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kill
kbd_mode kbd_mode [option]
Print or set the current keyboard mode, which may be RAW,
MEDIUMRAW, XLATE, or UNICODE.
Options
-a Set mode to XLATE (ASCII mode).
-k Set mode to MEDIUMRAW (keycode mode).
-s Set mode to RAW (scancode mode).
-u Set mode to UNICODE (UTF-8 mode).
kbdrate kbdrate [options]
System administration command. Control the rate at which the
keyboard repeats characters, as well as its delay time. Using this
command without options sets a repeat rate of 10.9 characters per
second; the default delay is 250 milliseconds. On boot, most Linux
systems set the keyboard rate to 30 characters per second.
Options
-d delay
Specify the delay, which must be one of the following (in milli-
seconds): 250, 500, 750, or 1000.
-r rate
Specify the repeat rate, which must be one of the following
numbers (all in characters per second): 2.0, 2.1, 2.3, 2.5, 2.7,
3.0, 3.3, 3.7, 4.0, 4.3, 4.6, 5.0, 5.5, 6.0, 6.7, 7.5, 8.0, 8.6, 9.2,
10.0, 10.9, 12.0, 13.3, 15.0, 16.0, 17.1, 18.5, 20.0, 21.8, 24.0,
26.7, or 30.0.
-s Suppress printing of messages.
-V Print version number and exit.
kill kill [options] [pids]
Send a signal to terminate one or more process IDs. You must own
the process or be a privileged user. If no signal is specified, TERM
is sent.
This entry describes the /bin/kill command. There are also built-in
shell commands of the same name; the bash version is described in
Chapter 6.
In some Linux distributions, /bin/kill allows you to specify a
command name, such as gcc or xpdf, instead of a process ID (PID).
All processes running that command with the same UID as the
process issuing /bin/kill are sent the signal.
If /bin/kill is issued with a pid of 0, it sends the signal to all
processes of its own process group. If /bin/kill is issued with a pid
of -1, it sends the signal to all processes except process 1 (the
system’s init process).
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killall
Options
-a Kill all processes of the given name (if privileges allow), not
just processes with the same UID. To use this option, specify
the full path (e.g., /bin/kill -a gcc).
-l List all signals.
-p Print the process ID of the named process, but don’t send it a
signal. To use this option, specify the full path (e.g., /bin/kill -p).
-s SIGNAL, -SIGNAL
The signal number (from /usr/include/sys/signal.h) or name
(from kill -l). With a signal number of 9 (KILL), the kill
cannot be caught by the process; use this to kill a process that
a plain kill doesn’t terminate. The default signal is TERM. The
letter flag itself is optional: both kill -9 1024 and kill -s 9 1024
terminate process 1024.
killall killall [options]names
Kill processes by command name. If more than one process is
running the specified command, kill all of them. Treats command
names that contain a / as files; kill all processes that are executing
that file.
Options
-e, --exact
Require an exact match to kill very long names (i.e., longer than
15 characters). Normally, killall kills everything that matches
within the first 15 characters. With -e, such entries are skipped.
(Use -v to print a message for each skipped entry.)
-g, --process-group
Kill the process group to which the process belongs.
-i, --interactive
Prompt for confirmation before killing processes.
-I, --ignore-case
Ignore case when matching process names.
-l, --list
List known signal names.
-q, --quiet
Quiet; do not complain of processes not killed.
-r, --regexp
Interpret process name as an extended regular expression.
-ssignal, --signalsignal
Send signal to named processes. signal may be a name or a
number. The most commonly used signal is 9, which termi-
nates processes no matter what. The default signal is
SIGTERM.
-uuser, --useruser
Kill only processes owned by the specified user.
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klogd
-v, --verbose
Verbose; after killing process, report success and process ID.
-V, --version
Print version information.
-w, --wait
Wait for all killed processes to die. Note that killall may wait
forever if the signal was ignored or had no effect, or if the
process stays in zombie state.
klogd klogd [options]
System administration command. Control which kernel messages
are displayed on the console, prioritize all messages, and log them
through syslogd. On many operating systems, syslogd performs all
the work of klogd, but on Linux the features are separated. Kernel
messages are gleaned from the /proc filesystem and from system
calls to syslogd. By default, no messages appear on the console.
Messages are sorted into eight levels, 0–7, and the level number is
prepended to each message.
Priority levels
0 Emergency situation (KERN_EMERG).
1 A crucial error has occurred (KERN_ALERT).
2 A serious error has occurred (KERN_CRIT).
3 An error has occurred (KERN_ERR).
4 A warning message (KERN_WARNING).
5 The situation is normal but should be checked (KERN_
NOTICE).
6 Information only (KERN_INFO).
7 Debugging message (KERN_DEBUG).
Options
-c level
Print all messages of a higher priority (lower number) than
level to the console.
-d Debugging mode.
-f file
Print all messages to file; suppress normal logging.
-i Signal executing daemon to reload kernel module symbols.
-I Signal executing daemon to reload both static kernel symbols
and kernel module symbols.
-k file
Use file as source of kernel symbols.
-n Avoid auto-backgrounding. This is needed when klogd is
started from init.
-o One-shot mode. Prioritize and log all current messages, then
immediately exit.
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last
-p Reload kernel-module symbol information whenever an Oops
string is detected.
-P file
Use file as the source for kernel messages instead of /proc/kmsg.
-s Suppress reading of messages from the /proc filesystem. Read
from kernel message buffers instead.
-v Print version, then exit.
-x Don’t translate instruction pointers (EIP). klogd will not read
the System.map file.
-2 Print two lines for each symbol, one showing the symbol and
the other showing its numerical value (address).
Files
/usr/include/linux/kernel.h, /usr/include/sys/syslog.h
Sources for definitions of each logging level.
/proc/kmsg
A file examined by klogd for messages.
/var/run/klogd.pid
klogd’s process ID.
last last [options] [username] [ttynumber]
Display a list of the most recent logins, taken from the file /var/log/
wtmp by default. If you specify a tty number or username, the
output displays only the logins for that user or terminal.
Options
-a Display the hostname from which logins originated in the last
column.
-d For remote logins, display both IP address and hostname.
-f filename
Get the list of logins from filename. The default source is /var/
log/wtmp.
-i Like –d, but display the IP address in numbers-and-dots
notation.
-n number, -number
Choose how many lines of logins to display. Thus, last -7 or
last -n 7 displays seven lines.
-R Do not show the hostname.
-x Display shutdown messages and runlevel messages.
lastb lastb [options] [username] [ttynumber]
Display a list of recent bad login attempts (from the /var/log/btmp
file). Accepts the same option flags and arguments as last.
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ld
lastlog lastlog [options]
System administration command. Print the last login times for
system accounts. Login information is read from the file /var/log/
lastlog.
Options
-tn, --timen
Print only logins more recent than n days ago.
-uname, --username
Print only login information for user name.
ld ld [options]objfiles
Combine several objfiles, in the specified order, into a single
executable object module (a.out by default). ld is the link editor
and is often invoked automatically by compiler commands. ld
accepts many options, the most common of which are listed here.
Options
-b format, --format=format
If ld is configured to accept more than one kind of object file,
this option can be used to specify the input format. format
should be a GNU Binary File Descriptor (BFD), as described
in the BFD library. Use objdump -i to list available formats.
-call_shared
Link with dynamic libraries.
-d, -dc, -dp
Force the assignment of space to common symbols.
-defsym symbol=expression
Create the global symbol with the value expression.
-demangle[=style]
Force demangling of symbol names. Optionally set the deman-
gling style. Turn off demangling with -nodemangle.
-e symbol
Set symbol as the address of the output file’s entry point.
-f name
Set the DT_AUXILIARY field of ELF shared object to name.
-fini name
Set the DT_FINI field of ELF shared object to the address of
function name. The default function is _fini.
-h name
Set the DT_SONAME field of ELF shared object to name.
--help
Print help message, then exit.
-i Produce a linkable output file; attempt to set its magic number
to OMAGIC.
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ld
-init name
Set the DT_INIT field of ELF shared object to the address of
function name. The default function is _init.
-larch, --library=archive
Include the archive file arch in the list of files to link.
-m linker
Emulate linker. List supported emulations with the -V option.
-n Make text read-only; attempt to set NMAGIC.
-o output
Place output in output, instead of in a.out.
-oformat format
Specify output format.
-q Retain relocation sections and contents in linked executables.
-r Produce a linkable output file; attempt to set its magic number
to OMAGIC.
-rpath dir
Add directory dir to the runtime library search path. Ignore
additional paths normally read from the LD_RUN_PATH
environment variable.
-rpath-link dirs
Specify path to search for shared libraries required by another
shared library. The dirs argument can be a single directory, or
multiple directories separated by colons. This overrides search
paths specified in shared libraries themselves.
-s Do not include any symbol information in output.
-shared
Create a shared library.
-static
Do not link with shared libraries.
-sort-common
Do not sort global common symbols by size.
-t Print each input file’s name as it is processed.
--target-help
Print target-specific options, then exit.
-u symbol
Force symbol to be undefined.
-v, --version
Show version number.
--verbose
Print information about ld; print the names of input files while
attempting to open them.
--warn-common
Warn when encountering common symbols combined with
other constructs.
--warn-once
Provide only one warning per undefined symbol.
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ld
-x With -s or -S, delete all local symbols. These generally begin
with L.
-z keyword
Mark the object for special behavior specified by keyword. ld
recognizes the following keywords:
combreloc
Object combines and sorts multiple relocation sections
for dynamic symbol lookup caching.
defs
Disallow undefined symbols.
initfirst
Initialize object first at runtime.
execstack
Marks the object as requiring an executable stack.
interpose
Interpose object’s symbol table before all but the primary
executable’s symbol table.
loadfltr
Process object’s filter immediately at runtime.
multidefs
Allow multiple definitions of a single symbol. Use the
first definition.
nocombreloc
Disable combining multiple relocation sections.
nocopyreloc
Disable copy relocation.
nodefaultlib
Ignore default library search path when seeking depen-
dencies for object.
nodelete
Do not unload object at runtime.
nodlopen
Object is not available to dlopen.
nodump
Object cannot be dumped by dldump.
now
Non-lazy runtime binding.
origin
Object may contain $ORIGIN.
relro
Create an ELF PT_GNU_RELRO segment header in the
object.
-E, --export-dynamic
Add all symbols to dynamic symbol table, not just those refer-
enced by linked objects.
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ldconfig
-EB
Link big-endian objects.
-EL
Link little-endian objects.
-F name
Set DT_FILTER field of ELF shared object to name.
-Ldir, --library-path=dir
Search directory dir before standard search directories (this
option must precede the -l option that searches that directory).
-M Display a link map on standard output.
-Map file
Print a link map to file.
-N Allow reading of and writing to both data and text. Mark
ouput if it supports Unix magic numbers. Do not page-align
data.
-O level
Optimize. level should be 1, 2, 3, or 0. The default is 1. 0
turns off optimization; 3 optimizes the most.
-R file
Obtain symbol names and addresses from file, but suppress
relocation of file and its inclusion in output.
-S Do not include debugger symbol information in output.
-T file
Execute script file instead of the default linker script.
-Tbss address
Begin bss segment of output at address.
-Tdata address
Begin data segment of output at address.
-Ttext address
Begin text segment of output at address.
-Ur
Synonymous with -r except when linking C++ programs,
where it resolves constructor references.
-X With -s or -S, delete local symbols beginning with L.
-V Show version number and emulation linkers for -m option.
ldconfig ldconfig [options]directories
System administration command. Examine the libraries in the
given directories, /etc/ld.so.conf.d, /usr/lib, and /lib; update links and
cache where necessary. Usually run in startup files or after the instal-
lation of new shared libraries.
Options
-C filename
Use filename instead of /etc/ld.so.cache.
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less
-ffilename
Use filename instead of /etc/ld.so.conf.
-l Library mode. Expect libraries as arguments, not directories.
Manually link specified libraries.
-n Suppress examination of /usr/lib and /lib and reading of /etc/ld.
so.conf; do not cache.
-N Do not cache; only link.
-p Print all directories and candidate libraries in the cache. Used
without arguments.
-v Verbose mode. Include version number, and announce each
directory as it is scanned and links as they are created.
-X Do not link; only rebuild cache.
Files
/lib/ld.so
Linker and loader.
/etc/ld.so.conf
List of directories that contain libraries.
/etc/ld.so.cache
List of the libraries found in those libraries mentioned in /etc/
ld.so.conf.
ldd ldd [options]programs
Display a list of the shared libraries each program requires.
Options
-d, --data-relocs
Process data relocations. Report missing objects (for ELF objects
only).
-r, --function-relocs
Process relocations for both data objects and functions.
Report any that are missing (for ELF objects only).
-v, --verbose
Verbose mode. Display extra information, including symbol
versions.
--help
Print help message, then exit.
--version
Display the linker’s version, then exit.
less less [options] [filename]
less is a program for paging through files or other output. It was
written in reaction tothe perceived primitiveness of more (hence its
name) and allows backward as well as forward paging. Some
commands may be preceded by a number.
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less
Options
-[z]num, --window=num
Set number of lines to scroll to num. Default is one screenful.
A negative num sets the number to num lines less than the
current number.
+[+]command
Run command on startup. If command is a number, jump to
that line. The option ++ applies this command to each file in
the command-line list.
-?, --help
Print help screen.
-a, --search-skip-screen
When searching, begin after last line currently displayed.
(Default is to search from second line displayed.)
-bbuff, --buffers=buff
Specify the amount of buffer space to use for each file in 1 KB
units. (Default is to use 64 KB per file.)
-B, --auto-buffers
Do not automatically allocate buffer space to hold all data
read from a pipe. If -b is specified, allocate that amount of
space, or default to 64 KB. If necessary, allow information
from previous screens to be lost.
-c, --clear-screen
Redraw screen from top, not bottom.
-f, --force
Force opening of directories and devices; do not print warning
when opening binaries.
-F, --quit-if-one-screen
Exit without displaying anything if first file can fit on a single
screen.
-g, --hilite-search
Highlight only string found by past search command, not all
matching strings.
-G, --HILITE-SEARCH
Never highlight matching search strings.
-hnum, --max-back-scroll=num
Never scroll backward more than num lines at once.
-i, --ignore-case
Make searches case-insensitive, unless the search string
contains uppercase letters.
-I, --IGNORE-CASE
Make searches case-insensitive, even when the search string
contains uppercase letters.
-jnum, --jump-target=num
Position target line on line num of screen. Target line can be the
result of a search or a jump. Count lines beginning from 1 (top
line). A negative num is counted back from bottom of screen.
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less
-kfile, --lesskey-file=file
Read file to define special key bindings. See lesskey for more
information.
-K, --quit-on-intr
Exit immediately on interrupt (usually ^-C).
-m, --long-prompt
Display more-like prompt, including percent of file read.
-M, --LONG-PROMPT
Prompt more verbosely than with -m, including percentage,
line number, and total lines.
-n, --line-numbers
Do not calculate line numbers. Affects -m and -M options and
= and v commands (disables passing of line number to editor).
-N, --LINE-NUMBERS
Print line number before each line.
-ofile, --log-file=file
When input is from a pipe, copy output to file as well as to
screen. (Prompt for overwrite authority if file exists.)
-O file, --LOG-FILE=file
Similar to -o, but do not prompt when overwriting file.
-ppattern, --pattern=pattern
At startup, search for first occurrence of pattern.
-P[mM=]prompt
Set the prompt displayed by less at the bottom of each screen
to prompt. The m sets the prompt invoked by the -m option,
the M sets the prompt invoked by the -M option, and the =
sets the prompt invoked by the = command. Special charac-
ters (described in the less manpage), can be used to print
statistics and other information in these prompts.
-q, --quiet, --silent
Disable ringing of bell on attempts to scroll past EOF or
before beginning of file. Attempt to use visual bell instead.
-Q, --QUIET, --SILENT
Never ring terminal bell.
-r, --raw-control-chars
Display “raw” control characters instead of using ^x notation.
This sometimes leads to display problems, which might be
fixed by using -R instead.
-R, --RAW-CONTROL-CHARS
Like r, but only output “raw” ANSI color escape characters.
-s, --squeeze-blank-lines
Print successive blank lines as one line.
-S, --chop-long-lines
Cut, do not fold, long lines.
-ttag, --tag=tag
Edit file containing tag. Consult ./tags (constructed by ctags).
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less
-T file, --tag-file=file
With the -t option or :t command, read file instead of ./tags.
-u, --underline-special
Treat backspaces and carriage returns as printable input
characters.
-U, --UNDERLINE-SPECIAL
Treat backspaces, tabs and carriage returns as control
characters.
-V, --version
Display version and exit.
-w, --hilite-unread
Show the line to which a movement command has skipped,
phrases displayed by a search command, or the first unread
line during a normal scroll by highlighting text in reverse
video.
-W, --HILITE-UNREAD
Show phrases displayed by a search command, or the first
unread line of any forward movement that is more than one
line, by highlighting text in reverse video.
-x n..., --tabs=n...
Set tab stops to every n characters. Default is 8. If multiple
values are given for n in a comma-separated list, set the tab
stops to those values.
-X, --no-init
Do not send initialization and deinitialization strings from
termcap to terminal.
-y n, --max-forw-scroll=n
Never scroll forward more than n lines at once.
Commands
Many commands can be preceded by a numeric argument, referred
to as number in the command descriptions.
SPACE, ^V, f, ^F
Scroll forward the specified number of lines (default one
windowful).
ESC-SPACE
Like SPACE, but scroll forward a complete screenful.
z Similar to SPACE, but if number is specified, reset the default
to that number.
RETURN, ^N, e, ^E, j, ^J
Scroll forward. Default is one line. Display all lines, even if the
default is more lines than the screen size.
d, ^D, PageDown
Scroll forward. Default is one-half the screen size. The number
of lines may be specified, in which case the default is reset.
b, ^B, ESC-v
Scroll backward, but if number is specified, scroll back that
number of lines. Default is one windowful.
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less
w Like b, but if number is specified, reset the default to that
number.
y, ^Y, ^P, k, ^K
Scroll backward. Default is one line. Display all lines, even if
the default is more lines than the screen size.
u, ^U, PageUp
Scroll backward. Default is one-half the screen size. The
number of lines may be specified, in which case the default is
reset.
r, ^R, ^L
Redraw screen.
R Like r, but discard buffered input.
F Scroll forward. On EOF, continue trying to find more output,
behaving similarly to tail -f.
g, <, ESC-<
Skip to a line. Default is 1.
G, >, ESC->
Skip to a line. Default is the last line.
p, %
Skip to a position number percent of the way into the file.
{ If the top line on the screen includes a {, find its matching }. If
the top line contains multiple {s, use number to determine
which one to use in finding a match.
} If the bottom line on the screen includes a }, find its matching
{. If the bottom line contains multiple }s, use number to deter-
mine which one to use in finding a match.
( If the top line on the screen includes a (, find its matching ). If
the top line contains multiple (s, use number to determine
which one to use in finding a match.
) If the bottom line on the screen includes a ), find its matching
(. If the bottom line contains multiple )s, use number to deter-
mine which one to use in finding a match.
[ If the top line on the screen includes a [, find its matching ]. If
the top line contains multiple [s, use number to determine
which one to use in finding a match.
] If the bottom line on the screen includes a ], find its matching
[. If the bottom line contains multiple ]s, use number to deter-
mine which one to use in finding a match.
ESC-^Fchar1 char2
Behave like { but substitute char1 and char2 for { and } in the
search.
ESC-^Bchar1 char2
Behave like } but substitute char1 and char2 for { and } in the
search.
mlet
Use the specified lowercase letter to mark the current position.
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less
' (single apostrophe)let
Use the specified lowercase letter and to return to the position
marked by that letter. With a second apostrophe, return to the
previous position where the last “large” movement began.
With ^, return to the beginning of the file; with $, return to
the end of the file.
^X^X
Same as '.
/pattern
Find next occurrence of pattern, starting at second line
displayed. Some special characters can be entered before
pattern:
!, ^N
Find lines that do not contain pattern.
*, ^E
If current file does not contain pattern, continue through
the rest of the files in the command-line list.
@, ^F
Search from the first line in the first file specified on the
command line, no matter what the screen currently
displays.
^K
Hightlight matching text on the current screen, but do
not move there.
^R
Use text comparison; do not interpret regular expressions.
?pattern
Search backward, beginning at the line before the top line. The
use of special characters is the same as for /pattern.
ESC-/pattern
Same as /*.
ESC-?pattern
Same as ?*.
n Repeat last pattern search.
N Repeat last pattern search in the reverse direction.
ESC-n
Repeat previous search command, but as though it were pref-
aced by *.
ESC-N
Repeat previous search command, but as though it were pref-
aced by * and in the reverse direction.
ESC-u
Toggle search highlighting.
&pattern
Display only lines that match the pattern. With ^N or !,
display lines that do not match; with ^R, do not interpret
regular expressions.
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less
:d Remove the current file from the list of files.
:e [filename]
Read in filename and insert it into the command-line list of
filenames. Without filename, reread the current file. Replace a
percent sign (%) in the filename with the name of the current
file; replace a hash mark (#), with the name of the previous file.
^X^V, E
Same as :e.
:n Read in next file in command-line list or the file indicated by
number, if specified.
:p Read in previous file in command-line list or the file indicated
by number, if specified.
:x Read in first file in command-line list or the file indicated by
number, if specified.
sfilename
If input is a pipe, save to the specified file.
t Go to the next tag. See the -t option.
T Go to the previous tag. See the -T option.
:f, =, ^G
Print filename, position in command-line list, line number on
top of window, total lines, byte number, and total bytes.
- (single dash)
Expects to be followed by a command-line option letter.
Toggle the value of that option or, if appropriate, prompt for
its new value.
-- Like -, but takes a long option name.
-+ Expects to be followed by a command-line option letter. Reset
that option to its default.
--+ Like -+, but takes a long option name.
_ (underscore)
Expects to be followed by a command-line option letter.
Display that option’s current setting.
__ Like _, but takes a long option name.
+command
Execute command each time a new file is read in.
q, :q, :Q, ZZ
Exit.
v Not valid for all versions. Invoke editor specified by $VISUAL
or $EDITOR, or vi if neither is set.
! [command]
Not valid for all versions. Invoke $SHELL or sh. If command
is given, run it and then exit. Replace % with the name of the
current file, # with the name of the previous file, and !! with
the last shell command.
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lesskey
| mark-letter command
Not valid for all versions. Pipe fragment of file (from first line
on screen to mark-letter) to command. mark-letter may be ^
for the beginning of the file, $ for the end of the file, or . or
newline to pipe the current screen.
Prompts
The prompt interprets certain sequences specially. Those begin-
ning with % are always evaluated. Those beginning with ? are
evaluated if certain conditions are true. Some prompts determine
the position of particular lines on the screen. These sequences
require that a method of determining that line be specified. See the
-P option and the manpage for more information.
lesskey lesskey [-ooutput-file | --output = output-file] [input-file]
Configure keybindings for the less command using a configuration
file. The input file defaults to ~/.lesskey and the output file to ~/.less
unless you specify otherwise.
Configuration file format
The configuration file for lesskey has one to three sections. These
are marked by a line containing a # symbol and the name of the
section: #command, #line-edit, and #env.
The #command section
The command section determines the keys used for actions
within less. Each line should contain the key or key combina-
tion you wish to define, a space or tab, and the name of the
action to perform. You may also add an extra string at the
end, which will be performed at the end of the first action.
Keys you define should be entered as you plan to type them,
with the following exceptions:
Backspace: \b
Backslash: \\
Caret: \^
Escape: \e
Newline: \n
Return: \r
Tab: \t
Up arrow: \ku
Down arrow: \kd
Right arrow: \kr
Left arrow: \kl
Page up: \kU
Page down: \kD
Home: \kh
End: \ke
Delete: \kx
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lesskey
The actions that can be defined are:
invalid (creates error)
noaction
forw-line
back-line
forw-line-force
forw-scroll
back-scroll
forw-screen
back-screen
forw-window
back-window
forw-screen-force
forw-forever
repaint-flush
repaint
undo-hilite
goto-line
percent
left-scroll
right-scroll
forw-bracket
back-bracket
goto-end
status
forw-search
back-search
repeat-search
repeat-search-all
reverse-search
reverse-search-all
filter
set-mark
goto-mark
examine
next-file
index-file
prev-file
next-tag
previous-tag
remove-file
toggle-option
display-option
pipe
visual
shell
firstcmd
help
version (display version)
digit (display number)
quit
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lftp
The #line-edit section
The line editing section lets you choose keys for the line-
editing capabilities of less in a similar manner to the
#command section, although without the “extra” string after
the command. The line editing actions that can be defined are:
forw-complete
back-complete
expand
literal
right
left
word-left
word-right
insert
delete
word-delete
word-backspace
home
end
up
down
The #env section
The third section, like the second, is optional, and you can use
it to override environment variables that affect less. Each line
consists of a variable, the equals sign (=), and the value to
which you wish to set the variable. The most important ones
are LESS, which allows you to select additional flags to pass to
less when you run it, and LESSCHARSET, which lets you
choose a character set. See the less manpage for a complete list
of environment variables that affect the program.
lftp lftp [options] [url]
File transfer program with more features than ftp. The lftp
command allows FTP and HTTP protocol transfers, plus other
protocols including FISH (SSH based), FTPS, and HTTPS. It uses a
shell-like command interface and offers job control in a manner
similar to bash. lftp has two important reliability features: it
resumes failed or interrupted transactions, and it goes into the
background automatically if it is quit in the middle of a file
transfer.
Options
-d Run in debug mode.
-e commands
Start, execute the specified commands, and then wait for
further instructions.
-p portnumber
Connect to the specified port number.
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lftp
-u user[,pass]
Login to the server with the username (and, optionally, pass-
word) you specify.
-f scriptfile
Run the specified script file of lftp commands, then exit.
-c commands
Run the commands specified, then exit.
Commands
The lftp commands are similar to those for ftp. However, lftp lacks
or uses different mechanisms for a number of commands, including
$, ascii, binary, case, and macdef. It also adds the following:
alias [name [value]]
Create an alias for a command. For example, you could set dir
to be an alias for ls -lf.
anon
Set the username to anonymous. This is the default username.
at
Execute a command at a given time, as with the at command
in an actual shell.
bookmark [arguments]
The lftp bookmark command used with the following argu-
ments will add, delete, edit, import, or list bookmarks,
respectively:
• add name url
• del name
• edit
• import type
• list
cache
Work with the local memory cache. This command should be
followed by the arguments:
stat
Display the status for the cache.
on|off
Turn caching on or off.
flush
Empty the cache.
size n
Set the maximum size for the cache. Setting it to -1 means
unlimited.
expire nu
Set the cache to expire after n units of time. You can set
the unit (u) to seconds (s), minutes (m), hours (h), or
days (d). For example, for a cache that expires after an
hour, use the syntax cache expire 1h.
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lftp
close
Close idle connections with the current server. This differs
from ftp, which closes all connections. If you have connec-
tions to multiple servers and wish to close all idle connections,
add the -a flag.
command cmd args
Execute the specified lftp command, with the specified argu-
ments, ignoring any aliases created with the alias command.
mirror [options] [remotedir [localdir]]
Copy a directory exactly. The mirror command accepts the
following arguments:
-c, --continue
If mirroring was interrupted, resume it.
-e, --delete
Delete local files that are not present at the remote site.
-s, --allow-suid
Keep the suid/sgid bits as set on the remote site.
-n, --only-newer
Get only those files from the remote site that have more
recent dates than the files on the local system. Cannot be
used with the -c argument.
-r, --no-recursion
Do not get any subdirectories.
--no-umask
Do not use umask when getting file modes. See umask
for more information about file modes.
-R, --reverse
Mirror files from the local system to the remote system.
With this argument, make sure that you specify the local
directory first and the remote directory second. If you do
not specify both directories, the second is assumed to be
the same as the first. If you choose neither, the operation
occurs in the current working directories.
-L, --dereference
When mirroring a link, download the file the link points
to rather than just the link.
-Nfilename, --newer-than filename
Get all files newer than the file filename.
-Pn, --parallel[=n]
Download n files in parallel.
-iregex, --include regex
Get only the files whose names match the regular expres-
sion regex. See Chapter 7 for information about regular
expressions.
-xregex, --exclude regex
Do not get the files whose names match regex. See
Chapter 7 for information about regular expressions.
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ln
-vn, --verbose=n
Set the verbose level. You can set n from 0 (no output) to
3 (full output) using a number or by repeating the v. For
example, -vvv is level 3 verbose mode.
--use-cache
Use the cache to get directory listings.
--remove-source-files
Move, rather than copy, files when mirroring.
set [variable | value]
Set a preference variable for lftp. With no arguments, list the
variables that have been changed; with no arguments and with
the -a or -d flags, list all values or default values, respectively.
See the lftp manpage for a complete list of preference vari-
ables that can be set.
wait [n | all]
Wait for the job or jobs you specify by number, or all jobs, to
terminate.
lftpget lftpget [options]url
Uses the lftp program to fetch the specified URL, which may be
HTTP, FTP, or any of the protocols supported by lftp.
Options
-c Continue or restart a paused transaction.
-d Display debugging output.
-v Verbose mode; display more information about transactions.
link linkfile1 file2
Create a link between two files. This is the same as the ln
command, but it has no error checking because it uses the link()
system call directly.
ln ln [options]sourcename [destname]
ln [options]sourcenames destdirectory
Create pseudonyms (links) for files, allowing them to be accessed
by different names. Links may be “hard” or “soft.” A hard link
creates two names for the same file, and a soft, or symbolic, link
creates a second file which acts as a shortcut to the first. The
default is to create hard links; use -s or --symbolic to create
symbolic links.
The first form links sourcename to destname, where destname is
usually either a new filename or (by default) a file in the current
directory with the same name as sourcename. If destname is an
existing file, it is overwritten; if destname is an existing directory, a
link named sourcename is created in that directory. The second
form creates links in destdirectory, each link having the same name
as the file specified.
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loadkeys
Options
-b, --backup[=control]
Back up any existing files. With the long version of the
command, the optional control parameter controls the kind of
backup. When no control is specified, ln attempts to read the
control value from the VERSION_CONTROL environment
variable. Accepted values are:
none, off
Never make backups.
numbered, t
Make numbered backups.
existing, nil
Match existing backups, numbered or simple.
simple, never
Always make simple backups.
-d, -F, --directory
Allow hard links to directories. Available to privileged users.
-f, --force
Force the link (don’t prompt for overwrite permission).
--help
Print a help message and then exit.
-i, --interactive
Prompt for permission before removing files.
-n, --no-dereference
Replace symbolic links to directories instead of dereferencing
them. --force is useful with this option.
-s, --symbolic
Create a symbolic link. This lets you link across filesystems,
and also see the name of the link when you run ls -l (other-
wise, there’s no way to know the name that a file is linked to).
-S suffix, --suffix=suffix
Append suffix to files when making backups, instead of the
default ~.
-tdirectory, --target-directory=directory
Create links in the specified directory.
-v, --verbose
Verbose mode.
--version
Print version information and then exit.
loadkeys loadkeys [options] [filename]
Load a keymap from a specified file, usually one of the keymaps
stored in /lib/kbd/keymaps. If you create your own keymap file, the
related commands showkey, keymaps, and dumpkeys will be
useful as well. Note that loadkeys applies only to virtual consoles; to
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locale
change your X keyboard configuration, use xmodmap or setxkbmap,
or the graphical keyboard-layout switching tools that are included
with your desktop environment.
Options
-c, --clearcompose
Clear the compose, or accent, table in the kernel.
-d, --default
Load the default keymap. The same as running loadkeys
defkeymap.
-h, --help
Display help and usage information.
-m, --mktable
Instead of loading the table, output maps as C language
declarations.
-s, --clearstrings
Clear the string table in the kernel.
-v, --verbose
Operate verbosely. For extra effect, repeat.
locale locale [options] [names]
Print report on current locale settings. Locales determine the
country-specific settings for a system, including character encod-
ings, the formatting of dates, honorifics, diagnostic messages,
currency, printer-paper sizes, and default measurements. Locale
settings are essentially a dictionary of settings specified by
keyword. The keywords are grouped together into related catego-
ries whose names begin with LC_. Each category has a related
environment variable of the same name from which it reads its
locale setting. Supply keyword or category names as names to
examine their values. You can also use the special keyword
charmap to see the current character mapping. When executed
with no arguments, locale prints the value of all locale-related envi-
ronment variables.
Options
-a, --all-locales
Print all available locale settings installed on the system.
-c, --category-name
Print the category related to each name argument.
-k, --keyword-name
Print keywords along with their settings for each name argument.
-m, --charmaps
Print all available character maps.
Environment variables
LANG
The default value for unset internationalization variables. If
not set, the system’s default value is used.
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locate
LC_ADDRESS
Postal settings, country, and language names and abbreviation.
LC_COLLATE
String and character sorting and comparison settings.
LC_CTYPE
Character attributes, including case conversion mappings, and
categories of characters (whitespace, digit, lower, upper, punc-
tuation, etc.).
LC_IDENTIFICATION
Information related to the current locale definition, including
its title, source, revision, and contact information for its
author.
LC_MEASUREMENT
Measurement units, metric or other.
LC_MESSAGES
Settings for yes/no prompts and other informative and diag-
nostic messages.
LC_MONETARY
Currency formats and symbols.
LC_NAME
Formats for names and honorifics.
LC_NUMERIC
Nonmonetary number formats.
LC_PAPER
Default paper sizes for printing and pagination.
LC_TELEPHONE
Telephone number formats.
LC_TIME
Date and time formats.
LC_ALL
When set, overrides the values of all other internationaliza-
tion variables.
Examples
Print the category name and all keywords for date and time
settings:
locale -ck LC_TIME
Print the strings used for days of the week and months of the year:
locale day mon
locate locate [options]pattern
Search database(s) of filenames and print matches. Matches
include all files that contain pattern unless pattern includes meta-
characters, in which case locate requires an exact match. *, ?, [, and
] are treated specially; / and . are not. Searches are conducted
against a database of system contents that is updated periodically.
To update the database, use the updatedb command.
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lockfile
Options
-b, --basename
Look only at the basename when searching for matches.
-c, --count
List only the match count, not the individual filenames.
-d path, --database=path
Search databases in path. path must be a colon-separated list.
-h, --help
Print a help message and then exit.
-i, --ignore-case
Ignore case when performing matches.
-q, --quiet
Run quietly, printing no error messages.
-rregexp, --regexpregexp
Search for a basic regular expression, with no patterns allowed.
May be issued more than once.
--regex
Treat all patterns as extended regular expressions.
-S, --statistics
Print statistics about each database and then exit.
-V, --version
Print version information and then exit.
-w, --wholename
Look at the entire pathname when searching for matches (the
default).
lockfile lockfile [options]filenames
Create semaphore file(s), used to limit access to a file. When lock-
file fails to create some of the specified files, it pauses for eight
seconds and retries the last one on which it failed. The command
processes flags as they are encountered (i.e., a flag that is specified
after a file will not affect that file). This command is most often
used by scripts and applications as a way to avoid multiple users
changing the same file at once.
Options
-sleeptime
Number of seconds lockfile waits before retrying after a failed
creation attempt. Default is 8.
-! Invert return value. Useful in shell scripts.
-l lockout_time
Time (in seconds) after a lockfile was last modified at which it
will be removed by force. See also -s.
-ml, -mu
If the permissions on the system mail spool directory allow it
or if lockfile is suitably setgid, lockfile can lock and unlock
your system mailbox with the options -ml and -mu, respectively.
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logger
-r retries
Stop trying to create files after this many retries. The default is -1
(never stop trying). When giving up, remove all created files.
-s suspend_time
After a lockfile has been removed by force (see -l), a suspen-
sion of 16 seconds takes place by default. (This is intended to
prevent the inadvertent immediate removal of any lockfile
newly created by another program.) Use -s to change the
default suspend time.
logger logger [options] [message...]
TCP/IP command. Add entries to the system log (via syslogd). If
no message is given on the command line, standard input is logged.
Options
-d When writing to a socket with -s, use a datagram instead of a
stream.
-f file
Read message from file.
-i Include the process ID of the logger process.
-p pri
Enter message with the specified priority pri. Default is user.
notice.
-s Log message to standard error as well as to the system log.
-t tag
Mark every line in the log with the specified tag.
-u socket
Write log to socket instead of to the syslog.
-- Accept no further options. Consider whatever is to the right of
the hyphens as the message to be logged.
login login [name |option]
Log into the system. login asks for a username (name can be
supplied on the command line) and password (if appropriate).
If successful, login updates accounting files, sets various environ-
ment variables, notifies users if they have mail, and executes
startup shell files.
Only the root user can log in when /etc/nologin exists. That file is
displayed before the connection is terminated. Furthermore, root
may connect only on a tty that is listed in /etc/securetty. If ~/.hush-
login exists, execute a quiet login. If /var/adm/lastlog exists, print
the time of the last login.
Options
-f Suppress second login authentication.
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logrotate
-h host
Specify name of remote host. Normally used by servers, not
humans; may be used only by root.
-p Preserve previous environment.
logrotate logrotate [options]config_files
System administration command. Manipulate logfiles according to
commands given in config_files.
Options
-d, --debug
Debug mode. No changes will be made to logfiles.
-f, --force
Force rotation of logfiles.
-h, --help
Describe options.
-m command, --mail command
Use the specified command to mail logfiles. The default
command is /bin/mail -s.
-s file, --state file
Save state information in file. The default is /var/lib/logrotate.
status.
--usage
Show syntax and options.
-v, --verbose
Describe what is being done and what logfiles are affected.
Configuration commands
Logrotate directives may appear on their own or as part of logfile
definitions—instructions for specific logfiles. You may use wild-
cards to specify those files. Enclose directives for logfile definitions
in a beginning and ending curly brace. For example:
compress
/var/log/messages {
rotate 5
weekly
}
compress
Compress old versions of logfiles with gzip.
compresscmd command
Use command to compress logfiles. Default is gzip.
compressext extension
Append filename extension to compressed files instead of the
compress command’s default.
compressoptions options
Specify options to pass to the compress command. Default for
gzip is -9 for maximum compression.
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logrotate
copy
Copy logfile, but do not change the original.
copytruncate
Copy logfile, then truncate it in place. For use with programs
whose logging cannot be temporarily halted.
create [permissions] [owner] [group]
After rotation, re-create logfile with the specified permissions,
owner, and group. permissions must be in octal. If any of these
parameters is missing, the logfile’s original attributes will be
used.
daily
Rotate logfiles every day.
delaycompress
Don’t compress logfile until the next rotation.
endscript
End a postrotate or prerotate script.
extension extension
Give rotated logfiles the specified extension. Any compression
extension will be appended to this.
firstaction
May only be used as part of a logfile definition. Begin a shell
script to execute once if any files match. The script ends when
the endscript directive is read.
ifempty
Rotate logfile even if it is empty. Overrides the default
notifempty option.
include file
Read the file into current file. If file is a directory, read all files
in that directory into the current file.
lastaction
May only be used as part of a logfile definition. Begin a shell
script to execute once after rotating all matching files and
running any postrotate script. The script ends when the
endscript directive is read.
mail address
Mail any deleted logs to address.
mailfirst
When using the mail command, mail the newly rotated log
instead of the one being deleted.
maillast
When using the mail command, mail the log that is about to
expire. This is the default behavior.
missingok
Skip missing logfiles. Do not generate an error.
monthly
Rotate logfiles only the first time logrotate is run in a month.
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logrotate
nocompress
Override compress.
nocopy
Override copy.
nocopytruncate
Override copytruncate.
nocreate
Override create.
nodelaycompress
Override delaycompress.
nomail
Override mail.
nomissingok
Override missingok.
noolddir
Override olddir.
nosharedscripts
Override sharedscripts. Run prerotate and postrotate scripts
for each log rotated. This is the default.
notifempty
Override ifempty.
olddir directory
Move logs into directory for rotation. directory must be on the
same physical device as the original logfiles.
postrotate
May only be used as part of a logfile definition. Begin a shell
script to apply after the logfile is rotated. The script ends when
the endscript directive is read.
prerotate
May only be used as part of a logfile definition. Begin a shell
script to apply before a logfile is rotated. The script ends when
the endscript directive is read.
rotate number
The number of times to rotate a logfile before removing it.
size n[k|M]
Rotate logfile when it is greater than n bytes. n can optionally
be followed by k for kilobytes or M for megabytes.
sharedscripts
Run prescript and postscript only once for the session.
start n
Use n as the starting number for rotated logs. Default is 0.
tabooext [+] extlist
Replace taboo extension list with the given extlist. If + is speci-
fied, add to existing list. The default list is .rpmorig .rpmsave ,v
.swp .rpmnew ~.
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look
weekly
Rotate logfiles if more than a week has passed since their last
rotation.
uncompresscmd command
Use command to uncompress logfiles. Default is gunzip.
look look [options]string [file]
Search for lines in file (/usr/dict/words by default) that begin with
string.
Options
-a Use alternate dictionary, /usr/dict/web2.
-d Compare only alphanumeric characters.
-f Search is not case-sensitive.
-t character
Stop checking after the first occurrence of character.
losetup losetup [options]loopdevice [file]
System administration command. Set up and control loop devices.
Attach a loop device to a regular file or block device, detach a loop
device, or query a loop device. A loop device can be used to mount
an image file as if it were a normal device.
Options
-d Detach specified loopdevice.
-e encryption, -Enumber
Use specified kernel encryption module when performing
writes and reads. (Usually NONE, DES, and XOR.) You may
also specify the encryption module by number. When using
DES encryption, you will be prompted for an initialization
passphrase.
-o offset
Start reading data at offset bytes from the beginning of file.
-p fd
Read the passphrase from file descriptor fd.
lpadmin lpadmin [options]
System administration command. Configure CUPS printer queues.
The command requires one of the following options: -d, -p, or -x.
When a queue is configured to require a password, the lpadmin
command will prompt for one.
Options
-d queue
Set the default destination for CUPS commands like lp and lpr
to the specified queue.
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lpadmin
-E Always use encryption when connecting to the server.
-h server
Apply configuration commands remotely to the specified
CUPS server.
-p printer print-options
Apply print-options (documented below) to the specified
printer.
-x queue
Delete the specified queue. Abort any current print job and
discard any pending print jobs.
Print options
Use these additional options with the -p option just listed:
-c class
Add printer to the specified class. Create class if it does not
already exist.
-D description
Set the text description of the printer.
-E Enable printer.
-L location
Set the printer location text.
-i script
Use the specified System V-style interface script.
-m filename
Use the specified System V interface script or PPD file found in
the model directory.
-o name=value
Set the value of PPD or server option name. For a list of avail-
able PPD options, use the lpoptions command.
-P filename
Use the PPD specified by filename. This option overrides the -i
printer option.
-r class
Remove printer from the specified class. Remove class if it has
no printer entries.
-u allow:[@]name, -u deny:[@]name
Set user level access control. To specify a group instead of a
user name, preface the name with @ . You may also use the
special names all and none.
-v uri
Set the device universal resource indicator, uri.If given as a
filename, the command will automatically convert it to a file
URI.
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lpinfo
lpinfo lpinfooptions
System administration command. Print information on available
printer devices and drivers.
Options
-E Force the use of encryption connecting to the server.
-l Show a long, or verbose, listing.
-m List available printer drivers.
-v List available printer devices.
lpmove lpmove [option]jobdestination
System administration command. Move the specified print job to a
new destination.
Option
-E Force the use of encryption connecting to the server.
lpq lpq [options] [+interval]
Check the print spool queue for status of print jobs. For each job,
display username, rank in the queue, filenames, job number, and
total file size (in bytes). We document the CUPS printing system
here; other versions will vary slightly.
Options
-a Report on all printers listed in the server’s printcap database.
-E Use encryption when connecting to a print server.
-hserver[:port]
Specify an alternate server and optional port.
-l Verbose mode. Print information about each file composing a
job. Use -l multiple times to increase the information
provided.
-P printer
Specify which printer to query. Without this option, lpq uses
the default printer, normally set through lpadmin.
-Uusername
Specify an alternate username.
+interval
Check the queue every interval seconds until it is empty. For
example, +10 reloads the queue every ten seconds.
lpr lpr [options] [files]
Send files to be printed. If no files are given, accept standard input.
We document the CUPS printing system here; the older LPRng and
BSD systems will vary slightly. CUPS lpr, for example, does not
accept the options c, d, f, g, i, m, n, t, v, or w, used by LPRng.
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lprm
Options
-#copies
Set the number of copies to print, from 1 to 100.
-C, J, T name
Set a name for the print job.
-E Use encryption when connecting to a print server.
-Hserver[:port]
Specify an alternate server and optional port.
-l Expect a binary or literal file on which minimal processing
should be done. The same as -o raw.
-m Send email when printing is complete.
-o option[=value]
Set printer-specific options. These vary by printer, but may
include paper type and orientation, paper-tray selection,
output order, and so forth. Check the complete CUPS user
manual and your printer’s PPD file for the full list.
-p Pretty-print a text document. Provides a shaded header
containing page numbers, the job name, and the time and date
of printing. Equivalent to -o prettyprint.
-P printername
Print to the specified printer. If no printer is given, prints to
the default printer, usually set with lpadmin.
-q Hold job for printing.
-r Delete files after printing them.
-Uusername
Specify an alternate username.
Example
Print a simple file:
Lprfilename.txt
lprm lprm [options] [jobid]
Cancel print jobs. Job IDs can be obtained from lpq; if no job is
specified, cancels the current job on the default printer.
Options
- Remove all jobs available to the user. Same as specifying jobid
as ALL.
-E Use encryption.
-hserver[:port]
Specify an alternate server and optional port.
-P printer
Specify printer queue. If no printer is specified, the default
printer is used.
-Uusername
Specify an alternate username.
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lpstat
lpstat lpstat [options] [queues]
Show the status of the print queue or queues. With options that
take a list argument, omitting the list produces all information for
that option. list can be separated by commas or, if enclosed in
double quotes, by spaces. For the LPRng print service, lpstat is a
frontend to the lpq program. With no arguments, lpstat shows jobs
queued by the current user.
Options
-a [list]
Show whether the list of printer or class names is accepting
requests.
-c [list]
Show information about printer classes named in list.
-d Show the default printer destination.
-E Use encryption when connecting to the print server.
-l When showing printers, classes, or jobs, print a long listing.
-o [list]
Show the status of output requests. list contains printer
names, class names, or request IDs.
-p [list]
Show the status of printers named in list.
-r Show whether the print scheduler is on or off.
-s Summarize the print status (show almost everything).
-t Show all status information (report everything).
-u [list]
Show request status for users on list. Use all to show informa-
tion on all users.
-Uusername
Specify an alternate username.
-v [list]
Show printers and the devices they are attached to.
ls ls [options] [names]
List contents of directories. If no names are given, list the files in
the current directory. With one or more names, list files contained
in a directory name or that match a file name. names can include
filename metacharacters. The options let you display a variety of
information in different formats. The most useful options include
-F, -R, -l, and -s. Some options don’t make sense together (e.g., -u
and -c).
Options
-1, --format=single-column
Print one entry per line of output.
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ls
-a, --all
List all files, including the normally hidden files whose names
begin with a period.
-A, --almost-all
List all files, including the normally hidden files whose names
begin with a period. Does not include the . and .. directories.
-b, --escape
Display nonprinting characters in octal and alphabetic format.
-B, --ignore-backups
Do not list files ending in ~ unless given as arguments.
-c, --time=ctime, --time=status
List files by status change time (ctime), not creation/modifica-
tion time. With -l, show ctime and sort by filename; with -lt,
show and sort by ctime; otherwise, sort by ctime.
-C, --format=vertical
List files in columns (the default format).
--color[=when]
Colorize the names of files depending on the type of file.
Accepted values for when are never, always, or auto.
-d, --directory
Report only on the directory, not its contents; do not derefer-
ence symbolic links.
-D, --dired
List in a format suitable for Emacs dired mode.
-f Print directory contents in order, without attempting to sort
them.
-F, --classify, --indicator-style=classify
Flag filenames by appending / to directories, * to executable
files, @ to symbolic links, | to FIFOs, and = to sockets.
--full-time
List times in full, rather than using the standard abbreviations.
-g Long listing like -l, but don’t show file owners.
-G, --no-group
In long format, do not display group name.
--group-directories-first
Display directories before files.
-h, --human-readable
Print sizes in kilobytes and megabytes.
-H, --dereference-command-line
When symbolic links are given on the command line, follow
the link and list information from the actual file.
--help
Print a help message and then exit.
-i, --inode
List the inode for each file.
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ls
-I, --ignore pattern
Do not list files whose names match the shell pattern pattern,
unless they are given on the command line.
--indicator-style=none
Display filenames without the flags assigned by -p or -f
(default).
-k If file sizes are being listed, print them in kilobytes. This
option overrides the environment variable POSIXLY_
CORRECT.
-l, --format=long, --format=verbose
Long format listing (includes permissions, owner, size, modifi-
cation time, etc.).
-L, --dereference
List the file or directory referenced by a symbolic link rather
than the link itself.
-m, --format=commas
Merge the list into a comma-separated series of names.
-n, --numeric-uid-gid
Like -l, but use group ID and user ID numbers instead of
owner and group names.
-N, --literal
Display special graphic characters that appear in filenames.
-o Long listing like -l, but don’t show group information.
-p, --indicator-style=slash
Mark directories by appending / to them.
-q, --hide-control-chars
Show nonprinting characters as ? (default for display to a
terminal).
-Q, --quote-name
Quote filenames with "; quote nongraphic characters.
-r, --reverse
List files in reverse order (by name or by time).
-R, --recursive
List directories and their contents recursively.
-s, --size
Print file size in blocks.
-S, --sort=size
Sort by file size, largest to smallest.
--show-control-chars
Show nonprinting characters verbatim (default for printing to
a file).
--si
Similar to -h, but uses powers of 1000 instead of 1024.
-t, --sort=time
Sort files according to modification time (newest first).
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lspci
-u, --time=atime, --time=access, --time=use
Sort files according to file-access time. With -l, show access
time and sort by filename; with -lt, show and sort by access
time; otherwise sort by access time.
-U, sort=none
Do not sort files.
-v, --sort=version
Interpret the digits in names such as file.6 and file.6.1 as
versions, and order filenames by version.
--version
Print version information on standard output, then exit.
-wn, --width=n
Format output to fit n columns.
-x, --format=across, --format=horizontal
List files in rows going across the screen.
-X, sort=extension
Sort by file extension, then by filename.
lsattr lsattr [options] [files]
Print attributes of files on a Linux Second Extended File System.
See also chattr.
Options
-a List all files in specified directories.
-d List attributes of directories, not of contents.
-R List directories and their contents recursively.
-v List version of files.
-V List version of lsattr and then exit.
lspci lspci [options]
System administration command. List all Peripheral Component
Interconnect (PCI) devices. This command has many options that
are useful for debugging device drivers. Here we document some of
the more common options:
Options
-b Show IRQ and addresses as seen by the cards instead of the
kernel.
-t Print a tree showing connections between devices.
-m Print information with quoted strings suitable for use by
scripts.
-n Print vendor and device codes as numbers.
-v, -vv
List devices verbosely. Use the second form for very verbose
listings.
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lsmod
lsmod lsmod
System administration command. List all loaded modules: name,
size (in 4 KB units), and, if appropriate, a list of referring modules.
The same information is available in /proc/modules if the /proc
directory is enabled on the system.
lsusb lsusb [options]
System administration command. List all Universal Serial Bus
(USB) devices. This command has many options of use for debug-
ging device drivers. Here we document some of the more common
options.
Options
-b Show IRQ and addresses as seen by the cards instead of the
kernel.
-D device
Only show information about the specified device. This should
be given as a file in the /proc/bus/usb directory—e.g., /proc/bus/
usb/001/001.
-t Print a tree showing connections between devices.
-v, -vv
List devices verbosely. Use the second form for very verbose
listings.
m4 m4 [options] [macros] [files]
Macro processor for C and other files.
Options
-e, --interactive
Operate interactively, unbuffered, ignoring interrupts.
-dflags, --debug=flags
Specify flag-level debugging.
--help
Print help message, then exit.
-ln, --arglength=n
Specify the length of debugging output.
-o file, --error-output=file
Place output in file. Despite the name, print error messages on
standard error.
-P, --prefix-built-ins
Prepend m4_ to all built-in macro names.
-s, --synclines
Insert #line directives for the C preprocessor.
-tname, --trace=name
Insert name into symbol table as undefined. Trace macro from
the point it is defined.
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mailq
--version
Print version, then exit.
-Bn
Set the size of the pushback and argument collection buffers to
n (default is 4096).
-Dname[=value], --define=name[=value]
Define name as value or, if value is not specified, define name
as null.
-E, --fatal-warnings
Consider all warnings to be fatal, and exit after the first of
them.
-Ffile, --freeze-state=file
Record m4’s frozen state in file for later reloading.
-G, --traditional
Behave like traditional m4, ignoring GNU extensions.
-Hn, --hashsize=n
Set symbol-table hash array to n (default is 509).
-Idirectory, --include=directory
Search directory for include files.
-Ln, --nesting-limit=n
Change artificial nesting limit to n.
-Q, --quiet, --silent
Suppress warning messages.
-Rfile, --reload-state=file
Load state from file before starting execution.
-Uname, --undefine=name
Undefine name.
mail mail [options] [users]
Read mail or send mail to other users. mail is now generally a
symbolic link to mailx.
mailq mailq [options]
List all messages in the sendmail mail queue. Equivalent to send-
mail -bp.
Options
-Ac
Show queue specified in /etc/mail/submit.cf instead of queue
specified in /etc/mail/sendmail.cf.
-q[ ! ]Isubstring
Show items in mail queue with queue ids containing substring.
In this, and in similar options below, invert the match when !
is specified.
-qL
Show lost items in mail queue.
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mailstats
-qQ
Show quarantined items in the mail queue.
-q[ ! ]Qsubstring
Show quarantined messages with quarantine reasons
containing substring.
-q[ ! ]Rsubstring
Show items in mail queue with recipients containing substring.
-q[ ! ]Ssubstring
Show items in mail queue with senders containing substring.
-v Verbose mode.
mailstats mailstats [options]
System administration command. Display a formatted report of the
current sendmail mail statistics.
Options
-c Use configuration in /etc/mail/submit.cf instead of /etc/mail/
sendmail.cf.
-C file
Use sendmail configuration file file instead of the default
sendmail.cf file.
-f file
Use sendmail statistics file file instead of the file specified in
the sendmail configuration file.
-o Don’t show the name of the mailer in the report.
-p Print stats without headers or separators. Output suitable for
use by other programs. Reset statistics.
-P Print stats without headers or separators. Output suitable for
use by other programs. Do not reset statistics.
mailx mailx [options] [users]
Read mail or send mail to other users. mailx is based on the tradi-
tional mail command, extended to provide support for MIME,
IMAP, POP3, SMTP, and S/MIME. The mailx command allows
you to compose, send, receive, forward, and reply to mail. mailx
has two main modes: compose mode, in which you create a
message, and command mode, in which you manage your mail.
mailx is most commonly seen nowadays in scripts. Most Linux
distributions include several utilities that are richer in features and
easier to use: mailers built into browsers such as Mozilla and
Firefox, graphical mail programs distributed with GNOME (Evolu-
tion) and KDE (Kmail), and the terminal-based, full-screen utilities
pine and elm. The GNU Emacs editor can also send and receive
mail.
To get you started, here are two of the most basic commands.
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mailx
To enter interactive mail-reading mode, type:
mailx
To begin writing a message to user, type:
mailxuser
Enter the text of the message, one line at a time, pressing Enter at
the end of each line. To end the message, enter a single period (.) in
the first column of a new line and press Enter.
You can also provide much of the information on the command
line, as shown in the following example:
mailx james -s "System Log" </var/log/messages
This command sends a message to the user james, with a subject
line of System Log, and the text of the message read from the
system logfile, /var/log/messages.
mailx has many more options and commands than we can describe
here. For complete details, as well as a full description of managing
and using the command, see the manpage.
Command-line options
-~ Allow tilde escapes even when not in interactive mode.
-afile
Attach the specified file to the message.
-Aaccount
Run the account command for the specified email account
after the startup files have been read.
-b list
Set blind-carbon-copy field to comma-separated list.
-c list
Set carbon-copy field to comma-separated list.
-D Start disconnected.
-e Check for presence of mail in the system mailbox, but do not
read. Returns exit status of 0 if there is mail, otherwise returns
nonzero.
-E Discard an outgoing message with no text in its first or only
part.
-f [file]
Process contents of file instead of /var/spool/mail/$user. If file
is omitted, process mbox in the user’s home directory.
-H Print message header summaries and exit.
-i Do not respond to tty interrupt signals.
-I Show Newsgroup: or Article-Id: fields in the header summary;
used with -f.
-n Do not consult /etc/mail.rc when starting up.
-N When printing a mail message or entering a mail folder, do
not display message headers.
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mailx
-qfile
In compose mode, insert the contents of file at the beginning
of the message.
-R Open folders read-only.
-s subject
Set subject to subject. Use quotes around subjects that contain
spaces.
-Svar[=value]
Set the internal option var. If var is a string variable, assign the
given value to it.
-t Expect the message to contain To:, Cc:, and/or Bcc: fields to
identify recipients and ignore any set on the command line.
-uuser
Process contents of /var/spool/mail/$user for the specified user.
-v Verbose; print information about mail delivery to standard
output.
Compose-mode commands
The following commands are known as tilde escapes and are only
recognized at the beginning of a line in the message:
~!command
Execute a shell escape from compose mode and run the speci-
fied command.
~<!command
Execute a shell escape and run the specified command, then
insert its standard output into the message.
~? List tilde escapes.
~| command
Pipe message through command.
~: mailx-command
Execute mailx-command.
~~string
Insert string in text of message, prefaced by a single tilde (~). If
string contains a ~, it must be escaped with a \.
~b names
Add names to or edit the Bcc: header.
~c names
Add names to or edit the Cc: header.
~d Read in the dead.letter file.
~e Invoke text editor.
~f messages
Insert messages into message being composed. Only the first
printable part of a MIME multipart message is inserted.
~F messages
Similar to ~f, but include message headers and all MIME parts.
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mailx
~h Add to or change To:, Cc:, Bcc:, and Subject: headers
interactively.
~H Like ~h but edit From:, Reply-To:, Sender:, and Organiza-
tion: headers.
~m messages
Similar to ~f, but indent with a tab.
~M messages
Similar to ~m, but include message headers and all MIME
parts.
~p Print message header fields, message being sent, and attach-
ment list.
~q Abort current message composition, and save to dead.letters
file.
~r filename
Include file in current message.
~s string
Change Subject: header to string.
~t names
Add names to or edit the To: list.
~v Invoke editor specified with the VISUAL environment
variable.
~w filename
Write the message to the named file, appending it if the file
already exists.
~x Like ~q, but don’t save the message to dead.letters file.
Command-mode commands
? List summary of commands (help screen).
! Execute a shell command.
- [num]
Print numth previous message; defaults to immediately
previous.
account (ac)
Create, select, or list an email account.
alias (a)
Print or create alias lists.
alternates (alt)
Specify remote accounts on remote machines that are yours.
Tell mailx not to reply to them.
cache
For IMAP mailboxes only, read specified messages into the
IMAP cache.
chdir (c)
cd to home or specified directory.
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mailx
classify
Check contents of messages for junk mail, using Bayesian
filtering, and mark as junk.
copy (co)
Similar to save, but do not mark message for deletion.
delete (d)
Delete message.
dp (dt)
Delete current message and display next one.
edit (e)
Edit message.
exit (ex, x)
Exit mailx without updating folder or user’s system mailbox.
file (fi)
Switch folders.
folder (fold)
Read messages saved in a file. If no file is specified, display
the name of the current file. In addition to filenames, the
following are allowed:
# Previous file
% System mailbox
%user
user’s system mailbox
& mbox
+folder
File in folder directory.
folders
List folders, and subfolders with an existing folder as argument.
forward (fwd)
Forward a message to a recipient.
from (f)
Print headers for messages.
good (go)
Mark messages as good (not junk mail).
headers (h)
List message headers in groups of 18 at current prompt.
headers+ (h+)
Move forward one window of headers.
headers- (h-)
Move back one window of headers.
help
Same as ?.
hold (ho)
Hold messages in system mailbox.
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mailx
ignore
Append list of fields to ignored fields. With no arguments, list
currently ignored fields.
imap
Send commands to the current IMAP server.
junk (j)
Mark messages as junk mail.
list
Print list of available commands.
mail user (m)
Compose message to user.
mbox
Move specified messages to mbox on exiting (the default).
move (mv)
Like copy, but mark messages for deletion after the move.
next (n)
Type next message or next message that matches argument.
pipe (pi), |
Pipe messages through a shell command.
preserve (pre)
Synonym for hold.
print [list] (p)
Display each message in list. For MIME multipart messages,
display parts that are labeled “text” or “message”.
Print [list] (P)
Similar to print, but include ignored header fields and all parts
of MIME multipart messages.
quit (q)
Exit mailx and update folder.
remove (rem)
Remove named folders.
rename (ren)
Rename an existing folder.
reply (r)
Send mail to all on distribution list.
Reply (R)
Send mail to author only.
replyall
Reply to all recipients.
respond
Same as reply.
retain
Always include this list of header fields when printing
messages. With no arguments, list retained fields.
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mailx
save (s)
Save message to folder.
saveignore
Remove ignored fields when saving.
saveretain
Override saveignore to retain specified fields.
seen
Mark list of messages as read.
set (se)
Set or print mailx options.
shell (sh)
Enter a new shell.
show (Sh)
Like print, but show raw message text, with no decoding, for
MIME or encrypted messages.
size
Print size of each specified message.
source
Read commands from specified file.
thread (th)
Show current folder in threaded format.
top
Print first few lines of each specified message.
touch
Mark messages to be saved in mbox.
type (t)
Same as print.
Type (T)
Same as Print.
unalias
Discard previously defined aliases.
unanswered
Mark specified messages as unanswered.
uncollapse (unc)
Uncollapse threaded messages so the messages and replies are
visible in header summaries again.
undelete (u)
Restore specified deleted messages.
ungood
Undo the effect of an earlier good command.
unjunk
Undo the effect of an earlier junk command.
unread (U)
Mark specified messages as unread.
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mailx
unset (uns)
Unset mailx options.
verify (verif)
Verify that specified messages are S/MIME signed messages.
visual (v)
Edit message with editor specified by the VISUAL environ-
ment variable.
write (w)
Write message, without headers, to file.
xit (x)
Same as exit.
z
Move mailx’s attention to next windowful of text. Use z- to
move it back.
Configuration options
These options are set inside the user’s .mailrc configuration file.
The syntax is set option or unset option. The system default config-
uration is in /etc/mail.rc.
append
Append (do not prepend) messages tombox.
ask, asksub
Prompt for subject.
askattach
Prompt at end of message for attachments.
askbcc
Prompt for blind-carbon-copy recipients.
askcc
Prompt for carbon-copy recipients.
asksign
Ask if message is to be signed.
autobcclist
Specify recipients who are always to receive a blind carbon
copy.
autocclist
Specify recipients who are always to receive a carbon copy.
autoprint
Print next message after a delete.
autothread
Always enter threaded mode when a folder is opened.
cmdcommand
Specify the default command for a pipe.
crtnum
Use the default pager to display a message of more than num
lines. Defaults to the height of the terminal screen.
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mailx
debug
Same as -d on command line.
dot
Interpret a solitary . as an EOF.
encodingvalue
The default MIME encoding to use for outgoing messages.
Possible values are 8bit (the default) or quoted-printable.
escape char
Specify escape character to use instead of a tilde (~).
folderdir
Define directory to hold mail folders.
fromaddr
The default address to put in the From: field.
hold
Keep message in system mailbox upon quitting.
ignore
Ignore interrupt signals from terminal. Print them as @.
ignoreeof
Do not treat ^D as an EOF.
indentprefix string
Use the specified string with ~m as the prefix for indented
messages.
junkdbaddr
Location of the junk mail database.
keep
Do not delete user’s system mailbox when empty.
metoo
Do not remove sender from groups when mailing to them.
noheader
Same as -N on command line.
nosave
Do not save aborted letters to dead.letter.
pop3-use-apop
If set, connection to POP3 server uses APOP authentication.
quiet
Do not print version at startup.
record file
Use file as the path to record outgoing mail. If not set, outgoing
mail is not saved.
Replyall
Switch roles of Reply and reply.
replytolist
Specify addresses for the Reply-To: field.
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make
searchheaders
When given the specifier /x:y, expand all messages that
contain the string y in the x header field.
senderaddr
Specify the address to put into the Sender: field.
showlast
Start at the last message, not the first, when folder is opened.
toplines num
Print num lines of message with the top command. Default
value is 5.
verbose
Same as -v on command line.
make make [options] [targets] [macrodefinitions]
Update one or more targets according to dependency instructions
in a description file in the current directory. By default, this file is
called makefile or Makefile. Options, targets, and macro defini-
tions can be in any order. Macro definitions are typed as:
name=string
For more information on make, see Robert Mecklenburg’s
Managing Projects with GNU Make (O’Reilly).
Options
-d, --debug
Print detailed debugging information.
-e, --environment-overrides
Override Makefile macro definitions with environment
variables.
-f Makefile, --file=Makefile, --makefile=Makefile
Use Makefile as the description file; a filename of - denotes
standard input.
-h, --help
Print options to make command.
-i,--ignore-errors
Ignore command error codes (same as .IGNORE).
-j [jobs], --jobs [=jobs]
Attempt to execute this many jobs simultaneously or, if no
number is specified, as many jobs as possible.
-k, --keep-going
Abandon the current target when it fails, but keep working
with unrelated targets.
-l [load], --load-average [=load], --max-load [=load]
Attempt to keep load below load, which should be a floating-
point number. Used with -j.
-n, --just-print, --dry-run, --recon
Print commands but don’t execute (used for testing).
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make
-o file, --old-file=file, --assume-old=file
Never remake file or cause other files to be remade on account
of it.
-p, --print-data-base
Print rules and variables in addition to normal execution.
-q, --question
Query; return 0 if file is up to date, nonzero otherwise.
-r, --no-built-in-rules
Do not use default rules.
-s, --silent, --quiet
Do not display command lines (same as .SILENT).
-t, --touch
Touch the target files without remaking them.
-v, --version
Show version of make.
-w, --print-directory
Display the current working directory before and after execution.
--warn-undefined-variables
Print warning if a macro is used without being defined.
-C directory, --directory directory
cd to directory before beginning make operations. A subsequent
-C directive will cause make to attempt to cd into a directory
relative to the current working directory.
-I directory, --include-dir directory
Include directory in list of directories containing included files.
-S, --no-keep-going, --stop
Cancel previous -k options. Useful in recursive makes.
-W file, --what-if file, --new-file file, --assume-new file
Behave as though file has been recently updated.
Description-file lines
Instructions in the description file are interpreted as single lines. If
an instruction must span more than one input line, use a backslash
(\) at the end of the line so that the next line is considered a contin-
uation. The description file may contain any of the following types
of lines:
Blank lines
Blank lines are ignored.
Comment lines
A pound sign (#) can be used at the beginning of a line or
anywhere in the middle. make ignores everything after the #.
Dependency lines
Depending on one or more targets, certain commands that
follow will be executed. Possible formats include:
targets :dependencies
targets :dependencies ;command
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make
Subsequent commands are executed if dependency files (the
names of which may contain wildcards) do not exist or are
newer than a target. If no prerequisites are supplied, then
subsequent commands are always executed (whenever any of
the targets are specified). No tab should precede any targets.
Conditionals
Conditionals are evaluated when the Makefile is first read and
determine what make sees—i.e., which parts of the Makefile
are obeyed and which parts are ignored. The general syntax
for a conditional is:
Conditional
Text if true
Else
Text if false
endif
ifeq (arg1, arg2), ifeq "arg1" "arg2"
True if the two arguments are identical. The arguments should
either be placed in parentheses and separated by a comma—
(arg1, arg2)—or individually quoted with either single or
double quotes.
ifneq (arg1, arg2), ifneq "arg1" "arg2"
True if the two arguments are not identical. The arguments
should either be placed in parentheses and separated by a
comma, or individually quoted with either single or double
quotes.
ifdef variable
True if variable has a nonempty value.
ifndef variable
True if variable has an empty value.
Suffix rules
These specify that files ending with the first suffix can be
prerequisites for files ending with the second suffix (assuming
the root filenames are the same). Either of these formats can
be used:
.suffix.suffix:
.suffix:
The second form means that the root filename depends on the
filename with the corresponding suffix.
Commands
Commands are grouped below the dependency line and are
typed on lines that begin with a tab. If a command is preceded
by a hyphen (-), make ignores any error returned. If a
command is preceded by an at sign (@), the command line
won’t echo on the display (unless make is called with -n).
Macro definitions
These have the following form:
name =string
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make
or:
definename
string
endef
Blank space is optional around the =.
Include statements
Similar to the C include directive, these have the form:
includefiles
Internal macros
$? The list of prerequisites that have been changed more recently
than the current target. Can be used only in normal description-
file entries, not in suffix rules.
$@The name of the current target, except in description-file
entries for making libraries, where it becomes the library
name. Can be used both in normal description-file entries and
in suffix rules.
$< The name of the current prerequisite that has been modified
more recently than the current target.
$* The name (without the suffix) of the current prerequisite that
has been modified more recently than the current target. Can
be used only in suffix rules.
$%The name of the corresponding .o file when the current target
is a library module. Can be used both in normal description-
file entries and in suffix rules.
$^ A space-separated list of all dependencies with no duplications.
$+ A space-separated list of all dependencies, which includes
duplications.
Pattern rules
These are a more general application of the idea behind suffix
rules. If a target and a dependency both contain %, GNU make will
substitute any part of an existing filename. For instance, the stan-
dard suffix rule:
$(cc) -o $@ $<
can be written as the following pattern rule:
%.o : %.c
$(cc) -o $@ $<
Macro modifiers
D The directory portion of any internal macro name except $?.
Valid uses are:
$(*D) $$(@D) $(?D) $(<D)
$(%D) $(@D) $(^D)
F The file portion of any internal macro name except $?. Valid
uses are:
$(*F) $$(@F) $(?F) $(<F)
$(%F) $(@F) $(^F)
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make
Functions
$(subst from,to,string)
Replace all occurrences of from with to in string.
$(patsubst pattern,to,string)
Similar to subst, but treat % as a wildcard within pattern.
Substitute to for any word in string that matches pattern.
$(strip string)
Remove all extraneous whitespace.
$(findstring substring,mainstring)
Return substring if it exists within mainstring; otherwise,
return null.
$(filter pattern,string)
Return those words in string that match at least one word in
pattern. pattern may include the wildcard %.
$(filter-out pattern,string)
Remove those words in string that match at least one word in
pattern. pattern may include the wildcard %.
$(sort list)
Return list, sorted in lexical order.
$(dir list)
Return the directory part (everything up to the last slash) of
each filename in list.
$(notdir list)
Return the nondirectory part (everything after the last slash) of
each filename in list.
$(suffix list)
Return the suffix part (everything after the last period) of each
filename in list.
$(basename list)
Return everything but the suffix part (everything up to the last
period) of each filename in list.
$(addsuffix suffix,list)
Return each filename given in list with suffix appended.
$(addprefix prefix,list)
Return each filename given in list with prefix prepended.
$(join list1,list2)
Return a list formed by concatenating the two arguments
word by word (e.g., $(join a b,.c .o) becomes a.c b.o).
$(word n,string)
Return the nth word of string.
$(wordlist start,end,string)
Return words in string between word start and word end,
inclusive.
$(words string)
Return the number of words in string.
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make
$(firstword list)
Return the first word in the list list.
$(wildcard pattern)
Return a list of existing files in the current directory that
match pattern.
$(foreach variable,list,string)
For each whitespace-separated word in list, expand its value
and assign it to variable; then expand string, which usually
contains a function referencing variable. Return the list of
results.
$(if condition,then-string[,else-string])
Expand string condition if it expands to a nonempty string,
then expand the then-string. If condition expands to an empty
string, return the empty string or, if specified, expand and
return the else-string.
$(call variable,parameters)
Expand each item in comma-separated list parameters and
assign it to a temporary variable, $(n), where n is an incre-
mented number beginning with 0. Then expand variable, a
string referencing these temporary variables, and return the
result.
$(origin variable)
Return one of the following strings that describes how variable
was defined: undefined, default, environment, environment
override, file, command line, override, or automatic.
$(shell command)
Return the results of command. Any newlines in the result are
converted to spaces. This function works similarly to back-
quotes in most shells.
$(error string)
When evaluated, generate a fatal error with the message string.
$(warning string)
When evaluated, generate a warning with the message string.
Macro string substitution
$(macro:s1=s2)
Evaluates to the current definition of $(macro), after substi-
tuting the string s2 for every occurrence of s1 that occurs
either immediately before a blank or tab, or at the end of the
macro definition.
Special target names
.DEFAULT:
Commands associated with this target are executed if make
can’t find any description-file entries or suffix rules with which
to build a requested target.
.DELETE_ON_ERROR:
If this target exists in a Makefile, delete the target of any rule
whose commands return a nonzero exit status.
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makedbm
.EXPORT_ALL_VARIABLES:
If this target exists, export all macros to all child processes.
.IGNORE:
Ignore error codes. Same as the -i option.
.INTERMEDIATE:
This target’s dependencies should be treated as intermediate
files.
.NOTPARALLEL:
If this target exists in a Makefile, run make serially, ignoring
option -j.
.PHONY:
Always execute commands under a target, even if it is an
existing, up-to-date file.
.PRECIOUS:
Files you specify for this target are not removed when you
send a signal (such as an interrupt) that aborts make or when
a command line in your description file returns an error.
.SECONDARY:
Like .INTERMEDIATE, this target’s dependencies should be
treated as intermediate files, but never automatically deleted.
.SILENT:
Execute commands, but do not echo them. Same as the -s option.
.SUFFIXES:
Suffixes associated with this target are meaningful in suffix
rules. If no suffixes are listed, the existing list of suffix rules is
effectively “turned off.”
makedbm makedbm [options]infileoutfile
makedbm [option]
NFS/NIS command. Create or dump an NIS dbm file. makedbm will
take a text infile and convert it to a gdbm database file named outfile.
This file is suitable for use with ypserv. Each line of the input file is
converted to a single record. All characters up to the first TAB or
SPACE form the key, and the rest of the line is the data. If a line ends
with \&, the data for that record is continued onto the next line.
The # character is given no special treatment. infile can be -, in
which case the standard input is read.
makedbm generates two special keys: the YP_M*ER_NAME key,
which is the value of the current host (unless another name is speci-
fied with -m), and the YP_L*_MODIFIED key, which is the date of
infile (or the current time if infile is -).
Options
-a Add support for mail aliases.
-b Insert YP_INTERDOMAIN key into map. This indicates that
ypserv should fall back to DNS lookups when a host’s address
is not found in NIS.
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makemap
-c Send a YPPROC_CLEAR signal to ypserv, causing it to clear
all cached entries.
-i file_name
Create a YP_INPUT_NAME key with the value file_name.
-l Convert keys of the given map to lowercase.
-m master_name
Specify the value of the YP_M*ER_NAME key. The default
value is the current hostname.
--no-limit-check
Don’t enforce NIS size limits for keys or data.
-o file_name
Create a YP_OUTPUT_NAME key with the value file_name.
-r Treat lines beginning with # as comments. Do not include
them in the datafile.
-s Add the key YP_SECURE, indicating that ypserv should
accept connections to the database only from secure NIS
networks.
-u filename
Undo a gdbm file: print out a dbm file, one entry per line,
with a single space separating keys from values.
Example
It’s easy to write shell scripts to convert standard files such as /etc/
passwd to the key-value form used by makedbm. For example, the
awk program:
BEGIN { FS =":";OFS = "\t";}{ print $1, $0}
takes the /etc/passwd file and converts it to a form that can be read
by makedbm to make the NIS file passwd.byname. That is, the key
is a username and the value is the remaining line in the /etc/passwd
file.
makemap makemap [options]typename
System administration command. Create database maps for use by
sendmail in keyed map lookups. makemap will read from stan-
dard input and create a database file of type type with filename
name.db. If the TrustedUser option is set in /etc/sendmail.cf and
makemap is invoked as root, the ouput file will be owned by
TrustedUser.
Input should be formatted as:
key value
Comment lines with #. Indicate parameter substitution with %n.
Specify a literal % character by entering it twice: %%. The type
may be btree or hash.
Options
-c size
Specify hash or B-Tree cache size.
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man
-C file
Look up TrustedUser in the specified sendmail configuration
file.
-d Allow duplicate entries. Valid only with btree type maps.
-D x
Treat x as the comment marker instead of #.
-e Allow empty value data fields.
-f Suppress conversion of uppercase to lowercase.
-l List supported map types.
-N Append the zero-byte string terminator specified in send-
mail’s configuration file to mapped entries.
-o Append to existing file instead of replacing it.
-r If some keys already exist, replace them. (By default,
makemap will exit when encountering a duplicated key.)
-s Ignore safety checks.
-t delimiter
Use delimiter instead of whitespace.
-u Undo a map: print out the specified database file, one entry
per line.
-v Verbose mode.
man man [options] [section] [title]
Display information from the online reference manuals. man
locates and prints the named title from the designated reference
section.
Traditionally, manpages are divided into nine sections, where
section 1 consists of user commands, section 2 contains system
calls, and so forth (see “Section names,” coming up, for the full
list). By default, all sections are consulted, so the section option
serves to bypass the most common entry and find an entry of the
same name in a different section (e.g., man 2 nice).
Numerous other utilities—such as info, xman, and the Konqueror
browser—can also display manpages.
Options
-a Show all pages matching title.
-B Specify the browser to use on HTML files. Overrides the
BROWSER environment variable. The default is /usr/bin/less -is.
-c Reformat output even if there is a current cat file.
-Cfile
Specify a configuration file to use. Default is /etc/man.config.
-d Display debugging information but not the manpage.
-D Display debugging information and also display the manpage.
-f Same as whatis command.
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man
-F, --preformat
Format the manpage but do not display it.
-h, --help
Print a help message and exit.
-Hcommand
Specify a command to render HTML files as text. Overrides the
HTMLPAGER environment variable. The default is /bin/cat.
-k Same as apropos command.
-K directory
A kind of super-k option. Search for a term in all manpages
and display the name of each page, along with a prompt asking
whether you want to view the page. This can be very slow.
-m systems
Search manual pages on the specified system or systems.
systems should be a comma-separated list.
-M path
Search for manual pages in path. Ignore -m option.
-p preprocessors
Preprocess manual pages with preprocessors before turning
them over to nroff, troff, or groff. Always runs soelim first to
read in files to be included in the one currently being
processed. preprocessors can be any combination of e for eqn,
g for grap, p for pic, r for refer, t for tbl, and v for vgrind.
-Ppager
Specify the pager to use. Overrides the MANPAGE environ-
ment variable. The default is /usr/bin/less -is.
-S sections
Colon-separated list of sections to look in for an entry.
-t Format the manual page with /usr/bin/groff -Tgv -mandoc.
-w, -W, --path
Print only the pathnames of entries on standard output, one
per line.
Section names
Manual pages are divided into sections for various audiences:
1 Executable programs or shell commands.
2 System calls (functions provided by the kernel).
3 Library calls (functions within system libraries).
4 Special files (usually found in /dev).
5 File formats and conventions (e.g., /etc/passwd).
6 Games.
7 Macro packages and conventions.
8 System administration commands (usually only for a privileged
user).
9 Kernel routines (nonstandard).
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md5sum
manpath manpath [options]
Attempt to determine path to manual pages. Check $MANPATH
first; if that is not set, consult /etc/man.conf, user environment vari-
ables, and the current working directory. The manpath command
is a symbolic link to man and is equivalent to man --path. Most of
the options are ignored for manpath.
Options
-d, --debug
Print debugging information.
-h Print help message and then exit.
md5sum md5sum [option] [files]
md5sum [option] --check [file]
Compute or check 128-bit MD5 checksums. Used to verify that no
change has been made to a file. With no files or - specified, read
from standard input. The exit status is 0 for success and nonzero
for failure.
Options
-b, --binary
Read the files in binary mode.
-c, --check
Check the MD5 sum and file information in the file argument
(or standard input) against the corresponding files and verify
that they are consistent. The input must have been generated
by an earlier md5sum command.
--help
Print usage information and exit.
--status
Don’t generate output messages; the exit code indicates
success or failure. Used only with --check.
--string=string
Compute the MD5 sum for the specified string. This option
does not take a file argument. Put quotes around the string if it
contains spaces.
-t, --text
Read files in text mode. The default.
--version
Print version information and exit.
-w, --warn
Warn about improperly formatted checksum lines. Used only
with --check.
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merge
merge merge [options]file1file2 file3
Perform a three-way file merge, putting the result in file1. The
effect is easiest to understand if file2 is considered the original
version of a file, file3 an altered version of file2, and file1 a later
altered version of file2.
After the merge, file1 contains both the changes from file2 to file1
and the changes from file2 to file3. In other words, file1 keeps its
changes and incorporates the changes in file3 as well. merge does
not change file2 or file3.
If a line from file2 was changed in different ways in both file1 and
file3, merge recognizes a conflict. By default, the command outputs
a warning and puts brackets around the conflict, with lines
preceded by <<<<<<< and >>>>>>>. A typical conflict looks like
this:
<<<<<<< file1
relevant lines from file1
=======
relevant lines from file3
>>>>>>> file3
If there are conflicts, the user should edit the result and delete one
of the alternatives.
Options
-A Output conflicts using the -A style of diff3. This merges all
changes leading from file2 to file3 into file1 and generates the
most verbose output.
-e Don’t warn about conflicts.
-E Output conflict information in a less verbose style than -A;
this is the default.
-L label
Specify up to three labels to be used in place of the corre-
sponding filenames in conflict reports. That is:
merge –Lx -Ly -Lzfile_afile_b file_c
generates output that looks as if it came from x, y, and z
instead of from file_a, file_b, and file_c.
-p Send results to standard output instead of overwriting file1.
-q Quiet; do not warn about conflicts.
-V Print version number.
mesg mesg [option]
Change the ability of other users to send write messages to your
terminal. With no options, display the permission status.
Options
n Forbid write messages.
y Allow write messages (the default).
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mkdosfs
mkdir mkdir [options]directories
Create one or more directories. You must have write permission in
the parent directory in order to create a directory. See also rmdir.
The default mode of the new directory is 0777, modified by the
system or user’s umask.
Options
-m mode, --mode mode
Set the access mode for new directories. See chmod for an
explanation of acceptable formats for mode.
-p, --parents
Create intervening parent directories if they don’t exist.
-v, --verbose
Print a message for each directory created.
--help
Print help message and then exit.
--version
Print version number and then exit.
-Z context, --context=context
Set security context in SELinux.
Examples
Create a read-only directory named personal:
mkdir -m 444 personal
The following sequence:
mkdir work; cd work
mkdir junk; cd junk
mkdir questions; cd ../..
can be accomplished by typing this:
mkdir -p work/junk/questions
mkdosfs mkdosfs [options]device [blocks]
mkfs.msdos [options]device [blocks]
System administration command. Format device as an MS-DOS
filesystem. You may specify the number of blocks on the device or
allow mkdosfs to guess.
Options
-A Create an Atari MS-DOS filesystem.
-b backup-sector
Specify sector for backup boot sector. The default value
depends on the number of reserved sectors, but is usually
sector 6.
-c Scan device for bad blocks before execution.
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mke2fs
-C Create and format a file suitable for use on a floppy disk. The
device given on the command line should be a filename, and
the number of blocks must also be specified.
-f n
Specify number of File Allocation Tables (FATs) to create
(either 1 or 2).
-F fat-size
Create File Allocation Tables (FATs) of size fat-size. By default
this will be between 12 and 16 bits. Set to 32 to create a
FAT32 filesystem.
-i volume-id
Use the specified 32-bit hexadecimal volume-id instead of
calculating a number based on the time of creation.
-I Force installation to a device without partitions. This is useful
when formating magneto-optical disks.
-l file
Read list of bad blocks from file.
-m message-file
Set the message to be used when the filesystem is booted
without an installed operating system to the contents of the
file message-file. The message may be up to 418 bytes in size.
If filename is a hyphen, read text from standard input.
-n label
Set volume name for filesystem to label. The volume name
may be up to 11 characters long.
-r maximum-entries
Set the maximum-entries allowed in the root directory. The
default is 112 or 224 for floppies, and 512 for hard disks.
-R reserved-sectors
Create the specified number of reserved-sectors. The default
depends on the size of the File Allocation Table (FAT). For 32-
bit FAT, the default is 32; for all other sizes, the default is 1.
-s sectors
Set the number of disk sectors per cluster. The number must
be a power of 2.
-S sector-size
Create logical sectors of sector-size bytes. Size must be a power
of 2 and at least 512 bytes.
-v Print verbose information about progress.
mke2fs mke2fs [options]device [blocks]
mkfs.ext2 [options]device [blocks]
System administration command. Format device as a Linux Second
Extended Filesystem. You may specify the number of blocks on the
device or allow mke2fs to guess.
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mke2fs
Options
-b block-size
Specify block size in bytes.
-c Scan device for bad blocks before execution.
-E featurelist
Specify extended features. This option’s parameters may be
given in a comma-separated list:
stride=size
Configure filesystem for a RAID array. Set stride size to
size blocks per stripe.
resize=blocks
Reserve descriptor table space to grow filesystem to the
specified number of blocks.
-f fragment-size
Specify fragment size in bytes.
-F Force mke2fs to run even if filesystem is mounted or device is
not a block special device. This option is probably best avoided.
-i bytes-per-inode
Create an inode for each bytes-per-inode of space. bytes-per-
inode must be 1024 or greater; it is 4096 by default.
-j Create an ext3 journal. This is the same as invoking mkfs.ext3.
-J parameterlist
Use specified parameterlist to create an ext3 journal. The
following two parameters may be given in a comma-separated
list:
size=journal-size
Create a journal of journal-size megabytes. The size may
be between 1024 filesystem blocks and 102,400 file-
system blocks in size (e.g., 1–100 megabytes if using 1K
blocks, 4–400 megabytes if using 4K blocks).
device=journal-device
Use an external journal-device to hold the filesystem
journal. The journal-device can be specified by name, by
volume label, or by UUID.
-l filename
Consult filename for a list of bad blocks.
-L label
Set volume label for filesystem.
-m percentage
Reserve percentage percent of the blocks for use by privileged
users.
-M directory
Set the last mounted directory for filesystem to directory.
-n Don’t create the filesystem; just show what would happen if it
were run. This option is overridden by -F.
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mke2fs
-N inodes
Specify number of inodes to reserve for filesystem. By default,
this number is calculated from the number of blocks and the
inode size.
-o os
Set filesystem operating system type to os. The default value is
usually Linux.
-O featurelist
Use specified featurelist to create filesystem. The sparse_super
and filetype features are used by default on kernels 2.2 and
later. The following parameters may be given in a comma-
separated list:
dir_index
Use hashed B-trees to index directories.
filetype
Store file type information in directory entries.
has_journal
Create an ext3 journal. Same as using the -j option.
journal_dev
Prepare an external journaling device by creating an ext3
journal on device instead of formatting it.
sparse_super
Save space on a large filesystem by creating fewer super-
block backup copies.
-q Quiet mode.
-r revision
Set filesystem revision number to revision.
-S Write only superblock and group descriptors; suppress writing
of inode table and block and inode bitmaps. Useful only when
attempting to salvage damaged systems.
-T use
Set bytes-per-inode based on the intended use of the file-
system. Supported filesystem usage types are defined in /etc/
mke2fs.conf. Common types include:
news
Four kilobytes per inode.
largefile
One megabyte per inode.
largefile4
Four megabytes per inode.
-v Verbose mode.
-V Print version number, then exit.
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mkfs.ext3
mkfifo mkfifo [option]names
Make one or more named pipes (FIFOs) with the specified names.
Options
-m mode, --mode=mode
Set permission mode. Default is 666, with the bits in the
umask subtracted.
--help
Print help information and exit.
--version
Print version information and exit.
mkfs mkfs [options] [fs-options]filesys [blocks]
System administration command. Construct a filesystem on a
device (such as a hard disk partition). filesys is either the name of
the device or the mountpoint. mkfs is actually a frontend that
invokes the appropriate version of mkfs according to a filesystem
type specified by the -t option. For example, a Linux Second
Extended Filesystem uses mkfs.ext2 (which is the same as
mke2fs); MS-DOS filesystems use mkfs.msdos. fs-options are
options specific to the filesystem type. blocks is the size of the file-
system in 1024-byte blocks.
Options
-V Produce verbose output, including all commands executed to
create the specific filesystem.
-t fs-type
Tells mkfs what type of filesystem to construct.
Filesystem-specific options
These options must follow generic options and cannot be
combined with them. Most filesystem builders support these three
options:
-c Check for bad blocks on the device before building the
filesystem.
-l file
Read the file file for the list of bad blocks on the device.
-v Produce verbose ouput.
mkfs.ext3 mkfs.ext3 [options]devicesize
Create a journaling ext3 filesystem. Options are identical to
mke2fs. See mkfs.
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mkisofs
mkisofs mkisofs [options]-o pathspecs
Generate an ISO9660/Joliet/HFS filesystem for writing to a CD.
(HFS is the native Macintosh Hierarchical File System.) mkisofs
takes a snapshot of a directory tree and generates a binary image
that corresponds to an ISO9660 or HFS filesystem when it is
written to a block device. Each specified pathspec describes the
path of a directory tree to be copied into the ISO9660 filesystem; if
multiple paths are specified, the files in all the paths are merged to
form the image.
mkisofs is now generally a symbolic link to genisoimage.
mklost+found mklost+found
System administration command. Create a lost+found directory in
the current working directory. Intended for Linux Second
Extended Filesystems.
mknod mknod [options]name type [major minor]
Create a special file (a file that can send or receive data). Special
files can be character files (read one character at a time), block files
(read several characters at a time), or FIFO pipes (see mkfifo).
To choose which type of device to create, use one of the following
arguments:
p Create a FIFO file (named pipe). You do not need to specify
the major and minor device numbers.
b Create a block file. You must specify the major and minor
device numbers the file represents.
c or u
Create a character file. You must specify the major and minor
device numbers the file represents.
Linux’s /dev/MAKEDEV utility is useful for creating one or more
devices of a given type in a single command.
Options
--help
Print usage information and exit.
-m mode, --mode=mode
Set the file mode of the device, as with chmod. The default
mode is a=rw unless you have chosen other settings via
umask.
--version
Print version information and exit.
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mktemp
mkswap mkswap [options]device
System administration command. Prepare swapspace on device: a
disk partition or a prepared file. This command can create old and
new style swap areas. The older style provides backward compati-
bility with 2.2 kernels, but is less efficient and more limited in size.
The mkswap command has some dangerous options we have
omitted here. They provide backward compatibility and solutions
to problems with older libraries, but can destroy a disk if specified
incorrectly.
Options
-c Check for bad blocks before creating the swapspace.
-L label
Create a label for use with swapon.
-v0Create an old style swap area.
-v1Create a new style swap area. (The default behavior on newer
kernels.)
mktemp mktemp [options] [template]
Generate a unique temporary filename for use in a script. The file-
name is based on the specified template, which may be any
filename with at least six Xs appended (e.g., /tmp/mytemp.
XXXXXX). mktemp replaces the Xs with the current process
number and/or a unique letter combination. The file is created with
mode 0600 (unless -u is specified), and the filename is written to
standard output. With no template specified, the default file tmp.
XXXXXXXXXX is created.
Options
-d, --directory
Make a directory, not a file.
--help
Print usage information and exit.
-q, --quiet
Fail silently in case of error. Useful to prevent error output
from being sent to standard error.
-u, --dryrun
Operate in “unsafe” mode and unlink the temporary file
before mktemp exits. Use of this option is not recommended.
-V, --version
Print version information and exit.
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modinfo
modinfo modinfo [options]object-file
System administration command. Print information about kernel
module object-file. Information is read from tag names in the mod-
info section of the module file. By default, it will print the module’s
filename, description, author, license, and parameters.
Options
-0, --null
Separate fields with the null character instead of newlines.
-F fieldname, --field fieldname
Print only the value of the specified fieldname (e.g., author,
license, depends, etc.).
-h, --help
Print usage message, then exit.
-k kernel
Specify kernel to use (e.g., a kernel other than the running
kernel).
-V, --version
Print version number of the module.
modprobe modprobe [options] [modules] [moduleoptions]
System administration command. With no options, attempt to load
the specified module, as well as all modules on which it depends. If
more than one module is specified, attempt to load further modules
only if the previous module failed to load. When specifying a
module, use only its name without its path or trailing .o. modprobe
will pass to the kernel any options following the module name.
Options
-a, --all
Load all modules matching the given wildcard.
-c, --showconfig
Print modprobe’s current configuration.
-C file, --config file
Read additional configuration fromfile instead of/etc/modules.conf.
-f, --force
Ignore all versioning information during module insertion. Even
if the module does not match the running kernel, modprobe
will try to insert it anyway.
--force-modversion
Ignore module versioning mismatches.
--force-vermagic
Ignore kernel versioning mismatches.
--first-time
Return failure if told to insert a module that is already present
or remove a module that is not loaded. Normally, modprobe
will return success if asked to perform an unnecessary action.
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more
-i, --ignore-install, --ignore-remove
Ignore any install and remove directives in the configuration
file.
-l, --list
List modules matching the given wildcard (or “*” if no wild-
card is given).
-n, --dry-run
Perform all of the actions except actually inserting or removing
the module.
-q, --quiet
Suppress warnings during failure to load a module and
continue processing other modules.
-r, --remove
Remove the specified modules, as well as the modules on
which they depend.
-s, --syslog
Send error messages to syslogd instead of to standard error.
-ttype, --type type
Load only a specific type of module.
-v, --verbose
Print commands as they are executed.
-V, --version
Print version, then exit.
more more [options] [files]
Display the named files on a terminal, one screenful at a time. See
less for an alternative to more.
Options
+num
Begin displaying at line number num.
-num number
Set screen size to number lines.
+/pattern
Search for pattern and begin displaying at that point.
-c Repaint screen from top instead of scrolling.
-d Display the prompt “[Press space to continue, ‘q’ to quit]”
instead of ringing the bell. Also display “[Press ‘h’ for instruc-
tions]” in response to illegal commands.
-f Count logical rather than screen lines. Useful when long lines
wrap past the width of the screen.
-l Ignore form-feed (Ctrl-L) characters.
-p Page through the file by clearing each window instead of
scrolling. This is sometimes faster.
-s Squeeze; display multiple blank lines as one.
-u Suppress underline characters.
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more
Commands
All commands in more are based on vi commands. You can specify
a number before many commands to have them executed multiple
times. For instance, 3:p causes more to skip back three files, the
same as issuing :p three times. The optional number is indicated by
num in the following list:
SPACE
Display next screen of text.
z Display next num lines of text, and redefine a screenful to num
lines. Default is one screenful.
RETURN
Display next num lines of text, and redefine a screenful to num
lines. Default is one line.
d, ^D
Scroll num lines of text, and redefine scroll size to num lines.
Default is one line.
q, Q, INTERRUPT
Quit.
s Skip next num lines of text. Default is one line.
f Skip forward num screens of text. Default is one screen.
b, ^B
Skip backward num screens of text. Default is one screen.
Does not work on pipes.
' Return to point where previous search began.
= Print number of current line.
/pattern
Search for pattern, skipping to numth occurrence if an argu-
ment is specified.
?, h
Display a summary of commands.
n Repeat last search, skipping to numth occurrence if an argu-
ment is specified.
!cmd, :!cmd
Invoke shell and execute cmd in it.
v Invoke an editor on the file at the current line. Use the editor
in the environment variable VISUAL if defined, or EDITOR if
that is defined; otherwise, default to vi.
^L Redraw screen.
:n Skip to next file, or numth file if an argument is specified.
:p Skip to previous file, or numth previous if an argument is
specified.
:f Print current filename and line number.
. Reexecute previous command.
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mount
Examples
Page through file in “clear” mode, and display prompts:
more –cdfile
Format doc to the screen, removing underlines:
nroffdoc| more -u
View the manpage for the more command; begin at the first
appearance of the word “scroll”:
man more|more +/scroll
mount mount [options] [[device]directory]
System administration command. Mount a file structure. The file
structure on device is mounted on directory. If no device is speci-
fied, mount looks for an entry in /etc/fstab to find out what device
is associated with the given directory. The directory, which must
already exist and should be empty, becomes the name of the root
of the newly mounted file structure. If mount is invoked with no
arguments, it displays the name of each mounted device, the direc-
tory on which it is mounted, its filesystem type, and any mount
options associated with the device.
Options
-a Mount all filesystems listed in /etc/fstab. Use -t to limit this to
all filesystems of a particular type.
--bind olddirectory newdirectory
Bind a mounted subtree to a new location. The tree will be
available from both the old and new directory. This binding
does not include any volumes mounted below the specified
directory.
-f Fake mount. Go through the motions of checking the device
and directory, but do not actually mount the filesystem.
-F When used with -a, fork a new process to mount each system.
-h Print help message, then exit.
-l When reporting on mounted filesystems, show filesystem
labels for filesystems that have them.
-L label
Mount filesystem with the specified label.
--move olddirectory newdirectory
Move a mounted device to a new location. Maintains options
and submounts.
-n Do not record the mount in /etc/mtab.
-o option
Qualify the mount with a mount option. Many filesystem
types have their own options. The following are common to
most filesystems:
async
Read input and output to the device asynchronously.
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mount
atime
Update inode access time for each access. This is the
default behavior.
auto
Allow mounting with the -a option.
defaults
Use all options’ default values (async, auto, dev, exec,
nouser, rw, suid).
dev
Interpret any special devices that exist on the filesystem.
dirsync
Perform all directory updates to the filesystem
synchronously.
exec
Allow binaries to be executed.
_netdev
Filesystem is a network device requiring network access.
noatime
Do not update inode access time for each access.
noauto
Do not allow mounting via the -a option.
nodev
Do not interpret any special devices that exist on the
filesystem.
noexec
Do not allow the execution of binaries on the filesystem.
nofail
Do not report errors if device doesn’t exist.
nosuid
Do not acknowledge any suid or sgid bits.
nouser
Only privileged users will have access to the filesystem.
remount
Expect the filesystem to have already been mounted, and
remount it.
ro
Allow read-only access to the filesystem.
rw
Allow read/write access to the filesystem.
suid
Acknowledge suid and sgid bits.
sync
Read input and output to the device synchronously.
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mount
user
Allow unprivileged users to mount or unmount the file-
system. The defaults on such a system will be nodev,
noexec, and nosuid, unless otherwise specified.
users
Allow any user to mount or unmount the filesystem. The
defaults on such a system will be nodev, noexec, and
nosuid, unless otherwise specified.
-O option
Limit systems mounted with -a by -O’s filesystem options (as
used with -o). Use a comma-separated list to specify more
than one option, and prefix an option with no to exclude file-
systems with that option. Options -t and -O are cumulative.
-r Mount filesystem read-only.
--bind olddirectory newdirectory
Bind a mounted subtree to a new location. The tree will be
available from both the old and new directory. Include any
volumes mounted below the specified directory.
-s Where possible, ignore mount options specified by -o that are
not supported by the filesystem.
-t type
Specify the filesystem type. Possible values include adfs, affs,
autofs, coda, cramfs, devpts, efs, ext2, ext3, hfs, hpfs,
iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4,
reiserfs, romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, vfat,
xfs, and xiafs. The default type is iso9660. The type auto may
also be used to set mount to autodetect the filesystem. When
used with -a, this option can limit the types mounted. Use a
comma-separated list to specify more than one type to mount.
Prefix a list (or type) with no to exclude those types.
-U uuid
Mount filesystem with the specified uuid.
-v Display mount information verbosely.
-V Print version, then exit.
-w Mount filesystem read/write. This is the default.
Files
/etc/fstab
List of filesystems to be mounted and options to use when
mounting them.
/etc/mtab
List of filesystems currently mounted and the options with
which they were mounted.
/proc/partitions
Used to find filesystems by label and uuid.
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mountd
mountd rpc.mountd [options]
NFS/NIS command. NFS mount request server. mountd reads the
file /etc/exports to determine which filesystems are available for
mounting by which machines. It also provides information about
which filesystems are mounted by which clients. See also nfsd.
Options
-d kind, --debug kind
Specify debugging facility. Accepted values for kind are
general, call, auth, parse, and all.
-f file, --exports-file file
Read the export permissions from file instead of /etc/exports.
-F, --foreground
Run mountd in the foreground.
-h, --help
Print help message, then exit.
-n, --no-tcp
Use UDP for mounts.
-N n, --no-nfs-version n
Do not offer NFS version n.
-o n, --descriptors n
Allow no more than n open file descriptors. The default is 256.
-p n, --port n
Bind to specified port instead of accepting a port from
portmapper.
-r, --reverse-lookup
Perform a reverse lookup on ip address when requested to
report mounting hosts (a DUMP request).
-v, --version
Print the version number, then exit.
-V n, --nfs-version n
Explicity offer NFS version n.
Files
/etc/exports
Information about mount permissions.
/var/lib/nfs/rmtab
List of filesystems currently mounted by clients.
mt mt [option]operation [count |arguments]
Control a magnetic tape drive used to back up or restore system
data. The version of the mt command documented here is the
GNU version of mt. The operation argument determines what
action will be taken, and, unless the -f or -t option is used, the
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mt
action is applied to the default tape drive named in the TAPE
environment variable. The count argument determines how many
times the operation is to be repeated. If not specified, it defaults to
1. Some operations take one or more arguments other than a
count, as noted in the descriptions below.
Options
-f device, -t device
Name the tape device to use. This may be a local device, a
character special file (see mknod), or a remote device, named
in the format host:/path/to/drive or user@host:path/to/drive.
--help
Print usage message and exit.
-V, --version
Print version number and exit. Also tells you if you are
running the GNU version of mtor the mt-stversion.
Operations
mt can perform the following operations on tape drives. Unique
abbreviations are allowed.
asf n
Move to file number n on the tape. This is the same as
rewinding the tape and moving forward n files with fsf.
bsf n
Move backward n files, positioning the tape at the last block of
the previous file.
bsfm n
Move backward n file marks, to a position on the side of the
file mark closer to the beginning of the tape.
bsr n
Move backward n records.
eof, weof n
Write n end-of-file (EOF) notations at the current location on
the tape.
erase
Erase the tape.
fsf n
Move forward n files, positioning the tape at the first block of
the next file.
fsfm n
Move forward n file marks, to a position on the side of the file
mark closer to the beginning of the tape.
fsr n
Move forward n records.
offline, rewoffl
Rewind and unload the tape (if drive supports unload).
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mv
retension
Used when the tape has become loosely wound, usually
because it has been dropped, shaken, or transported. Rewinds
the tape, moves forward to the end of the tape, then rewinds
again.
rewind
Return to the beginning of the tape.
seek n
Seek to block n on the tape.
status
Display the status of the tape drive.
mv mv [option]sources target
Move or rename files and directories. The source (first column) and
target (second column) determine the result (third column).
The mv command is often aliased as mv -i in the .bashrc file, espe-
cially for the root account, to prevent inadvertently overwriting
files.
Options
-b Back up existing files before removing.
--backup[=type]
Like -b, but can take an argument specifying the type of
version-control file to use for the backup. The value of type
overrides the VERSION_CONTROL environment variable,
which determines the type of backups made. The acceptable
values for version control are:
t, numbered
Always make numbered backups.
nil, existing
Make numbered backups of files that already have them,
and make simple backups of the others. This is the
default.
never, simple
Always make simple backups.
none, off
Never make backups.
Source Target Result
File name (nonexistent) Rename file toname.
File Existing file Overwrite existing file with source file.
Directory name (nonexistent) Rename directory toname.
Directory Existing directory Move directory to be a subdirectory of
existing directory.
One or more files Existing directory Move files to directory.
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named
-f, --force
Force the move, even if target file exists; suppress messages
about restricted access modes. Same as --reply=yes.
--help
Print a help message and then exit.
-i, --interactive
Query user before removing files. Same as --reply=query.
--reply=prompt
Specify how to handle prompt if the destination exists already.
Possible values are yes, no, and query.
--strip-trailing-slashes
Remove trailing slashes from source paths.
-S suffix, --suffix=suffix
Override the SIMPLE_BACKUP_SUFFIX environment vari-
able, which determines the suffix used for making simple
backup files. If the suffix is not set either way, the default is a
tilde (~).
-T, --no-target-directory
Treat the destination as a file.
--target-directory=dir
Move all source files and directories into the specified
directory.
-u, --update
Do not remove a file or link if its modification date is the same
as or newer than that of its replacement.
-v, --verbose
Print the name of each file before moving it.
--version
Print version information and then exit.
named named [options]
TCP/IP command. Internet domain nameserver. named is used by
resolver libraries to provide access to the Internet distributed
naming database. With no arguments, named reads /etc/named.
conf for any initial data and listens for queries on a privileged port.
See RFC 1034 and RFC 1035 for more details.
There are several named binaries available at different Linux
archives, displaying various behaviors. Here we describe named as
provided by Internet Software Consortium’s Berkeley Internet
Name Domain (BIND) version 9.2.x.
Options
-c file
Read configuration information from file instead of /etc/
named.conf.
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namei
-d debuglevel
Print debugging information. debuglevel is a number indi-
cating the level of messages printed.
-f Run named in the foreground.
-g Run named in the foreground and send all log messages to
standard error.
-n n
Specify the number of processors in a multiprocessor system.
Normally named can autodetect the number of CPUs.
-p port
Use port as the port number. Default is 53.
-t dir
Change root to specified directory after reading command
arguments but before reading the configuration file. Useful
only when running with option -u.
-u user
Set the user ID to user after completing any privileged
operations.
-v Print version, then exit.
File
/etc/named.conf
Read when named starts up.
namei namei [options]pathname [pathname . . .]
Follow a pathname until a terminal point is found (e.g., a file,
directory, char device, etc.). If namei finds a symbolic link, it shows
the link and starts following it, indenting the output to show the
context. namei prints an informative message when the maximum
number of symbolic links has been exceeded, making it helpful for
resolving errors resulting from too many levels of links.
Options
-m Show mode bits of each file type in the style of ls (e.g., “rwxr-
xr-x”).
-x Show mountpoint directories with a D rather than a d.
File-type characters
For each line of output, namei prints the following characters to
identify the file types found:
- A regular file.
? An error of some kind.
b A block device.
c A character device.
d A directory.
f: The pathname namei is currently trying to resolve.
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nc
l A symbolic link (both the link and its contents are output).
p A FIFO (named pipe).
s A socket.
nameif nameif [options] [namemacaddress]
System administration command. Assign an interface name to a
network device specified by macaddress, the unique serial number
that identifies a network card. If no name and macaddress are
given, nameif will attempt to read addresses from the configura-
tion file /etc/mactab. Each line of the configuration file should
contain either a comment beginning with # or an interface name
and MAC address.
Options
-c filename
Read interface names and MAC addresses from filename
instead of /etc/mactab.
-s Send any error messages to syslog.
nc nc [options] [host] [port]
TCP/IP command. nc (also known as netcat) is a versatile
networking utility that reads and writes data across network
connections using TCP or UDP. It’s a simple tool that has many
uses. Unlike telnet, you can easily script nc. It can also be used to
listen for as well as make connections.
Options
-C Send CRLF as line ending.
-i seconds
Send and read data one line at a time with a delay of the specified
interval in seconds. By default netcat reads and writes in 8 KB
blocks.
-k Listen for further connections when a current connection
ends. Used with -l.
-l Listen for an incoming connection on the specified port or
ports.
-n Don’t perform any DNS lookups.
-o file
Hex-dump data sent and received to file.
-p [port]
Read from the specified source port.
-r Choose ports randomly.
-s [address]
Read from the specified source IP address.
-u Use UDP instead of the default TCP.
-U Use Unix Domain Sockets instead of the default TCP.
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netstat
-v Verbose output. Use multiple times to increase verbosity. If not
using -n, include reports on forward/reverse DNS mismatches.
-w seconds
Set the inactivity timeout for a connection. Silently close a
connection if idle for more than the specified seconds.
-x address[:port]
Use the proxy found at the specified IP address and port. If no
port is specified, the well-known port for the protocol is used.
-X protocol
Use the specified proxy protocol. Valid values are 4 (SOCKS
v. 4), 5 (SOCKS v. 5) and connect (HTTPS proxy). The
default value is 5.
-z Scan for listening daemons. With this option port can be given
as a port range or sets of ranges.
Examples
Connect to an SMTP port reporting connection information and
timing out after 2 seconds of inactivity:
$nc -w 2 -v remotehost 25
Copy a directory over the network, preserving permissions. On the
receiving server, use this:
$nc -l -p 1234 | tar xzfp -
On the server sending the directory files, use this:
$tar czfp - /dir/ | nc -w 3 remotehost 1234
Perform a simple port scan:
$nc -w 1 -z remotehost 20-80 400-500
netstat netstat [options] [delay]
TCP/IP command. Show network status. Print information on
active sockets, routing tables, interfaces, masquerade connections,
or multicast memberships. By default, netstat lists open sockets.
When a delay is specified, netstat will print new information every
delay seconds.
Options
The first five options (-g, -i, -M, -r, and -s) determine what kind of
information netstat should display.
-g, --groups
Show multicast group memberships.
-i, --interface[=name]
Show all network interfaces, or just the interface specified by
name.
-M, --masquerade
Show masqueraded connections.
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netstat
-r, --route
Show kernel routing tables.
-s, --statistics
Show statistics for each protocol.
-a, --all
Show all entries.
-A family, --protocol=family
Show connections only for the specified address family.
Accepted values are inet, unix, ipx, ax25, netrom, and ddp.
Specify multiple families in a comma-separated list.
-c, --continuous
Display information continuously, refreshing once every second.
-C Print routing information from the route cache.
-e, --extend
Increase level of detail in reports. Use twice for maximum
detail.
-F Print routing information from the forward information data-
base (FIB). This is the default.
-l, --listening
Show only listening sockets.
-n, --numeric
Show network addresses, ports, and users as numbers.
--numeric-hosts
Show host addresses as numbers, but resolve others.
--numeric-ports
Show ports as numbers, but resolve others.
--numeric-users
Show user ID numbers for users, but resolve others.
-N, --symbolic
Where possible, print symbolic host, port, or usernames
instead of numerical representations. This is the default behavior.
-o, --timers
Include information on network timers.
-p, --program
Show the process ID and name of the program owning the
socket.
-t, --tcp
Limit report to information on TCP sockets.
-u, --udp
Limit report to information on UDP sockets.
-v, --verbose
Verbose mode.
-w, --raw
Limit report to information on raw sockets.
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newaliases
newaliases newaliases
Rebuild the mail aliases database, /etc/aliases, after a change.
Return 0 on success, or a number greater than 0 if there was an
error. newaliases must be run whenever /etc/aliases has been
changed for the change to take effect. newaliases is a sendmail
command and is identical to sendmail -bi.
newgrp newgrp [-] [group]
Change user’s current group ID to the specified group. If no
group is specified, change to the user’s login group. The new
group is then used for checking permissions. If - is specified, also
reinitialize the user’s environment.
newusers newusersfile
System administration command. Create or update system users
from entries in file. Each line in file has the same format as an entry
in /etc/passwd, except that passwords are unencrypted and group
IDs can be given as a name or number. During an update, the pass-
word age field is ignored if the user already exists in the /etc/shadow
password file. If a group name or ID does not already exist, it will
be created. If a home directory does not exist, it will be created.
nfsd rpc.nfsd [options]n
System administration command. Launch n kernel threads for the
Network File System (NFS) kernel module. The threads will handle
client filesystem requests. By default, only one thread is launched.
Most systems require eight or more, depending on the number of
NFS clients using the system. Use nfsstat to check NFS performance.
Option
-H hostname, --hosthostname
Specify the hostname or address that will accept NFS requests.
The default is to accept on all addresses.
-N version, --no-nfs-versionversion
Do not provide support for the specified NFS version. By
default support is provided for versions 2, 3, and 4.
-p port, --porthostname
Listen for NFS requests on port instead of the default port
2049.
-T, --no-tcp
Do not accept TCP requests.
-U, --no-udp
Do not accept UDP requests.
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nice
nfsstat nfsstat [options]
System administration command. Print statistics on NFS and
remote procedure call (RPC) activity for both clients and server.
Options
-2, -3, -4
Shows server statistics for version 2, 3, or 4.
-c Display only client-side statistics.
-m, --mounts
Show statistics for mounted filesystems.
-n Display only NFS statistics.
-o facility
Only display statistics for the specified facility. The following
are valid values for facility:
all All of the following facilities.
fh Server file handle cache.
net Network layer statistics.
nfs Same as -n.
rc Server request reply cache.
rpc Same as -r.
-r Display only RPC statistics.
-s Display only server-side statistics.
-z Reset statistics to zero. Use with above options to zero out
specific sets of statistics (e.g., -zr to reset the RPC statistics).
-Z, --sleep
Take a snapshot of current stats then sleep until receiving a
SIGINT signal (e.g., Ctrl-C) then take another snapshot and
display a diff of the two.
nice nice [option] [command [arguments]]
Execute a command (with its arguments) with lower priority (i.e.,
be “nice” to other users). With no command, nice prints the
current scheduling priority (niceness). If nice is a child process, it
prints the parent process’s scheduling priority. Niceness has a
range of -20 (highest priority) to 19 (lowest priority).
Options
--help
Print a help message and then exit.
-n adjustment, -adjustment, --adjustment=adjustment
Run command with niceness incremented by adjustment
(1–19); default is 10. A privileged user can raise the priority by
specifying a negative adjustment (e.g., –5).
--version
Print version information and then exit.
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nm
nm nm [options] [objfiles]
Print the symbol table in alphabetical order from one or more object
files. If no object files are specified, perform operations on a.out.
Output includes each symbol’s value, type, size, name, and so on. A
key letter categorizing the symbol can also be displayed.
Options
-a, --debug-syms
Print debugger symbols.
--defined-only
Display only defined symbols.
-f format, --format=format
Specify output format (bsd, sysv, or posix). Default is bsd.
-g, --extern-only
Print external symbols only.
--help
Print help message, then exit.
-l, --line-numbers
Print source filenames and line numbers for each symbol from
available debugging information.
-n, -v, --numeric-sort
Sort the external symbols by address.
-p, --no-sort
Don’t sort the symbols at all.
-r, --reverse-sort
Sort in reverse, alphabetically or numerically.
-s, --print-armap
Include mappings stored by ar and ranlib when printing
archive symbols.
--size-sort
Sort by size.
-t radix, --radix=radix
Use the specified radix for printing symbol values. Accepted
values are d for decimal, o for octal, and x for hexadecimal.
--target=format
Specify an object code format other than the system default.
-u, --undefined-only
Report only the undefined symbols.
-A, -o, --print-file-name
Print input filenames before each symbol.
-B Same as --format=bsd.
-C, --demangle[=style]
Translate low-level symbol names into readable versions. You
may specify a style to use when demangling symbol names
from a foreign compiler.
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nsupdate
-D, --dynamic
Print dynamic, not normal, symbols. Useful only when
working with dynamic objects (some kinds of shared libraries,
for example).
-P, --portability
Same as -f posix.
-S, --print-size
Print the size of defined symbols.
-V, --version
Print nm’s version number on standard error.
nohup nohupcommand [arguments]
nohupoption
Run the named command with its optional command arguments,
continuing to run it even after you log out (make command
immune to hangups—i.e., no hangup). Terminal output is
appended to the file nohup.out by default, or $HOME/nohup.out if
nohup.out can’t be written to. Modern shells preserve background
commands by default; this command is necessary only in the orig-
inal Bourne shell.
Options
--help
Print usage information and exit.
--version
Print version information and exit.
nslookup nslookup
TCP/IP command. Query Internet domain nameservers. nslookup
is deprecated; its functionality is replaced by the dig and host
commands. nslookup may not be included in some distributions.
nsupdate nsupdate [options] [filename]
System administration command. Interactively submit dynamic
DNS update requests to a nameserver. Use nsupdate to add or
remove records from a zone without manually editing the zone file.
Commands may be entered interactively or read from filename. An
update message is built from multiple commands, some establishing
prerequisites, some adding or deleting resource records. Messages
are executed as a single transaction. A blank line or the send
command will send the current message. Lines beginning with a
semicolon are treated as comments. For additional information on
dynamic DNS updates, see RFC 2136.
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nsupdate
Options
-d Print additional tracing information usable for debugging.
-k keyfile
Read encrypted transaction signature key from keyfile. The
key should be encrypted using the HMAC-MD5 algorithm.
Keyfiles are generated by the dnssec-keygen command.
-r n
Retry UDP n times. Default is 3.
-t seconds
Set request timeout. Default is 300 seconds. 0 disables timeout.
-u seconds
Set UDP retry interval. Default is 3 seconds. If 0, then interval
is computed from the time out and retry values.
-v Use TCP instead of UDP to send update requests.
-y keyname:secret
Generate transaction signature from specified keyname and
secret.
Interactive commands
answer
Print answer.
class classname
Set default class to classname instead of the normal default IN.
key keyname secret
Generate transaction signature from specified keyname and
secret. This command overrides command-line options -k or -y.
local address [port]
Use local address and, if specified, port to send updates.
prereq criteria
Specify prerequisites for updating a domain. Provide the
criteria in one of the following forms:
nxdomain domain-name
Perform updates only if there are no preexisting records
with the name domain-name.
nxrrset domain-name [class] type
Perform updates only if there is no preexisting record of
the specified type and class for domain-name. When no
class is given, IN is assumed.
yxdomain domain-name
Perform updates only if there is a preexisting record with
the name domain-name.
yxrrset domain-name [class] type [data]
Perform updates only if there is a preexisting record of
the specified type and class for domain-name. If data is
given, the RDATA of the specified resource must match it
exactly. When no class is given, IN is assumed.
send
Send the current message. Same as entering a blank line.
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objcopy
server servername [port]
Update records on DNS server servername instead of the
master server listed in the MNAME field of the appropriate
zone’s SOA record.
show
Print all commands in current message.
update command
Update the records according to one of the following commands:
add domain-name [ttl] [class] type data
Add a resource record with the specified values.
delete domain-name [ttl] [class] [type [data]]
Delete resource records for domain-name. The ttl field is
always ignored, but if other fields are given, only delete
records that match all criteria.
zone zonename
Apply updates to the specified zonename. If no zone command
is given, nsupdate attempts to determine the correct zone
based on other input.
objcopy objcopy [options]infile [outfile]
Copy the contents of the input object file to another file, option-
ally changing the file format in the process (but not the endian-
ness). If outfile is not specified, objcopy creates a temporary file
and renames it to infile when the copy is complete, destroying the
original input file. The GNU Binary File Descriptor (BFD) library is
used to read and write the object files.
Options
--add-section section=file
Add a new section to the output object file with the specified
section name and the contents taken from the specified file.
Available only for formats that allow arbitrarily named
sections.
--alt-machine-code=n
If the output architecture has alternate machine codes, use the
nth code instead of the default.
-b n, --byte=n
Copy only every nth byte. Header data is not affected. The
value of n can be from 0 to interleave-1, where interleave is
specified by -i (default is 4). This option is useful for creating
files to program ROM and is typically used with srec as the
output format.
-B bfdarch, --binary-architecture=bfdarch
Set the output architecture to bfdarch (e.g., i386) for trans-
forming a raw binary file into an object file. Otherwise, this
option is ignored. After the conversion, your program can
access data inside the created object file by referencing the
special symbols _binary_objfile_start, _binary_objfile_end,
and _binary_objfile_size.
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objcopy
--change-addresses=incr, --adjust-vma=incr
Change the VMA and LMA addresses of all sections, plus the
start address, by adding incr. Changing section addresses is
not supported by all object formats. Sections are not relocated.
--change-leading-char
For object formats that use a special character (such as an
underscore) to begin symbols, change the leading character
when converting between formats. If the character is the same
in both formats, the option has no effect. Otherwise, it adds,
removes, or changes the leading character as appropriate for
the output format.
--change-section-address section{=|+|-}val,
--adjust-section-vma section{=|+|-}val
Set or change the VMA and LMA addresses of the specified
section. With =, set the section address to the specified value;
otherwise, add or subtract the value to get the new address.
--change-section-lma section{=|+|-}val
Set or change the LMA address of the specified section. With
=, set the section address to the specified value; otherwise, add
or subtract the value to get the new address.
--change-section-vma section{=|+|-}val
Set or change the VMA address of the specified section. With
=, set the section address to the specified value; otherwise, add
or subtract the value to get the new address.
--change-start incr, --adjust-start incr
Add incr to the start address to get a new start address. Not
supported by all object formats.
--change-warnings, --adjust-warnings
Issue a warning if the section that is specified in one of the
options --change-section-address, --change-section-lma, or
--change-section-vma does not exist.
--debugging
Convert debugging information if possible.
-F bfdname, --target=bfdname
Set the binary format for both input and output files to the
binary file descriptor name bfdname. No format translation is
done. Use the -h option for a list of supported formats for your
system.
-g, --strip-debug
Do not copy debugging information.
-G symbol, --keep-global-symbol=symbol
Copy only the specified global symbol, making all other
symbols local to the file. May be specified multiple times.
--gap-fill=val
Fill gaps between sections with the specified value; applies to
the load address (LMA) of the sections.
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objcopy
-h, --help
Print help information, including a list of supported target
object formats, then exit.
-i interleave, --interleave=interleave
Copy one out of every interleave bytes. Use -b to set the byte
to copy (default is 4). This option is ignored if -b is not
specified.
-I bfdname, --input-target=bfdname
Set the binary file format of the input file using its binary file
descriptor name, bfdname.
-j section, --only-section=section
Copy only the specified section. May be specified multiple
times.
-K symbol, --keep-symbol=symbol
Copy only the specified symbol from the source file. May be
specified multiple times.
--keep-global-symbols=filename
Apply the option --keep-global-symbol to each symbol listed
in the specified file. The file should have one symbol per line,
with comments beginning with a hash mark (#). May be spec-
ified multiple times.
--keep-symbols=file
Apply the option --keep-symbol to each symbol listed in the
specified file. The file should have one symbol per line, with
comments beginning with a hash mark (#). May be specified
multiple times.
-L symbol, --localize-symbol=symbol
Make the specified symbol local. May be specified multiple
times.
--localize-symbols=filename
Apply the option --localize-symbol to each symbol listed in
the specified file. The file should have one symbol per line,
with comments beginning with a hash mark (#). May be spec-
ified multiple times.
-N symbol, --strip-symbol=symbol
Do not copy the specified symbol. May be specified multiple
times.
--no-change-warnings, --no-adjust-warnings
Do not issue a warning even if the section specified in one of
the options --change-section-address, --change-section-lma,
or --change-section-vma does not exist.
-O bfdname, --output-target=bfdname
Set the binary file format of the output file using its binary file
descriptor name, bfdname. The format srec generates S-records
(printable ASCII versions of object files), and binary generates
a raw binary file. Use -h for other available formats.
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objcopy
-p, --preserve-dates
Preserve the input file’s access and modification dates in the
output file.
--pad-to=addr
Pad the output file up to the load address. Use the fill value
specified by --gap-fill (default is 0).
-R section, --remove-section=section
Do not copy any section with the specified name. May be
specified multiple times.
--redefine-sym old=new
Change the name of the symbol old to new.
--remove-leading-char
If the first character of a global symbol is a special character
(such as an underscore) used by the input object file format,
remove it. Unlike --change-leading-char, this option always
changes the symbol name when appropriate, regardless of the
output object format.
--rename-section oldname=newname[,flags]
Rename a section from oldname to newname, optionally also
changing the flags to flags.
-S, --strip-all
Do not copy relocation and symbol information.
--set-section-flags section=flags
Set flags for the specified section as a comma-separated string
of flag names. Not all flags are meaningful for all object
formats. The possible flags are alloc, code, contents, data,
debug, load, noload, readonly, rom, and share.
--set-start=val
Set the start address of the new file to the specified value. Not
supported by all object formats.
--srec-forceS3
Force all srec output records to be type S3 records.
--srec-len=ival
Set the maximum length of srec output records to the speci-
fied value. The length includes the address, data, and crc
fields.
--strip-symbols=filename
Apply the option --strip-symbol to each symbol listed in the
specified file. The file should have one symbol per line, with
comments beginning with a hash mark (#). May be specified
multiple times.
--strip-unneeded
Strip all symbols not needed for relocation processing.
-v, --verbose
Run in verbose mode, listing all object files modified; for
archives, list all archive members.
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objdump
-V, --version
Print version information and exit.
-W symbol, --weaken-symbol=symbol
Make the specified symbol weak. May be specified multiple
times.
--weaken
Make all global symbols weak.
--weaken-symbols=filename
Apply the option --weaken-symbol to each symbol listed in
the specified file. The file should have one symbol per line,
with comments beginning with a hash mark (#). May be spec-
ified multiple times.
-x, --discard-all
Do not copy nonglobal symbols.
-X, --discard-locals
Do not copy compiler-generated local symbols (usually those
starting with L or .. ).
objdump objdump [options]objfiles
Display information about one or more object files. If an archive is
specified, objdump displays information on each object file in the
archive. At least one of the options -a, -d, -D, -f, -g, -G, -h, -H, -p, -r,
-S, -t, -T, -V, or -x must be given to tell objdump what information
to show.
Options
-a, --archive-header
If any input files are archives, display the archive header infor-
mation. The output includes the object file format of each
archive member.
--adjust-vma=offset
Add offset to all section headers before dumping information.
Useful if the section addresses do not correspond to the
symbol table.
-b bfdname, --target=bfdname
Set the binary file format using its binary file descriptor name,
bfdname. Use the -h option for a list of supported formats for
your system.
-C [style], --demangle[=style]
Decode (demangle) low-level symbol names into user-level
names, optionally specifying a mangling style. Removes any
initial underscores and makes C++ function names readable.
-d, --disassemble
Display assembler mnemonic names for the machine instruc-
tions. Disassemble only sections that are expected to contain
instructions.
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objdump
-D, --disassemble-all
Disassemble all sections, not just those expected to contain
instructions.
-EB, --endian=big
-EL, --endian=little
Specify whether the object files are big- or little-endian, for
disassembling. Useful for disassembling formats such as S-records
(printable ASCII versions of object files) that do not include
that information.
-f, --file-header
Display overall header summary information.
--file-start-context
When using -S and displaying source code from a file that
hasn’t been displayed yet, include context from the start of the
file.
-g, --debugging
Display debugging information.
-G, --stabs
Display any stabs (debugging symbol table entries) informa-
tion, in addition to the contents of any sections requested.
-h, --section-header, --header
Display section-header summary information.
-H, --help
Display help information and exit.
-i, --info
Display the architectures and object formats available on your
system for use with -b or -m.
-j name, --section=name
Display information for section name.
-l, --line-numbers
Label the display with filename and source code line numbers
corresponding to the object code or relocation entries shown.
Use with -d, -D, or -r.
-m arch, --architecture=arch
Specify the architecture for disassembling object files. Useful
when disassembling files such as S-records that do not include
this information.
-M options, --disassembler-options=options
Pass target-specific information to the disassembler.
Supported only on some targets.
--no-show-raw-insn
Do not show instructions in hexadecimal when disassem-
bling. This is the default with --prefix-addresses.
-p, --private-headers
Display information specific to the object format. For some
formats, no additional information is displayed.
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od
--prefix-addresses
When disassembling, print the complete address on each line.
-r, --reloc
Display relocation entries. With -b or -D, the entries are inter-
mixed with the disassembly.
-R, --dynamic-reloc
Print dynamic relocation entries. Meaningful only for dynamic
objects such as certain types of shared libraries.
-s, --full-contents
Display the full contents of any requested sections.
-S, --source
Display source code intermixed with disassembly, if possible.
Implies -d.
--show-raw-insn
When disassembling, show instructions in hexadecimal as well
as symbolic form. This is the default, except with --prefix-
addresses.
--start-address=addr
Start displaying data at the specified address. Applies to -d, -r,
and -s.
--stop-address=addr
Stop displaying data at the specified address. Applies to -d, -r,
and -s.
-t, --syms
Print symbol table entries.
-T, --dynamic-syms
Print dynamic symbol table entries. Meaningful only for
dynamic objects such as certain types of shared libraries.
-V, --version
Print version information and exit.
-w, --wide
Format lines for output devices wider than 80 characters, and
do not truncate symbol table names.
-x, --all-headers
Display all available header information. Equivalent to speci-
fying -a -f -h -r -t.
-z, --disassemble-zeroes
Disassemble blocks of zeroes. The default is to skip such blocks.
od od [options] [files]
od --traditional [file] [[+]offset [[+]label]]
Dump the specified files to standard output. The default is to
dump in octal format, but other formats can be specified. With
multiple files, concatenate them in the specified order. If no files
are specified or file is -, read from standard input. With the second
form, using the --traditional option, only one file can be specified.
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od
Options
For the following options, see the upcoming “Arguments” section
for an explanation of the arguments bytes, size, and type. If no
options are specified, the default is -A o -t d2 -w 16.
-a Print as named characters. Same as -t a.
-A radix, --address-radix=radix
Specify the radix (base) for the file offsets printed at the begin-
ning of each output line. The possible values are:
d Decimal.
n None; do not print an offset.
o Octal; the default.
x Hexadecimal.
-b Print as octal bytes. Same as -t o1.
-c Print as ASCII characters or backslash escapes. Same as -t c.
-d Print as unsigned decimal shorts. Same as -t u2.
-f Print as floating-point. Same as -t fF.
--help
Display a usage message and exit.
-i Print as decimal integers. Same as -t dI.
-j bytes, --skip-bytes=bytes
Skip the specified number of input bytes before starting.
-l Print as decimal longs. Same as -t dL.
-N bytes, --read-bytes=bytes
Format and print only the specified number of input bytes.
-o Print as octal shorts. Same as -t o2.
-s Print as decimal shorts. Same as -t d2.
-S bytes, --strings[=bytes]
Output strings that are at least bytes ASCII graphic characters
long (default is 3 if bytes is not specified for --strings).
-t type, --format=type
Format the output according to type, where type is a string of
one or more of the characters listed in the “Arguments”
section. If more than one type is specified, each output line is
written once in each specified format. If a trailing z is
appended to type, od appends any printable characters to the
end of each output line.
--traditional
Accept arguments in the traditional form, which takes a single
file specification with an optional offset and label, as shown in
the second form of the command. offset is an octal number
indicating how many input bytes to skip over. label specifies
an initial pseudo-address, which is printed in parentheses after
any normal address. Both the offset and the label can begin with
an optional plus sign (+), and can have a trailing decimal point
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od
( . ) to force the offset to be interpreted as a decimal number
and/or a trailing b to multiply the number of bytes skipped by
offset by 512.
-v, --output-duplicates
Print all lines, including duplicates. By default, only the first of
a series of identical lines is printed, and an asterisk is printed
at the beginning of the following line to indicate that there
were duplicates.
--version
Display version information and exit.
-w bytes, --width[=bytes]
Dump bytes input bytes to each output line. Defaults to 16 if
this option is omitted. If --width is specified but bytes is
omitted, the default is 32.
-x Print as hexadecimal shorts. Same as -t x2.
Arguments
bytes
Specify a number of bytes. Treated as hexadecimal if it begins
with 0x or 0X, as octal if it begins with 0, or as decimal other-
wise. Append b to multiply by 512, k to multiply by 1024, or
m to multiply by 10,248,576.
size
Specified as part of type to indicate how many bytes to use in
interpreting each number. Types a and c do not take a size.
For other types, size is a number. For type f, size can also be
one of the following:
D Double.
F Float.
L Long double.
For the remaining types (d, o, u, x), size can be one of the
following in addition to a number:
C Character.
I Integer.
L Long.
S Short.
type
Specify the format type. The possible types are:
a Named character.
c ASCII character or backslash escape.
dsize
Signed decimal, with size bytes per integer.
fsize
Floating point, with size bytes per integer.
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openvt
osize
Octal, with size bytes per integer.
usize
Unsigned decimal, with size bytes per integer.
xsize
Hexadecimal, with size bytes per integer.
openvt openvt [options] [--] [command] [arguments]
Locate the first available virtual terminal (VT) and run command
with any arguments given. If no command is specified, the shell
$SHELL is started.
Options
-- Indicates the end of openvt options. Required before the
command name to pass options to the command.
-c vt
Use the specified VT number instead of the first available. You
must have write access to vt.
-e Execute command without forking. For use in /etc/inittab,
rather than on the command line.
-l Run the command as a login shell, prepending a dash (-) to
the command name.
-s Switch to the new VT when the command is started and make
it the current VT.
-u Determine the owner of the current VT, and log in as that
user. You must be root to use this option, which is also suit-
able for calling by init. Don’t use with -l.
-v Verbose mode.
-w Wait for the command to complete. If used with -s, switch
back to the controlling terminal when the command is done.
passwd passwd [options] [user]
Create or change a password associated with a user name. Only the
owner or a privileged user may change a password. Owners need
not specify their user name. Users can change their own pass-
words. For all other operations, you must be root.
Options
-d, --delete
Delete the password for the user’s account.
-f, --force
Force the operation. Overrides -u.
-?, --help
Display a help message describing the options. See also --usage.
-i days, --inactive=days
Set the number of days after a password has expired before the
account is disabled.
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paste
-k, --keep-tokens
Keep passwords (authentication tokens) that have not expired.
-l, --lock
Lock the user’s account.
-n days, --minimum=days
Set the minimum number of days that the password is valid.
-S, --status
Print the status of the user’s password.
--stdin
Read new passwords from standard input.
-u, --unlock
Unlock the user’s account
--usage
Display a brief usage message. See also --help.
-w days, --warning=days
Set the number of days of warning users will get before their
password expires.
-x days, --maximum=days
Set the maximum number of days that the password is valid.
paste paste [options]files
Merge corresponding lines of one or more files into tab-separated
vertical columns and write to standard output. Use - to read from
standard input, instead of specifying a file. See also cut, join, and pr.
Options
-dchar, --delimiters=char
Separate columns with char instead of a tab. You can separate
columns with different characters by supplying more than one
char.
--help
Print a help message and then exit.
-s, --serial
Merge lines from one file at a time.
--version
Print version information and then exit.
Examples
Create a three-column file from files x, y, and z:
paste x y z > file
List users in two columns:
who | paste - -
Merge each pair of lines into one line:
paste -s -d"\t\n" list
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patch
patch patch [options] [original [patchfile]]
Apply the patches specified in patchfile to original. Replace the orig-
inal with the new, patched version; move the original to original.orig
or original~. The patch file is a difference listing produced by the
diff command.
Options
-b, --backup
Back up the original file.
-B prefix, --prefix=prefix
Prepend prefix to the backup filename.
--backup-if-mismatch, --no-backup-if-mismatch
When not backing up all original files, these options control
whether a backup should be made when a patch does not
match the original file. The default is to make backups unless
--posix is specified.
-c, --context
Interpret patchfile as a context diff.
-d dir, --directory=dir
cd to directory dir before beginning patch operations.
-D string, --ifdef=string
Mark all changes with:
#ifdef
string
#endif
--dry-run
Print results of applying a patch, but don’t change any files.
-e, --ed
Treat the contents of patchfile as ed commands.
-E, --remove-empty-files
If patch creates any empty files, delete them.
-f, --force
Force all changes, even those that look incorrect. Skip patches
if the original file does not exist; force patches for files with
the wrong version specified; assume patches are never
reversed.
-F num, --fuzz=num
Specify the maximum number of lines that may be ignored
(fuzzed over) when deciding where to install a hunk of code.
The default is 2. Meaningful only with context diffs.
-g num, --get num
Specify whether to check the original file out of source control
if it is missing or read-only. If num is a positive number, get
the file. If it is negative, prompt the user. If it is 0, do not
check files out of source control. The default is negative or the
value of the PATCH_GET environment variable when set,
unless the --posix option is given. In that case, the default is 0.
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patch
--help
Print help message, then exit.
-i file, --input=file
Read patch from file instead of stdin.
-l, --ignore-whitespace
Ignore whitespace while pattern matching.
-n, --normal
Interpret patch file as a normal diff.
-N, --forward
Ignore patches that appear to be reversed or to have already
been applied.
-o file, --output=file
Print output to file.
-pnum, --strip=num
Specify how much of preceding pathname to strip. A num of 0
strips everything, leaving just the filename. 1 strips the leading
/. Each higher number after that strips another directory from
the left.
--posix
Conform more strictly to the POSIX standard.
--quoting-style=style
Set the quoting style used when printing names. The default
style is shell, unless set by the environment variable
QUOTING_STYLE. style may be one of the following:
c Quote as a C language string.
escape
Like c, but without surrounding double-quote characters.
literal
Print without quoting.
shell
Quote for use in shell when needed.
shell-always
Quote for use in shell even if not needed.
-r file, --reject-file=file
Place rejects (hunks of the patch file that patch fails to place
within the original file) in file. Default is original.rej.
-R, --reverse
Do a reverse patch: attempt to undo the damage done by
patching with the old and new files reversed.
-s, --silent, --quiet
Suppress commentary.
-t, --batch
Force changes as with -f but make different decisions. Skip
patches if headers don’t contain filenames; skip patches for
files with the wrong version specified; assume patches are
reversed if they look like they are. Also see -Z.
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pathchk
-T, --set-time
When original file timestamps match the times given in the
patch header, set timestamps for patched files according to the
context diff headers. Use option -f to force date changes.
Assume timestamps are in local time.
-u, --unified
Interpret patch file as a unified context diff.
-v, --version
Print version number and exit.
-V method, --version-control=method
Specify method for creating backup files (overridden by -B):
t, numbered
Make numbered backups.
nil, existing
Back up files according to preexisting backup schemes,
with simple backups as the default. This is patch’s default
behavior.
never, simple
Make simple backups.
--verbose
Verbose mode.
-Y prefix, --basename-prefix=prefix
Use the specified prefix with a file’s basename to create backup
filenames. Useful for specifying a directory.
-z suffix, --suffix=suffix
Back up the original file in original.suffix.
-Z, --set-utc
When original file timestamps match the times given in the
patch header, set timestamps for patched files according to the
context diff headers. Use option -f to force date changes.
Assume timestamps are in Coordinated Universal Time
(UTC). Also see -T.
pathchk pathchk [options]filenames
Determine validity and portability of filenames. Specifically, deter-
mine if all directories within the path are searchable and if the
length of the filenames is acceptable.
Options
--help
Print a help message and then exit.
-p Check for most POSIX systems.
-P Check for empty names and names that start with -.
--portability
Check portability for all POSIX systems. Equivalent to -p -P.
--version
Print version information and then exit.
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ping
pccardctl pccardctlcommand
System administration command. Monitor and control PCMCIA
sockets. Commands operate on a named card socket number, or all
sockets if no number is given.
Commands
config [socket]
Display current socket configuration.
eject [socket]
Prepare the system for the card(s) to be ejected.
ident [socket]
Display card identification information.
info [socket]
Display card identification information as Bourne shell variable
definitions for use in scripts.
insert [socket]
Notify system that a card has been inserted.
resume [socket]
Restore power to socket and reconfigure for use.
status [socket]
Display current socket status.
suspend [socket]
Shut down device and cut power to socket.
pidof pidof [options]programs
Display the process IDs of the listed program or programs. pidof is
actually a symbolic link to killall5.
Options
-c Return only processes running in the same root directory.
Ignored for nonroot users.
-o pid
Omit all processes with the specified process ID. Can be speci-
fied more than once to omit multiple IDs.
-s Return a single process ID.
-x Also return process IDs of shells running the named scripts.
ping ping [options]host
System administration command. Confirm that a remote host is
online and responding. ping is intended for use in network testing,
measurement, and management. Because of the load it can impose
on the network, it is unwise to use ping during normal operations
or from automated scripts.
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ping
Options
-a Make ping audible. Beep each time response is received.
-A Adapt to return interval of packets. Like -f ping, sends packets
at approximately the rate at which they are received. This
option may be used by an unprivileged user.
-b Ping a broadcast address.
-B Bind to original source address and do not change.
-c count
Stop after sending (and receiving) count ECHO_RESPONSE
packets.
-f Flood ping-output packets as fast as they come back or 100
times per second, whichever is greater. This can be very hard
on a network and should be used with caution. Only a privi-
leged user may use this option.
-i wait
Wait wait seconds between sending each packet. Default is to
wait one second between each packet. This option is incom-
patible with the -f option.
-I name
Set source address to interface name. name may also be speci-
fied as an IP address.
-l preload
Send preload number of packets as fast as possible before
falling into normal mode of behavior.
-L If destination is a multicast address, suppress loopback.
-M hint
Specify Path MTU Discovery strategy. Accepted values are do,
want, or dont.
-n Numeric output only. No attempt will be made to look up
symbolic names for host addresses.
-p digits
Specify up to 16 pad bytes to fill out packet sent. This is useful
for diagnosing data-dependent problems in a network. digits
are in hex. For example, -p ff will cause the sent packet to be
filled with all 1s.
-q Quiet output—nothing is displayed except the summary lines
at startup time and when finished.
-Q tos
Set Quality of Service on ICMP datagrams.
-r Bypass the normal routing tables and send directly to a host
on an attached network.
-R Set the IP record route option, which will store the route of the
packet inside the IP header. The contents of the record route
will be printed if the -v option is given, and will be set on
return packets if the target host preserves the record route
option across echoes or if the -l option is given.
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portmap
-s packetsize
Specify number of data bytes to be sent. Default is 56, which
translates into 64 ICMP data bytes when combined with the
8 bytes of ICMP header data.
-S size
Set send buffer (SNDBUF) size. The default is the size of one
packet.
-t n
Set the IP Time to Live to n seconds.
-T option
Set IP timestamp options. Accepted option values are:
tsonly
Timestamps only.
tsandaddr
Timestamps and addresses.
tsprespec hosts
Timestamps with prespecified hops of one or more hosts.
-U Use older ping behavior and print full user-to-user latency
instead of network round-trip time.
-v Verbose; list ICMP packets received other than ECHO_
RESPONSE.
-V Print version, then exit.
-w n
Exit ping after n seconds.
-W n
When waiting for a response, time out after n seconds.
pmap pmap [options]pids
Display the memory maps of a process.
Options
-d Display the offset and device number of each mapping.
-q Be more quiet. Displays less header and footer information.
-x Provide a more detailed and verbose display.
-V Display the version number and exit.
portmap rpc.portmap [options]
NFS/NIS command. RPC program number to IP port mapper.
portmap is a server that converts RPC program numbers to IP port
numbers. It must be running in order to make RPC calls. When an
RPC server is started, it tells portmap which port number it is
listening to and which RPC program numbers it is prepared to
serve. When a client wishes to make an RPC call to a given
program number, it first contacts portmap on the server machine
to determine the port number where RPC packets should be sent.
portmap must be the first RPC server started. On newer systems
portmap is deprecated. Use rpcbind instead.
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poweroff
Options
-d Run portmap in debugging mode. Does not allow portmap to
run as a daemon.
-l Bind to loopback device. This only works from the localhost.
-v Verbose mode.
poweroff poweroff [options]
System administration command. Close out filesystems, shut down
the system, and power off. Because this command immediately
stops all processes, it should be run only in single-user mode. If the
system is not in runlevel 0 or 6, poweroff calls shutdown -h, then
performs a poweroff.
Options
-d Suppress writing to /var/log/wtmp.
-f Call reboot or halt and not shutdown, even when shutdown
would normally be called. This option is used to force a hard
halt or reboot.
-h Place hard drives in standby mode before halt or poweroff.
-i Shut down network interfaces before reboot.
-n Suppress normal call to sync.
-w Suppress normal execution; simply write to /var/log/wtmp.
pppd pppd [tty] [speed] [options]
System administration command. PPP stands for the Point-to-Point
Protocol; it allows datagram transmission over a serial connection.
pppd attempts to configure tty for PPP (searching in /dev) or, by
default, the controlling terminal. You can also specify a baud rate
of speed. pppd accepts many options. Only the most common
options are listed here.
Options
[local_IP_address]:[remote_IP_address]
Specify the local and/or remote interface IP addresses, as host-
names or numeric addresses.
asyncmap map
Specify which control characters cannot pass over the line.
map should be a 32-bit hex number, where each bit repre-
sents a character to escape. For example, bit 00000001
represents the character 0x00; bit 80000000 represents the
character 0x1f or _. You may specify multiple characters.
auth
Require self-authentication by peers before allowing packets
to move.
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pppd
call file
Read options from file in /etc/ppp/peers/. Unlike the file
option, call file may contain privileged options, even when
pppd is not run by root.
connect command
Connect as specified by command, which may be a binary or
shell command.
crtscts
Use hardware flow control.
debug
Log contents of control packets to syslogd.
defaultroute
Add a new default route in which the peer is the gateway.
When the connection shuts down, remove the route.
nodetach
Operate in the foreground. By default, pppd forks and oper-
ates in the background.
disconnect command
Close the connection as specified by command, which may be
a binary or shell command.
escape character-list
Escape all characters in character-list, which should be a
comma-separated list of hex numbers. You cannot escape
0x20-0x3f or 0x5e.
file file
Consult file for options.
init script
Run specified command or shell script to initialize the serial
line.
lock
Allow only pppd to access the device.
mru bytes
Refuse packets of more than bytes bytes.
mtu bytes
Do not send packets of more than bytes bytes.
passive, -p
Do not exit if peer does not respond to attempts to initiate a
connection. Instead, wait for a valid packet from the peer.
silent
Send no packets until after receiving one.
Files
/var/run/pppn.pid
pppd’s process ID. The n in pppn.pid is the number of the PPP
interface unit corresponding to this pppd process.
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pr
/etc/ppp/ip-up
Binary or script to be executed when the PPP link becomes
active.
/etc/ppp/ip-down
Binary or script to be executed when the PPP link goes down.
/etc/ppp/pap-secrets
Contains usernames, passwords, and IP addresses for use in
PAP authentication.
/etc/ppp/options
System defaults. Options in this file are set before the command-
line options.
~/.ppprc
The user’s default options. These are read before command-
line options but after the system defaults.
/etc/ppp/options.ttyname
Name of the default serial port.
pr pr [options] [files]
Convert a text file or files to a paginated or columned version, with
headers, suitable for printing. If - is provided as the filename, read
from standard input.
Options
+beg_pag[:end-pag], --pages=beg_pag[:end-pag]
Begin printing on page beg_pag and end on end-pag if
specified.
-num_cols, --columns=num_cols
Set the number of columns to print, balancing the number of
lines in the columns on each page. Print vertical columns,
except with -a.
-a, --across
Print columns horizontally, not vertically.
-c, --show-control-chars
Convert control characters to hat notation (such as ^C), and
other unprintable characters to octal backslash format.
-d, --double-space
Double space.
-D format, --date-format=format
Format the header date using format. See the date command
for the possible formats.
-e[tab-char[width]], --expand-tabs[=tab-char[width]]
Convert tabs (or tab-chars) to spaces. If width is specified,
convert tabs to width characters (default is 8).
-f, -F, --form-feed
Separate pages with form feeds, not newlines. With -F, print a
three-line page header; otherwise, print a five-line header and
trailer.
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pr
-h header, --header=header
Use header for the header instead of the filename. The header
is centered.
--help
Print a help message and then exit.
-i[out-tab-char[out-tab-width]],
--output-tabs[=out-tab-char[out-tab-width]]
Replace spaces with tabs on output. You can specify an alter-
native tab character (default is tab) and width (default is 8).
-J, --join-lines
Merge full lines; ignore -W if set.
-l lines, --length=lines
Set page length to lines (default is 66). If lines is less than 10,
omit headers and footers. Thus the default number of lines of
text (i.e., not header or trailer) is 56, or 63 with -F.
-m, --merge
Print all files, one per column.
-n[delimiter[digits]], --number-lines[=delimiter[digits]]
Number columns, or, with the -m option, number lines.
Append delimiter to each number (default is a tab) and limit
the size of numbers to digits (default is 5).
-N num, --first-line-number=num
Start counting with num at the first line of the first page
printed. Also see +beg_page.
-o width, --indent=width
Indent left margin to width. Does not affect the page width set
with -w or -W.
-r, --no-file-warnings
Continue silently when unable to open an input file.
-s[delimiter], --separator[=delimiter]
Separate columns with the single-character delimiter (default is
a tab) instead of spaces.
-S[string], --sep-string[=string]
Separate columns with string. Default is a tab with -J and a
space otherwise.
-t, --omit-header
Suppress headers, footers, and fills at end of pages.
-T, --omit-pagination
Like -t but also suppress form feeds.
-v, --show-non-printing
Convert unprintable characters to octal backslash format.
-w page_width, --width=page_width
Set the page width to page_width characters for multicolumn
output. Default is 72.
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praliases
-W page_width, --page-width=page_width
Set the page width to always be page_width characters. Lines
longer than the specified width are truncated unless -J is also
specified. Default is 72.
--version
Print version information and then exit.
praliases praliases [options] [keys]
System administration command. praliases prints the current send-
mail mail aliases. (Usually defined in the /etc/aliases or /etc/aliases.
db file.) Limit output to the specified keys when given.
Options
-f file
Read the aliases from the specified file instead of sendmail’s
default alias files.
-C file
Read sendmail configuration from the specified file instead of
from /etc/mail/sendmail.cf.
printenv printenv [variables]
printenvoption
Print values of all environment variables or, optionally, only the
specified variables.
Options
--help
Print usage information and exit.
--version
Print version information and exit.
printf printfformats [strings]
printfoption
Print strings using the specified formats. formats can be ordinary
text characters, C-language escape characters, C format specifica-
tions ending with one of the letters diouxXfeEgGcs or, more
commonly, a set of conversion arguments listed here.
Options
--help
Print usage information and exit.
--version
Print version information and exit.
Arguments
%% Print a single %.
%bPrint string with \ escapes interpreted.
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ps
%sPrint the next string.
%n$s
Print the nth string.
%[-]m[.n]s
Print the next string, using a field that is m characters wide.
Optionally, limit the field to print only the first n characters of
string. Strings are right-adjusted unless the left-adjustment
flag, -, is specified.
Examples
printf '%s %s\n' "My files are in" $HOME
printf '%-25.15s %s\n' "My files are in" $HOME
ps ps [options]
Report on active processes. ps has three types of options. GNU
long options start with two hyphens, which are required. BSD
options may be grouped and do not start with a hyphen, while
Unix98 options may be grouped and require an initial hyphen. The
meaning of the short options can vary depending on whether or
not there is a hyphen. In options, list arguments should either be
comma-separated or space-separated and placed inside double
quotes. In comparing the amount of output produced, note that e
prints more than a and l prints more than f for each entry.
Options
nums, p nums, -p nums, --pid=nums
Include only specified processes, which are given in a space-
delimited list.
-nums, -s nums, --sid=nums
Include only specified session IDs, which are given in a space-
delimited list.
[-]a
As a, list all processes on a terminal. As -a, list all processes
except session leaders and processes not associated with a
terminal.
[-]c
As -c, show different scheduler information with -l. As c, show
the true command name.
-C cmds
Select by command name.
--cols=cols, --columns=cols
Set the output width (the number of columns to display).
-d Select all processes except session leaders.
-e, -A
Select all processes.
e Include environment information after the command.
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ps
[-]f, --forest
As -f, display full listing. As f or --forest, display “forest”
family tree format, with ASCII art showing the relationships.
-F Set extra-full format; implies -f.
-g list, -G list, --group=groups, --Group=groups
For -g, select by session leader if list contains numbers, or by
group if it contains group names. For -G, select by the group
IDs in list. --group selects by effective group and --Group
selects by real group, where groups can be either group names
or group IDs.
h, --no-headers
Suppress header. If you select a BSD personality by setting the
environment variable PS_PERSONALITY to bsd, then h prints
a header on each page.
-H Display “forest” family tree format, but without ASCII art.
H Display threads as if they were processes.
--headers
Repeat headers on every output page.
--help
Display help information and exit.
--info
Print debugging information.
[-]j
Jobs format. j prints more information than -j.
k spec, --sort spec
Specify sort order. Syntax for the specification is:
[+|-]key[,[+|-]key...]]
The default direction is +, for increasing numerical or alpha-
betic order. See “Format and sort specifiers” on page 338 for
possible keys.
[-]l
Produce a long listing. -l prints more information than l and is
often used with -y.
L Print list of field specifiers that can be used for output format-
ting or for sorting.
-L Show threads, possibly with LWP and NLWP columns.
--lines=num, --rows=num
Set the screen height to num lines. If --headers is also set, the
headers repeat every num lines.
[-]m
Show threads after processes.
n Print user IDs and WCHAN numerically.
-n file, N file
Specify the System.map file for ps to use as a namelist file. The
map file must correspond to the Linux kernel—e.g., /boot/
System.map-2.6.27.5-117.fc10.x86_64.
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ps
-N, --deselect
Negate the selection, selecting all processes that do not meet
the specified conditions.
[-]o fields, --format=fields
Specify user-defined format with a list of fields to display.
[-]O fields
As -O, this option is like -o, but some common fields are
predefined. As O, this option can be either the same as -O in
specifying fields to display, or can specify single-letter fields
for sorting. For sorting, each field specified as a key can
optionally have a leading + (return to default sort direction on
key) or - (reverse the default direction).
--ppid=nums
Select by parent process IDs.
r Show only processes that are currently running.
s Display signal format.
S, --cumulative
Include some dead child process data in parent total.
[-]tttys, --tty=ttys
Display processes running on the specified terminals. t with
no terminal list displays processes for the terminal associated
with ps. Specify - to select processes not associated with any
terminal.
T Display all processes on this terminal. Like t with no argument.
-T Display threads, possibly with SPID column,
[-]u [users], U users, --user=users
As u with no argument, display user-oriented output. As -u, U,
or --user, display by effective user ID (and also support names),
showing results for users. With no argument, -u displays
results for the current user.
-U users, --User=users
Display processes for users by real user ID (and also support
names).
v Display virtual memory format.
[-]V, --version
Display version information and then exit.
[-]w
Wide format. Don’t truncate long lines. Use twice to set an
unlimited width.
--width=cols
Set screen width.
x Display processes without an associated terminal.
-y Do not show flags; show rss instead of addr. Requires -l.
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ps
Format and sort specifiers
The following are the keywords for formatting and for sorting with
--sort, followed by a desciption and the output column header in
parentheses:
%cpu, pcpu
Percent of CPU time used recently. (%CPU)
%mem, pmem
Percent of memory used. (%MEM)
args, cmd, command
The command the process is running with all its arguments.
(CMD for cmd; otherwise COMMAND)
blocked, sig_block, sigmask
Mask, in hexadecimal, of blocked signals. (BLOCKED)
bsdstart
Command start time. (START)
bsdtime
Accumulated CPU time for user plus system. (TIME)
c Integer value of %cpu. (C)
caught, sig_catch, sigcatch
Mask, in hexadecimal, of caught signals. (CAUGHT)
class, cls, policy
Scheduling class. (POL for policy, otherwise CLS). Possible
values are:
- Unreported
? Unknown value
FF SCHED_FIFO (first in, first out)
RR SCHED_RR (round robin)
TS SCHED_OTHER (standard time-sharing)
comm, ucmd, ucomm
Name of the command executable. (CMD for ucmd; other-
wise, COMMAND)
cp Per-mill CPU usage, where mill is 1000. Equivalent to %cpu
with no decimal point. (CP)
cputime, time
Cumulative CPU time. (TIME)
egid, gid
Effective group ID number in decimal. (EGID or GID,
respectively)
egroup, group
Effective group ID; as text value if it is available and if it fits,
otherwise shown as decimal value. (EGROUP or GROUP,
respectively)
eip
Effective instruction pointer. (EIP)
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ps
esp
Effective stack pointer. (ESP)
etime
Elapsed time since the start of the process. (ELAPSED)
euid, uid
Effective user ID. (EUID or UID, respectively)
euser, uname, user
Effective username; as text value if it is available and if it fits,
otherwise shown as decimal value. (EUSER for euser; other-
wise, USER)
f, flag, flags
Process flags. Can be summed. (F) Possible values are 1 (the
process forked but didn’t exec) and 4 (the process used super-
user privileges).
fgid, fsgid
Filesystem access group ID. (FGID)
fgroup, fsgroup
Filesystem access group ID; as text if available and if it fits,
otherwise as a decimal number. (FGROUP)
fname
First eight bytes of the executable’s basename. (COMMAND)
fuid, fsuid
Filesystem access user ID. (FUID)
fuser
Filesystem access user ID; as text if available and if it fits,
otherwise as a decimal number. (FUSER)
ignored, sig_ignore, sigignore
Mask of ignored signals in hexadecimal format. (IGNORED)
lstart
Command start time. (STARTED)
lwp, spid, tid
Light-weight process, or thread, ID. (LWP, SPID, TID,
respectively)
ni, nice
The nice value of the process. A higher number indicates less
CPU time. (NI)
nlwp, thcount
Number of LWPs, or threads, in the process. (NLWP or
THCNT, respectively)
nwchan
Address of kernel function where process is sleeping. See also
wchan to get the function by name. (WCHAN)
pending, sig, sig_pend
Mask of pending signals. Use with the m or -m option to see
both signals pending on the process and on individual threads.
(PENDING)
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ps
pgid, pgrp
Process group ID or ID of process group leader, which are
equivalent. (PGID or PGRP, respectively)
pid
Process ID. (PID)
ppid
Parent process ID. (PPID)
pri
Process’s scheduling priority. A higher number indicates lower
priority. (PRI)
psr
Current processor that the process is running on. (PSR)
rgid
Real group ID. (RGID)
rgroup
Real group name; as text if available and it fits, otherwise as a
decimal number. (RGROUP)
rss, rssize, rsz
Resident set size (the amount of physical memory), in kilo-
bytes. (RSZ for rsz; otherwise RSS)
rtprio
Real-time priority. (RTPRIO)
ruid
Real user ID number. (RUID)
ruser
Real user ID; as text if available and it fits, otherwise as a
decimal number. (RUSER)
s, state
A single-character state display. See stat for the possible char-
acters or for a multicharacter display. (S)
sched
Scheduling policy. Also see class. (SCH) Possible values are:
0 SCHED_OTHER
1 SCHED_FIFO
2 SCHED_RR
sess, session, sid
Session ID, or the process ID of the session leader, which is
equivalent. (SID for sid; otherwise SESS)
sgi_p
Processor on which the process is currently running, or "*" if
the process is not running. (P)
sgid, svgid
Saved group ID. (SGID or SVGID, respectively)
sgroup
Saved group name; as text if available and it fits, otherwise as
a decimal number.
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ps
size
Size of virtual image. Provides a rough estimate of the
swapspace required to swap the process out. Note that sz uses
the same column header, but has a different meaning. (SZ)
stackp
Address of the stack bottom (start of the stack). (STACKP)
start
Start time of the command. (STARTED)
start_time
Starting time or date of the process. (START)
stat
Status. Multiple status characters can appear. See also s to
display a single character. (STAT)
+ Part of foreground process group.
< High priority (not “nice”).
D Asleep and not interruptible.
l Multithreaded.
L Pages locked into memory.
N Low priority (“nice”).
R Running or runnable.
s Session leader.
S Asleep.
T Stopped.
Z Zombie.
suid, svuid
Saved user ID. (SUID or SVUID, respectively)
suser, svuser
Saved username; as text if it is available and it fits, otherwise
as a decimal number. (SUSER or SVUSER, respectively)
sz
Physical page size of the core image of the process, including
text, data and stack space. (SZ)
tpgid
ID of the foreground process group on the associated terminal
for the process, or -1 if not connected to a terminal. (TPGID)
tt, tty, tname
Associated (controlling) terminal. (TTY for tname; otherwise
TT)
vsz, vsize
Virtual memory size, in kilobytes of the entire process. (VSZ)
wchan
Kernel function in which process is sleeping, or "-" if running,
or "*" if multithreaded process and ps is not displaying
threads. (WCHAN)
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ptx
ptx ptx [options] [infiles]
ptx -G [options] [infile [outfile]]
Create a permuted index, including context, from the contents of
the specified input files. If the input files are omitted, or are - , read
from standard input. The results are written to standard output. In
the second form, with the -G option, ptx behaves like the System V
version rather than the GNU version; you specify only one input
file, and you can also specify an output file. Because they show
words in context, permuted indexes are often used in such places
as bibliographic or medical databases, thesauruses, or websites to
aid in locating entries of interest.
Options
-A, --auto-reference
Produce automatically generated references, consisting of the
filename and line number, separated by a colon, and print
them at the beginning of each line.
-b file, --break-file=file
The specified file contains word-break characters—characters
that are not part of words, but separate them.
-f, --ignore-case
Ignore case when sorting, by folding lowercase into uppercase.
-F string, --flag-truncation=string
Use string to flag line truncations.
-g num, --gap-size=num
Specify the number of spaces between output columns.
-G, --traditional
Behave like System V ptx; don’t use the GNU extensions. If an
output file is specified, any existing contents are lost.
--help
Display a help message and exit.
-i file, --ignore-file=file
Read the list of words that are not to be used as keywords in
the concordance output from file.
-M string, --macro-name=string
Select a string for use when generating output suitable for
nroff, troff or T E X. The default is xx.
-o file, --only-file=file
Specify the “only” file, which contains a list of words to be
used in the concordance output. Any words not in file are
ignored. If both an only file and an ignore file are specified, a
word must appear in the only file and not appear in the ignore
file to be used as a keyword.
-O [roff], --format=roff
Format the output as roff directives suitable to be used as
input to nroff or troff. Use -T for T E X output.
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pwck
-r, --references
Use the first field of each line as a reference to identify the line
in the permuted index.
-R, --right-side-refs
Put references on the right, instead of the left. Used with -r
and -A. The space taken up by the references is not taken into
account by -w, even if -R is specified without -r or -A.
-S regexp, --sentence-regexp=regexp
Specify a regular expression to identify the end of a line or a
sentence. Without -G and without -r, the end of a sentence is
used. With -G, or with -r, the end of a line is used. An empty
regex disables end-of-line or end-of-sentence recognition.
-T [tex], --format=tex
Format the output as T E X directives suitable to be used as
T E X input. Use -O for roff output.
--version
Print version information and exit.
-w num, --width=num
Select the maximum output-line width (excluding the width of
any reference if -R is specified).
-W regexp, --word-regexp=regexp
Use the specified regular expression to match each keyword.
pwck pwck [options] [files]
System administration command. Remove corrupt or duplicate
entries in the /etc/passwd and /etc/shadow files. pwck will prompt
for a “yes” or “no” before deleting entries. If the user replies “no,”
the program will exit. Alternate passwd and shadow files can be
checked. If correctable errors are found, the user will be encour-
aged to run the usermod command.
Option
-q Run in quiet mode. Only report serious problems.
-r Run in noninteractive read-only mode, answering all ques-
tions no.
-s Don’t check integrity, just sort entries by UID.
Exit status
0 Success.
1 Syntax error.
2 One or more bad password entries found.
3 Could not open password files.
4 Could not lock password files.
5 Could not write password files.
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pwconv
pwconv pwconv
pwunconv
System administration command. Convert unshadowed entries
in /etc/passwd into shadowed entries in /etc/shadow. Replace the
encrypted password in /etc/password with an x. Shadowing pass-
words keeps them safer from password-cracking programs.
pwconv creates additional expiration information for the /etc/
shadow file from entries in your /etc/login.defs file. If you add new
entries to the /etc/passwd file, you can run pwconv again to transfer
the new information to /etc/shadow. Already shadowed entries are
ignored. pwunconv restores the encrypted passwords to your /etc/
passwd file and removes the /etc/shadow file. Some expiration infor-
mation is lost in the conversion. See also grpconv and grpunconv.
pwd pwd
Print the full pathname of the current working directory. See also
the dirs shell command built into bash.
quota quota [options] [user|group]
Display disk usage and total space allowed for a designated user or
group. With no argument, the quota for the current user is
displayed. Most users can display only their own quota informa-
tion, but the superuser can display information for any user. This
command reports quotas for all filesystems listed in /etc/mtab. For
NFS-mounted filesystems, quota calls rpc.rquotad on the server
machine for the information.
Options
-A, --all-nfs
Report quotas for all NFS filesystems.
-F format, --format=format
Check quota files for the specified format.
-g, --group
Given with a user argument, display the quotas for the groups
of which the user is a member, instead of the user’s quotas.
With no argument, shows group quotas for the current user.
-i, --no-autofs
Igonore mountpoints that are mounted by the automounter.
-l, --local-only
Only report quotas on local filesystems.
-p, --raw-grace
When user is in a grace period, print a timestamp (seconds
since epoch) marking when the grace period expires.
-q, --quiet
Display information only for filesystems in which the user is
over quota.
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quotacheck
-Q, --quiet-refuse
For NFS-mounted filesystems. do not print an error message if
the connection to rpc.rquotad is refused (usually because it is
not running on the server).
-s, --human-readable
Try to choose units for displaying limits, space used, and
inodes used.
-u, --user
The default behavior. When used with -g, display both user
and group quota information.
-v, --verbose
Display quotas for filesystems even if no storage is currently
allocated.
-w, --no-wrap
Do not wrap line for long device names.
Formats
rpc
Quota over NFS.
vfsold
Version 1 quota.
vfsv0
Version 2 quota.
xfs
Quota on XFS filesystem.
quotacheck quotacheck [options] [filesystems]
System administration command. Audit and correct quota informa-
tion by building a table of current disk usage and comparing it to
the recorded usage in both the kernel and the quota files.
quotacheck will update quota information when possible and
prompt the user if it requires input. Most systems that support
quotas run this command at system startup. To prevent damage to
filesystems or loss of quota data, turn off quotas with quotaoff and
umount the system. quotacheck will attempt to remount any
mounted filesystem as read-only before scanning.
Options
-a, --all
Check all non-NFS filestystems in /etc/mtab.
-b, --backup
Back up quota files before writing new data to them.
-c, --create-files
Skip reading existing quota information; just write new files.
-f, --force
Force checking on filesystems with quotas currently enabled.
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quotaon
-F format, --format=format
Check quota files for the specified format. (See quota for valid
formats.)
-g, --group
Only check group quotas.
-i, --interactive
Prompt user for input upon finding errors.
-m, --no-remount
Don’t try to remount mounted filesystems.
-M, --try-remount
Force check to run in read-write mode if it cannot successfully
remount the filesystem in read-only mode.
-n, --use-first-dquot
If multiple entries for a user or group are found in a corrupt
quota file, use the first entry found.
-R, --exclude-root
Don’t check the root filesystem when using the -a option.
-u, --user
Only check user quotas. This is the default.
-v, --verbose
Print information on the progress of the command.
quotaon quotaon [options] [filesystems]
System administration command. Turn on enforcement of file-
system quotas. To work, the filesystems must have a gpquota,
quota, or usrquota option listed in the /etc/fstab file. On most file-
systems, user and group quota files must also exist. XFS filesystems
store quota information as metadata instead of as files. Use
edquota or setquota to create the appropriate quota information.
Options
-a, --all
Turn on quotas for all autoloading filesystems in /etc/fstab that
support them.
-f, --off
Invoke quotaoff instead of quotaon.
-F format, --format=format
Check quota files for the specified format. (See quota for valid
formats.)
-g, --group
Turn group quotas on.
-p, --print-state
Print current quota status, then exit.
-u, --user
Turn user quotas on.
-v, --verbose
Print a message for each filesystem affected by the command.
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rcp
quotaoff quotaoff [options] [filesystems]
System administration command. Turn off enforcement of file-
system quotas. This command is a synonym for quotaon -f.
Options
-a, --all
Turn off quotas for all filesystems in /etc/fstab.
-F format, --format=format
Check quota files for the specified format. (See quota for valid
formats.)
-g, --group
Turn group quotas off.
-p, --print-status
Print current quota status, then exit.
-u, --user
Turn user quotas off.
-v, --verbose
Print a message for each filesystem affected by the command.
-x command, -xfs-commandcommand
On an XFS system, perform one of the following commands:
delete
Remove quota metadata from the XFS filesystem.
enforcement
Turn off limit enforcement on an XFS filesystem.
quotastats quotastats
System administration command. Print a report of quota system
statistics gathered from the kernel.
ranlib ranlibfilename
ranliboption
Generate an index for archive file filename. This is equivalent to
running ar -s.
Option
-v, -V, --version
Print version information and exit.
rcp rcp [options]file1file2
rcp [options]file ... directory
Copy files between two machines. Each file or directory is either a
remote filename of the form rname@rhost:path, or a local file-
name. Files can be copied between two remote machines, where
neither file1 nor file2 is on the local machine. Use of rcp has gener-
ally been replaced by scp, which offers better security.
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rdate
Options
-p Preserve modification times and modes of the source files.
-r If any of the source files are directories, descend into each
directory and recursively copy all files and directories within
it. The destination must be a directory.
rdate rdate [options] [host...]
TCP/IP command. Retrieve the date and time from a host or hosts
on the network and optionally set the local system time.
Options
-l Send errors and output to syslogd.
-p Print the retrieved dates.
-s Set the local system time from the host; must be specified by
root.
-t n Timeout each retrieval attempt after n seconds.
-u Use UDP instead of TCP.
rdist rdist [options] [names]
System administration command. Remote file distribution client
program. rdist maintains identical copies of files over multiple
hosts. It reads commands from a file named distfile to direct the
updating of files and/or directories. An alternative distfile can be
specified with the -f option or the -c option.
Options
-a num
Do not update filesystems with fewer than num bytes free.
-A num
Specify the minimum number of inodes that rdist requires.
-c name [login@]host[:dest]
Interpret the arguments as a small distfile, where login is the
user to log in as, host is the destination host, name is the local
file to transfer, and dest is the remote name where the file
should be installed.
-d var=value
Define var to have value. This option defines or overrides vari-
able definitions in the distfile. Set the variable var to value.
-D Debugging mode.
-f file
Read input from file (by default, distfile). If file is -, read from
standard input.
-F Execute all commands sequentially, without forking.
-l options
Specify logging options on the local machine.
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rdist
-L options
Specify logging options on the remote machine.
-m machine
Update only machine. May be specified multiple times for
multiple machines.
-M num
Do not allow more than num child rdist processes to run
simultaneously. Default is 4.
-n Suppress normal execution. Instead, print the commands that
would have been executed.
-ooptions
Specify one or more options, which must be comma-separated.
chknfs
Suppress operations on files that reside on NFS
filesystems.
chkreadonly
Check filesystem to be sure it is not read-only before
attempting to perform updates.
chksym
Do not update files that exist on the local host but are
symbolic links on the remote host.
compare
Compare files; use this comparison rather than age as the
criteria for determining which files should be updated.
follow
Interpret symbolic links, copying the file to which the
link points instead of creating a link on the remote
machine.
ignlnks
Ignore links that appear to be unresolvable.
nochkgroup
Do not update a file’s group ownership unless the entire
file needs updating.
nochkmode
Do not update file mode unless the entire file needs
updating.
nochkowner
Do not update file ownership unless the entire file needs
updating.
nodescend
Suppress recursive descent into directories.
noexec
Suppress rdist of executables that are in a.out format.
numchkgroup
Check group ownership by group ID instead of by name.
numchkowner
Check file ownership by user ID instead of by name.
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rdistd
quiet
Quiet mode; do not print commands as they execute.
remove
Remove files that exist on the remote host but not the
local host.
savetargets
Save updated files in name.old.
sparse
Check for sparse files—for example, ndbm files.
verify
Print a list of all files on the remote machine that are out
of date, but do not update them.
whole
Preserve directory structure by creating subdirectories
on the remote machine. For example, if you rdist the file
/foo/bar into the directory /baz, it would produce the
file /baz/foo/bar instead of the default /baz/bar.
younger
Do not update files that are younger than the master files.
-p path
Specify the path to search for rdistd on the remote machine.
-P path
Specify path to the transport command to use on the local
machine. This is normally rsh, but may also be ssh. The path
argument may also be specified as a colon-separated list of
acceptable transports to use in order of preference.
-t seconds
Specify the timeout period (default 900 seconds) after which
rdist will sever the connection if the remote server has not yet
responded.
-V Display version, then exit.
rdistd rdistdoptions
System administration command. Start the rdist server. Note that
you must specify the -S option unless you are simply querying for
version information with -V.
Options
-D Debugging mode.
-S Start the server.
-V Display the version number and exit.
readcd readcd dev=device [options]
Read or write compact discs. readcd is now generally a link to
readom.
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readelf
readelf readelfoption[...]elffiles
Display information about one or more ELF (Executable and
Linking Format) object files. At least one option is required to
specify the information to be displayed for each file.
Options
-a, --all
Display all. Equivalent to -A -d -h -I -l -r -s -S -V.
-A, --arch-specific
Display architecture-specific information, if any.
-d, --dynamic
Display the dynamic section.
-D, --use-dynamic
When displaying symbols, use the symbol table in the dynamic
section, not the symbols section.
-e, --headers
Display all headers. Equivalent to -h -l -s.
-h, --file-header
Display the ELF header at the beginning of the file.
-H, --help
Display help information and exit.
-I, --histogram
Display a histogram of bucket bit lengths when displaying the
symbol tables.
-l, --program-headers, --segments
Display the segment headers, if any.
-n, --notes
Display the NOTE segment, if any.
-r, --relocs
Display the relocation segment, if any.
-s, --symbols, --syms
Display entries in symbol table sections, if any.
-S, --section-headers, --sections
Display the section headers, if any.
-u, --unwind
Display the unwind section, if any (currently applies only to
IA64 ELF files).
-v, --version
Display version information and exit.
-V, --version-info
Display the version sections, if any.
-w[option], --debug-dump[=option]
Display the debug sections. If specified with an option, display
only that section. The options shown here in parentheses are
for -w; the words preceding them are for --debug-dump. The
options are abbrev (a), frames (f), frames-interp (F), info (i),
line (l), loc (o), macro (m), pub-names (p), ranges (r), and str (s).
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readlink
-W, --wide
Don’t break output lines at 80 columns. The default is to
break them. Useful for wide terminals.
-x num, --hex-dump=num
Display a hexadecimal dump of the section number.
readlink readlinkfile
readlinkoption
Print the contents of the symbolic link file—that is, the name of
the file to which the link points.
Options
-f, --canonicalize
Canonicalize by recursively following symbolic links.
--help
Print usage information and exit.
-n, --no-newline
Do not output a trailing newline.
-q, --quiet, -s, --silent
Suppress most error messages.
-v, --verbose
Print all error messages.
--version
Print version information and exit.
readom readom dev=device [options]
Read or write compact discs. The device is usually specified as
dev=scsibus/target/lun or dev=target/lun if the device is on the
default SCSI bus. The default SCSI bus is bus 0, the target is the ID
number, and the lun is the logical unit number.
Options
-c2scan
Do a C2 error scan. If any C2 errors are found, specifying the
speed= option to reduce the speed may help.
-clone
Read all data and the table of contents, and put the table-of-
contents data into a file with the same filename as specified
with f= but with a .toc extension.
-d, debug=num
Increment the debugging level by 1 with -d or set the level to
num with debug. Specifying -dd is the equivalent of debug=2.
dev=target
Set the SCSI target.
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readom
f=filename
Specify the file from which input should be read, or to which
output should be written. If the filename is given as -, use stan-
dard input or standard output, respectively.
-factor
Print the speed factor for the meshpoints= option, based on
the current medium’s single speed. Works only if readom can
determine the current medium type.
-fulltoc
Read the full table of contents from the current CD and
display it in hexadecimal.
kd=num, kdebug=num
Modify the kernel debugging level while SCSI commands are
running, to do kernel debugging.
meshpoints=num
Print the read speed at num locations, and produce a list of
values suitable for plotting. The output is written to standard
output.
-nocorr
Ignore read errors, doing no error correction. Switches the
drive into a mode to ignore the errors; if readom completes, it
switches the drive back to the previous mode.
-noerror
Do not abort if an uncorrectable error is found in the data
stream.
-notrunc
Do not truncate the output file on open.
-overhead
Measure SCSI command overhead. The measurement is done
by running several commands 1000 times and printing the
total time used for each.
retries=num
Set the retry count to num. The default is 128.
-s, -silent
Do not print a status report for SCSI command failures.
-scanbus
Scan all SCSI devices on all SCSI buses, print the results, and
exit. Useful for finding the SCSI addresses of devices.
sectors=range
Specify the range of sectors to read.
speed=num
Set the reading and writing speed, as an integer value. Useful
only for MMC-compliant drives. Defaults to maximum speed.
timeout=num
Set the default SCSI command timeout to num seconds.
Defaults to 40 seconds.
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reboot
ts=num
Set the maximum transfer size for a single SCSI command to
num. Defaults to 256 KB.
-v, -verbose
Increment the general verbosity level by 1. Useful for
displaying progress.
-V, -Verbose
Increment the verbosity level for SCSI command transport by
1. Useful for debugging. Specifying -VV adds data-buffer
content to the output.
-version
Print version information and exit.
-w Switch to write mode. The default is to read from the device.
reboot reboot [options]
System administration command. Close out filesystems, shut down
the system, then reboot. Because this command immediately stops
all processes, it should be run only in single-user mode. If the
system is not in runlevel 0 or 6, reboot calls shutdown -r.
Options
-f Call reboot even when shutdown would normally be called.
-i Shut down network interfaces before reboot.
-n Suppress normal call to sync.
-w Suppress normal execution; simply write to /var/log/wtmp.
reject reject [options]destination
System administration command. Instruct printing system to reject
jobs for the specified print queue destinations. Depending on queue
settings, the system may prompt for a password. Also invoked as
cupsreject.
Options
-E Require encryption when connecting.
-h server
Apply command remotely to the specified CUPS server.
-r reason
Reject with the specified reason instead of the default “Reason
Unknown.”
rename renamefromto files
Rename files by replacing the first occurrence of from in each file-
name with to.
Example
Rename files that start with test so they start with mytest:
$rename test mytest test*
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repquota
renice renice [priority] [options] [target]
Control the scheduling priority of running processes. May be
applied to a process, process group, or user (target). A privileged
user may alter the priority of other users’ processes. priority must,
for ordinary users, lie between 0 and the environment variable
PRIO_MAX (normally 20), with a higher number indicating
increased niceness. A higher niceness value means that the process
will run at a lower priority. A privileged user may set a negative
priority, as low as PRIO_MIN (normally –20), to speed up
processes. See the nice command for setting the scheduling priority
for processes when they are initially run.
Options
+num
Specify number by which to increase current priority of
process, rather than an absolute priority number.
-num
Specify number by which to decrease current priority of
process, rather than an absolute priority number.
-g, --pgrp
Interpret target parameters as process group IDs.
-p, --pid
Interpret target parameters as process IDs (default).
-u, --user
Interpret target parameters as usernames.
repquota repquota [options] [filesystem]
System administration command. Generate a report on disk usage
and quotas for the specified filesystem.
Options
-a, --all
Generate report for all filesystems in /etc/mtab that support
quotas.
-c, --batch-translation
Translate UIDs and GIDs in batches. (Faster for /etc/passwd.)
-C, --no-batch-translation
Translate UIDs and GIDs individually. (Faster for database
lookups.)
-F format, --format=format
Report on quotas for the specified format. (See quota for valid
formats.)
-g, --group
Report group quotas.
-i, --no-autofs
Ignore automount mount points.
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reset
-n, --no-names
Use UIDs and GIDs instead of names. (Generates faster
reports.)
-p, --raw-grace
When user is in a grace period, print a timestamp (seconds
since epoch) marking when the grace period expires.
-s, --human-readable
Report sizes in more human-readable units.
-t, --truncate-names
Truncate user and group names to nine characters.
-u, --user
Report user quotas. (This is the default.)
reset reset [options] [terminal]
Clear screen (reset terminal). If terminal is specified on the
command line, the value is used as the terminal type. reset is a
symbolic link to the tset command. Invoking the command as reset
is useful for clearing your terminal when a program dies and leaves
the terminal in an abnormal state. You may have to run the
command with a linefeed character (usually Ctrl-J) before and after
it:
Ctrl-JresetCtrl-J
See the tset command for the available options.
resize2fs resize2fs [options]device [size]
System administration command. Enlarge or shrink an ext2 file-
system on device so it has size blocks. The filesystem size cannot be
larger than the underlying partition. This command changes only
the filesystem size, not the underlying partition. To change the
partition, use fdisk.
Options
-d flags
Print debugging information on resize activity. The value of
the flags parameter determines what activity is reported.
Compute its value by summing the numbers of the items you
wish to debug:
2 Block relocations.
4 Inode relocations.
8 Inode table movement.
-f Force resize, overriding safety checks.
-M Shrink filesystem to minimum size.
-p Print progress information for each resize task.
-P Print maximum filesystem size then exit.
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restore
restore restoreflag [options] [files]
System administration command. Restore backed-up files from a
dump archive. Execute this command with one of the following
flags.
Flags
-C Compare files on disk to files in the backup and print report.
-i Restore files interactively. This will open a shell-like interface
that accepts the following commands.
add [name]
Add the current working directory, or the specified file or
directory name to the list of files to extract.
cd directory
Change the current working directory.
delete [name]
Remove the current working directory or the specified file
or directory name from the list of files to extract.
extract
Extract selected files. This will prompt for the volume on
which the files to be extracted can be found. Once the
files are extracted, the system will prompt if you want to
change the ownership and mode of the current directory
(the one to which you extracted the files) to match the
settings on the dump’s original base directory.
help
Print a command summary.
ls [name]
Like the shell command, list files in the current working
directory, or the specified file or directory name. A *
before a name indicates items marked for extraction. In
verbose mode, the listing will include each item’s inode.
pwd
Like the shell command, print the working directory.
quit
Exit the command.
setmodes
Set ownership and mode of the directory to which you
extract the files to match the settings on the dump’s orig-
inal base directory.
quit
Exit the command.
verbose
Verbose mode. Print inodes along with file and directory
names when using ls.
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restore
-P filename
Create a Quick File Access file suitable for use with the -Q
option.
-r Fully restore the backup to a clean, newly created ext2 file-
system. Execute this command in the root directory of the new
filesystem.
-R Prompt for the tape volume to fully restore.
-t Print files if they exist in the archive or an error if they do not.
If no files are specified, list all files in the archive.
-x Recursively extract files if they exist in the archive. Restore
owner, modification times, and modes. If no files are speci-
fied, restore the entire backup.
Options
-a Read all volumes to find the files to extract, beginning with
volume 1. This will skip any volume prompts.
-A file
Read the table of contents from the specified archive file.
-bblocksize
Specify the block size in kilobytes used for a block in the
archive. Restore can usually determine this when reading
the dump media.
-c Read dumps made prior to version 4.4.
-d Print debugging information.
-D filesystem
When using the -C flag, compare the dump to files on the
specified filesystem.
-f file
Read the backup from the specified file: a device file, an ordi-
nary file, or - to read from standard input. Use host:file or
user@host:file to read from a networked host using either the
rmt program or the program specified by the RMT environ-
ment variable.
-F script
Run the specified script at the beginning of each volume.
restore will pass the current device and volume number to the
script. The script should return 0 to continue, 1 to prompt for
a new tape, or any other exit value to abort the restore. The
script will run with the process’s real user and group ID.
-h Do not recursively restore directory. Only restore the speci-
fied directory.
-k Use Kerberos authentication when connecting to a remote
server.
-l Treat file as a regular file instead of a tape device. Use this
option when restoring from remote compressed files.
-L n
Used with the -C flag. Abort the comparison after encoun-
tering n errors.
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rexec
-m Expect filenames to be given as inodes.
-M Restore from a multivolume backup. Treat any filename
provided with -f as a prefix.
-N Perform all actions indicated by other flags and options, but
don’t write anything to the disk.
-o Automatically set ownership and mode of the current directory
to match the original base directory of the dump.
-Q file
Read tape positions from the specified Quick File Access
mode file.
-S n
Read from volume n of a multifile backup.
-u Unlink (remove) any existing files before writing a file with the
same name.
-v Verbose mode. Print information about files being restored.
-V Enable multivolume mode for devices other than tapes.
-X file
Read list of files and directories to extract from the specified file.
Use - to retrieve list of files from standard input.
-y Attempt to skip over errors without prompting for operator input.
rev rev [files]
Reverse the order of characters on each line of the specified files
and print the results on standard output. If no files are specified,
rev reads from standard input.
rexec rexec [options]rhost command
Execute commands remotely. This client program connects to a
remote host running rexecd, and passes it command. It uses a login
name and password for authentication. These can be passed on the
command line using the options below, provided through the
$HOME/.netrc file or the environment variables REXEC_USER and
REXEC_PASS. If it cannot determine the username and password,
rexec prompts the user for the information. Note that because rexec
sends passwords to the remote system in cleartext, you should use
it only on a secure network. See ssh for a more secure alternative.
Options
-a Send both error messages and output to standard output.
-b When received locally, only echo signals SIGINT, SIGQUIT
and SIGTERM to the remote process.
-c Leave remote standard input open when the local input closes.
-d Debugging mode. Echo commands sent locally.
-l username
Specify a different username for the remote login. Default is
the same as your local username.
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rexecd
-n Prompt user for name and password even if otherwise provided.
-p password
Specify the password for the remote account.
-s Do not echo any signals to the remote process.
rexecd rexecdcommand-line
TCP/IP command. Server for the rexec routine, providing remote
execution facilities with authentication based on usernames and
passwords. rexecd is started by inetd and must have an entry in
inetd’s configuration file, /etc/inetd.conf.
Option
-D Disable reverse DNS lookup; use IP addresses in logs.
rlogin rlogin [options]rhost
Remote login. rlogin connects the terminal on the current local
host to the remote host rhost. The remote terminal type is the same
as your local terminal type. The terminal or window size is also
copied to the remote system if the server supports it. Use of rlogin
has generally been replaced with ssh, which offers better security.
Options
-8 Allow an 8-bit input data path at all times.
-d Debugging mode.
-ec Specify escape character c (default is ~).
-E Do not interpret any character as an escape character.
-l username
Specify a different username for the remote login. Default is
the same as your local username.
-L Allow rlogin session to be run without any output postprocessing
(i.e., run in litout mode).
rlogind in.rlogind [options]
TCP/IP command. Server for the rlogin program, providing a
remote login facility, with authentication based on privileged port
numbers from trusted hosts. rlogind is invoked by inetd when a
remote login connection is requested. The login process propagates
the client terminal’s baud rate and terminal type as found in the
TERM environment variable.
Options
-a Verify hostname.
-h Permit superuser .rhosts files to be used. Ignored if pluggable
authentication module (PAM) support is enabled. Control
through /etc/pam.conf instead.
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rm
-l Do not authenticate hosts via a nonroot .rhosts file. Ignored if
pluggable authentication module (PAM) support is enabled.
Control through /etc/pam.conf instead.
-L Do not authenticate hosts via .rhosts or hosts.equiv files.
Ignored if pluggable authentication module (PAM) support is
enabled. Control through /etc/pam.conf instead.
-n Suppress keep-alive messages.
rm rm [options]files
Delete one or more files. To remove a file, you must have write
permission in the directory that contains the file, but you need not
have permission on the file itself. If you do not have write permis-
sion on the file, you will be prompted (y or n) to override. rm is
often aliased to rm -i, especially for the root user, to protect against
inadvertently deleting files.
Options
-d, --directory
Remove directories, even if they are not empty. Available only
to a privileged user.
-f, --force
Remove write-protected files without prompting.
--help
Print a help message and then exit.
-i Prompt for y (remove the file) or n (do not remove the file) for
each file.
--interactive[=when]
Specify when to prompt. The possible values for when are
never, no, none, once, always, yes.
-I Prompt only once before deleting recursively or before
deleting more than three files.
--no-preserve-root
Do not treat root (/) specially. This is the default.
--one-file-system
When removing recursively, only remove files on the same file-
system as files.
--preserve-root
Do not remove root (/).
-r, -R, --recursive
If file is a directory, remove the entire directory and all its
contents, including subdirectories. Be forewarned: use of this
option can be dangerous.
-v, --verbose
Verbose mode (print the name of each file before removing it).
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rmail
--version
Print version information and then exit.
-- Mark the end of options. Use this when you need to supply a
filename beginning with -.
rmail rmail [options]users
TCP/IP command. Handle remote mail received via uucp. rmail
transforms trace information from mail in UUCP format to the
equivalent RFC 822 format, then forwards messages to sendmail.
Options
-D domain
Use domain instead of UUCP as the UUCP hostname in From
fields.
-T Print debugging information.
rmdir rmdir [options]directories
Delete the named directories (not the contents). directories are
deleted from the parent directory and must be empty (if not, rm -r
can be used instead). See also mkdir.
Options
--help
Print a help message and then exit.
--ignore-fail-on-non-empty
Ignore failure to remove directories that are not empty.
-p, --parents
Remove directories and any intervening parent directories that
become empty as a result. Useful for removing subdirectory
trees.
-v, --verbose
Verbose mode; print message for each directory as it is
processed.
--version
Print version information and then exit.
rmmod rmmod [options]modules
System administration command. Unload a module or list of
modules from the kernel. This command is successful only if the
specified modules are not in use and no other modules are depen-
dent on them. This simplified program provides some backward
compatibility. In general, use modprobe -r instead.
Options
-s, --syslog
Write messages to syslogd instead of to the terminal.
-v, --verbose
Verbose mode.
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rndc
-V, --version
Print version number, then exit.
-w, --wait
If module is in use, disable it so no new processes can use it.
Remove the module when it is no longer in use.
rndc rndc [options] [command]
TCP/IP command. Send commands to a BIND DNS server via a
TCP connection (see the named command.) This command reads
authentication and connection information from the file /etc/rndc.
conf, and its authentication key from /etc/rndc.key. If entered
without a command, display a help message listing the available
commands.
Options
-c file
Read configuration information from file instead of /etc/rndc.conf.
-kfile
Perform command on the routing cache instead of the
forwarding information base (FIB) routing table.
-pport
Connect to the specified port instead of the default control
channel port, 953.
-s server
Send command to the specified server. There must be an entry
for server in the configuration file.
-V Use verbose log messages.
-y keyname
Specify the key to use by keyname. There must be a key entry
for keyname in the /etc/rndc.conf file.
Commands
You can send the following commands to a BIND nameserver:
dumpdb
Dump current cache to the dump file (specified in /etc/named.
conf), or to named_dump.db when not specified.
flush [view]
Flush all server caches, or only the cache for the specified
view.
halt
Stop server immediately.
querylog
Toggle query logging.
reconfig
Reload the configuration file and any new zones.
reload [zone [class [view]]]
Reload configuration file and zones. When specified, limit the
reload to the given zone, class, or view.
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route
refresh zone
Refresh database information for zone.
stats
Write statistics to the statistics file (specified in /etc/named.
conf).
status
Display server status.
stop
Save any recent dynamic zone transfer updates (IXFR) to the
master files, then stop the server.
trace [debuglevel], notrace
Increase the server’s debug level by 1, or set it to the specified
debuglevel. Use the notrace command to set the level to 1.
route route [options] [command]
TCP/IP command. Add or remove entries in the routing tables
maintained by routed. route accepts two commands: add, to add a
route, and del, to delete a route. The two commands have the
following syntax:
add [-net | -host]address [modifiers]
del [-net | -host]address [modifiers]
address is treated as a plain route, unless -net is specified or address
is found in /etc/networks. -host can be used to specify that address
is a plain route whether or not it is found in /etc/networks. Using
route modifiers, you can specify the gateway through which to
route packets headed for that address, its netmask, TCP mss, or the
device with which to associate the route; you can also mask certain
routes. Only a privileged user may modify the routing tables.
If no command is specified, route prints the routing tables.
Options
-A family, --family
Specify an address family to use with an add or del command.
family may be inet, inet6, ax25, netrom, ipx, ddp, or x25.
-C, --cache
Perform command on the routing cache instead of the
forwarding information base (FIB) routing table.
-e, --extend
Use netstat -r format to print routing table. Use twice to print
extended information. Same as netstat -ree.
-F, --fib
Perform command on the forwarding information base (FIB)
routing table. This is the default behavior.
-h, --help
Print help message, then exit.
-n, --numeric
Show numerical addresses; do not look up hostnames. (Useful
if DNS is not functioning properly.)
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rpcbind
-v, --verbose
Verbose mode.
-V, --version
Print version and configuration options, then exit.
Route modifiers
[dev] interface
Associate route with specified device. When the interface is
given as the last argument on a command line, the word dev
is optional.
netmask mask
Use netmask mask.
gw gateway
Route packets through gateway.
metric n
Set routing metric to n.
mss bytes
Set maximum segment size for connections over this route.
reject
Cause route lookup for target to fail. Used to mask out
networks from a default route.
Example
Add a default gateway for interface eth0:
route add default gw 192.168.0.1 dev eth0
rpcbind rpcbind [options]
NFS/NIS command. portmap is renamed rpcbind in newer Linux
systems. It maps RPC program numbers into universal addresses.
This server must be running in order to make RPC calls. RPC
servers run on a host register their program number with rpcbind.
Clients wishing to make an RPC call first check with rpcbind to
find the address for a given program number.
-a Abort on errors if debugging (-d).
-d Run in debug mode. Do not fork.
-h [address]
Bind to the specified IP address for UDP requests. This option
may be given multiple times. You need not specify the local-
host. When using this option rpcbind automatically binds to
127.0.0.1 and ::1 (if using IPv6) as well.
-i Insecure mode. Allow calls to SET and UNSET from any host.
-l Enable libwrap connection logging (tcp wrappers).
-s Change to user daemon sooner. Bind to nonprivileged ports
for outgoing connections, refuse connections to privileged
ports from nonprivileged clients.
-w Warm start. Read stat from a previous rpcbind.
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rpcgen
rpcgen rpcgen [options]file
Parse file, which should be written in the RPC (Remote Procedural
Call) language, and produce a program written in C that imple-
ments the RPC code. Place header code generated from file.x in file.
h, XDR routines in file_xdr.c, server code in file_svc.c, and client
code in file_clnt.c. Lines preceded by % are not parsed. By default,
rpcgen produces Sun OS 4.1–compatible code.
-a Produce all files (client and server).
-b Produce SunOS 4.1–compatible code. This is the default.
-5 Produce SVR4-compatible code.
-c Create XDR routines. Cannot be used with other options.
-C Produce ANSI C code (the default).
-k Produce K&R C code.
-Dname[=value]
Define the symbol name, and set it equal to value or 1.
-h Produce a header file. With -T, make the file support RPC
dispatch tables. Cannot be used with other options.
-I Produce an inetd-compatible server.
-K secs
Specify amount of time that the server should wait after
replying to a request and before exiting. Default is 120. Setting
secs to -1 prevents the program from ever exiting.
-l Produce client code. Cannot be used with other options.
-m Produce server code only, suppressing creation of a “main”
routine. Cannot be used with other options.
-N New style. Allow multiple arguments for procedures. Not
necessarily backward-compatible.
-o [file]
Print output to file or standard output.
-Sc Print sample client code to standard output.
-Ss Create skeleton server code only.
-t Create RPC dispatch table. Cannot be used with other
options.
-T Include support for RPC dispatch tables.
rpcinfo rpcinfo [options] [host] [program] [version]
NFS/NIS command. Report RPC information. program can be either
a name or a number. If a version is specified, rpcinfo attempts to
call that version of the specified program. Otherwise, it attempts to
find all the registered version numbers for the specified program by
calling version 0, and then attempts to call each registered version.
Options
-b Make an RPC broadcast to the specified program and version
using UDP, and report all hosts that respond.
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rshd
-d Delete the specified version of program’s registration. Can be
executed only by the user who added the registration or by a
privileged user.
-n portnum
Use portnum as the port number for the -t and -u options,
instead of the port number given by the portmapper.
-p Probe the portmapper on host and print a list of all registered
RPC programs. If host is not specified, it defaults to the value
returned by hostname.
-t Make an RPC call to program on the specified host using TCP,
and report whether a response was received.
-u Make an RPC call to program on the specified host using UDP,
and report whether a response was received.
rpm rpm [options]
The Red Hat Package Manager. A freely available packaging system
for software distribution and installation. RPM packages are built,
installed, and queried with the rpm and rpmbuild commands. For
detailed information on RPM, see Chapter 5.
rsh rsh [options]host [command]
Execute command on remote host, or, if no command is specified,
begin an interactive shell on the remote host using rlogin. The
options can be specified before or after host. Use of rsh has gener-
ally been replaced with ssh, which offers better security.
Options
-d Enable socket debugging.
-l username
Attempt to log in as username. By default, the name of the
user executing rsh is used.
-n Redirect the input to rsh from the special device /dev/null.
(This should be done when backgrounding rsh from a shell
prompt, to direct the input away from the terminal.)
rshd rshd [options]
TCP/IP command. Remote shell server for programs such as rcmd
and rcp, which need to execute a noninteractive shell on remote
machines. rshd is started by inetd and must have an entry in
inetd’s configuration file, /etc/inetd.conf.
All options are exactly the same as those in rlogind, except for -L,
which is unique to rshd.
Option
-L Log all successful connections and failed attempts via syslogd.
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rsync
rsync rsync [options]sources dest
Transfer files; used frequently for updating files across a network.
File transfer with rsync is fast and efficient because it checks local
files against remote files in small chunks, or blocks, and transfers
only the blocks that differ between the files.
sources and the final dest are in the form of:
user@host:port/filename
If the file is on the local host, a plain filename can be specified. If
the file is on a remote host, the host must also be specified. user can
optionally be specified to log in as a different user on the remote
site (in which case a password prompt might appear) and port can
optionally be specified with a remote host to make rsync use a TCP
port other than its default, 873.
Relative filenames (names without initial slashes) are handled rela-
tive to the user’s home directory. If a source directory is listed with
a trailing slash, the whole directory is transferred and will appear
under the destination directory; if the directory is listed without
the slash, its files and subdirectories will appear directly under the
destination directory. Normally, regular directories and files are
transferred, but not symbolic links or other special files such as
sockets and FIFOs.
Two other formats for sources and dest, which refer to files on an
rsync server (rsyncd), are:
user@host::filename
rsync://user@host:port/filename
rsync servers are beyond the scope of this book.
Options
-0, --from0
Specify that the file specified in options such as --files-from is
formatted with null characters to separate the filenames; when
this option is not used, the file must include each filename on
a separate line.
-4, --ipv4, -6, --ipv6
Opt for IPv4 or IPv6 when creating sockets.
-8, --8-bit-output
Leave high-bit characters unescaped in output.
-a, --archive
Transfer recursively, reproducing most characteristics of the
files and directories being transferred, such as modification
times, symbolic links, ownership, and permissions. Equivalent
to -rlptgoD. With --files-from, transfer is not recursive.
--address=addr
Specify the IP address of an rsync server to connect to; useful
when multiple servers are running on the same host.
--append
Append new data to the end of an existing file. Implies --inplace.
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rsync
--append-verify
Like --append, but include existing data in full-file checksum
verification.
-b, --backup
Preserve existing files at the destination by appending a suffix
such as ~ while transferring new versions of those files.
-B n, --block-size=n
Change block size used for transfers.
--backup-dir
Specify where files created by the --backup option are stored.
--blocking-io
Use blocking I/O when starting the remote shell used for
transfer.
--bwlimit=n
Set a limit to the speed of transfer, specified in kilobytes per
second.
-c, --checksum
Perform a full checksum on each file transferred.
-C, --cvs-exclude
Don’t transfer files that are normally considered temporary or
otherwise uninteresting; obeys the same rules for ignoring files
as CVS (Concurrent Versions Systems).
--compare-dest=dir
Compare source files to files of the same name in dir as well as
the destination directory.
--compress-level=num
Set the compression level to num. If nonzero, -z/--compress is
implied.
--config=configfile
When running as server, take configuration from configfile
instead of /etc/rsyncd.conf.
--contimeout=n
Set time in seconds to wait for a connection to an rsync
daemon.
--copy-unsafe-links
If files to which symbolic links point are being transferred,
copy even those files that exist outside the directories being
transferred.
-d, --dirs
Transfer directories with no recursion unless the directory
name is . or ends in a trailing slash (/).
-D Equivalent to --devices --specials.
--daemon
Run rsync as server.
--devices
Transfer device (/dev) files; requires superuser permission on
both systems.
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rsync
--delete-after
After transferring files from a source directory, delete any files
from the destination directory that do not exist in the source
directory.
--delete
Before transferring files from a source directory, delete any
files from the destination directory that do not exist in the
source directory.
--delete-excluded
Invoke --delete, and additionally delete from the destination
directory any files that match exclude options.
-e shell, --rsh=shell
Use shell (which can be a complete command with arguments,
enclosed in quotes) to create the connection between two
systems for file transfer. rsync uses rsh by default. Nowadays,
most users prefer the secure shell ssh. This can be made the
default by setting the environment variable RSYNC_
RSH=ssh.
--exclude=glob-pattern
Don’t transfer files whose names match glob-pattern. Rules for
glob-pattern are complex and are described in the manpage. In
general, filenames can include the shell globbing characters *
to match everything, ? to match a single character, and [] to
enclose a set of matching characters. Furthermore, to specify
the beginning of a filename, start the name with a / character
(it does not mean the file has to be an absolute pathname).
--exclude-from=file
Like --exclude, but globbing patterns are taken from file; each
pattern on a separate line.
--existing, --ignore-non-existing
Transfer only files that already exist on the destination host.
--files-from=file
Take names of files to transfer from file.
--force
Allow a file to replace a nonempty directory of the same name.
-g, --group
Set the group (normally identified by name, not number) of the
destination file to match that of the source file, instead of
using the group running the rsync program.
-H, --hard-links
Set hard links on destination system to match source system.
--help
Display command syntax and options, then exit.
-h, --human-readable
Output numbers in a more easily read format, using larger
units with a K, M, or G suffix.
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rsync
--ignore-errors
Delete files even when there are I/O errors.
--ignore-existing
Do not transfer files to replace existing files of the same name.
-I, --ignore-times
Consider files for transfer even if they have the same size and
timestamp as destination files.
--include=glob-pattern
Specify files to be transferred even if further exclude options
would cause them to be ignored. rsync processes the include
and exclude options in the order they appear on the command
line, so earlier include options override later exclude options.
--include-from=file
Like --include, but take globbing patterns from file, which has
each pattern listed on a separate line.
--inplace
Update files in place instead of creating a new copy and then
moving it.
-l, --links
Set symbolic links on destination system to match source
system.
-L, --copy-links
Transfer the files to which symbolic links are made instead of
just the pointer information in the links.
--log-file=file
Write log data to the specified file.
--log-format=format
Display information about each file transferred in a format
specified by % sequences; see rsyncd.conf manpage for formats.
Used with --log-file.
--max-delete=n
Delete at most n files when deleting from destination host.
--max-size=n, --min-size=n
Don’t transfer files that are larger than or smaller than the
specified size.
-n, --dry-run
Display the names of files that would be transferred and statis-
tics related to a transfer, without performing a transfer.
--no-blocking-io
Do not use blocking I/O when starting the remote shell used
for transfer.
--no-detach
When running as a daemon, do not restart as a background
process.
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rsync
--no-implied-dirs
When preserving directory structures with --relative, do not
force the creation of new directories or symbolic links if the
destination host is set up differently from the source host.
--no-relative
Transfer only the plain files without preserving the entire
directory structure of files whose names include directories;
otherwise, --files-from would create the entire directory struc-
ture to contain the file.
--no-whole-file
Use rsync’s block checks to transfer parts of files where
possible.
--numeric-ids
Set user and group IDs on destination files by number rather
than name.
-o, --owner
Set the user (normally identified by name, not number) of the
destination file to match that of the source file, instead of
settng it to the user running the rsync program.
-O, --omit-dir-times
When using --times to preserve modification times, don’t
preserve directory times.
-p, --perms
Set the permissions of the destination file to match that of the
source file, instead of using the existing file’s permissions or
the default umask of the destination user.
-P Combination of --partial and --progress.
--partial
Preserve partial files transferred if rsync is interrupted. The
default is to delete them.
--partial-dir=dir
Specify a directory for keeping partial files instead of using
--partial. Useful for speeding up the resumption of the
transfer later. The file is deleted from dir once the transfer is
complete.
--password-file=file
Take password for accessing a remote rsync server from file.
--port=n
Use port n instead of default rsync port.
--progress
Display ongoing statistics about the progress of the transfer of
each file.
-q, --quiet
Do not display statistics or server error messages.
-r, --recursive
Copy directories with all their contents.
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rsync
-R, --relative
Preserve the entire path of a specified source file or directory,
instead of creating the file directly under the destination direc-
tory. That is, if project/tmp/main.c is specified, create project/
tmp/main.c instead of just main.c. Create intermediate directo-
ries if needed.
--read-batch=file
Apply all changes stored in the specified file, written by a
preceding --write-batch.
--remove-source-files
After files have been successfully transferred, remove them
from the source system. Directories are not removed.
--rsync-path=file
Use the rsync binary located in file on the destination system.
--safe-links
Don’t copy links that point to absolute paths or to files
outside the directories being transferred.
-s, --protect-args
Protect arguments sent to the remote system from intrepreta-
tion by the remote shell.
-S, --sparse
Perform special optimizations on sparse files (files that contain
holes and actually contain less data than their sizes indicate).
--size-only
Skip files that have the same size on the source and destina-
tion hosts, even if their timestamps differ; usually, this check
is based on both size and timestamp.
--specials
Transfer special files such as named sockets and FIFOs.
--stats
Like -v, but also prints a number of statistics about each file
transferred, such as the number of bytes actually transferred
and the number transferred to compare the files on the two
hosts.
--suffix=string
Set the suffix placed on backup files to string. Default is a tilde
(~).
-t, --times
Set the timestamps of the destination file to match those of the
source file, instead of using the time of transfer (that is,
reflecting the existence of a new file on the destination host).
-T dir, --temp-dir=dir
Use dir as rsync’s temporary directory instead of the destination
directory.
--timeout=n
Stop rsync if n seconds pass with no data being transferred.
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rsync
-u, --update
Don’t change a destination file if it is newer than the source
file.
--version
Display rsync’s version and compiled-in features, then exit.
-v, --verbose
Display the names of files transferred and statistics related to
the transfer.
-W, --whole-file
Transfer the entire files, instead of usingrsync’s block checks
to transfer just parts of files where possible.
--write-batch=prefix
Prepare to synchronize systems by writing files, whose names
start with prefix, that describe the transfers to take place.
-x, --one-file-system
When traversing directories, do not transfer files on directories
that are mounted on other filesystems.
-z, --compress
Use compression during transmission.
Examples
Transfer the entire directory proj to the /planning directory on
remote host ourhub:
$rsync -r proj/ ourhub:/planning
Transfer the files and subdirectories under proj to the /planning
directory on remote host ourhub:
$rsync -r proj ourhub:/planning
Return files from local directory active to the /tmp/active directory
on remote host ourhub. Files to be transferred are listed in active/
current_work.txt:
$cat active/current_work.txt
workplan.doc
workplan.sxw
$rsync -v --files-from=active/current_work.txt active \
ourhub:/tmp/active
building file list ... done
workplan.doc
workplan.sxw
...
Copy the source directory’s OpenOffice.org (.sxw) files and Kim’s
status report, but exclude the other status reports.
$ls proj
conclusion.sxw Status_joem Status_leigh
incentives.sxw Status_kim unified.sxw
$ rsync -rv --include=*kim --exclude=/proj/Status* proj \
ourhub:tmp
building file list ... done
proj/Status_kim
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rsyslogd
proj/conclusion.sxw
proj/incentives.sxw
proj/unified.sxw
...
rsyslogd rsyslogd [options]
System administration command. rsyslogd provides local and
remote logging functions. It is based on sysklogd and on some
systems replaces that program. It adds support for logging over
TCP, SSL, TLS, logging to databases and more. By default rsys-
logd is command-line compatible with sysklogd and can be used as
a drop-in replacement. In native mode, some of the old command
line options have been moved to the configuration file. rsyslogd
will log warnings for these deprecated commands. Its compati-
bility mode can be changed with the -c3 option.
rsyslogd logs system messages into a set of files described by the
configuration file /etc/rsyslog.conf. Each message is one line. A
message can contain a priority code, marked by a number in angle
brackets at the beginning of the line.
Options
-4 Listen on IPV4 addresses only.
-6 Listen on IPV6 addresses only.
-A If there are multiple paths to a UDP target, send to all paths.
-cmode
Set compatibility mode. Values for mode are 0, for sysklogd
and 3 to enable native rsyslogd options. The default value is 0
though this also generates a warning that you are not using
native mode.
-d Turn on debugging. Don’t fork.
-f configfile
Specify alternate configuration file.
-i pidfile
Specify alternate pid file.
-l hostlist
Specify hostnames that should be logged with just the host-
name, not the fully qualified domain name (fqdn). Multiple
hosts should be separated by a colon (:).
-n Avoid auto-backgrounding. This is needed when starting
syslogd from init.
-p socket
Send log to socket instead of /dev/log.
-q If DNS is not available when determining which systems are
AllowedSenders (from the configuration file), use the host-
name instead of the hosts IP address.
-Q Don’t resolve hostnames to IP addresses when determining
AllowedSenders.
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runlevel
-s domainlist
Strip off domain names specified in domainlist before logging.
Multiple domain names should be separated by a colon (:).
-v Print version number, then exit.
-w Don’t warn when receiving messages from systems not in the
AllowedSender list.
-x Don’t perform DNS lookups for remote hosts sending logs.
runlevel runlevel [utmp]
System administration command. Display the previous and current
system runlevels as reported in the utmp file. The default utmp file
is /var/run/utmp. See “Starting and Stopping the System” on page 19.
sane-find-
scanner
sane-find-scanner [options]
Locate SCSI and USB scanners and print their device files, to be
sure the scanners can be detected by SANE (Scanner Access Now
Easy) backends.
Options
devname
Check only the specified device for a scanner.
-f Force the opening of any SCSI and USB devices specified with
devname, in case the command is wrong in determining the
device type.
-h, -?
Print a usage message and exit.
-p Test for parallel-port scanners. Note that most parallel-port
scanners won’t be detected, even with this option.
-q Run quietly, printing only the devices.
-v Run verbosely. When specified as -v, show every device name
and test result; as -vv, also print SCSI inquiry information and
USB device descriptors.
scanimage scanimage [options]
Read images from devices such as scanners and cameras, writing
the images to standard output in one of the PNM (Portable
aNyMap) formats. scanimage uses the SANE interface to access the
scanner and can support any device for which there is a SANE
backend.
Formats
PBM
Black-and-white
PGM
Grayscale
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scanimage
PPM
Color
TIFF
Black-and-white, grayscale, or color
Options
--accept-md5-only
Only accept MD5 authorization requests.
-b [format], --batch[=format]
Work in batch mode, using a document feeder. Each page is
written to a file, as specified by format, using a printf-type
string. The default format is out%d.pnm for the PNM formats
and out%d.tif for TIFF.
-B, --buffersize
Change the buffersize from the default 32 KB to 1 MB.
--batch-count=num
The number of pages to scan in batch mode. Use this option
for scanners that do not signal when they are empty; the
default is to continue scanning until such a signal is received.
--batch-double
Increment the page number by 2 in batch mode. Used for
scanning two-sided originals on a single-sided scanner.
--batch-increment=num
Increment the number in the filename by num in batch mode.
--batch-prompt
In batch mode, prompt the user to press Return before scan-
ning a page. Useful for manually feeding multiple pages.
--batch-start=num
Specify the page number in batch mode to use in the first file-
name. The default is 0.
-d device, --device-name=device
Specify the scanner device to use. See -L to show the available
devices.
-f format, --formatted-device-list=format
Show the available scanner devices, as with -L, but also format
the output. Possible format specifications are:
%d Device name
%i Index number
%m Model
%t Scanner type
%v Vendor
--format=format
Specify the file format of the output file. The possible values
are pnm (default) and tiff.
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scp
-h, --help
Print a help message and exit. You can get device-specific help
by running scanimage as follows:
scanimage -h –ddevice
-i profile, --icc-profile=profile
Include the specified ICC profile in the TIFF output file.
-L, --list-devices
Display a list of available devices. The list may not be
complete, particularly when accessing scanners across the
network. Only scanners listed in a configuration file (typically
in the directory /etc/sane.d) are displayed. A scanner with no
configuration file entry must be accessed by its full device
name.
-n, --dont-scan
Set the specified options, but don’t actually scan anything.
-p, --progress
Print progress information.
-T, --test
Run some sanity tests to be sure the backend works as defined
by the SANE API.
-v, --verbose
Run in verbose mode, providing additional messages.
-V, --version
Print version information and exit.
scp scp [options]file1[...]file2
Securely copy files between hosts on a network, using ssh. Part of
the OpenSSH suite of network tools. scp requests a password or
passphrase if required. The transfer can be between two remote
hosts. If more than one file is specified for file1, file2 should be a
directory; otherwise, only the last file in the list is copied. file1 and
file2 can be specified in any of the following ways:
file
host:file
user@host:file
The first format is used for a local file; a remote file can be speci-
fied in either of the other two formats.
Options
-1 Force the use of SSH protocol 1.
-2 Force the use of SSH protocol 2
-4 Use IPv4 addresses.
-6 Use IPv6 addresses.
-B Run in batch mode. Don’t ask for passwords or passphrases.
-c cipher
Specify the cipher to be used for encrypting the data.
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screen
-C Enable ssh compression.
-F config
Specify an ssh user configuration file (default is $HOME/.ssh/
config).
-i file
Specify the file that contains the identity (private key) for RSA
authentication.
-l limit
Limit bandwidth used to limit, specified in kilobits/second.
-o option
Specify an option to pass to ssh.
-p Preserve modification time, access time, and mode.
-P port
Connect to port on the remote host.
-q Don’t display the progress meter or messages.
-r Copy directories recursively.
-S program
Specify the program to use for the encrypted connection. The
program must understand ssh options.
-v Verbose mode.
Example
Copy the local file user.server1.pub to the remote system server2,
putting it in james’s home directory:
$scp user.server1.pub james@server2:/home/james/
screen screen [options] [command [args]]
Provide ANSI/VT100 terminal emulation, making it possible to run
multiple full-screen pseudo-terminals from one real terminal, and
letting you manipulate and save your screen input and output,
copy and paste between windows, etc. screen allows you to detach
from a running session without interrupting the processing, and
reattach to it later.
Options
-a Include all capabilities in each window’s termcap.
-A Adapt all windows to the size of the current terminal. Default
is to try to use the previous window size.
-c file
Use file as the configuration file instead of the default
$HOME/.screenrc.
-d[pid.tty.host]
Detach session running elsewhere. With -r, reattach to this
terminal. With -R, reattach to this terminal or create it if it
doesn’t already exist. With -RR, use the first session when
reattaching if more than one session is available.
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screen
-D[pid.tty.host]
Detach session running elsewhere, logging out before detaching.
With -r, reattach to this terminal. With -R, reattach to this
terminal or create it if it doesn’t already exist. With -RR, do
whatever is necessary to create a new session.
-e xy
Change command characters. Specify x as the command char-
acter (default Ctrl-a) and y as the character that generates a
literal command character (default a). Specify in caret nota-
tion (e.g., -e ^Pp to set Ctrl-p as the command character,
which is useful for emacs-mode shell).
-f, -fn, -fa
Turn flow control on, off, or to automatic-switching mode.
-h num
Specify the size of the history scrollback buffer.
-i Cause the interrupt key (usually Ctrl-c) to interrupt the display
immediately when flow control is on. Use of this option is
discouraged.
-l, -ln
Turn login mode on or off for /etc/utmp updating.
-ls, -list
Print list of pid.tty.host strings identifying screen sessions.
-L Turn on automatic output logging.
-m Ignore the $STY environment variable and create a new
session. With -d, start session in detached mode; useful for
scripts. With -D, start session in detached mode but don’t fork
a new process; the command exits if the session terminates.
-O Use optimal output mode for terminal rather than true VT100
emulation.
-p window
Preselect the specified window by number or name if it exists.
-q Suppress error message printing on startup. Exit with nonzero
return code if unsuccessful.
-r [pid.tty.host]
-r sessionowner/[pid.tty.host]
Resume detached session. No other options except -d or -D
can be specified. With sessionowner, resume another user’s
detached session; requires setuid root.
-R Attempt to resume the first session found, or start a new
session with the specified options. Set by default if screen is
run as a login shell.
-s shell
Set the default shell, overriding the $SHELL environment
variable.
-S name
Specify a name for the session being started, for use with the
-list and -r options.
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screen
-t name
Set the window’s title.
-T term
Set $TERM to term instead of “screen”.
-U Run in UTF-8 mode and set the default for new windows to
utf8.
-v Print version information and exit.
-wipe [match]
Like -ls, but remove destroyed sessions instead of marking
them dead. If a match is specified, it should be in the same
form as the argument to the -r option.
-x Attach to a session that is not detached. Requires multi-
display mode.
-X Run specified command in specified session. Requires multi-
display mode, and session must not be password-protected.
Key bindings
screen commands consist of a command character (Ctrl-a by default)
followed by another character. For many of the commands, you
can also specify the character as Ctrl-character—e.g., Ctrl-a Ctrl-d
as well as Ctrl-a d. The default key bindings are listed here. You
can change the bindings for yourself in the $HOME/.screenrc config-
uration file, or for all users in /etc/screenrc. The term in parentheses
that follows the description is the equivalent configuration-file
command for changing the key binding.
Ctrl-a '
Prompt for window name or number to switch to. (select)
Ctrl-a "
List all windows for selection. (windowlist -b)
Ctrl-a num
Switch to window num, where num is a digit in the range 0–9
or - (the blank window). (select num)
Ctrl-a Tab
Switch input focus to next region. (focus)
Ctrl-a Ctrl-a
Toggle to previously displayed window. (other)
Ctrl-a a
Send the command character (Ctrl-a) to the window. (meta)
Ctrl-a A
Prompt user to enter a name for the current window. (title)
Ctrl-a b
Send a break to the window. (break)
Ctrl-a B
Reopen the terminal line and send a break. (pow-break)
Ctrl-a c
Create a new window with a shell and switch to it. (screen)
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screen
Ctrl-a C
Clear the screen. (clear)
Ctrl-a d
Detach screen from this terminal. (detach)
Ctrl-a D D
Detach and log out. (pow-detach)
Ctrl-a f
Toggle flow control between on, off, and auto. (flow)
Ctrl-a F
Resize window to current region size. (fit)
Ctrl-a Ctrl-g
Toggle visual bell mode. (vbell)
Ctrl-a h
Write contents of the current window to the file hardcopy.n.
(hardcopy)
Ctrl-a H
Begin/end logging of the current window to the file screenlog.n.
(log)
Ctrl-a i
Show information about this window. (info)
Ctrl-a k
Kill current window. (kill)
Ctrl-a l
Refresh current window. (redisplay)
Ctrl-a L
Toggle window’s login slot. Requires that screen be configured
to update the utmp database. (login)
Ctrl-a m
Redisplay last message. (lastmsg)
Ctrl-a M
Toggle monitoring of the current window. (monitor)
Ctrl-a Space
Ctrl-a n
Switch to next window. (next)
Ctrl-a N
Show number and title of current window. (number)
Ctrl-a Backspace
Ctrl-a h
Ctrl-a p
Switch to previous window. (prev)
Ctrl-a q
Send a start signal (associated with Ctrl-q by terminals) to
current window. (xon)
Ctrl-a Q
Delete all regions except the current one. (only)
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screen
Ctrl-a r
Toggle current window’s line-wrap setting. (wrap)
Ctrl-a s
Send a stop signal (associated with Ctrl-s by terminals) to
current window. (xoff)
Ctrl-a S
Split current region into two new regions. (split)
Ctrl-a t
Show system information, including time and date. (time)
Ctrl-a v
Display version information. (version)
Ctrl-a Ctrl-v
Enter digraph for entering characters that can’t normally be
entered. (digraph)
Ctrl-a w
List all windows. (windows)
Ctrl-a W
Toggle 80/132 columns. (width)
Ctrl-a x
Lock terminal. (lockscreen)
Ctrl-a X
Kill the current region. (remove)
Ctrl-a z
Suspend screen. (suspend)
Ctrl-a Z
Reset virtual terminal to its “power-on” values. (reset)
Ctrl-a .
Write out a .termcap file. (dumptermcap)
Ctrl-a ?
Show all key bindings. (help)
Ctrl-a Ctrl-\
Kill all windows and terminate screen. (quit)
Ctrl-a :
Enter command-line mode. (colon)
Ctrl-a [
Ctrl-a Esc
Enter copy/scrollback mode. (copy)
Ctrl-a ]
Write contents of the paste buffer to the standard input queue
of the current window. (paste)
Ctrl-a {
Ctrl-a }
Copy and paste a previous line. (history)
Ctrl-a >
Write paste buffer to a file. (writebuf)
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script
Ctrl-a <
Read screen-exchange file into paste buffer. (readbuf)
Ctrl-a =
Remove file used by Ctrl-a < and Ctrl-a >. (removebuf)
Ctrl-a,
Show where screen comes from, where it went to, and why you
can use it. (license)
Ctrl-a _
Start/stop monitoring the current window for inactivity.
(silence)
Ctrl-a *
List all currently attached displays. (displays)
script script [option] [file]
Fork the current shell and make a typescript of a terminal session.
The typescript is written to file. If no file is given, the typescript is
saved in the file typescript. The script ends when the forked shell
exits, usually with Ctrl-D or exit.
Options
-a Append to file or typescript instead of overwriting the previous
contents.
-c command
Run the specified command instead of an interactive shell.
-f Flush output after each write. Useful if another person is
monitoring the output file.
-q Operate in quiet mode.
-t Write timing data to standard error. Each entry has two fields:
the first is the elapsed time since the last output, and the
second is the number of characters in the current output.
sdiff sdiff –ooutfile [options]from to
Find differences between the two files from and to and merge inter-
actively, writing the results to outfile.
Options
-- Treat remaining options as filenames, even if they begin with -.
-a, --text
Treat all files as text and compare line by line.
-b, --ignore-space-change
Ignore differences in whitespace.
-B, --ignore-blank-lines
Ignore added or missing blank lines.
-d, --minimal
Use a different algorithm to find fewer changes. This option
causes sdiff to run more slowly.
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sendmail
-H, --speed-large-files
Heuristically speed comparison of large files with many small
scattered changes.
-i, --ignore-case
Ignore case changes.
-I regexp, --ignore-matching-lines=regexp
Ignore any changes that insert or delete lines matching the
regular expression regexp.
--ignore-all-space
Ignore whitespace when comparing lines.
-l, --left-column
Print only the left column of common lines.
-o file, --output=file
Write merged output to the specified file.
-s, --suppress-common-lines
Suppress common lines.
-t, --expand-tabs
Convert tabs to spaces in the output to preserve alignment.
-v, --version
Print version information and exit.
-w cols, --width=cols
Set the output to cols columns wide.
-W Ignore horizontal whitespace when comparing lines.
sed sed [options] [command] [files]
Stream editor. Edit one or more files without user interaction. See
Chapter 10 for more information.
sendmail sendmail [flags] [address...]
System administration command. sendmail is a mail transfer agent
(MTA) or, more simply, a mail router. It accepts mail from a user’s
mail program, interprets the mail address, rewrites the address into
the proper form for the delivery program, and routes the mail to
the correct delivery program.
Command-line flags
-- End of options marker. Only addresses should follow this
option.
-Ac
Use local submission configuration file /etc/mail/submit.cf,
even when no mail is sent from the command line.
-Am
Use configuration file /etc/mail/sendmail.cf, even when mail is
sent from the command line.
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sendmail
-Btype
Set message body type. Accepted values are 7BIT and
8BITMIME.
-bx
Set operation mode to x. Operation modes are:
a Run in ARPAnet mode.
d Run as a daemon.
D Run as a daemon, but remain in the foreground.
h Print persistent host status information.
H Purge expired entries from persistent host status
information.
i Initialize the alias database.
m Deliver mail (the default).
p Print the mail queue.
s Speak SMTP on input side.
t Run in test mode.
v Verify addresses; do not collect or deliver.
-C file
Use configuration file file.
-d level
Set debugging level.
-D file
Send debugging output to file instead of stdout.
-f name
Sender’s name is name.
-F name
Set full name of user to name.
-G Relay message submission. Used by rmail.
-h cnt
Set hop count (number of times message has been processed
by sendmail) to cnt.
-i Do not interpret dots on a line by themselves as a message
terminator.
-L identifier
Use the specified log identifier for messages sent to syslogd.
-N conditions
Specify conditions for delivery status notification (DSN) as a
comma-separated list. Accepted values are never, delay,
failure, and success.
-n Do not alias or forward.
-oXvalue
Set an option specified by its short name X. Options are
described in the next section.
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sendmail
-O option=value
Set an option specified by its long name. Options are described
in the next section.
-pprotocol
Receive messages via the protocol protocol.
-q[time]
Process queued messages immediately, or at intervals indi-
cated by time (for example, -q30m for every half hour).
-qf Process saved messages in the queue using the foreground
process.
-qG group
Process saved messages in the named queue group.
-q[!]Isubstring
Process jobs for named queues containing substring. Use !
to process mail for all queues not containing substring.
-qp[time]
Same as -q, but create a persistent process to handle the queue
instead of initiating a new process at each time interval.
-q[!]Qsubstring
Process quarantined messages containing substring. Use !
to process mail for recipients not containing substring.
-q[!]Rsubstring
Process jobs with recipients containing substring. Use !
to process mail for recipients not containing substring.
-q[!]Ssubstring
Process jobs from senders containing substring. Use ! to process
mail from senders not containing substring.
-Q[reason]
Quarantine messages for the given reason. Use query options
above to specify the message to quarantine.
-R portion
When bouncing messages, return only the specified portion of
the bounced message. portion may be hdrs for headers, or full
for the full message.
-t Read header for To:, Cc:, and Bcc: lines, and send to everyone
on those lists.
-v Verbose mode.
-V envid
Use envid as the original envelope ID.
-X file
Log all traffic to file. Not to be used for normal logging.
Configuration options
Command-line configuration options are the same options
normally set with an O in the sendmail configuration file. On the
command line, they are set using -O and the option’s long name.
Many of these options have short-name variations that are used
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with the -o option. Here, we document items most likely to be
useful on the command line, providing both their short- and long-
name forms. Many of the commands call for timeout values. These
should be given as a number followed by a letter indicating the
interval: s for seconds, m for minutes, h for hours, or d for days.
For example, 30s is 30 seconds, 10m is 10 minutes, and 3d is 3
days. The default is minutes when no letter is given.
Aliasfile=file, Afile
Use alternate alias file.
AliasWait=min, amin
If the D option is set, wait min minutes for the aliases file to be
rebuilt before returning an alias database out-of-date warning.
BlankSub=char, Bchar
Set unquoted space replacement character.
CheckAliases, n
When running newaliases, validate the right side of aliases.
CheckpointInterval=num, Cnum
Checkpoint the queue when mailing to multiple recipients.
sendmail will rewrite the list of recipients after each group of
num recipients has been processed.
ClassFactor=factor, zfactor
Multiplier for priority increments. This determines how much
weight to give to a message’s precedence header. sendmail’s
default is 1800.
ConnectionCacheSize=num, knum
Specify the maximum number of open connections to cache.
ConnectionCacheTimeout=timeout, Ktimeout
Time out connections after timeout.
ConnectionRateThrottle=num
Restrict SMTP connections per second to num.
DefaultUser=uid[:gid], uuid[:gid]
Use user ID and group ID for mailers instead of 1:1. If no
group ID is specified, the user’s default group is used.
DefaultCharSet=label
Use the specified label for 8-bit data.
DeliveryMode=x, dx
Set the delivery mode to x. Delivery modes are d for deferred
delivery, i for interactive (synchronous) delivery, b for back-
ground (asynchronous) delivery, and q for queue only (i.e.,
deliver the next time the queue is run).
DialDelay=seconds
Specify the number of seconds to wait before redialing after a
connection fails.
DontPruneRoutes, R
Don’t prune route addresses.
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EightBitMode=mode, 8mode
Specify how to handle 8-bit input. Accepted values for mode
are mimefy (convert to 7-bit), pass (send as is), or strict
(bounce the message).
ErrorHeader=text, Etext
Set error-message header. text is either text to add to an error
message, or the name of a file. A filename must include its full
path and begin with a /.
ErrorMode=x, ex
Set error processing to mode x. Valid modes are m to mail
back the error message, w to write back the error message, p
to print the errors on the terminal (default), q to throw away
error messages, and e to do special processing for the BerkNet.
FallbackMXhost=host, Vhost
Set fallback MX host. host should be the fully qualified
domain name of the fallback host.
ForkEachJob, Y
Deliver each job that is run from the queue in a separate
process. This helps limit the size of running processes on
systems with very low amounts of memory.
ForwardPath=path, Jpath
Set an alternative .forward search path.
HelpFile=file, Hfile
Specify SMTP help file to use instead of /etc/mail/helpfile.
HoldExpensive, c
On mailers that are considered “expensive” to connect to,
don’t initiate immediate connection.
IgnoreDots, i
Do not take dots on a line by themselves as a message
terminator.
LogLevel=n, Ln
Specify log level. Default is 9.
MatchGECOS, G
Compare local mail names to the GECOS section in the pass-
word file.
MaxDaemonChildren=num
Restrict incoming SMTP daemon to no more than num child
processes.
MaxHopCount=num, hnum
Allow a maximum of num hops per message.
MeToo, m
Also send to me (the sender) if I am in an alias expansion.
MinFreeBlocks=minblocks, bminblocks
Require at least minblocks on the filesystem to be free.
MinQueueAge=timeout
Wait the specified time before processing a new job in the
queue.
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sendmail
NoRecipientAction=action
Specify what headers, if any, to add to a message without
recipient headers. Accepted values are none, add-to, add-
apparently-to, add-bcc, and add-to-undisclosed.
OldStyleHeaders, o
If set, this message may have old-style headers. If not set, this
message is guaranteed to have new-style headers (i.e., commas
instead of spaces between addresses).
PostmasterCopy=user, Puser
Send copies of all failed mail to user (usually postmaster).
PrivacyOptions=optionlist, poptionlist
Adjust the privacy of the SMTP daemon. The optionlist argu-
ment should be a comma-separated list of the following
values:
public
Make SMTP fully public (the default).
needmailhelo
Require site to send HELO or ELHO before sending mail.
needexpnhelo
Require site to send HELO or ELHO before answering an
address expansion request.
needvrfyhelo
Like preceding argument, but for verification requests.
noetrn
Deny requests to reverse the connection using extended
TURN.
noexpn
Deny all expansion requests.
noverb
Deny requests for verbose mode.
novrfy
Deny all verification requests.
authwarnings
Insert special headers in mail messages advising recipi-
ents that the message may not be authentic.
goaway
Set all of the previous arguments (except public).
nobodyreturn
Don’t return message body with a delivery status
notification.
noreceipts
Turn off delivery status notification on success.
restrictexpand
Deny untrusted users access to aliases, forwards, or
include files. Restrict sendmail -bv and disallow -v.
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sendmail
restrictmailq
Allow only users of the same group as the owner of the
queue directory to examine the mail queue.
restrictqrun
Limit queue processing to root and the owner of the
queue directory.
QueueDirectory=dir, Qdir
Select the directory in which to queue messages.
QueueFactor=factor, qfactor
Multiplier (factor) for high-load queuing. Default is 600000.
QueueLA=load, xload
Queue messages when load level is higher than load.
QueueTimeout=timeout, Ttimeout
Set the timeout on undelivered messages in the queue to the
specified time (overridden by Timeout.queuereturn).
RecipientFactor=factor, yfactor
Penalize large recipient lists by factor.
RefuseLA=load, Xload
Refuse SMTP connections when load is higher than load.
ResolverOptions=arg, I arg
Use DNS lookups and tune them. Queue messages on connec-
tion refused. The arg arguments are identical to resolver flags
without the RES_ prefix. Each flag can be preceded by a plus
or minus sign to enable or disable the corresponding
nameserver option. There must be whitespace between the I
and the first flag.
RetryFactor=inc, Zinc
Increment priority of items remaining in queue by inc after
each job is processed. sendmail uses 90000 by default.
SaveFromLine, f
Save Unix-style From lines at the front of messages.
SendMimeErrors, j
Use MIME format for error messages.
SevenBitInput, 7
Format all incoming messages in 7 bits.
StatusFile=file, Sfile
Save statistics in the named file.
SuperSafe, s
Always instantiate the queue file, even when it is not strictly
necessary.
TempFileMode=mode, Fmode
Set default file permissions for temporary files. If this option is
missing, default permissions are 0600.
Timeout.queuereturn=timeout
Return undelivered mail that has been in the queue longer
than the specified timeout. The default is 5d (five days).
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sensors
TimeZoneSpec=timezone, ttimezone
Set name of the time zone.
UseErrorsTo, l
Do not ignore Errors-To header.
UserDatabaseSpec=database, Udatabase
Consult the user database for forwarding information.
Verbose, v
Run in verbose mode.
sendmail support files
/usr/lib/sendmail
Traditional location of sendmail binary.
/usr/bin/newaliases
Link to /usr/lib/sendmail; rebuilds the alias database from
information in /etc/aliases.
/usr/bin/mailq
Prints a listing of the mail queue.
/etc/mail/sendmail.cf
Configuration file, in text form.
/etc/mail/submit.cf
Configuration file used for local message submissions.
/etc/mail/helpfile
SMTP help file.
/etc/mail/statistics
Statistics file.
/etc/aliases
Alias file, in text form.
/etc/aliases.db
Alias file in dbm format. Created by newaliases.
/var/spool/mqueue
Directory in which the mail queue and temporary files reside.
sensors sensors [options] [chips]
Display current readings of all sensor chips and set limits (with -s)
as specified in the configuration file. The default configuration file
is /etc/sensors.conf.
Options
-A Omit adapter and algorithm for each chipset.
--bus-list
Generate bus statements for use in the configuration file. If
multiple chips share an address on different buses of the same
type, this lets you refer to each bus by name, not number.
-c config-file
Specify a configuration file to use in place of the default.
-f Print temperatures in Fahrenheit, not Celsius.
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setleds
-h Display help information and exit.
-s Evaluate all set statements in the configuration file. Requires
superuser privileges.
-u Produce raw output. Used for testing and debugging.
-v Display version information and exit.
seq seq [options] [first [increment]]last
Print the numbers from first through last by increment. The default
is to print one number per line to standard output. Both first and
increment can be omitted and default to 1, but if first is omitted
then increment must also be omitted. In other words, if only two
numbers are specified, they are taken to be the first and last
numbers. The numbers are treated as floating-point.
Options
-f format, --format=format
Write the output using the specified printf floating-point
format, which can be one of %e, %f, or %g (the default).
--help
Print help message and exit.
-s string, --separator=string
Use string to separate numbers in the output. Default is
newline.
-w, --equal-width
Equalize the width of the numbers by padding with leading
zeros. (Use -f for other types of padding.)
--version
Print version information and exit.
setkeycodes setkeycodesscancode keycode
System administration command. Assign a keycode event to the
specified keyboard scancode. The kernel matches these to its own
keycodes. Scancodes in the range of 1–88 are hardwired in the
kernel, but the remaining scancodes can be assigned to keycodes in
the range of 1–127. Use getkeycodes to see current assignments.
Use showkey to discover what scancode a key is sending.
setleds setleds [options]
Display or change the LED flag settings (NumLock, CapsLock, and
ScrollLock) for the current virtual terminal. With no options,
display the current settings for all three flags. Can be used in a
startup script to set the initial state of the LEDs.
Options
+num, -num
Set or clear NumLock.
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setmetamode
+caps, -caps
Set or clear CapsLock
+scroll, -scroll
Set or clear ScrollLock.
-D Change both the current and the default flag settings. Useful
for always having NumLock set, for example.
-F Only change the flags (and their settings may be reflected by
the keyboard LEDs). The default behavior.
-L Change the LEDs but not the flags, so the leds no longer
reflect the virtual terminal (VT) flags. Run setleds -L with no
other options to restore the default behavior.
-v Report the settings before and after the change.
setmetamode setmetamode [options]
Display or set Meta key handling for the current virtual terminal.
With no option, print the current Meta key mode. Otherwise, set
the mode and display the setting before and after the change.
Options
esc, prefix, escprefix
Set the Meta key to send an escape sequence.
meta, bit, metabit
Set the Meta key to set the high-order bit of the character.
setquota setquota [options] [name] [limits]filesystems
System administration command. Set quotas from the command
line. Provide limits in the format soft-block-limit hard-block-limit
soft-inode-limit hard-inode-limit. To disable a quota, set it to 0. See
also edquota, a vi editor interface for editing and setting quotas.
Options
-a, --all
Apply settings to all filesystems listed in /etc/mtab that support
quotas.
-b, --batch
Read new settings from standard input. Provide as a list, each
line in the form of “name limits.”
-Fformat, --format=format
Specify filesystem quota format to use. See quota for a list of
accepted values.
-g, --group
Set group quotas instead of users.
-pprototype, --prototype=prototype
Apply the same settings as used for the specified user or
group: prototype.
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setterm
-tblockgrace inodegrace, --edit_periodblockgrace inodegrace
Specify overall grace times in seconds for block and inode
quotas.
-T name blockgrace inodegrace, --edit-times name blockgrace
inodegrace
Specify grace times in seconds for individual user or group
name. Use the string unset to remove existing grace times.
-u, --user
Set user quotas. (This is the default.)
setsid setsidcommand [arguments]
System administration command. Execute the named command
and optional command arguments in a new session.
setterm setterm [options]
Set terminal attributes by writing a character string to standard
output to invoke the specified attributes.
Options
For Boolean options, the default value is on. Where 8-color is
specified, the possible colors are black, red, green, yellow, blue,
magenta, cyan, and white. Where 16-color is specified, the possible
colors include the 8-color colors, plus grey, bright red, bright
green, bright yellow, bright blue, bright magenta, bright cyan, and
bright white.
-appcursorkeys [on|off]
Set cursor key application mode on or off. Virtual consoles
only. Can cause problems with vi.
-append [num]
Write a snapshot of virtual console num to the file specified
with the -file option, appending the snapshot to any existing
contents. With no argument, write a snapshot of the current
virtual terminal. Overridden by -dump.
-background 8-color|default
Set background color. Virtual consoles only.
-bfreq [freq]
Set the bell frequency in Hz (default 0).
-blank [min]
Set the delay before the screen blanks to the specified number
of minutes. Virtual consoles only.
-blength [millisec]
Set the bell duration in milliseconds (default 0). Possible
values are 0–2000.
-blink [on|off]
Turn blinking mode on or off. If the terminal is not a virtual
console, -blink off also turns off bold, half-bright, and reverse
modes.
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setterm
-bold [on|off]
Turn bold on or off. If the terminal is not a virtual console, -bold
off also turns off blink, half-bright, and reverse modes.
-clear [all]
Clear the screen.
-clear rest
Clear from the current cursor position to the end of the screen.
-clrtabs [tab1...tabn]
With no arguments, clear all tab stops. Otherwise, clear the
specified tab stops. Virtual consoles only.
-cursor [on|off]
Turn the cursor on or off.
-default
Set rendering options to defaults.
-dump [num]
Write a snapshot of virtual console num to the file specified with
the -file option, overwriting any existing contents. With no argu-
ment, dump the current virtual console. Overrides -append.
-file file
Write output from the -dump or -append option to the specified
file. If no filename is specified, write to the file screen.dump in
the current directory.
-foreground 8-color|default
Set foreground color. Virtual consoles only.
-half-bright [on|off]
Turn half-bright (dim) mode on or off. If the terminal is not a
virtual console, -half-bright off also turns off bold, blink, and
reverse modes.
-hbcolor 16-color
Set color for half-bright characters. Virtual consoles only.
-initialize
Display the terminal initialization string to reset the rendering
options and other attributes to their defaults.
-inversescreen [on|off]
Invert the screen colors, swapping foreground and back-
ground, and underline and half-bright. Virtual consoles only.
-linewrap [on|off]
Turn line-wrapping on or off. Virtual consoles only.
-msg [on|off]
Enable or disable the sending of kernel printk() messages to
the console. Virtual consoles only.
-msglevel [num]
Set the console logging level for kernel printk() messages. The
value of num can be in the range 0–8. Messages more impor-
tant than the specified number are printed, with 8 printing all
kernel messages, and 0 equivalent to -msg on. Virtual consoles
only.
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setterm
-powerdown [min]
Set the VESA powerdown interval to the specified number of
minutes, from 0–60. If no value is specified for min, defaults to
0, disabling powerdown.
-powersave [mode]
Put the monitor in the specified VESA powersave mode. Speci-
fying no mode is equivalent to off. The possible values of
mode are:
on, vsync
vsynch suspend mode.
hsync
hsync suspend mode.
powerdown
Powerdown mode.
off
Turn off VESA powersaving features.
-regtabs [num]
Clear all existing tab stops and set a regular tab stop pattern at
every num number (default is 8). num is a number in the range
1–160. Virtual consoles only.
-repeat [on|off]
Turn keyboard repeat on or off. Virtual consoles only.
-reset
Display the terminal reset string to reset the terminal to its
power-on state.
-reverse [on|off]
Turns reverse-video mode on or off. If the terminal is not a
virtual console, -reverse off also turns off bold, half-bright,
and blink modes.
-store
Store the current rendering options as the defaults. Virtual
consoles only.
-tabs [tab1...tabn]
Set tab stops at the specified cursor positions, which can range
from 1 to 160. Virtual consoles only.
-term term
Replace the value of the TERM environment variable with
term.
-ulcolor 16-color
Set color for underlining. Virtual consoles only.
-underline [on|off]
Turn underlining on or off.
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sftp
sftp sftp [options]host
An interactive file transfer program, similar to ftp except that it
uses ssh to perform file transfers securely. sftp connects to host and
logs in, prompting for a password if required. The host can be
specified in the following ways:
Host
[user@]host[:file [file] ...]
[user@]host[:dir[/]]
If user is specified, that username is used for the login. If any files
are specified, the sftp client automatically retrieves them after the
user has been authenticated, and then exits. If a directory dir is
specified, the client starts in that directory on the remote host. sftp
is part of the OpenSSH suite of network tools.
Options
-1 Use SSH1. The default is to use SSH2, which offers stronger
security.
-b file
Run in batch mode, taking commands from the specified file.
Requires the use of a noninteractive authentication mechanism.
-B bytes
Specify the size of the buffer sftp uses for file transfers. Default
is 32768 bytes.
-C Enable compression (uses ssh -C).
-F file
Use file as the ssh configuration file instead of the default
system configuration file. The systemwide file is usually /etc/
ssh/ssh_config, and per-user files are $HOME/.ssh/config.
-ooption
Pass an option to ssh. The passed option is in the format used
by ssh_config(5) (e.g., -o PORT=nn, where nn is the port
number). -o can appear more than once to pass multiple
options to ssh. This option is useful for passing options that
don’t have an equivalent sftp command-line option.
-P server_path
Connect directly to the local sftp server specified in server_path.
Useful for debugging.
-R num
Specify the number of requests that may be outstanding at any
time (default 64).
-s subsys|server_path
Specify the SSH2 subsystem or path to the sftp server on the
remote system. Specifying the path is useful for using sftp via
SSH1 or if the remote sshd does not have an sftp subsystem
configured.
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showkey
-S program
Specify the name of a program that understands ssh options
and that you want to use for the encrypted connection.
-v Raise the logging level.
sh sh [options] [file [arguments]]
The standard Unix shell, a command interpreter into which all
other commands are entered. On modern versions of Linux, this is
just another name for the bash shell. For more information, see
Chapter 6. For legacy Linux versions and other Unix flavors, be
careful not to rely on sh and bash being equivalent.
sha1sum sha1sum [option] [files]
Compute or check 160-bit SHA1 checksums to verify file integrity.
If the file is not specified, or specified as -, read from standard
input.
Options
-b, --binary
Read files in binary mode.
-c, --check
Read and check the SHA1 sums in the files (or standard input)
and verify that they are consistent. The input must have been
generated by an earlier sha1sum command.
--help
Print usage information and exit.
--status
Don’t generate output messages; the exit code indicates
success or failure. Used only with --check.
-t, --text
Read files in text mode. The default.
--version
Print version information and exit.
-w, --warn
Warn about improperly formatted checksum lines. Used only
with --check.
showkey showkey [options]
Print keycodes, scancodes, or ASCII codes of keys pressed on the
keyboard. The default is to show keycodes. In keycode and scan-
code mode, the program terminates 10 seconds after the last key is
pressed. In ASCII mode, press Ctrl-D to exit. This command may
not function properly under the X Window System, which also
reads from the console device.
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showmount
Options
-a, --ascii
Print the ASCII character, decimal, octal, and hexadecimal
values of keys pressed.
-h, --help
Print version number and help message, then exit.
-k, --keycodes
Print keycodes associated with key-press events. This is the
default mode.
-s, --scancodes
Print the keyboard scancodes associated with key-press events.
showmount showmount [options] [host]
NFS/NIS command. Show information about an NFS server. This
information is maintained by the mountd server on host. The default
value for host is the value returned by hostname. With no options,
show the clients that have mounted directories from the host.
showmount is usually found in /usr/sbin, which is not in the default
search path.
Options
-a, --all
Print all remote mounts in the format hostname:directory,
where hostname is the name of the client and directory is the
root of the filesystem that has been mounted.
-d, --directories
List directories that have been remotely mounted by clients.
-e, --exports
Print the list of exported filesystems.
-h, --help
Provide a short help summary.
--no-headers
Do not print headers.
-v, --version
Report the current version of the program.
shred shred [options]files
Overwrite a file to make the contents unrecoverable, and delete the
file afterward if requested.
Options
- Shred standard output.
-f, --force
Force permissions to allow writing to files.
--help
Print help message and exit.
-nnum, --iterations=num
Overwrite files num times (default is 25).
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shutdown
--random-source=file
Use file as the source of random bytes for overwriting. Default
is /dev/urandom.
-snum, --size=num
Shred num bytes. num can be expressed with suffixes (e.g., K,
M, or G).
-u, --remove
Remove file after overwriting. shred does not remove the file
unless this option is specified.
-v, --verbose
Verbose mode.
--version
Print version information and exit.
-x, --exact
Shred the exact file size; do not round up to the next full
block.
-z, --zero
On the final pass, overwrite with zeros to hide the shredding.
shutdown shutdown [options]when [message]
System administration command. Terminate all processing. when
may be a specific time (in hh:mm format), a number of minutes to
wait (in +m format), or now. A broadcast message notifies all users
to log off the system. Processes are signaled with SIGTERM to
allow them to exit gracefully. /etc/init is called to perform the actual
shutdown, which consists of placing the system in runlevel 1. Only
privileged users can execute the shutdown command, although init
may call shutdown with root privileges when the Ctrl-Alt-Del key
combination is pressed from the console keyboard. Broadcast
messages, default or defined, are displayed at regular intervals
during the grace period; the closer the shutdown time, the more
frequent the message.
Options
-a When called from init, shut down only if one of the users
listed in the file /etc/shutdown.allow is currently logged in.
-c Cancel a shutdown that is in progress.
-f Reboot fast, by suppressing the normal call to fsck when
rebooting.
-F Force a filesystem check (fsck) on reboot.
-h Halt or power off the system when shutdown is complete.
Which it does depends on system hardware/BIOS.
-H Halt the system when shutdown is complete.
-k Print the warning message, but suppress actual shutdown.
-P Power off the system when shutdown is complete.
-r Reboot the system when shutdown is complete.
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size
size size [options] [objfile...]
Print the number of bytes of each section of objfile and its total size.
If objfile is not specified, a.out is used.
Options
-d Display the size in decimal and hexadecimal.
--format=format
Imitate the size command from either System V (--format
sysv) or BSD (--format berkeley).
--help
Print help message, then exit.
-o Display the size in octal and hexadecimal.
--radix=num
Specify how to display the size: in hexadecimal and decimal (if
num is 10 or 16) or hexadecimal and octal (if num is 8).
-t, --totals
Show object totals. Works only with Berkeley format listings.
--target=bfdname
Specify object format by binary file descriptor name. Use -h for
a list of supported object formats.
-x Display the size in hexadecimal and decimal.
-A Imitate System V’s size command.
-B Imitate BSD’s size command.
-V, --version
Print version, then exit.
slabtop slabtop [options]
Display kernel slab cache information in real time. slabtop displays
a listing of the top caches as sorted by a given sort criteria.
Options
-d n, --delay=n
Refresh the display every n seconds. By default, the display is
refreshed every three seconds.
-s S, --sort=S
Sort by S, where S is one of the following sort criteria:
a Sort by the number of active objects in each cache.
b Sort by the number of objects per slab.
c Sort by cache size.
l Sort by the number of slabs in each cache.
n Sort by the name of each cache.
o Sort by the number of objects in each cache (this is the
default).
p Sort by the number of pages per slab.
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sleep
s Sort by the size of objects in each cache.
u Sort by cache utilization.
v Sort by the number of active slabs.
-o, --once
Display once and then exit.
--help
Display usage information and then exit.
-V, --version
Display version information and then exit.
slattach slattach [options] [tty]
TCP/IP command. Attach serial lines as network interfaces,
thereby preparing them for use as point-to-point connections. Only
a privileged user may attach or detach a network interface.
Options
-c command
Run command when the connection is severed.
-d Debugging mode.
-e Exit immediately after initializing the line.
-h Exit when the connection is severed.
-l Create UUCP-style lockfile in /var/spool/uucp.
-L Enable three-wire operation.
-m Suppress initialization of the line to 8-bit raw mode.
-n Similar to mesg -n.
-p protocol
Specify protocol, which may be slip, adaptive, ppp, or kiss.
-q Quiet mode; suppress messages.
-s speed
Specify line speed.
sleep sleepamount[units]
sleepoption
Wait a specified amount of time before executing another
command. units may be s (seconds), m (minutes), h (hours), or d
(days). The default for units is s.
Options
--help
Print usage information and exit.
--version
Print version information and exit.
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sort
sort sort [options] [files]
Sort the lines of the named files. Compare specified fields for each
pair of lines; if no fields are specified, compare them by byte, in
machine-collating sequence. If no files are specified or if the file is -,
the input is taken from standard input. See also uniq, comm, and
join.
Options
-b, --ignore-leading-blanks
Ignore leading spaces and tabs.
-c, --check
Check whether files are already sorted and, if so, produce no
output.
-C, --check=quiet, --check=silent
Like -c, but do not report the first bad line.
-d, --dictionary-order
Sort in dictionary order.
-f, --ignore-case
Fold; ignore uppercase/lowercase differences.
-g, --general-numeric-sort
Sort in general numeric order.
--help
Print a help message and then exit.
-i, --ignore-nonprinting
Ignore nonprinting characters (those outside ASCII range
040–176).
-k n[,m], --key=n[,m]
Skip n–1 fields and stop at m–1 fields (i.e., start sorting at the
nth field, where the fields are numbered beginning with 1). If
m is omitted, stop at the end of the line.
-m, --merge
Merge already sorted input files.
-M, --month-sort
Attempt to treat the first three characters as a month designa-
tion (JAN, FEB, etc.). In comparisons, treat JAN < FEB and
any invalid name for a month as less than a valid month.
-n, --numeric-sort
Sort in arithmetic order.
-ofile, --output=file
Put output in file.
-r, --reverse
Reverse the order of the sort.
-s, --stable
Stabilize sort by disabling last-resort comparison.
-Ssize, --buffer-size=size
Set the size of the main memory buffer to size, which may
include a suffix—e.g., K (1024, the default) or M.
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split
-tc, --field-separator=c
Separate fields with c instead of nonblank to blank transition.
-Tdir, --temporary-directory=dir
Specify the directory pathname to be used for temporary files
instead of $TMPDIR or /tmp. May be given more than once
for multiple directories.
-u, --unique
Identical lines in input file appear only one time in output.
With -c, check for strict ordering.
--version
Print version information and then exit.
-z, --zero-terminated
End lines with zero byte, not with newline.
Examples
List files by decreasing number of lines:
wc -l * | sort -r
Alphabetize a list of words, remove duplicates, and print the
frequency of each word:
sort -fd wordlist | uniq -c
Sort the password file numerically by the third field (user ID):
sort -nk3,4 -t: /etc/passwd
split split [options] [infile [prefix]]
Split infile into equal-sized segments. infile remains unchanged, and
the results are written to prefixaa, prefixab, and so on. The default
prefix is x, giving the output files xaa, xab, etc. If infile is - or
missing, standard input is read. See also csplit.
Options
-a n, --suffix-length=n
Use suffixes of length n (default is 2).
-b n[b|k|m], --bytes=n[b|k|m]
Split infile into n-byte segments. Alternate block sizes may be
specified:
b 512 bytes.
k 1 kilobyte.
m 1 megabyte.
-C bytes[b|k|m], --line-bytes=bytes[b|k|m]
Put a maximum of bytes into file; insist on adding complete
lines.
-d, --numeric-suffixes
Use numeric suffixes instead of alphabetic suffixes for the
output filenames.
-n, -l n, --lines=n
Split infile into n-line segments (default is 1000).
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ssh
--help
Print a help message and then exit.
--verbose
Print a message for each output file.
--version
Print version information and then exit.
Examples
Break bigfile into 1000-line segments:
split bigfile
Concatenate four files, then split them into 10-line files named
new.aa, new.ab, and so on. Note that without the -, new. would be
treated as a nonexistent input file:
cat list[1-4] | split -10 - new.
ssh ssh [options]hostname [command]
Securely log a user into a remote system and run commands on
that system. The version of ssh described here is the OpenSSH
client. ssh can use either version 1 (SSH1) or version 2 (SSH2) of
the SSH protocol. SSH2 is preferable, as it provides stronger
encryption methods and greater connection integrity. The host-
name can be specified either as hostname or as user@hostname. If a
command is specified, the user is authenticated, the command is
executed, and the connection is closed. Otherwise, a terminal
session is opened on the remote system. See “Escape characters,”
later in this command, for functions that can be supported through
an escape character. The default escape character is a tilde (~). The
exit status returned from ssh is the exit status from the remote
system, or 255 if there was an error.
Commonly, authentication is handled with standard username/
password credentials, but it can also be useful to authenticate with
a key exchange. This is done by generating a key on the client with
ssh-keygen and populating the authorized_keys file on the remote
host.
Options
-1 Try only SSH1.
-2 Try only SSH2.
-4 Use only IPv4 addresses.
-6 Use only IPv6 addresses.
-a Disable forwarding of the authentication agent connection.
-A Allow forwarding of the authentication agent connection. Can
also be specified on a per-host basis in a configuration file.
-b bind_address
Specify the interface to transmit from when there are multiple
available interfaces or aliased addresses.
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ssh
-c blowfish|3des|des|ciphers
Select the cipher for encrypting the session. The default is
3des. For SSH2, a comma-separated list of ciphers can also be
specified, with the ciphers listed in order of preference. des is
supported only for legacy SSH1 compatibility and otherwise
should not be used.
-C Enable compression. Useful mainly for slow connections. The
default compression level can be set on a per-host basis in
the configuration file with the CompressionLevel option.
-D [bind_address:]port
Enable dynamic application-level port forwarding using port
on the local side. Can be specified in the configuration file.
Only root can forward privileged ports. For IPv6, an alterna-
tive syntax is [bind_address/]port or the address can be
enclosed in square brackets.
-e char|^char|none
Set the escape character (default ~). The escape character must
be the first character on a line. If none is specified, disable the
use of an escape character.
-f Run interactively for user authentication, then go into back-
ground mode for command execution. Implies -n.
-F configfile
Specify a per-user configuration file (default is $HOME/.ssh/
config).
-g Allow remote hosts to connect to local forwarded ports.
-i idfile
Use idfile to read identity (private key) for RSA or DSA
authentication. Default is $HOME/.ssh/id_rsa or $HOME/.ssh/
id_dsa for SSH2, or $HOME/.ssh/identity for SSH1. You can
specify more than one -i option on the command line or in the
configuration file.
-I device
Specify a smartcard device from which to get the user’s private
RSA key.
-k Disable forwarding of GSSAPI (Generic Security Service Appli-
cation Programming Interface) credentials to the server. Can be
set on a per-host basis in the configuration file.
-K Enable forwarding of GSSAPI credentials to the server.
-l user
Log in as user on the remote system. Can be specified on a
per-host basis in the configuration file.
-L [bind_address:]port:host:hostport
Forward port on the local host to the specified remote host
and port. Can be specified in the configuration file. Only root
can forward privileged ports. For IPv6, an alternative syntax is
[bind_address/]port/host/hostport or the address can be
enclosed in square brackets.
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ssh
-m macspec
For SSH2, the contents of macspec specify message authentica-
tion code (MAC) algorithms to use. macspec is a comma-
separated list of algorithms in order of preference.
-M Put the ssh client into master mode for connection sharing.
-n Get standard input as a redirection from /dev/null. Used to
prevent reading from standard input, which is required when
running ssh in the background. Useful for running X programs
on a remote host.
-N Do not execute a remote command. Useful with SSH2 for port
forwarding.
-o option
Specify options in configuration-file format. Useful for specifying
options that have no command-line equivalent. For details on
the options, see the manpage for ssh_config(5).
-p port
Specify the port on the remote host to which ssh is to connect.
Can be specified on a per-host basis in the configuration file.
-q Run quietly, suppressing warnings and error messages.
-R [bind_address:]port:host:hostport
Forward port on the remote host to the local host:hostport.
Can be specified in the configuration file. You can forward
privileged ports only if you are logged in as root on the remote
host. For IPv6, an alternative syntax is [bind_address/]port/
host/hostport or the address can be enclosed in square
brackets.
-s For SSH2, request invocation of a subsystem on the remote
host to be used for another application, such as sftp. The
desired subsystem is specified as the remote command.
-S ctl
Specify the location of a control socket for connection sharing.
-t Force pseudo-tty allocation. Multiple -t options can be speci-
fied to force tty allocation even when ssh has no local tty.
-T Disable pseudo-tty allocation.
-v Verbose mode. Useful for debugging. Specify multiple -v
options to increase verbosity.
-V Display version information and exit.
-wlocal[:remote]
Request tunnel device forwarding with the specified local
(client) and remote (server) tunnel devices.
-x Disable X11 forwarding.
-X Enable X11 forwarding. Can be specified on a per-host basis in
the configuration file.
-Y Enable trusted X11 forwarding.
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ssh-add
Escape characters
~. Disconnect.
~~ Send a single ~.
~#List forwarded connections.
~&Run ssh in the background at logout, while waiting for a
forwarded connection or X11 sessions to terminate.
~? Display the available escape characters.
~B Send a BREAK to the remote system. Only for SSH2 and if the
remote system supports it.
~COpen a command line. Useful for adding port forwardings
when using the -L and -R options.
~R Request rekeying of the connection. Useful only for SSH2 and
if the peer supports it.
~^Z
Run in the background.
ssh-add ssh-add [options] [files]
ssh-add -e|-sreader
Add RSA or DSA identities to the authentication agent (see ssh-
agent), which must be running and must be an ancestor of the
current process. ssh-add reads the files created by ssh-keygen for
private keys. It reads the information in these private keys to obtain
RSA or DSA identities. With no arguments specified, ssh-add adds
the files $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa, and $HOME/.ssh/
identity. If any files are specified, it adds those instead, prompting
for a passphrase if required.
Options
-c Confirm identities being added, by running the program speci-
fied in the SSH_ASKPASS environment variable. A 0 exit status
from the program indicates successful confirmation.
-d Remove an identity from the agent instead of adding one.
-D Delete all identities from the agent.
-e reader
Remove key in specified smartcard reader.
-l List fingerprints of all identities known to the agent.
-L List public key parameters of all identities known to the agent.
-s reader
Add key in smartcard reader.
-t life
Set maximum lifetime when adding identities to an agent. The
value of life can be in seconds or another time format speci-
fied in sshd_config(5).
-x Lock the agent with a password.
-X Unlock the agent.
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ssh-agent
ssh-agent ssh-agent [options] [command [arguments]]
Hold private keys used for public key authentication. ssh-agent is
usually executed at the beginning of an X or login session; then all
other windows or programs given as command are run as clients of
ssh-agent. When a command is specified, the command and any
arguments are executed. The agent dies when the command
completes. Use ssh-add to add keys (identities) to the agent. Oper-
ations that require a private key are performed by the agent, which
returns the results to the requestor.
Options
-a bind_addr
Bind the agent to the socket bind_addr (default is /tmp/ssh-
nnnnnnnn/agent, where nnnnnnnn is a generated number).
-c Write csh commands to standard output. This is the default if
the environment variable SHELL looks like a csh-type shell.
-d Debug mode.
-k Kill the current agent.
-s Write Bourne shell commands to standard output. This is the
default if the environment variable SHELL does not look like a
csh-type shell.
-t life
Set a default value for maximum identity lifetime for added
identities. May be specified in seconds or in a format specified
in sshd(8). This value can be overridden by a lifetime speci-
fied for an identity with ssh-add. The default maximum
lifetime is forever.
ssh-keygen ssh-keygen [options]
Generate, manage, and convert authentication keys for ssh. When
using ssh-keygen to create a key, the -t option must be specified to
identify the type of key to create.
Options
-b bits
Specify the number of bits in the key. For RSA keys, the
minimum is 512, and the default is 2048. DSA keys must be
exactly 1024 bits.
-B Show the bubblebabble digest (a digest represented as a string
that looks like real words) for the private or public keyfile
specified with -f.
-c Change the comment in the private and public keyfiles (for
RSA1 keys only).
-C comment
Specify a new comment.
-D reader
Download the RSA public key from the smartcard in reader.
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ssh-keyscan
-e Read an OpenSSH private or public keyfile and write it in
SECSH Public Key File Format to standard output for
exporting to a commercial SSH.
-f file
Specify the filename of the keyfile.
-Fhostname
List occurrences of the specified hostname found in a known_
hosts file. Useful with -H to print keys that were found in a
hashed format.
-H Hash a known_hosts file.
-i Read an SSH2-compatible unencrypted private or public
keyfile and write an OpenSSH-compatible key to standard
output. Used to import keys from a commercial SSH.
-l Show fingerprint of public or private RSA1 keyfile specified
with -f. With -v, also displays an ASCII art representation of
the key.
-N passphrase
Specify the new passphrase.
-p Change the passphrase for a private keyfile. Prompt for the
file, the old passphrase, and twice for the new passphrase.
-P passphrase
Specify the old passphrase.
-q Operate in quiet mode.
-t type
Specify the type of key to create. Possible values of type are
rsa1 for SSH1, and rsa or dsa for SSH2.
-U reader
Upload an existing RSA private key to the smartcard in reader.
-v Verbose mode; print debugging messages. Use multiple -v
options for greater verbosity.
-y Read a private OpenSSH-format file and print a public key to
standard output.
ssh-keyscan ssh-keyscan [options]
Gather public and private host keys from a number of hosts. Can
be used in scripts.
Options
-4 Use IPv4 addresses only.
-6 Use IPv6 addresses only.
-f file
Read hostnames or addrlist namelist pairs from file. If - is spec-
ified instead of a filename, read hosts or addrlist namelist pairs
from standard input.
-H Hash hostnames and addresses in the output.
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sshd
-p port
Specify the port to connect to on the remote host.
-t type
Specify the type of key to get from the scanned hosts. Possible
values are rsa1 for SSH1 (default), or rsa or dsa for SSH2.
Specify multiple values in a comma-separated list.
-T timeout
Specify the timeout for attempting a connection, in seconds.
Default is 5 seconds.
-v Verbose mode.
sshd sshd [options]
TCP/IP command. Server for the ssh program, providing a secure
remote-login and remote-execution facility equivalent to rlogin and
rsh. Normally started at boot, sshd listens for incoming connec-
tions, forking a new daemon when one is detected. The forked
daemon handles authentication, command execution, and encryp-
tion. Most implementations of sshd support both SSH protocols 1
and 2. The following options are those used by OpenSSH,
OpenBSD’s Secure Shell implementation.
Options
-4 Use only IPv4 addresses.
-6 Use only IPv6 addresses.
-b bits
Use the specified number of bits in the server key. Default is
768.
-d Run sshd in the foreground and send verbose debug informa-
tion to the system log. Process only one connection. Use the
specified number of bits in the server key. This option may be
specified from one to three times. Each additional -d increases
the level of information sent to the system log.
-D Do not detach from the foreground process.
-e Send output to standard error instead of the system log.
-f file
Read configuration information from file instead of the default
configuration file /etc/ssh/sshd_config.
-g seconds
Set the grace time a client has to authenticate itself before the
server disconnects and exits. The default is 600 seconds. A
value of 0 means there is no limit.
-h keyfile
Read the host’s cryptographic key from the specified keyfile
instead of from the default file /etc/ssh/ssh_host_key for SSH
protocol 1, and the default files /etc/ssh/ssh_host_rsa_key and
/etc/ssh/ssh_host_dsa_key for SSH protocol 2. The -h option
may be given more than once to specify multiple keyfiles.
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stat
-i Use when running sshd from inetd.
-k seconds
Set how often the version 1 server key should be regenerated.
Default value is 3600 seconds. If set to 0 seconds, the key will
never be regenerated.
-o setting
Pass a configuration file setting as an option.
-p port
Listen for connections on port. The default is 22. More than
one -p option may be specified. This option overrides ports
specified in a configuration file.
-q Send no messages to the system log.
-t Test configuration files and keys, then exit.
-u namelength
Specify the length of the remote hostname field in the UTMP
structure as specifed in utmp.h. A namelength of 0 will cause
sshd to write dotted decimal values instead of hostnames to
the utmp file and prevent DNS requests unless required by the
authentication mechanism.
stat stat [options]files
Print out the contents of an inode as they appear to the stat system
call in a human-readable format. The error messages “Can’t stat
file” and “Can’t lstat file” usually mean the file doesn’t exist.
“Can’t readlink file” generally indicates that something is wrong
with a symbolic link.
Options
-c format, --format=format
Display the output as specified by format.
-f, --filesystem
Display information about the filesystem where the file is
located, not about the file itself.
--help
Display help information and exit.
-L, --dereference
Follow links and display information about the files found.
-t, --terse
Print the output tersely, in a form suitable for parsing by other
programs.
--version
Print version information and exit.
Output
stat and stat -L display the following:
• Device number
• Inode number
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stat
• Access rights
• Number of hard links
• Owner’s user ID and name, if available
• Owner’s group ID and name, if available
• Device type for inode device
• Total size, in bytes
• Number of blocks allocated
• I/O block size
• Last access time
• Last modification time
• Last change time
• Security context for SELinux
If -f is specified, stat displays the following information about the
filesystem:
• Filesystem type
• Filesystem block size
• Total blocks in the filesystem
• Number of free blocks
• Number of free blocks for nonroot users
• Total number of inodes
• Number of free inodes
• Maximum filename length
Format
The printf(3) flag characters #, 0, -, +, and space can be used in
format. In addition, the field width and precision options can be
used.
If -c format is specified, the following sequences can be used for
format:
%a Access rights in octal.
%A Access rights in human-readable form.
%b Number of blocks allocated.
%B Size in bytes of each block reported by %b.
%d Device number in decimal.
%D Device number in hex.
%f Raw mode in hex.
%F File type.
%g Owner’s group ID.
%G Owner’s group name.
%h Number of hard links.
%i Inode number.
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stat
%n Filename.
%N Quoted filename. If file is a symbolic link, include path to
original.
%o I/O block size.
%s Total size, in bytes.
%t Major device type in hex.
%T Minor device type in hex.
%u Owner’s user ID.
%U Owner’s username.
%x Last access time.
%X Last access time as seconds since the Epoch.
%y Last modification time (modification of the file contents).
%Y Last modification time as seconds since the Epoch.
%z Time of last change (modification of the inode).
%Z Time of last change as seconds since the Epoch.
If both -c format and -f are specified, the following sequences can
be used for format:
%a Free blocks available to nonroot user.
%b Total data blocks in filesystem.
%c Total file nodes in filesystem.
%d Free file nodes in filesystem.
%f Free blocks in filesystem.
%i Filesystem ID, in hex.
%l Maximum filename length.
%n Filename.
%s Optimal transfer block size.
%S Fundamental block size (for block counts).
%t Type in hex.
%T Type in human-readable form.
Examples
Sample output from the command stat /:
stat /
File: "/"
Size: 4096 Blocks: 8 IO Block: 4096
Directory
Device: 303h/771d Inode: 2 Links: 19
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: (
0/ root)
Access: 2009-04-27 21:47:29.000000000 -0400
Modify: 2009-04-27 20:10:22.000000000 -0400
Change: 2009-04-27 20:10:22.000000000 -0400
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statd
Sample output with -f, displaying information about the filesystem:
stat -f /
File: "/"
ID: 0 0 Namelen: 255 Type: ext2/ext3
Blocks: Total: 2612475 Free: 1869472 Available:
1736735 Size: 4096
Inodes: Total: 1329696 Free: 1150253
statd rpc.statd [options]
System administration command. The NFS status server, statd,
reports server status to clients like the rup command.
Options
-d Debugging mode; log verbose information to standard error.
-F Run statd in the foreground.
-n hostname, --name hostname
Specify a name to use for the local hostname. By default, this
is read using the gethostname function.
-o port, --outgoing-port port
Specify the port that statd should use for its outgoing requests
to other servers. When not specified, a port is assigned by
portmap.
-p port, --port port
Specify the incoming port that statd should listen on. When
not specified, a port is assigned by portmap.
-P directory, --state-directory-path directory
Store state information in directory instead of the default, /var/
lib/nfs.
-V Print version information, then exit.
-? Print help message, then exit.
strace strace [options]command [arguments]
Trace the system calls and signals for command with optional argu-
ments. strace shows you how data is passed between the program
and the kernel. With no options, strace prints a line for each
system call. It shows the call name, given arguments, return value,
and any generated error messages. A signal is printed with both its
signal symbol and a descriptive string. As it shows the data transfer
between user and kernel-space, strace is very useful as both a diag-
nostic utility for system administrators and a debugging tool for
programmers. By default, the output is written to standard error.
Options
-a n
Align the return values in column n. The default is 40.
-c Count system calls, errors, signals, and time and provide a
summary report when the program has ended.
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strace
-d Debug mode. Print debugging information for strace on
stderr.
-e [keyword=][!]values
Pass an expression to strace to limit the types of calls or
signals that are traced or to change how they are displayed. If
no keyword is given, trace is assumed. The values can be given
as a comma-separated list. Preceding the list with an exclama-
tion point (!) negates the list. The special values all and none
are valid, as are the values listed with the following keywords:
abbrev=names
Abbreviate output from large structures for system calls
listed in names.
read=descriptors
Print all data read from the given file descriptors.
signal=symbols
Trace the listed signal symbols (for example,
signal=SIGIO,SIGHUP).
trace=sets
sets may be a list of system call names or one of the
following:
desc
File descriptor related calls.
file
Calls that take a filename as an argument.
ipc
Interprocess communication.
network
Network-related.
process
Process management.
signal
Signal-related.
raw=names
Print arguments for the given system calls in hexadecimal.
verbose=names
Unabbreviate structures for the given system calls.
Default is none.
write=descriptors
Print all data written to the given file descriptors.
-f Trace forked processes.
-ff Write system calls for forked processes to separate files named
filename.pid when using the -o option.
-h Print help and exit.
-i Print the current instruction pointer with each system call.
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strings
-o filename
Write output to filename instead of stderr. If filename starts
with the pipe symbol |, treat the rest of the name as a
command to which output should be piped.
-O n
Override strace’s built-in timing estimates, and just subtract n
microseconds from the timing of each system call to adjust for
the time it takes to measure the call.
-p pid
Attach to the given process ID and begin tracking. strace can
track more than one process if more than one option -p is
given. Type Ctrl-C to end the trace.
-q Quiet mode. Suppress attach and detach messages from
strace.
-r Relative timestamp. Print time in microseconds between
system calls.
-s n
Print only the first n characters of a string. Default value is 32.
-S value
Sort output of -c option by the given value. value may be calls,
name, time, or nothing. Default is time.
-t Print time of day on each line of output.
-tt Print time of day with microseconds on each line of output.
-ttt Print timestamp on each line as the number of seconds and
microseconds since the Epoch.
-T Print time spent in each system call.
-u username
Run command as username. Needed when tracing setuid and
setgid programs.
-V Print version and exit.
-v Verbose. Do not abbreviate structure information.
-x Print all non-ASCII strings in hexadecimal.
-xx Print all strings in hexadecimal.
strings strings [options]files
Search each file specified and print any printable character strings
found that are at least four characters long and followed by an
unprintable character. Often used to find human-readable content
within binary files.
Options
@file
Read command-line options as a whitespace-separated list of
options from file.
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strip
-, -a, --all
Scan entire object files; default is to scan only the initialized
and loaded sections for object files.
-e encoding, --encoding=encoding
Specify the character encoding of the strings to be found.
Possible values are:
b 16-bit big-endian
B 32-bit big-endian
l 16-bit little-endian
L 32-bit little-endian
s Single-7-bit-byte characters, such as ASCII, ISO-8859,
etc. (the default)
S Single-8-bit-byte characters.
-f, --print-file-name
Print the name of the file before each string.
-min-len, -n min-len, --bytes=min-len
Print only strings that are at least min-len characters.
-o The same as -t o.
-t base, --radix=base
Print the offset within the file before each string, in the format
specified by base:
d Decimal
o Octal
x Hexadecimal
-Tformat, --target=format
Specify an alternative object code format to the system default.
See strings --help for a list of valid target formats.
--help
Print help message and then exit. The help message includes a
list of valid targets.
-v, --version
Print version information and then exit.
strip strip [options]files
Remove symbols from object files, thereby reducing file sizes and
freeing disk space.
Options
-Fbfdname, --target=bfdname
Specify object format for both input and output by binary file
descriptor name bfdname. Use option -h to see a list of
supported formats.
-I bfdname, --input-target=bfdname
Expect object format bfdname for input.
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stty
--help
Print help message, then exit.
-K symbol, --keep-symbol=symbol
Delete all symbols except the specified symbol. This option
may be used more than once.
-N symbol, --strip-symbol=symbol
Remove symbol from the source file.
-O bfdname, --output-target=bfdname
Use object format bfdname for output.
-o file
Write stripped object to file instead of replacing the original.
Only one object file at a time may be stripped when using this
option.
-p, --preserve-dates
Preserve access and modification times.
-R section, --remove-section=section
Delete section.
-S, -g, -d, --strip-debug
Strip debugging symbols.
-s, --strip-all
Strip all symbols.
--strip-unneeded
Remove symbols not needed for relocation processing.
-V, --version
Print version and exit.
-v, --verbose
Verbose mode.
-X, --discard-locals
Strip local symbols that were generated by the compiler.
-x, --discard-all
Strip nonglobal symbols.
stty stty [options] [modes]
Set terminal I/O options for the current standard input device.
Without options, stty reports the terminal settings that differ from
those set by running stty sane, where ^ indicates the Ctrl key and
^` indicates a null value. Most modes can be negated using an
optional - (shown in brackets). The corresponding description is
also shown in brackets. Some arguments use non-POSIX exten-
sions; these are marked with *.
Options
-a, --all
Report all option settings.
-F dev, --device=dev
Open the specified device and use it instead of standard input.
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stty
-g, --save
Report settings in stty-readable form (i.e., hex).
--help
Print help message and exit.
--version
Print version information and exit.
Control modes
[-]clocal
[Enable] disable modem control.
[-]cread
[Disable] enable the receiver.
[-]crtscts*
[Disable] enable RTS/CTS handshaking.
csbits
Set character size to bits, which must be 5, 6, 7, or 8.
[-]cstopb
[1] 2 stop bits per character.
[-]hup, [-]hupcl
[Do not] hang up connection on last close.
[-]parenb
[Disable] enable parity generation and detection.
[-]parodd
Use [even] odd parity.
Input modes
[-]brkint
[Do not] signal INTR on break.
[-]icrnl
[Do not] map CR to NL on input.
[-]ignbrk
[Do not] ignore break on input.
[-]igncr
[Do not] ignore CR on input.
[-]ignpar
[Do not] ignore parity errors.
[-]imaxbel*
When input buffer is too full to accept a new character, [flush
the input buffer] beep without flushing the input buffer.
[-]inlcr
[Do not] map NL to CR on input.
[-]inpck
[Disable] enable input parity checking.
[-]istrip
[Do not] strip input characters to 7 bits.
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stty
[-]iuclc*
[Do not] map uppercase to lowercase on input.
[-]iutf8*
[Do not] assume input characters are UTF-8 encoded.
[-]ixany*
Allow [only XON] any character to restart output.
[-]ixoff, [-]tandem
[Enable] disable sending of START/STOP characters.
[-]ixon
[Disable] enable XON/XOFF flow control.
[-]parmrk
[Do not] mark parity errors.
Output modes
bsn*
Select style of delay for backspaces (0 or 1).
crn*
Select style of delay for carriage returns (0–3).
ffn*
Select style of delay for formfeeds (0 or 1).
nln*
Select style of delay for linefeeds (0 or 1).
tabn, [-]tabs*
Select style of delay for horizontal tabs (0–3). tabs is the same
as tab0 and -tabs is the same as tab3.
vtn*
Select style of delay for vertical tabs (0 or 1).
[-]ocrnl*
[Do not] map CR to NL on output.
[-]ofdel*
Set fill character to [NULL] DEL.
[-]ofill*
Delay output with [timing] fill characters.
[-]olcuc*
[Do not] map lowercase to uppercase on output.
[-]onlcr*
[Do not] map NL to CR-NL on output.
[-]onlret*
On the terminal, NL performs [does not perform] the CR
function.
[-]onocr*
Do not [do] output CRs at column 0.
[-]opost
[Do not] postprocess output.
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stty
Local modes
[-]echo
[Do not] echo every character typed.
[-]echoe,[-]crterase
[Do not] echo ERASE character as BS-space-BS string.
[-]echok
[Do not] echo NL after KILL character.
[-]echonl
[Do not] echo NL.
[-]icanon
[Disable] enable canonical input (ERASE, KILL, WERASE,
and RPRNT processing).
[-]iexten
[Disable] enable extended functions for input data.
[-]isig
[Disable] enable checking of characters against INTR,
SUSPEND, and QUIT.
[-]noflsh
[Enable] disable flush after INTR or QUIT.
[-]tostop*
[Do not] send SIGTTOU when background processes write to
the terminal.
[-]xcase*
[Do not] change case on local output.
[-]echoprt,[-]prterase*
When erasing characters, echo them backward, enclosed in \
and /.
[-]echoctl,[-]ctlecho*
Do not echo control characters literally. Use hat notation (e.g.,
^Z).
[-]echoke, [-]crtkill*
Erase characters as specified by the echoprt and echoe settings
(default is echoctl and echok settings).
Combination modes
[-]cooked
Same as [raw]-raw.
[-]evenp, [-]parity
Same as [-]parenb and cs[8]7.
ek
Reset ERASE and KILL characters to Ctrl-h and Ctrl-u, their
defaults.
[-]lcase,[-]LCASE
[Unset] set xcase, iuclc, and olcuc.
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stty
[-]nl
[Unset] set icrnl and onlcr. -nl also unsets inlcr, igncr, ocrnl,
and onlret.
[-]oddp
Same as [-]parenb, [-]parodd, and cs[8]7.
[-]raw
[Disable] enable raw input and output (no ERASE, KILL,
INTR, QUIT, EOT, SWITCH, or output postprocessing).
sane
Reset all modes to reasonable values.
[-]cbreak
Same as [icanon]-icanon.
[-]pass8
Same as [parenb]-parenb[istrip]-istrip cs[7]8.
[-]litout
Same as [parenb]-parenb[istrip]-istrip[opost]-opost cs[7]8.
[-]decctlq*
Same as [-]ixany.
crt
Same as echoe echoctl echoke.
dec
Same as echoe echoctl echoke -ixany. Additionally, set
INTERRUPT to Ctrl-C, ERASE to Del, and KILL to Ctrl-U.
Control assignments
ctrl-char c
Set control character to c. ctrl-char is dsusp (flush input and
then send stop), eof, eol, eol2 (alternate end-of-line), erase,
intr, lnext (treat next character literally), kill, rprnt (redraw
line), quit, start, stop, susp, swtch, or werase (erase previous
word). c can be a literal control character, a character in hat
notation (e.g., ^Z), in hex (must begin with 0x), in octal (must
begin with 0), or in decimal. Disable the control character
with values of ^- or undef.
Special settings
n Set terminal baud rate to n (e.g., 2400).
ispeed speed
Specify input speed.
line i*
Set line discipline to i (1–126).
min n
Set the minimum number of characters that will satisfy a read
until the time value has expired when -icanon is set.
ospeed speed
Specify output speed.
rows rows*
Specify number of rows.
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su
cols columns, columns columns*
Specify number of columns.
size*
Display current row and column settings.
speed
Display terminal speed.
time n
Set the number of tenths of a second before reads time out if
the min number of characters has not been read when -icanon
is set.
su su [option] [user] [shell_args]
Create a shell with the effective user ID user. If no user is specified,
create a shell for a privileged user (i.e., become a superuser). Enter
EOF to terminate. You can run the shell with particular options by
passing them as shell_args (e.g., if the shell runs bash, you can
specify -c command to execute command via bash, or -r to create a
restricted shell).
Options
-, -l, --login
Go through the entire login sequence (i.e., change to user’s
environment).
-c command, --command=command
Execute command in the new shell and then exit immediately.
If command is more than one word, it should be enclosed in
quotes. For example:
su -c 'find / -name \*.c -print' nobody
-f, --fast
Start the shell with the -f option, which suppresses the reading
of the .cshrc or .tcshrc file. Applies to csh and tcsh.
-m, -p, --preserve-environment
Do not reset environment variables.
-s shell, --shell=shell
Execute shell, not the shell specified in /etc/passwd, unless shell
is restricted.
--help
Print a help message and then exit.
--version
Print version information and then exit.
Examples
Become root and obtain all of root’s user environment:
$su -
Become root long enough to restart the Apache httpd web server,
then revert to the current user:
$su -c /etc/rc.d/init.d/httpd restart
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sudo
sudo sudo [options] [command]
sudoedit [options]files
If you are allowed, execute command as the superuser. Authorized
users of sudo and the commands they are permitted to execute are
listed in the sudo configuration file, /etc/sudoers. If an unauthorized
user attempts to run a command, sudo informs an administrator
via email. By default, it sends the message to the root account.
Users attempting to run commands are prompted for their pass-
word. Once authenticated, sudo sets a timestamp for the user. For
five minutes from the timestamp, the user may execute further
commands without being prompted for her password. This grace
period may be overridden by settings in the /etc/sudoers file. Also
see /etc/sudoers for configuration examples. The sudoedit form of
sudo is equivalent to running sudo -e.
Options
-b Execute command in the background.
-e Edit one or more files instead of running a command, running
the editor specified by the VISUAL or EDITOR environment
variable. If a specified file does not exist, it is created.
-h Print help message, then exit.
-H Set the HOME environment variable to the home directory of
the target user (default is root).
-i Run the shell specified in /etc/passwd for the user sudo is being
run as.
-k Revoke user’s sudo permissions. Similar to -K, but changes
user’s timestamp to the Epoch instead of revoking it.
-K Remove user’s timestamp.
-l List all allowed and forbidden commands for the user on the
current host, then exit.
-L List parameters that may be set as defaults for a user in the /etc/
sudoers file.
-p promptstring
Use the specified promptstring to prompt for a password. The
string may contain the following escape codes, which are
replaced with the current user’s login name and local hostname.
%h Local hostname without the domain name.
%H Local hostname with the domain name.
%u Current user’s login name
%U Login name of the user the command will run under. The
default is root.
%% A single percent (%) character.
-P Preserve invoking user’s group membership.
-s Run the shell specified in the SHELL environment variable, or
the default shell specified in /etc/passwd. If a command is
given, it should be a shell script and not a binary file.
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swapon
-S Read password from standard input instead of from the
console.
-u user
Run command as the specified user instead of the root user.
This may also be specified as a user ID number using #uid.
-v Update timestamp for user to extend the timeout. Prompt for
password if necessary. No command is run.
-V Print version number, then exit. When run by the root user,
print sudo’s defaults and the local network address as well.
-- Stop reading command-line arguments. Useful with -s.
sum sum [options]files
Calculate and print a checksum and the number of (1 KB) blocks
for file. If no files are specified, or file is -, read from standard input.
Useful for verifying data transmission.
Options
-r The default setting. Use the BSD checksum algorithm.
-s, --sysv
Use alternate checksum algorithm as used on System V. The
block size is 512 bytes.
--help
Print a help message and then exit.
--version
Print the version number and then exit.
swapoff swapoff [options] [devicelist]
System administration command. Stop making devices and files
specified in devicelist available for swapping and paging.
Option
-a Consult /etc/fstab for devices marked sw. Use those in place of
the device argument.
-h Print help message and then exit.
-V Display version number and then exit.
swapon swapon [options]devices
System administration command. Make the listed devices available
for swapping and paging.
Options
-a Consult /etc/fstab for devices marked sw. Use those in place of
the devices argument.
-e Used with -a. Don’t complain about missing devices.
-h Print help message, then exit.
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sync
-p priority
Specify a priority for the swap area. Higher priority areas will
be used up before lower priority areas are used.
-s Print swap usage summaries, then exit.
-V Print version information, then exit.
sync sync
System administration command. Write filesystem buffers to disk.
sync executes the sync() system call. If the system is to be stopped,
sync must be called to ensure filesystem integrity. Note that shut-
down automatically calls sync before shutting down the system.
sync may take several seconds to complete, so the system should be
told to sleep briefly if you are about to manually call halt or
reboot. Note that shutdown is the preferred way to halt or reboot
your system, as it takes care of sync-ing and other housekeeping for
you.
sysctl sysctl [options] [key]
System administration command. Examine or modify kernel para-
meters at runtime using the /proc/sys filesystem. While many of
these kernel keys can be altered by other utilities, sysctl provides a
single interface to kernel settings.
Options
-a, -A
Display all available values.
-e Ignore requests for unknown keys.
-n Print values only, no keynames.
-N Print keynames only.
-p[file]
Reset keys from information specified in /etc/sysctl.conf, or the
specified file.
-q When setting values, don’t print the values to stdout.
-w key=value
Write a new value to the specified key.
sysklogd syslogd [options]
System administration command. sysklogd provides both syslogd
and klogd functionality. By default, it is meant to behave exactly
like the BSD version of syslogd. While the difference should be
completely transparent to the user, sysklogd supports an extended
syntax. It is invoked as syslogd.
sysklogd logs system messages into a set of files described by the
configuration file /etc/syslog.conf. Each message is one line. A
message can contain a priority code, marked by a number in angle
brackets at the beginning of the line. Priorities are defined in <sys/
syslog.h>. syslogd reads from an Internet domain socket specified
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tac
in /etc/services. To bring syslogd down, send it a terminate signal.
See also klogd. On some newer systems sysklogd is replaced by
rsyslogd.
Options
-a socket
Add socket to the list of sockets syslogd listens to.
-d Turn on debugging.
-f configfile
Specify alternate configuration file.
-h Forward messages from remote hosts to forwarding hosts.
-l hostlist
Specify hostnames that should be logged with just the host-
name, not the fully qualified domain name. Multiple hosts
should be separated by a colon (:).
-m markinterval
Select number of minutes between mark messages.
-n Avoid auto-backgrounding. This is needed when starting
syslogd from init.
-p socket
Send log to socket instead of /dev/log.
-r Receive messages from the network using an internet domain
socket with the syslog service.
-s domainlist
Strip off domain names specified in domainlist before logging.
Multiple domain names should be separated by a colon (:).
-u user
Drop root privileges and run with the privileges of user while
logging. While it will initially open logfiles as root, upon
receiving a SIGHUP it will reopen them as user. This will fail if
the logfiles are not writable by user.
-v Print version number, then exit.
syslogd syslogd
System administration command. See sysklogd.
tac tac [options] [file]
Named for the common command cat, tac prints files in reverse to
standard output. Without a filename or with -, it reads from stan-
dard input. By default, tac reverses the order of the lines, printing
the last line first.
Options
-b, --before
Print separator (by default a newline) before the string it
delimits.
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tail
-r, --regex
Expect separator to be a regular expression.
-s string, --separator=string
Specify alternate separator (default is newline).
--help
Print a help message and then exit.
--version
Print version information and then exit.
tail tail [options] [files]
Print the last 10 lines of each named file on standard output. Print
from standard input with no filename or with -. If more than one
file is specified, the output includes a header at the beginning of
each file:
==>filename <==
For options that take the number of bytes or lines as an argument,
you can prepend a plus sign (+) to num to begin printing with the
numth item. These options can also specify a block size:
b 512 bytes
K 1 kilobyte
M 1 megabyte
G 1 gigabyte
Options
-c num, --bytes num
Print the last num bytes.
-f, --follow[=name|descriptor]
Don’t quit at the end of file; “follow” file as it grows and end
when the user presses Ctrl-C. Following by file descriptor is
the default, so -f, --follow, and --follow=descriptor are equiv-
alent. Use --follow=name to track the actual name of a file
even if the file is renamed, as with a rotated logfile.
-F Identical to --follow=name --retry.
--help
Print a help message and exit.
-n num, --lines=num
Print the last num lines.
--max-unchanged-stats=num
Used with --follow=name to reopen a file whose size hasn’t
changed after num iterations (default 5), to see if it has been
unlinked or renamed (as with rotated logfiles).
--pid=pid
Used with -f to end when process ID pid dies.
-q, --quiet, --silent
Suppress filename headers.
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tar
--retry
Keep trying to open a file even if it isn’t accessible when tail
starts or if it becomes inaccessible later. Useful with
--follow=name.
-s sec, --sleep-interval=sec
With -f, sleep approximately sec seconds between iterations.
Default is 1 second.
-v, --verbose
With multiple files, always output the filename headers.
--version
Print version information and then exit.
Examples
Show the last 20 lines containing instances of .Ah:
grep '\.Ah'file |tail -20
Show the last 10 characters of variable name:
echo "$name" | tail -c
Print the last two blocks of bigfile:
tail -2b bigfile
tailf tailffile
Print the last 10 lines of a file, then wait for the file to grow. tailf is
similar to tail -f, but it does nothing when the file is not growing.
Useful for following a logfile, particularly on a laptop when you
want to conserve the battery power.
talk talkperson [ttyname]
Talk to another user. person is either the login name of someone on
your own machine or user@host on another host. To talk to a user
who is logged in more than once, use ttyname to indicate the
appropriate terminal name. Once communication has been estab-
lished, the two parties may type simultaneously, with their output
appearing in separate windows. To redraw the screen, type Ctrl-L.
To exit, type your interrupt character; talk then moves the cursor
to the bottom of the screen and restores the terminal.
tar tar [options] [tarfile] [other-files]
Copy files to or restore files from an archive medium. If any files are
directories, tar acts on the entire subtree. tar was originally used to
create tape archives and still has options related to that use.
However, here we document the options commonly used today.
Options need not be preceded by - (though they may be). The
exception to this rule is when you are using a long-style option
(such as --touch). In that case, the exact syntax is:
tar--long-option-function-options files
For example:
tar --touch -xvf tarfile.tar
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tar
Function options
You must use exactly one of these, and it must come before any
other options:
-A, --catenate, --concatenate
Concatenate a second tar file to the end of the first.
-c, --create
Create a new archive.
-d, --diff, --compare
Compare the files stored in tarfile with other-files. Report any
differences: missing files, different sizes, different file
attributes (such as permissions or modification time).
--delete
Delete from the archive. This option cannot be used with
magnetic tape.
-r, --append
Append other-files to the end of an existing archive.
-t, --list
Print the names of other-files if they are stored in the archive
(if other-files are not specified, print names of all archived
files).
-u, --update
Add files if not in the archive or if modified.
-x, --extract, --get
Extract other-files from an archive (if other-files are not speci-
fied, extract all files).
Options
--anchored
Exclude patterns must match the start of the filename (the
default).
--atime-preserve
Preserve original access time on extracted files.
-b n, --blocking-factor=n
Set block size to n × 512 bytes. By default, n=20.
-B, --read-full-records
Reblock while reading; used for reading from 4.2BSD pipes.
--backup[=type]
Back up files rather than deleting them. If no backup type is
specified, a simple backup is made with ~ as the suffix. (See
also --suffix.) The possible values of type are:
t, numbered
Make numbered backups.
nil, existing
Make numbered backups if there are already numbered
backups; otherwise, make simple backups.
never, simple
Always make simple backups.
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tar
-C directory, --directory=directory
cd to directory before beginning tar operation.
--checkpoint
List directory names encountered.
--exclude=pattern
Remove files matching pattern from any list of files.
-f file, --file=file
Store files in or extract files from archive file. Note that file
may take the form hostname:filename.
-F script, --info-script=script, --new-volume-script=script
Implies -M (multiple archive files). Run script at the end of
each file.
--force-local
Interpret filenames in the form hostname:filename as local
files.
-g file, --listed-incremental=file
Create, list, or extract new-style incremental backup.
-G, --incremental
Create, list, or extract old-style incremental backup.
--group=group
Use group as the group for files added to the archive.
-h, --dereference
Dereference symbolic links, and archive the files they point to
rather than the symbolic link.
--help
Print help message and exit.
-i, --ignore-zeros
Ignore blocks of zeros (i.e., EOFs).
--ignore-case
Ignore case when excluding files.
--ignore-failed-read
Ignore unreadable files to be archived. Default behavior is to
exit when encountering these.
--index-file=file
With -v, send output to file.
-j, --bzip2
Compress files with bzip2 before archiving them, or uncom-
press them with bunzip2 before extracting them.
-k, --keep-old-files
When extracting files, do not overwrite files with similar
names. Instead, print an error message.
-K file, --starting-file=file
Begin tar operation at file in archive.
--keep-newer-files
When extracting files, do not overwrite files that are newer
than the archive files.
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tar
-m, --touch
Do not restore file modification times; update them to the
time of extraction.
-M, --multivolume
Expect archive to be multivolume. With-c, create such an archive.
--mode=permissions
Use permissions when adding files to an archive. The permis-
sions are specified the same way as for the chmod command.
-N date, --newer=date, --after-date=date
Ignore files older than date.
--newer-mtime=date
Add only files whose contents have changed since date to the
archive.
--no-anchored
Exclude patterns may match anything following a slash.
--no-ignore-case
Do not ignore case when excluding files.
--no-same-permissions
Do not extract permissions information when extracting files
from the archive. This is the default for users, and therefore
affects only the superuser.
--no-recursion
Do not move recursively through directories.
--no-wildcards
Don’t use wildcards when excluding files; treat patterns as
strings.
--no-wildcards-match-slash
Wildcards do not match / when excluding files.
--null
Allow filenames to be null-terminated with -T. Override -C.
--numeric-owner
Use the numeric owner and group IDs rather than the names.
-o, --no-same-owner
When extracting, create files with yourself as owner.
-O, --to-stdout
Print extracted files to standard output.
--occurrence[=n]
Process only the nth occurrence of each file (default is 1). Use
with --delete, --diff, --extract, or --list.
--one-file-system
Do not archive files from other filesystems.
--overwrite
Overwrite existing files and directory metadata when extracting
from archive.
--overwrite-dir
Overwrite existing directory metadata when extracting from
archive.
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tar
--owner=owner
Set owner as the owner of extracted files instead of the original
owner. owner is first assumed to be a username, then, if there
is no match, a numeric user ID.
-p, --same-permissions, --preserve-permissions
Keep permissions of extracted files the same as the originals.
-P, --absolute-names
Do not remove initial slashes (/) from input filenames.
--posix
Create a POSIX-compliant archive.
--preserve
Equivalent to invoking both the -p and -s options.
-R, --block-number
Display archive’s block number in messages.
--record-size=size
Treat each record as having size bytes, where size is a multiple
of 512.
--recursion
Move recursively through directories.
--recursive-unlink
Remove existing directory hierarchies before extracting direc-
tories with the same name.
--remove-files
Remove originals after inclusion in archive.
--rsh-command=command
Do not connect to remote host with rsh; instead, use command.
-s, --same-order, --preserve-order
When extracting, sort filenames to correspond to the order in
the archive.
-S, --sparse
Treat sparse files more efficiently when adding to archive.
--same-owner
When extracting, create files with the same ownership as the
originals.
--show-defaults
Display the default tar options.
--show-omitted-dirs
List directories being omitted when operating on an archive.
--strip-components=num, --strip-path=num
Strip the specified number of leading components from file-
names before extracting. Use --strip-components for tar
versions beginning with tar-1.14.90. Earlier versions of tar-1.14
use --strip-path.
--suffix=suffix
Use suffix instead of the default ~ when creating a backup file.
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tar
-T file, --files-from=file
Consult file for files to extract or create.
--totals
Print byte totals.
-U, --unlink-first
Remove each existing file from the filesystem before extracting
from the archive.
--use-compress-program=program
Compress archived files with program, or uncompress extracted
files with program.
--utc
Display file modification dates in UTC format.
-v, --verbose
Verbose. Print filenames as they are added or extracted.
-V name, --label=name
Name this volume name.
--version
Print version information and exit.
--volno-file=file
Use/update the volume number in file.
-w, --interactive, --confirmation
Wait for user confirmation (y) before taking any actions.
-W, --verify
Check archive for corruption after creation.
--wildcards
Use wildcards when excluding files.
--wildcards-match-slash
Wildcards match / when excluding files.
-X file, --exclude-from file
Consult file for list of files to exclude.
-z, --gzip, --gunzip, --ungzip
Compress files with gzip before archiving them, or uncom-
press them with gunzip before extracting them.
-Z, --compress, --uncompress
Compress files with compress before archiving them, or
uncompress them with uncompress before extracting them.
Examples
Create an archive of book chapter files (c), show the command
working (v), and store the results in Chapters.tar:
tar cvf Chapters.tar chapter*
List the archive’s contents in a format like ls -l:
tar tvf Chapters.tar
Extract Chapter 1:
tar xvf Chapters.tar chapter1
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tcpdump
Create an archive of the current directory and store it in a file
backup.tar:
tar cvf - `find . -print` > backup.tar
(The - tells tar to store the archive on standard output, which is
then redirected.)
Create an archive and filter it through bzip2 to compress it:
tar cvfj Chapters.tar.bz2 chapter*
Filter an existing archive through gzip, extracting the contents but
leaving the original file compressed:
tar xvfz chapters.tar.gz
taskset taskset [options] [mask |list] [pid |command [args]]
taskset is used to retrieve or set the processor affinity mask of
either an existing process, given its PID, or to run a new a process,
given its command name, with a specified affinity mask. The Linux
scheduler will then honor the given affinity mask, ensuring that the
process in question runs only on allowed processors.
Options
-c, --cpu-list
The affinity mask is provided in list form, for example, “0,2,5-6,”
not as a bitmask.
-p, --pid
Set or retrieve the mask of the given PID. Do not start a new
process.
-h, --help
Display usage information and then exit.
-V, --version
Display version information and then exit.
tcpdump tcpdump [options] [expression]
System administration command. Dump headers and packets of
network traffic that match expression. The command continues to
capture packets until it receives a SIGTERM or SIGINT signal
(usually generated by typing the interrupt character control-C).
When finished, it will generate a report on traffic captured,
received, or dropped by the kernel.
Expressions
Create matching expressions using the following primitives
followed by an ID or name.
direction
A qualifier indicating whether to match source or destination
information. Accepted values are src, dst, src or dst, and src
and dst. When not specified, the expression will match either
source or destination traffic.
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tcpdump
protocol
A qualifier restricting matches to a particular kind of packet.
Accepted values are: ether, fddi, tr, wlan, ip, ip6, arp, rarp,
decnet, tcp, and udp. If not specified, the match defaults to
any appropriate protocol matching type.
type
A qualifier indicating what kind of thing the ID or name refer-
ences, such as a part of a hostname (host), IP address (net) or
port (port). When not specified, the match defaults to host.
Options
-A Print packets in ASCII text.
-c n
Exit after receivingn packets.
-C n
When saving to a file, do not write files larger than n million
bytes. Open a new file with the same basename appended by a
number. Start with the number 1.
-d, -dd, -ddd
Compile and dump the packet-matching code for the given
expression, then exit. Use the second form to dump it as a C
programming fragment. Use the third form to dump the code
in decimal.
-D Print a list of the available interfaces, then exit.
-e Print the link-level header on each line.
-F file
Read expression from the specified file.
-i interface
Listen on the specified interface. If not specified, tcpdump will
listen on the lowest-numbered interface available, other than
the loopback interface. Use any to listen to all available
interfaces.
-l Line buffer standard out.
-L Print the data link types for an interface, then exit.
-n, -nn
Print IP addresses instead of converting them to hostnames.
Use the second form to leave protocols and port numbers in
numeric form, as well.
-N Print hostnames instead of fully qualified domain names.
-p Don’t put the interface into promiscuous mode.
-q Abbreviate output, printing less protocol information.
-r file
Read packets from the specified file. (You can create such a file
with the -w option.)
-s n
Read n bytes of data from each packet. (The default is 68.)
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tcpslice
-S Print absolute TCP sequence numbers.
-T n
Read n bytes of data from each packet. (The default is 68.)
-t, -tt, -ttt, -tttt
Change display of timestamp. Use the first form to omit the
timestamp from each line. Use the second form to print an
unformatted timestamp. Use the third form to print the time
in seconds between the current and the previous dump line.
The final form prints the date before the timestamp on each
dump line.
-u Print undecoded NFS handles.
-v, -vv, -vvv
Increase the verbosity of the printout. Each additional v
increases the detail of the information printed.
-w file
Write the raw packet information to file without parsing or
printing it. Specify - to write to standard output.
-W n
Wrap files creating a rotating buffer. Used with -C, this will
set a limit on the number of files created. Upon reaching the
limit, tcpdump will begin overwriting earlier files.
-x, -xx
Print packets in hex. Use the second form to print the packet’s
link level header in hex as well.
-X, -XX
Print packets in hex and ASCII text. Use the second form to
print the packet’s link level header in hex and ASCII as well.
-Z user
Drop root privileges and change to the specified user. Use the
primary group of the specified user.
Examples
Place full packets into a file named tcpdump.cap for later analysis:
tcpdump -v -w tcpdump.cap -xX -s 0
Read all packet headers received on the eth0 interface, except for
arp and SSH packets:
tcpdump -i eth0 not arp and not port ssh
tcpslice tcpslice [options] [start [end]]files
System administration command. Reads and manipulates packet
capture files created by tcpdump -w. Based on timestamps, extract
portions of or merge together files. Display all packets between the
given start and end times.tcpslice understands most time and date
formats. tcpslice also understands a relative time format specified
as a unit of time—e.g., +1h10m to specify the first hour and ten
minutes of packets in the specified files. This format is named
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tee
ymdhmsu after the letters it uses to denote units of time: years,
months, days, hours, minutes, seconds, and microseconds. If no
constraining dates are specified, the command will print out all
packets contained in files.
Options
-d Print the start and end time of the specified range, then exit.
-D When merging files, don’t discard duplicate packets.
-l Merge packets based on the time relative to the start of the
file. The default is to merge based on the absolute timestamp.
-r Print the time and date of the first and last packet in each file,
then exit.
-R Print the raw timestamp of the first and last packet in each file,
then exit.
-t Print times associated with the first and last packet in each file
in ymdhmsu format.
-w file
Write output to file instead of standard output.
tee tee [options]files
Accept output from another command and send it both to standard
output and to files (like a T or fork in the road).
Options
-a, --append
Append to files; do not overwrite.
-i, --ignore-interrupts
Ignore interrupt signals.
--help
Print a help message and then exit.
--version
Print version information and then exit.
Example
ls -l | tee savefile View listing and save for later
telinit telinit [option] [runlevel]
System administration command. Signal init to change the system’s
runlevel. telinit is actually just a link to init, the ancestor of all
processes.
Option
-t seconds
Send SIGKILL seconds after SIGTERM. Default is 20.
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telnet
Runlevels
The default runlevels vary from distribution to distribution, but
these are standard:
0 Halt the system.
1, s, S
Single user.
6 Reboot the system.
a, b, c
Process only entries in /etc/inittab that are marked with
runlevel a, b, or c.
q, Q
Reread /etc/inittab.
Check the /etc/inittab file for runlevels on your system.
telnet telnet [options] [host [port]]
Access remote systems. telnet is the user interface that communi-
cates with another host using the Telnet protocol. If telnet is
invoked without host, it enters command mode, indicated by its
prompt, telnet> , and accepts and executes commands. Type ? at
the command prompt to see the available commands. If invoked
with arguments, telnet performs an open command (shown in the
following list) with those arguments. host indicates the host’s official
name, alias, or Internet address. port indicates a port number
(default is the Telnet port).
The Telnet protocol is often criticized because it uses no encryption
and makes it easy for snoopers to pick up user passwords. Most
sites now use ssh instead.
Options
-7 Request 7-bit operation.
-8 Request 8-bit operation.
-a Automatic login to the remote system.
-b hostalias
Use bind to bind the local socket to an aliased address or the
address of an interface other than the one that would be
chosen by connect.
-c Disable reading of the user’s .telnetrc file.
-d Turn on socket-level debugging.
-e[escape_char]
Set initial telnet escape character to escape_char. If escape_char
is omitted, no escape character is predefined.
-E Disable the escape character functionality.
-f With Kerberos V5 authentication, allow forwarding of the
local credentials to the remote system.
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telnetd
-F With Kerberos V5 authentication, allow local credentials to be
forwarded to the remote system, including any that were
already forwarded to the local environment.
-k realm
With Kerberos authentication, obtain tickets for the remote
host in realm, instead of in the remote host’s realm.
-K Do not allow automatic login to the remote system.
-l user
When connecting to remote system and if remote system
understands ENVIRON, send user to the remote system as the
value for variable USER. Implies the -a option.
-L Specify an 8-bit data path on output.
-n tracefile
Open tracefile for recording the trace information.
-r Emulate rlogin. The default escape character for this mode is a
tilde (~); an escape character followed by a dot causes telnet
to disconnect from the remote host; a ^Z instead of a dot
suspends telnet; and a ^] (the default telnet escape character)
generates a normal telnet prompt. These codes are accepted
only at the beginning of a line.
-x Turn on data-stream encryption if possible.
-X atype
Disable the atype type of authentication.
telnetd telnetd [options]
TCP/IP command. Telnet protocol server. telnetd is invoked by the
Internet server for requests to connect to the Telnet port (port 23
by default). telnetd allocates a pseudo-terminal device for a client,
thereby creating a login process that has the slave side of the
pseudo-terminal serving as stdin, stdout, and stderr. telnetd manip-
ulates the master side of the pseudo-terminal by implementing the
Telnet protocol and by passing characters between the remote
client and the login process.
The Telnet protocol is often criticized because it uses no encryp-
tion and makes it easy for snoopers to pick up user passwords.
Most sites now use ssh instead.
Options
-a type
When compiled with authentication support, this option sets
the authentication type. Accepted values are:
debug
Debug authentication code.
none
No authentication required, but accept it if offered. Use
login for any further verification needed to access an
account.
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test
off
Disable authentication.
user
Allow only authenticated remote users with permission to
access their accounts without giving a password.
valid
Allow only authenticated remote users. Use login for any
additional verification needed to access an account.
-debug [port]
Start telnetd manually instead of through inetd. port may be
specified as an alternate TCP port number on which to run
telnetd.
-D modifier(s)
Debugging mode. This allows telnet to print out debugging
information to the connection, enabling the user to see what
telnet is doing. Several modifiers are available for the debug-
ging mode:
netdata
Display data stream received by telnetd.
options
Print information about the negotiation of the Telnet
options.
ptydata
Display data written to the pseudo-terminal device.
report
Print options information, as well as some additional
information about what processing is going on.
-edebug
When compiled with support for encryption, enable encryption
debugging code.
-h Don’t print host-specific information until after login is complete.
-L path
Specify path to alternative login program. By default telnetd
uses /bin/login.
-n Disable checking for lost connections with TCP keep-alives.
-U Refuse connections from IP addresses with no reverse DNS
information.
-X type
Disable authentication type.
test testexpression
[expression]
Evaluate an expression and, if its value is true, return a zero exit
status; otherwise, return a nonzero exit status. In shell scripts, you
can use the alternate form [expression]. This command is generally
used with conditional constructs in shell programs. Also exists as a
built-in in most shells.
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test
File testers
The syntax for all of these options is test option file. If the specified
file does not exist, they return false. Otherwise, they test the file as
specified in the option description.
-b Is the file block special?
-c Is the file character special?
-d Is the file a directory?
-e Does the file exist?
-f Is the file a regular file?
-g Does the file have the set-group-ID bit set?
-G Is the file owned by the process’s effective group ID?
-k Does the file have the sticky bit set?
-L, -h
Is the file a symbolic link?
-O Is the file owned by the process’s effective user ID?
-p Is the file a named pipe?
-r Is the file readable by the current user?
-s Is the file nonempty?
-S Is the file a socket?
-t [file-descriptor]
Is the file associated with file-descriptor (or 1, standard output,
by default) connected to a terminal?
-u Does the file have the set-user-ID bit set?
-w Is the file writable by the current user?
-x Is the file executable?
File comparisons
The syntax for file comparisons is test file1 option file2. A string by
itself, without options, returns true if it’s at least one character long.
-ef Do the files have identical device and inode numbers?
-nt Is file1 newer than file2? Check modification date, not creation
date.
-ot Is file1 older than file2? Check modification date, not creation
date.
String tests
The syntax for string tests is test option string or test string1 [!]=
string2.
-n Is the string at least 1 character long?
-z Is the string 0 characters long?
string1 = string2
Are the two strings equal?
string1 != string2
Are the strings unequal?
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time
Expression tests
Note that an expression can consist of any of the previous tests.
(expression)
Is the expression true?
! expression
Is the expression false?
expression -a expression
Are the expressions both true?
expression -o expression
Is either expression true?
Integer tests
The syntax for integer tests is test integer1 option integer2. You may
substitute -l string for an integer; this evaluates to string’s length.
-eq Are the two integers equal?
-ge Is integer1 greater than or equal to integer2?
-gt Is integer1 greater than integer2?
-le Is integer1 less than or equal to integer2?
-lt Is integer1 less than integer2?
-ne Are the two integers unequal?
time time [options]command [arguments]
Run the specified command, passing it any arguments, and time the
execution. Note that there is also a shelltime command, so you
might need to specify the full path, usually /usr/bin/time, to run this
version of time. time displays its results on standard error. The
output includes elapsed time, user CPU time, system CPU time,
and other information such as memory used and number of I/O
operations. The output can be formatted using printf format
strings specified with the -f option or the TIME environment
variable.
Options
-- The end of the options. Anything after the -- is treated as the
command or one of its arguments.
-a, --append
Used with -o to append the output to file instead of over-
writing it.
-f format, --format=format
Specify the output format. Overrides any format specified in
the TIME environment variable.
--help
Print help message and exit.
-o file, --output=file
Send the output from time to the specified file instead of to
standard error. If file exists, it is overwritten.
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time
-p, --portability
Use portable output format (POSIX).
-v, --verbose
Give verbose output, providing all available information.
-V, --version
Print version information and exit.
Resources
The following resources can be specified in format strings:
c Number of involuntary context switches because of time slice
expiring.
C Name and arguments of command being timed.
D Average size of unshared data area, in kilobytes.
e Elapsed real time, in seconds.
E Elapsed real time as hours:minutes:seconds.
F Number of major (I/O-requiring) page faults.
I Number of filesystem inputs.
k Number of signals delivered to the process.
K Average total (data+stack+text) memory use, in kilobytes.
M Maximum resident set size, in kilobytes.
O Number of filesystem outputs.
p Average unshared stack size, in kilobytes.
P Percent of CPU used.
r Number of socket messages received.
R Number of minor (recoverable) page faults.
s Number of socket messages sent.
S Total CPU seconds used by the system on behalf of the
process.
t Average resident set size, in kilobytes.
U Total CPU seconds used directly by the process.
w Number of voluntary context switches.
W Number of times the process was swapped out of main
memory.
x Exit status of the command.
X Average shared text size, in kilobytes.
Z System page size, in bytes.
Example
Time the execution of the command ls -l and display the user time,
system time, and exit status of the command:
/usr/bin/time -f "\t%U user,\t%S system,\t%x status" ls -Fs
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tmpwatch
tload tload [options] [tty]
Display system load average in graph format. If tty is specified,
print it to that terminal.
Options
-d delay
Specify the delay, in seconds, between updates.
-s scale
Specify scale (number of characters between each graph tick).
A smaller number results in a larger scale.
-V Print version information and exit.
tmpwatch tmpwatch [options]hours directory
System administration command. Recursively remove regular files
and directories in directory with access times older than hours.
Specify the directory as an absolute path. This command is usually
invoked by cron to remove old files in the /tmp directory.
Options
-a, --all
Remove all file types.
-c, --ctime
Make decision on last inode change time for files and modifi-
cation time for directories instead of access time.
-d, --nodirs
Do not remove directories.
-f, --force
Force removal of read-only files (similar to rm -f).
-l, --nosymlinks
Don’t remove symbolic links.
-m, --mtime
Make decision on last modification time instead of access time.
-M, --dirmtime
Make directory deletion decisions based on modification time.
-q, --quiet
Report only fatal errors.
-s, --fuser
Before deleting, attempt to use fuser to see if a file is in use.
-t, --test
Verbosely test command, but don’t actually remove files.
-u, --atime
Make decision on access time. (This is the default.)
-Uuser, --exclude-useruser
Don’t delete files owned by user, specified by name or user ID.
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top
-v, --verbose
Print more details. Use two times to further increase the detail
of the output.
-x, --exclude=path
Skip the specified path, the absolute path of a directory or file.
top top [options]
Provide information (frequently refreshed) about the most CPU-
intensive processes currently running. You do not need to include a
- before options. See ps for explanations of the field descriptors.
Options
-b Run in batch mode; don’t accept command-line input. Useful
for sending output to another command or to a file.
-c Show command line or program name in display. -c is a
toggle; top starts with the last remembered setting.
-d delay
Specify delay between refreshes. Specify as ss.tt (seconds and
tenths).
-f Add or remove fields or columns.
-h Print a help message and exit.
-H Display either all individual threads or a summary of all
threads in process. -H is a toggle; top starts with the last
remembered setting.
-i Suppress display of idle and zombie processes. -i is a toggle;
top starts with the last remembered setting.
-n num
Update display num times, then exit.
-p pids
Monitor only processes with the specified process IDs.
-s Secure mode. Disable some (dangerous) interactive commands.
-S Cumulative mode toggle. Print total CPU time of each
process, including dead child processes when on. top starts
with the last remembered setting.
-u user
Monitor only processes with the specified effective UID or
username.
-U user
Monitor only processes with the specified UID or username,
matching real, effective, saved, and filesystem ids.
-v Print version information and exit.
Interactive commands
= Remove restrictions on which tasks are shown. Reverses the
effect of an active i or n command.
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top
space, Enter
Update display immediately.
<, >
Move the sort field. Use < to move one column left and > to
move one column to the right.
A Toggle alternate display mode between a single window or
multiple windows. See the following section, “Alternate display
mode commands,” for the commands that work with A.
b Toggle between bold and reverse display. Only works with x
and/or y.
B Globally toggle bold display.
c Toggle display of program name or full command line.
d, s
Change delay between refreshes. Prompt for new delay time,
which should be in seconds. Suppressed in secure mode.
f Prompt to add fields to or remove fields from the display.
F, O
Select sort field.
G Select another field group and make it current, or change by
selecting a number from the following list:
1 Def
2 Job
3 Mem
4 Usr
h, ?
Display help about commands and the status of secure and
cumulative modes.
H Toggle between displaying all individual threads and a
summary of all threads in process.
I, 1
Toggle SMP view. Use I to toggle IRIX/Solaris mode (divide
CPU usage by number of CPUs), 1 to toggle single/separate
states.
k Prompt for process ID to kill, and signal to send (default is
SIGTERM) to kill it.
i Toggle suppression of idle and zombie processes.
l Toggle display of load-average and uptime information.
m Toggle display of memory information.
n, #
Prompt for maximum number of processes to show. If 0 is
entered, show as many as will fit on the screen (default).
o Prompt to change order of displayed fields.
q Exit.
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top
r Apply renice to a process. Prompt for PID and renice value.
Suppressed in secure mode.
R Toggle normal or reverse sort.
S Toggle cumulative mode. (See the -S option.)
t Toggle display of processes and CPU states lines.
u Prompt for user to show; matches on effective UID.
U Prompt for user to show; matches on real, effective, saved, and
filesystem UID.
W Write current setup to ~/.toprc. This is the recommended way
to write a top configuration file.
x Toggle highlighting for sort field.
y Toggle highlights for running tasks.
z Toggle between color and mono display.
Z Globally change color mappings.
Alternate display mode commands
= Rebalance tasks in the current window.
+ Rebalance tasks in every window.
- Show or hide the current window.
_ Show all invisible windows or hide all visible windows.
a Cycle forward through all four windows.
g Change the name of the current window or group.
w Cycle backward through all four windows.
Field descriptions
The first five entries in the following list describe the lines that
appear at the top of the top display. The rest are the fields that can
be displayed for each task (sizes are in kilobytes). Use the interac-
tive f command to add or remove fields.
top
Display the time the system has been up, the number of users,
and three load averages consisting of the average number of
processes ready to run in the last 1, 5, and 15 minutes.
Tasks
The total number of processes running when the last update
was taken, shown as the number of running, sleeping, stopped,
or undead tasks.
Cpu(s)
The percentage of CPU time spent in user mode, in system
mode, on tasks with a negative nice value, and idle.
Mem
Memory statistics, including total available memory, free
memory, memory used, shared memory, and memory used for
buffers.
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top
Swap
Swapspace statistics, including total, available, used, and
cached.
PID
Process ID.
PPID
Parent process ID.
UID
Effective user ID of task’s owner.
USER
Effective username of task’s owner.
RUSER
Real username of task’s owner.
GROUP
The effective group name of task’s owner.
PR
Priority.
NI
Nice value.
nFLT
Page fault count.
CODE
Code size.
DATA
Data plus stack size.
RES
Resident task size.
SWAP
Size of swapped-out portion of task.
VIRT
The total amount of virtual memory used by the task.
nDRT
Number of pages marked dirty.
#C
Last-used processor, for multiprocessor systems.
SHR
Amount of shared memory used.
S State of the task. Values are S (sleeping), D (uninterruptible
sleep), R (running), Z (zombies), or T (stopped or traced).
WCHAN
Address or name of the kernel function in which the task is
currently sleeping.
TIME
Total CPU time used by task and any children.
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touch
TIME+
Like TIME, but shows the time down to hundredths of a
second.
%CPU
Share of CPU time since last update, as percentage of total
CPU time.
%MEM
Share of physical memory.
TTY
Controlling tty.
COMMAND
Command line (truncated if too long) or name of program
depending on the state of the C toggle. Processes with no
command line are shown in parentheses.
FLAGS
Task flags.
touch touch [options]files
For one or more files, update the access time and modification time
(and dates)to the current time and date. touch is useful in forcing
other commands to handle files a certain way; for example, the
operation of make, and sometimes find, relies on a file’s access and
modification time. If a file doesn’t exist, touch creates it with a file
size of 0.
Options
-a, --time=atime, --time=access, --time=use
Update only the access time.
-c, --no-create
Do not create any file that doesn’t already exist.
-d time, --date=time
Change the time value to the specified time instead of the
current time. time can use several formats and may contain
month names, time zones, a.m. and p.m. strings, etc.
-m, --time=mtime, --time=modify
Update only the modification time.
-r file, --reference=file
Change times to be the same as those of the specified file,
instead of the current time.
-t time
Use the time specified in time instead of the current time. This
argument must be of the format [[cc]yy]mmddhhmm[.ss], indi-
cating optional century and year, month, date, hours, minutes,
and optional seconds.
--help
Print help message and then exit.
--version
Print the version number and then exit.
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tr
tr tr [options] [string1 [string2]]
Translate characters. Copy standard input to standard output,
substituting characters from string1 to string2, or deleting charac-
ters in string1.
Options
-c, -C, --complement
Complement characters in string1 with respect to ASCII 001-377.
-d, --delete
Delete characters in string1 from output.
-s, --squeeze-repeats
Squeeze out repeated output characters in string2.
-t, --truncate-set1
Truncate string1 to the length of string2 before translating.
--help
Print help message and then exit.
--version
Print the version number and then exit.
Special characters
Include brackets ([ ]) where shown.
\a Ctrl-G (bell)
\b Ctrl-H (backspace)
\f Ctrl-L (form feed)
\n Ctrl-J (newline)
\r Ctrl-M (carriage return)
\t Ctrl-I (tab)
\v Ctrl-K (vertical tab)
\nnn
Character with octal value nnn
\\ Literal backslash
char1-char2
All characters in the range char1 through char2. If char1 does
not sort before char2, produce an error.
[char*]
In string2, expand char to the length of string1.
[char*number]
Expand char to number occurrences. [x*4] expands to xxxx,
for instance.
[:class:]
Expand to all characters in class, where class can be:
alnum
Letters and digits
alpha
Letters
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tracepath
blank
Whitespace
cntrl
Control characters
digit
Digits
graph
Printable characters except space
lower
Lowercase letters
print
Printable characters
punct
Punctuation
space
Whitespace (horizontal or vertical)
upper
Uppercase letters
xdigit
Hexadecimal digits
[=char=]
The class of characters to which char belongs.
Examples
Change uppercase to lowercase in a file:
cat file | tr 'A-Z' 'a-z'
Turn spaces into newlines (ASCII code 012):
tr ' ' '\012' < file
Strip blank lines from file and save in new.file:
cat file | tr -s "" "\012" > new.file
Delete colons from file and save result in new.file:
tr -d : < file > new.file
tracepath tracepath [options]host [port]
TCP/IP command. Trace path to host and report the Maximum
Transmission Unit (MTU). A simplified version of traceroute
without options meant for use by unprivileged users. If specified, it
will use port to send UDP probe packets. host is the destination
hostname or the IP number of the host to reach.
Options
-lnUse alternative packet length of n. The default is 65536 for
IPv4 and 128000 for IPv6.
-n Don’t look up host names, just print IP addresses.
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traceroute
traceroute traceroute [options]host [packetsize]
TCP/IP command. Trace route taken by packets to reach network
host. traceroute attempts tracing by launching UDP probe packets
with a small TTL (time-to-live), then listening for an ICMP “time
exceeded” reply from a gateway. host is the destination hostname
or the IP number of the host to reach. packetsize is the packet size
in bytes of the probe datagram. Default is 40 bytes.
Options
-4, -6
Force IPv4 or IPv6 tracerouting.
-A Perform AS path lookups.
-d Turn on socket-level debugging.
-e Show ICMP extensions.
-f n
Set the initial time-to-live to n hops.
-F Set the “don’t fragment” bit.
-g addr
Enable the IP LSRR (Loose Source Record Route) option in
addition to the TTL tests, to ask how someone at IP address
addr can reach a particular target.
-i interface
Specify the network interface for getting the source IP address
for outgoing probe packets. Useful with a multihomed host.
Also see the -s option.
-I Use ICMP ECHO requests instead of UDP datagrams.
-m max_ttl
Set maximum time-to-live used in outgoing probe packets to
max-ttl hops. Default is 30.
-n Show numerical addresses; do not look up hostnames. (Useful
if DNS is not functioning properly.)
-N n
Send n probe packets simultaneously. The default is 16.
-p port
Set base UDP port number used for probe packets to port.
Default is (decimal) 33434.
-q n
Set number of probe packets per hop to the value n. Default
is 3.
-r Bypass normal routing tables and send directly to a host on an
attached network.
-s src_addr
Use src_addr as the IP address that will serve as the source
address in outgoing probe packets.
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troff
-t tos
Set the type-of-service in probe packets to tos (default is 0).
The value must be a decimal integer in the range 0 to 255.
-T Use TCP SYN packets instead. This may help bypass some
firewall rules.
-v Verbose; received ICMP packets (other than TIME_
EXCEEDED and PORT_UNREACHABLE) will be listed.
-w wait
Set time to wait for a response to an outgoing probe packet to
wait seconds (default is 5).
-x Toggle IP checksums, usually to turn them off. IP checksums
are always calculated if -I is specified.
-z msecs
Set the delay between probes, in milliseconds. The default is 0.
troff troff
See groff.
true true
A null command that returns a successful (0) exit status. See also
false.
tset tset [options] [terminal]
reset [options] [terminal]
Initialize a terminal. The terminal to be initialized is whichever is
found first from the value of terminal, the value of the TERM envi-
ronment variable, or the default terminal type. See also the reset
command.
Options
-c Set control characters.
-echar
Set the erase character to char.
-ichar
Set the interrupt character to char.
-I Do not send terminal or tab initialization strings to the
terminal.
-kchar
Set line-kill character to char.
-m arg
Specify a mapping from a port type to a terminal, where arg
looks like this:
[port_type][operator][baud_rate][:]terminal_type
operator can be any combination of < (less than), > (greater
than), @ (equal), and ! (not). The terminal type is a string (e.g.,
vt100 or xterm).
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tune2fs
-q Print the terminal type on standard output but do not initialize
the terminal.
-Q Don’t display values for the erase, interrupt, and line kill
characters.
-r Print the terminal type to standard error.
-s Print the shell commands that initialize the TERM environment
variable on standard output.
-V Print the version of ncurses used for this program and exit.
tsort tsort [option] [file]
Perform a topological sort on partially ordered strings in the speci-
fied file. If no file is specified or is -, read standard input. Multiple
strings on a line are separated by spaces, where each line indicates a
partial ordering. The fully ordered results are written to standard
output. See the tsort info page for an example of the use of tsort for
sorting lists of functions into the order they are called.
Options
--help
Print help information and exit.
--version
Print version information and exit.
tty tty [options]
Print the filename of the terminal connected to standard input.
Options
--help
Print help message and exit.
-s, --silent, --quiet
Print nothing to standard output, but return an exit status.
--version
Display version information and exit.
tune2fs tune2fs [options]device
System administration command. Tune the parameters of a Linux
Second Extended Filesystem by adjusting various parameters. You
must specify the device on which the filesystem resides; it must not
be mounted read/write when you change its parameters.
Options
-c max-mount-counts
Specify the maximum number of mount counts between two
checks on the filesystem.
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tune2fs
-e behavior
Specify the kernel’s behavior when encountering errors.
behavior must be one of:
continue
Continue as usual.
remount-ro
Remount the offending filesystem in read-only mode.
panic
Cause a kernel panic.
-f Force completion even if there are errors.
-g group
Allow group (a group ID or name) to use reserved blocks.
-j Add an ext3 journal to the filesystem. If specified without -J,
use the default journal parameters.
-J jrnl-options
Specify ext3 journal parameters as a comma-separated list of
option=value pairs. The specified options override the default
values. Only one size or device option can be specified for a
filesystem. Possible options are:
device=ext-jrnl
Attach to the journal block device on ext-jrnl, which must
exist and must have the same block size as the filesystem
to be journaled. ext-jrnl can be specified by its device
name, by the volume label (LABEL=label), or by the
Universal Unique Identifier (UUID) stored in the journal’s
ext2 superblock (UUID=uuid; see uuidgen). Create the
external journal with:
mke2fs –Ojrnl-devext-jrnl
size=jrnl-size
The size of the journal in megabytes. The size must be at
least equivalent to 1024 blocks and not more than
102,400 blocks.
-l Display a list of the superblock’s contents.
-L label
Specify the volume label of filesystem. The label must be no
more than 16 characters.
-m percentage
Specify the percentage of blocks that will be reserved for use
by privileged users.
-M dir
Specify the filesystem’s last-mounted directory.
-o mount-options
Set or clear the specified default mount-options. Mount
options specified in /etc/fstab or on the command line for
mount will override these defaults. Specify multiple options as
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tune2fs
a comma-separated list. Prefixing an option with a caret (^)
clears the option. No prefix or a plus sign (+) causes the
option to be set. The following options can be cleared or set:
acl
Enable Posix Acess Control Lists.
bsdgroups
Assign new files the group-id of the directory in which
they are created instead of the group-id of the process
creating them.
debug
Enable debugging code.
journal_data
When journaling, commit all data to journal before
writing to the filesystem.
journal_data_ordered
When journaling, force data to the filesystem before
committing metadata to the journal.
journal_data_writeback
When journaling, force data to the filesystem after
committing metadata to the journal.
-O option
Set or clear the specified filesystem options in the filesystem’s
superblock. Specify multiple options as a comma-separated
list. Prefixing an option with a caret (^) clears the option. No
prefix or a plus sign (+) causes the option to be set. Run
e2fsck after changing filetype or sparse_super. The following
options can be cleared or set:
dir_index
Use B-trees to speed up lookups on large directories.
filetype
Save file type information in directory entries.
has_journal
Create an ext3 journal. Same as the -j option.
sparse_super
Save space on large filesystems by limiting the number of
backup superblocks. Same as -s.
-r num
Specify the number of blocks that will be reserved for use by
privileged users.
-s [0|1]
Turn the sparse superblock feature on or off. Run e2fsck after
changing this feature.
-u user
Allow user (a user ID or name) to use reserved blocks.
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tunelp
-U uuid
Set the UUID of the filesystem to a UUID generated by
uuidgen or to one of the following:
clear
Clear the existing UUID.
random
Randomly generate a new UUID.
time
Generate a new time-based UUID.
tunelp tunelpdevice [options]
System administration command. Control a line printer’s device
parameters. Without options, print information about device(s).
Options
-a [on|off]
Specify whether or not to abort if the printer encounters an
error. By default, do not abort.
-c n
Retry device n times if it refuses a character. (Default is 250.)
After exhausting n, sleep before retrying.
-i irq
Use irq for specified parallel port. Ignore -t and -c. If 0, restore
noninterrupt-driven (polling) action.
-o [on|off]
Specify whether to abort if device is not online or is out of
paper.
-q [on|off]
Specify whether to print current IRQ setting.
-r Reset port.
-s Display printer’s current status.
-t time
Specify a delay of time in jiffies to sleep before resending a
refused character to the device. A jiffy is defined as either one
tick of the system clock or one AC cycle time; it should be
approximately 1/100 of a second.
-w time
Specify a delay of time in jiffies to sleep before resending a
strobe signal.
ul ul [options] [filenames]
Translate underscores to underlining. The process will vary by
terminal type. Some terminals are unable to handle underlining.
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uname
Options
-i When on a separate line, translate - to underline instead of
translating underscores.
-t terminal-type
Specify terminal type. By default, TERM is consulted.
umount umount [options] [directory]
System administration command. Unmount filesystem specified by
directory. You may also specify the filesystem by device name.
umount announces to the system that the removable file structure
previously mounted on the specified directory is to be removed.
Any pending I/O for the filesystem is completed, and the file struc-
ture is flagged as clean. A busy filesystem cannot be unmounted.
Options
-a Unmount all filesystems listed in /etc/mtab other than /proc.
-d If the unmounted device was a loop device, free the loop
device too. See also the losetup command.
-f Force the unmount. This option requires kernel 2.1.116 or
later.
-h Print help message and exit.
-i Don’t execute /sbin/umount.<filesystem> helper programs.
-l Lazy unmount. Detach the filesystem from the hierarchy
immediately, but don’t clean up references until it is no longer
busy. Requires kernel 2.4.11 or later.
-n Unmount, but do not record changes in /etc/mtab.
-O options
Unmount only filesystems with the specified options in /etc/
fstab. Specify multiple options as a comma-separated list. Add
no as a prefix to an option to indicate filesystems that should
not be unmounted.
-r If unmounting fails, try to remount read-only.
-t type
Unmount only filesystems of type type. Multiple types can be
specified as a comma-separated list, and any type can be prefixed
with no to specify that filesystems of that type should not be
unmounted.
-v Verbose mode.
-V Print version information and exit.
uname uname [options]
Print information about the machine and operating system.
Without options, print the name of the kernel (Linux).
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unexpand
Options
-a, --all
Combine all the system information from the other options.
-i, --hardware-platform
Print the system’s hardware platform.
-m, --machine
Print the name of the hardware that the system is running on.
-n, --nodename
Print the machine’s hostname.
-o, --operating-system
Print the operating system name.
-p, --processor
Print the type of processor.
-r, --kernel-release
Print the release number of the kernel.
-s, --kernel-name
Print the name of the kernel (Linux). This is the default action.
-v, --kernel-version
Print build information about the kernel.
--help
Display a help message and then exit.
--version
Print version information and then exit.
unexpand unexpand [options] [files]
Convert strings of initial whitespace, consisting of at least two
spaces and/or tabs, to tabs. Read from standard input if given no
file or a file named -.
Options
-a, --all
Convert all, not just leading, strings of spaces and tabs.
--first-only
Convert only leading spaces and tabs. Overrides -a.
-t nums, --tabs nums
nums is a comma-separated list of integers that specify the
placement of tab stops. If a single integer is provided, the tab
stops are set to every integer spaces. By default, tab stops are
eight spaces apart. This option implies -a.
--help
Print help message and then exit.
--version
Print the version number and then exit.
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uniq
unicode_start unicode_start [font [umap]]
Put keyboard and console in Unicode mode, setting the font to font
and the Unicode map to umap if the font doesn’t have its own map.
If no font is specified, use the default.
unicode_stop unicode_stop
Take keyboard and console out of Unicode mode.
uniq uniq [options] [file1 [file2]]
Remove duplicate adjacent lines from sorted file1 or from standard
input, sending one copy of each line to file2 (or to standard
output). Often used as a filter. Specify only one of -d or -u. See also
comm and sort.
Options
-c, --count
Print each line once, prefixing number of instances.
-d, --repeated
Print duplicate lines once but no unique lines.
-D, --all-repeated[=method]
Print all duplicate lines. -D takes no delimiter method. The
delimiter method method takes one of the following values:
none (default), prepend, or separate. Blank lines are used as
the delimiter.
-f n, --skip-fields=n
Ignore first n fields of a line. Fields are separated by spaces or
by tabs.
-i, --ignore-case
Ignore case differences when checking for duplicates.
-s n, --skip-chars=n
Ignore first n characters of a field.
-u, --unique
Print only unique lines (no copy of duplicate entries is kept).
-w n, --check-chars=n
Compare only first n characters per line (beginning after
skipped fields and characters).
--help
Print a help message and then exit.
--version
Print version information and then exit.
Examples
Send one copy of each line from list to output file list.new:
uniq list list.new
Show which names appear more than once:
sort names | uniq -d
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unlink
unlink unlinkfilename
unlinkoption
Remove the specified file using the system unlink function.
Options
--help
Print help information and exit.
--version
Print version information and exit.
uptime uptime [option]
Print the current time, how long the system has been running, the
number of users currently logged in (which may include the same
user multiple times), and system load averages. This output is also
produced by the first line of w command output.
Option
-V Print version information and exit.
useradd useradd [options] [user]
System administration command. Create new user accounts or
update default account information. Unless invoked with the -D
option, user must be given. useradd will create new entries in
system files. Home directories and initial files may also be created
as needed.
Options
-b dir, --base-dir dir
Specify base dir for home directories. The default is /home.
-c comment, --comment comment
Comment field.
-d dir, --home dir
Home directory. The default is to use user as the directory
name under the home directory specified with the -D option.
-D [options]
Set or display defaults. If options are specified, set them. If no
options are specified, display current defaults. The options
are:
-b dir, --base-dir dir
Home directory prefix to be used in creating home direc-
tories. If the -d option is not used when creating an
account, the user name is appended to dir.
-e date, --expiredate date
Expire date. Requires the use of shadow passwords.
-f days, --inactive days
Number of days after a password expires to disable an
account. Requires the use of shadow passwords.
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useradd
-g group, --gid group
Initial group name or ID number.
-s shell, --shell shell
Default login shell.
-e date, --expiredate date
Account expiration date. Use the format MM/DD/YYYY. Two-
digit year fields are also accepted. The value is stored as the
number of days since January 1, 1970. This option requires
the use of shadow passwords.
-f days, --inactive days
Permanently disable account this many days after the pass-
word has expired. A value of -1 disables this feature. This
option requires the use of shadow passwords.
-g group, --gid group
Initial group name or ID number. If a different default group
has not been specified using the -D option, the default group is 1.
-G groups, --groups groups
Supplementary groups given by name or number in a comma-
separated list with no whitespace.
-k [dir], --skel [dir]
Copy default files to the user’s home directory. Meaningful
only when used with the -m option. Default files are copied
from /etc/skel/ unless an alternate dir is specified.
-Kkey=value, --keykey=value
Override /etc/login.defs defaults. This option can be given
multiple times.
-l Keep old entries for user in lastlog and faillog databases. By
default old user data in these are reset.
-m, --create-home
Make user’s home directory if it does not exist. The default is
not to make the home directory.
-M Do not create a home directory for the user, even if the system
default in /etc/login.defs is to create one.
-o, --non-unique
Override. Accept a nonunique uid with the -u option. (Probably
a bad idea.)
-p passwd, --password passwd
The encrypted password, as returned by crypt(3).
-r, --system
Red Hat-specific option. Create a system account with a non-
expiring password and a UID lower than the minimum
defined in /etc/login.defs. Do not create a home directory for
the account unless -m is also specified.
-s shell, --shell shell
Login shell.
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userdel
-u uid, --uid uid
Numerical user ID. The value must be unique unless the -o
option is used. The default value is the smallest ID value
greater than 99 and greater than every other uid.
userdel userdel [option]user
System administration command. Delete all entries for user in
system account files.
Option
-f, --force
Remove the user even if they are currently logged in. Remove
home directory and mail spool even if they are used by
another user. Remove group too, if USERGROUPS_ENAB is
set to yes in /etc/login.defs.
-r, --remove
Remove the home directory of user and any files contained in it.
usermod usermod [options]user
System administration command. Modify user account information.
Options
-a, --append
Used with the -G option. Add user to the specified groups, but
don’t remove user from groups not in the current list.
-c comment, --comment comment
Comment field.
-d dir, --home dir
Home directory.
-e date, --expiredate date
Account expiration date. date is in the format MM/DD/YYYY;
two-digit year fields are also accepted. The value is stored as
the number of days since January 1, 1970. This option requires
the use of shadow passwords.
-f days, --inactive days
Permanently disable account this many days after the pass-
word has expired. A value of -1 disables this feature. This option
requires the use of shadow passwords.
-g group, --gid group
Initial group name or number.
-G groups, --groups groups
Supplementary groups given by name or number in a comma-
separated list with no whitespace. user will be removed from
any groups to which it currently belongs that are not included
in groups.
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usleep
-l name, --login name
Login name. This cannot be changed while the user is logged in.
-L, --lock
Lock user’s password by putting a ! in front of it. This option
cannot be used with -p or -U.
-o, --non-unique
Override. Accept a nonunique uid with the -u option.
-p pw, -password pw
Encrypted password, as returned from crypt(3).
-s shell, --shell shell
Login shell.
-u uid, --uid uid
Numerical user ID. The value must be unique unless the -o
option is used. Any files owned by user in the user’s home
directory will have their user ID changed automatically. Files
outside of the home directory will not be changed. user should
not be executing any processes while this is changed.
-U, --unlock
Unlock the user’s password by removing the ! that -L put in
front of it. This option cannot be used with -p or -L.
users users [file]
usersoption
Print a space-separated list of each login session on the host. Note
that this may include the same user multiple times. Consult file or,
by default, /var/log/utmp or /var/log/wtmp.
Options
--help
Print usage information and exit.
--version
Print version information and exit.
usleep usleep [microseconds]
usleep [option]
Sleep some number of microseconds (default is 1).
Options
-?, --help
Print help information and then exit.
--usage
Print brief usage message and then exit.
-v, --version
Print version information.
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uuidgen
uuidgen uuidgen [option]
Create a new Universal Unique Identifier (UUID) and print it to
standard output. The generated UUID consists of five hyphen-
separated groups of hex digits (e.g., 3cdfc61d-87d3-41b5-ba50-
32870b33dc67). The default is to generate a random-based UUID,
but this requires that a high-quality random-number generator be
available on the system.
Options
-r Generate a random-based UUID.
-t Generate a time-based UUID.
vdir vdir [options] [files]
Verbosely list directory contents. Equivalent to ls -lb. By default,
list the current directory. Directory entries are sorted alphabetically
unless overridden by an option. vdir takes the same options as ls.
vi vi [options] [files]
A screen-oriented text editor based on ex. vi is bi-modal, with a
command mode and an insert mode. For more information on vi,
see Chapter 9.
vidmode vidmode [option]image [mode [offset]]
System administration command. Set the video mode for a kernel
image. If no arguments are specified, print current mode value.
mode is a 1-byte value located at offset 506 in a kernel image. You
may change the mode by specifying the kernel image to change, the
new mode, and the byte offset at which to place the new informa-
tion (the default is 506). Note that rdev -v is a synonym for
vidmode. If LILO is used, vidmode is not needed. The video mode
can be set from the LILO prompt during a boot.
Modes
-3 Prompt
-2 Extended VGA
-1 Normal VGA
0 Same as entering 0 at the prompt
1 Same as entering 1 at the prompt
2 Same as entering 2 at the prompt
3 Same as entering 3 at the prompt
n Same as entering n at the prompt
Option
-o offset
Same as specifying an offset as an argument.
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vmstat
vim vim
An enhanced version of the vi screen editor. Both vi and vim are
covered in Chapter 9.
vmstat vmstat [options] [interval [count]]
System administration command. Print report on virtual memory
statistics, including information on processes, memory, paging
block I/O, traps, system and CPU usage. vmstat initially reports
average values since the last system reboot. If given a sampling
period interval in seconds, it prints additional statistics for each
interval. If specified, vmstat exits when it has completed count
reports. Otherwise, it continues until it receives a Ctrl-C, printing a
new header line each time it fills the screen.
Options
-a Display active and inactive memory.
-d Display disk statistics.
-f Display the number of forks since the system was booted.
-m Display the names and sizes of various kernel objects stored in
a cache known as the slab layer. Also see the slabtop
command.
-n Don’t print new header lines when the screen is full.
-p partition
Display detailed statistics for the specified partition.
-s Display various event counters and memory statistics.
-S units
Switch the output units. Possible values are k, K, m, or M.
-t Add a timestamp to output.
-V Print version number, then exit.
VM mode fields
procs
r Processes waiting for runtime.
b Uninterruptible sleeping processes.
memory
swpd
Virtual memory used, in kilobytes.
free
Idle memory, in kilobytes.
buff
Memory used as buffers, in kilobytes.
cache
Cache memory, in kilobytes.
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vmstat
inactive
Inactive memory, in kilobytes, displayed with -a.
active
Active memory, in kilobytes; displayed with -a.
swap
si Memory swapped in from disk each second, in kilobytes.
so Memory swapped out to disk each second, in kilobytes.
io
bi Blocks received from block devices each second.
bo Blocks sent to block devices each second.
system
in Interrupts per second, including clock interrupts.
cs Context switches per second.
cpu
us Percentage of CPU time consumed by user processes.
sy Percentage of CPU time consumed by system processes.
id Percentage of CPU time spent idle.
wa Percentage of CPU time spent waiting for I/O.
Disk mode fields
Reads and Writes
total
Total reads or writes completed successfully.
merged
Reads or writes grouped into one I/O.
sectors
Sectors read or written successfully.
ms
Milliseconds spent reading or writing.
IO
cur I/O in progress
s Seconds spent doing I/O.
Disk partition mode fields
reads
Total reads issued to this partition.
read sectors
Total sectors read for this partition.
writes
Total writes issued to this partition.
requested writes
Total write requests for this partition.
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wall
Slab mode fields
cache
Cache name.
num
Number of currently active objects.
total
Total number of available objects.
size
Size of each object.
pages
Number of pages with at least one active object.
totpages
Total number of allocated pages.
pslab
Number of pages per slab.
volname volname [devfile]
Return the volume name for a device such as a CD-ROM that was
formatted with an ISO-9660 filesystem. The default device file
devfile is /dev/cdrom.
w w [options] [user]
Print summaries of system usage, currently logged-in users, and what
those users are doing. w is essentially a combination of uptime,
who, and ps -a. Display output for one user by specifying user.
Options
-f Toggle printing the from (remote hostname) field.
-h Suppress heading and uptime information.
-s Use the short format.
-u Ignore the username while figuring out the current process
and CPU times.
-V Display version information.
File
/var/run/utmp
List of users currently logged in.
wall wall [file]
wall [-n] [message]
Write to all users. Depending on your Linux distribution, wall
uses one of the two syntaxes shown. In both versions, the default is
for wall to read a message from standard input and send the
message to all users currently logged in, preceded by “Broadcast
Message from....” With the first syntax, which comes with
Debian-based systems, for example, if file is specified, wall reads
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warnquota
input from that file rather than from standard input, and only the
superuser can write to a terminal if the user has disallowed
messages. With the second syntax, distributed with Red Hat-based
systems, for example, the text of the message can be included on
the command line, and the message is limited to 20 lines. In this
form, if -n is specified, the default banner message is replaced with
“Remote broadcast message.” -n can only be specified by the super-
user, and only if wall was installed set-group-id.
Example
Send the message contained in the file message.txt to all users:
$wall < message.txt
warnquota warnquota [options] [filesystem]
System administration command. Mail warning messages to users
that have exceeded their soft limit.
Options
-a file, --admins-file=file
Read group administrator information from file instead of /etc/
quotagrpadmins.
-c file, --config=file
Read configuration information from file instead of /etc/
warnquota.conf.
-d, --no-details
Send messages without attaching quota reports.
-F format, -format=format
Read quota information of the specified format. (See quota for
valid formats.)
-g, --group
Send messages for group quotas. Send the message to the user
specified in /etc/quotagrpadmins.
-i, --no-autofs
Ignore automount mount points.
-q file, -quota-tab=file
Read device description strings from file instead of /etc/
quotagrpadmins.
-s, --human-readable
Report sizes in more human-readable units.
-u, --user
Send messages for user quotas. (This is the default.)
watch watch [options]command [cmd_options]
Run the specified command repeatedly (by default, every two
seconds) and display the output so you can watch it change over
time. The command and any options are passed to sh -c, so you
may need to use quotes to get correct results.
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wc
Options
-d, --differences[=cumulative]
Highlight changes between iterations. If cumulative is specified,
the highlighting remains on the screen throughout, giving a
cumulative picture of the changes.
-h, --help
Display help message and exit.
-n secs, --interval=secs
Run the command every secs seconds.
-t, --no-title
Do not display the header or the blank line following the
header.
-v, --version
Print version information and exit.
wc wc [options] [files]
Print byte, word, and line counts for each file. Print a total line for
multiple files. If files is omitted or is -, read standard input. See
other examples under ls and sort.
Options
-c, --bytes
Print byte count only.
-l, --lines
Print line count only.
-L, --max-line-length
Print length of longest line.
-m, --chars
Print character count only.
-w, --words
Print word count only.
--help
Print help message and then exit.
--version
Print the version number and then exit.
Examples
Count the number of users logged in:
who | wc -l
Count the words in three essay files:
wc -w essay.[123]
Count lines in the file named by variable $file (don’t display
filename):
wc -l < $file
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wget
wget wget [options] [urls]
Perform noninteractive file downloads from the Web. wget works
in the background and can be used to set up and run a download
without the user having to remain logged on. wget supports HTTP,
HTTPS, and FTP, as well as downloads through HTTP proxies. wget
uses a global startup file that you may find at /etc/wgetrc or /usr/local/
etc/wgetrc. In addition, users can define their own $HOME/.wgetrc
files.
Options
-4, --inet4-only
Force connection to IPv4 hosts only.
-6, --inet6-only
Force connection to IPv6 hosts only.
-a logfile, --append-output=logfile
Append output messages to logfile, instead of overwriting the
contents as -o does. If logfile doesn’t exist, create it.
-A acclist, --accept=acclist
Specify a comma-separated list of filename suffixes or patterns
to accept.
-b, --background
Go into the background immediately after startup, writing
output to the file specified with -o or to wget-log.
-B url, --base=url
Used with -F to prepend the specified URL to relative links in
the input file specified with -i.
--bind-address=address
When making client TCP/IP connections, bind() to the speci-
fied local address, which can be specified as a hostname or
IP address. Useful if your system is bound to multiple IP
addresses.
-c, --continue
Continue getting a partially downloaded file. Affects the
restarting of downloads from an earlier invocation of wget.
Works only with FTP servers and HTTP servers that support
the Range header.
--connect-timeout=seconds
Set the timeout for a connection to be established in seconds.
The default is never to time out, unless a timeout is imple-
mented by system libraries.
--cut-dirs=num
Ignore the specified number of directory components when
creating the local directory structure.
-d, --debug
Turn on debugging. wget must have been compiled with
debug support.
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wget
-D domainlist, --domains=domainlist
Specify a comma-separated list of domains to be followed.
Does not turn on -H.
--delete-after
Delete each retrieved file from the local machine after down-
loading it. Useful for prefetching pages through a proxy. -k is
ignored if specified with --delete-after.
--dns-timeout=seconds
Set the DNS lookup timeout to seconds. The default is to never
time out.
-e command, --execute=command
Execute the specified command after the commands in .wgetrc,
overriding any .wgetrc commands. Can be included multiple
times, once for each command to execute.
-E, --html-extension
Append the suffix .html to the filenames of downloaded files
where the URL does not include it (for example, an .asp file).
--exclude-domains=domainlist
Specify a comma-separated list of names that are never to be
followed.
-F, --force-html
When reading input from a file, force the file to be treated as
an HTML file.
--follow-ftp
Follow FTP links from HTML documents. The default is to
ignore FTP links.
--follow-tags=list
Specify a comma-separated list of tags to be considered, over-
riding the internal table that wget normally uses during a
recursive retrieval.
--ftp-user, --ftp-password
Specify the user name and password on an FTP server.
-h, --help
Display usage information and exit.
-H, --span-hosts
Enable spanning across hosts when doing recursive retrieval.
--header=header
Add an additional header to be passed to the HTTP server.
The header must include a colon (:) preceded by at least one
nonblank character, and with no newline characters. Can be
specified multiple times. If header is an empty string, all user-
defined headers are cleared.
--http-user=user, --http-password=password
Specify the username and password on an HTTP server.
-i file, --input-file=file
Read URLs from the specified file. URLs specified on the
command line are accessed before URLs in the file. If file is
given as -, read from standard input.
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wget
-I list, --include-directories=list
Specify a comma-separated list of directories to follow when
downloading. The list elements may contain wildcards.
--ignore-case
Ignore case when matching files and directories. Affects the
behavior of -A, -I, -R, -X, and FTP globbing.
--ignore-length
Ignore the “Content-Length” header on the HTTP server.
--ignore-tags=list
Specify a comma-separated list of tags to be ignored for recur-
sive retrievals.
-k, --convert-links
Convert document links after the download is complete so
they work locally.
-K, --backup-converted
When converting a file, back up the original and add an .orig
suffix. Affects the behavior of -N.
--keep-session-cookies
Causes --save-cookies to also save session cookies.
-l depth, --level=depth
For recursive retrievals, specify the maximum recursion depth.
The default depth is 5.
-L, --relative
Follow relative links only.
--limit-rate=rate
Set the maximum download speed, The default is to specify
the rate in bytes, or add a k suffix for kilobytes or m for
megabytes.
--load-cookies=file
Load cookies from the specified file before the first HTTP
retrieval.
-m, --mirror
Turn on options suitable for mirroring a remote site. Equiva-
lent to -r -N -l inf --no-remove-listing.
--max-redirect=num
Set the maximum number of redirections to follow (default
is 20).
-N, --timestamping
Turn on timestamping.
-nc, --no-clobber
Do not download a file if there is already a copy on the disk.
The default is to preserve the original copy and rename succes-
sive downloads, adding .1, .2, etc. to their name. May not be
specified with -N.
-nd, --no-directories
Do not create a directory hierarchy when doing recursive
retrievals.
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wget
-nH, --no-host-directories
Disable creation of directories prefixed by the name of the
host. The default is to include the hostname.
--no-cache
Disable server-side cache for an HTTP retrieval. The default is
for caching to be on.
--no-cookies
Disable the use of cookies.
--no-dns-cache
Disable caching of DNS lookups; look up hostname again for
each new connection.
--no-glob
Turn off FTP globbing to prevent the use of wildcards for
multiple file retrievals.
--no-http-keep-alive
Turn off the keep-alive feature for HTTP retrievals.
--np, --no-parent
In recursive retrievals, do not ever go up to the parent directory.
--no-passive-ftp
Do not allow use of passive FTP transfer mode.
--no-proxy
Do not use proxies.
--no-remove-listing
Do not remove the temporary .listing files generated by FTP
retrievals.
-nv, --non-verbose
Turn off verbose mode, but don’t run completely quietly.
Displays error messages and basic information.
-o logfile, --output-file=logfile
Log output messages to logfile, instead of the default standard
error.
-O file, --output-document=file
Concatenate all documents into the specified file. If the file
exists, it is overwritten. Specify the file as - to write to standard
output.
-p, --page-requisites
Download all files necessary to display an HTML page.
-P prefix, --directory-prefix=prefix
Set the directory prefix to the specified value.
--post-data=string, --post-file=file
Use POST as the method for HTTP requests and send the
specified data in the request body. Use --post-data to send
string as data and --post-file to send the file contents.
--prefer-family=family
Connect to the addresses of the specified family first when
there is a choice. The possible values for family are IPv4 (the
default), IPv6, and none.
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wget
--progress=type[:style]
Set the progress indicator to type. Valid types are dot and bar;
the default is bar. With --progress=dot, you can also set a
style. The default style is for each dot to represent 1 KB, with
10 dots in a cluster and 50 dots per line. Alternatives are
binary, with each dot representing 8 KB, 16-dot clusters, and
48 dots per line; mega, for downloading very large files, with
each dot representing 64 KB, 8 dots per cluster, and 48 dots
per line; and giga, with each dot representing 1 MB, 8 dots per
cluster, and 4 clusters per line.
--protocol-directories
Use the protocol name as part of the local filename.
--proxy-user=user, --proxy-passwd=password
Specify the username and password for authentication on a
proxy server.
-q, --quiet
Run quietly; don’t produce output.
-Q quota, --quota=quota
Specify download quota for automatic retrievals. The default
value is in bytes; add k suffix for kilobytes, or m for megabytes.
-r, --recursive
Turn on recursive retrieving.
-R rejlist, --reject=rejlist
Specify a comma-separated list of filename suffixes or patterns
to reject.
--random-wait
Set a random wait time to prevent being identified by websites
that look for patterns in time between requests so they can
block access.
--read-timeout=seconds
Set the read (and write) timeout to the specified number of
seconds. The default is 900 seconds.
--referer=url
Include a “Referer: url” header in an HTTP request.
--restrict-file-names=mode[,nocontrol]
Restrict the characters found in remote URLs from appearing
in local filenames. The value of mode is the operating
system—e.g., unix or windows (use unix for Linux). Such
characters are escaped with a percent sign (%). The default is
to escape characters not valid on your operating system.
Appending ,nocontrol turns off escaping of control characters.
--retr-symlinks
When retrieving FTP directories recursively, follow symbolic
links and retrieve the linked-to files.
--retry-connrefused
Retry after getting a “connection refused” error. Useful for
mirroring unreliable sites whose servers are likely to go down
briefly.
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wget
-S, --server-response
Print HTTP server headers and FTP server responses.
--save-cookies=file
Save cookies in the specified file before exiting. Does not save
expired cookies, and only saves session cookies if --keep-
session-cookies is also specified.
--save-headers
Save the headers sent by an HTTP server to the file, preceding
the contents and separated by a blank line.
--spider
Behave like a web spider, checking that pages exist but not
downloading them.
--strict-comments
Turn on strict parsing of HTML comments, instead of termi-
nating comments at the first occurrence of -->.
-t num, --tries=num
Set the number of retries to the specified value of num. Set num
to 0 or inf to keep trying forever (infinitely) (default is 20 retries),
unless there is a fatal error such as “connection refused.”
-T seconds, --timeout=seconds
Set network timeout to the specified number of seconds.
Equivalent to specifying all of --dns-timeout, --connect-
timeout, and --read-timeout.
--user=user, --password=password
Specify the user name and password for both FTP and HTTP
file retrieval.
-U agent, --user-agent=agent
Specify an agent string to the HTTP server to replace the
default identification of Wget/version, where version is the
current wget version. This string is used in the User-Agent
header field.
-v, --verbose
Turn on verbose output, printing all available data. This is the
default.
-V, --version
Display version information and exit.
-w seconds, --wait=seconds
Specify the wait in seconds between retrievals. Used to lighten
server load. Use the suffix m to specify the wait in minutes, h
for hours, or d for days.
--waitretry=seconds
Specify the number of seconds to wait between retries if the
download fails. The default in the global configuration file is
not to wait.
-x, --force-directories
Create a hierarchy of directories even if one wouldn’t other-
wise be created.
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whatis
-X list, --exclude-directories=list
Specify a comma-separated list of directories to exclude from
download. List elements may contain wildcards.
whatis whatiskeywords
Search the short manual page descriptions in the whatis database
for each keyword and print a one-line description to standard
output for each match. Like apropos, except that it searches only
for complete words. Equivalent to man -f.
whereis whereis [options]files
Locate the binary, source, and manual page files for specified
commands/files. The supplied filenames are first stripped of
leading pathname components and any (single) trailing extension
of the form .ext (for example, .c). Prefixes of s. resulting from use of
source code control are also dealt with. whereis then attempts to
locate the desired program in a list of standard Linux directories (/bin,
/etc, /usr/bin, /usr/local/bin/, etc.).
Options
-b Search only for binaries.
-B directories
Change or otherwise limit the directories to search for
binaries.
-f Terminate the last directory list and signal the start of file-
names. Required when the -B, -M, or -S option is used.
-m Search only for manual sections.
-M directory
Change or otherwise limit the directories to search for manual
sections.
-s Search only for sources.
-S directory
Change or otherwise limit the directories to search for sources.
-u Search for unusual entries—that is, files that do not have one
entry of each requested type. Thus, the command whereis -m
-u * asks for those files in the current directory that have no
documentation.
Example
Find all files in /usr/bin that are not documented in /usr/share/man/
man1 but that have source in /usr/src:
$cd /usr/bin
$whereis -u -M /usr/share/man/man1 -S /usr/src -f *
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which
which which [options] [--] [commands]
List the full pathnames of the files that would be executed if the
named commands had been run. which searches the user’s $PATH
environment variable.
Options
-a, --all
Print all matches, not just the first.
-i, --read-alias
Read aliases from standard input and write matches to stan-
dard output. Useful for using an alias for which.
--read-functions
Read shell functions from standard input and report matches
to standard output. Useful for also using a shell function for
which itself.
--skip-alias
Ignore --read-alias if present. Useful for finding normal binaries
while using --read-alias in an alias for which.
--show-dot
If a matching command is found in a directory that starts with
a dot, print ./cmdname instead of the full pathname.
--show-tilde
Print a tilde (~) to indicate the user’s home directory. Ignored
if the user is root.
--skip-dot
Skip directories that start with a dot.
--skip-functions
Ignore --read-functions if present. Useful when searching for
normal binaries while using --read-functions in an alias or
function for which.
--skip-tilde
Skip directories that start with a tilde (~) and executables in
$HOME.
--tty-only
Stop processing options on the right if not on a terminal.
-v, -V, --version
Print version information and then exit.
--help
Print help information and then exit.
Example
$which cc ls
/usr/bin/cc
ls: aliased to ls -sFC
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who
who who [options] [file]
who am i
Show who is logged into the system. With no options, list the
names of users currently logged in, their terminal, the time they
have been logged in, and the name of the host from which they
have logged in. An optional system file (default is /etc/utmp) can be
supplied to give additional information.
Options
-a, --all
Equivalent to -b -d --login -p -r -t -T -u.
am i
Print information for the invoking user.
-b, --boot
Print time of last system boot.
-d, --dead
Print a list of dead processes.
-H, --heading
Print column headings.
--help
Print a help message and then exit.
-l, --login
Print list of system login processes.
--lookup
Attempt to include canonical hostnames via DNS.
-m Same as who am i.
-p, --process
Print active processes spawned by init.
-q, --count
“Quick.” Display all usernames and the total number of users.
-r, --runlevel
Print the current runlevel.
-s, --short
Print only name, line, and time. This is the default behavior.
-t, --time
Print the last system clock change.
-u, --users
Print a list of the users who are logged in.
--version
Print version information and then exit.
-w, -T, --mesg, --message, --writable
Include user’s message status in the output:
+ mesg y (write messages allowed)
- mesg n (write messages refused)
? Cannot find terminal device
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whois
Example
This sample output was produced at 8 a.m. on April 17:
$who -uH
NAME LINE TIME IDLE PID COMMENTS
Earvin ttyp3 Apr 16 08:14 16:25 2240
Larry ttyp0 Apr 17 07:33 . 15182
Since Earvin has been idle since yesterday afternoon (16 hours), it
appears that he isn’t at work yet. He simply left himself logged in.
Larry’s terminal is currently in use.
whoami whoami
Print current user ID. Equivalent to id -un.
whois whois[options]query[@server[:port]]
jwhois [options]query[@server[:port]]
Search a whois database for a domain name, IP address, or NIC
name. The information returned varies, but usually contains
administrative and technical contacts so that you can find a person
to handle problems at that domain. By default, the command
returns information on .com, .net, and .edu domains, but other
hosts can be queried for other domains using host or the -h option.
Options
-- Indicate the end of whois options. A subsequent string that
begins with a hyphen on the command line is taken as a query
string.
-a, --raw
Do not rewrite query according to configuration before
sending to server.
-c file, --config=file
Specify a configuration file to use instead of the default /etc/
jwhois.conf.
-d, --disable-cache
Disable reading and writing to the cache.
-f, --force-lookup
Force the lookup query to go to the host, even if it is available
from the cache.
-h host, --host=host
Query the whois server on the specified host. Same as host on
the command line. By default, queries the server in the envi-
ronment variable NICNAMESERVER or WHOISSERVER if
either is set; otherwise queries whois.internic.net.
--help
Print help message and exit.
-i, --display-redirections
Display every step in a redirection. The default is to display
only the last step.
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wodim
-n, --no-redirect
Disable redirection from one server to the next.
-p port, --port=port
Connect to the specified port. Same as port on the command
line. Default is 43.
-r, --rwhois
Force use of the rwhois protocol, instead of HTTP or whois.
--rwhois-display=display
Request receiving rwhois servers to display the results in the
specified display instead of the default.
--rwhois-limit=limit
Request receiving rwhois servers to limit the number of
matches to the specified limit.
-s, --no-whoisservers
Disable built-in support for whois-servers.net.
-v Verbose. Print debugging information while running. Specify
-vv to increase verbosity.
--version
Print version information and exit.
wodim wodim [options]track1,track2...
Record data or audio CD or DVD media. This program normally
requires root access to the device file; run as root or install suid-
root. It has a large number of options and settings; see the
manpage for a complete list as well as a number of useful examples.
General options
General option flags go directly after the wodim command and
before any track options or arguments. The general options are:
-atip
Display the ATIP (Absolute Time In Pregroove) information
for a disc. Not all drives allow you to read this information.
blank=type
Erase data from a CD-RW in one of the following ways:
all
Erase all information on the disc. May take a long time.
fast
Perform a quick erase of the disc, erasing only the PMA,
TOC, and pregap.
help
Display a possible list of blanking methods.
session
Blank the last session.
track
Blank a track.
trtail
Blank the tail of a track only.
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wodim
unclose
Unclose the last session.
unreserve
Unreserve a track previously marked as reserved.
-checkdrive
Check to see if there are valid drivers for the current drive.
Returns 0 if the drive is valid.
-d, debug=n
Set the debug level to an integer (greater numbers are more
verbose), or use multiple -d flags as with the -v and -V flags.
-dao, -sao
Disk-at-once (session-at-once) mode. Works only with MMC
drives that support nonraw session-at-once modes.
dev=target
Set the SCSI target for the CD/DVD recorder. May be specified
as a device name or as three comma-separated integers repre-
senting bus, target, and logical unit. To check the options that
are available, use the -scanbus option. By default wodim looks
in the CDR_DEVICE environment variable.
driver=name
Lets you specify a driver for your system. Suggested for experts
only. The special drivers cdr_simul and dvd_simul are used
for simulation and profiling tests if your drive does not
support the -dummy option.
driveropts=optlist
Specify a comma-separated list of driver options. To get a list of
valid options, use driveropts=help together with -checkdrive.
-dummy
Perform a dry run, doing all the steps of recording with the
laser turned off. This will let you know whether the process is
going to work.
-eject
Eject disc after recording. Some hardware may need to eject a
disc after a dummy recording and before the actual recording.
-fix
Close (“fixate”) the session, preventing future multisession
recordings and allowing the disc to be played in standard
audio CD players (some can also play a disc that has not been
closed).
-force
Override errors if possible. May allow you to blank an other-
wise broken CD-RW.
fs=n
Set the FIFO buffer size to n, in bytes. You may use k, m, s, or
f to specify kilobytes, megabytes, or units of 2048 and 2352
bytes, respectively. The default is 4 MB.
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wodim
gracetime=n
Set the number of seconds of grace time before writing. The
value of n should be at least 2 (default is 4 seconds).
kdebug=n, kd=n
Set the kernel’s debug notification value to n during SCSI
command execution. Works through the usal-driver.
mcn=n
Set the Media Catalog Number to n.
msifile=file
Like -msinfo, but also saves the information in the specified
file.
-msinfo
Get multisession information from the CD. Used only with
multisession discs onto which you can still record more
sessions.
-multi
Set to record in multisession mode. Must be present on all
sessions but the last one for a multisession disc.
-nofix
Do not close the disc after writing.
-reset
Attempt to reset the SCSI bus. Does not work on all systems.
-s, -silent
Silent mode. Do not print any SCSI command errors.
speed=n
Set the speed to n, a multiple of the audio speed. Normally,
wodim gets the speed from /etc/wodim.conf or the CDR_
SPEED environment variable. If your drive has trouble with
higher numbers, try 0 as a value.
timeout=n
Set the SCSI command timeout to n seconds. Defaults to 40.
-tao
Track-at-once (TAO) write mode. Most drives require TAO
mode for multisession recording.
-toc
Display the table of contents for the CD currently in the drive.
Works for CD-ROM, as well as CD-R and CD-RW drives.
ts=n
Set the maximum transfer size for a single SCSI command to
n. Defaults to 63 KB.
-scanbus
Scan SCSI devices. Useful for finding the SCSI address of the
drive.
-useinfo
Use .inf files to override audio options set elsewhere.
-v Verbose mode. Use one v for each level of verbosity. -vv would
be very verbose, and -vvv would be even more so.
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wodim
-V A verbose mode counter that applies only to SCSI transport
messages. This slows the application but can be useful for
debugging.
-version
Print version information and exit.
-waiti
Wait for input on standard input before opening the SCSI
driver. Useful for letting wodim read input from a pipe while
writing additional sessions to a multisession disk.
Track options and arguments
Track options may be mixed with track arguments, and normally
apply to the track immediately after them or to all tracks after
them. The track arguments themselves should be the files that you
will be writing to the CD. Options are:
-audio
Write all tracks after this track in digital audio format (playable
by standard CD players). If you do not use this flag or the -data
flag, wodim assumes that .au and .wav files are to be recorded
as raw audio and that all other files are data.
-cdi
Write subsequent tracks in CDI format. Use with XA disks
only.
-data
Record subsequent tracks as CD-ROM data. If you do not use
this flag or the -audio flag, all files except for those that end in
.wav or .au are assumed to be data.
-index=a,b,c
Set the index list for the next track. The values should be
increasing comma-separated integers, starting with index 1
and counting in sectors (75ths of a second). For example, you
could set three indices in a track with index=0,750,7500
and they would occur at the beginning of the track, after 10
seconds, and after 100 seconds.
-isosize
The size of the next track should match the size of the ISO-
9660 filesystem. This is used when duplicating CDs or
copying from raw-data filesystems.
isrc=n
Set the International Standard Recording Number for the
track argument following this option.
-mode2
Write all subsequent tracks in CD-ROM mode 2 format.
-nopad
Do not insert blank data between data tracks following this
flag. This is the default behavior.
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write
-pad
Insert 15 sectors of blank data padding between data tracks.
Applies to all subsequent tracks or until you use the -nopad
argument, and is overridden by the padsize=n argument.
padsize=n
Insert n sectors of blank data padding after the next track.
Applies only to the track immediately after it.
-swab
Declare that your data is in byte-swapped (little-endian) byte
order. This is not normally necessary.
tsize=n
Set the size of the next track. Useful only if you are recording
from a raw disk for which wodim cannot determine the file
size. If you are recording from an ISO 9660 filesystem, use the
-isosize flag instead.
-xa, -xa1, -xa2
Write subsequent tracks in CD-ROM XA mode 2 format. -xa1
writes in mode 2 form 1 format, and subheaders must be
supplied by the application providing the data. -xa and -xa2
write in mode 2 form 1 and mode 2 form 2, respectively, and
subheaders are created by the drive.
write writeuser [tty]
message
Initiate or respond to an interactive conversation with user. A write
session is terminated with EOF. If the user is logged into more than
one terminal, specify a tty number. See also talk; use mesg to keep
other users from writing to your terminal.
xargs xargs [options] [command]
Execute command (with any initial arguments), but read remaining
arguments from standard input instead of specifying them directly.
xargs passes these arguments in several bundles to the command,
allowing it to process more arguments than it could normally
handle at once. The arguments are typically a long list of filenames
(generated by ls or find, for example) that get passed to xargs via a
pipe. The default command is /bin/echo.
Options
-0, --null
Expect filenames to be terminated by NULL instead of white-
space. Do not treat quotes or backslashes specially.
-afile, --arg-file=file
Read arguments from file, not standard input.
-E string
Set EOF to string. Default is no EOF string.
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xargs
--help
Print usage information and then exit.
-I string
Replace all occurrences of string in the initial arguments with
names read from standard input. Unquoted blanks are not
considered argument terminators; newline character is used.
Implies -x and -L 1.
-L lines
Allow no more than lines nonblank input lines on the
command line (default is 1). Implies -x.
-n args, --max-args=args
Allow no more than args arguments on the command line.
Overridden by the maximum number of characters set with -s.
-p, --interactive
Prompt for confirmation (y or Y) before running each command
line. Implies -t.
-P max, --max-procs=max
Allow no more than max processes to run at once. The default
is 1. A maximum of 0 allows as many as possible to run at once.
-r, --no-run-if-empty
Do not run command if standard input contains only blanks.
-s max, --max-chars=max
Allow no more than max characters per command line.
--show-limits
Display upper and lower limits on command-line length
(based on system limits, xarg buffer size, and -s if specified)
before running the command.
-t, --verbose
Verbose mode. Print command line on standard error before
executing.
-x, --exit
If the maximum size (as specified by -s) is exceeded, exit.
--version
Print the version number of xargs and then exit.
Examples
grep for pattern in all files on the system:
find / | xargs greppattern> out &
Run diff on file pairs (e.g., f1.a and f1.b, f2.a and f2.b, etc.):
echo $* | xargs -n2 diff
The previous line would be invoked as a shell script, specifying
filenames as arguments. Display file, one word per line (same as
deroff -w):
catfile| xargs -n1
Move files in olddir to newdir, showing each command:
ls olddir | xargs -i -t mv olddir/{ } newdir/{ }
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xinetd
xinetd xinetd [options]
TCP/IP command. The extended Internet services daemon. xinetd
saves system resources by listening to multiple sockets on the
behalf of other server programs, invoking necessary programs as
requests are made for their services. Beyond this, xinetd provides
better logging facilities, including remote user ID, access times, and
server-specific information. It also provides access-control facili-
ties. Not limited to system administration use, it can launch
services that are not listed in /etc/services. Unprivileged users can
use this tool to start their own servers.
Options
-cc num
Perform an internal-state consistency check every num seconds.
-d Turn on debugging support.
-dontfork
Execute in the foreground. This option automatically sets the
-stayalive option.
-f file
Read configuration from the specified file instead of /etc/
xinetd.conf.
-filelog file
Write log messages to the specified file. Cannot be combined
with -syslog or -d.
-inetd_compat
Read the /etc/inetd.conf file after reading /etc/xinetd.conf.
-limit num
Start no more than num concurrent processes.
-logprocs num
Limit processes used to look up remote user IDs to num.
-pidfile file
Write xinetd’s process ID to file.
-stayalive
Keep running even when no services have been specified.
-syslog facility
Log messages to the specified syslogd facility. Accepted values
are daemon, auth, user, and localn, where n can range from 0
to 7. Cannot be combined with -syslog or -d. The default
behavior is to write messages to syslogd using the daemon
facility.
-version
Print version information, then exit.
Configuration files
By default xinetd reads its configuration information from file /etc/
xinetd.conf. Lines in this file beginning with # are treated as
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xinetd
comments. The entries for each service differ completely from /etc/
inetd entries. xinetd configuration entries for services follow the
pattern:
serviceservicename
{
attribute1 = valueset1
attribute2 = valueset2
}
Some attributes allow assignment operators other than = . Other
operators are += , to add to a value set, and -= , to remove a value
from a value set. There are many attributes available to control
services. The following are the most common:
cps
Limit incoming connection rate. Accepts two numeric argu-
ments: the number of connections per second to allow and the
number of seconds to wait to accept a new connection when
the rate is exceeded. The default is 50 incoming connections
and a 10-second wait.
disable
Accept a Boolean yes or no. When disabled, xinetd will ignore
the entry.
flags
Accept a set of the following values defining xinetd’s behavior:
IDONLY
Accept only connections when the remote user’s ID can
be verified by an identification server. Cannot be used
with USERID logging.
INTERCEPT
Intercept packets to ensure they are coming from allowed
locations. Cannot be used with internal or multithreaded
services.
IPv4
Service is an IPv4 service.
IPv6
Service is an IPv6 service.
KEEPALIVE
Set flag on socket, enabling periodic checks to determine
if the line is still receiving data.
NAMEINARGS
Expect the first argument for the server_args attribute to
be the command to run. This flag is necessary to wrap
services with tcpd.
NODELAY
Set socket’s NODELAY flag.
NOLIBWRAP
Don’t use xinetd’s internal TCP wrapping facilities.
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xinetd
NORETRY
If service fails to fork, don’t try to fork again.
SENSOR
Instead of launching a service, add IP addresses that
attempt to access this service to a list of denied addresses
for a time specified by the deny_time attribute.
group
Specify a group ID for the server process. This may be used
only when xinetd runs as root.
nice
Set service priority. This attribute accepts the same values as
the renice command.
id
Specify a unique identifier for the service. Useful when
creating multiple entries with the servicename. For example,
two versions of the echo service, one supporting UDP and the
other TCP, might be given the identifiers echo-stream and
echo-dgram.
log_on_failure
Specify values to log when a server cannot be started.
Accepted values are HOST, USERID, or just ATTEMPT.
log_on_success
Specify values to log when a server is started. Accepted values
are PID, HOST, USERID, EXIT, and DURATION.
no_access
Specify hosts that should not be allowed access to a service.
May be given as an IP address, a netmask, a hostname, a
network name from /etc/networks, or a group of IP addresses
like so: 192.168.1.{10,11,12,15,32}.
only_from
Restrict access to the service to the specified hosts. This
attribute accepts the same values as no_access.
per_source
Specify the maximum number of instances allowed to a single
source IP address. The default is “UNLIMITED”.
port
Specify the service port to listen to. This attribute is required
for non-RPC services not listed in /etc/services. If the service is
listed, the value of port cannot differ from what is listed.
protocol
Specify protocol to use, usually tcp or udp. The protocol must
be listed in /etc/protocols. This attribute is required for RPC
services, as well as services not found in /etc/services.
rpc_version
The RPC version used by the service. This can be a single
number or a range of numbers from x-y. This attribute is
required for RPC services.
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yacc
rpc_number
Specify RPC ID number. This is required only for services not
listed in /etc/rpc; otherwise it’s ignored.
server
The program to execute for the service. When using tcpd to
wrap a service, also set the NAMEINARGS flag and use the
server’s program name as the first argument for server_args.
This attribute is required for all noninternal services.
server_args
Arguments to pass to the server program.
socket_type
Specify the socket type to create. Accepted values are stream,
dgram, raw, and seqpacket.
type
Describe the type of service. Accepted values are RPC,
INTERNAL, and UNLISTED.
user
Specify a user ID for the server process. This may be used only
when xinetd runs as root.
wait
Determine whether services should be treated as single-
threaded (yes) and xinetd should wait until the server exits to
resume listening for new connections, or multithreaded (no)
and xinetd should not wait to resume listening. This attribute
is required for all serices.
Files
/etc/xinetd.conf
Default configuration file.
/etc/xinetd.d
Common directory containing configuration files included
from /etc/xinetd.conf.
yacc yacc [options]file
Given a file containing context-free grammar, convert file into
tables for subsequent parsing, and send output to y.tab.c. This
command name stands for yet another compiler-compiler. See also
flex, bison, and the book lex & yacc (O’Reilly).
Options
-b prefix
Prepend prefix, instead of y, to the output file.
-d Generate y.tab.h, producing #define statements that relate
yacc’s token codes to the token names declared by the user.
-g Generate a VCG description.
-l Exclude #line constructs from code produced in y.tab.c. (Use
after debugging is complete.)
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yes
-o outfile
Write generated code to outfile instead of the default y.tab.c.
-p prefix
Change the symbol yacc uses for symbols it generates from the
default yy to prefix.
-t Compile runtime debugging code.
-v Generate y.output, a file containing diagnostics and notes
about the parsing tables.
yes yes [strings]
yes [option]
Print the command-line arguments, separated by spaces and
followed by a newline, until killed. If no arguments are given, print
y followed by a newline until killed. Useful in scripts and in the
background; its output can be piped to a program that issues
prompts.
Options
--help
Print a help message and then exit.
--version
Print version information and then exit.
ypbind ypbind [options]
NFS/NIS command. NIS binder process. ypbind is a daemon
process typically activated at system startup time. Its function is to
remember information that lets client processes on a single node
communicate with some ypserv process. The information ypbind
remembers is called a binding—the association of a domain name
with the Internet address of the NIS server and the port on that host
at which the ypserv process is listening for service requests. This
information is cached in the file /var/yp/binding/domainname.version.
Options
-broadcast
Ignore configuration information in /etc/yp.conf and directly
request configuration information from a remote system using
ypset.
-broken-server
Allow connections to servers using normally illegal port
numbers. Sometimes needed for compatibility with other
versions of ypserv.
-c Check configuration file for syntax errors, then exit.
-debug
Run in the foreground process instead of detaching and
running as a daemon.
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ypinit
-f file
Read configuration information from file instead of /etc/yp.conf.
-no-ping
Don’t ping remote servers to make sure they are alive.
--version
Print version information, then exit.
-ypset
Allow remote machine to change the local server’s bindings.
This option is very dangerous and should be used only for
debugging the network from a remote machine.
-ypsetme
ypset requests may be issued from this machine only. Security
is based on IP address checking, which can be defeated on
networks on which untrusted individuals may inject packets.
This option is not recommended.
ypcat ypcat [options]map
NFS/NIS command. Print values in an NIS database specified by
map name or nickname.
Options
-d domain
Specify domain other than the default domain.
-h host
Specify a ypbind host other than the default.
-k Display keys for maps in which values are null or key is not
part of value.
-t Do not translate mname to map name.
-x Display map nickname table listing the nicknames (mnames)
known and map name associated with each nickname. Do not
require an mname argument.
ypinit ypinit [options]
NFS/NIS command. Build and install an NIS database on an NIS
server. ypinit can be used to set up a master server, slave server, or
slave copier. Only a privileged user can run ypinit.
Options
-m Indicate that the local host is to be the NIS master server.
-s master_name
Set up a slave server database. master_name should be the
hostname of an NIS server, either the master server for all the
maps, or a server on which the database is up to date and
stable.
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ypmatch
ypmatch ypmatch [options]key... mname
NFS/NIS command. Print value of one or more keys from an NIS
map specified by mname. mname may be either a map name or a
map nickname.
Options
-d domain
Specify domain other than default domain.
-k Before printing value of a key, print the key itself, followed by
a colon (:).
-t Do not translate nickname to map name.
-x Display map nickname table listing the nicknames (mnames)
known, and the map name associated with each nickname. Do
not require an mname argument.
yppasswd yppasswd [options] [name]
NFS/NIS command. Change login password in Network Informa-
tion Service. Create or change your password, and distribute the new
password over NIS. The superuser can change the password for any
user. This command may also be invoked as ypchfn and ypchsh.
Options
-f Update the password information field (the GECOS field).
Using this option is the same as ypchfn.
-l Update the login shell. Using this option is the same as ypchsh.
-p Update the password. This is the default behavior for yppasswd.
yppasswdd rpc.yppasswdd [options]
NFS/NIS command. Server for modifying the NIS password file.
yppasswdd handles password-change requests from yppasswd. It
changes a password entry only if the password represented by
yppasswd matches the encrypted password of that entry and if the
user ID and group ID match those in the server’s /etc/passwd file.
Then it updates /etc/passwd and the password maps on the local
server. If the server was compiled with the CHECKROOT=1 option,
the password is also checked against the root password.
Options
-D dir
Specify a directory that contains the passwd and shadow files
for rpc.yppasswdd to use instead of /etc/passwd and /etc/
shadow. Useful to prevent all users in the NIS database from
automatically gaining access to the NIS server.
-e [chsh|chfn]
Permit users to change the shell or user information in the
GECOS field of their passwd entry. By default, rpc.yppasswdd
does not permit users to change these fields.
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yppush
-E program
Specify a program to edit the passwd and shadow files instead
of rpc.yppasswdd. The program should return 0 for successful
completion; 1 for successful completion, but the pwupdate
program should not be run to update the NIS server’s maps;
and anything else if the change failed.
-p pwfile
Specify an alternative passwd file to /etc/passwd, to prevent all
users in the NIS database from automatically gaining access to
the NIS server.
--port num
Specify a port that rpc.yppasswdd will try to register itself,
allowing a router to filter packets to the NIS ports.
-s shadowfile
Use shadowfile instead of /etc/passwd for shadow password
support.
-v Print version information and whether the package was compiled
with CHECKROOT.
-x program
Modify files using the specified program instead of using
internal default functions. rpc.yppasswdd passes information
to program in the following format:
username o:oldpassword p:password s:shell g:gcos
Any of the fields p, s, or g may be missing.
yppoll yppoll [options]map
NFS/NIS command. Determine version of NIS map at NIS server.
yppoll asks a ypserv process for the order number and the host-
name of the master NIS server for the map.
Options
-h host
Ask the ypserv process at host about the map parameters. If
host is not specified, the hostname of the NIS server for the
local host (the one returned by ypwhich) is used.
-d domain
Use domain instead of the default domain.
yppush yppush [options]mapnames
NFS/NIS command. Force propagation of changed NIS map.
yppush copies a new version of an NIS map, mapname, from the
master NIS server to the slave NIS servers. It first constructs a list of
NIS server hosts by reading the NIS map ypservers with the -d
option’s domain argument. Keys within this map are the ASCII
names of the machines on which the NIS servers run. A map
transfer request is sent to the NIS server at each host, along with
the information needed by the transfer agent to call back to
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ypserv
yppush. When the attempt has been completed and the transfer
agent has sent yppush a status message, the results may be printed
to standard error. Normally invoked by /var/yp/Makefile after
commenting out the NOPUSH=true line.
Options
-d domain
Specify a domain.
-h host
Specify one or a group of systems to which a map should be
transferred instead of using the list of servers in the ypservers
map. Multiple -h options can be specified to create a list of
hosts.
-p count, --parallel count
Send maps to count NIS slaves simultaneously (in parallel). By
default, yppush sends maps to one server at a time (serially).
--port num
Specify a port to listen on for callbacks. This will not work
when sending maps in parallel. By default, the command
chooses a random port.
-t secs
Specify a timeout value in seconds. The timeout determines
how long yppush will wait for a response from a slave server
before sending a map transfer request to the next server. The
default timeout is 90 seconds, but for big maps a longer
timeout may be needed.
-v Verbose; print message when each server is called and for each
response. Specify twice to make yppush even more verbose.
ypserv ypserv [options]
NFS/NIS command. NIS server process. ypserv is a daemon
process typically activated at system startup time. It runs only on
NIS server machines with a complete NIS database. Its primary
function is to look up information in its local database of NIS
maps. The operations performed by ypserv are defined for the
implementor by the NIS protocol specification, and for the
programmer by the header file <rpcvc/yp_prot.h>. Communication
to and from ypserv is by means of RPC calls. On startup or when
receiving the signal SIGHUP, ypserv parses the file /etc/ypserv.conf.
ypserv supports securenets, which can be used to restrict access to
a given set of hosts.
Options
-d [path], --debug [path]
Run in debugging mode without going into background
mode, and print extra status messages to standard error for
each request. If path is specified, use it instead of /var/yp.
-i interface, --iface interface
Only provide service on the specified network interface.
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yptest
-p port, --port port
Bind to the specified port. For use with a router to filter
packets so that access from outside hosts can be restricted.
-v, --version
Print version information and exit.
Files and directories
/etc/yp.conf
Configuration file.
/var/yp/ domainname
Location of NIS databases for domainname.
/var/yp/Makefile
Makefile that is responsible for creating NIS databases.
/var/yp/securenets
securenets information containing netmask/network pairs
separated by whitespace.
ypset ypset [options]server
NFS/NIS command. Point ypbind at a particular server. ypset tells
ypbind to get NIS services for the specified domain from the ypserv
process running on server. server indicates the NIS server to bind to
and can be specified as a name or an IP address.
Options
-d domain
Use domain instead of the default domain.
-h host
Set ypbind’s binding on host instead of the local host. host can
be specified as a name or an IP address.
yptest yptest [options]
NFS/NIS command. Check configuration of NIS services by calling
various NIS functions. Without arguments, yptest queries the NIS
server for the local machine.
Options
-d domainname
Use domainname instead of the current host’s default domain.
This option may cause some tests to fail.
-h host
Test ypserv on the specified host instead of the current host.
This option may cause some tests to fail.
-m map
Use the specified map instead of the default map.
-q Quiet mode. Print no messages.
-u user
Run tests as user instead of as nobody.
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ypwhich
ypwhich ypwhich [options] [host]
NFS/NIS command. Return hostname of NIS server or map
master. Without arguments, ypwhich cites the NIS server for the
local machine. If host is specified, that machine is queried to find
out which NIS master it is using.
Options
-d domain
Use domain instead of the default domain.
-m [map]
Find master NIS server for a map. No host can be specified
with -m. map may be a map name or a nickname for a map. If
no map is specified, display a list of available maps.
-t mapname
Inhibit nickname translation.
-Vn
Version of ypbind (default is v2).
-x Display map nickname table. Do not allow any other options.
ypxfr ypxfr [options]mapname
NFS/NIS command. Transfer an NIS map from the server to the
local host by making use of normal NIS services. ypxfr creates a
temporary map in the directory /var/yp/domain (where domain is
the default domain for the local host), fills it by enumerating the
map’s entries, and fetches the map parameters and loads them. If
run interactively, ypxfr writes its output to the terminal. However,
if it is invoked without a controlling terminal, its output is sent to
syslogd.
Options
-c Do not send a “Clear current map” request to the local ypserv
process.
-C tid prog ipadd port
This option is for use only by ypserv. When ypserv invokes
ypxfr, it specifies that ypxfr should call back a yppush process
at the host with IP address ipadd, registered as program
number prog, listening on port port, and waiting for a
response to transaction tid.
-d domain
Specify a domain other than the default domain.
-f Force the transfer to occur even if the version on the master
server is older than the local version.
-h host
Get the map from host instead of querying NIS for the map’s
master server. host may be specified by name or IP address.
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zforce
-p dir
Use dir as the path to the NIS map directory instead of /var/yp.
-s domain
Specify a source domain from which to transfer a map that
should be the same across domains (such as the services.byname
map).
ypxfrd rpc.ypxfrd [options]
NFS/NIS command. This server is used to copy a master’s NIS map
using an RPC based file transfer program instead of building a local
map the way ypxfr would. This will speed up the transfer of large
maps.
Options
--debug
Debug mode. Do not fork.
-d dir
Use dir instead of /var/yp.
-p port
Bind to the specified port.
-v, --version
Print version information and exit.
zcat zcat [options] [files]
Read one or more files that have been compressed with gzip or
compress and write them to standard output. Read standard input
if no files are specified or if - is specified as one of the files; end
input with EOF. zcat is identical to gunzip -c and takes the options
described for gzip/gunzip.
zcmp zcmp [options]files
Read compressed files and pass them uncompressed to the cmp
command, along with any command-line options. If a second file is
not specified for comparison, look for a file called file.gz.
zdiff zdiff [options]files
Read compressed files and pass them, uncompressed, to the diff
command, along with any command-line options. If a second file is
not specified for comparison, look for a file called file.gz.
zforce zforce [names]
Rename all gzipped files to filename.gz, unless file already has a .gz
extension.
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zgrep
zgrep zgrep [options] [files]
Uncompress files and pass to grep, along with any command-line
arguments. If no files are provided, read from (and attempt to
uncompress) standard input. May be invoked as zegrep or zfgrep
and will in those cases invoke egrep or fgrep.
zless zlessfiles
Uncompress files and allow paging through them. Equivalent to
running zmore with the environment variable PAGER set to less.
See zmore for the available commands.
zmore zmore [files]
Similar to more. Uncompress files and print them one screenful at
a time. Works on files compressed with compress, gzip, or pack,
and with uncompressed files. The argument i in the following
zmore commands is an optional integer argument.
Commands
space
Print next screenful.
ispace
Print next i lines.
Return
Print one more line.
id,i^D
Print next i, or 11, lines.
iz Print next i lines or a screenful. If i is specified, treat it as the
new window size for the rest of the current file, then revert to
the default.
is Skip i lines, then print the next screenful.
if Skip i screens, then print the next screenful.
q, Q, :q, :Q
Go to next file or, if current file is the last, exit zmore.
e, q
Exit zmore when the prompt “--More-- (Next file: file)” is
displayed.
s Skip next file and continue when the prompt “--More-- (Next
file: file)” is displayed.
= Print line number.
i/expr
Search forward for ith occurrence (in all files) of expr, which
should be a regular expression. Display occurrence, including
the two previous lines of context.
in Search forward for the ith occurrence of the last regular
expression searched for.
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znew
!command
Execute command in shell. If command is not specified,
execute last shell command. To invoke a shell without passing
it a command, enter \!.
. Repeat the previous command.
znew znew [options] [files]
Uncompress .Z files and recompress them in .gz format.
Options
-9 Optimal (and slowest) compression method.
-f Recompress even if filename.gz already exists.
-K If the original .Z file is smaller than the .gz file, keep it.
-P Pipe data to conversion program. This saves disk space.
-t Test new .gz files before removing .Z files.
-v Verbose mode.
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504
Chapter 4Boot Methods
4
Boot Methods
This chapter describes techniques for booting your Linux system. Depending on
your hardware and whether you want to run any other operating systems, you can
configure the system to automatically boot Linux or to provide a choice between
several operating systems. Choosing between operating systems is generally
referred to as dual booting, although you can select between more than two. We
talk more about dual booting in the section “Dual-Booting Linux and Windows
2000/XP/Vista” on page 536.
An alternative to dual booting is virtualization, where you run one or more virtual
operating systems inside a real operating system. The real system is known as the
host, and the virtual systems are known as guests. Virtualization makes it easy to
switch between systems without having to reboot. Two ways to run virtual
systems are to make Linux the host system with another operating system running
in a virtual machine. See Chapter 15 for an overview of virtualization concepts
and for information on how to run guest systems under Linux. You can also run
Linux as a guest with another operating system such as Windows as the host.
Two ways to do this are with Microsoft’s Virtual PC and VMware server. Both are
free downloads and are available at www.microsoft.com and www.vmware.com,
respectively.
Once your Linux system is installed, rebooting the system is generally straightfor-
ward. There are several possibilities for configuring your boot process. The most
common choices are:
• Boot Linux from a bootable disk, most likely a CD or an installation CD/DVD,
leaving another operating system to boot from the hard drive.
• Use the Linux Loader, LILO. This used to be the traditional method of boot-
ing and lets you boot both Linux and other operating systems.
• Use GRUB (GRand Unified Bootloader), the GNU graphical boot loader and
command shell. Like LILO, GRUB lets you boot both Linux and other oper-
ating systems. GRUB, which has additional functionality not found in LILO,
is now the de facto Linux boot loader.
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The Boot Process | 505
Boot Methods
Whatever method you choose for booting, be sure to have a working boot disk
available for emergency use. In particular, don’t experiment with the files and
options in this chapter unless you have a boot disk, because any error could leave
you unable to boot from the hard disk. Note, though, that one of the advantages
of using GRUB is that if there is a problem booting from the menu, it drops you
down to the command-line interface so you can enter commands directly and try
to recover. In addition, your distribution CD or DVD undoubtedly has a recovery
option on it. Or you can boot from a live Linux CD such as Knoppix.
The Boot Process
On an x86-based PC, the first sector of every hard disk is known as the boot sector
and contains the partition table for that disk and possibly also code for booting an
operating system. The boot sector of the first hard disk is known as the master
boot record (MBR), because when you boot the system, the BIOS transfers control
to a program that lives on that sector along with the partition table. That code is
the boot loader, the code that initiates an operating system. When you add Linux
to the system, you need to modify the boot loader, replace it, or boot from a
floppy or CD to start Linux.
In Linux, each disk and each partition on the disk is treated as a device. For
example, the entire first hard disk is known as /dev/hda, and the entire second
hard disk is /dev/hdb. The first partition of the first hard drive is /dev/hda1, and the
second partition is /dev/hda2. The first partition of the second hard drive is /dev/
hdb1, and so on. If your drives are SCSI or SATA instead of IDE, the naming
works the same way, except that the devices are /dev/sda, /dev/sda1, and so on.
Thus, if you want to specify that the Linux partition is the second partition of the
first hard drive (as in the examples in this chapter), you refer to it as /dev/hda2.
Note that GRUB has its own disk naming convention, described later in this
chapter in “GRUB: The Grand Unified Bootloader” on page 516.
Once you’ve made the decision to install LILO or GRUB, you still need to decide
how it should be configured. Most Linux distributions will automatically set up
the booting environment for you, whether you are installing Linux as the primary
operating system or into a dual-booting environment (or in a virtual guest system
where the real MBR is not modified). If for some reason your distribution doesn’t
do it for you, or you want to do it manually, the rest of this chapter will help you.
If your distribution does set up the boot environment for you, you might still want
to read the sections on LILO or GRUB to find out how the customize your boot
loader.
If you want your system to dual-boot Linux and Windows, you need to know that
Windows has its own loader installed on the MBR, and it expects that loader to
be in charge. The standard solution described in this chapter is to add Linux as an
option in the Windows loader and install LILO or GRUB in the Linux partition as
a secondary boot loader. The result is that the Windows loader transfers control
to the secondary loader, which then boots Linux. See “Dual-Booting Linux and
Windows 2000/XP/Vista” on page 536 for more information. You can also install
one of the Linux boot loaders in the MBR and use it to boot Windows. (See the
“Linux+WinNT” and the “Multiboot with GRUB” mini-HOWTOs at the Linux
Documentation Project [www.tldp.org] if you’re interested in doing that.)
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When you install the boot loader (either LILO or GRUB) on the MBR, it replaces
the Windows boot loader. If you have problems with your installation or you
simply want to restore the original boot loader, you can do one of the following:
• If you’re running LILO, you can boot Linux from a boot disk (CD or floppy)
and restore the boot sector, which LILO automatically backs up:
$/sbin/lilo -u
• For Windows 2000, XP, and Vista, boot your computer from the Windows CD.
When you see “Welcome to Setup,” press R (for repair) and, in Windows 2000,
then press C. Select your Windows installation from the numbered list that is
displayed (there may be only one entry) and enter the administrator pass-
word at the prompt. Enter the command fixmbr at the command-line
prompt and confirm it with y. After the MBR has been restored, type exit to
reboot.
The common element in both methods is that they replace the boot loader on the
MBR with the original Microsoft boot loader.
Whatever boot loader is on the MBR is the one that will be used to boot the system.
This means that if you want to switch from LILO to GRUB, say, or from GRUB to
LILO, you don’t need to uninstall the old loader; simply install the new one.
The rest of this chapter describes the various techniques for booting Linux and
the options that you can specify to configure both the boot loader and the Linux
kernel. Whether you use GRUB or LILO, you can pass options to the loader and
specify options for the kernel.
LILO: The Linux Loader
In addition to booting Linux, LILO can boot other operating systems, such as
Windows or any of the BSD systems. During installation, some Linux distribu-
tions provide the opportunity to install LILO (most now install GRUB by default).
LILO can also be installed later if necessary. LILO can be installed on the MBR of
your hard drive or as a secondary boot loader on the Linux partition. LILO
consists of several pieces, including the boot loader itself, a configuration file (/etc/
lilo.conf), a map file (/boot/map) containing the location of the kernel, and the lilo
command (/sbin/lilo), which reads the configuration file and uses the information
to create or update the map file and to install the files LILO needs.
One thing to remember about LILO is that it has two aspects: the boot loader and
the lilo command. The lilo command configures and installs the boot loader and
updates it as necessary. The boot loader is the code that executes at system boot
time and boots Linux or another operating system.
You can make a rescue CD for LILO with the LILO command mkrescue --iso to
make an image that can be burned to CD. Use mkrescue by itself or with other
options to make a rescue floppy disk. See the mkrescue manpage for more
information.
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The LILO Configuration File
The lilo command reads the LILO configuration file, /etc/lilo.conf, to get the infor-
mation it needs to install LILO. Among other things, it builds a map file containing
the locations of all disk sectors needed for booting.
Note that any time you change /etc/lilo.conf or rebuild or move a kernel image,
you need to rerun lilo to rebuild the map file and update LILO.
The configuration file starts with a section of global options, described in the next
section. Global options are those that apply to every system boot, regardless of the
operating system you are booting. Here is an example of a global section (a hash
sign, #, begins a comment):
boot=/dev/hda # The boot device is /dev/hda
map=/boot/map # Save the map file as /boot/map
install=/boot/boot.b # The file to install as the new boot sector
prompt # Always display the boot prompt
timeout=30 # Set a 3-second (30 tenths of a second) timeout
Following the global section, there is one section of options for each Linux kernel
and for each non-Linux operating system that you want LILO to be able to boot.
Each of these sections is referred to as an image section because each boots a
different kernel image (shorthand for a binary file containing a kernel) or another
operating system. Each Linux image section begins with an image= line.
image=/boot/vmlinuz # Linux image file
label=linux # Label that appears at the boot prompt
root=/dev/hda2 # Location of the root filesystem
vga=ask # Always prompt the user for VGA mode
read-only # Mount read-only to run fsck for a filesystem check
The equivalent section for a non-Linux operating system begins with other=
instead of image=. For example:
other=/dev/hda1 # Location of the partition
label=winxp
table=/dev/hda # Location of the partition table
Put LILO configuration options that apply to all images into the global section of
/etc/lilo.conf, and options that apply to a particular image into the section for that
image. If an option is specified in both the global section and an image section,
the setting in the image section overrides the global setting for that image.
Here is an example of a complete /etc/lilo.conf file for a system that has the Linux
partition on /dev/hda2:
## Global section
boot=/dev/hda2
map=/boot/map
delay=30
timeout=50
prompt
vga=ask
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## Image section: For regular Linux
image=/boot/vmlinuz
label=linux
root=/dev/hda2
install=/boot/boot.b
map=/boot/map
read-only
## Image section: For testing a new Linux kernel
image=/testvmlinuz
label=testlinux
root=/dev/hda2
install=/boot/boot.b
map=/boot/map
read-only
optional # Omit image if not available when map is built
## Image section: For booting Windows XP
other=/dev/hda1
label=winxp
loader=/boot/chain.b
table=/dev/hda # The current partition table
Global options
In addition to the options listed here, the kernel options append, read-only, read-
write, root, and vga (described later in “Kernel options” on page 513) can also be
set as global options.
backup=backup-file
Copy the original boot sector to backup-file instead of to /boot/boot.nnnn,
where nnnn is a number that depends on the disk device type.
boot=boot-device
Set the name of the device that contains the boot sector. boot defaults to the
device currently mounted as root, such as /dev/hda2. Specifying a device such
as /dev/hda (without a number) indicates that LILO should be installed in the
master boot record; the alternative is to set it up on a particular partition,
such as /dev/hda2.
change-rules
Begin a section that redefines partition types at boot time for hiding and
unhiding partitions. See the LILO User’s Guide, which comes with the LILO
distribution, for detailed information on using this option and creating a new
rule set.
compact
Merge read requests for adjacent disk sectors to speed up booting. Use of
compact is particularly recommended when booting from a floppy disk. Use
of compact may conflict with linear.
default=name
Use the image name as the default boot image. If default is omitted, the first
image specified in the configuration file is used.
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delay=tsecs
Specify, in tenths of a second, how long the boot loader should wait before
booting the default image. If serial is set, delay is set to a minimum of 20.
The default is not to wait. See “Boot-Time Kernel Options” on page 539 for
ways to get the boot prompt if no delay is set.
disk=device-name
Define parameters for the disk specified by device-name if LILO can’t figure
them out. Normally, LILO can determine the disk parameters itself, and this
option isn’t needed. When disk is specified, it is followed by one or more
parameter lines, such as:
disk=/dev/sda
bios=0x80 # First disk is usually 0x80, second is usually 0x81
sectors=...
heads=...
Note that this option is not the same as the disk geometry parameters you
can specify with the hd boot command-line option. With disk, the informa-
tion is given to LILO; with hd, it is passed to the kernel. Note also that if
either heads or sectors is specified, they must both be specified. The parame-
ters that can be specified with disk are listed briefly here; they are described
in detail in the LILO User’s Guide.
bios=bios-device-code
The number the BIOS uses to refer to the device. See the previous example.
cylinders=cylinders
The number of cylinders on the disk.
heads=heads
The number of heads on the disk.
inaccessible
Tell LILO that the BIOS can’t read the disk; used to prevent the system
from becoming unbootable if LILO thinks the BIOS can read it. If this
parameter is specified, it must be the only parameter.
partition=partition-device
Start a new section for a partition. The section contains one variable,
start=partition-offset, which specifies the zero-based number of the first
sector of the partition:
partition=/dev/sda1
start=2048
sectors=sectors
The number of sectors per track.
disktab=disktab-file
This option has been superseded by the disk= option.
fix-table
If set, allow lilo to adjust 3-D addresses (addresses specified as sector/head/
cylinder) in partition tables. This is sometimes necessary if a partition isn’t
track-aligned and another operating system is on the same disk. See the lilo.conf
manpage for details.
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force-backup=backup-file
Like backup, but overwrite an old backup copy if one exists.
ignore-table
Tell lilo to ignore corrupt partition tables.
install=boot-sector
Install the specified file as the new boot sector. If install is omitted, the boot
sector defaults to /boot/boot.b.
lba32
Generate 32-bit Logical Block Addresses instead of sector/head/cylinder
addresses, allowing booting from any partition on hard disks greater than 8.4
GB (i.e., remove the 1024-cylinder limit). Requires BIOS support for the EDD
packet call interface * and at least LILO version 21–4.
linear
Generate linear sector addresses, which do not depend on disk geometry,
instead of 3-D (sector/head/cylinder) addresses. If LILO can’t determine your
disk’s geometry itself, you can try using linear; if that doesn’t work, then you
need to specify the geometry with disk=. Note, however, that linear some-
times doesn’t work with floppy disks, and it may conflict with compact.
lock
Tell LILO to record the boot command line and use it as the default for
future boots until it is overridden by a new boot command line. lock is useful
if there are kernel options that you need to enter on the boot command line
every time you boot the system.
map=map-file
Specify the location of the map file. Defaults to /boot/map. The map file
records the location of the kernel(s) used on the system.
message=message-file
Specify a file containing a message to be displayed before the boot prompt.
The message can include a formfeed character (Ctrl-L) to clear the screen.
The map file must be rebuilt by rerunning the lilo command if the message
file is changed or moved. The maximum length of the file is 65,535 bytes.
nowarn
Disable warning messages.
optional
Specify that any image that is not available when the map is created should be
omitted and not offered as an option at the boot prompt. Like the per-image
option optional, but applies to all images.
password=password
Specify a password that the user is prompted to enter when trying to load an
image. The password is not encrypted in the configuration file, so if pass-
words are used, permissions should be set so that only the superuser is able
to read the file. This option is like the per-image version, except that all
images are password-protected and they all have the same password.
*As long as your BIOS is dated after 1998, it should include EDD packet call interface support.
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prompt
Automatically display the boot prompt without waiting for the user to press
the Shift, Alt, or Scroll Lock key. Note that setting prompt without also
setting timeout prevents unattended reboots.
restricted
Can be used with password to indicate that a password needs to be entered
only if the user specifies parameters on the command line. Like the per-image
restricted option, but applies to all images.
serial=parameters
Allow the boot loader to accept input from a serial line as well as from the
keyboard. Sending a break on the serial line corresponds to pressing a Shift
key on the console to get the boot loader’s attention. All boot images should
be password-protected if serial access is insecure (e.g., if the line is connected
to a modem). Setting serial automatically raises the value of delay to 20 (i.e.,
two seconds) if it is less than that. The parameter string parameters has the
following syntax:
port[,bps[parity[bits]]]
For example, to initialize COM1 with the default parameters:
serial=0,2400n8
The parameters are:
port
The port number of the serial port. The default is 0, which corresponds
to COM1 (/dev/ttys0). The value can be one of 0 through 3, for the four
possible COM ports.
bps
The baud rate of the serial port. Possible values of bps are 110, 300,
1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200. The
default is 2400 bps.
parity
The parity used on the serial line. Parity is specified as n or N for no
parity, e or E for even parity, and o or O for odd parity. However, the
boot loader ignores input parity and strips the 8th bit.
bits
Specify whether a character contains 7 or 8 bits. Default is 8 with no
parity and 7 otherwise.
timeout=tsecs
Set a timeout (specified in tenths of a second) for keyboard input. If no key
has been pressed after the specified time, the default image is booted auto-
matically. timeout is also used to determine when to stop waiting for
password input. The default timeout is infinite.
verbose=level
Turn on verbose output, where higher values of level produce more output. If
-v is also specified on the lilo command line, the level is incremented by 1 for
each occurrence of -v. The maximum verbosity level is 5.
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Image options
The following options are specified in the image section for a particular boot
image. The image can be a Linux kernel or a non-Linux operating system.
alias=name
Provide an alternate name for the image that can be used instead of the name
specified with the label option.
image=pathname
Specify the file or device containing the boot image of a bootable Linux
kernel. Each per-image section that specifies a bootable Linux kernel starts
with an image option. See also the range option.
label=name
Specify the name that is used for the image at the boot prompt. Defaults to
the filename of the image file (without the path).
loader=chainloader
For a non-Linux operating system, specify the chain loader to which LILO
should pass control for booting that operating system. The default is /boot/
chain.b. If the system will be booted from a drive that is neither the first hard
disk nor a floppy or CD, the chainloader must be specified.
lock
Like lock, as described in the previous global options section; it can also be
specified in an image section.
optional
Specify that the image should be omitted if it is not available when the map is
created by the lilo command. Useful for specifying test kernels that are not
always present.
other=pathname
Specify the path to a file that boots a non-Linux system. Each per-image section
that specifies a bootable non-Linux system starts with an other option.
password=password
Specify that the image is password-protected and provide the password that
the user is prompted for when booting. The password is not encrypted in the
configuration file, so if passwords are used, permissions should be set so only
the superuser can read the file.
range=sectors
Used with the image option, when the image is specified as a device (e.g.,
image=/dev/fd0), to indicate the range of sectors to be mapped into the map
file. sectors can be given as the range start-end or as start+number, where start
and end are zero-based sector numbers and number is the increment beyond
start to include. If only start is specified, only that one sector is mapped. For
example:
image=/dev/fd0
range=1+512 # take 512 sectors, starting with sector 1
restricted
Specify that a password is required for booting the image only if boot para-
meters are specified on the command line.
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table=device
Specify, for a non-Linux operating system, the device that contains the partition
table. If table is omitted, the boot loader does not pass partition information
to the operating system being booted. Note that /sbin/lilo must be rerun if the
partition table is modified. This option cannot be used with unsafe.
unsafe
Can be used in the per-image section for a non-Linux operating system to
indicate that the boot sector should not be accessed when the map is created.
If unsafe is specified, then some checking isn’t done, but the option can be
useful for running the lilo command without having to insert a floppy disk
when the boot sector is on a fixed-format floppy disk device. This option
cannot be used with table.
Kernel options
The following kernel options can be specified in /etc/lilo.conf as well as on the
boot command line:
append=string
Append the options specified in string to the parameter line passed to the
kernel. This typically is used to specify certain hardware parameters. For
example, while BIOSes on modern systems can recognize more than 64 MB
of memory, BIOSes on older systems were limited to 64 MB. If you are
running Linux on such a system, you can use append:
append="mem=128M"
initrd=filename
Specify the file to load into /dev/initrd when booting with a RAM disk. See
also the options load_ramdisk (in “Boot-Time Kernel Options” on page 539)
and prompt_ramdisk, ramdisk_size, and ramdisk_start in this section.
literal=string
Like append, but replace all other kernel boot options.
noinitrd
Preserve the contents of /dev/initrd so they can be read after the kernel is
booted.
prompt_ramdisk=n
Specify whether the kernel should prompt you to insert the floppy disk that
contains the RAM disk image, for use during Linux installation. Values of
n are:
0 Don’t prompt. Usually used for an installation in which the kernel and
the RAM disk image both fit on one floppy.
1 Prompt. This is the default.
ramdisk_size=n
Specify the amount of memory, in kilobytes, to be allocated for the RAM
disk. The default is 4096, which allocates 4 MB.
ramdisk_start=offset
Used for a Linux installation in which both the kernel and the RAM disk
image are on the same floppy. offset indicates the offset on the floppy where
the RAM disk image begins; it is specified in kilobytes.
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read-only
Specify that the root filesystem should be mounted read-only for filesystem
checking (fsck), after which it is typically remounted read/write.
read-write
Specify that the root filesystem should be mounted read/write.
root=root-device
Specify the device that should be mounted as root. If the special name
current is used as the value, the root device is set to the device on which the
root filesystem currently is mounted. Defaults to the root-device setting
contained in the kernel image.
vga=mode
Specify the VGA text mode that should be selected when booting. The mode
defaults to the VGA mode setting in the kernel image. The values are case-
insensitive. They are:
ask
Prompt the user for the text mode. Pressing Enter in response to the
prompt displays a list of the available modes.
extended (or ext)
Select 80×50 text mode.
normal
Select normal 80×25 text mode.
number
Use the text mode that corresponds to number. A list of available modes
for your video card can be obtained by booting with vga=ask and
pressing Enter.
The lilo Command
You need to run the lilo command to install the LILO boot loader and to update
it whenever the kernel changes or to reflect changes to /etc/lilo.conf. Note that if
you replace your kernel image without rerunning lilo, your system may be unable
to boot.
The path to the lilo command is usually /sbin/lilo. The syntax of the command is:
lilo [options]
Some of the options correspond to /etc/lilo.conf keywords:
Configuration keyword Command option
boot=bootdev -bbootdev
compact -c
delay=tsecs -dtsecs
default=label -Dlabel
disktab=file -ffile
install=bootsector -ibootsector
lba32 -L
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These options should be put in the configuration file whenever possible; putting
them on the lilo command line instead of in /etc/lilo.conf is deprecated. The next
section describes those options that can be given only on the lilo command line;
the others were described earlier.
lilo Command Options
The following list describes lilo command options that are available only on the
command line. Multiple options are given separately; for example:
$lilo -q -v
-C config-file
Specify an alternative to the default configuration file (/etc/lilo.conf). lilo uses
the configuration file to determine which files to map when it installs LILO.
-I label
Print the path to the kernel specified by label to standard output, or an error
message if no matching label is found. For example:
$lilo -I linux
/boot/vmlinuz-2.0.34-0.6
-q List the currently mapped files. lilo maintains a file (/boot/map by default)
containing the name and location of the kernel(s) to boot. Running lilo with
this option prints the names of the files in the map file to standard output, as
in this example (the asterisk indicates that linux is the default):
$lilo -q
linux *
test
-r root-directory
Specify that before doing anything else, lilo should chroot to the indicated
directory. Used for repairing a setup from a boot CD or floppy; you can boot
from that disk but have lilo use the boot files from the hard drive. For
example, if you issue the following commands, lilo will get the files it needs
from the hard drive:
$mount /dev/hda2 /mnt
$lilo -r /mnt
-R command-line
Set the default command for the boot loader the next time it executes. The
command executes once and then is removed by the boot loader. This option
typically is used in reboot scripts, just before calling shutdown -r.
linear -l
map=mapfile -mmapfile
fix-table -P fix
ignore-table -P ignore
backup=file -sfile
force-backup=file -Sfile
verbose=level -v
Configuration keyword Command option
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-t Indicate that this is a test—do not really write a new boot sector or map file.
Can be used with -v to find out what lilo would do during a normal run.
-u device-name
Uninstall lilo by restoring the saved boot sector from /boot/boot.nnnn, after
validating it against a timestamp. device-name is the name of the device on
which LILO is installed, such as /dev/hda2.
-U device-name
Like -u, but do not check the timestamp.
-V Print the lilo version number.
LILO Boot Errors
As LILO loads itself, it displays the letters of the word LILO, one at a time as it
proceeds. Once LILO is correctly loaded, you’ll see the full word printed on the
screen. If nothing prints, then LILO has not been loaded at all; most likely LILO
isn’t installed or it is installed, but on a partition that is not active. If LILO started
loading, but there was a problem, you can see how far it got by how many letters
printed:
L The first stage boot loader is loaded and running, but it can’t load the second
stage. There should be an error code indicating the type of problem; usually
the problem is a media failure or bad disk parameters. See the LILO User’s
Guide for the meaning of the error codes.
LI The first stage boot loader loaded the second stage but was not able to run it.
The problem is most likely bad disk parameters or the file /boot/boot.b (the
boot sector) was moved but the lilo command wasn’t run.
LIL
The second stage boot loader was run, but it couldn’t load the descriptor
table from the map file. This is usually caused by a media failure or bad disk
parameters.
LIL?
The second stage boot loader was loaded at an incorrect address, probably
because of bad disk parameters or by moving /boot/boot.b without running
lilo.
LIL-
The descriptor table is corrupt. The problem is probably bad disk parameters
or moving /boot/map without running lilo.
LILO
LILO was successfully loaded.
GRUB: The Grand Unified Bootloader
Like LILO, the GRUB boot loader can load other operating systems in addition to
Linux. GRUB has become the default bootloader for most Linux variants. It was
written by Erich Boleyn to boot operating systems on PC-based hardware and is
now developed and maintained by the GNU project. GRUB was intended to boot
operating systems that conform to the Multiboot Specification, which was
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Boot Methods
designed to create one booting method that would work on any conforming PC-
based operating system. In addition to multiboot-conforming systems, GRUB can
boot directly into Linux, FreeBSD, OpenBSD, and NetBSD. It can also boot other
operating systems such as Microsoft Windows indirectly, through the use of a
chainloader. The chainloader loads an intermediate file, and that file loads the
operating system’s boot loader.
GRUB provides a graphical menu interface. It also provides a command interface
that is accessible both while the system is booting (the native command environ-
ment) and from the command line once Linux is running.
While LILO works perfectly well, especially if you usually boot the default image,
GRUB has some advantages. The graphical menu interface shows you exactly
what your choices are for booting, so you don’t have to remember them. It also
lets you easily edit an entry on the fly, or drop down into the command interface.
In addition, if you are using the menu interface and something goes wrong, GRUB
automatically puts you into the command interface so you can attempt to recover
and boot manually. Another advantage of GRUB is that if you install a new kernel
or update the configuration file, that’s all you have to do; with LILO, you also
have to remember to rerun the lilo command to reinstall the boot loader. On the
other hand, if you are used to LILO, don’t need to see the prompts often, and
have a stable system, LILO is quick and convenient.
A GRUB installation consists of at least two and sometimes three executables,
known as stages. The stages are:
Stage 1
Stage 1 is the piece of GRUB that resides in the MBR or the boot sector of
another partition or drive. Since the main portion of GRUB is too large to fit
into the 512 bytes of a boot sector, Stage 1 is used to transfer control to the
next stage, either Stage 1.5 or Stage 2.
Stage 1.5
Stage 1.5 is loaded by Stage 1 only if the hardware requires it. Stage 1.5 is
filesystem-specific; that is, there is a different version for each filesystem
that GRUB can load. The name of the filesystem is part of the filename
(e2fs_stage1_5, fat_stage1_5, etc.). Stage 1.5 loads Stage 2.
Stage 2
Stage 2 runs the main body of the GRUB code. It displays the menu, lets you
select the operating system to be run, and starts the system you’ve chosen.
If it was compiled with netboot support, GRUB can also be used to boot over a
network. We don’t describe that process here; see the file netboot/README.
netboot in the GRUB source directory for detailed information.
One of the first things to understand about GRUB is that it uses its own naming
conventions. Drives are numbered starting from 0; thus, the first hard drive is
hd0, the second hard drive is hd1, the first floppy drive is fd0, and so on. Parti-
tions are also numbered from 0, and the entire name is put in parentheses. For
example, the first partition of the first drive, /dev/hda1, is known as (hd0,0) to
GRUB, and the third partition of the second drive is (hd1,2). GRUB makes no
distinction between drive types; thus the first drive is hd0 regardless of whether it
is IDE, SCSI, or SATA.
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Files are specified either by the filename or by blocklist, which is used to specify
files such as chainloaders that aren’t part of a filesystem. A filename looks like a
standard Unix path specification with the GRUB device name prepended; for
example:
(hd0,0)/grub/grub.conf
If the device name is omitted, the GRUB root device is assumed. The GRUB root
device is the disk or partition where the kernel image is stored, set with the root
command. See “GRUB Commands” on page 525 for the command descriptions.
When you use blocklist notation, you tell GRUB which blocks on the disk contain
the file you want. Each section of a file is specified as the offset on the partition
where the block begins plus the number of blocks in the section. The offset starts
at 0 for the first block on the partition. The syntax for blocklist notation is:
[device][offset]+length[,offset]+length...
In this case, too, the device name is optional for a file on the root device. With
blocklist notation, you can also omit the offset if it is 0. A typical use of blocklist
notation is when using a chainloader to boot Windows. If GRUB is installed in
the MBR, you can chainload Windows by setting the root device to the partition
that has the Windows boot loader, making it the active partition, and then using
the chainloader command to read the Windows boot sector:
rootnoverify (hd0,0)
makeactive
chainloader +1
In this example, the blocklist notation (+1) does not include either the device
name or the offset because we set the root device to the Windows partition, and
the Windows loader begins at offset 0 of that partition.
GRUB also includes a device map. The device map is an ASCII file, usually /boot/
grub/device.map. Since the operating system isn’t loaded yet when you use GRUB
to boot Linux (or any other operating system), GRUB knows only the BIOS drive
names. The purpose of the device map is to map the BIOS drives to Linux devices.
For example:
(fd0) /dev/fd0
(hd0) /dev/hda
Installing GRUB
Installing GRUB involves two stages. First, you install the GRUB files on your
system, either by compiling and installing the source tarball or from a package.
That puts the GRUB files in the correct locations on your system. The second step
is to install the GRUB software as your boot manager. This is the step we describe
in this section.
If you installed GRUB as part of your Linux installation, the distribution’s instal-
lation program took care of both stages of installing GRUB, and you’ll see the
GRUB menu when you boot Linux. If you didn’t install GRUB as part of your
Linux installation, you have two choices. The easiest way to install GRUB is with
the grub-install shell script that comes with GRUB. If grub-install doesn’t work,
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or if you want to do the installation manually, you can run the grub command
and issue the installation commands yourself.
Thefollowing sections describe how to create a GRUB boot CD, a GRUB boot
floppy, and how to install GRUB. You can create a GRUB boot disk for everyday
use or to have for an emergency.
Creating a GRUB boot CD
The following instructions make a CD that boots to GRUB:
1. Make a directory that will hold the GRUB iso image to be written to CD:
$mkdir -p grubiso/boot/grub # make parent dirs if needed
2. Copy the file stage2_eltorito * to the new directory from the directory where
GRUB was installed (in this example /usr/lib/grub/x86_64-pc):
$cp /usr/lib/grub/x86_64-pc grubiso/boot/grub
You can move other files to the directory as well, such as menu.lst to display
the menu when you boot.
3.Run genisoimage to make an ISO9660 image file, grub.iso:
$genisoimage -R -b boot/grub/stage2_eltorito -no-emul-boot \
-boot-load-size 4 -boot-info-table -o grub.iso grubiso
This command takes the contents of grubiso/boot/grub (only the top of the
directory tree needs to be specified) and makes the image file grub.iso. See the
genisoimage command in Chapter 3 for information on the options.
4.The image file can now be burned onto a CD (or DVD) with the burning soft-
ware of your choice.
Creating a GRUB boot floppy
The following instructions make a floppy that boots to the GRUB command line:
1. From the directory where GRUB was installed (e.g., /usr/share/grub/i386-pc),
use the dd command to write the file stage1 to the floppy:
$dd if=stage1 of=/dev/fd0 bs=512 count=1
This command writes one block, with a block size of 512, from the input file
stage1 to the floppy device /dev/fd0.
2. Now write the file stage2 to the floppy, skipping over the first block (seek=1)
so you don’t overwrite stage1:
$dd if=stage2 of=/dev/fd0 bs=512 seek=1
Put together, the process looks like this:
$dd if=stage1 of=/dev/fd0 bs=512 count=1
1+0 records in
1+0 records out
$dd if=stage2 of=/dev/fd0 bs=512 seek=1
254+1 records in
254+1 records out
*El Torito is a specification that lets you create a bootable CD.
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The boot floppy is now ready to boot to the GRUB command line.
You can also make a boot floppy that boots to the GRUB menu:
1. Create a GRUB configuration file (/boot/grub/menu.lst) if you don’t already
have one. The configuration file is described later in “The GRUB Configuration
File” on page 521.
2. Create a filesystem on your floppy disk. For example:
$mke2fs /dev/fd0
3. Mount the floppy drive and create the directory /boot/grub:
$mount /mnt
$mkdir /mnt/boot
$mkdir /mnt/boot/grub
4. Copy the stage1, stage2, and grub.conf GRUB images from /boot/grub on your
Linux partition to /mnt/boot/grub.
5. Run the grub command. This example assumes the command is in /sbin/
grub, but it might be in /usr/sbin/grub on your system:
$/sbin/grub --batch <<EOT
root (fd0)
setup (fd0)
quit
EOT
You should now be able to boot to the GRUB menu from the floppy disk you just
created.
Using grub-install
GRUB comes with a shell script, grub-install, which uses the GRUB shell to auto-
mate the installation. The command syntax is:
grub-installoptions install-device
where install-device is the name of the device on which you want to install GRUB,
specified as either the GRUB device name (e.g., (hd0)) or the system device (e.g.,
/dev/hda). For example, you might issue the following command (as root):
$grub-install /dev/hda
This command installs GRUB into the MBR of the first hard drive. The grub-
install options are:
--force-lba
Force GRUB to use LBA mode, to allow booting from partitions beyond
cylinder 1024.
--grub-shell=file
Specify that file is to be used as the GRUB shell. You might want to use this
option to append options to grub. For example:
$grub-install --grub-shell="grub --read-only" /dev/fd0
-h, --help
Print a help message on standard output and exit.
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--recheck
Force probing of a device map. You should run grub-install with this
option if you add or remove a disk from your system. The device map is
found at /boot/grub/device.map.
--root-directory=dir
Install GRUB images in the directory dir instead of the GRUB root directory.
-v, --version
Print the GRUB version number to standard output and exit.
Installing from the GRUB command line
To install GRUB from the native command environment, make a GRUB boot disk
as described previously. You will use that disk to boot to the GRUB command
line to do the installation. If you know which partition holds the GRUB files,
you’re all set. Otherwise, you can find the partition with the find command:
grub>find /boot/grub/stage1
(hd0,0)
Here, the files are on (hd0,0). Use that information to set the GRUB root device:
grub>root (hd0,0)
Run the setup command to install GRUB. To install GRUB on the MBR, run
setup as follows:
grub>setup (hd0)
If you are going to chainload Linux and want to install GRUB on the boot sector
of the Linux partition, run setup like this:
grub>setup (hd0,0)
The GRUB Configuration File
GRUB uses a configuration file that sets up the menu interface. The configuration
file is called menu.lst and is found with the other GRUB files in the /boot/grub
directory. In some distributions (e.g., Fedora and Red Hat) the configuration file
is called grub.conf, which is a symbolic link to menu.lst.
The configuration file begins with a section containing global commands that
apply to all boot entries, followed by an entry for each Linux image or other oper-
ating system that you want to be able to boot. Here is an example of a global
section (a hash sign, #, begins a comment):
default=0 # default to the first entry
timeout=20 # set the timeout to 20 seconds
splashimage=(hd0,0)/grub/splash.xpm.gz # the splash image displayed with
# the menu
Certain GRUB commands are available only in the global section of the configura-
tion file, for use with the GRUB menu. These commands are described in the
following list. All other commands can be used either in the configuration file or
on the command line and are described later in “GRUB Commands” on page 525.
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default num
Set the default menu entry to num. The default entry is started if the user
does not make a selection before the timeout time. Menu entries are
numbered from 0. If no default is specified, the first entry (0) is used as the
default.
fallback num
Specify the entry to be used if for any reason the default entry has errors. If
this command is specified and the default doesn’t work, GRUB boots the fall-
back entry automatically instead of waiting for user input.
hiddenmenu
Specify that the menu is not to be displayed. The user can press Esc before
the end of the timeout period to have the menu displayed; otherwise, the
default entry is booted at the end of the timeout.
timeout time
Specify the timeout period, in seconds. The timeout is the amount of time
GRUB waits for user input before booting the default entry.
title name
Start a new boot entry with specified name.
Following the global section, the configuration file includes an entry for each boot
image. An entry begins with a title command that specifies the text that will
appear on the menu for that entry when the system boots. A typical boot entry
might look like this:
title Linux 2.6.28
root (hd0,1)
kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28
This entry provides the information GRUB needs to boot to Linux. When the
menu is displayed, it will include an entry that says:
Linux 2.6.28
The GRUB root is on the second partition of the first hard drive (hd0,1). The
kernel command specifies which Linux kernel to run and passes some parameters
to the kernel, and the initrd command sets up an initial RAM disk.
The configuration file also provides some security features, such as the ability to
set passwords and to lock certain entries so only the root user can boot them. The
configuration file can be set up so that a password is required to run interactively
(i.e., for editing menu entries or using the command interface) or simply to
protect certain menu entries while leaving other entries available to all users. See
the explanation of the password and lock commands in “GRUB Commands” on
page 525.
In addition to providing a password feature, GRUB provides the command
md5crypt to encrypt passwords in MD5 format, and a corresponding Linux
command, grub-md5-crypt. grub-md5-crypt is a shell script that acts as a
frontend to the grub shell, calling md5crypt. Passwords encrypted either directly
with md5crypt or with grub-md5-crypt can be used with the password command
to set up a GRUB password. grub-md5-crypt has three possible options:
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--help
Print help message and exit.
--grub-shell=file
Specify that file is to be used as the GRUB shell.
--version
Print version information and exit.
Using the Menu Interface
The most common way to use GRUB is with the menu interface. The Stage 2
loader reads the configuration file menu.lst and displays the menu. If a timeout is
set in the configuration file, GRUB displays a countdown at the bottom of the
window showing how much time is left before it boots to the default entry. Move
the cursor to an entry and press Enter to boot; or, press e to edit the command
line for that entry, a to modify the kernel arguments, or c to go to the command-line
interface to issue commands manually.
If you go to the command line, you can return to the menu at any time by pressing Esc.
Selecting a and e are similar, except that a displays only the kernel command line
and lets you append options to it, while e displays the entire boot entry for you to
edit. In either case, the available editing commands are similar to those available
on the shell command line. When you are through editing, press Esc to return to
the main menu. Your changes take effect for this session only; the configuration
file is not permanently changed.
One common use for editing a kernel command is to boot to single-user mode.
To do that, select a from the menu and append the word “single” to the end of the
kernel command. Then press Esc to return to the menu and select the entry.
The GRUB Shell
In addition to using the command line from within the GRUB menu interface (or
booting directly to the command line), you can run a GRUB shell directly from
the Linux command line with the grub command. For the most part, using the
grub shell is the same as running in the native command-line environment. The
major difference is that the shell uses operating system calls to emulate the BIOS calls
that the native environment uses. That can lead to some differences in behavior.
The syntax of the grub command is:
grub [options]
For example:
$grub --no-floppy
The grub command-line options are:
--batch
Turn on batch mode for noninteractive use. Equivalent to grub --no-config-
file --no-curses --no-pager.
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524 | Chapter4: Boot Methods
--boot-drive=drive
Use drive as the Stage 2 boot drive, specified as a decimal, hexadecimal, or
octal integer. The default is hexadecimal 0x0.
--config-file=file
Use file as the GRUB configuration file. The default is /boot/grub/menu.lst.
--device-map=file
Use file for the device map. The value of file is usually /boot/grub/device.map.
--help
Display a help message to standard output and exit.
--hold
Wait for a debugger to attach before starting grub.
--install-partition=partition
Use partition as the Stage 2 installation partition, specified as a decimal, hexa-
decimal, or octal number. The default is hexadecimal 0x20000.
--no-config-file
Run without reading the configuration file.
--no-curses
Don’t use the curses interface for managing the cursor on the screen.
--no-floppy
Don’t probe for a floppy drive. This option is ignored if --device-map is also
specified.
--no-pager
Don’t use the internal pager.
--preset-menu
Use a preset menu, for example if your system has no console and you need
to get a serial terminal set up to see messages. To use this option, compile
GRUB with the --enable-preset-menu=file option and create a menu file. See
the GRUB documentation for more information.
--probe-second-floppy
Probe the second floppy drive (which is not probed by default). This option is
ignored if --device-map is also specified.
--read-only
Do not write to any disk drives.
--verbose
Print verbose messages.
--version
Print version information and exit.
When you run grub, you will see something like this:
GRUB version 0.94 (640K lower / 3072K upper memory)
[ Minimal BASH-like line editing is supported. For the first word, TAB
lists possible command completions. Anywhere else TAB lists the possible
completions of a device/filename. ]
grub>
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Boot Methods
You can now enter commands at the grub> prompt. Press Tab to get a brief help
message, listing all the commands:
grub>
Possible commands are: blocklist boot cat chainloader cmp color configfile
debug device displayapm displaymem dump embed find fstest geometry halt help
hide impsprobe initrd install ioprobe kernel lock makeactive map md5crypt
module modulenounzip pager partnew parttype password pause quit read reboot
root rootnoverify savedefault serial setkey setup terminal testload testvbe
unhide uppermem vbeprobe
Using Tab is a quick way to remind yourself of the commands, but it can be
confusing to see them all run together and wrapping across lines. You can also
run the help command, which lists the most frequently used commands and their
syntax:
grub> help
blocklist FILE boot
cat FILE chainloader [--force] FILE
color NORMAL [HIGHLIGHT] configfile FILE
device DRIVE DEVICE displayapm
displaymem find FILENAME
geometry DRIVE [CYLINDER HEAD SECTOR [ halt [--no-apm]
help [--all] [PATTERN ...] hide PARTITION
initrd FILE [ARG ...] kernel [--no-mem-option] [--type=TYPE]
makeactive map TO_DRIVE FROM_DRIVE
md5crypt module FILE [ARG ...]
modulenounzip FILE [ARG ...] pager [FLAG]
partnew PART TYPE START LEN parttype PART TYPE
quit reboot
root [DEVICE [HDBIAS]] rootnoverify [DEVICE [HDBIAS]]
serial [--unit=UNIT] [--port=PORT] [-- setkey [TO_KEY FROM_KEY]
setup [--prefix=DIR] [--stage2=STAGE2_ terminal [--dumb] [--timeout=SECS] [--
testvbe MODE unhide PARTITION
uppermem KBYTES vbeprobe [MODE]
You can add the --all option to see all the commands.
To get help for a specific command, add the command name (e.g., help read).
help treats the text you enter as a pattern; therefore, if you enter help find, you’ll
get help for the find command, but if you enter help module, you’ll get help for
both module and modulenounzip.
GRUB Commands
The following sections describe two sets of commands. Both can be used at the
GRUB command line. In addition, the first set can be used in the global section of
the menu, and the second can be used in individual menu entries. A few
commands can be used only on the GRUB shell command line; this is noted in the
command entry. The commands default, fallback, hiddenmenu, timeout, and
title are available only in the configuration file, for use with the menu interface.
They are described in “The GRUB Configuration File” on page 521.
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526 | Chapter4: Boot Methods
When running commands, if you find that you aren’t sure how to complete a
pathname, you can use the Tab key to find the possible completions. For
example:
grub> blocklist (hd0,1)/grub/[Tab]
Possible files are: grub.conf splash.xpm.gz menu.lst device.map stage1
stage2 e2fs_stage1_5 fat_stage1_5 ffs_stage1_5 jfs_stage1_5 minix_stage1_5
reiserfs_stage1_5 vstafs_stage1_5 xfs_stage1_5
grub> blocklist (hd0,1)/grub/stage2
(hd0,1)33306+24,33332+231
Command-Line and Global Menu Commands
The commands available at the command line and in the global section of the
configuration file are as follows.
bootp bootp [--with-configfile]
Initialize a network device via the Bootstrap Protocol (BOOTP).
This command is available only if GRUB was compiled with
netboot support. If --with-configfile is specified, GRUB automati-
cally loads a configuration file specified by your BOOTP server.
color colornormal [highlight]
Specify colors for the menu. normal represents the color used for
normal menu text, while highlight represents the color used to
highlight the line the cursor is on. Both normal and highlight are
specified as two symbolic color names, for foreground and back-
ground color, separated by a slash. For example:
color light-gray/blue cyan/black
You can prefix the foreground color with blink- (e.g., blink-cyan/
red) to get a blinking foreground. The colors black, blue, green,
cyan, red, magenta, brown, and light-gray can be specified for
foreground or background. Additional colors that can be used only
for the foreground are dark-gray, light-blue, light-green, light-
cyan, light-red, light-magenta, yellow, and white.
device devicedrive file
Specify a file to be used as a BIOS drive. This command is useful
for creating a disk image and/or for fixing the drives when GRUB
fails to determine them correctly. The device command is available
only from within the grub shell, not from the native command line.
For example:
grub>device (fd0) /floppy-image
grub>device (hd0) /dev/sd0
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Boot Methods
dhcp dhcp [--with-configfile]
Initialize a network device via the DHCP protocol. Currently, this
command is just an alias for bootp and is available only if GRUB
was compiled with netboot support. If specified with --with-config-
file, GRUB will fetch and load a configuration file specified by your
DHCP server.
hide hidepartition
Hide the specified partition. This is useful when you are booting
Windows and there are multiple primary partitions on one disk.
Hide all but the one you want to boot. Also see unhide.
ifconfig ifconfig [--server=server] [--gateway=gateway] [--mask=mask]
[--address=address]
Configure a network device manually. If no options are specified,
displays the current network configuration. With the server
address, gateway, netmask, and IP address specified, ifconfig
configures the device. The addresses must be in dotted decimal
format (e.g., 192.168.0.4), and the options can be specified in any
order.
pager pager [flag]
Enable or disable the internal pager by setting flag to on (enable) or
off (disable).
partnew partnewpart type from to
Make a new primary partition, part, specified in GRUB syntax. type
is the partition type, specified as a number in the range 0-0xff. from
and to are the starting and ending sectors, specified as absolute
numbers. Some of the common partition types are:
Type Number
None 0
FAT 16, lt 32M 4
FAT 16, gt 32M 6
FAT 32 0xb
FAT 32, with LBA 0xc
WIN 95, extended 0xf
EXT2FS 0x83
Linux extended 0x85
Linux RAID 0xfd
FreeBSD 0xa5
OpenBSD 0xa6
NetBSD 0xfd
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parttype parttypepart type
Change the type of partition part to type. The type must be a
number in the range 0-0xff. See partnew for a list of partition
types.
password password [--md5]passwd [file]
Set a password for the menu interface. If used in the global section
of the configuration file, outside the menu entries, GRUB prompts
for a password before processing an a, e, or c entered by the user.
Once the password passwd has been entered, if no file was speci-
fied, GRUB allows the user to proceed. Otherwise, GRUB loads the
file as a new configuration file and restarts Stage 2. If password
appears in an individual menu entry, GRUB prompts for the pass-
word before continuing. Specify --md5 to tell GRUB that the
password was encrypted with the md5crypt command.
rarp rarp
Initialize a network device via the Reverse Address Resolution
Protocol (RARP). This command is available only if GRUB was
compiled with netboot support. The use of RARP is deprecated.
serial serial [options]
Initialize a serial device. The serial port is not used for communica-
tion unless terminal is also specified. This command is available
only if GRUB was compiled with serial support.
Options
--device=device
Specify the tty device to be used in the host operating system.
This option can be used only in the grub shell.
--parity=parity
Specify the parity. The possible values are no, odd, and even;
the default is no.
--port=port
Specify the I/O port. The value of port overrides any value
specified for --unit.
--speed=speed
Specify the transmission speed (default is 9600).
--stop=num
Specify the number of stop bits. The value of num is either 1 or
2 (default is 1).
--unit=num
Specify the serial port to use. The value of num is a number in
the range 0–3; the default is 0, corresponding to COM1.
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Boot Methods
--word=num
Specify the number of data bits. The value ofnum is a number
in the range 5–8 (default is 8).
setkey setkey [to-key from-key]
Configure the keyboard map for GRUB by mapping the key from-
key to the key to-key. With no mappings specified, reset the
keyboard map. setkey is useful for setting up international
keyboards. Possible key values are letters; digits; one of the strings
alt, backspace, capslock, control, delete, enter, escape, Fn (where
n is one of the function key numbers), shift, tab; or one of the
strings in the “Key value” columns of the following table.
splashimage splashimagefile
Use the image in file as the background (splash) image. The file
should be a gzipped .xpm (X pixmap) file, created with a 14-color
palette at 640 × 480 resolution and specified with standard GRUB
device syntax:
splashimage=(hd0,0)/grub/splash.xpm.gz
Programs that you can use to create .xpm files include the GIMP,
xv, and xpaint.
terminal terminal [options] [console] [serial]
Specify a terminal for user interaction. This command is available
only if GRUB was compiled with serial support. If both console
Key value Character Key value Character
ampersand & asterisk *
at @ backquote `
backslash \ bar |
braceleft { braceright }
bracketleft [ bracketright ]
caret ^ colon :
comma , dollar $
doublequote “ equal =
exclam ! greater >
less < minus -
numbersign # parenleft (
parenright ) percent %
period . plus +
question ? quote `
semicolon ; slash /
space tilde ~
underscore _
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530 | Chapter4: Boot Methods
and serial are specified, GRUB uses the first terminal where a key is
pressed, or the first after the timeout has expired. If neither is speci-
fied, GRUB displays the current setting.
Options
--dumb
The terminal is a dumb terminal; if this option is not speci-
fied, the terminal is assumed to be VT100-compatible.
--lines=num
The terminal has num lines. The default is 24.
--silent
Suppress the prompt to hit any key (useful if your system does
not have a terminal).
--timeout=secs
Specify the timeout in seconds.
tftpserver tftpserveripaddress
Specify a TFTP server, overriding the address returned by a
BOOTP, DHCP, or RARP server. The IP address must be specified
in dotted decimal format. This command is available only if GRUB
was compiled with netboot support. This command is deprecated;
use ifconfig instead.
unhide unhidepartition
Unhide the specified partition. This is useful when booting DOS or
Windows when there are multiple primary partitions on one disk.
You can unhide the partition you want to boot and hide the others.
Command-Line and Menu-Entry Commands
The commands available at the command line and in the individual menu entries
of the configuration file are as follows.
blocklist blocklistfile
Print the specified file in blocklist notation, where file is an abso-
lute pathname or a blocklist. For example:
grub>blocklist (hd0,1)/grub/grub.conf
(hd0,1)33746+2
boot boot
Boot the operating system or chainloader that has been loaded.
You need to run this command only if you are in the interactive
command-line mode.
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Boot Methods
cat catfile
Display the contents of the specified file.
chainloader chainloader [--force]file
Load file as a chainloader. You can use blocklist notation to specify
the first sector of the current partition with +1. If --force is speci-
fied, the file is loaded forcibly.
cmp cmpfile1 file2
Compare the two files file1 and file2. Report differences by printing
nothing if the files are identical, the sizes if they are different, or the
bytes at an offset if they differ at that offset.
configfile configfilefile
Load file as the configuration file.
debug debug
Toggle debug mode, which prints extra messages to show disk
activity. The default debug mode is off.
displayapm displayapm
Display Advanced Power Management (APM) BIOS information.
displaymem displaymem
Display the system address space map of the machine, including all
regions of physical RAM installed. For example:
grub>displaymem
displaymem
EISA Memory BIOS Interface is present
Address Map BIOS Interface is present
Lower memory: 640K, Upper memory (to first chipset hole):
3072K
[Address Range Descriptor entries immediately follow
(values are 64-bit)]
Usable RAM: Base Address: 0x0 X 4GB + 0x0,
Length: 0x0 X 4GB + 0xa0000 bytes
Reserved: Base Address: 0x0 X 4GB + 0xa0000,
Length: 0x0 X 4GB + 0x60000 bytes
Usable RAM: Base Address: 0x0 X 4GB + 0x100000,
Length: 0x0 X 4GB + 0x300000 bytes
dump dumpfrom to
Dump the contents of one file into another. The file you’re
dumping from is a GRUB file, and the file you’re dumping to is an
operating system file.
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embed embedstage1.5 device
Embed the specified Stage 1.5 file in the sectors following the MBR
if device is a drive, or in the boot loader area if it is an FFS (Berkeley
Fast File System) partition (or, in the future, a ReiserFS partition).
If successful, print the number of sectors the Stage 1.5 file occupies.
You don’t usually need to run this command directly.
find findfile
Search all partitions for the specified file and print the list of
devices where it was found. The filename specified should be an
absolute filename, such as /boot/grub/stage1, or a blocklist.
fstest fstest
Toggle the filesystem test mode, which prints data for device reads
and the values being sent to the low-level routines. The install and
testload commands turn off filesystem test mode. The test output
is in the following format:
<partition-offset-sector, byte-offset, byte-length>
for high-level reads in a partition, and:
[disk-offset-sector]
for low-level sector requests from the disk.
geometry geometrydrive [cylinder head sector [total_sector]]
Print geometry information for drive. From the GRUB shell, you
can specify the number of cylinders, heads, sectors, and total
sectors to set the drive’s geometry. If total_sector is omitted, it is
calculated from the other values.
halt halt [--no-apm]
Shut down the computer. The computer is halted with an APM
BIOS call unless the option --no-apm is specified.
help help [--all] [patterns]
Provide help for built-in commands. With no options, show the
command and any options or parameters for the most common
commands. With --all, show the same information for all possible
commands. If you specify a pattern (i.e., a partial command name)
or a full command name, a more complete description of the
command or commands matching the pattern is displayed.
impsprobe impsprobe
Probe the Intel Multiprocessor Specification 1.1 or 1.4 configura-
tion table and boot the CPUs that are found into a tight loop. This
command can be used only in Stage 2.
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Boot Methods
initrd initrdfile [args]
Load an initial ramdisk file and pass any arguments.
install install [options]stage1_file [d]dest_devstage2_file [addr]
[p] [config_file] [real_config_file]
Perform a full GRUB install. See also the setup command, which
acts as a frontend to install and is easier to use. The Stage 2 or
Stage 1.5 file (both referred to as stage2_file here because they are
loaded the same way) must be in its final install location (e.g., in
the /boot/grub directory). install loads and validates stage1_file,
installs a blocklist in the Stage 1 file for loading stage2_file as Stage
2 or Stage 1.5, and writes the completed Stage 1 file to the first
block of the device dest_dev.
Options
--force-lba
If the BIOS has LBA support but might return the incorrect
LBA bitmap (which sometimes happens), --force-lba forces
install to ignore the incorrect bitmap.
--stage2=os_stage2_file
This option is required to specify the operating system name
of the Stage 2 file if the filesystem where it is located cannot be
unmounted.
Parameters
addr
Specify the address at which Stage 1 is to load Stage 2 or Stage
1.5. The possible values are 0x8000 for Stage 2 and 0x2000 for
Stage 1.5. If omitted, GRUB determines the address
automatically.
config_file
Specify the location of the configuration file for Stage 2.
d Tell Stage 1 to look for the actual disk on which stage2_file
was installed if it’s not on the boot drive.
dest_dev
Specify the destination device. The final Stage 1 file is written
to this device.
p If present, the partition where stage2_file is located is written
into the first block of Stage 2.
real_config_file
If stage2_file is really a Stage 1.5 file, real_config_file specifies
the real configuration filename and is written into the Stage 2
configuration file.
stage1_file
Specify the Stage 1 file to be written.
stage2_file
Specify the file that Stage 1 is to load for Stage 2.
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ioprobe ioprobedrive
Probe the I/O ports used for drive and write the results to standard
output.
kernel kernel [--non-mem-option]file [...]
Load the kernel image from file. Any text following file is passed on
as the kernel command line. After running this command, you
must reload any modules. The option --type specifies the kernel
type and is required only for loading a NetBSD ELF kernel; GRUB
automatically determines other types. The possible values of type
are linux, biglinux, freebsd, multiboot, netbsd, and openbsd. For
Linux, --no-mem-option tells GRUB not to pass the mem= option
to the kernel.
lock lock
Lock the entry until a valid password is entered. This is used in a
menu entry immediately after title to prevent nonroot users from
executing the entry. This command is most useful in conjunction
with the password command.
makeactive makeactive
Set the active partition on the root disk to GRUB’s root device. Use
only on primary PC hard disk partitions.
map mapto from
Map the from drive to the to drive. You need to do this when chain-
loading an operating system such as Windows, if it is not on the
first drive. For example, if Windows is on (hd1):
grub>map (hd0) (hd1)
grub>map (hd1) (hd0)
This swaps the mappings of the first and second hard drives,
tricking Windows into thinking it’s on the first drive so it can boot.
md5crypt md5crypt
Prompt for a password and encrypt it in MD5 format for use with
the password command.
module modulefile [...]
Load the boot module file for a multiboot format boot image.
Anything after the filename is passed as the module command line.
modulenounzip modulenounzipfiles
Like module, except that automatic decompression is disabled.
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Boot Methods
pause pausemessages
Print the specified message and wait for a key to be pressed before
continuing.
quit quit
Used only from within the grub shell to exit from the shell. In the
native command environment, use reboot instead to reboot the
computer.
read readaddr
Read a 32-bit value from memory at the specified address and
display it in hex.
reboot reboot
Reboot the system.
root rootdevice [hdbias]
Set the root device to the specified device and attempt to mount it
to get the partition size (and some additional information for
booting BSD kernels). If you are booting a BSD kernel, you can
specify hdbias to tell the kernel how many BIOS drive numbers are
before the current one.
rootnoverify rootnoverifydevice [hdbias]
Similar to root, but don’t attempt to mount the partition. Used
when you are booting a non-GRUB-readable partition such as
Windows.
savedefault savedefault
Save the current menu entry as the default. GRUB will default to
that entry the next time you boot the system.
setup setup [options]install_device [image_device]
Set up installation of GRUB and run the install command to actu-
ally install GRUB onto the device install_device. Find the GRUB
images on image_device if it is specified; otherwise use the current
root device as set by the root command. If install_device is a hard
disk, embed a Stage 1.5 file in the disk if possible.
Options
--force-lba
Force install to use LBA mode. Specify this option if your
BIOS supports LBA mode but you find that GRUB isn’t
working in LBA mode without it.
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--prefix=dir
Specify the directory where the GRUB images are located. If
not specified, GRUB searches for them in /boot/grub and /grub.
--stage2=os_stage2_file
Passed to install to tell GRUB the operating system name of
the Stage 2 file.
testload testloadfile
Read the contents of a file in different ways and compare the results
to test the filesystem code. If no errors are reported and the final
output reports an equal value for the reported variables i and
filepos, then the filesystem is consistent and you can try loading a
kernel.
testvbe testvbemode
For a VBE (VESA BIOS Extension) BIOS, test the specified VESA
BIOS extension mode. You should see an animation loop, which
you can cancel by pressing any key.
uppermem uppermemkbytes
Tell GRUB to assume that only the specified number of kilobytes of
upper memory are installed. You should need to use this command
only for old systems, where not all the memory may be recognized.
vbeprobe vbeprobe [mode]
For a VBE BIOS, probe VESA BIOS extension information. If mode
is specified, the output shows only information for that mode;
otherwise, all available VBE modes are listed.
Dual-Booting Linux and Windows 2000/XP/Vista
As mentioned earlier, when you run Windows, its boot loader expects to be the
one in charge; therefore, the standard way to dual-boot Windows and Linux is to
add Linux as an option on the Windows boot menu. This section describes how
to do that. The information provided here applies to Windows 2000 and
Windows XP, which use the Windows NT loader ntldr (so called because it was
developed for Windows NT). Windows Vista uses a different boot loader. If you
want to set up Vista to dual-boot Linux, you can use the free download EasyBCD
by Neosmart Technologies (neosmart.net).
Note again that you do not need the information in this section if your Linux
installation software set up the dual-booting for you, which it probably did.
To set up dual booting with the NT loader manually, you need to provide the
loader with a copy of the Linux boot sector. We’ll describe how to do that on a
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computer running Windows with an NTFS filesystem (note that Windows should
be installed on your system already). See the “Linux+NT-loader” mini-HOWTO
for more information and other alternatives.
You should have a Linux boot floppy or CD available so that if necessary you can
boot Linux before the Windows boot loader has been modified. You should also
have a DOS-formatted floppy to transfer the boot sector to the Windows parti-
tion. If you are running LILO and it is already installed, you may need to modify
/etc/lilo.conf as described later. Otherwise, install LILO or GRUB to the boot
sector of the Linux partition; once the Linux boot manager is installed and you
have a configuration file, you can set up the system for dual booting.
The following instructions assume your Linux partition is on /dev/hda2. If Linux
is on another partition in your system, be sure to replace /dev/hda2 in the
following examples with the correct partition. The instructions also assume that
you have a floppy drive to make a diskette for transferring the boot sector to your
NTFS filesystem. If you don’t have a floppy drive, you will have to use some other
means of doing the transfer. If you have a FAT partition, you can mount that on
Linux and transfer the file there. Other possibilities include putting it on a CD,
transferring it over a network to another system while you reboot to Windows, or
even emailing it to yourself and reading it from the Windows side.
1. If you are running LILO, specify the Linux root partition as your boot device
in /etc/lilo.conf. If you are editing /etc/lilo.conf manually, your entry will look
like this:
boot=/dev/hda2
and will be the same as the root= entry.
If you are running GRUB, make sure your configuration file, /boot/grub/menu.
lst, includes a menu entry for booting Linux. The exact values of the entries
in the menu depend on the filename of the kernel image that you wish to
boot. For example:
title Linux 2.6.28
root (hd0,1)
kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28
You can then skip to Step 3.
2.Run the lilo command to install LILO on the Linux root partition.
3. At this point, if you need to reboot Linux, you’ll have to use a boot floppy or
CD because the NT loader hasn’t been set up yet to boot Linux.
4. From Linux, run the dd command to make a copy of the Linux boot sector:
$dd if=/dev/hda2 of=/bootsect.lnx bs=512 count=1
This command copies one block, with a block size of 512 bytes, from the
input file /dev/hda2 to the output file /bootsect.lnx. Note that if you are
running GRUB, the boot sector is actually the stage1 file. (The output file-
name can be whatever makes sense to you; it doesn’t have to be bootsect.lnx.)
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538 | Chapter4: Boot Methods
5. Copy bootsect.lnx to a DOS-formatted floppy disk if that is how you are going
to transfer it to Windows:
$mount -t msdos /dev/fd0 /mnt
$cp /bootsect.lnx /mnt
$umount /mnt
6. Reboot the system to Windows and copy the boot sector from the floppy disk
to the hard disk. You can drag and drop the file to the hard drive, or use the
command line to copy the file, as in the following example:
C:>copy a:\bootsect.lnx c:\bootsect.lnx
It doesn’t matter where on the hard drive you put the file because you’ll tell
the NT loader where to find it in step 8.
7.Modify the attributes of the file boot.ini * to remove the system and read-only
attributes so you can edit it:
C:>attrib -s -r c:\boot.ini
8. Edit boot.ini with a text editor to add the line:
C:\bootsect.lnx="Linux"
This line adds Linux to the boot menu and tells the NT boot loader where to
find the Linux boot sector. You can insert the line anywhere in the [operating
systems] section of the file. Its position in the file determines where it will
show up on the boot menu when you reboot your computer. Adding it at the
end, for example, results in a boot.ini file that looks something like this (the
second multi(0) entry is wrapped to fit the margins of this page):
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows NT Server Version 4.00"
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows NT Server Version
4.00 [VGA mode]" /basevideo /sos
C:\bootsect.lnx="Linux"
If you want Linux to be the default operating system, modify thedefault= line:
default=C:\bootsect.lnx
9. Rerun attrib to restore the system and read-only attributes:
C:>attrib +s +r c:\boot.ini
Now you can shut down Windows and reboot. Windows will prompt you with a
menu that looks something like this:
OS Loader V4.00
Please select the operating system to start:
Windows NT Workstation Version 4.00
Windows NT Workstation Version 4.00 [VGA mode]
Linux
*boot.ini is the Windows counterpart to /etc/lilo.conf. It defines which operating systems the
Windows loader can boot.
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Boot-Time Kernel Options | 539
Boot Methods
Select Linux, and the NT loader will read the Linux boot sector and transfer
control to LILO or GRUB on the Linux partition.
If you are using LILO and you later modify /etc/lilo.conf or rebuild the kernel, you
need to rerun the lilo command, create a new bootsect.lnx file, and replace the
version of bootsect.lnx on the Windows partition with the new version. In other
words, you need to rerun steps 2–6.
If you have any problems or you simply want to remove LILO or
GRUB later, you can reverse the installation procedure: boot to
Windows, change the system and read-only attributes on boot.ini,
re-edit boot.ini to remove the Linux entry, save the file, restore the
system and read-only attributes, and remove the Linux boot sector
from the Windows partition.
Boot-Time Kernel Options
The earlier sections of this chapter described some of the options you can specify
when you boot Linux. There are many more options that can be specified. This
section touches on the ways to pass options to the kernel and then describes some
of the kinds of parameters you might want to use. The parameters in this section
affect the kernel and therefore apply regardless of which boot loader you use.
If LILO is your boot loader, you can add to or override the parameters specified in
/etc/lilo.conf during the boot process as follows:
• If prompt is set in /etc/lilo.conf, LILO always presents the boot prompt and
waits for input. At the prompt, you can choose the operating system to be
booted. If you choose Linux, you can also specify parameters.
• If prompt isn’t set, press Ctrl, Shift, or Alt when the word “LILO” appears.
The boot prompt will then appear. You also can press the Scroll Lock key
before LILO is printed and not have to wait poised over the keyboard for the
right moment.
• At the boot prompt, specify the system you want to boot, or press Tab to get
a list of the available choices. You then can enter the name of the image to
boot. For example:
LILO boot: <press Tab>
linux test winxp
boot:linux
You also can add boot command options:
boot:linux single
• If you don’t provide any input, LILO waits the amount of time specified in
the delay parameter and then boots the default operating system with the
default parameters, as set in /etc/lilo.conf.
If you are using GRUB, you can pass parameters to the kernel on the kernel
command line, either in the configuration file or from the command-line inter-
face. If you are booting from the GRUB menu, you can edit or add parameters by
entering e or a when the menu appears.
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540 | Chapter4: Boot Methods
Some of the boot parameters have been mentioned earlier. Many of the others are
hardware-specific and are too numerous to mention here. For a complete list of
parameters and a discussion of the booting process, see the “BootPrompt
HOWTO.” Some of the parameters not shown earlier that you might find useful
are listed next; many more are covered in the HOWTO. Most of the following
parameters are used to provide information or instructions to the kernel, rather
than to LILO or GRUB:
acpi=off
Disable ACPI (Advanced Configuration and Power Interface) if it was to be
enabled. This is useful for debugging possible hardware problems.
debug
Print all kernel messages to the console.
hd=cylinders,heads,sectors
Specify the hard drive geometry to the kernel. Useful if Linux has trouble
recognizing the geometry of your drive, especially if it’s an IDE drive with
more than 1024 cylinders.
load_ramdisk=n
Tell the kernel whether to load a RAM disk image for use during Linux instal-
lation. Values of n are:
0 Don’t try to load the image. This is the default.
1 Load the image from a floppy disk to the RAM disk.
mem=size
Specify the amount of system memory installed. Useful if your BIOS reports
memory only up to 64 MB and your system has more memory installed.
Specify as a number with M or k (case-insensitive) appended:
mem=128M
Because mem would have to be included on the command line for every boot,
it often is specified on a command line saved with lock or with append to be
added to the parameters passed to the kernel.
noinitrd
When set, disable the two-stage boot and preserve the contents of /dev/initrd
so the data is available after the kernel has booted. /dev/initrd can be read
only once, and then its contents are returned to the system.
number
Start Linux at the runlevel specified by number. A runlevel is an operating
state that the system can be booted to, such as a multiuser system or a system
configuration running the X Window System. A runlevel is generally one of the
numbers from 1 to 6; the default is usually 3. On modern distributions using
Upstart, the runlevels and their corresponding states are defined in the ttyN
files in the directory /etc/event.d. On older systems using SysVinit, the runlevels
are defined in the file /etc/inittab. See Chapter 2 for a discussion of the init
process.
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Boot Methods
ro Mount the root filesystem read-only. Used for doing system mainte-
nance, such as checking the filesystem integrity, when you don’t want
anything written to the filesystem.
rw Mount the root filesystem read/write. If neither ro nor rw is specified,
the default value (usually rw) stored in the kernel image is used.
single
Start Linux in single-user mode. This option is used for system administra-
tion and recovery. It gives you a root prompt as soon as the system boots,
with minimal initialization. No other logins are allowed.
initrd: Using a RAM Disk
Modern Linux distributions use a modular kernel, which allows modules to be
added without requiring that the kernel be rebuilt. If your root filesystem is on a
device whose driver is a module (as is frequently true of SCSI disks), you can use
the initrd facility, which provides a two-stage boot process, to first set up a
temporary root filesystem in a RAM disk containing the modules you need to add
(e.g., the SCSI driver) and then load the modules and mount the real root file-
system. The RAM disk containing the temporary filesystem is the special device
file /dev/initrd.
Similarly, you need to use a RAM disk if your root partition uses the ext3 file-
system and ext3 was not compiled into the kernel image. In that case, the ext3
module must be loaded with initrd.
Before you can use initrd, both RAM disk support (CONFIG_BLK_DEV_
RAM=y) and initial RAM disk support (CONFIG_BLK_DEV_INITRD=y) must
be compiled into the Linux kernel. Then you need to prepare the normal root file-
system and create the RAM disk image. Your Linux distribution may have utilities
to do some of the setup for you; for example, the Red Hat distribution comes with
the mkinitrd command, which builds the initrd image. For detailed information,
see the initrd manpage and the file initrd.txt (the path may vary, but it is usually
something like /usr/src/linux/Documentation/initrd.txt).
Once your Linux system has been set up for initrd, you can do one of the
following, depending on which boot loader you are using:
• If you are using LILO, add the initrd option to the appropriate image section:
image=/vmlinuz
initrd=/boot/initrd # The file to load as the contents of /dev/initrd
...
• Run the /sbin/lilo command, and you can reboot with initrd.
• If you are using GRUB, add the initrd option to the kernel line of the
configuration-file boot entry, or to the kernel command if you are booting
from the command-line interface:
kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28
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542
Chapter 5Package Management
5
Package Management
This chapter describes the two major Linux packaging systems: the Red Hat
Package Manager (RPM) and the Debian GNU/Linux Package Manager. It also
describes the major frontend applications designed to simplify and automate
package management: yum for RPM-based systems, and apt, aptitude, and
synaptic for Debian-based systems (apt is now also available for RPM-based
systems).
When you install applications on your Linux system, most often you’ll find a
binary or a source package containing the application you want, instead of (or in
addition to) a .tar.gz file. A package is a file containing the files necessary to install
an application. However, while the package contains the files you need for instal-
lation, the application might require the presence of other files or packages that
are not included, such as particular libraries (and even specific versions of the
libraries), to actually be able to run. Such requirements are known asdependencies.
Package-management systems offer many benefits. As a user, you may want to
query the package database to find out what packages are installed on the system
and their versions. As a system administrator, you need tools to install and
manage the packages on your system. And if you are a developer, you need to
know how to build a package for distribution.
Among other things, package managers do the following:
• Provide tools for installing, updating, removing, and managing the software
on your system.
• Allow you to install new or upgraded software directly across a network.
• Tell you what software package a particular file belongs to or what files a
package contains.
• Maintain a database of packages on the system and their status, so you can
determine what packages or versions are installed on your system.
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Package Management | 543
Package
Management
• Provide dependency checking, so you don’t mess up your system with incom-
patible software.
• Provide GPG, PGP, MD5, or other signature-verification tools.
• Provide tools for building packages.
Any user can list or query packages. However, installing, upgrading, or removing
packages generally requires root privileges. This is because the packages normally
are installed in system-wide directories that are writable only by root. Sometimes
you can specify an alternate directory to install a package into your home direc-
tory or into a project directory where you have write permission, if you aren’t
running as root.
Signature verification is an important feature of package-management systems
that helps maintain the security of your system. An MD5 checksum is used to
check the integrity of a package, making sure, for example, that it was down-
loaded correctly and that it was not tampered with by a malicious user. GPG (and
PGP) encrypt a digital signature into the package, which is used to verify the iden-
tity of the package creator.
Most often you’ll install a binary package, in which the source code has been
compiled and the software is ready to run once it is installed. You may also want
or need to install source packages, which provide the source code and instruc-
tions for compiling and installing it. Source code packages do not contain
executable files. Packages follow certain naming conventions, and you can tell
from the name whether it is a binary or source package. RPM and Debian package
names contain the same information, but they are expressed slightly differently.
An RPM package has the form:
package-version-release.architecture.rpm
A Debian package has the form:
package_version-revision_architecture.deb
In both cases, package is the name of the package, version is the version number of
the software, release (RPM) and revision (Debian) indicate the revision number of the
package for that version, and architecture shows what system architecture the
software was packaged for (e.g., i386 or amd64). The value of architecture may
also be noarch for a package that is not hardware-specific or src for an RPM
source package (Debian source packages come as tarred, gzipped files).
All the package managers check for dependencies when you install a package. In
the case of RPM, if there are missing dependencies, it prints an error and termi-
nates without installing the package. To proceed, you need to first install the
missing package (or packages). This can become an involved process if
the missing package has its own dependencies. A major advantage of the high-
level package managers described in this chapter (i.e., yum, apt, aptitude, and
synaptic) is that they automatically resolve dependencies and install missing pack-
ages for you. Another advantage is that they locate and download the package
automatically, based on information in configuration files specifying where to
look for packages. With RPM, you first have to locate the package, then down-
load it, and only then can you run RPM to do the install. On the other hand, if
you already have the package file on your system or on a CD, RPM is quick and
easy to run.
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544 | Chapter5: Package Management
Both RPM and the apt system back up old files before installing an updated
package. Not only does this let you go back if there is a problem, but it also
ensures that you don’t lose your changes (to configuration files, for example).
The following list shows the package-management programs described in the rest
of this chapter. Which program to use is very much a matter of personal prefer-
ence, and you can use more than one at different times. However, it’s best to pick
the program you prefer and use it consistently, so all your packages are main-
tained in a single database that you can query.
The Advanced Package Tool (APT)
APT is a modern, user-friendly package-management tool that consists of a
number of commands. The most frequently used of these commands is apt-
get, which is used to download and install a Debian package. apt-get can be
run from the command line or selected as a method from dselect.
Note that there are versions of the apt commands that can be used on an
RPM-based system. If you plan to do that, it’s best to install the version of
apt that comes with your Linux distribution.
aptitude
High-level text-based interface to APT. Runs either from the command line or
in a visual mode inside a terminal window such as an xterm.
dpkg
The original Debian packaging tool. Used to install or uninstall packages, or
as a frontend to dpkg-deb. Getting and installing packages is usually done
with apt-get, but dpkg is still commonly used to install a package that is
already on your system. In fact, apt-get calls dpkg to do the installation once
it’s gotten the package.
dpkg-deb
Lower-level packaging tool. Used to create and manage the Debian package
archives. Accepts and executes commands from dpkg or can be called
directly.
dselect
An interactive frontend to dpkg. With the advent of the newer tools and the
increased number of packages, the use of dselect is deprecated.
synaptic
A graphical frontend to APT.
RPM
The original command-line system for installing and managing RPM pack-
ages. RPM has two commands: rpm for installing and managing packages,
and rpmbuild for creating packages.
yum
A frontend to RPM that runs from the command line.
Another RPM-based package manager, up2date, used to be the default for Red
Hat Enterprise Linux systems. Red Hat has since switched to yum as the default,
but up2date is still available if you prefer it. up2date has both command line and
graphical interfaces, and like yum, it resolves dependencies as needed.
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Yum: Yellowdog Updater Modified | 545
Package
Management
If you want to update your system regularly, to keep it current and to be sure you
have the latest security fixes, you can set up a command that you can reissue at
some regular interval (say, every day or once a week), or you can set it up as a
cron job to run overnight daily or weekly. (See the descriptions of the cron and
crontab commands in Chapter 3 for more information on setting up a cron job.)
You can set up your cron job to automatically download and install updated
packages, but a safer approach is to have your job download the updates and
email you a summary, leaving it up to you when and how to do the installation.
This is particularly true in a production environment where you want to test
changes thoroughly before incorporating them into your system.
Yum: Yellowdog Updater Modified
Yum is a system for managing RPM packages, including installing, updating,
removing, and maintaining packages; it automatically handles dependencies
between packages. Yum is derived from yup, an updating system written for
Yellow Dog Linux, an RPM-based PowerPC distribution. Yum downloads the
information in the package headers to a directory on your system, which it then
uses to make decisions about what it needs to do. Yum obtains both the headers
and the RPMs themselves from a collection of packages on a server, known as a
repository.
A repository consists of a set of RPM packages and the package headers, which
are on a server that can be accessed via FTP or HTTP, from an NFS server, or
from a local filesystem. A single server can contain one or multiple repositories;
repositories are often mirrored on many servers, and you can configure yum to
use multiple repositories. When they are downloaded to your system, the header
and package files are maintained in /var/cache/yum.
The configuration file, /etc/yum.conf, is where you customize yum. It consists of
two section types. The first section, [main], sets configuration defaults for yum
operation. This section is followed by [server] sections, where each server is
named according to the repository it specifies. For example, for Fedora, you might
have [base] for the base Fedora repository and [development] for the develop-
ment repository.
The server sections can also be stored, one to a file, in /etc/yum.repos.d. yum
comes with a default yum.conf/ file, which you can use as is or as a starting point
from which to add additional repositories.
The yum Command
The yum command is an automated system for updating rpm-based packages,
particularly on Fedora and Red Hat Enterprise Linux. Yum can automatically
install, upgrade, and remove packages. In addition to individual packages or a list
of packages, yum can operate on an entire group of packages at a time.
When you run yum, it first updates the cache (unless you tell it not to with the -C
option); then it proceeds to perform the requested operation.
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546 | Chapter5: Package Management
The format of the yum command is:
yum [options] [command] [package ...]
Any general options are specified first, followed by a command telling yum what
you want it to do, usually followed by a list of one or more packages. The
command is always required, except with the --help, -h, and --version options.
Package names can be specified in various combinations of name, architecture,
version, and release. For example, you could refer to the bash package as bash,
bash.x86_64, bash-3.2, bash-3.2-30, or bash-3.2-30.fc10.x86_64.
General options
The following general options can be set on the command line. For those that can
alsobe set in the [main] section of the yum.conf configuration file, the name of
the configuration option is given.
-c [config-file]
Specify the location of the yum configuration file. The file can be specified as
a path to a local file or as an HTTP or FTP URL. The default is /etc/yum.conf.
-C Run entirely from the local cache. Don’t download or update headers unless
required to complete the requested action.
-d [num]
Set the debug level to num, which is generally a number between 0 and 10, to
specify how much debugging information to print. The configuration option
is debuglevel.
--disableexcludes=option
Disable the excludes defined in yum.conf. The possible options are all to
disable all excludes, main to disable only the excludes defined in [main] in
yum.conf, or repoid to disable any excludes defined for the specified repository.
--disableplugin=plugin
Run with the specified plugins disabled, where plugin is a comma-separated
list of plugins.
--disablerepo=repoid
Disable the repository specified by repoid so yum won’t use it for this opera-
tion. The configuration option is enabled.
-e [num]
Set the error level to num, where num is a number, generally between 0 and 10.
If the value is 0, print only critical errors. If it is 1, print all errors. Values
greater than 1 mean print more errors, if there are any. The configuration
option is errorlevel.
--enablerepo=repoid
Enable the specified repository that is marked as disabled (enable=0) in the
configuration file. This allows the repository to be used for this operation.
The configuration option is enabled.
-h [command], --help [command]
Display a help message and exit. With a command, display help for that
command.
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Package
Management
--installroot=root
Specify an alternative root for package installation. All packages will be
installed relative to root. The configuration option is installroot.
--nogpgcheck
Disable GPG signature checking. The configuration option is gpgcheck.
--noplugins
Disable all plugins. The configuration option is plugins.
--obsoletes
Enable obsoletes processing logic, taking into consideration packages that are
obsoleted by other packages in the repository. Meaningful only with the yum
update command. The configuration option is obsoletes.
-q, --quiet
Run without producing output. See also -y.
-R [minutes]
Set the maximum amount of time in minutes that yum will wait before
performing a command.
--showduplicates
For the info, list, and search commands, show all matching packages, not
just the latest versions.
--skipbroken
If yum finds dependency problems in a transaction, resolve them by
removing the packages causing problems. The configuration option is skip_
broken.
-t, --tolerant
Currently does nothing. This option was originally intended to allow yum to
keep going (be tolerant) in spite of any package errors on the command line.
The configuration option is tolerant.
-v, --verbose
Display debugging information.
--version
Display the version of yum and exit.
-x[package], --exclude=package
Exclude the specified package from updates on all repositories. package can
be given as a name or a glob. The configuration option is exclude.
-y Assume that the answer to any question is yes. The configuration option is
assumeyes.
yum Command Summary
The individual yum commands are listed here.
check-update check-update
Determine if updates are available, without running yum interac-
tively. If any package updates are available, returns an exit value of
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548 | Chapter5: Package Management
100 and a list of packages. If there are no updates, returns 0.
Returns 1 on error.
clean clean [options]
Clean up the yum cache directory.
Options
all
Clean everything: headers, packages, metadata, and the cache.
dbcache
Clean up the sqlite database cache, forcing yum to recreate it
the next time it runs.
headers
Remove all header files, forcing yum to download new headers
the next time it runs.
metadata
Remove the metadata files, which maintain information about
the packages such as package name, file size, description,
dependencies, etc. The metadata will be downloaded again the
next time yum is run.
packages
Remove cached packages from the system.
deplist deplistpackages
Generate a list of dependencies for the specified packages,
including what packages satisfy the dependencies.
groupinfo groupinfogroups
Like info, but operates on package groups instead of individual
packages.
groupinstall groupinstallgroups
groupupdategroups
Like install, but operates on package groups instead of individual
packages.
grouplist grouplist
Generate a list of installed and available groups to standard output.
You can use these groups as input parameters to the other group
commands, with their names in quotes (" ").
groupremove groupremovegroups
Like remove, but operates on package groups instead of individual
packages.
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Package
Management
help help [command]
Display help information for the specified command, or if no
command is given, for all commands.
info info [options] [packages]
Display version information, a summary, and a description for each
package, or for all packages if none is specified. See the list
command for a description of the options.
install installpackages
Install the latest version of a package or packages, ensuring that all
dependencies are met. If no package matches the name as speci-
fied, the name is treated as a shell glob and any matches are
installed.
list list [options] [packages]
Display a list of packages that match the packages specification and
that are installed or available for installation.
Options
all
List all installed or available packages.
available
List packages on the repository that are available for installation.
extras
List packages on the system that are not available on any
repository specified in the configuration file.
installed
List installed packages.
obsoletes
List installed packages that are made obsolete by any pack-
ages in any repository in the configuration file.
recent
List packages that have been recently added to any repository
in the configuration file.
updates
List packages that have updates available for installation.
localinstall localinstallpackages
Install the specified packages, which reside on the local system,
rather than downloading them from a repository.
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550 | Chapter5: Package Management
localupdate localupdatepackages
Update the specified packages, which reside on the local system,
rather than downloading them from a repository.
makecache makecache
Download and cache the metadata files from the repository. Once
the cache has been built, you can use the -C option to run the
commands that use the metadata (check-update, info, list, provides,
and search) directly from the cache.
provides providesfeature1 [feature2 ...]
whatprovidesfeature1 [feature2 ...]
List packages that are available or installed that provide the speci-
fied features. The features can be specified as a name or as a
wildcard in file-glob syntax format, and Perl or Python regular
expressions can be used.
reinstall reinstallpackage1 [package2 ...]
Reinstall the specified packages. The packages must already exist
on the system.
remove removepackage1 [package2 ...]
erasepackage1 [package2 ...]
Remove the specified packages from the system. Also remove any
packages that depend on the specified packages.
repolist repolist [option]
Generate a list of configured repositories. With no option or if the
option is all, list all repositories. The other options are disabled to
list disabled repositories, and enabled to list enabled repositories.
resolvedep resolvedepdep1 [dep2 ...]
List the packages that provide the specified dependencies.
search searchstring1 [string2 ...]
Find packages matching the specified string or strings in the
description, summary, packager, or package name fields. Perl or
Python regular expressions can be used for the strings. Useful for
finding a package if you don’t know the name.
shell shell [filename]
Run an interactive yum shell, allowing multiple commands to be
run within one yum execution. A filename can be specified that
contains the commands to be run.
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update update [packages]
With no packages specified, update all installed packages. Other-
wise, update the specified packages. In either case, yum makes sure
that all dependencies are satisfied. If no package matches, the
names specified are assumed to be shell globs, and any matches are
installed.
With the --obsoletes option, yum includes package obsoletes in its
calculations.
upgrade upgrade [packages]
Equivalent to update --obsoletes.
Plugins and yum-utils
You can install plugins to extend the capabilities of yum. Plugins are Python
programs that are installed in a directory specified with the pluginpath option in /etc/
yum.conf. In addition, to enable plugins, set the plugins option in /etc/yum.conf to 1.
One set of such plugins is yum-utils, a collection of tools for managing packages
and repositories. The following list briefly describes each tool. For more informa-
tion on a tool, run it with the -h or --help option.
debuginfo-install
Install debuginfo packages, which contain debugging information for
programs.
package-cleanup
Clean up packages, handling duplicates, orphaned packages, and dependency
problems.
repoclosure
Read the metadata of one or more repositories, check dependencies, and
display a list of any unresolved dependencies.
repodiff
Compare two or more repositories and display a list of added, removed, or
changed packages.
repo-graph
Display a full package dependency list in dot format.
repomanage
Manage a directory of rpm packages, returning a list of the newest or oldest
packages in a directory.
repoquery
Query yum repositories for additional information.
repo-rss
Generate an RSS feed from one or more repositories.
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reposync
Synchronize a remote repository to a local directory, using yum to retrieve
packages.
repotrack
Keep track of packages and their dependencies, and download them.
yum-builddep
Install missing dependencies to build specified packages.
yum-complete-transaction
Find incomplete or aborted transactions and try to complete them.
yumdownloader
Download binary and source packages from yum repositories for specified
packages.
The Red Hat Package Manager
The Red Hat Package Manager (RPM) is a freely available packaging system for
software distribution and installation. In addition to the Red Hat Enterprise Linux
and Fedora distributions, both SUSE and Mandriva are among the Linux distribu-
tions that use RPM.
Using RPM is straightforward. A single command, rpm, has options to perform all
package-management functions except building packages. * For example, to find
out if the Emacs editor is installed on your system, you could enter:
$rpm -q emacs
emacs-22.2-5.fc9.x86_64
This command prints the full package name, confirming its presence.
The rpmbuild command is used to build both binary and source packages.
RPM Package Concepts
This section provides an overview of some of the parts of an RPM package. Much
of the information is of primary use to developers, but because some of the terms
are referenced in the RPM command descriptions, they are explained briefly here.
An RPM package has three primary components. The header contains all the
information about the package, such as its name and version, a description, a list
of included files, the copyright terms, and where the source file can be found. The
signature contains information used to verify the integrity and authenticity of
the package. The archive contains the actual files that make up the package.
When a package is being built, one of the requirements for its developers is to
create a spec file. If you download the source rpm for a package, you can look at
the spec file; it has a filename of package.spec (e.g., yum.spec for the yum spec
file). The spec file contains all the information required to build a package,
*In older versions of RPM, the build options were part of the rpm command.
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including a description of the software, instructions telling the rpmbuild
command how to build the package, and a list of the files included and where
they get installed. Some other features of spec files include the following:
Macros
Macros are sequences of commands stored together and executed by
invoking the macro name. The RPM build process provides two standard
macros: %setup to unpack the original sources and %patch to apply patches.
Other macros appear later in this chapter in the command descriptions and
are described there.
Scripts
Scripts are used to control the build process. Some of the scripts RPM uses
include %prep to begin the build process, %build primarily to run make and
perhaps do some configuration, %install to do a make install and %clean to
clean up afterward. Four additional scripts may be created to run when a
package is actually installed on a system. These scripts are %pre for scripts
run before package installation, %post for scripts run after package installa-
tion, %preun for scripts run before a package is uninstalled, and %postun for
scripts run after a package is uninstalled.
Trigger scriptlets
Trigger scriptlets are extensions of the normal install and uninstall scripts.
They provide for interaction between packages. A trigger scriptlet provided
with one package will be triggered to run by the installation or removal of
some other package. For example, a newly installed RPM package may cause
an existing application to run or restart once installation is complete. In many
cases, a newly installed package requires services to be restarted.
The rpm Command
RPM packages are built, installed, and queried with the rpm command. RPM
package filenames usually end with a .rpm extension. rpm has a set of modes,
each with its own options. The format of the rpm command is:
rpm [options] [packages]
With a few exceptions, as noted in the lists of options that follow, the first option
specifies the rpm mode (install, query, update, etc.), and any remaining options
affect that mode.
Options that refer to packages are sometimes specified as package-name and
sometimes as package-file. The package name is the name of the program or
application, such as xpdf. The package file is the name of the RPM file, such as
xpdf-3.00-10.1.i386.rpm.
RPM provides a configuration file for specifying frequently used options. The
default global configuration file is usually /usr/lib/rpm/rpmrc, the local system
configuration file is /etc/rpmrc, and users can set up their own $HOME/.rpmrc
files. You can use the --showrc option to show the values RPM will use by default
for all the options that may be set in an rpmrc file:
rpm --showrc
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The rpm command includes FTP and HTTP clients, so you can specify an ftp:// or
http:// URL to install or query a package across the Internet. You can use an FTP
or HTTP URL wherever package-file is specified in the commands presented here.
Be careful, however, when downloading packages from the Internet. Always verify
package contents by checking MD5 hashes and signatures. Whenever possible,
install from trusted sites.
Any user can query the RPM database. Most of the other functions, such as
installing and removing packages, require superuser privileges.
General options
The following options can be used with all modes:
--dbpath path
Use path as the path to the RPM database instead of the default /var/lib/rpm.
-?, --help
Print a long usage message (run rpm with no options for a shorter usage
message).
--pipecommand
Pipe the query output to the specified command.
--quiet
Display only error messages.
--rcfile filelist
Get configuration from the files in the colon-separated filelist. If --rcfile is
specified, the list must contain at least one file and that file must exist. filelist
defaults to /usr/lib/rpm/rpmrc:/usr/lib/rpm/redhat/rpmrc:/etc/rpmrc:~/.rpmrc.
Use with --showrc to see what options will be used if alternate configuration
files are specified.
--root dir
Perform all operations within the directory tree rooted at dir.
-v Verbose. Print progress messages.
--version
Print the rpmversion number.
-vv Print debugging information.
Install, upgrade, and freshen options
Use the install command to install or upgrade an RPM package. Upgrading with
install leaves any existing versions on the system. The install syntax is:
rpm -i [install-options]package_file ...
rpm --install [install-options]package_file ...
To install a new version of a package and remove an existing version at the same
time, use the upgrade command instead:
rpm -U [install-options]package_file ...
rpm --upgrade [install-options]package_file ...
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If the package doesn’t already exist on the system, -U acts like -i and installs it. To
prevent that behavior, you can freshen a package instead; in that case, rpm
upgrades the package only if an earlier version is already installed. The freshen
syntax is:
rpm -F [install-options]package_file ...
rpm --freshen [install-options]package_file ...
For all forms, package-file can be specified as an FTP or HTTP URL to download
the file before installing it. See “FTP/HTTP options” on page 563.
The installation and upgrade options are:
--aid
If rpm suggests additional packages, add them to the list of package files.
--allfiles
Install or upgrade all files.
--badreloc
Used with --relocate to force relocation even if the package is not relocatable.
--excludedocs
Don’t install any documentation files.
--excludepath path
Don’t install any file whose filename begins with path.
--force
Force the installation. Equivalent to --replacepkgs --replacefiles --oldpackage.
-h, --hash
Print 50 hash marks as the package archive is unpacked. Use this option with
-v or --verbose for a nicer display.
--ignorearch
Install even if the binary package is intended for a different architecture.
--ignoreos
Install binary package even if the operating systems don’t match.
--ignoresize
Don’t check disk space availability before installing.
--includedocs
Install documentation files. This is needed only if excludedocs: 1 is specified
in an rpmrc file.
--justdb
Update the database only; don’t change any files.
--nodeps
Don’t check whether this package depends on the presence of other packages.
--nodigest
Don’t verify package or header digests.
--nomanifest
Don’t process nonpackage files as manifests.
--noorder
Don’t reorder packages to satisfy dependencies before installing.
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--nopost
Don’t execute any post-install script.
--nopostun
Don’t execute any post-uninstall script.
--nopre
Don’t execute any pre-install script.
--nopreun
Don’t execute any pre-uninstall script.
--noscripts
Don’t execute any pre-install or post-install scripts. Equivalent to specifying
--nopre --nopost --nopreun --nopostun.
--nosignature
Don’t verify package or header signatures.
--nosuggest
Don’t suggest packages that provide a missing dependency.
--notriggerin
Don’t execute any install trigger scriptlet.
--notriggerun
Don’t execute any uninstall trigger scriptlet.
--notriggerpostun
Don’t execute any post-uninstall trigger scriptlet.
--notriggers
Don’t execute any scripts triggered by package installation. Equivalent to
specifying --notriggerin --notriggerun --notriggerpostun.
--oldpackage
Allow an upgrade to replace a newer package with an older one.
--percent
Print percent-completion messages as files are unpacked. Useful for running
rpm from other tools.
--prefix path
Set the installation prefix to path for relocatable binary packages.
--relocate oldpath=newpath
For relocatable binary files, change all file paths from oldpath to newpath.
Can be specified more than once to relocate multiple paths.
--replacefiles
Install the packages even if they replace files from other installed packages.
--replacepkgs
Install the packages even if some of them are already installed.
--test
Go through the installation to see what it would do, but don’t actually install
the package. This option lets you test for problems before doing the installation.
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Query options
The syntax for the query command is:
rpm -q [package-selection-options] [package-query-options]
rpm --query [package-selection-options] [package-query-options]
There are two subsets of query options. Package-selection options determine
which packages to query, and package-query options determine which informa-
tion to provide.
Package-selection options
package_name
Query the installed package package_name.
-a, --all
Query all installed packages.
-f file, --file file
Find out which package owns file.
--fileid md5
Query package with the specified MD5 digest.
-g group, --group group
Find out which packages have group group.
--hdrid sha1
Query package with the specified SHA1 digest in the package header.
-p package_file, --package package_file
Query the uninstalled package package_file, which can be a URL. If package_file
is not a binary package, it is treated as a text file containing a package
manifest, with each line of the manifest containing a path or one or more
whitespace-separated glob expressions to be expanded to paths. These paths
are then used instead of package_file as the query arguments. The manifest
can contain comments that begin with a hash mark (#).
--pkgid md5
Query the package with a package identifier that is the given MD5 digest of
the combined header and contents.
--querybynumber num
Query the numth database entry. Useful for debugging.
-qf, --queryformat string
Specify the format for displaying the query output, using tags to represent
different types of data (e.g., NAME, FILENAME, DISTRIBUTION). The
format specification is a variation of the standard printf formatting, with the
type specifier omitted and replaced by the name of the header tag inclosed in
brackets ({ }). For example:
%{NAME}
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The tag names are case-insensitive. Use --querytags (see “Miscellaneous
options” on page 563) to view a list of available tags. The tag can be followed
by :type to get a different output format type. The possible types are:
:armor
Wrap a public key in ASCII armor.
:arraysize
Display number of elements in array tags.
:base64
Encode binary data as base64.
:date
Use %c format as in strftime(3) to display the preferred date and time
format for this locale.
:day
Use %a %b %d %Y format as in the function strftime(3). This format
displays the day, the month, the month as a decimal number, and the
four-digit year.
:depflags
Format dependency flags.
:fflags
Format file flags.
:hex
Use hexadecimal format.
:octal
Use octal format.
:perms
Format file permissions.
:pgpsig
Display the PGP signature and time.
:shescape
Escape single quotes for use in a script.
:triggertype
Display trigger suffix (i.e., in, un, or postun, indicating whether it’s an
install, uninstall, or post-uninstall trigger).
:xml
Wrap data in simple XML markup.
--specfile specfile
Query specfile as if it were a package. Useful for extracting information from
a spec file.
--tid tid
List packages with the specified transaction identifier (tid), which is a Unix
timestamp. All packages installed or erased in a single transaction have the
same tid.
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--triggeredby pkg
List packages containing triggers that are run when the installation status of
package pkg changes. For example:
$rpm -q --triggeredby glibc
redhat-lsb-3.2-2.fc10.x86_64
In this example, the package redhat-lsb-3.2-2.fc10.x86_64 contains a
triggerpostun scriptlet that runs after glibc is uninstalled.
--whatrequires capability
List packages that require the given capability to function. For example:
$rpm -q --whatrequires popt
popt-devel-1.13-4.fc10.x86_64
logrotate-3.7.7-1.fc10.x86_64
nash-6.0.71-2.fc10.x86_64
initscripts-8.86-1.x86_64
rpm-4.6.0-0.rc1.7.x86_6
--whatprovides capability
List packages that provide the given capability. For example:
$rpm -q --whatprovides popt
popt-1.13-4.fc10.x86_64
Package-query options
-c, --configfiles
List configuration files in the package. Implies -l.
--changelog
Display the log of change information for the package.
-d, --docfiles
List documentation files in the package. Implies -l.
--dump
Dump information for each file in the package. The output includes the
following information in this order:
path size mtime md5sum mode owner group isconfig isdoc rdev symlink
--filesbypkg
List all files in each package.
-i, --info
Display package information, including the name, version, and description.
The results are formatted according to --queryformat if specified.
-l, --list
List all files in the package.
--last
List packages by install time, with the latest packages listed first.
--provides
List the capabilities this package provides.
-R, --requires
List any packages this package depends on.
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-s, --state
List each file in the package and its state. The possible states are normal, not
installed, or replaced. Implies -l.
--scripts
List any package-specific shell scripts used during installation and uninstalla-
tion of the package.
--triggers, --triggerscript
Display any trigger scripts in the package.
Uninstall options
The syntax for erase, the uninstall command, is:
rpm -e [uninstall-options]package_name ...
rpm --erase [uninstall-options]package_name ...
The uninstall options are:
--allmatches
Remove all versions of the package. Only one package should be specified;
otherwise, an error results.
--nodeps
Don’t check dependencies before uninstalling the package.
--nopostun
Don’t run any post-uninstall scripts.
--nopreun
Don’t run any pre-uninstall scripts.
--noscripts
Don’t execute any pre-uninstall or post-uninstall scripts. This option is equiv-
alent to --nopreun --nopostun.
--notriggerpostun
Don’t execute any post-uninstall scripts triggered by the removal of this
package.
--notriggers
Don’t execute any scripts triggered by the removal of this package. Equiva-
lent to --notriggerun --notriggerpostun.
--notriggerun
Don’t execute any uninstall scripts triggered by the removal of this package.
--test
Don’t really uninstall anything; just go through the motions. Use with -vv for
debugging.
Verify options
The syntax for the verify command is:
rpm -V | --verify [package-selection-options] [verify-options]
Verify mode compares information about the installed files in a package with
information about the files that came in the original package and displays any
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discrepancies. The information compared includes the size, MD5 sum, permis-
sions, type, owner, and group of each file. Uninstalled files are ignored.
The package selection options include those available for query mode. In addi-
tion, the following verify options are available:
--nodeps
Ignore package dependencies.
--nodigest
Ignore package or header digests.
--nofiles
Ignore attributes of package files.
--nogroup
Ignore group ownership errors.
--nolinkto
Ignore symbolic-link errors.
--nomd5
Ignore MD5 checksum errors.
--nomode
Ignore file mode (permissions) errors.
--nordev
Ignore major and minor device number errors.
--nomtime
Ignore modification time errors.
--noscripts
Ignore any verify script.
--nosignature
Ignore package or header signatures.
--nosize
Ignore file size errors.
--nouser
Ignore user ownership errors.
The output is formatted as an eight-character string, possibly followed by an
attribute marker, and then the filename. Each of the eight characters in the string
represents the result of comparing one file attribute to the value of that attribute
from theRPM database. A period (.) indicates that the file passed that test. The
following characters indicate failure of the corresponding test:
5 MD5 sum
D Device
G Group
L Symlink
M Mode (includes permissions and file type)
S File size
T Mtime
U User
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The possible attribute markers are:
c Configuration file
d Documentation file
g Ghost file (contents not included in package)
l License file
r Readme file
Database rebuild options
The syntax of the command to rebuild the RPM database is:
rpm --rebuilddb [options]
You also can build a new database:
rpm --initdb [options]
The options available with the database rebuild mode are the --dbpath, --root,
and -v options described earlier under “General options” on page 546.
Signature-check options
RPM packages may have a GPG signature built into them. There are three types of
digital signature options: you can check signatures, add signatures to packages,
and import signatures.
The syntax of the signature check mode is:
rpm --checksig [options]package_file...
rpm -K [options]package_file...
The signature-checking options -K and --checksig check the digests and signatures
contained in the specified packages to insure the integrity and origin of the pack-
ages. Note that RPM now automatically checks the signature of any package
when it is read; these options are still useful, however, for checking all headers
and signatures associated with a package.
The --nosignature and --nodigest options described earlier, under “Verify
options” on page 560, are available for use with signature check mode.
The syntax for adding signatures to binary packages is:
rpm --addsignbinary-pkgfile...
rpm --resignbinary-pkgfile...
Both --addsign and --resign generate and insert new signatures, replacing any that
already exist in the specified binary packages. *
The syntax for importing signatures is:
rpm --importpublic-key
*In older versions of RPM, --addsign was used to add new signatures without replacing existing
ones, but currently both options work the same way and replace any existing signatures.
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The --import option is used to import an ASCII public key to the RPM database
so that digital signatures for packages using that key can be verified. Imported
public keys are carried in headers, and keys are kept in a ring, which can be
queried and managed like any package file.
Miscellaneous options
Several additional rpm options are available:
--querytags
Print the tags available for use with the --queryformat option in query mode.
--setperms packages
Set file permissions of the specified packages to those in the database.
--setugids packages
Set file owner and group of the specified packages to those in the database.
--showrc
Show the values rpm will use for all options that can be set in an rpmrc file.
FTP/HTTP options
The following options are available for use with FTP and HTTP URLs in install,
update, and query modes.
--ftpport port
Use port for making an FTP connection on the proxy FTP server instead of
the default port. Same as specifying the macro %_ftpport.
--ftpproxy host
Use host as the proxy server for FTP transfers through a firewall that uses a
proxy. Same as specifying the macro %_ftpproxy.
--httpport port
Use port for making an HTTP connection on the proxy HTTP server instead
of the default port. Same as specifying the macro %_httpport.
--httpproxy host
Use host as the proxy server for HTTP transfers. Same as specifying the macro
%_httpproxy.
RPM Examples
Query the RPM database to find Emacs-related packages:
$rpm -q -a | grep emacs
Query an uninstalled package, printing information about the package and listing
the files it contains:
$rpm -qpil ~/downloads/bash-3.2-29.fc10.x86_64.rpm
Install a package (assumes superuser privileges):
$rpm -i sudo-1.6.9p17-2.fc10.x86_64.rpm
Do the same thing, but report on the progress of the installation:
$rpm -ivh sudo-1.6. 9p17-2.fc10.x86_64.rpm
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The rpmbuild Command
The rpmbuild command is used to build RPM packages. The syntax forrpmbuild is:
rpmbuild -[b|t]stage [build-options]spec-file ...
Specify -b to build a package directly from a spec file, or -t to open a tarred,
gzipped file and use its spec file.
Both forms take the following single-character stage arguments, which specify the
stages, or steps, required to build a package. The stages are listed in the order they
would be performed:
p Perform the prep stage, unpacking source files and applying patches.
l Do a list check, expanding macros in the files section of the spec file and
verifying that each file exists.
c Perform the prep and build stages; generally equivalent to doing a make.
i Perform the prep, build, and install stages; generally equivalent to doing a
make install.
b Perform the prep, build, and install stages, then build a binary package.
s Build a source package.
a Perform the prep, build, and install stages, then build both binary and source
packages.
The difference between the build stage, which is one of the early steps, and
building a binary package in b or a is the difference between building a working
binary for the software and putting all the pieces together into a final rpm
package.
rpmbuild options
The general rpm options described under “General options” on page 546 can be
used with rpmbuild.
The following additional options can also be used when building an rpm file with
rpmbuild:
--buildroot dir
Override the BuildRoot tag with dir when building the package.
--clean
Clean up (remove) the build files after the package has been made.
--nobuild
Go through the motions, but don’t execute any build stages. Used for testing
spec files.
--rmsource
Remove the source files when the build is done. Can be used as a standalone
option to clean up files separately from creating the packages.
--rmspec
Remove the spec file when the build is done. Can be used as a standalone
option.
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--short-circuit
Can be used with -bc and -bi to skip previous stages that already ran success-
fully. With --short-circuit, -bc starts directly at the build stage and -bi starts
with the install stage.
--sign
Add a GPG signature to the package for verifying its integrity and origin.
--target platform
When building the package, set the macros %_target, %_target_arch, and
%_target_os to the value indicated by platform.
Two other options can be used standalone with rpmbuild to recompile or rebuild
a package:
--rebuild source-pkgfile...
Like --recompile, but also build a new binary package. Remove the build
directory, the source files, and the spec file once the build is complete.
--recompile source-pkgfile...
Install the named source package, and prep, compile, and install the package.
Finally, the --showrc option is used to show the current rpmbuild configuration:
rpmbuild --showrc
This option shows the values that will be used for all options that can be set in
rpmrc and macros files.
The Debian Package Manager
Debian GNU/Linux provides several package-management tools, primarily intended
to facilitate the building, installation, and management of binary packages. In
addition, the tools described here also work on other Debian-based systems such
as Ubuntu, Xandros, Knoppix, and numerous others.
Debian package names generally end in .deb. The Debian package-management
tools we describe include the apt commands, aptitude, dpkg, dpkg-deb, dselect,
and synaptic. Each of these tools is described in detail in “Debian Package
Manager Command Summary” on page 569.
Files
Some important files used by the Debian package-management tools are described
briefly here:
control
Comes with each package. Documents dependencies; contains the name and
version of the package, a description, maintainer, installed size, the package
priority, etc.
conffiles
Comes with each package. Contains a list of the configuration files associ-
ated with the package.
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preinst, postinst, prerm, postrm
Scripts developers can include in a package to be run before installation, after
installation, before removal, or after removal of the package.
/var/lib/dpkg/available
Contains information about packages available on the system.
/var/lib/dpkg/status
Contains information about the status of packages available on the system.
/etc/apt/sources.list
A list for APT of package sources, used to locate packages. The sources are
listed one per line, in order of preference.
/etc/apt/apt.conf
The main APT configuration file.
/etc/apt/preferences
A preferences file that controls various aspects of APT, such as letting a user
select the version or release of a package to install.
/etc/dpkg/dpkg.cfg
A configuration file containing default options for dpkg.
For a user, the important file is /etc/apt/sources.list. This file is where you set up
the paths to the package archives, telling apt where to go to find packages. apt is
installed with a default file. You aren’t required to modify the sources in the file,
but you’ll probably want to change some sources or add additional ones at some
point. You might also want to change some of the options in the configuration
files apt.conf, preferences, and dpkg.config if you aren’t satisfied with the defaults.
The control, conffiles, and the pre- and post-install and removal script files are
created by the package developers and used internally by the package-management
system.
Package Priorities
Every Debian package has a priority associated with it, indicating how important
the package is to the system. The priorities are:
required
The package is essential to the proper functioning of the system.
important
The package provides important functionality that enables the system to run
well.
standard
The package is included in a standard system installation.
optional
The package is one that you might want to install, but you can omit it if you
are short on disk space, for example.
extra
The package either conflicts with other packages that have a higher priority,
has specialized requirements, or is one that you would want to install only if
you need it.
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Package
Management
The control file for dpkg, for example, shows that dpkg itself has a priority of
required; dpkg-dev (which provides tools for building Debian packages) has a
priority of standard; and dpkg-doc is optional.
Package and Selection States
The possible states that a package can be in are:
config-files
Only the configuration files for the package are present on the system.
half-configured
The package is unpacked, and configuration was started but not completed.
half-installed
Installation was started but not completed.
installed
The package is unpacked and configured.
not-installed
The package is not installed.
unpacked
The package is unpacked but not configured.
The possible package selection states are:
deinstall
The package has been selected for deinstallation (i.e., for removal of every-
thing but the configuration files).
install
The package has been selected for installation.
purge
The package has been selected to be purged (i.e., for removal of everything
including the configuration files).
Package Flags
Two possible package flags can be set for a package:
hold
The package should not be handled by dpkg unless forced with the --force-
hold option. Holding a package keeps it at the current version, preventing it
from being updated. You might hold a package, for example, if the latest
version is broken and you want to stay with the version you have until a
newer one is released.
reinst-required
The package is broken and needs to be reinstalled. Such a package cannot be
removed unless forced with the --force-reinstreq option.
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Scripts
In addition to the commands described in the next section, a number of shell
and Perl scripts are included with the package manager for use in managing and
building packages:
apt-file
Search for packages, specifying an action and a pattern to search for. (Perl script)
apt-rdepends
Recursively list dependencies. (Perl script)
dpkg-architecture
Determine and set the build and host architecture for package building. (Perl
script)
dpkg-checkbuilddeps
Check installed packages against the build dependencies and build conflicts
listed in the control file. (Perl script)
dpkg-buildpackage
A control script to help automate package building. (Shell script)
dpkg-distaddfile
Add an entry for a file to debian/files. (Perl script)
dpkg-divert
Create and manage the list of diversions, used to override the default loca-
tion for installing files. (Perl script)
dpkg-genchanges
Generate an upload control file from the information in an unpacked, built
source tree and the files it has generated. (Perl script)
dpkg-gencontrol
Read information from an unpacked source tree, generate a binary package
control file (by default, debian/tmp/DEBIAN/control), and add an entry for
the binary file to debian/files. (Perl script)
dpkg-name
Rename Debian packages to their full package names. (Shell script)
dpkg-parsechangelog
Read and parse the changelog from an unpacked source tree and write the
information to standard output in machine-readable form. (Perl script)
dpkg-preconfigure
Let packages ask questions prior to installation. (Perl script)
dpkg-reconfigure
Reconfigure a package that is already installed. (Perl script)
dpkg-scanpackages
Create a Packages file from a tree of binary packages. The Packages file is
used by dselect to provide a list of packages available for installation. (Perl
script)
dpkg-shlibdeps
Calculate shared library dependencies for named executables. (Perl script)
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Package
Management
dpkg-source
Pack and unpack Debian source archives. (Perl script)
dpkg-statoverride
Manage the list of stat overrides, which let dpkg override file ownership and
mode when a package is installed. (Perl script)
Debian Package Manager Command Summary
For the apt- commands, options can be specified on the command line or set in the
configuration file. Boolean options set in the configuration file can be overridden on
the command line in a number of different ways, such as --no-opt and -opt=no,
where opt is the single-character or full name of the option.
apt-cache apt-cache [ options ] command
Perform low-level operations on the APT binary cache, including
the ability to perform searches and produce output reports from
package metadata.
Commands
add files
Add the specified package index files to the source cache.
Useful for debugging.
depends pkgs
For each specified package, show a list of dependencies and
packages that can fulfill them.
dotty pkgs
Graph the relationships between the specified packages. The
default is to trace out all dependent packages; turn this
behavior off by setting the APT::Cache::GivenOnly configura-
tion option.
dump
List every package in the cache. Used for debugging.
dumpavail
Print a list of available packages to standard output, suitable
for use with dpkg.
gencaches
Build source and package caches from the sources in sources.
list and from /var/lib/dpkg/status. Equivalent to running apt-get
check.
madison [pkgs]
Display a table showing the available versions of each speci-
fied package. Similar to madison, a Debian tool that checks
for package versions and reports their status. This option
works locally and doesn’t require access to the Debian
project’s internal archive.
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pkgnames [prefix]
Print a list of packages in the system. If prefix is specified,
print only packages whose names begin with that prefix. Most
useful with the --generate option.
policy [pkgs]
Print detailed information about the priority selection of each
specified package. With no arguments, print the priorities of
all sources. Useful for debugging issues related to the prefer-
ences file.
rdepends [pkgs]
Show a list of reverse dependencies for each specified package—
i.e., list any packages that depend on the specified packages.
search regex
Search package names and descriptions of all available
package files for the specified regular expression and print
the name and short description of each matching package.
With --full, the output is identical to that from the show
command. With --names-only, only the package name is
searched. Multiple regular expressions can be specified.
Useful for finding packages when you don’t know the actual
package name.
show pkgs
Display the package records for each specified package. See
the -a option for more details.
showpkg pkgs
Display information about the specified packages. For each
package, the output includes the available versions, packages
that depend on this package, and packages that this package
depends on.
showsrc pkgs
Display source package records for each specified package.
stats
Display statistics about the cache.
unmet
Display the unmet dependencies in the package cache.
Options
-a, --all-versions
Print full records for all available versions. For use with the show
command. The default is to show all versions; use with --no-all-
versions to display only the version that would be installed. The
configuration option is APT::Cache::AllVersions.
--all-names
Cause pkgnames to print all names, including virtual pack-
ages and missing dependencies. The configuration option is
APT::Cache::AllNames.
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Package
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-c file, --config-file=file
Specify a configuration file to be read after the default configu-
ration file.
-f, --full
Print full package records when searching. The configuration
option is APT::Cache::ShowFull.
-g, --generate
Automatically regenerate the package cache rather than using
the current cache. Default is to regenerate; turn it off with --no-
generate. The configuration option is APT::Cache::Generate.
-h, --help
Print usage information and exit.
-i, --important
Print only important dependencies (Depends and Pre-Depends
relations). For use with unmet. The configuration option is
APT::Cache::Important.
--installed
Only produce output for currently installed packages. For use
with depends and rdepends. The configuration option is
APT::Cache::Installed.
-n, --names-only
Search only on package names, not long descriptions. The
configuration option is APT::Cache::NamesOnly.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-p file, --pkg-cache=file
Use the specified file for the package cache, the primary cache
used by all operations. The configuration option is
Dir::Cache::pkgcache.
-q, --quiet
Operate quietly, producing output for logging but no progress
indicators. Use -qq for even quieter operation. The configura-
tion option is quiet.
--recurse
Run depends or rdepends recursively, so all specified pack-
ages are printed once. The configuration option is
APT::Cache::RecurseDepends.
-s file, --src-cache=file
Specify the source cache file used by gencaches. The configu-
ration option is Dir::Cache::srcpkgcache.
-v, --version
Print version information and exit.
apt-cdrom apt-cdrom [options]command
Add a new CD or DVD to apt’s list of available sources. The data-
base of CD-ROM IDs that apt maintains is /var/lib/apt/cdroms.list.
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Commands
add
Add a disk to the source list.
ident
Print the identity of the current disk and the stored filename.
Used for debugging.
Options
-a, --thorough
Do a thorough package scan. May be needed with some old
Debian CDs to find all package locations.
-c file, --config-file=file
Specify a configuration file to be read after the default configu-
ration file.
-d mount-point, --cdrom=mount-point
Specify the CD-ROM mount point, which must be listed in /etc/
fstab. The configuration option is Acquire::cdrom::mount.
-f, --fast
Do a fast copy, assuming the files are valid and don’t all need
checking. Specify this only if the disk has been run before
without error. The configuration option is APT::CDROM::Fast.
-h, --help
Print help message and exit.
-m, --no-mount
Don’t mount or unmount the mount point. The configuration
option is APT::CDROM::NoMount.
-n, --just-print, --recon, --no-act
Check everything, but don’t actually make any changes. The
configuration option is APT::CDROM::NoAct.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-r, --rename
Prompt for a new label and rename the disk to the new value.
The configuration option is APT::CDROM::Rename.
-v, --version
Print the version information and exit.
apt-config apt-config [options] shellargs
apt-config [options] dump
An internal program for querying configuration information,
accessing the main configuration file /etc/apt/apt.conf.
Commands
dump
Display the contents of the configuration space.
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Package
Management
shell
Access the configuration information from a shell script. The
arguments are in pairs, specifying the name of a shell variable
and a configuration value to query. The value may be post-
fixed with /x, where x is one of the following letters:
b Return true or false.
d Return directories.
f Return filenames.
i Return an integer.
Options
-c file, --config-file=file
Specify a configuration file to be read after the default configu-
ration file.
-h, --help
Print help message and exit.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-v, --version
Print the version information and exit.
apt-
extracttemplates
apt-extracttemplates [options]files
Extract configuration scripts and templates from the specified
Debian package files. For each specified file, a line of output is
generated with the following information:
package version template-file config-script
and the template files and configuration scripts are written to the
directory specified with -t or --temp-dir, or by the configuration
option APT::ExtractTemplates::TempDir. The filenames are in the
form package.template.xxxx and package.config.xxxx.
Options
-c file, --config-file=file
Specify a configuration file to be read after the default configu-
ration file.
-h, --help
Print help message and exit.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-t dir, --tempdir=dir
Write the extracted template files and configuration scripts to
the specified directory. The configuration option is
APT::ExtractTemplates::TempDir.
-v, --version
Print the version information and exit.
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apt-ftparchive apt-ftparchive [options]command
Generate package and other index files used to access a distribution
source. The files should be generated on the source’s origin site.
Commands
clean config-file
Clean the databases used by the specified configuration file by
removing obsolete records.
contents path
Search the specified directory tree recursively to generate a
contents file. For each .deb file found, read the file list, sort the
files by package, and write the results to standard output. Use
with --db to specify a binary caching database.
generate config-file sections
Build indexes according to the specified configuration file.
packages path [override [pathprefix]]
Generate a package file from the specified directory tree. The
optional override file contains information describing how
the package fits into the distribution, and the optional path
prefix is a string prepended to the filename fields. Similar to
dpkg-scanpackages. Use with --db to specify a binary caching
database.
release path
Generate a release file from the specified directory tree.
sources paths [override [pathprefix]]
Generate a source index file from the specified directory tree.
The optional override file contains information used to set
priorities in the index file and to modify maintainer informa-
tion. The optional path prefix is a string prepended to the
directory field in the generated source index. Use --source-
override to specify a different source override file. Similar to
dpkg-scansources.
Options
-c file, --config-file=file
Specify a configuration file to be read after the default configu-
ration file.
--contents
Perform contents generation. If set and if package indexes are
being generated with a cache database, the file listing is
extracted and stored in the database. If used with generate,
allows the creation of any contents files. The default is on. The
configuration option is APT::FTPArchive::Contents.
-d, --db
Use a binary caching database. This option has no effect on
generate. The configuration option is APT::FTPArchive::DB.
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Package
Management
--delink
Enable delinking of files when used with the External-Links
setting. The default is on; turn off with --no-delink. The
configuration option is APT::FTPArchive::DeLinkAct.
-h, --help
Print help message and exit.
--md5
Generate MD5 sums for the index files. The default is on. The
configuration option is APT::FTPArchive::MD5.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-q, --quiet
Run quietly, producing logging information but no progress
indicators. Use -qq for quieter operation. The configuration
option is quiet.
--read-only
Make the caching databases read-only. The configuration
option is APT::FTPArchive::ReadOnlyDB.
-s file, --source-override=file
Specify a source override file. Use with the sources command.
See the sources command description for more information. The
configuration option is APT::FTPArchive::SourceOverride.
-v, --version
Print the version information and exit.
apt-get apt-get [options]command [package...]
A command-line tool for handling packages. Also serves as a
backend to other APT tools such as dselect, synaptic, and aptitude
(all described later in this section).
Commands
autoclean
Like clean, but remove only package files that can no longer be
downloaded. Set the configuration option APT::Clean-Installed
to off to prevent installed packages from being erased.
autoremove
Remove packages that were automatically installed to satisfy a
dependency and are no longer needed.
build-dep
Install or remove packages to satisfy the build dependencies
for a source package.
clean
Clear the local repository of retrieved package files. Useful for
freeing up disk space.
check
Update the package cache and check for broken dependencies.
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dist-upgrade
Like upgrade, but also handle changing dependencies for new
package versions intelligently. See the -f option for more
information.
dselect-upgrade
Used with dselect. Track the changes made by dselect to the
Status field of available packages and take actions necessary to
realize that status.
install packages
Install one or more packages. Specify the package name, not
the full filename. Other required packages are also retrieved
and installed. With a hyphen appended to the package name,
the package is removed if it is already installed. Select a
version to install by appending an equals sign and the version.
Select a distribution to install by appending a slash and the
distribution.
purge packages
Like remove, but also purge the specified packages from the
system.
remove packages
Remove one or more packages. Specify the package name, not
the full filename. With a plus sign appended to the name, the
package is installed.
source packages
Find source packages and download them into the current
directory. If specified with --compile, the source packages are
compiled into binary packages. With --download-only, the
source packages are not unpacked. Select a specific version by
appending an equals sign and the version.
update
Resynchronize the package overview files from their sources.
Must be done before an upgrade or dist-upgrade.
upgrade
Install the latest versions of all packages currently installed.
Run update first.
Options
--arch-only
Process only architecture-dependent build dependencies.
Configuration option is APT::Get::Arch-Only.
--auto-remove
With install or remove, remove unused dependencies; like
running the autoremove command. Configuration option is
APT::Get::AutomaticRemove.
-b, --compile, --build
Compile source packages after download. The configuration
option is APT::Get::Compile.
-c file, --config-file=file
Specify a configuration file to read after the default.
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Package
Management
-d, --download-only
Retrieve package files, but don’t unpack or install them. The
configuration option is APT::Get::Download-only.
--diff-only
Download only the diff file from a source archive. The config-
uration option is APT::Get::Diff-Only.
--dsc-only
Download only the dsc file from a source archive. The configu-
ration option is APT::GET::Dsc-Only.
-f, --fix-broken
Try to fix a system with broken dependencies. Can be used
alone or with a command. Run with the install command if
you have problems installing packages. You can run the
sequence:
apt-get -f install
apt-get dist-upgrade
several times to clean up interlocking dependency problems.
The configuration option is APT::Get::Fix-Broken.
--force-yes
Force yes. Cause apt to continue without prompting even if it
is doing something that could damage your system. Use with
great caution and only if absolutely necessary. The configuration
option is APT::Get::force-yes.
-h, --help
Display a help message and exit.
--ignore-hold
Ignore a hold placed on a package, which would normally
prevent the package from being upgraded. Use with dist-upgrade
to override many undesired holds. The configuration option is
APT::Get::Ignore-Hold.
--list-cleanup
Erase obsolete files from /var/lib/apt/lists. The default is on;
use --no-list-cleanup to turn it off, which you would normally
do only if you frequently modify your list of sources. The
configuration option is APT::Get::List-Cleanup.
-m, --ignore-missing, --fix-missing
Ignore missing or corrupted packages or packages that cannot
be retrieved. Can cause problems when used with -f. The
configuration option is APT::Get::Fix-Missing.
--no-download
Disable package downloading; use with --ignore-missing to
force APT to use only the packages that have already been
downloaded. The configuration option is APT::Get::Download.
--no-remove
Do not remove any packages; instead, abort without
prompting. The configuration option is APT::Get::Remove.
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--no-upgrade
Do not upgrade packages. Use with install to prevent upgrade
of packages that are already installed. The configuration
option is APT::Get::Upgrade.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
--only-source
Do not map the names specified with the source or build-dep
commands through the binary table. With this option, only
source package names can be specified. The configuration
option is APT::Get::Only-Source.
--print-uris
Print Uniform Resource Indicators (URIs) of files instead of
fetching them. Prints path, destination filename, size, and
expected MD5 hash. The configuration option is
APT::Get::Print-URIs.
--purge
Tell dpkg to do a purge instead of a remove for items that
would be removed. Purging removes packages completely,
including any configuration files. The configuration option is
APT::Get::Purge.
-q, --quiet
Quiet mode. Omit progress indicators and produce only
logging output. Use -qq to make even quieter. The configura-
tion option is quiet.
--reinstall
Reinstall packages that are already installed, upgrading them
to the latest version. The configuration option is
APT::Get::ReInstall.
-s, --simulate, --just-print, --dry-run, --recon, --no-act
Go through the motions, but don’t actually make any changes
to the system. The configuration option is APT::Get::Simulate.
-t rel, --target-release=rel, --default-release=rel
Retrieve packages only from the specified release. The value of
rel can be a release number or a value such as “unstable.” The
configuration option is APT::Default-Release.
--tar-only
Download only the tar file from a source archive. The configu-
ration option is APT::Get::Tar-Only.
--trivial-only
Perform only operations that are considered trivial—i.e., ones
that won’t harm your system, by, say, removing needed files.
Unlike --assume-yes, which always answers “yes” to any
prompts, --trivial-only always answers “no.” The configura-
tion option is APT::Get::Trivial-Only.
-u, --show-upgraded
Print a list of all packages to be upgraded. The configuration
option is APT::Get::Show-Upgraded.
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Package
Management
-v, --version
Display the version and exit.
-V, --verbose-versions
Show full versions for upgraded and installed packages. The
configuration option is APT::Get::Show-Versions.
-y, --yes, --assume-yes
Automatically reply “yes” to prompts and run noninterac-
tively. Abort if there is an error. The configuration option is
APT::Get::Assume-Yes.
apt-sortpkgs apt-sortpkgs [options]indexfiles
Sort the records in a source or package index file by package name
and write the results to standard output. apt-sortpkgs also sorts
the internal fields of each record.
Options
-c file, --config-file=file
Specify a configuration file to read after the default.
-h, --help
Display a help message and exit.
-o, --option
Set a configuration option. Syntax is -o group::tool=option.
-s, --source
Order by source index field. The configuration option is
APT::SortPkgs::Source.
-v, --version
Display the version and exit.
aptitude aptitude [options] [action [arguments]]
A text-based frontend to apt, which can be run either directly from
the command line or from a visual mode that runs in a terminal
window.
Actions
The following actions are supported. Running aptitude with no
action invokes the visual mode. Package names can be entered indi-
vidually or as search patterns. A search pattern consists of terms
starting with a tilde (~), followed by a character indicating the type
of term, followed by the text to be searched for. The most common
usage is to use ~n to search for a package name (e.g., ~nemacs, to
search for packages that have emacs in their name). You can find
the full list of term types in the Aptitude User’s Manual. The
manual can be found in /usr/share/doc/aptitude/README on a
Debian-based system. On an RPM-based system with aptitude
installed, the README file may be in /usr/share/aptitude or /usr/
share/doc/aptitude.
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autoclean
Clean out the cache by removing only packages that can no
longer be downloaded.
changelog package[=version | /archive] ...
Download and display the Debian changelog for each specified
package.
clean
Clean out the cache by removing all previously down-
loaded .deb files.
download package[=version | /archive] ...
Download the .deb file for each specified package to the
current directory. With a version, install that version; with an
archive, install the version from that archive.
forbid-version package[=version] ...
Don’t allow aptitude to upgrade the package to a particular
version. If no version is specified, it is assumed to be the
version that would normally be used. To override later, use
the install action.
forget-new
Remove internal information about what packages are “new.”
full-upgrade
Upgrade as many installed packages as possible, installing and
removing packages as needed to satisfy dependencies.
Formerly called dist-upgrade, which is now deprecated.
help
Display help information and exit.
hold packages
Place a hold on each specified package.
install [package[=version | /archive] ...]
Install the specified packages. With a version, install that
version. With an archive, install the version in that archive.
With no arguments, install any stored or pending actions. You
can also use install to perform different actions on multiple
packages with a single command. Append - to the package
name to remove, + to install, _ to purge, = to hold a package, or
: to leave the package at the current version.
keep packages
Cancel any scheduled action on the specified packages.
keep-all
Cancel all scheduled actions on all packages.
markauto packages
Mark the specified packages as automatically installed.
purge [package[=version] ...]
Remove the specified packages and their configuration files.
remove [package[=version] ...]
Remove the specified packages.
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Package
Management
safe-upgrade
Upgrade as many packages as possible; if a package has
dependency problems, avoid upgrading that package (but
don’t remove it).
search patterns
Search for packages matching each of the specified patterns
and display a list of matches. The full list of search terms can
be found in the Aptitude User’s Manual.
show patterns
Search for packages matching each of the specified patterns
and display detailed information for every match found.
unhold packages
Remove the hold on each specified package.
unmarkauto packages
Mark the specified packages as manually installed.
update
Update the list of available packages by downloading the
names of new and upgradeable packages.
why, why-not packages
Display reasons why the specified packages can or cannot be
installed.
Options
Most of the aptitude options have corresponding configuration
options that can be set in the configuration file.
-d, --download-only
Download packages to the cache but do not install them.
Configuration option is Aptitude::CmdLine::Download-Only.
-D, --show-deps
Show summaries of why packages will be automatically installed
or removed. Configuration option is Aptitude::CmdLine::Show-
Deps.
-f Attempt to fix dependencies of broken packages. Configuration
option is Aptitude::CmdLine::Fix-Broken.
-F format, --display-format format
Specify the output format for search. See the Aptitude User’s
Manual for details on specifying the format. Configuration
option is Aptitude::CmdLine::Package-Display-Format.
-h, --help
Print help message and exit.
-O order, --sort order
Specify the sort order for search output. See the Aptitude
User’s Manual for details.
-P, --prompt
Always display a prompt even for actions that were explicitly
requested. The corresponding configuration option is
Aptitude::CmdLine::Always-Prompt.
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--purge-unused
Purge packages that are no longer required by any installed
package.
-q[=n], --quiet[=n]
Run in quiet mode, suppressing progress indicators. Use
multiple qs to run even quieter, or specify a number n to indi-
cate directly the degree of quietness.
-r, --with-recommends
Treat recommendations as dependencies when installing new
packages. The corresponding configuration option is Apti-
tude::CmdLine::Recommends-Important.
-R, --without-recommends
Do not treat recommendations as dependencies when
installing new packages. The corresponding configuration
option is Aptitude::CmdLine::Recommends-Important.
-s, --simulate
Go through the motions, but do not actually perform the
actions. Print the actions that would be performed. Configura-
tion option is Aptitude::Simulate.
--schedule-only
Schedule actions to be performed later, but don’t perform
them now. Works with actions that modify package states; to
run them later, use aptitude install with no arguments.
-t release, --target-release release
Specify the release to use for installing packages. Equivalent to
adding /release to package names for the changelog, down-
load, and show actions.The corresponding configuration
option is Aptitude::CmdLine::Default-Release.
-v, --verbose
Operate verbosely, displaying additional information.
Specify multiple times to get even more information
displayed. The corresponding configuration option is
Aptitude::CmdLine::Verbose.
-V, --show-versions
Display the version for packages being installed. Configura-
tion option is Aptitude::CmdLine::Show-Versions.
--version
Display the version information for aptitude and exit.
--visual-preview
Start the visual interface and display the preview screen.
-w width, --width width
Specify the output display width for search. The default is the
terminal width. The corresponding configuration option is
Aptitude::CmdLine::Package-Display-Width.
-y, --assume-yes
Assume a yes response to a yes/no prompt and don’t display
the prompt. Prompts for dangerous actions are still shown.
This option overrides -P. The corresponding configuration
option is Aptitude::CmdLine::Assume-Yes.
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-Z Display the disk space that will be used or freed by the pack-
ages being acted upon. The corresponding configuration
option is Aptitude::CmdLine::Show-Size-Changes.
Internal options
The following options are used internally for aptitude’s visual
mode. You shouldn’t need to issue them directly.
-i Display a download preview when the program starts. Cannot
be used with -u.
-S filename
Load extended state information from the specified file, not
the default state file.
-u Begin updating the package lists when the program starts.
Cannot be used with -i.
dpkg dpkg [options]action
A tool for installing, managing, and building packages. Also serves
as a frontend to dpkg-deb and dpkg-query.
dpkg actions
These actions are carried out by dpkg itself:
-A pkgfile, --record-avail pkgfile
Update the record of available files kept in /var/lib/dpkg/
available with information from pkgfile. This information is
used by dpkg and dselect to determine which packages are
available. With -R or --recursive, pkgfile must be a directory.
-C, --audit
Search for partially installed packages and suggest how to get
them working.
--clear-avail
Remove existing information about which packages are available.
--clear-selections
Set the state of every nonessential package to deinstall to
deselect them before running dpkg --set-selections.
--command-fd n
Accept commands passed on the file descriptor given by n.
Note that any additional options set through this file
descriptor or on the command line are not reset, but remain
for other commands issued during the same session.
--compare-versions ver1 op ver2
Perform a binary comparison of two version numbers. The
operators lt le eq ne ge gt treat a missing version as earlier.
The operators lt-nl le-nl ge-nl gt-nl treat a missing version as
later (where nl is “not later”). A third set of operators (< <<
<= = >= >> >) is provided for compatibility with control-file
syntax. dpkg returns zero for success (i.e., the condition is
satisfied) and nonzero otherwise.
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--configure [packages | -a| --pending]
Reconfigure one or more unpacked packages. If -a or --pending
is given instead of packages, configure all packages that are
unpacked but not configured. Configuring a package involves
unpacking the configuration files, backing up the old configu-
ration files, and running the postinst script if one is present.
-Dh, --debug=help
Print debugging help message and exit.
--force-help
Print help message about the --force-list options and exit. See
the --force-list option description for the possible values of list.
--forget-old-unavail
Forget about uninstalled, unavailable packages.
--get-selections [pattern]
Get list of package selections and write to standard output.
With pattern specified, write selections that match the pattern.
--help
Print help message and exit.
-i pkgfile, --install pkgfile
Install the package specified as pkgfile. With -R or --recursive,
pkgfile must be a directory.
--license, --licence
Print dpkg license information and exit.
--print-architecture
Print the target architecture.
--print-installation-architecture
Print the host architecture for installation.
-r, --remove [packages | -a| --pending]
-P, --purge [packages | -a| --pending]
Remove or purge one or more installed packages. Removal
gets rid of everything except the configuration files listed in
debian/conffiles; purging also removes the configuration files.
If -a or --pending is given instead of packages, dpkg removes or
purges all packages that are unpacked and marked (in /var/lib/
dpkg/status) for removing or purging.
--set-selections
Set package selections based on input file read from standard
input.
--unpack pkgfile
Unpack the package, but don’t configure it. When used with -R
or --recursive, pkgfile must be a directory.
--update-avail pkgs-file
--merge-avail pkgs-file
Update the record of available files kept in /var/lib/dpkg/
available. This information is used by dpkg and dselect to
determine what packages are available. Update replaces the
information with the contents of the pkgs-file, distributed as
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Package
Management
Packages. Merge combines the information from Packages
with the existing information. You can also use dselect update
to do the same thing.
--version
Print dpkg version information and exit.
--yet-to-unpack
Search for uninstalled packages that have been selected for
installation.
dpkg-deb actions
The following actions can be specified for dpkg and are passed to
dpkg-deb for execution. Also see dpkg-deb.
-b dir [archive], --build dir [archive]
Build a package.
-c archive, --contents archive
List the contents of a package.
-e archive [dir], --control archive [dir]
Extract control information from a package.
-f archive [control-fields], --field archive [control-fields]
Display the control field or fields of a package.
-I archive [control-files], --info archive [control-files]
Show information about a package.
--fsys-tarfile archive
Write the filesystem tree contained in a package to standard
output in tar format.
-x archive dir, --extract archive dir
Extract the files from a package.
-X archive dir, --vextract archive dir
Extract the files and display the filenames from a package.
dpkg-query actions
The following actions can be specified for dpkg and are passed to
dpkg-query for execution. Also see dpkg-query.
-l, --list [pkg-name-pattern]
List all packages whose names match the specified pattern.
With no pattern, list all packages in /var/lib/dpkg/available.
-L packages, --listfiles packages
List installed files that came from the specified package or
packages.
-p, --print-avail package
Print the details about package from /var/lib/dpkg/available.
-s packages, --status packages
Report the status of one or more packages.
-S filename-pattern, --search filename-pattern
Search installed packages for a filename.
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Options
dpkg options can be specified on the command line or set in the
configuration file. Each line in the configuration file contains a
single option, specified without the leading dash (-).
--abort-after=num
Abort processing after num errors. Default is 50.
--admindir= dir, --instdir= dir, --root=dir
Change default directories. admindir contains administrative
files with status and other information about packages; it
defaults to /var/lib/dpkg. instdir is the directory into which
packages are installed; it defaults to /. Changing the root direc-
tory to dir automatically changes instdir to dir and admindir
to /dir/var/lib/dpkg.
-B, --auto-deconfigure
When a package is removed, automatically deconfigure any
other package that depended on it.
-Doctal, --debug=octal
Turn on debugging, with the octal value specifying the desired
level of debugging information. Use -Dh or --debug=help to
display the possible values. You can OR the values to get the
desired output.
-E, --skip-same-version
Don’t install the package if this version is already installed.
--force-list, --no-force-list, --refuse-list
Force or refuse to force an operation. list is specified as a
comma-separated list of options. With --force, a warning is
printed, but processing continues. --refuse and --no-force
cause processing to stop with an error. Use --force-help to
display a message describing the options. The force/refuse
options are:
all
Turn all force options on or off.
architecture
Process even if intended for a different architecture.
bad-path
Some programs are missing from the path.
bad-verify
Install package even if it fails to verify.
confdef
Always choose the default action for modified configura-
tion files. If there is no default and confnew or confold is
also specified, use that to decide; otherwise, ask the user.
configure-any
Configure any unpacked but unconfigured package that
the package depends on.
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Package
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conflicts
Permit installation of conflicting packages. Can result in
problems from files being overwritten.
confmiss
Always install a missing configuration file. Be careful
using this option, since it means overriding the removal
of the file.
confnew
Always install the new version of a modified configura-
tion file, unless confdef is also specified. In that case, use
the default action if there is one.
confold
Keep the old version of a modified configuration file,
unless confdef is also specified. In that case, use the
default action if there is one.
depends
Turn dependency problems into warnings.
depends-version
Warn of version problems when checking dependencies,
but otherwise ignore.
downgrade
Install even if a newer version is already installed. Forced
by default. Note that no dependency checking is done, so
use of this option can cause serious system problems.
hold
Process packages even if they are marked to be held.
not-root
Try to install or remove even when not logged on as root.
overwrite
Overwrite a file from one package with the same file from
another package.
overwrite-dir
Overwrite one package’s directory with a file from
another package.
overwrite-diverted
Overwrite a diverted file with an undiverted version.
remove-essential
Remove a package even if it is essential. Note that this
can cause your system to stop working.
remove-reinstreq
Remove a package even if it is broken and is marked to
require reinstallation.
-G, --refuse-downgrade
Don’t install a package if a newer version is already installed.
--ignore-depends=pkglist
Dependency problems result only in a warning for the pack-
ages in pkglist.
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588 | Chapter5: Package Management
--log=filename
Log status updates and actions to the specified file instead of
the default /var/log/dpkg.log.
--new
New binary package format. This is a dpkg-deb option.
--no-act, --dry-run, --simulate
Go through the motions, but don’t actually write any changes.
Used for testing. Be sure to specify before the action; otherwise,
changes might be written.
--nocheck
Ignore the contents of the control file when building a package.
This is a dpkg-deb option.
--no-debsig
Do not verify package signatures.
-O, --selected-only
Process only packages that are marked as selected for
installation.
--old
Old binary package format. This is a dpkg-deb option.
-R, --recursive
Recursively handle .deb files found in the directories and
their subdirectories specified with-A, -i, --install, --unpack,
and --avail.
--status-fd n
Send the package status information to the specified file
descriptor. Can be given more than once.
dpkg-deb dpkg-debaction [options]
Backend command for building and managing Debian package
archives. Also see dpkg; you’ll often want to use dpkg to pass
commands through to dpkg-deb, rather than call dpkg-deb
directly.
Actions
-b dir [archive], --build dir [archive]
Create an archive from the filesystem tree starting with direc-
tory dir. The directory must have a DEBIAN subdirectory
containing the control file and any other control information.
If archive is specified and is a filename, the package is written
to that file; if no archive is specified, the package is written to
dir.deb. If the archive already exists, it is replaced. If archive is
the name of a directory, dpkg-deb looks in the control file for
the information it needs to generate the package name. (Note
that for this reason, you cannot use --nocheck with a direc-
tory name.)
-c archive, --contents archive
List the filesystem-tree portion of archive.
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Package
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-e archive [dir], --control archive [dir]
Extract control information from archive into the directory dir,
which is created if it doesn’t exist. If dir is omitted, a DEBIAN
subdirectory in the current directory is used.
-f archive [control-fields], --field archive [control-fields]
Extract information about one or more fields in the control file
for archive. If no fields are provided, print the entire control
file.
-h, --help
Print help information and exit.
-I archive [control-files], --info archive [control-files]
Write information about binary package archive to standard
output. If no control files are provided, print a summary of the
package contents; otherwise, print the control files in the
order they were specified. An error message is printed to stan-
dard error for any missing components.
--fsys-tarfile archive
Extract the filesystem tree from archive, and send it to stan-
dard output in tar format. Can be used with tar to extract
individual files from an archive.
--license, --licence
Print the license information and exit.
--version
Print the version number and exit.
-W archive, --showarchive
Show information about the specified archive. Display package
name and version on one line or customize with the --show-
format option.
-x archive dir, --extract archive dir
-X archive dir, --vextract archive dir
Extract the filesystem tree from archive into the specified
directory, creating dir if it doesn’t already exist. -x (--extract)
works silently, while -X (--vextract) lists the files as it extracts
them. Do not use this action to install packages; use dpkg
instead.
Options
-D, --debug
Turn on debugging.
--new
Build a new-style archive format (this is the default).
--nocheck
Don’t check the control file before building an archive. This
lets you build a broken archive.
--old
Build an old-style archive format; obsolete.
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590 | Chapter5: Package Management
--showformat=format
Specify the output format for -W/--show. The format can
include the standard escape sequences \n (newline), \r
(carriage return), or \\ (backslash). Specify package fields with
the syntax ${var[;width]}. Fields are right-aligned by default,
or left-aligned if width is negative.
-z#
Set the compression level to the value specified by # when
building an archive.
-Z type
Set the type of compression to use when building an archive.
Possible values are gzip, bzip2, and none.
dpkg-query dpkg-query [option]command
Display information about packages listed in the dpkg database.
You can also use dpkg-query as a backend for dpkg, instead of
calling dpkg-query directly.
Commands
--help
Print help information and exit.
-l [patterns], --list [patterns]
List packages whose names match any of the specified
patterns. With no pattern specified, list all packages in /var/lib/
dpkg/status. The pattern may need to be in quotes to avoid
expansion by the shell.
-L packages, --listfiles packages
List files installed on your system from each of the specified
packages. This command does not list files created by
package-specific installation scripts.
--license, --licence
Print the license information and exit.
-p package, --print-avail package
Display details for the specified package, as found in /var/lib/
dpkg/available.
-s package, --status package
Report on the status of the specified package.
-S patterns, --search patterns
Search the installed packages for filenames matching one of
the specified patterns. At least one pattern must be specified.
-W [patterns], --show [patterns]
Like -l, but the output can be customized with the --showformat
option.
--version
Print version information and exit.
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Package
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Options
--admindir=dir
Use dir as the location of the dpkg database. The default is /var/
lib/dpkg.
-fformat, --showformat=format
Specify the output format for -W/--show. The format can
include the standard escape sequences \n (newline), \r
(carriage return), or \\ (backslash). Specify package fields with
the syntax ${var[;width]}. Fields are right-aligned by default,
or left-aligned if width is negative.
dpkg-split dpkg-split [action] [options]
Split a binary package into smaller pieces and reassemble the
pieces, either manually or in automatic mode. The automatic mode
maintains a queue of parts for reassembling.
Actions
-a -o output part, --auto -o output part
Add part to the queue for automatic reassembly, and if all the
parts are available, reassemble the package as output. Requires
the use of the -o (or --output) option, as shown.
-d [packages], --discard [packages]
Discard parts from the automatic-assembly queue. If any pack-
ages are specified, discard only parts from those packages.
Otherwise, empty the queue.
-I parts, --info parts
Print information about the specified part file or files to stan-
dard output.
-j parts, --join parts
Join the parts of a package file together from the parts speci-
fied. The default output file is package-version.deb.
-l, --listq
List the contents of the queue of parts waiting for reassembly,
giving the package name, the parts that are on the queue, and
the number of bytes.
-s full-package [prefix], --split full-package [prefix]
Split the package full-package into parts N of M, named prefix-
NofM.deb. The prefix defaults to the full-package name
without the .deb extension.
-h, --help
Print help message and exit.
--license, --licence
Print license information and exit.
--version
Print version information and exit.
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Options
--depotdir dir
Specify an alternate directory dir for the queue of parts waiting
for reassembly. Default is /var/lib/dpkg.
--msdos
Force --split output filenames to be MS-DOS-compatible.
-Q, --npquiet
Do not print an error message for a part that doesn’t belong to
a binary package when doing automatic queuing or reassembly.
-o output, --output output
Use output as the filename for a reassembled package.
-S num, --partsize num
When splitting, specify the maximum part size (num) in kilo-
bytes. Default is 450 KB.
dselect dselect [options] [action]
A screen-oriented user frontend to dpkg, used to install and
manage packages. See dpkg and dpkg-deb for information on
building packages.
Actions
If dselect is run with no action specified on the command line, it
displays the following menu:
* 0. [A]ccess Choose the access method to use.
1. [U]pdate Update list of available packages, if
possible.
2. [S]elect Request which packages you want on your
system.
3. [I]nstall Install and upgrade wanted packages.
4. [C]onfig Configure any packages that are
unconfigured.
5. [R]emove Remove unwanted software.
6. [Q]uit Quit dselect.
The asterisk (on the first line) shows the currently selected option.
Any of the menu items can be specified directly on the command
line as an action (access, update, select, install, config, remove,
quit) to go directly to the desired activity. For example:
$dselect access
If you enter quit on the command line, dselect exits immediately
without doing anything. An additional command-line action is
menu, which displays the menu and is equivalent to running
dselect with no action.
Options
Options can be specified both on the command line and in the
dselect configuration file, /etc/dpkg/dselect.cfg.
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Package
Management
--admindir dir
Change the directory that holds internal datafiles to dir.
Default is /var/lib/dpkg.
--color colorspec, --colour colorspec
Set colors for different parts of the screen, as specified by
colorspec as follows:
screenpart:[fgcolor],[bgcolor][:attr[+attr+...]]
This option can be specified multiple times, to override the
default colors for different screenparts. Rather than having to
specify the colors on the command line each time you run
dselect, you might prefer to set them in the configuration file.
The possible screen parts (going from the top of the screen to
the bottom) are:
title
The screen title.
listhead
The header line above the package list.
list
The scrolling list of packages and some help text.
listsel
The selected item in the list.
pkgstate
The text showing the current state of each package.
pkgstatesel
The text showing the current state of the selected
package.
infohead
The header line showing the state of the selected package.
infodesc
The short description of the package.
info
The text that displays information such as the package
description.
infofoot
The last line of the screen when selecting packages.
query
Query lines.
helpscreen
The color of help screens.
Either the foreground color, the background color, or both
can be specified for each screen part. The colors are given as
the standard curses colors. After the color specification, you
can specify a list of attributes separated by plus signs (+). The
possible attributes are normal, standout, underline, reverse,
blink, bright, dim, and bold. Not all attributes work on all
terminals.
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594 | Chapter5: Package Management
--expert
Run in expert mode; don’t print help messages.
-D [file], --debug [file]
Turn on debugging. Send output to file if specified.
--help
Print help message and exit.
--license, licence
Print license information and exit.
--version
Print version information and exit.
synaptic synaptic [options]
Graphical frontend for APT. Use in place of apt-get to install,
upgrade, or remove packages from your system. With synaptic,
you can view a list of all available packages, or you can break the
list down in various ways to make it more manageable. From the
synaptic window, you can select from a list of categories. The cate-
gories are section (e.g., view only development-related packages),
package status, origin, search history, or filter.
If you choose to display by filter, there is a set of predefined filters,
or you can define your own. The predefined filters include ones to
display all packages, packages marked for a status change, pack-
ages that can be configured with debconf (Debian systems only),
packages with broken dependencies, and packages that can be
upgraded to a later version. You can edit the existing filters or
define your own, by selecting Filters from the Settings menu.
Once you’ve used the selection criteria to find the list of packages,
you can select a single package, or you can select multiple pack-
ages by holding down the Shift or Ctrl key. Like apt-get, first do an
update to update the package lists, then you can do an install or
upgrade.
To start synaptic from Gnome, select Administration ➝ Synaptic
Package Manager from the System menu. From the KDE menu,
select System ➝ Synaptic Package Manager. You can also start the
graphical interface from the command line, with the command:
synaptic [options]
Options
In addition to the following options, synaptic accepts the standard
GTK+ toolkit command-line options.
-f filename, --filter-file=filename
Use the specified file as an alternative filter settings file.
-h, --help
Print help message and exit.
-i num, --initial-filter=num
Start up with the filter numbered num as the initial filter.
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Package
Management
--non-interactive
Run without prompting for user input.
-ooption, --option=option
Set an internal option. Don’t use this option unless you are
sure you know what you are doing.
-r Open with the file repository window displayed. This window
lists the repositories and shows which are active.
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596
Chapter 6The Bash Shell
6
The Bash Shell
The shell is a program that acts as a buffer between you and the operating system.
In its role as a command interpreter, it should (for the most part) act invisibly.
There are three main uses for the shell: interactive use; customizing your Linux
session by defining variables and startup files; and programming, by writing and
executing shell scripts.
The original Bourne shell became the standard shell for writing shell scripts. The
Bourne shell is still found in /bin/sh on Linux systems but is now usually a
symbolic link to Bash. Because the Berkeley C shell (csh and later tcsh) offered
better features for interactive use, such as command history and job control, for a
long time the standard practice was to use the Bourne shell for programming and
the C shell for daily use. David Korn at Bell Labs enhanced the Bourne shell by
adding csh-like features; his shell is known as the Korn shell (ksh).
The Free Software Foundation developed a clone of the Bourne shell, written from
scratch, named “Bash,” the Bourne-Again SHell. Over time, Bash has become a
POSIX-compliant version of the shell, incorporating many popular features from
other shells, such as csh, tcsh, and ksh. Bash is the primary shell for Linux.
Another popular shell is the Z Shell, zsh, which is similar to ksh but with many
extensions. zsh differs from Bash both in being based on ksh and because it does
not attempt to be POSIX-compliant the way Bash does.
This chapter covers Bash. All references are to Bash version 4, which among
numerous other changes includes new features such as associative arrays and
coprocesses. The following topics are presented:
• Overview of features
• Invoking the shell
• Syntax
• Functions
• Variables
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Invoking the Shell | 597
The Bash Shell
• Arithmetic expressions
• Command history
• Job control
• Command execution
• Restricted shells
• Built-in commands
http://www.gnu.org/software/bash/bash.html provides information about the Bash
shell, as does http://tiswww.case.edu/php/chet/bash/bashtop.html. See also Classic
Shell Scripting and Learning the bash Shell (both from O’Reilly).
Overview of Features
The Bash shell provides the following features:
• Input/output redirection
• Wildcard characters (metacharacters) for filename abbreviation
• Shell variables and options for customizing your environment
• A built-in command set for writing shell programs
• Shell functions, for modularizing tasks within a shell program
• Job control
• Command-line editing (using the command syntax of either vi or emacs)
• Access to previous commands (command history)
• Integer arithmetic
• Arrays and arithmetic expressions
• Command-name abbreviation (aliasing)
• Upward compliance with POSIX
• Internationalization facilities
• An arithmetic for loop
• More ways to substitute variables
Invoking the Shell
The command interpreter for the Bash shell (bash) can be invoked as follows:
bash [options] [arguments]
Bash can execute commands from a terminal, from a file (when the first argument
is an executable script), or from standard input (if no arguments remain or if -s is
specified). Bash automatically prints prompts if standard input is a terminal, or
if -i is given on the command line.
On Linux systems, /bin/sh is generally a link to Bash. When invoked as sh, Bash acts
more like the traditional Bourne shell: Login shells read /etc/profile and ~/.profile,
and regular shells read $ENV, if it’s set. Full details are available on the bash
manpage.
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598 | Chapter6: The Bash Shell
Options
If both single- and multi-character options appear on the command line, the
multi-character options must appear first.
-, --
End option processing.
-c str
Read commands from string str.
-D, --dump-strings
Print all $"..." strings in the program.
--debugger
Read the debugging profile at startup, turn on the extdebug option to shopt,
and enable function tracing. For use by the Bash debugger.
--dump-po-strings
Same as -D, but output in GNU gettext po (portable object) format.
--help
Print a usage message and exit successfully
-i Create an interactive shell (prompt for input).
--init-file file, --rcfile file
Use file as the startup file instead of ~/.bashrc for interactive shells.
--login
Shell is a login shell.
--noediting
Do not use the readline library for input, even in an interactive shell.
--noprofile
Do not read /etc/profile or any of the personal startup files.
--norc
Do not read ~/.bashrc. Enabled automatically when invoked as sh.
-O option
Enable the shopt built-in command option option.
-p Start up as a privileged user. Don’t read $ENV or $BASH_ENV, don’t import
functions from the environment, and ignore the value of $SHELLOPTS.
--posix
Turn on POSIX mode.
-r, --restricted
Create a restricted shell.
-s Read commands from standard input; output from built-in commands goes
to file descriptor 1 (standard output); all other shell output goes to file
descriptor 2 (standard error).
--verbose
Same as set -v; the shell prints lines as it reads them.
--version
Print a version message and exit.
The remaining options to Bash are listed under the set built-in command.
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Arguments
Arguments are assigned in order to the positional parameters $1, $2, etc. If
the first argument is an executable script, commands are read from it, and the
remaining arguments are assigned to $1, $2, etc. The name of the script is avail-
able as $0.
Syntax
This section describes the many symbols peculiar to the Bash shell. The topics are
arranged as follows:
• Special files
• Filename metacharacters
• Quoting
• Command forms
• Redirection forms
• Coprocesses
Special Files
Bash reads one or more startup files. Some of the files are read only when a shell is
a login shell.
The startup files are, in the order they are read:
1. /etc/profile. Executed automatically at login.
2. The first file found from this list: ~/.bash_profile, ~/.bash_login, or ~/.profile.
Executed automatically at login.
3. ~/.bashrc is read by every shell, after the login files. However, if invoked as sh,
Bash instead reads $ENV.
The getpwnam() and getpwuid() functions are the sources of home directories
for ~name abbreviations. (On single-user systems, the user database is stored
in /etc/passwd. However on networked systems, this information may come from
NIS, NIS+, or LDAP—not your workstation password file.)
Filename Metacharacters
Characters Meaning
* Match any string of zero or more characters.
? Match any single character.
[abc...] Match any one of the enclosed characters; a hyphen can specify a range (e.g.,a-z,A-Z,0-9).
[!abc...], [^abc...] Match any characternot enclosed as above.
~ Home directory of the current user.
~name Home directory of username.
~+ Current working directory ($PWD).
~- Previous working directory ($OLDPWD).
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600 | Chapter6: The Bash Shell
With the extglob option on:
This pattern can be a sequence of patterns separated by |, meaning that the match
applies to any of the patterns. This extended syntax resembles that available in
egrep and awk.
Bash supports the POSIX [[=c=]] notation for matching characters that have the
same weight, and [[.c.]] for specifying collating sequences. In addition, character
classes, of the form [[:class:]], allow you to match the following classes of
characters.
Bash also accepts the [:word:] character class, which is not in POSIX. [[:word:]] is
equivalent to [[:alnum:]_].
Examples
$ls new* List new and new.1
$cat ch? Match ch9 but not ch10
$vi [D-R]* Match files that begin with uppercase D through R
$pr !(*.o|core) | lp Print files that are not object files or core dumps
On modern systems, ranges such as [D-R] are not portable; the sys-
tem’s locale may include more than just the uppercase letters from
D to R in the range.
Quoting
Quoting disables a character’s special meaning and allows it to be used literally, as
itself. The following table displays characters that have special meaning to the
Bash shell.
Characters Meaning
?(pattern) Match zero or one instance ofpattern.
*(pattern) Match zero or more instances ofpattern.
+(pattern) Match one or more instances ofpattern.
@(pattern) Match exactly one instance ofpattern.
!(pattern) Match any strings that don’t matchpattern.
Class Characters matched Class Characters matched
alnum Alphanumeric characters graph Nonspace characters
alpha Alphabetic characters print Printable characters
blank Space or tab punct Punctuation characters
cntrl Control characters space Whitespace characters
digit Decimal digits upper Uppercase characters
lower Lowercase characters xdigit Hexadecimal digits
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Syntax | 601
The Bash Shell
These characters can be used for quoting:
" " Everything between " and " is taken literally, except for the following charac-
ters that keep their special meaning:
$ Variable (or command and arithmetic) substitution will occur.
' Command substitution will occur.
" This marks the end of the double quote.
' ' Everything between ' and ' is taken literally except for another '. You cannot
embed another ' within such a quoted string.
\ The character following a \ is taken literally. Use within " " to escape ", $,
and '. Often used to escape itself, spaces, or newlines.
$" "
Just like " ", except that locale translation is done.
$' '
Similar to ' ', but the quoted text is processed for the following escape
sequences.
Examples
$echo 'Single quotes "protect" double quotes'
Single quotes "protect" double quotes
$echo "Well, isn't that \"special\"?"
Well, isn't that "special"?
Character Meaning
; Command separator
& Background execution
() Command grouping
| Pipe
< > & Redirection symbols
* ? [ ] ~ + - @ ! Filename metacharacters
” ’ \ Used in quoting other characters
` Command substitution
$ Variable substitution (or command or arithmetic substitution)
space tab newline Word separators
Sequence Value Sequence Value
\a Alert \t Tab
\b Backspace \v Vertical tab
\cX Control character X \nnn Octal valuennn
\e Escape \xnn Hexadecimal valuenn
\E Escape \’ Single quote
\f Form feed \” Double quote
\n Newline \\ Backslash
\r Carriage return
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602 | Chapter6: The Bash Shell
$echo "You have `ls | wc -l` files in `pwd`"
You have 43 files in /home/bob
$echo "The value of \$x is $x"
The value of $x is 100
Command Forms
Examples
$nroff file > file.txt & Format in the background
$cd; ls Execute sequentially
$(date; who; pwd) > logfile All output is redirected
$sort file | pr -3 | lp Sort file, page output, then print
$vi `grep -l ifdef *.c` Edit files found by grep
$egrep '(yes|no)' `cat list` Specify a list of files to search
$egrep '(yes|no)' $(cat list) POSIX version of previous
$egrep '(yes|no)' $(< list) Faster, not in POSIX
$grep XX file && lp file Print file if it contains the pattern;
$grep XX file || echo "XX not found" Otherwise, echo an error message
Redirection Forms
The usual input source or output destination can be changed, as seen in the
following sections.
Syntax Effect
cmd& Executecmd in background.
cmd1;cmd2 Command sequence; execute multiplecmds on the same line.
{cmd1;cmd2; } Execute commands as a group in the current shell.
(cmd1;cmd2) Execute commands as a group in a subshell.
cmd1|cmd2 Pipe; use output fromcmd1 as input tocmd2.
cmd1‘cmd2‘ Command substitution; usecmd2 output as arguments tocmd1.
cmd1$(cmd2) POSIX shell command substitution; nesting is allowed.
cmd$((expression)) POSIX shell arithmetic substitution. Use the result ofexpression as argument tocmd.
cmd1&&cmd2 AND;executecmd1andthen(ifcmd1succeeds)cmd2.Thisisa“short-circuit”operation;
cmd2 is never executed ifcmd1 fails.
cmd1||cmd2 OR; execute eithercmd1 or (ifcmd1 fails)cmd2. This is a “short-circuit” operation;
cmd2 is never executed ifcmd1 succeeds.
!cmd NOT; executecmd, and produce a zero exit status ifcmd exits with a nonzero status.
Otherwise, produce a nonzero status whencmd exits with a zero status.
File descriptor Name Common abbreviation Typical default
0 Standard input stdin Keyboard
1 Standard output stdout Screen
2 Standard error stderr Screen
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Syntax | 603
The Bash Shell
Simple redirection
cmd > file
Send output of cmd to file (overwrite).
cmd >> file
Send output of cmd to file (append).
cmd < file
Take input for cmd from file.
cmd << text
The contents of the shell script up to a line identical to text become the stan-
dard input for cmd (text can be stored in a shell variable). This command
form is sometimes called a Here document. Input is usually typed at the
keyboard or in the shell program. Commands that typically use this syntax
include cat, ex, and sed. (If <<- is used, leading tabs are stripped from the
contents of the here document, and the tabs are ignored when comparing
input with the end-of-input text marker.) If any part of text is quoted, the
input is passed through verbatim. Otherwise, the contents are processed for
variable, command, and arithmetic substitutions.
cmd <<< word
Supply text of word, with trailing newline, as input to cmd. (This is known as
a here string, from the free version of the rc shell.)
cmd <> file
Open file for reading and writing on the standard input. The contents are not
destroyed. *
cmd >| file
Send output of cmd to file (overwrite), even if the shell’s noclobber option is
set.
Redirection using file descriptors
*With <, the file is opened read-only, and writes on the file descriptor will fail. With <>, the file is
opened read-write; it is up to the application to actually take advantage of this.
Syntax Effect
cmd>&n Sendcmd output to file descriptorn.
cmdm>&n Same, except that output that would normally go to file descriptorm is sent to file
descriptorn instead.
cmd>&- Close standard output.
cmd<&n Take input forcmd from file descriptorn.
cmdm<&n Same,exceptthatinputthatwouldnormallycomefromfiledescriptormcomesfrom
file descriptorn instead.
cmd<&- Close standard input.
cmd<&n- Move input file descriptorn instead of duplicating it.
cmd>&n- Move output file descriptorn instead of duplicating it.
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604 | Chapter6: The Bash Shell
Multiple redirection
No space should appear between file descriptors and a redirection symbol; spacing
is optional in the other cases.
Examples
$cat part1 > book
$cat part2 part3 >> book
$mail tim < report
$sed 's/^/XX /g' << END_ARCHIVE
>This is often how a shell archive is "wrapped",
>bundling text for distribution. You would normally
>run sed from a shell program, not from the command line.
>END_ARCHIVE
XX This is often how a shell archive is "wrapped",
XX bundling text for distribution. You would normally
XX run sed from a shell program, not from the command line.
To redirect standard output to standard error:
$echo "Usage error: see administrator" 1>&2
The following command sends output (files found) to filelist and error messages
(inaccessible files) to file no_access:
$find / -print > filelist 2>no_access
Coprocesses
A coprocess is a shell command that runs asynchronously in a subshell, connected
to the originating shell by a two-way pipe. Set up a coprocess with the coproc
reserved word:
coproc [ NAME ] command [ redirections ]
The reserved word coproc sets up the pipe to communicate with command and
runs command in the background. NAME is the name of the coprocess (COPROC
by default). If command is a complex command, NAME is optional; with a simple
Syntax Effect
cmd2>file Send standard error tofile; standard output remains the same (e.g., the screen).
cmd>file2>&1 Send both standard error and standard output tofile.
cmd &>>file Append both standard error and standard output tofile.
cmd&>file Same. Preferred form.
cmd>&file Same.
cmd>f12>f2 Send standard output to filef1, standard error to filef2.
cmd| teefiles Send output ofcmd to standard output (usually the terminal) and tofiles. (See the
example in Chapter3 undertee.)
cmd2>&1 | teefiles Send standard output and error output ofcmd to standard output (usually the
terminal) and tofiles.
cmd|& Same ascmd2>&1 | to send standard error through a pipe.
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Functions | 605
The Bash Shell
command, NAME must not be given and the default is used. If any redirections
are specified, they are set up after the pipe has been set up.
The coprocess establishes an array with two values: NAME[0] contains the file
descriptor for command output and NAME[1] contains the file descriptor for
command input. The variable NAME_PID contains the process id of the coprocess.
The return status is the exit status of command. You can use the wait built-in
command to wait for the output of command.
Functions
A shell function is a grouping of commands within a shell script. Shell functions
let you modularize your program by dividing it up into separate tasks. This way
the code for each task need not be repeated every time you need to perform the
task. The POSIX shell syntax for defining a function follows the Bourne shell:
name () {
function body's code come here
}
Functions are invoked just as are regular shell built-in commands or external
commands. The command line parameters $1, $2, and so on receive the func-
tion’s arguments, temporarily hiding the global values of $1, etc. For example:
# fatal --- print an error message and die:
fatal () { # defining function fatal
echo "$0: fatal error:" "$@" >&2 # messages to standard error
exit 1
}
...
if [ $# = 0 ] # not enough arguments
then
fatal "not enough arguments" # call function with message
fi
A function may use the return command to return an exit value to the calling shell
program. Be careful not to use exit from within a function unless you really wish
to terminate the entire program.
Bash allows you to define functions using an additional keyword, function, as
follows:
function fatal {
echo "$0: fatal error:" "$@" >&2 # messages to standard error
exit 1
}
All functions share traps with the “parent” shell (except the DEBUG trap, if func-
tion tracing has been turned on). With the errtrace option enabled (either set -E
or set -o errtrace), functions also inherit the ERR trap. If function tracing has been
enabled, functions inherit the RETURN trap. Functions may have local variables,
and they may be recursive. The syntax used to define a function is irrelevant.
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606 | Chapter6: The Bash Shell
Variables
This section describes the following:
• Variable substitution
• Built-in shell variables
• Other shell variables
• Arrays
• Special prompt strings
Variable Substitution
No spaces should be used in the following expressions. The colon (:) is optional;
if it’s included, var must be nonnull, as well as set.
You can indirectly reference a variable by “aliasing” one variable name to affect
the value of the other:
$greet="hello, world" Create initial variable
$friendly_message=greet Aliasing variable
$echo ${!friendly_message} Use the alias
hello, world
Variable expression Description
var=value ... Set each variablevar to avalue.
${var} Use value ofvar; braces are optional ifvar is separated from the following text. They are
required for array variables.
${var:-value} Usevar if set; otherwise, usevalue.
${var:=value} Usevar if set; otherwise, usevalue and assignvalue tovar.
${var:?value} Usevar if set; otherwise, printvalue and exit (if not interactive). Ifvalue isn’t supplied,
print the phrase “parameter null or not set.”
${var:+value} Usevalue ifvar is set; otherwise, use nothing.
${#var} Use the length ofvar.
${#*}, ${#@} Use the number of positional parameters.
${var#pattern} Usevalueofvarafterremovingpatternfromtheleft.Removetheshortestmatchingpiece.
${var##pattern} Same as#pattern, but remove the longest matching piece.
${var%pattern} Use value ofvar after removingpattern from the right. Remove the shortest matching piece.
${var%%pattern} Same as%pattern, but remove the longest matching piece.
${!prefix*}, ${!prefix@} List of variables whose names begin withprefix.
${var:pos}, ${var:pos:len} Starting at positionpos (0-based) in variablevar, extractlen characters, or rest of string if
nolen.pos andlen may be arithmetic expressions.
${var/pat/repl} Use value ofvar, with first match ofpat replaced withrepl.
${var/pat} Use value ofvar, with first match ofpat deleted.
${var//pat/repl} Use value ofvar, with every match ofpat replaced withrepl.
${var/#pat/repl} Use value ofvar, with match ofpat replaced withrepl. Match must occur at beginning of
the value.
${var/%pat/repl} Use value ofvar, with match ofpat replaced withrepl. Match must occur at end of the value.
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The Bash Shell
Examples
$u=up d=down blank= Assign values to three variables (last is null)
$echo ${u}root Braces are needed here
uproot
$echo ${u-$d} Display value of u or d; since u is set, it’s printed
up
$echo ${tmp-`date`} If tmp is not set, the date command is executed
Thu May 7 02:09:09 EDT 2009
$echo ${blank="no data"} blank is set, so it is printed (a blank line)
$echo ${blank:="no data"} blank is set but null, so the string is printed
no data
$echo $blank blank now has a new value
no data
$tail=${PWD##*/} Take the current directory name and remove the
longest character string ending with /, which
removes the leading pathname and leaves the tail
Built-in Shell Variables
Built-in variables are automatically set by the shell and are typically used inside
shell scripts. Built-in variables can make use of the variable substitution patterns
shown previously. Note that the $ is not actually part of the variable name,
although the variable is always referenced this way.
Variable Description
$# Number of command-line arguments.
$- Options currently in effect (arguments supplied on command line or toset).
$? Exit value of last executed command.
$$ Process number of current process.
$! Process number of last background command.
$0 First word; that is, command name. This will have the full pathname if it was found via a PATH search.
$n Individual arguments on command line (positional parameters). Ifn is greater than 9, it must be
specified as${n}.
$*,$@ All arguments on command line ($1$2 ...).
"$*" All arguments on command line as one string ("$1 $2 ..."). The values are separated by the first
character in the IFS special variable.
"$@" All arguments on command line, individually quoted ("$1" "$2" ...).
$_ Temporary variable; initialized to pathname of script or program being executed. Later, stores the
last argument of previous command. Also stores name of matching MAIL file during mail checks.
HISTCMD The history number of the current command.
LINENO Current line number within the script or function.
OLDPWD Previous working directory (set bycd).
OPTARG Name of last option processed bygetopts.
OPTIND Numerical index of OPTARG.
PPID Process number of this shell’s parent.
PWD Current working directory (set bycd).
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608 | Chapter6: The Bash Shell
In addition, Bash sets the following variables. Many of these variables are for use
by the Bash debugger (see http://bashdb.sourceforge.net) or for providing program-
mable completion (see the section “Programmable Completion” on page 615).
RANDOM[=n] Generate a new random number with each reference; start with integern, if given.
REPLY Default reply, used byselect andread.
SECONDS[=n] Number of seconds since the shell was started, or, ifn is given, number of seconds +n since the
shell started.
Variable Description
BASH The full pathname used to invoke this instance of Bash.
BASH_ARGC Array variable. Each element holds the number of arguments for the corresponding
function or dot-script invocation. Set only in extended debug mode, withshopt -s
extdebug.
BASH_ARGV AnarrayvariablesimilartoBASH_ARGC.Eachelementisoneoftheargumentspassed
toafunctionordot-script.Itfunctionsasastack,withvaluesbeingpushedonateach
call. Thus, the last element is the last argument to the most recent function or script
invocation. Set only in extended debug mode, withshopt -sextdebug.
BASH_COMMAND The command currently executing or about to be executed. Inside a trap handler, it is
the command running when the trap was invoked.
BASH_EXECUTION_STRING The string argument passed to the-c option.
BASH_LINENO Array variable, corresponding to BASH_SOURCE and FUNCNAME. For any given func-
tionnumberi(startingat0),${FUNCNAME[i]}wasinvokedinfile${BASH_SOURCE[i]}
on line${BASH_LINENO[i]}. The information is stored with the most recent function
invocation first.
BASH_REMATCH Array variable, assigned by the=~ operator of the[[ ]] construct. Index0 is the text
that matched the entire pattern. The other indices are the text matched by parenthe-
sized subexpressions. This variable is read-only.
BASH_SOURCE Array variable, containing source filenames. Each element corresponds with those in
FUNCNAME and BASH_LINENO.
BASH_SUBSHELL This variable is incremented by one each time a subshell or subshell environment is
created.
BASH_VERSINFO[0] The major version number, or release, of Bash.
BASH_VERSINFO[1] The minor version number, or version, of Bash.
BASH_VERSINFO[2] The patch level.
BASH_VERSINFO[3] The build version.
BASH_VERSINFO[4] The release status.
BASH_VERSINFO[5] The machine type; same value as in MACHTYPE.
BASH_VERSION A string describing the version of Bash.
COMP_CWORD For programmable completion. Index into COMP_WORDS, indicating the current
cursor position.
COMP_LINE For programmable completion. The current command line.
COMP_POINT For programmable completion. The position of the cursor as a character index in
COMP_LINE.
COMP_WORDBREAKS Forprogrammablecompletion.Thecharactersthatthereadlinelibrarytreatsasword
separators when doing word completion.
COMP_WORDS For programmable completion. Array variable containing the individual words on the
command line.
Variable Description
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The Bash Shell
Other Shell Variables
The following variables are not automatically set by the shell, although many of
them can influence the shell’s behavior. They are typically used in your .profile
file, where you can define them to suit your needs. Variables can be assigned
values by issuing commands of the form:
variable=value
This list includes the type of value expected when defining these variables.
DIRSTACK Array variable, containing the contents of the directory stack as displayed bydirs.
Changing existing elements modifies the stack, but onlypushd andpopd can add or
remove elements from the stack.
EUID Read-only variable with the numeric effective UID of the current user.
FUNCNAME Array variable, containing function names. Each element corresponds with those in
BASH_SOURCE and BASH_LINENO.
GROUPS Array variable containing the list of numeric group IDs in which the current user is a
member.
HISTCMD The history number of the current command.
HOSTNAME The name of the current host.
HOSTTYPE A string that describes the host system.
MACHTYPE A string that describes the host system in the GNUcpu-company-system format.
OSTYPE A string that describes the operating system.
PIPESTATUS An array variable containing the exit statuses of the commands in the most recent
foreground pipeline.
SHELLOPTS Acolon-separatedlistofshelloptions(forset-o).Ifsetintheenvironmentatstartup,
Bash enables each option present in the list.
SHLVL Incremented by one every time a new Bash starts up.
UID Read-only variable with the numeric real UID of the current user.
Variable expression Description
CDPATH=dirs Directories searched bycd; allows shortcuts in changing directories; unset by
default.
COLUMNS=n Screen’s column width; used in line edit modes andselect lists.
COMPREPLY=(words ...) Array variable from which Bash reads the possible completions generated by a
completion function.
EDITOR=file Pathname of line-edit mode to turn on (can end inemacs orvi); used when
VISUAL is not set.
EMACS If the value starts witht, Bash assumes it’s running in an Emacs buffer and
disables line editing.
ENV=file Nameofscriptthatgetsexecutedatstartup;usefulforstoringaliasandfunction
definitions. For example,ENV=$HOME/.bashrc.
FCEDIT=file Editor used byfc command (default is/bin/ed).
FIGNORE=pattern Colon-separated list of patterns describing filenames to ignore when doing file-
name completion.
GLOBIGNORE=patlist Colon-separatedlistofpatternsdescribingthesetoffilenamestoignoreduring
pattern matching.
Variable Description
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610 | Chapter6: The Bash Shell
HISTCONTROL=list Colon-separated list of values controlling how commands are saved in the
historyfile.Recognizedvaluesare:ignoredups,ignorespace,ignoreboth,and
erasedups.
HISTFILE=file File in which to store command history. Default is~/.bash_history.
HISTFILESIZE=n Number of lines to be kept in the history file. This may be different than the
number of commands.
HISTIGNORE=list A colon-separated list of patterns that must match the entire command line.
Matching lines arenot saved in the history file. An unescaped& in a pattern
matches the previous history line.
HISTSIZE=n Number of history commands to be kept in the history file.
HISTTIMEFORMAT=string A format string forstrftime(3) to use for printing timestamps along with
commands from thehistory command. If set (even if null), Bash saves time-
stamps in the history file along with the commands.
HOME=dir Home directory; set bylogin (from/etc/passwd file).
HOSTFILE=file Nameofafileinthesameformatas/etc/hoststhatBashshouldusetofindhost-
names for hostname completion.
IFS='chars' Input field separators; default is space, tab, and newline.
IGNOREEOF=n Numeric value indicating how many successive EOF characters must be typed
before Bash exits. If null or nonnumeric value, default is 10.
INPUTRC=file Initialization file for thereadline library. This overrides the default value of
~/.inputrc.
LANG=dir Default value for locale, used if noLC_* variables are set.
LC_ALL=locale Current locale; overridesLANG and the otherLC_* variables.
LC_COLLATE=locale Locale to use for character collation (sorting order).
LC_CTYPE=locale Locale to use for character class functions.
LC_MESSAGES=locale Locale to use for translating$"..." strings.
LC_NUMERIC=locale Locale to use for the decimal-point character.
LINES=n Screen’s height; used forselect lists.
MAIL=file Default file to check for incoming mail; set bylogin.
MAILCHECK=n Number of seconds between mail checks; default is 600 (10 minutes).
MAILPATH=files One or more files, delimited by a colon, to check for incoming mail. Along with
eachfile,youmaysupplyanoptionalmessagethattheshellprintswhenthefile
increases in size. Messages are separated from the filename by a? character,
and the default message isYou have mail in $_.$_ is replaced with the name
of the file. For example, you might have:
MAILPATH="$MAIL?Ring! Candygram!:/etc/motd?New Login
Message"
OPTERR=n When set to1 (the default value), Bash prints error messages from the built-in
getopts command.
PATH=dirlist One or more pathnames, delimited by colons, in which to search for commands
to execute.
POSIXLY_CORRECT=string When set at startup or while running, Bash enters POSIX mode, disabling
behavior and modifying features that conflict with the POSIX standard.
PROMPT_COMMAND=command If set, Bash executes this command each time before printing the primary
prompt.
PS1=string Primary prompt string; default is$.
PS2=string Secondary prompt (used in multiline commands); default is>.
PS3=string Prompt string inselect loops; default is#?.
Variable expression Description
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The Bash Shell
Arrays
Bash supports one-dimensional arrays. Elements are referenced by an index; the
first element is numbered 0 and there is no upper limit on the number of
elements. Arrays are initialized with a special form of assignment:
message=(hi there how are you today)
where each value (in this example, each word) becomes an element of the array.
Elements may also be assigned individually:
message[0]=hi This is the hard way
message[1]=there
message[2]=how
message[3]=are
message[4]=you
message[5]=today
Declaring arrays is not required. Any valid reference to a subscripted variable can
create an array.
Bash also provides associative arrays, where the indices are strings instead of
numbers. In this case, [ and ] act like double quotes. Associative arrays are created
with declare -A arrayname. Unlike indexed arrays, when assigning a value to an
associative array, a subscript is always required.
When referencing arrays, use the ${ ... } syntax. This isn’t needed when refer-
encing arrays inside (()) (the form of let that does automatic quoting). Note that [
and ] are typed literally (i.e., they don’t stand for optional syntax).
PS4=string Prompt string for execution trace (bash -x orset -x); default is+.
SHELL=file Name of default shell (e.g.,/bin/bash). Bash sets this if it’s not in the environ-
ment at startup.
TERM=string Terminal type.
TIMEFORMAT=string A format string for the output for thetime keyword.
TMOUT=n If no command is typed aftern seconds, exit the shell. Also affects theread
command and theselect loop.
VISUAL=path Same as EDITOR, but VISUAL is checked first.
auto_resume=list Enables the use of simple strings for resuming stopped jobs. With a value of
exact, the string must match a command name exactly. With a value of
substring, it can match a substring of the command name.
histchars=chars Two or three characters that control history expansion. The first character
signalsahistoryevent.Thesecondisthe“quicksubstitution”character,andthe
third indicates the start of a comment. The default value is!^#.
Syntax Effect
${name[i]} Useelementiofarrayname.icanbeanyarithmeticexpressionasdescribedunderlet.
${name} Use element 0 of indexed arrayname.
${name[*]}, ${name[@]} Use all elements of arrayname.
${#name[*]}, ${#name[@]} Use the number of elements in arrayname.
Variable expression Description
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612 | Chapter6: The Bash Shell
The built-in commands declare, local, and readonly accept the -a option for an
indexed array and the -A option for an associative array. Use the unset built-in to
remove arrays or array elements. The built-ins are described in detail later in this
chapter.
Special Prompt Strings
Bash processes the values of the built-in shell variables PS1, PS2, and PS4 for the
following special escape sequences:
In Bash, the escape sequences are processed first. After that, variable, command,
and arithmetic substitutions are performed if the promptvars shell option is
enabled via the shopt command (the default).
Escape sequence Description
\a An ASCII BEL character (octal 07).
\A The current time in 24-hourHH:MM format.
\d The date in “weekday month day” format.
\D{format} The date as specified by thestrftime(3) formatformat. The braces are required.
\e An ASCII Escape character (octal 033).
\h The hostname, up to the first period.
\H The full hostname.
\j The current number of jobs.
\l The basename of the shell’s terminal device.
\n A newline character.
\r A carriage-return character.
\s The name of the shell (basename of$0).
\t The current time in 24-hourHH:MM:SS format.
\T The current time in 12-hourHH:MM:SS format.
\u The current user’s username.
\v The version of Bash.
\V The release (version plus patch level) of Bash.
\w The current directory, with $HOME abbreviated as~.
\W The basename of the current directory, with $HOME abbreviated as~.
\! The history number of this command.
\# The command number of this command.
\$ If the effective UID is 0, a#; otherwise a$.
\@ The current time in 12-hour a.m./p.m. format.
\nnn The character represented by octal valuennn.
\\ A literal backslash.
\[ Startasequenceofnonprintingcharacters,suchasforhighlightingorchangingcolors
on a terminal.
\] End a sequence of nonprinting characters.
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Arithmetic Expressions | 613
The Bash Shell
Arithmetic Expressions
The let built-in command performs integer arithmetic. You can substitute arith-
metic values (for use as command arguments or in variables); base conversion is
also possible.
Operators
The shell uses arithmetic operators from the C programming language; the
following table lists the operators in decreasing order of precedence.
Examples
See the let command for more information and examples:
let "count=0" "i = i + 1" Assign i and count
let "num % 2" Test for an even number
(( percent >= 0 && percent <= 100 )) Test the range of a value
Expression Meaning
$((expr)) Use the value of the enclosed arithmetic expression.
B#n Interpret integern in numeric baseB. For example,8#100 specifies the octal equiva-
lent of decimal 64.
Operator Description
++ -- Auto-increment and auto-decrement, both prefix and postfix.
+ - ! ~ Unary plus and minus, logical negation and binary inversion (one’s complement).
** Exponentiation.
* / % Multiplication; division; modulus (remainder).
+ - Addition; subtraction.
<< >> Bitwise left shift; bitwise right shift.
< <= > >= Less than; less than or equal to; greater than; greater than or equal to.
== != Equality; inequality (both evaluated left to right).
& Bitwise AND.
^ Bitwise exclusive OR.
| Bitwise OR.
&& Logical AND (short-circuit).
|| Logical OR (short-circuit).
?: Inline conditional evaluation.
= += -= Assignment.
*= /= %=
< <= > >=
&= ^= |=
‘ Sequential expression evaluation.
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614 | Chapter6: The Bash Shell
Command History
Bash lets you display or modify previous commands. Commands in the history list
can be modified using:
• Line-edit mode
• The fc and hist commands
Bash also supports a command-history mechanism very similar to that of the C
shell. This mechanism uses a history expansion character (! by default) to select a
line from the history. Portions of the line are then selected to be included in the
current line. Because the interactive line-editing features are considerably supe-
rior we do not cover those features here. See the Bash manpage for more
information.
Line-Edit Mode
Line-edit mode emulates many features of the vi and emacs editors. The history
list is treated like a file. When the editor is invoked, you type editing keystrokes to
move to the command line you want to execute. You can also change the line
before executing it. When you’re ready to issue the command, press the Enter
key.
Select an editor with either set -o vi or set -o emacs; assignment to the VISUAL or
EDITOR variables has no effect. Note that vi starts in input mode; to type a vi
command, press the Escape key first.
Common editing keystrokes
The fc Command
fc stands for either “find command” or “fix command,” since it does both jobs.
Use fc -l to list history commands and fc -e to edit them. See the fc entry in the
section “Built-in Commands” on page 619 for more information.
vi emacs Result
k Ctrl-P Get previous command.
j Ctrl-N Get next command.
/string Ctrl-Rstring Get previous command containingstring.
h Ctrl-B Move back one character.
l Ctrl-F Move forward one character.
b ESC-B Move back one word.
w ESC-F Move forward one word.
X DEL Delete previous character.
x Ctrl-D Delete character under cursor.
dw ESC-D Delete word forward.
db ESC-H Delete word backward.
xp Ctrl-R Transpose two characters.
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Command History | 615
The Bash Shell
Examples
$history List the last 16 commands
$fc -l 20 30 List commands 20 through 30
$fc -l -5 List the last five commands
$fc -l cat List all commands since the last command beginning with cat
$fc -l 50 List all commands since command 50
$fc -ln 5 > doit Save command 5 to file doit
$fc -e vi 5 20 Edit commands 5 through 20 using vi
$fc -e emacs Edit previous command using emacs
Interactive line editing is easier to use than fc, since you can move up and down in
the saved command history using your favorite editor commands (as long as your
favorite editor is either vi or Emacs!). You can also use the Up and Down arrow
keys to traverse the command history and the right and left arrow keys to move
around in the command line.
Programmable Completion
Bash and the readline library provide completion facilities, whereby you can type
part of a command name, press the Tab key, and have Bash fill in part or all of the
rest of the command or filename. Programmable completion lets you, as a shell
programmer, write code to customize the list of possible completions that Bash
will present for a particular, partially entered word. This is accomplished through
the combination of several facilities:
• The complete command allows you provide a completion specification, or
compspec, for individual commands. You specify, via various options, how to
tailor the list of possible completions for the particular command. This is
simple, but adequate for many needs. (See the complete entry in the section
“Built-in Commands” on page 619.)
• For more flexibility, you may use complete -F funcname command. This tells
Bash to call funcname to provide the list of completions for command. You
write the funcname function.
• Within the code for a -F function, the COMP* shell variables provide infor-
mation about the current command line. COMPREPLY is an array into
which the function places the final list of completion results.
• Also within the code for a -F function, you may use the compgen command
to generate is a list of results, such as “usernames that begin with a” or “all
set variables.” The intent is that such results would be used with an array
assignment:
...
COMPREPLY=( $( compgenoptions arguments ) )
...
Compspecs may be associated with either a full pathname for a command or,
more commonly, with an unadorned command name (/usr/bin/man versus plain
man). In the list that follows, completions are attempted based on the options
provided to the complete command.
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616 | Chapter6: The Bash Shell
1. Bash first identifies the command. If a pathname is used, Bash looks to see if
a compspec exists for the full pathname. Otherwise, it sets the command
name to the last component of the pathname, and searches for a compspec
for the command name.
2. If a compspec exists, Bash uses it. If not, Bash falls back to the default built-in
completions.
3. Bash performs the action indicated by the compspec to generate a list of
possible matches. Of this list, only those that have the word being completed
as a prefix are used for the list of possible completions. For the -d and -f
options, the variable FIGNORE is used to filter out undesirable matches.
4. Bash generates filenames as specified by the -G option. GLOBIGNORE is not
used to filter the results, but FIGNORE is.
5. Bash processes the argument string provided to -W. The string is split using
the characters in $IFS. The resulting list provides the candidates for comple-
tion. This is often used to provide a list of options that a command accepts.
6. Bash runs functions and commands as specified by the -F and -C options. For
both, Bash sets COMP_LINE and COMP_POINT as described previously.
For a shell function, COMP_WORDS and COMP_CWORD are also set.
Also for both, $1 is the name of the command whose arguments are being
completed, $2 is the word being completed, and $3 is the word in front of
the word being completed. Bash does not filter the results of the command or
function.
a. Functions named with -F are run first. The function should set the
COMPREPLY array to the list of possible completions. Bash retrieves the
list from there.
b. Commands provided with -C are run next, in an environment equiva-
lent to command substitution. The command should print the list of
possible completions, one per line. An embedded newline should be
escaped with a backslash.
7. Once the list is generated, Bash filters the results according to the -X option.
The argument to -X is a pattern specifying files to exclude. By prefixing the
pattern with a !, the sense is reversed, and the pattern instead specifies that
only matching files should be retained in the list.
An & in the pattern is replaced with the text of the word being completed.
Use \& to produce a literal &.
8. Finally, Bash prepends or appends any prefixes or suffixes supplied with -P or
-S options.
9. In the case that no matches were generated, if -o dirnames was used, Bash
attempts directory name completion.
10. On the other hand, if -o plusdirs was provided, Bash adds the result of direc-
tory completion to the previously generated list.
11. Normally, when a compspec is provided, Bash’s default completions are not
attempted, nor are the readline library’s default filename completions.
a. If the compspec produces no results and -o bashdefault was provided,
then Bash attempts its default completions.
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Job Control | 617
The Bash Shell
b. If neither the compspec, nor the Bash default completions with -o bash-
default produced any results, and -o default was provided, then Bash has
the readline library attempt its filename completions.
Ian Macdonald has collected a large set of useful compspecs, often distributed as
the file /etc/bash_completion.
Examples
Restrict files for the C compiler to C, C++ and assembler source files, and relocat-
able object files:
complete -f -X '!*.[Ccos]' gcc cc
For the man command, restrict expansions to things that have manpages:
# Simple example of programmable completion for manual pages.
# A more elaborate example appears in the bash_completion file.
# Assumes man [num] command command syntax.
shopt -s extglob Enable extended pattern matching
_man () {
local dir mandir=/usr/share/man Local variables
COMPREPLY=() Clear reply list
if [[ ${COMP_WORDS[1]} = +([0-9]) ]] Section number provided
then
# section provided: man 3 foo
dir=$mandir/man${COMP_WORDS[COMP_CWORD-1]} Look in that directory
else
# no section, default to commands
dir=$mandir/'man[18]' Look in command directories
fi
COMPREPLY=( $( find $dir -type f | Generate raw file list
sed 's;..*/;;' | Remove leading directories
sed 's/\.[0-9].*$//' | Remove trailing suffixes
grep "^${COMP_WORDS[$COMP_CWORD]}" | Keep those that match
given prefix
sort Sort final list
) )
}
complete -F _man man Associate function with command
Job Control
Job control lets you place foreground jobs in the background, bring background
jobs to the foreground, or suspend (temporarily stop) running jobs. Many job-
control commands take a jobID as an argument. This argument can be specified
as follows:
%n Job number n.
%s Job whose command line starts with string s.
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618 | Chapter6: The Bash Shell
%?s
Job whose command line contains string s.
%%
Current job.
%+
Current job (same as above).
%-
Previous job.
The following job-control commands are described more completely in the
section “Built-in Commands” on page 619.
bg Put a job in the background.
fg Put a job in the foreground.
jobs
List active jobs.
kill
Terminate a job.
stty tostop
Stop background jobs if they try to send output to the terminal. (Note that
stty is not a built-in command.)
suspend
Suspend a job-control shell (such as one created by su).
wait
Wait for background jobs to finish.
Ctrl-Z
Suspend a foreground job. Then use bg or fg. (Your terminal may use some-
thing other than Ctrl-Z as the suspend character.)
Command Execution
When you type a command to Bash, it looks in the following places until it finds
a match:
1. Keywords such as if and for.
2. Aliases. You can’t define an alias whose name is a shell keyword, but you can
define an alias that expands to a keyword, e.g., alias aslongas=while. (In non-
POSIX mode, Bash does allow you to define an alias for a shell keyword.)
3. Special built-ins like break and continue. The list of POSIX special built-ins is
. (dot), : , break, continue, eval, exec, exit, export, readonly, return, set,
shift, source, times, trap, and unset.
4. Functions. When in non-POSIX mode, Bash finds functions before built-in
commands.
5. Nonspecial built-ins like cd and test.
6. Scripts and executable programs, for which the shell searches in the directo-
ries listed in the PATH environment variable.
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# | 619
The Bash Shell
The distinction between “special” built-in commands and nonspecial ones comes
from POSIX. This distinction, combined with the command command, makes it
possible to write functions that override shell built-ins, such as cd. For example:
cd () { Shell function, found before built-in cd
command cd "$@" Use real cd to change directory
echo now in $PWD Other stuff we want to do
}
Restricted Shells
A restricted shell is one that disallows certain actions, such as changing directory,
setting PATH, or running commands whose names contain a / character. See the
Bash manpage for the full list of restrictions.
To run a restricted shell, enter the command bash -r. Depending on your Linux
distribution, you may also be able to enter the command as rbash.
You can still run shell scripts, since in that case the restricted shell calls the unrestricted
version of the shell to run the script after it reads /etc/profile, $HOME/.profile, and
other startup files.
Restricted shells are not used much in practice, as they are difficult to set up
correctly.
Built-in Commands
Examples to be entered as a command line are shown with the $ prompt. Other-
wise, examples should be treated as code fragments that might be included in a
shell script. For convenience, some of the reserved words used by multiline
commands are also included.
! !pipeline
Negate the sense of a pipeline. Returns an exit status of 0 if the
pipeline exited nonzero, and an exit status of 1 if the pipeline
exited zero. Typically used in if and while statements.
Example
This code prints a message if user jane is not logged on:
if ! who | grep jane > /dev/null
then
echo jane is not currently logged on
fi
# #
Ignore all text that follows on the same line. # is used in shell
scripts as the comment character and is not really a command.
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620 | Chapter6: The Bash Shell
#!shell #!shell [option]
Used as the first line of a script to invoke the named shell. Anything
given on the rest of the line is passed as a single argument to the
named shell. This feature is typically implemented by the kernel,
but may not be supported on some older systems. Some systems
have a limit of approximately 32 characters on the maximum
length of shell. For example:
#!/bin/sh
: :
Null command. Returns an exit status of 0. The line is still
processed for side effects, such as variable and command substitu-
tions, or I/O redirection. See the following Example and the
Example under case.
Example
Check whether someone is logged in:
if who | grep $1 > /dev/null
then : # Do nothing if user is found
else echo "User $1 is not logged in"
fi
. .file [arguments]
Read and execute lines in file. file does not have to be executable,
but must reside in a directory searched by PATH. The arguments
are stored in the positional parameters. If Bash is not in POSIX
mode and file is not found in PATH, Bash looks in the current
directory for the file.
[[ ]] [[expression ]]
Same as test expression or [ expression ], except that [[ ]] allows
additional operators. Word splitting and filename expansion are
disabled. Note that the brackets ([ ]) are typed literally and that
they must be surrounded by whitespace.
Additional operators
&&Logical AND of test expressions (short circuit).
|| Logical OR of test expressions (short circuit).
< First string is lexically “less than” the second.
> First string is lexically “greater than” the second.
alias alias [option] [name[='cmd']...]
Assign a shorthand name as a synonym for cmd. If ='cmd' is omitted,
print the alias for name; if name is also omitted, print all aliases. By
itself or with -p, alias prints one alias per line on standard output as
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bind | 621
The Bash Shell
alias name=value. If the value contains a trailing space, the next
word on the command line also becomes a candidate for alias
expansion. See also unalias.
Option
-p Print the word alias before each alias.
Example
alias dir='echo ${PWD##*/}'
bg bg [jobIDs]
Put current job or jobIDs in the background. See the section “Job
Control” on page 617.
bind bind [-mmap] [options]
bind [-mmap] [-qfunction] [-rsequence] [-ufunction]
bind [-mmap] -ffile
bind [-mmap] -xsequence:command
bind [-mmap]sequence:function
bindreadline-command
Manage the readline library. Nonoption arguments have the same
form as in an .inputrc file.
Options
-f file
Read key bindings from file.
-l List the names of all the readline functions.
-m map
Use map as the keymap. Available keymaps are: emacs, emacs-
standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
and vi-insert. vi is the same as vi-command, and emacs is the
same emacs-standard.
-p Print the current readline bindings such that they can be
reread from a .inputrc file.
-P Print the current readline bindings.
-q function
Query which keys invoke the readline function function.
-r sequence
Remove the binding for key sequence sequence.
-s Print the current readline key sequence and macro bindings
such that they can be reread from a .inputrc file.
-S Print the current readline key sequence and macro bindings.
-u function
Unbind all keys that invoke the readline function function.
-v Print the current readline variables such that they can be
reread from a .inputrc file.
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622 | Chapter6: The Bash Shell
-V Print the current readline variables.
-x sequence:command
Execute the shell command command whenever sequence is
entered.
break break [n]
Exit from a for, while, select, or until loop (or break out of n
loops).
builtin builtincommand [arguments ... ]
Run the shell built-in command command with the given argu-
ments. This allows you to bypass any functions that redefine a
built-in command’s name. The command command is more
portable.
Example
This function lets you do your own tasks when you change
directory:
cd () {
builtin cd "$@" Actually change directory
pwd Report location
}
caller caller [expression]
Print the line number and source filename of the current function
call or dot file. With nonzero expression, prints that element from
the call stack. The most recent is zero. This command is for use by
the Bash debugger.
case casevalue in
pattern1)cmds1;;
pattern2)cmds2;;
.
.
.
esac
Execute the first set of commands (cmds1) if value matches
pattern1, execute the second set of commands (cmds2) if value
matches pattern2, etc. The last command in each set ends with ;;
and no further matches are attempted. If the set ends in ;& instead,
execution continues with the commands for the next set of
patterns; if it ends in ;;&, the next pattern in the list is tested. value
is typically a positional parameter or other shell variable. cmds are
typically Linux commands, shell programming commands, or vari-
able assignments. Patterns can use file-generation metacharacters.
Multiple patterns (separated by |) can be specified on the same
line; in this case, the associated cmds are executed whenever value
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command | 623
The Bash Shell
matches any of these patterns. See the Examples here and under
eval.
A pattern may be preceded by an optional open parenthesis, as in
(pattern, necessary for balancing parentheses inside a $()
construct.
Examples
Check first command-line argument and take appropriate action:
case $1 in # Match the first arg
no|yes) response=1;;
-[tT]) table=TRUE;;
*) echo "unknown option"; exit 1;;
esac
Read user-supplied lines until user exits:
while : # Null command; always true
do
printf "Type . to finish ==> "
read line
case "$line" in
.) echo "Message done"
break ;;
*) echo "$line" >> $message ;;
esac
done
cd cd [-LP] [dir]
cd [-LP] [-]
With no arguments, change to the user’s home directory. Other-
wise, change the working directory to dir. If dir is a relative
pathname but is not in the current directory, the CDPATH vari-
able is searched. A directory of - stands for the previous directory.
Options
-L Use the logical path (what the user typed, including any
symbolic links) for cd .. and the value of PWD. This is the
default.
-P Use the actual filesystem physical path for cd .. and the value
of PWD.
command command [-pvV]name [arg ...]
Without -v or -V, execute name with given arguments. This
command bypasses any aliases or functions that may be defined for
name. When used with a special built-in, it prevents the built-in
from exiting the script if it fails.
Options
-p Use a predefined, default search path, not the current value of
PATH.
-v Print a description of how the shell interprets name.
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624 | Chapter6: The Bash Shell
-V Print a more verbose description of how the shell interprets
name.
Example
Create an alias for rm that gets the system’s version, and runs it
with the -i option:
$alias 'rm=command -p rm -i'
compgen compgen [options] [string]
Generate possible completions for string according to the options
and write to standard output. Options are those accepted by
complete, except for -p and -r. For more information, see the entry
for complete.
complete complete [options]command ...
Specify the way to complete arguments for each command. See
“Programmable Completion” on page 615 for more discussion.
Options
-A type
Use type to specify a list of possible completions. The type may
be one of the following. Options in parentheses are alternative
specifications for -A type.
alias(-a)
Alias names.
arrayvar
Array variable names.
binding
Bindings from the readline library.
builtin(-b)
Shell built-in command names.
command(-c)
Command names.
directory(-d)
Directory names.
disabled
Names of disabled shell built-in commands.
enabled
Names of enabled shell built-in commands.
export(-e)
Names of exported shell variables.
file(-f)
Filenames.
function
Names of shell functions.
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complete | 625
The Bash Shell
group(-g)
Group names.
helptopic
Help topics as allowed by the help built-in command.
hostname
Hostnames, as found in the file named by $HOSTFILE.
job(-j)
Job names.
keyword(-k)
Shell reserved keywords.
running
Names of running jobs.
service(-s)
Service names (from /etc/services).
setopt
Valid arguments for set -o.
shopt
Valid option names for the shopt built-in command.
signal
Signal names.
stopped
Names of stopped jobs.
user(-u)
Usernames.
variable(-v)
Shell variable names.
-C command
Run command in a subshell and use its output as the list of
completions.
-E Remaining options and actions apply to completion attempts
on a blank line.
-F function
Run shell function function in the current shell. Upon its
return, retrieve the list of completions from the COMPREPLY
array.
-G pattern
Expand pattern to generate completions.
-o option
Control the behavior of the completion specification. The value
for option is one of the following:
bashdefault
Fall back to the normal Bash completions if no matches
are produced.
default
Use the default readline completions if no matches are
produced.
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626 | Chapter6: The Bash Shell
dirnames
Do directory name completion if no matches are produced.
filenames
Inform the readline library that the intended output is
filenames, so that the library can do any filename-specific
processing, such as adding a trailing slash for directories
or removing trailing spaces.
nospace
Inform the readline library that it should not append a
space to words completed at the end of a line.
plusdirs
Attempt directory completion and add any results to the
list of completions already generated.
-p With no commands, print all completion settings in a way
that can be reread.
-P prefix
The prefix is added to each resulting string as a prefix after all
the other options have been applied.
-r Remove the completion settings for the given commands, or
all settings if no commands.
-S suffix
The suffix is added to each resulting string as a suffix after all
the other options have been applied.
-W wordlist
Split wordlist (a single shell word) using $IFS. The generated
list contains the members of the split list that matched the
word being completed. Each member is expanded using brace
expansion, tilde expansion, parameter and variable expan-
sion, command substitution, and arithmetic expansion. Shell
quoting is respected.
-X pattern
Exclude filenames matching pattern from the filename
completion list. With a leading ! in the pattern, the sense is
reversed, and only filenames matching pattern are retained.
continue continue [n]
Skip remaining commands in afor, while, select, or until loop,
resuming with the next iteration of the loop (or skipping n loops).
declare declare [options] [name[=value]]
typeset [options] [name[=value]]
Declare variables and manage their attributes. In function bodies,
variables are local, as if declared with the local command.
Options
-a Each name is an indexed array variable.
-A Each name is an associative array variable.
-f Each name is a function.
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dirs | 627
The Bash Shell
-F For functions, print just the function name and attributes, not
the function definition (body). Implies -f.
-i Each variable is an integer; in an assignment, the value is eval-
uated as an arithmetic expression.
-l Assign all values as lowercase only; convert uppercase to
lowercase.
-p With no names, print all variables and their values. With
names, print the names, attributes, and values of the given
variables. Used with -f, print all function names and
attributes. This option causes all other options to be ignored.
-r Mark names as read-only. Subsequent assignments will fail.
-t Apply the trace attribute to each name. Traced functions
inherit the DEBUG and RETURN traps from the shell. This
attribute has no meaning for variables.
-u Assign all values as uppercase only; convert lowercase to
uppercase.
-x Mark names for export into the environment of child processes.
With a + instead of a -, the given attribute is disabled. With no
variable names, all variables having the given attribute(s) are
printed in a form that can be reread as input to the shell.
Examples
$declare -i val Make val an integer
$val=4+7 Evaluate value
$echo $val Show result
11
$declare -r z=42 Make z read-only
$z=31 Try to assign to it
bash: z: readonly variable Assignment fails
$echo $z
42
$declare -p val z Show attributes and values
declare -i val="11"
declare -r z="42"
dirs dirs [-clpv] [+n] [-n]
Print the directory stack, which is managed with pushd and popd.
Options
+n Print the nth entry from the left; first entry is zero.
-n Print the nth entry from the right; first entry is zero.
-c Remove all entries from (clear) the directory stack.
-l Produce a longer listing, one that does not replace $HOME
with ~.
-p Print the directory stack, one entry per line.
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628 | Chapter6: The Bash Shell
-v Print the directory stack, one entry per line, with each entry
preceded by its index in the stack.
disown disown [-ahr] [job ...]
Remove job from the list of jobs managed by Bash.
Options
-a Remove all jobs. With -h, mark all jobs.
-h Instead of removing jobs from the list of known jobs, mark
them to not receive SIGHUP when Bash exits.
-r With no jobs, remove (or mark) only running jobs.
do do
Reserved word that precedes the command sequence in a for, while,
until, or select statement.
done done
Reserved word that ends a for, while, until, or select statement.
echo echo [-eEn] [string]
Write string to standard output. (See also echo in Chapter 3.)
Options
-e Enable interpretation of the following escape sequences,
which must be quoted (or escaped with a \) to prevent inter-
pretation by the shell:
\a Alert (ASCII BEL).
\b Backspace.
\c Suppress the terminating newline (same as -n).
\e ASCII Escape character.
\f Formfeed.
\n Newline.
\r Carriage return.
\t Tab character.
\v Vertical-tab character.
\\ Backslash.
\0nnn
ASCII character represented by octal number nnn, where
nnn is zero, one, two, or three digits and is preceded by a 0.
\nnn
ASCII character represented by octal number nnn, where
nnn is one, two, or three digits.
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eval | 629
The Bash Shell
\xHH
ASCII character represented by hexadecimal number HH,
where HH is one or two hexadecimal digits.
-E Do not interpret escape sequences, even on systems where the
default behavior of the built-in echo is to interpret them.
-n Do not print the terminating newline.
Examples
$echo "testing printer" | lp
$echo "Warning: ringing bell \a"
enable enable [-adnps] [-ffile] [command ...]
Enable or disable shell built-in commands. Disabling a built-in lets
you use an external version of a command that would otherwise
use a built-in version, such as echo or test.
Options
-a For use with -p, print information about all built-in
commands, disabled and enabled.
-d Remove (delete) a built-in previously loaded with -f.
-f file
Load a new built-in command command from the shared
library file file.
-n Disable the named built-in commands.
-p Print a list of enabled built-in commands.
-s Print only the POSIX special built-in commands. When combined
with -f, the new built-in command becomes a POSIX special
built-in.
esac esac
Reserved word that ends a case statement.
eval evalargs
Typically, eval is used in shell scripts, and args is a line of code that
contains shell variables. eval forces variable expansion to happen
first and then runs the resulting command. This “double-scanning”
is useful any time shell variables contain input/output redirection
symbols, aliases, or other shell variables. (For example, redirection
normally happens before variable expansion, so a variable
containing redirection symbols must be expanded first using eval;
otherwise, the redirection symbols remain uninterpreted.)
Example
This fragment of a shell script shows how eval constructs a
command that is interpreted in the right order:
for option
do
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630 | Chapter6: The Bash Shell
case "$option" in Define where output goes
save) out=' > $newfile' ;;
show) out=' | more' ;;
esac
done
eval sort $file $out
exec exec [-aname] [-cl] [commandargs ... ]
Execute command in place of the current process (instead of
creating a new process). exec is also useful for opening, closing, or
copying file descriptors.
Options
-aname
Use name for the value of argv[0].
-c Clear the environment before executing the program.
-l Place a minus sign at the front of argv[0], just as login(1) does.
Examples
trap 'exec 2>&-' 0 Close standard error when
shell script exits (signal 0)
$exec /bin/csh Replace shell with C shell
$exec < infile Reassign standard input to infile
exit exit [n]
Exit a shell script with status n (e.g., exit 1). n can be 0 (success) or
nonzero (failure). If n is not given, exit status is that of the most
recent command. exit can be issued at the command line to close a
window (log out). Exit statuses can range in value from 0 to 255.
Example
if [ $# -eq 0 ]
then
echo "Usage: $0 [-c] [-d] file(s)" 1>&2
exit 1 # Error status
fi
export export [-fn] [name=[value] ...]
export -p
Pass (export) the value of one or more shell variables, specified by
name, giving them global meaning (they are local by default). For
example, a variable defined in one shell script must be exported if
its value is used in other programs called by the script. If a value is
specified, the variable is set to that value. If no names are given, or
with -p, export lists the variables exported by the current shell.
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fg | 631
The Bash Shell
Options
-f Names refer to functions; the functions are exported in the
environment.
-n Remove the named variables or functions from the environment.
-p Print names and values of exported variables.
Example
In the original Bourne shell, you would type:
TERM=vt100
export TERM
In Bash, type this instead:
export TERM=vt100
false false
Built-in command that exits with a false return value.
fc fc [-lnr] [-e editor ] [first [last]]
fc -s [old=new] [command]
Display or edit commands in the history list. first and last are
numbers or strings specifying the range of commands to display or
edit. If last is omitted, fc applies to a single command (specified by
first). If both first and last are omitted, fc edits the previous
command or lists the last 16. The second form of fc takes a history
command, replaces old with new, and executes the modified
command. If no strings are specified, command is just reexecuted. If
no command is given either, the previous command is reexecuted.
command is a number or string like first. See the examples in the
earlier section “Command History” on page 614.
Options
Use only one of -e, -l or -s.
-e editor
Invoke editor to edit the specified history commands. If no
editor is specified, Bash defaults first to the value of FCEDIT,
then to the value of EDITOR, then to vi.
-l List the specified command or range of commands, or list the
last 16.
-n Suppress command numbering from the -l listing.
-r Reverse the order of the -l listing.
-s[old=new]
Replace the string old with new in the specified command and
execute the modified command.
fg fg [jobIDs]
Bring current job or jobIDs to the foreground. See the section “Job
Control” on page 617.
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632 | Chapter6: The Bash Shell
fi fi
Reserved word that ends an if statement. (Don’t forget to use it!)
for for x [inlist]
do
commands
done
For variable x (in optional list of values) do commands. If in list is
omitted, "$@" (the positional parameters) is assumed.
Examples
Paginate files specified on the command line; save each result:
for file; do
pr $file > $file.tmp
done
Search chapters for a list of words (like fgrep -f):
for item in `cat program_list`
do
echo "Checking chapters for"
echo "references to program $item..."
grep -c "$item.[co]" chap*
done
Extract a one-word title from each file and use as new filename:
for file
do
name=`sed -n 's/NAME: //p' $file`
mv $file $name
done
for for ((init;cond;incr))
do
commands
done
Arithmetic for loop, similar to C’s. Evaluate init. While cond is
true, execute the body of the loop. Evaluate incr before retesting
cond. Any one of the expressions may be omitted; a missing cond is
treated as being true.
Example
Search for a phrase in each odd chapter:
for ((x=1; x <= 20; x += 2))
do
grep $1 chap$x
done
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hash | 633
The Bash Shell
function [function]name () { commands; }
functionname {commands; }
Define name as a shell function. See the description of semantic
issues in the section “Functions” on page 605. If the reserved word
function is given, the parentheses following name are optional.
Example
Define a function to count files:
$function fcount {
> ls | wc -l
>}
getopts getoptsstringname [args]
Process command-line arguments (or args, if specified) and check
for legal options. getopts is used in shell-script loops and is
intended to ensure standard syntax for command-line options. Stan-
dard syntax dictates that command-line options begin with -.
Options can be stacked: i.e., consecutive letters can follow a single -.
End processing of options by specifying -- on the command line.
string contains the option letters to be recognized by getopts when
running the shell script. Valid options are processed in turn and
stored in the shell variable name. If an option is followed by a
colon, the option must be followed by one or more arguments.
(Multiple arguments must be given to the command as one shell
word. This is done by quoting the arguments or separating them
with commas. The application must be written to expect multiple
arguments in this format.) getopts uses the shell variables
OPTARG, OPTIND, and OPTERR.
hash hash [-dlrt] [-pfile] [commands]
As the shell finds commands along the search path ($PATH), it
remembers the found location in an internal hash table. The next
time you enter a command, the shell uses the value stored in its
hash table.
With no arguments, hash lists the current hashed commands. The
display shows hits (the number of times the command is called by
the shell) and the command name.
With commands, the shell adds those commands to the hash table.
Options
-d Remove (delete) just the specified commands from the hash
table.
-l Produce output in a format that can be reread to rebuild the
hash table.
-p file
Associate file, assumed to be the full pathname, with
command in the hash table rather than searching $PATH.
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634 | Chapter6: The Bash Shell
-r Remove all commands from the hash table.
-t With one name, print the full pathname of the command.
With more than one name, print the command name and the
full path, in two columns.
Besides the -r option, the hash table is also cleared when PATH is
assigned. Use PATH=$PATH to clear the hash table without
affecting your search path. This is most useful if you have installed
a new version of a command in a directory that is earlier in $PATH
than the current version of the command.
help help [-s] [pattern]
Print usage information on standard output for each Bash
command that matches pattern. The information includes descrip-
tions of each command’s options. With the -s option, print only
brief usage information.
Examples
$help -s cd Short help
cd: cd [-L|-P] [dir]
$help true Full help
true: true
Return a successful result.
Exit Status:
Always succeeds.
history history [count]
history [options]
Print commands in the history list or manage the history file. With
no options or arguments, display the history list with command
numbers. With a count argument, print only that number of the
most recent commands.
Options
-a Append new history lines (those executed since the beginning
of the session) to the history file.
-c Clear the history list (remove all entries).
-d position
Delete the history item at position position.
-n Read unread history lines from the history file into the history
list.
-p argument ...
Perform history substitution on each argument, printing the
results to standard output. The results are not saved in the
history list. Each argument must be quoted.
-r Read the history file and replace the history list with its
contents.
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jobs | 635
The Bash Shell
-s argument ...
Store the arguments in the history list as a single entry.
-w Write the current history list to the history file, overwriting the
file.
if ifcondition1
thencommands1
[ elifcondition2
thencommands2 ]
.
.
.
[ elsecommands3 ]
fi
If condition1 is met, do commands1; otherwise, if condition2 is met,
do commands2 ; if neither is met, do commands3. Conditions are
often specified with the test and [[ ]] commands. See test and [[ ]]
for a full list of conditions, and see additional Examples under :
and exit.
Examples
Insert a 0 before numbers less than 10:
if [ $counter -lt 10 ]
then number=0$counter
else number=$counter
fi
Make a directory if it doesn’t exist:
if [ ! -d $dir ]; then
mkdir $dir
chmod 775 $dir
fi
jobs jobs [options] [jobIDs]
List all running or stopped jobs, or list those specified by jobIDs.
For example, you can check whether a long compilation or text
format is still running. Also useful before logging out. See the
section “Job Control” on page 617.
Options
-l List job IDs and process group IDs.
-n List only jobs whose status changed since last notification.
-p List process group IDs only.
-r List running jobs only.
-s List stopped jobs only.
-x cmd
Replace each job ID found in cmd with the associated process
ID and then execute cmd.
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636 | Chapter6: The Bash Shell
kill kill [options]IDs
Terminate each specified process ID or job ID. You must own the
process or be a privileged user. This built-in command is similar to
/usr/bin/kill, described in Chapter 3. See the section “Job Control”
on page 617.
Options
-l List the signal names and numbers. (Used by itself.)
-n num
Send the given signal number.
-s name
Send the given signal name.
-signal
The signal number or name (from kill -l or /usr/include/sys/
signal.h). With a signal number of 9, the kill is absolute.
let letexpressions
or
((expressions))
Perform arithmetic as specified by one or more expressions. expres-
sions consist of numbers, operators, and shell variables (which
don’t need a preceding $). Expressions must be quoted if they
contain spaces or other special characters. The (()) form does the
quoting for you. For more information and examples, see “Arith-
metic Expressions” on page 613. See also expr in Chapter 3.
Examples
Each of these examples adds 1 to variable i:
i=`expr $i + 1`
let i=i+1
let "i = i + 1"
(( i = i + 1 ))
(( i += 1 ))
(( i++ ))
local local [option] [name[=value]]
Declares local variables for use inside functions. The option can be
any option accepted by declare; see declare for the full list. It is an
error to use local outside a function body.
logout logout
Exit a login shell. The command fails if the current shell is not a
login shell.
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popd | 637
The Bash Shell
mapfile mapfile [ options ] [ array ]
readarray [ options ] [ array ]
Populate an array by reading lines from standard input and placing
them into the specified array. The default array is MAPFILE.
Without the -O option, mapfile clears the array before assigning
entries to it.
Options
-ccount
Used with -C to specify the number of lines read between call-
back calls.
-Ccallback
Evaluate the callback code every time count lines are read,
where count is specified by -c (default is 5000).
-nnum
Read in at most num lines, or all lines if num is 0.
-Oorigin
Begin assigning entries to the array at index origin (default
index is 0).
-scount
Discard the first count lines read.
-t Remove a trailing line from each input line.
-ufd
Read from the given file descriptor instead of standard input.
name () [function]name () {commands; }
Define name as a function. POSIX syntax. The reserved word func-
tion is optional. The function definition can be written on one line
or across many. See “Functions” on page 605 for more detailed
information.
Example
$count () {
>ls | wc -l
>}
When issued at the command line, count displays the number of
files in the current directory.
popd popd [-n] [+count] [-count]
Pop the top directory off the directory stack (as shown by the dirs
command), and change to the new top directory, or manage the
directory stack.
Options
-n Don’t change to the new top directory; just manipulate the
stack.
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638 | Chapter6: The Bash Shell
+count
Remove the item count entries from the left, as shown by dirs.
Counting starts at zero. No directory change occurs.
-count
Remove the item count entries from the right, as shown by
dirs. Counting starts at zero. No directory change occurs.
printf printf [-vvar]format [val ...]
Format the specified values according to the format format and
write them to standard output. The possible format character
strings are those of the ANSI C printf function plus several addi-
tional strings.
Option
-v var
Write output to the variable var instead of standard output.
Additional format strings
%bExpand escape sequences in strings (e.g., \t to tab, and so on).
%q Print a quoted string that can be reread later on.
Example
$date Reformat date/time
Fri May 15 15:39:42 EDT 2009
$printf "%(It is now %m/%d/%Y %H:%M:%S)T\n" "$(date)"
It is now 05/15/2009 15:40:10
pushd pushd [-n] [directory]
pushd [-n] [+count] [-count]
Add directory to the directory stack, or rotate the directory stack.
With no arguments, swap the top two entries on the stack, and
change to the new top entry.
Options
-n Don’t change to the new top directory, just manipulate the
stack.
+count
Rotate the stack so that the count’th item from the left, as
shown by dirs, is the new top of the stack. Counting starts at
zero. The new top becomes the current directory.
-count
Rotate the stack so that the count’th item from the right, as
shown by dirs, is the new top of the stack. Counting starts at
zero. The new top becomes the current directory.
pwd pwd [-LP]
Print your present working directory on standard output.
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read | 639
The Bash Shell
Options
Options give control over the use of logical versus physical treat-
ment of the printed path. See alsothe entry for cd, earlier in this
section.
-L Use logical path (what the user typed, including any symbolic
links) and the value of PWD for the current directory. This is
the default.
-P Use the actual filesystem physical path for the current direc-
tory with no symbolic links.
read read [options] [variable1] [variable2 ...]
Read one line of standard input and assign each word to the corre-
sponding variable, with all leftover words assigned to the last
variable. If only one variable is specified, the entire line is assigned
to that variable. See the examples here and under case. The return
status is 0 unless EOF is reached. If no variables are given, input is
stored in the REPLY variable.
Options
-a array
Read into indexed array array.
-d delim
Read up to first occurrence of delim, instead of newline.
-e Use the readline library if reading from a terminal.
-itext
If readline is being used, put text into the editing buffer.
-n count
Read at most count bytes.
-p prompt
Print prompt before reading input.
-r Raw mode; ignore \ as a line-continuation character.
-s Read silently; do not echo characters.
-t timeout
When reading from a terminal or pipe, if no data is entered
after timeout seconds, return 1. This prevents an application
from hanging forever, waiting for user input.
-u[n]
Read input from file descriptor n (default is 0).
Example
Read three variables:
$read first last address
Sarah Caldwell 123 Main Street
$echo "$last, $first\n$address"
Caldwell, Sarah
123 Main Street
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640 | Chapter6: The Bash Shell
readonly readonly [-afp] [variable[=value] ...]
Prevent the specified shell variables from being assigned new
values. An initial value may be supplied using the assignment
syntax, but that value may not be changed subsequently. If no vari-
ables are specified, readonly displays a list of variables marked
read-only.
Options
-a Each variable must refer to an indexed array.
-A Each variable must refer to an associative array.
-f Each variable must refer to a function.
-p Display the output in a format that allows the list of read-only
variables to be saved for rereading later.
return return [n]
Use inside a function definition. Exit the function with status n or
with the exit status of the previously executed command.
select selectx [inlist]
do
commands
done
Display a list of menu items on standard error, numbered in the
order they are specified in list. If no in list is given, items are taken
from the command line (via "$@"). Following the menu is a
prompt string (set by the variable PS3). At the prompt, the user
selects a menu item by typing its line number, or redisplays the
menu by pressing the Enter key. User input is stored in the shell
variable REPLY and the value selected is stored in x. If a valid item
number is typed, the commands associated with the value in x are
executed and the prompt is redisplayed for the user to select a new
value. Typing EOF terminates the loop.
Example
PS3="Select the item number: "
select event in Format Page View Exit
do
case "$event" in
Format) nroff $file | lp;;
Page) pr $file | lp;;
View) more $file;;
Exit) exit 0;;
* ) echo "Invalid selection";;
esac
done
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set | 641
The Bash Shell
The output of this script looks like this:
1. Format
2. Page
3. View
4. Exit
Select the item number:
set set [options arg1 arg2 ...]
With no arguments, set prints the values of all variables known to
the current shell. Options can be enabled (-option) or disabled
(+option). Options can also be set when the shell is invoked. (See
the section “Invoking the Shell” on page 597.) Arguments are
assigned in order to $1,$2, etc.
Options
-a From now on, automatically mark variables for export after
defining or changing them.
-b Print job completion messages as soon as jobs terminate; don’t
wait until the next prompt.
-B Enable brace expansion. On by default.
-C Prevent overwriting via > redirection; use >| to overwrite files.
-e Exit if a command yields a nonzero exit status. The ERR trap
executes before the shell exits.
-E Cause shell functions, command substitutions, and subshells
to inherit the ERR trap.
-f Ignore filename metacharacters (e.g., * ? [ ]).
-h Locate and remember commands as they are defined. On by
default.
-H Enable csh-style (!-style) history substitution. On by default.
-k Assignment of environment variables (var=value) takes effect
regardless of where they appear on the command line. Normally,
assignments must precede the command name.
-m Enable job control; background jobs execute in a separate
process group. -m is usually on by default.
-n Read commands but don’t execute; useful for checking
syntax. Ignored if the shell is interactive.
+o [mode]
With mode, disable the given shell option. Plain set +o prints
the settings of all the current options in a form that can be
reread by the shell later.
-o [mode]
List shell modes, or turn on mode mode. Many modes can be
set by other options. Modes are:
allexport
Same as -a.
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642 | Chapter6: The Bash Shell
braceexpand
Same as -B.
emacs
Set command-line editor to emacs.
errexit
Same as -e.
errtrace
Same as -E.
functrace
Same as -T.
hashall
Same as -h.
histexpand
Same as -H.
history
Enable command history. On by default.
ignoreeof
Don’t process EOF signals. To exit the shell, type exit.
keyword
Same as -k.
monitor
Same as -m.
noclobber
Same as -C.
noexec
Same as -n.
noglob
Same as -f.
notify
Same as -b.
nounset
Same as -u.
onecmd
Same as -t.
physical
Same as -P.
pipefail
Change pipeline exit status to be that of the rightmost
command that failed, or zero if all exited successfully.
posix
Change to POSIX mode.
privileged
Same as -p.
verbose
Same as -v.
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shopt | 643
The Bash Shell
vi Set command-line editor to vi.
xtrace
Same as -x.
+p Reset effective UID to real UID.
-p Start up as a privileged user. Don’t read $ENV or $BASH_
ENV, don’t import functions from the environment, and ignore
the value of $SHELLOPTS.
-P Always use physical paths for cd and pwd; do not follow
symbolic links.
-t Exit after one command is executed.
-T Cause shell functions, command substitutions, and subshells
to inherit any DEBUG and RETURN traps.
-u In substitutions, treat unset variables as errors.
-v Show each shell command line when read.
-x Show commands and arguments when executed, preceded by
the value of PS4. This provides step-by-step tracing of shell
scripts.
- Turn off -v and -x, and turn off option processing. Included
for compatibility with older versions of the Bourne shell.
-- Used as the last option; -- turns off option processing so that
arguments beginning with - are not misinterpreted as options.
(For example, you can set $1 to -1.) If no arguments are given
after --, unset the positional parameters.
Examples
set -- "$num" -20 -30 Set $1 to $num, $2 to -20, $3 to -30
set -vx Read each command line; show it;
execute it; show it again (with arguments)
set +x Stop command tracing
set -o noclobber Prevent file overwriting
set +o noclobber Allow file overwriting again
shift shift [n]
Shift positional arguments (e.g., $2 becomes $1). If n is given, shift
to the left n places; otherwise n is assumed to be 1. Used in while
loops to iterate through command-line arguments.
shopt shopt [-opqsu] [options]
Set or unset shell options. With no options or just -p, print the
option names and whether they are set or not.
Options
-o Each option must be one of the shell option names for set -o,
instead of the options listed in the next section.
-p Print the option settings as shopt commands that can be
reread later.
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644 | Chapter6: The Bash Shell
-q Quiet mode. The exit status is zero if the given option is set,
nonzero otherwise. With multiple options, all of them must be
set for a zero exit status.
-s Set the given options. With no options, print only those that
are set.
-u Unset the given options. With no options, print only those that
are unset.
Settable shell options
The following list describes the behavior when set. Options marked
with an asterisk (*) are enabled by default.
autocd
Attempt to cd to a directory that is given as a command name.
Allowed in interactive shells only.
cdable_vars
Treat a nondirectory argument to cd as a variable whose value
is the directory to go to.
cdspell
Attempt spelling correction on each directory component of
an argument to cd. Allowed in interactive shells only.
checkhash
Check that commands found in the hash table still exist before
attempting to use them. If not, perform a normal PATH
search.
checkjobs
Display the status of any running or stopped jobs before
exiting an interactive shell.
checkwinsize
Check the window size after each command and update
LINES and COLUMNS if the size has changed.
cmdhist *
Save all lines of a multiline command in one history entry.
This permits easy reediting of multiline commands.
compat31
Behave like version 3.1 with respect to quoted arguments to
the conditional command’s =~ operator.
dirspell
During filename completion, attempt to correct the spelling of
directory names if the name as given is not found.
dotglob
Include filenames starting with a period in the results of file-
name expansion.
execfail
Do not exit a noninteractive shell if the command given to
exec cannot be executed. Interactive shells do not exit in such
a case, no matter the setting of this option.
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shopt | 645
The Bash Shell
expand_aliases *
Expand aliases created with alias. Disabled in noninteractive
shells.
extdebug
Enable behavior needed for debuggers:
•declare -F displays the source filename and line number
for each function name argument.
•When a command run by the DEBUG trap fails, the next
command is skipped.
• When a command run by the DEBUG trap inside a shell
function or script sourced with . (dot) or source returns
with an exit status of 2, the shell simulates a call to
return.
• BASH_ARGC and BASH_ARGV are set as described
earlier.
• Function tracing is enabled. Command substitutions,
shell functions, and subshells invoked via (...) inherit the
DEBUG and RETURN traps.
• Error tracing is enabled. Command substitutions, shell
functions, and subshells invoked via (...) inherit the
ERROR trap.
extglob
Enable extended pattern-matching facilities such as +(...).
extquote *
Allow $'...' and $"..." within ${variable} expansions inside
double quotes.
failglob
Cause patterns that do not match filenames to produce an
error.
force_fignore *
When doing completion, ignore words matching the list of
suffixes in FIGNORE, even if such words are the only possible
completions.
globstar
During filename expansion, the pattern ** matches all directories
and subdirectories, and filenames in directories, recursively.
Only directories and subdirectories match if the pattern ends
in /.
gnu_errfmt
Print error messages in the standard GNU format.
histappend
Append the history list to the file named by HISTFILE upon
exit, instead of overwriting the file.
histreedit
Allow a user to reedit a failed history substitution with the
readline library.
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646 | Chapter6: The Bash Shell
histverify
Place the results of history substitution into the readline
library’s editing buffer, in case the user wishes to modify it
further, instead of executing it directly.
hostcomplete *
If using readline, attempt hostname completion when a word
containing an @ is being completed.
huponexit
Send a SIGHUP to all running jobs upon exiting an interac-
tive shell.
interactive_comments *
Allow words beginning with # to start a comment in an inter-
active shell.
lithist
If cmdhist is also set, save multiline commands to the history
file with newlines instead of semicolons.
login_shell
Set by the shell when it is a login shell. This is a read-only
option.
mailwarn
Print the message “The mail in mailfile has been read” when a
file being checked for mail has been accessed since the last
time Bash checked it.
no_empty_cmd_completion
If using readline, do not search $PATH when a completion is
attempted on an empty line.
nocaseglob
Ignore letter case when doing filename matching.
nocasematch
Ignore case when pattern-matching in case or [[ ]] conditional
commands.
nullglob
Expand patterns that do not match any files to the null string,
instead of using the literal pattern as an argument.
progcomp *
Enable programmable completion.
promptvars *
Perform variable, command, and arithmetic substitution on
the values of PS1, PS2 and PS4.
restricted_shell
Set by the shell when it is a restricted shell. This is a read-only
option.
shift_verbose
Causes shift to print an error message when the shift count is
greater than the number of positional parameters.
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test | 647
The Bash Shell
sourcepath *
Causes the . (dot) and source commands to search $PATH in
order to find the file to read and execute.
xpg_echo
Causes echo to expand escape sequences, even without the -e
or -E options.
source sourcefile [arguments]
Identical to the . (dot) command; see that entry.
suspend suspend [-f]
Suspend the current shell. Often used to stop an su command.
Option
-f Force the suspension, even if the shell is a login shell.
test testcondition
or
[condition ]
or
[[condition ]]
Evaluate a condition and, if its value is true, return a zero exit
status; otherwise, return a nonzero exit status. An alternate form of
the command uses [ ] rather than the word test. An additional
alternate form uses [[ ]], in which case word splitting and path-
name expansion are not done. (See the [[ ]] entry.) condition is
constructed using the following expressions. Conditions are true if
the description holds true.
File conditions
-a file, -efile
file exists.
-b file
file exists and is a block special file.
-c file
file exists and is a character special file.
-d file
file exists and is a directory.
-f file
file exists and is a regular file.
-g file
file exists, and its set-group-id bit is set.
-G file
file exists, and its group is the effective group ID.
-h file, -L file
file exists and is a symbolic link.
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648 | Chapter6: The Bash Shell
-k file
file exists, and its sticky bit is set.
-N file
file exists and was modified after it was last read.
-O file
file exists, and its owner is the effective user ID.
-p file
file exists and is a named pipe (FIFO).
-r file
file exists and is readable.
-s file
file exists and has a size greater than zero.
-S file
file exists and is a socket.
-t [n]
The open file descriptor n is associated with a terminal device;
default n is 1.
-u file
file exists, and its set-user-id bit is set.
-w file
file exists and is writable.
-x file
file exists and is executable.
f1 -ef f2
Files f1 and f2 are linked (refer to same file).
f1 -nt f2
File f1 is newer than f2.
f1 -ot f2
File f1 is older than f2.
String conditions
string
string is not null.
-n s1
String s1 has nonzero length.
-z s1
String s1 has zero length.
s1 = = s2
Strings s1 and s2 are identical. s2 can be a wildcard pattern.
Quote s2 to treat it literally. Preferred over =.
s1 != s2
Strings s1 and s2 are not identical. s2 can be a wildcard
pattern. Quote s2 to treat it literally.
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test | 649
The Bash Shell
s1 =~ s2
String s1 matches extended regular expression s2. Quote s2 to
keep the shell from expanding embedded shell metacharac-
ters. Strings matched by parenthesized subexpressions are
placed into elements of the BASH_REMATCH array. See the
description of BASH_REMATCH earlier in this chapter.
s1 < s2
ASCII value of s1 precedes that of s2. (Valid only within [[ ]]
construct.)
s1 > s2
ASCII value of s1 follows that of s2. (Valid only within [[ ]]
construct.)
Internal shell conditions
-o opt
Shell option opt for set -o is on.
Integer comparisons
n1 -eq n2
n1 equals n2.
n1 -ge n2
n1 is greater than or equal to n2.
n1 -gt n2
n1 is greater than n2.
n1 -le n2
n1 is less than or equal to n2.
n1 -lt n2
n1 is less than n2.
n1 -ne n2
n1 does not equal n2.
Combined forms
(condition)
True if condition is true (used for grouping). For test and [ ],
the ()s should be quoted by a \. The form using [[ ]] doesn’t
require quoting the parentheses.
! condition
True if condition is false.
condition1 -a condition2
True if both conditions are true.
condition1 && condition2
True if both conditions are true. (Valid only within [[ ]]
construct.)
condition1 -o condition2
True if either condition is true.
condition1 || condition2
True if either condition is true. (Valid only within [[ ]]
construct.)
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650 | Chapter6: The Bash Shell
Examples
The following examples show the first line of various statements
that might use a test condition:
while test $# -gt 0 While there are arguments...
while [ -n "$1" ] While there are nonempty arguments..
if [ $count -lt 10 ] If $count is less than 10...
if [ -d RCS ] If the RCS directory exists...
if [ "$answer" != "y" ] If the answer is not y...
if [ ! -r "$1" -o ! -f "$1" ] If the first argument is not a readable
file or a regular file...
time timecommand
Execute command and print the total elapsed time, user time, and
system time (in seconds). Same as the Linux command time (see
Chapter 3), except that the built-in version can also time other
built-in commands as well as all commands in a pipeline.
times times
Print accumulated process times for user and system.
trap trap [options] [[commands]signals]
Execute commands if any signals are received. Common signals
include EXIT (0), HUP (1), INT (2), and TERM (15). Multiple
commands must be quoted as a group and separated by semi-
colons internally. If the command is the null string (i.e., trap ""
signals), the signals are ignored by the shell. If the commands are
omitted entirely, processing of the specified signals is reset to the
default action. If the command is -, the signals are reset to their
initial defaults.
If both commands and signals are omitted, list current trap assign-
ments. See the Examples here and in exec.
Options
-l List all signals and their numbers, like kill -l.
-p Print the current trap settings in a form suitable for rereading
later.
Signals
A list of signal names, numbers, and meanings were given earlier in
the kill entry; see the listing there. The shell allows you to use either
the signal number or the signal name (without the SIG prefix). In
addition, the shell supports “pseudo-signals,” signal names or
numbers that aren’t real operating system signals but which direct
the shell to perform a specific action. These signals are:
DEBUG
Execution of any command.
ERR
Nonzero exit status.
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type | 651
The Bash Shell
EXIT
Exit from shell (usually when shell script finishes).
0 Same as EXIT, for historical compatibility with the Bourne
shell.
RETURN
A return is executed, or a script run with . (dot) or source
finishes.
Examples
trap "" INT Ignore interrupts (signal 2)
trap INT Obey interrupts again
Remove a $tmp file when the shell program exits, or if the user logs
out, presses Ctrl-C, or does a kill:
trap "rm -f $tmp; exit" EXIT HUP INT TERM POSIX style
trap "rm -f $tmp; exit" 0 1 2 15 Pre-POSIX Bourne shell style
Print a “clean up” message when the shell program receives signals
SIGHUP, SIGINT, or SIGTERM:
trap 'echo Interrupt! Cleaning up...' HUP INT TERM
true true
Built-in command that exits with a true return value.
type type [-afpPt]commands
Show whether each command name is a Linux command, a built-
in command, an alias, a shell keyword, or a defined shell function.
Options
-a Print all locations in $PATH that include command, including
aliases and functions. Use -p together with -a to suppress
aliases and functions.
-f Suppress function lookup, as with command.
-p If type -t would print file for a given command, this option
prints the full pathname for the executable files. Otherwise, it
prints nothing.
-P Like -p, but force a PATH search, even if type -t would not
print file.
-t Print a word describing each command. The word is one of
alias, builtin, file, function, or keyword, depending upon the
type of each command.
Example
$type mv read if
mv is /bin/mv
read is a shell builtin
if is a shell keyword
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652 | Chapter6: The Bash Shell
ulimit ulimit [options] [n]
Print the value of one or more resource limits, or, if n is specified,
set a resource limit to n. Resource limits can be either hard (-H) or
soft (-S). By default, ulimit sets both limits or prints the soft limit.
The options determine which resource is acted on.
Options
-H Hard limit. Anyone can lower a hard limit; only privileged
users can raise it.
-S Soft limit. Anyone can raise a soft limit up to the value of the
hard limit.
-a Print all limits.
-b Maximum socket buffer size.
-c Maximum size of core files.
-d Maximum kilobytes of data segment or heap.
-e Maximum scheduling priority (“nice”).
-f Maximum size of files (the default option).
-i Maximum number of pending signals.
-l Maximum size of address space that can be locked in memory.
-m Maximum kilobytes of physical memory. (Not effective on all
Linux systems.)
-n Maximum number of file descriptors.
-p Maximum size of pipe buffers in 512-byte blocks. (May not
be set.)
-q Maximum number of bytes in POSIX message queues.
-r Maximum real-time scheduling priority.
-s Maximum stack size.
-t Maximum CPU seconds.
-T Maximum number of threads.
-u Maximum number of processes a single user can have.
-v Maximum kilobytes of virtual memory.
-x Maximum number of file locks
umask umask [-pS] [mask]
Display or set file creation mask. If mask begins with a digit, it is
treated as an octal number; otherwise it is treated as a symbolic
mask. The file creation mask determines which permission bits are
turned off (e.g., umask 002 produces rw-rw-r--). The mask is
similar to that accepted by the chmod command.
Options
-p Output is in a form that can be reread later by the shell.
-S Print the current mask using symbolic notation.
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while | 653
The Bash Shell
unalias unaliasnames
unalias -a
Remove names from the alias list. See also alias.
Option
-a Remove all aliases.
unset unset [options]names
Erase definitions of functions or variables listed in names.
Options
-f Unset functions names.
-v Unset shell variables names (default).
until untilcondition
do
commands
done
Until condition is met, do commands. condition is often specified
with the test command. See the Examples under case and test.
wait wait [ID]
Pause in execution until all background jobs complete (exit status 0
is returned), or pause until the specified background process ID or
job ID completes (exit status of ID is returned). Note that the shell
variable $! contains the process ID of the most recent background
process.
Example
wait $! Wait for most recent background process to finish
while whilecondition
do
commands
done
While condition is met, do commands. condition is often specified
with the test command. See the Examples under case and test.
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654
Chapter 7Pattern Matching
7
Pattern Matching
A number of Linux text-processing utilities let you search for, and in some cases
change, text patterns rather than fixed strings. These utilities include the editing
programs ed, ex, vi, and sed; the gawk programming language; and the
commands grep and egrep. Text patterns (called regular expressions in computer
science literature) contain normal characters mixed with special characters (called
metacharacters).
Perl’s regular expression support is so rich that it does not fit into this book; you
can find a description in the O’Reilly books Mastering Regular Expressions by
Jeffrey E.F. Friedl, Regular Expression Pocket Reference by Tony Stubblebine, Perl
in a Nutshell by Nathan Patwardhan et al., or Perl 5 Pocket Reference by Johan
Vromans. The Emacs editor also provides regular expressions similar to those
shown in this chapter. See the O’Reilly books Learning GNU Emacs by Debra
Cameron et al., or GNU Emacs Pocket Reference, also by Debra Cameron, for
details.
This chapter presents the following topics:
• Filenames versus patterns
• Description of metacharacters
• List of metacharacters available to each program
• Examples
For more information on regular expressions, see the aforementioned O’Reilly
book Mastering Regular Expressions.
Filenames Versus Patterns
Metacharacters used in pattern matching are different from metacharacters used
for filename expansion (see Chapter 6). However, several metacharacters have
meaning for both regular expressions and for filename expansion. This can lead to
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Metacharacters | 655
Pattern
Matching
a problem: the shell sees the command line first, and can potentially interpret an
unquoted regular expression metacharacter as a filename expansion. For example,
the command:
$grep [A-Z]* chap[12]
could be transformed by the shell into:
$grep Array.c Bug.c Comp.c chap1 chap2
and grep would then try to find the pattern Array.c in files Bug.c, Comp.c, chap1,
and chap2. To bypass the shell and pass the special characters to grep, use quotes
as follows:
$grep "[A-Z]*" chap[12]
Double quotes suffice in most cases, but single quotes are the safest bet, since the
shell does absolutely no expansions on single-quoted text.
Note also that in pattern matching, ? matches zero or one instance of a regular
expression; in filename expansion, ? matches a single character.
Metacharacters
Different metacharacters have different meanings, depending upon where they are
used. In particular, regular expressions used for searching through text (matching)
have one set of metacharacters, while the metacharacters used when processing
replacement text (such as in a text editor) have a different set. These sets also vary
somewhat per program. This section covers the metacharacters used for searching
and replacing, with descriptions of the variants in the different utilities.
Search Patterns
The characters in the following table have special meaning only in search patterns.
Character Pattern
. Match anysingle character except newline. Can match newline ingawk.
* Match any number (or none) of the single character that immediately precedes it. The preceding char-
acter can also be a regular expression. For example, since. (dot) means any character,.* means “match
any number of any character.”
^ Match the following regular expression at the beginning of the line or string.
$ Match the preceding regular expression at the end of the line or string.
[ ] Match anyone of the enclosed characters. A hyphen (-) indicates a range of consecutive characters. A
circumflex (^) as the first character in the brackets reverses the sense: it matches any one characternot
in the list. A hyphen or close bracket (]) as the first character is treated as a member of the list. All other
metacharacters are treated as members of the list (i.e., literally).
{n,m} Match a range of occurrences of the single character that immediately precedes it. The preceding char-
acter can also be a regular expression.{n} matches exactlyn occurrences,{n,} matches at leastn occur-
rences, and{n,m} matches any number of occurrences betweenn andm.n andm must be between 0
and 255, inclusive. (The GNU programs on Linux allow a range of 0 to 32767.)
\{n,m\} Just like{n,m}, earlier, but with backslashes in front of the braces.
\ Turn off the special meaning of the following character.
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656 | Chapter7: Pattern Matching
Linux allows the use of POSIX “character classes” within the square brackets that
enclose a group of characters. They are typed enclosed in [: and :]. For example,
[[:alnum:]] matches a single alphanumeric character.
Finally, the GNU utilities on Linux accept additional escape sequences that act
like metacharacters. (Because \b can also be interpreted as the sequence for the
ASCII Backspace character, different utilities treat it differently. Check each
utility’s documentation.)
Replacement Patterns
The characters in the following table have special meaning only in replacement
patterns, used for example in editing, when searching for and replacing text.
\( \) Savethesubpatternenclosedbetween\(and\)intoaspecialholdingspace.Uptoninesubpatternscan
be saved on a single line. The text matched by the subpatterns can be “replayed” in substitutions by the
escape sequences\1 to\9.
\n Replay thenth subpattern enclosed in\( and\) into the pattern at this point.n is a number from 1 to 9,
with 1 starting on the left. See the following Examples.
\< \> Match characters at beginning (\<) or end (\>) of a word.
+ Match one or more instances of preceding regular expression.
? Match zero or one instances of preceding regular expression.
| Match one or the other of the regular expressions specified before and after the vertical bar. (This is
known as alternation.)
() Apply a match to the enclosed group of regular expressions.
Class Characters matched Class Characters matched
alnum Alphanumeric characters lower Lowercase characters
alpha Alphabetic characters print Printable characters
blank Space or Tab punct Punctuation characters
cntrl Control characters space Whitespace characters
digit Decimal digits upper Uppercase characters
graph Non-space characters xdigit Hexadecimal digits
Sequence Meaning
\b Word boundary, either beginning or end of a word, as for the\< and\> metacharacters described
earlier.
\B Interword match; matches between two word-constituent characters.
\w Matches any word-constituent character; equivalent to[[:alnum:]_].
\W Matches any non-word-constituent character; equivalent to[^[:alnum:]_].
\` Beginning of an Emacs buffer. Used by most other GNU utilities to mean unambiguously “beginning of
string.”
\’ End of an Emacs buffer. Used by most other GNU utilities to mean unambiguously “end of string.”
Character Pattern
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Metacharacters, Listed by Program | 657
Pattern
Matching
Metacharacters, Listed by Program
Some metacharacters are valid for one program but not for another. Those that
are available are marked by a bullet (•) in the following table. Items marked with
a “P” are specified by POSIX. Full descriptions were provided in the previous
section.
Character Pattern
\ Turn off the special meaning of the following character.
\n Reuse the text matched by thenth subpattern previously saved by\( and\) as part of the replacement
pattern.n is a number from 1 to 9, with 1 starting on the left.
& Reuse the text matched by the search pattern as part of the replacement pattern.
~ Reuse the previous replacement pattern in the current replacement pattern. Must be the only character
in the replacement pattern (ex andvi).
% Reuse the previous replacement pattern in the current replacement pattern. Must be the only character
in the replacement pattern (ed).
\u Convert the first character of replacement pattern to uppercase.
\U Convert the entire replacement pattern to uppercase.
\l Convert the first character of replacement pattern to lowercase.
\L Convert the entire replacement pattern to lowercase.
\e Turn off previous\u or\l.
\E Turn off previous\U or\L.
Symbol ed ex vi sed gawk grep egrep Action
. • • • • • • • Match any character.
* • • • • • • • Match zero or more preceding
characters.
^ • • • • • • • Match beginning of line/string.
$ • • • • • • • Match end of line/string.
\ • • • • • • • Escape following character.
[ ] • • • • • • • Match one from a set.
\(\) • • • • • Store pattern for later replay. a
a Stored subpatterns can be “replayed” during matching. See the following table.
\n • • • • • Replay subpattern in match.
{ } • P • P Match a range of instances.
\{\} • • • Match a range of instances.
\<\> • • • Match word’s beginning or end.
+ • • Match one or more preceding
characters.
? • • Match zero or one preceding
characters.
| • • Separate choices to match.
() • • Group expressions to match.
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658 | Chapter7: Pattern Matching
Note that in ed, ex, vi, and sed, you specify both a search pattern (on the left) and
a replacement pattern (on the right). The metacharacters listed above are mean-
ingful only in a search pattern.
In ed, ex, vi, and sed, the metacharacters in the following table are valid only in a
replacement pattern.
Examples of Searching
When used with grep or egrep, regular expressions should be surrounded by
quotes. (If the pattern contains a $, you must use single quotes; e.g., 'pattern'.)
When used with ed, ex, sed, and gawk, regular expressions are usually
surrounded by /, although (except for gawk) any delimiter works. The following
tables show some sample patterns.
Symbol ex vi sed ed Action
\ • • • • Escape following character.
\n • • • • Text matching pattern stored in\(\).
& • • • • Text matching search pattern.
~ • • Reuse previous replacement pattern.
% • Reuse previous replacement pattern.
\u \U • • Change character(s) to uppercase.
\l \L • • Change character(s) to lowercase.
\e • • Turn off previous\u or\l.
\E • • Turn off previous\U or\L.
Pattern What does it match?
bag The stringbag.
^bag bag at the beginning of the line.
bag$ bag at the end of the line.
^bag$ bag as the only word on the line.
[Bb]ag Bag orbag.
b[aeiou]g Second letter is a vowel.
b[^aeiou]g Second letter is a consonant (or uppercase or symbol).
b.g Second letter is any character.
^...$ Any line containing exactly three characters.
^\. Any line that begins with a dot.
^\.[a-z][a-z] Same, followed by two lowercase letters (e.g.,troff requests).
^\.[a-z]\{2\} Same as previous;ed,grep, andsed only.
^[^.] Any line that doesn’t begin with a dot.
bugs* bug,bugs,bugss, etc.
“word” A word in quotes.
“*word"* A word, with or without quotes.
[A-Z][A-Z]* One or more uppercase letters.
[A-Z]+ Same;egrep orgawk only.
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Examples of Searching | 659
Pattern
Matching
Examples of Searching and Replacing
The examples in the following table show the metacharacters available to sed or
ex. Note that ex commands begin with a colon. A space is marked by a ❐; a tab is
marked by a tab.
[[:upper:]]+ Same as previous,egrep orgawk.
[A-Z].* An uppercase letter, followed by zero or more characters.
[A-Z]* Zero or more uppercase letters.
[a-zA-Z] Any letter, either lower- or uppercase.
[^0-9A-Za-z] Any symbol or space (not a letter or a number).
[^[:alnum:]] Same, using POSIX character class.
egrep or gawk pattern What does it match?
[567] One of the numbers5,6, or7.
five|six|seven One of the wordsfive,six, orseven.
80[2-4]?86 8086,80286,80386, or80486.
80[2-4]?86|(Pentium(-III?)?) 8086,80286,80386,80486,Pentium,Pentium-II, orPentium-III.
compan(y|ies) company orcompanies.
ex or vi pattern What does it match?
\<the Words liketheater orthe.
the\> Words likebreathe orthe.
\<the\> The wordthe.
ed, sed, or grep pattern What does it match?
0\{5,\} Five or more zeros in a row.
[0-9]\{3\}-[0-9]\{2\}-[0-9]\{4\} U.S. Social Security number (nnn-nn-nnnn).
\(why\).*\1 A line with two occurrences ofwhy.
\([[:alpha:]_][[:alnum:]_.]*\) = \1; C/C++ simple assignment statements.
Command Result
s/.*/( & )/ Redo the entire line, but add spaces and parentheses.
s/.*/mv & &.old/ Change a wordlist (one word per line) intomv commands.
/^$/d Delete blank lines.
:g/^$/d Same as previous, inex editor.
/^[❐tab]*$/d Delete blank lines, plus lines containing only spaces or tabs.
:g/^[❐tab]*$/d Same as previous, inex editor.
s/❐❐*/❐/g Turn one or more spaces into one space.
:%s/❐❐*/❐/g Same as previous, inex editor.
:s/[0-9]/Item &:/ Turn a number into an item label (on the current line).
:s Repeat the substitution on the first occurrence.
:& Same as previous.
:sg Same as previous, but for all occurrences on the line.
:&g Same as previous.
:%&g Repeat the substitution globally (i.e., on all lines).
Pattern What does it match?
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660 | Chapter7: Pattern Matching
Finally, some sed examples for transposing words. A simple transposition of two
words might look like this:
s/die or do/do or die/ Transpose words
The real trick is to use hold buffers to transpose variable patterns. For example:
s/\([Dd]ie\) or \([Dd]o\)/\2 or \1/ Transpose, using hold buffers
:.,$s/Fortran/\U&/g On current line to last line, change word to uppercase.
:.,$s/\(F\)\(ORTRAN\)/\1\L\2/g On current line to last line, change spelling of “FORTRAN” to correct, modern
usage.
:%s/.*/\L&/ Lowercase entire file.
:s/\<./\u&/g Uppercase first letter of each word on current line. (Useful for titles.)
:%s/yes/No/g Globally change a word toNo.
:%s/Yes/~/g Globally change a different word toNo (previous replacement).
Command Result
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661
Chapter 8The Emacs Editor
8
The Emacs Editor
The Emacs editor is found on many Unix systems, including Linux, because it is a
popular alternative to vi. Many versions are available, but this book documents
the most popular one, GNU Emacs (version 22.3), which is available from the
Free Software Foundation (http://www.gnu.org/software/emacs).
Emacs is much more than “just an editor”—in fact, it provides a fully integrated
user environment. From within Emacs, you can issue individual shell commands
or open a window where you can work in the shell, read and send mail, read
news, access the Internet, write and test programs, and maintain a calendar. To
fully describe Emacs would require more space than we have available. In this
chapter, therefore, we focus on the editing capabilities of Emacs.
This chapter presents the following topics:
• Conceptual overview
• Command-line syntax
• Summary of emacs commands by group
• Summary of emacs commands by key
• Summary of emacs commands by name
For more information about Emacs, see Learning GNU Emacs, by Debra Cameron
et al. (O’Reilly).
Conceptual Overview
This section describes some Emacs terminology that may be unfamiliar if you
haven’t used Emacs before.
Modes
One of the features that makes Emacs popular is its editing modes. The modes set
up an environment designed for the type of editing you are doing, with features
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662 | Chapter8: The Emacs Editor
such as having appropriate key bindings available and automatically indenting
according to standard conventions for that type of document. There are two types
of modes: major and minor. The major modes include modes for various program-
ming languages such as C or Perl, for text processing (e.g., XML, or even straight
text), and many more. One particularly useful major mode is Dired (Directory
Editor), which has commands that let you manage directories. Minor modes set or
unset features that are independent of the major mode, such as auto-fill (which
controls word wrapping), insert versus overwrite, and auto-save. For a full discussion
of modes, see Learning GNU Emacs (O’Reilly) or the Emacs Info documentation
system (C-h i).
Buffer and Window
When you open a file in Emacs, the file is put into a buffer so you can edit it. If
you open another file, that file goes into another buffer. The view of the buffer
contents that you have at any point in time is called a window. For a small file, the
window might show the entire file; for a large file, it shows only a portion of a file.
Emacs allows multiple windows to be open at the same time, to display the
contents of different buffers or different portions of a single buffer.
Point and Mark
When you are editing in Emacs, the position of the cursor is known as point. You
can set a mark at another place in the text to operate on the region between point
and mark. This is a very useful feature for such operations as deleting or moving
an area of text.
Kill and Yank
Emacs uses the terms kill and yank for the concepts more commonly known today
as cut and paste. You cut text in Emacs by killing it, and paste it by yanking it
back. If you do multiple kills in a row, you can yank them back all at once.
Notes on the Tables
Emacs commands use the Ctrl key and the Meta key (Meta is usually the Alt key
or the Escape key). In this chapter, the notation C- indicates that the Ctrl key is
pressed at the same time as the character that follows. Similarly, M- indicates the
use of the Meta key. When using Escape for Meta, press and release the Escape
key, then type the next key. If you use Alt (or Option on the Mac) for Meta, it is
just like Ctrl or Shift, and you should press it simultaneously with the other key(s).
In the command tables that follow, the first column lists the keystroke and the last
column describes it. When there is a middle column, it lists the command name.
If there are no keystrokes for a given command, you’ll see (none) in the first
column. Access these commands by typing M-x followed by the command name.
If you’re unsure of the name, you can type a tab or a carriage return, and Emacs
lists possible completions of what you’ve typed so far.
Because Emacs is such a comprehensive editor, containing literally thousands of
commands, some commands must be omitted for the sake of preserving a “quick”
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Summary of Commands by Group | 663
The Emacs
Editor
reference. You can browse the command set from within Emacs by typing C-h
(for help) or M-x Tab (for command names).
Absolutely Essential Commands
If you’re just getting started with Emacs, here’s a short list of the most important
commands.
Command-Line Syntax
To start an Emacs editing session, type:
emacs [file]
Summary of Commands by Group
Reminder: C- indicates the Ctrl key; M- indicates the Meta key.
File-Handling Commands
Keystrokes Description
C-h Enter the online help system.
C-x C-s Save the file.
C-x C-c Exit Emacs.
C-x u Undo last edit (can be repeated).
C-g Get out of current command operation.
C-p Move up to the previous line.
C-n Move down to the next line.
C-f Move forward one character.
C-b Move backward one character.
C-v Move forward by one screen.
M-v Move backward by one screen
C-s Search forward for characters.
C-r Search backward for characters.
C-d Delete the current character.
Del Delete the previous character.
Keystrokes Command name Description
C-x C-f find-file Find file and read it.
C-x C-v find-alternate-file Read another file; replace the one read with C-x C-f.
C-x i insert-file Insert file at cursor position.
C-x C-s save-buffer Save file (may hang terminal; use C-q to restart).
C-x C-w write-file Write buffer contents to file.
C-x C-c save-buffers-kill-emacs Exit Emacs.
C-z suspend-emacs Suspend Emacs (useexit orfg to restart).
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Cursor-Movement Commands
Deletion Commands
Keystrokes Command name Description
C-f forward-char Moveforward one character (right).
C-b backward-char Movebackward one character (left).
C-p previous-line Move toprevious line (up).
C-n next-line Move tonext line (down).
M-f forward-word Move one wordforward.
M-b backward-word Move one wordbackward.
C-a beginning-of-line Move to beginning of line.
C-e end-of-line Move toend of line.
M-a backward-sentence Move backward one sentence.
M-e forward-sentence Move forward one sentence.
M-{ backward-paragraph Move backward one paragraph.
M-} forward-paragraph Move forward one paragraph.
C-v scroll-up Move forward one screen.
M-v scroll-down Move backward one screen.
C-x [ backward-page Move backward one page.
C-x ] forward-page Move forward one page.
M-> end-of-buffer Move to end of file.
M-< beginning-of-buffer Move to beginning of file.
M-g g or M-g M-g goto-line Go to linen of file.
(none) goto-char Go to charactern of file.
C-l recenter Redraw screen with current line in the center.
M-n digit-argument Repeat the next commandn times.
C-un universal-argument Repeat the next commandn times.
Keystrokes Command name Description
Del backward-delete-char Delete previous character.
C-d delete-char Delete character under cursor.
M-Del backward-kill-word Delete previous word.
M-d kill-word Delete the word the cursor is on.
C-k kill-line Delete from cursor to end of line.
M-k kill-sentence Delete sentence the cursor is on.
C-x Del backward-kill-sentence Delete previous sentence.
C-y yank Restore what you’ve deleted.
C-w kill-region Delete a marked region (see next section).
(none) backward-kill-paragraph Delete previous paragraph.
(none) kill-paragraph Delete from the cursor to the end of the paragraph.
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The Emacs
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Paragraphs and Regions
Stopping and Undoing Commands
Transposition Commands
Search Commands
Keystrokes Command name Description
C-@ set-mark-command Mark the beginning (or end) of a region.
C-Space (same as above) (same as above)
C-x C-p mark-page Mark page.
C-x C-x exchange-point-and-mark Exchange location of cursor and mark.
C-x h mark-whole-buffer Mark buffer.
M-q fill-paragraph Reformat paragraph.
(none) fill-region Reformat individual paragraphs within a region.
M-h mark-paragraph Mark paragraph.
Keystrokes Command name Description
C-g keyboard-quit Abort current command.
C-x u advertised-undo Undo last edit (can be done repeatedly).
(none) revert-buffer Restorebuffertothestateitwasinwhenthefilewaslast
saved (or auto-saved).
Keystrokes Command name Description
C-t transpose-chars Transpose two letters.
M-t transpose-words Transpose two words.
C-x C-t transpose-lines Transpose two lines.
(none) transpose-sentences Transpose two sentences.
(none) transpose-paragraphs Transpose two paragraphs.
Keystrokes Command name Description
C-s isearch-forward Incremental search forward.
C-r isearch-backward Incremental search backward
M-% query-replace Search and replace.
C-M-s Enter re-search-forward Regular expression search forward.
C-M-r Enter re-search-backward Regular expression search backward
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666 | Chapter8: The Emacs Editor
Capitalization Commands
Word-Abbreviation Commands
Buffer-Manipulation Commands
Window Commands
Keystrokes Command name Description
M-c capitalize-word Capitalize first letter of word.
M-u upcase-word Uppercase word.
M-l downcase-word Lowercase word.
M- - M-c negative-argument; capitalize-word Capitalize previous word.
M- - M-u negative-argument; upcase-word Uppercase previous word.
M- - M-l negative-argument; downcase-word Lowercase previous word.
(none) capitalize-region Capitalize region.
C-x C-u upcase-region Uppercase region
C-x C-l downcase-region Lowercase region.
Keystrokes Command name Description
(none) abbrev-mode Enter (or exit) word abbreviation mode.
C-x a i g inverse-add-global-abbrev Type global abbreviation, then definition.
C-x a i l inverse-add-local-abbrev Type local abbreviation, then definition.
(none) unexpand-abbrev Undo the last word abbreviation.
(none) write-abbrev-file Write the word abbreviation file.
(none) edit-abbrevs Edit the word abbreviations.
(none) list-abbrevs View the word abbreviations.
(none) kill-all-abbrevs Kill abbreviations for this session.
Keystrokes Command name Description
C-x b switch-to-buffer Move to specified buffer.
C-x C-b list-buffers Display buffer list.
C-x k kill-buffer Delete specified buffer.
(none) kill-some-buffers Ask about deleting each buffer.
(none) rename-buffer Change buffer name to specified name.
C-x s save-some-buffers Ask whether to save each modified buffer.
Keystrokes Command name Description
C-x 2 split-window-vertically Divide the current window into two, one on top of
the other.
C-x 3 split-window-horizontally Divide the current window into two, side by side.
C-x > scroll-right Scroll the window right.
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The Emacs
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Special Shell Characters
Indentation Commands
C-x < scroll-left Scroll the window left.
C-x o other-window Move to the other window.
C-x 0 delete-window Delete current window.
C-x 1 delete-other-windows Delete all windows but this one.
(none) delete-windows-on Delete all windows on a given buffer.
C-x ^ enlarge-window Make window taller.
(none) shrink-window Make window shorter.
C-x } enlarge-window-horizontally Make window wider.
C-x { shrink-window-horizontally Make window narrower.
C-M-v scroll-other-window Scroll other window.
C-x 4 f find-file-other-window Find a file in the other window.
C-x 4 b switch-to-buffer-other-window Select a buffer in the other window.
C-x 5 f find-file-other-frame Find a file in a new frame.
C-x 5 b switch-to-buffer-other-frame Select a buffer in another frame.
(none) compare-windows Compare two buffers; show first difference.
Keystrokes Command Name Description
M-! shell-command Run a shell command and display the results.
(none) shell Start a shell buffer.
C-c C-c comint-interrupt-subjob Terminate the current job.
C-c C-d comint-send-eof End of file character.
C-c C-u comint-kill-input Erase current line.
C-c C-w backward-kill-word Erase the previous word.
C-c C-z comint-stop-subjob Suspend the current job.
Keystrokes Command name Description
C-x . set-fill-prefix Use characters from the beginning of the line up to
the cursor column as the “fill prefix.” This prefix is
prepended to each line in the paragraph. Cancel the
prefix by typing this command in column 1.
(none) indented-text-mode Major mode: each tab defines a new indent for
subsequent lines.
(none) text-mode Exit indented text mode; return to text mode.
C-M-\ indent-region Indent a region to match first line in region.
M-m back-to-indentation Move cursor to first nonblank character on line.
M-^ delete-indentation Join this line to the previous one.
C-M-o split-line Split line at cursor; indent to column of cursor.
(none) fill-individual-paragraphs Reformat indented paragraphs, keeping indentation.
Keystrokes Command name Description
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Centering Commands
Macro Commands
Detail Information Help Commands
Keystrokes Command name Description
M-s center-line Center line that cursor is on.
M-S center-paragraph Center paragraph that cursor is on.
(none) center-region Center currently defined region.
Keystrokes Command name Description
C-x (or F3 key start-kbd-macro Start macro definition.
C-x )or F4 key end-kbd-macro End macro definition.
C-x eor F4 key call-last-kbd-macro Execute last macro defined.
M-n C-x e digit-argument and call-last-kbd-
macro
Execute last macro definedn times.
C-u C-x ( universal-argument and start-kbd-
macro
Execute last macro defined, then add keystrokes.
(none) name-last-kbd-macro Name last macro you created (before saving it).
(none) insert-kbd-macro Insert the macro you named into a file.
(none) load-file Load macro files you’ve saved and loaded.
(none) macroname Execute a keyboard macro you’ve saved.
C-x q kbd-macro-query Insert a query in a macro definition.
C-u C-x q (none) Insert a recursive edit in a macro definition.
C-M-c exit-recursive-edit Exit a recursive edit.
Keystrokes Command name Description
C-h a command-apropos What commands involve this concept?
C-h d apropos What functions and variables involve this concept?
C-h c describe-key-briefly What command does this keystroke sequence run?
C-h b describe-bindings What are all the key bindings for this buffer?
C-h k describe-key What command does this keystroke sequence run,
and what does it do?
C-h l view-lossage What are the last 100 characters I typed?
C-h e view-echo-area-messages Display the *Messages* buffer.
C-h w where-is What is the key binding for this command?
C-h f describe-function What does this function do?
C-h v describe-variable What does this variable mean, and what is its value?
C-h m describe-mode Tell me about the mode the current buffer is in.
C-h s describe-syntax What is the syntax table for this buffer?
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The Emacs
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Help Commands
Summary of Commands by Key
Emacs commands are presented below in two alphabetical lists. Reminder: C- indicates
the Ctrl key; M- indicates the Meta key.
Control-Key Sequences
Keystrokes Command name Description
C-h t help-with-tutorial Run the Emacs tutorial.
C-h i info Start the Info documentation reader.
C-h r info-emacs-command View the Emacs documentation in the Info reader.
C-h n view-emacs-news View news about updates to Emacs.
C-h C-c describe-copying View the Emacs General Public License.
C-h C-d describe-distribution View information on ordering Emacs from the FSF.
C-h C-w describe-no-warranty View the (non)warranty for Emacs.
Keystrokes Command name Description
C-@ set-mark-command Mark the beginning (or end) of a region.
C-Space (same as previous)
C-] (none) Exit recursive edit and exit query-replace.
C-a beginning-of-line Move to beginning of line.
C-b backward-char Movebackward one character (left).
C-c C-c comint-interrupt-subjob Terminate the current job.
C-c C-d comint-send-eof End-of-file character.
C-c C-u comint-kill-input Erase current line.
C-c C-w backward-kill-word Erase the previous word.
C-c C-z comint-stop-subjob Suspend the current job.
C-d delete-char Delete character under cursor.
C-e end-of-line Move toend of line.
C-f forward-char Moveforward one character (right).
C-g keyboard-quit Abort current command.
C-h help-command Enter the online help system.
C-h a command-apropos What commands involve this concept?
C-h b describe-bindings What are all the key bindings for this buffer?
C-h C-c describe-copying View the Emacs General Public License.
C-h C-d describe-distribution View information on ordering Emacs from FSF.
C-h C-w describe-no-warranty View the (non)warranty for Emacs.
C-h c describe-key-briefly What command does this keystroke sequence run?
C-h d apropos What functions and variables involve this concept?
C-h e view-echo-area-messages Display the *Messages* buffer.
C-h f describe-function What does this function do?
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670 | Chapter8: The Emacs Editor
C-h i info Start the Info documentation reader.
C-h k describe-key What command does this keystroke sequence run,
and what does it do?
C-h l view-lossage What are the last 100 characters I typed?
C-h m describe-mode Tell me about the mode the current buffer is in.
C-h n view-emacs-news View news about updates to Emacs.
C-h r info-emacs-manual View the Emacs documentation in the Info reader.
C-h s describe-syntax What is the syntax table for this buffer?
C-h t help-with-tutorial Run the Emacs tutorial.
C-h v describe-variable What does this variable mean, and what is its value?
C-h w where-is What is the key binding for this command?
C-k kill-line Delete from cursor to end of line.
C-l recenter Redraw screen with current line in the center.
C-M-\ indent-region Indent a region to match first line in region.
C-M-c exit-recursive-edit Exit a recursive edit.
C-M-o split-line Split line at cursor; indent to column of cursor.
C-M-v scroll-other-window Scroll other window.
C-n next-line Move tonext line (down).
C-p previous-line Move toprevious line (up).
C-r isearch-backward Start incremental search backward.
C-s isearch-forward Start incremental search forward.
C-t transpose-chars Transpose two letters.
C-un universal-argument Repeat the next commandn times.
C-u C-x ( universal-argument and start-kbd-
macro
Execute last macro defined, then add keystrokes.
C-u C-x q (none) Insert recursive edit in a macro definition.
C-v scroll-up Move forward one screen.
C-w kill-region Delete a marked region.
C-x ( start-kbd-macro Start macro definition.
C-x ) end-kbd-macro End macro definition.
C-x [ backward-page Move backward one page.
C-x ] forward-page Move forward one page.
C-x ^ enlarge-window Make window taller.
C-x { shrink-window-horizontally Make window narrower.
C-x } enlarge-window-horizontally Make window wider.
C-x < scroll-left Scroll the window left.
C-x > scroll-right Scroll the window right.
C-x . set-fill-prefix Use characters from the beginning of the line up to
the cursor column as the “fill prefix.” This prefix is
prepended to each line in the paragraph. Cancel the
prefix by typing this command in column 1.
C-x 0 delete-window Delete current window.
C-x 1 delete-other-windows Delete all windows but this one.
Keystrokes Command name Description
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The Emacs
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Meta-Key Sequences
C-x 2 split-window-vertically Divide the current window into two, one on top of
the other.
C-x 3 split-window-horizontally Divide the current window into two, side by side.
C-x 4 b switch-to-buffer-other-window Select a buffer in the other window.
C-x 4 f find-file-other-window Find a file in the other window.
C-x 5 b switch-to-buffer-other-frame Select a buffer in another frame.
C-x 5 f find-file-other-frame Find a file in a new frame.
C-x C-b list-buffers Display the buffer list.
C-x C-c save-buffers-kill-emacs Exit Emacs.
C-x C-f find-file Find file and read it.
C-x C-l downcase-region Lowercase region.
C-x C-p mark-page Mark page.
C-x C-q (none) Toggle read-only status of buffer.
C-x C-s save-buffer Save file (may hang terminal; use C-q to restart).
C-x C-t transpose-lines Transpose two lines.
C-x C-u upcase-region Uppercase region
C-x C-v find-alternate-file Read an alternate file, replacing the one read with
C-x C-f.
C-x C-w write-file Write buffer contents to file.
C-x C-x exchange-point-and-mark Exchange location of cursor and mark.
C-x DEL backward-kill-sentence Delete previous sentence.
C-x a i g inverse-add-global-abbrev Type global abbreviation, then definition.
C-x a i l inverse-add-local-abbrev Type local abbreviation, then definition.
C-x b switch-to-buffer Move to the buffer specified.
C-x e call-last-kbd-macro Execute last macro defined.
C-x h mark-whole-buffer Mark buffer.
C-x i insert-file Insert file at cursor position.
C-x k kill-buffer Delete the buffer specified.
C-x o other-window Move to the other window.
C-x q kbd-macro-query Insert a query in a macro definition.
C-x s save-some-buffers Ask whether to save each modified buffer.
C-x u advertised-undo Undo last edit (can be done repeatedly).
C-y yank Restore what you’ve deleted.
C-z suspend-emacs Suspend Emacs (useexit orfg to restart).
Keystrokes Command name Description
Meta (none) Exit a query-replace or successful search.
M- - M-c negative-argument; capitalize-word Capitalize previous word.
M- - M-l negative-argument;downcase-word Lowercase previous word.
M- - M-u negative-argument; upcase-word Uppercase previous word.
Keystrokes Command name Description
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Summary of Commands by Name
The Emacs commands below are presented alphabetically by command name.
Use M-x to access the command name. Reminder: C- indicates the Ctrl key; M-
indicates the Meta key.
M-$ spell-word Check spelling of word after cursor.
M-< beginning-of-buffer Move to beginning of file.
M-> end-of-buffer Move to end of file.
M-{ backward-paragraph Move backward one paragraph.
M-} forward-paragraph Move forward one paragraph.
M-^ delete-indentation Join this line to the previous one.
M-n digit-argument Repeat the next commandn times.
M-n C-x e digit-argument and call-last-kbd-
macro
Execute the last defined macron times.
M-a backward-sentence Move backward one sentence.
M-b backward-word Move one wordbackward.
M-c capitalize-word Capitalize first letter of word.
M-d kill-word Delete word that cursor is on.
M-DEL backward-kill-word Delete previous word.
M-e forward-sentence Move forward one sentence.
M-f forward-word Move one wordforward.
M-g g or M-g M-g goto-line Go to linen of file.
M-h mark-paragraph Mark paragraph.
M-k kill-sentence Delete sentence the cursor is on.
M-l downcase-word Lowercase word.
M-m back-to-indentation Move cursor to first nonblank character on line.
M-q fill-paragraph Reformat paragraph.
M-s center-line Center line that cursor is on.
M-S cemter-paragraph Center paragraph that cursor is on.
M-t transpose-words Transpose two words.
M-u upcase-word Uppercase word.
M-v scroll-down Move backward one screen.
M-x (none) Access command by command name.
Command name Keystrokes Description
macroname (none) Execute a keyboard macro you’ve saved.
abbrev-mode (none) Enter (or exit) word abbreviation mode.
advertised-undo C-x u Undo last edit (can be done repeatedly).
apropos (none) What functions and variables involve this concept?
back-to-indentation M-m Move cursor to first nonblank character on line.
backward-char C-b Movebackward one character (left).
backward-delete-char Del Delete previous character.
Keystrokes Command name Description
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The Emacs
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backward-kill-paragraph (none) Delete previous paragraph.
backward-kill-sentence C-x Del Delete previous sentence.
backward-kill-word C-c C-w Erase previous word.
backward-kill-word M-Del Delete previous word.
backward-page C-x [ Move backward one page.
backward-paragraph M-{ Move backward one paragraph.
backward-sentence M-a Move backward one sentence.
backward-word M-b Move backward one word.
beginning-of-buffer M-< Move to beginning of file.
beginning-of-line C-a Move to beginning of line.
call-last-kbd-macro C-x e Execute last macro defined.
capitalize-region (none) Capitalize region.
capitalize-word M-c Capitalize first letter of word.
center-line M-s Center line that cursor is on.
center-paragraph M-S Center paragraph that cursor is on.
center-region (none) Center currently defined region.
comint-interrupt-subjob C-c C-c Terminate the current job.
comint-kill-input C-c C-u Erase current line.
comint-send-eof C-c C-d End of file character.
comint-stop-subjob C-c C-z Suspend current job.
command-apropos C-h a What commands involve this concept?
compare-windows (none) Compare two buffers; show first difference.
delete-char C-d Delete character under cursor.
delete-indentation M-^ Join this line to previous one.
delete-other-windows C-x 1 Delete all windows but this one.
delete-window C-x 0 Delete current window.
delete-windows-on (none) Delete all windows on a given buffer.
describe-bindings C-h b What are all the key bindings for in this buffer?
describe-copying C-h C-c View the Emacs General Public License.
describe-distribution C-h C-d View information on ordering Emacs from the FSF.
describe-function C-h f What does this function do?
describe-key C-h k Whatcommanddoesthiskeystrokesequencerun,andwhatdoesit
do?
describe-key-briefly C-h c What command does this keystroke sequence run?
describe-mode C-h m Tell me about the mode the current buffer is in.
describe-no-warranty C-h C-w View the (non)warranty for Emacs.
describe-syntax C-h s What is the syntax table for this buffer?
describe-variable C-h v What does this variable mean, and what is its value?
digit-argument and call-last-
kbd-macro
M-n C-x e Execute the last defined macron times.
digit-argument M-n Repeat next commandn times.
downcase-region C-x C-l Lowercase region.
Command name Keystrokes Description
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674 | Chapter8: The Emacs Editor
downcase-word M-l Lowercase word.
edit-abbrevs (none) Edit word abbreviations.
end-kbd-macro C-x ) or F4 key End macro definition.
end-of-buffer M-> Move to end of file.
end-of-line C-e Move to end of line.
enlarge-window C-x ^ Make window taller.
enlarge-window-horizontally C-x } Make window wider.
exchange-point-and-mark C-x C-x Exchange location of cursor and mark.
exit-recursive-edit C-M-c Exit a recursive edit.
fill-individual-paragraphs (none) Reformat indented paragraphs, keeping indentation.
fill-paragraph M-q Reformat paragraph.
fill-region (none) Reformat individual paragraphs within a region.
find-alternate-file C-x C-v Read an alternate file, replacing the one read with C-x C-f.
find-file C-x C-f Find file and read it.
find-file-other-frame C-x 5 f Find a file in a new frame.
find-file-other-window C-x 4 f Find a file in the other window.
forward-char C-f Moveforward one character (right).
forward-page C-x ] Move forward one page.
forward-paragraph M-} Move forward one paragraph.
forward-sentence M-e Move forward one sentence.
forward-word M-f Move forward one word.
goto-char (none) Go to charactern of file.
goto-line M-g g or M-g
M-g
Go to linen of file.
help-command C-h Enter the online help system.
help-with-tutorial C-h t Run the Emacs tutorial.
indent-region C-M-\ Indent a region to match first line in region.
indented-text-mode (none) Major mode: each tab defines a new indent for subsequent lines.
info C-h i Start the Info documentation reader.
info-emacs-manual C-h r View the Emacs documentation in the Info reader.
insert-file C-x i Insert file at cursor position.
insert-kbd-macro (none) Insert the macro you named into a file.
inverse-add-global-abbrev C-x a i g Type global abbreviation, then definition.
inverse-add-local-abbrev C-x a i l Type local abbreviation, then definition.
isearch-backward C-r Start incremental search backward.
isearch-backward-regexp C-r Same, but search for regular expression.
isearch-forward C-s Start incremental search forward.
isearch-forward-regexp C-r Same, but search for regular expression.
kbd-macro-query C-x q Insert a query in a macro definition.
keyboard-quit C-g Abort current command.
kill-all-abbrevs (none) Kill abbreviations for this session.
kill-buffer C-x k Delete the buffer specified.
Command name Keystrokes Description
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Summary of Commands by Name | 675
The Emacs
Editor
kill-line C-k Delete from cursor to end of line.
kill-paragraph (none) Delete from cursor to end of paragraph.
kill-region C-w Delete a marked region.
kill-sentence M-k Delete sentence the cursor is on.
kill-some-buffers (none) Ask about deleting each buffer.
kill-word M-d Delete word the cursor is on.
list-abbrevs (none) View word abbreviations.
list-buffers C-x C-b Display buffer list.
load-file (none) Load macro files you’ve saved.
mark-page C-x C-p Mark page.
mark-paragraph M-h Mark paragraph.
mark-whole-buffer C-x h Mark buffer.
name-last-kbd-macro (none) Name last macro you created (before saving it).
negative-argument;
capitalize-word
M- - M-c Capitalize previous word.
negative-argument;
downcase-word
M- - M-l Lowercase previous word.
negative-argument;
upcase-word
M- - M-u Uppercase previous word.
next-line C-n Move tonext line (down).
other-window C-x o Move to the other window.
previous-line C-p Move toprevious line (up).
query-replace M-% Search and replace.
query-replace-regexp C-% Meta Query-replace a regular expression.
recenter C-l Redraw screen, with current line in center.
rename-buffer (none) Change buffer name to specified name.
replace-regexp (none) Replace a regular expression unconditionally.
re-search-backward (none) Simple regular expression search backward.
re-search-forward (none) Simple regular expression search forward.
revert-buffer (none) Restorebuffertothestateitwasinwhenthefilewaslastsaved(or
auto-saved).
save-buffer C-x C-s Save file (may hang terminal; use C-q to restart).
save-buffers-kill-emacs C-x C-c Exit Emacs.
save-some-buffers C-x s Ask whether to save each modified buffer.
scroll-down M-v Move backward one screen.
scroll-left C-x < Scroll the window left.
scroll-other-window C-M-v Scroll other window.
scroll-right C-x > Scroll the window right.
scroll-up C-v Move forward one screen.
set-fill-prefix C-x . Use characters from the beginning of the line up to the cursor
column as the “fill prefix.” This prefix is prepended to each line in the
paragraph. Cancel the prefix by typing this command in column 1.
set-mark-command C-@ or
C-Space
Mark the beginning (or end) of a region.
Command name Keystrokes Description
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676 | Chapter8: The Emacs Editor
shell (none) Start a shell buffer.
shell-command M-! Run a shell command and display the results.
shrink-window (none) Make window shorter.
shrink-window-horizontally C-x { Make window narrower.
spell-buffer (none) Check spelling of current buffer.
spell-region (none) Check spelling of current region.
spell-string (none) Check spelling of string typed in minibuffer.
spell-word M-$ Check spelling of word after cursor.
split-line C-M-o Split line at cursor; indent to column of cursor.
split-window-vertically C-x 2 Divide the current window into two, one on top of the other.
split-window-horizontally C-x 3 Divide the current window into two, side by side.
start-kbd-macro C-x(orF3key Start macro definition.
suspend-emacs C-z Suspend Emacs (useexit orfg to restart).
switch-to-buffer C-x b Move to the buffer specified.
switch-to-buffer-other-frame C-x 5 b Select a buffer in another frame.
switch-to-buffer-other-
window
C-x 4 b Select a buffer in the other window.
text-mode (none) Exit indented text mode; return to text mode.
transpose-chars C-t Transpose two letters.
transpose-lines C-x C-t Transpose two lines.
transpose-paragraphs (none) Transpose two paragraphs.
transpose-sentences (none) Transpose two sentences.
transpose-words M-t Transpose two words.
unexpand-abbrev (none) Undo the last word abbreviation.
universal-argument C-un Repeat the next commandn times.
universal-argument and
start-kbd-macro
C-u C-x ( Execute last macro defined, then add keystrokes to it.
upcase-region C-x C-u Uppercase region.
upcase-word M-u Uppercase word.
view-emacs-news C-h n View news about updates to Emacs.
view-lossage C-h l What are the last 100 characters I typed?
where-is C-h w What is the key binding for this command?
write-abbrev-file (none) Write the word abbreviation file.
write-file C-x C-w Write buffer contents to file.
yank C-y Restore what you’ve deleted.
Command name Keystrokes Description
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677
Chapter 9vi, ex, and vim
9
The vi, ex, and vim Editors
The vi and ex editors are the “standard” editors on Unix systems. You can count
on there being some version of them, no matter what Unix flavor you are using.
The two editors are in fact the same program; based on how it was invoked, the
editor enters full-screen mode or line mode.
vim is a popular extended version of vi. On some Linux distributions, the vi
command invokes vim in a vi-compatible mode.
This chapter presents the following topics:
• Conceptual overview
• Command-line syntax
• Review of vi operations
• Alphabetical list of keys in command mode
• vi commands
• vi configuration
• ex basics
• Alphabetical summary of ex commands
vi is pronounced “vee eye.”
Besides the original Unix vi, there are a number of freely available vi clones
(including vim). Both the original vi and the clones are covered in Learning the vi
and Vim Editors by Arnold Robbins et al. (O’Reilly).
Conceptual Overview
vi is the classic screen-editing program for Unix. A number of enhanced versions
exist, including nvi, vim, vile, and elvis. On GNU/Linux systems, the vi
command is usually one of these programs (either a copy or a link). The Emacs
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678 | Chapter9: The vi, ex, and vim Editors
editor, covered in Chapter 8, has several vi modes that allow you to use many of
the same commands covered in this chapter.
The vi editor operates in two modes: command mode and insert mode. The dual
modes make vi an attractive editor for users who separate text entry from editing.
For users who edit as they type, the modeless editing of Emacs can be more
comfortable. However, vim supports both ways of editing, through the insert-
mode option.
vi is based on an older line editor called ex. (ex, in turn, was developed by Bill Joy
at the University of California, Berkeley, from the primordial Unix line editor, ed.)
A user can invoke powerful editing capabilities within vi by typing a colon (:),
entering an ex command, and pressing the Enter key. Furthermore, you can place
ex commands in a startup file called ~/.exrc, which vi reads at the beginning of
your editing session. Because ex commands are such an important part of vi, they
are also described in this chapter.
One of the most common versions of vi found on Linux systems is Bram
Moolenaar’s Vi IMproved, or vim. On some Linux distributions, vim is the
default version of vi and runs when you invoke vi. vim offers many extra features,
and optionally changes some of the basic features of vi, most notoriously
changing the undo key to support multiple levels of undo.
Fully documenting vim is beyond the scope of this chapter, but we do cover some
of its most commonly used options and features. Beyond what we cover here, vim
offers enhanced support to programmers through an integrated build and debug-
ging process, syntax highlighting, extended ctags support, and support for Perl
and Python, as well as GUI fonts and menus, function-key mapping, independent
mapping for each mode, and more. Fortunately, vim comes with a powerful
internal help system that you can use to learn more about the things we just
couldn’t fit into this chapter. See http://www.vim.org for more information.
Command-Line Syntax
The three most common ways of starting a vi session are:
vi [options]file
vi [options] +num file
vi [options] +/pattern file
You can open file for editing, optionally at line num or at the first line matching
pattern. If no file is specified, vi opens with an empty buffer.
Command-Line Options
Because vi and ex are the same program, they share the same options. However,
some options only make sense for one version of the program. Options specific to
vim are so marked.
+[num]
Start editing at line number num, or the last line of the file if num is omitted.
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Command-Line Syntax | 679
vi, ex, and vim
+/pattern
Start editing at the first line matching pattern. (For ex, fails if nowrapscan is
set in your .exrc startup file, since ex starts editing at the last line of a file.)
-b Edit the file in binary mode. {vim}
-c command
Run the given ex command upon startup. Only one -c option is permitted for
vi; vim accepts up to 10. An older form of this option, +command, is still
supported.
--cmd command
Like -c, but execute the command before any resource files are read. {vim}
-C vim: Start the editor in vi-compatible mode.
-d Run in diff mode. Can also be invoked by running the command vimdiff.
{vim}
-D Debugging mode for use with scripts. {vim}
-e Run as ex (line editing rather than full-screen mode).
-h Print help message, then exit. {vim}
-i file
Use the specified file instead of the default (~/.viminfo) to save or restore
vim’s state. {vim}
-l Enter Lisp mode for running Lisp programs (not supported in all versions).
-L List files that were saved due to an aborted editor session or system crash (not
supported in all versions). For vim, this option is the same as -r.
-m Start the editor with the write option turned off so the user cannot write to
files. {vim}
-M Do not allow text in files to be modified. {vim}
-n Do not use a swapfile; record changes in memory only. {vim}
--noplugin
Do not load any plug-ins. {vim}
-N Run vim in a non-vi-compatible mode. {vim}
-o[num]
Start vim with num open windows. The default is to open one window for
each file. {vim}
-O[num]
Start vim with num open windows arranged horizontally (split vertically) on
the screen. {vim}
-r [file]
Recovery mode; recover and resume editing on file after an aborted editor
session or system crash. Without file, list files available for recovery.
-R Edit files read-only.
-s Silent; do not display prompts. Useful when running a script. This behavior
also can be set through the older - option. For vim, only applies when used
together with -e.
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680 | Chapter9: The vi, ex, and vim Editors
-s scriptfile
Read and execute commands given in the specified scriptfile as if they were
typed in from the keyboard. {vim}
-S commandfile
Read and execute commands given in commandfile after loading any files for
editing specified on the command line. Shorthand for the option vim -c
'source commandfile'. {vim}
-t tag
Edit the file containing tag and position the cursor at its definition. (See ctags
in Chapter 3 for more information.)
-T type
Set the terminal type. This value overrides the $TERM environment variable.
{vim}
-u file
Read configuration information from the specified resource file instead of
default .vimrc resource file. If the file argument is NONE, vim will read no
resource files, load no plug-ins, and run in compatible mode. If the argument
is NORC, it will read no resource files, but it will load plug-ins. {vim}
-v Run in full-screen mode (default for vi).
--version
Print version information, then exit. {vim}
-V[num]
Verbose mode; print messages about what options are being set and what
files are being read or written. You can set a level of verbosity to increase or
decrease the number of messages received. The default value is 10 for high
verbosity. {vim}
-w rows
Set the window size so rows lines at a time are displayed; useful when editing
over a slow dial-up line (or long distance Internet connection). Older versions
of vi do not permit a space between the option and its argument. vim does
not support this option.
-W scriptfile
Write all typed commands from the current session to the specified scriptfile.
The file created can be used with the -s command. {vim}
-x Prompt for a key that will be used to try to encrypt or decrypt a file using
crypt (not supported in all versions). *
-y Modeless vi; run vim in insert mode only, without a command mode. {vim}
-Z Start vim in restricted mode. Do not allow shell commands or suspension of
the editor. {vim}
While most people know ex commands only by their use within vi, the editor also
exists as a separate program and can be invoked from the shell (for instance, to
edit files as part of a script). Within ex, you can enter the vi or visual command to
start vi. Similarly, within vi, you can enter Q to quit the vi editor and enter ex.
*The crypt command’s encryption is weak. Don’t use it for serious secrets.
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Review of vi Operations | 681
vi, ex, and vim
You can exit ex in several ways:
:x Exit (save changes and quit).
:q! Quit without saving changes.
:vi Enter the vi editor.
Review of vi Operations
This section provides a review of the following:
• vi modes
• Syntax of vi commands
• Status-line commands
Command Mode
Once the file is opened, you are in command mode. From command mode, you can:
• Invoke insert mode
• Issue editing commands
• Move the cursor to a different position in the file
• Invoke ex commands
• Invoke a Unix shell
• Save the current version of the file
• Exit vi
Insert Mode
In insert mode, you can enter new text in the file. You normally enter insert mode
with the i command. Press the Escape key to exit insert mode and return to
command mode. The full list of commands that enter insert mode is provided
later, in the section “Insert Commands” on page 686.
Syntax of vi Commands
In vi, editing commands have the following general form:
[n]operator[m]motion
The basic editing operators are:
c Begin a change.
d Begin a deletion.
y Begin a yank (or copy).
If the current line is the object of the operation, the motion is the same as the
operator: cc, dd, yy. Otherwise, the editing operators act on objects specified by
cursor-movement commands or pattern-matching commands. (For example, cf.
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682 | Chapter9: The vi, ex, and vim Editors
changes up to the next period.) n and m are the number of times the operation is
performed, or the number of objects the operation is performed on. If both n and
m are specified, the effect is n × m.
An object of operation can be any of the following text blocks:
word
Includes characters up to a whitespace character (space or tab) or punctua-
tion mark. A capitalized object is a variant form that recognizes only
whitespace.
sentence
Is up to ., !, or ?, followed by two spaces.
paragraph
Is up to the next blank line or paragraph macro defined by the para= option.
section
Is up to the next nroff/troff section heading defined by the sect= option.
motion
Is up to the character or other text object as specified by a motion specifier,
including pattern searches.
Examples
2cw
Change the next two words.
d} Delete up to next paragraph.
d^ Delete back to beginning of line.
5yy
Copy the next five lines.
y]]
Copy up to the next section.
cG Change to the end of the edit buffer.
More commands and examples may be found in the section “Changing and
deleting text” on page 687.
Visual mode (vim only)
vim provides an additional facility, “visual mode.” This allows you to highlight
blocks of text which then become the object of edit commands such as deletion or
saving (yanking). Graphical versions of vim allow you to use the mouse to high-
light text in a similar fashion. See the vim help file visual.txt for the full story.
v Select text in visual mode one character at a time.
V Select text in visual mode one line at a time.
Ctrl-V
Select text in visual mode in blocks.
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vi Commands | 683
vi, ex, and vim
Status-Line Commands
Most commands are not echoed on the screen as you input them. However, the
status line at the bottom of the screen is used to edit these commands:
/ Search forward for a pattern.
? Search backward for a pattern.
: Invoke an ex command.
! Invoke a Unix command that takes as its input an object in the buffer and
replaces it with output from the command. You type a motion command
after the ! to describe what should be passed to the Unix command. The
command itself is entered on the status line.
Commands that are entered on the status line must be entered by pressing the
Enter key. In addition, error messages and output from the Ctrl-G command are
displayed on the status line.
vi Commands
vi supplies a large set of single-key commands when in command mode. vim
supplies additional multi-key commands.
Movement Commands
Some versions of vi do not recognize extended keyboard keys (e.g., arrow keys,
Page Up, Page Down, Home, Insert, and Delete); some do. All, however, recog-
nize the keys in this section. Many users of vi prefer to use these keys, as it helps
them keep their fingers on the home row of the keyboard. A number preceding a
command repeats the movement. Movement commands are also used after an
operator. The operator works on the text that is moved.
Character
Text
Command Action
h,j,k,l Left, down, up, right (←,↓,↑,→)
Space Right
Backspace Left
Ctrl-H Left
Command Action
w,b Forward, backward by “word” (letters, numbers, and underscore make up words).
W,B Forward, backward by “WORD” (only whitespace separates items).
e End of word.
E End of WORD.
ge End of previous word. {vim}
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684 | Chapter9: The vi, ex, and vim Editors
Lines
Long lines in a file may show up on the screen as multiple lines. (They wrap
around from one screen line to the next.) While most commands work on the
lines as defined in the file, a few commands work on lines as they appear on the
screen. The vim option wrap allows you to control how long lines are displayed.
Screens
gE End of previous WORD. {vim}
),( Beginning of next, current sentence.
},{ Beginning of next, current paragraph.
]],[[ Beginning of next, current section.
][,[ ] End of next, current section. {vim}
Command Action
0,$ First, last position of current line.
^,_ First nonblank character of current line.
+,- First nonblank character of next, previous line.
Enter First nonblank character of next line.
num| Columnnum of current line.
g0,g$ First, last position of screen line. {vim}
g^ First nonblank character of screen line. {vim}
gm Middle of screen line. {vim}
gk,gj Move up, down one screen line. {vim}
H Top line of screen (Home position).
M Middle line of screen.
L Last line of screen.
numH num lines after top line.
numL num lines before last line.
Command Action
Ctrl-F,Ctrl-B Scroll forward, backward one screen.
Ctrl-D,Ctrl-U Scroll down, up one-half screen.
Ctrl-E,Ctrl-Y Show one more line at bottom, top of screen.
z Enter Reposition line with cursor to top of screen.
z. Reposition line with cursor to middle of screen.
z- Reposition line with cursor to bottom of screen.
Ctrl-L Redraw screen (without scrolling).
Ctrl-R vi: Redraw screen (without scrolling).
vim: Redo last undone change.
Command Action
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vi Commands | 685
vi, ex, and vim
Searches
Line numbering
Marks
Command Action
/pattern Search forward forpattern. End with Enter.
/pattern/+num Go to linenum afterpattern.
?pattern Search backward forpattern. End with Enter.
?pattern?-num Go to linenum beforepattern.
:noh Suspend search highlighting until next search. {vim}.
n Repeat previous search.
N Repeat search in opposite direction.
/ Repeat previous search forward.
? Repeat previous search backward.
* Search forward for word under cursor. Matches only exact words. {vim}
# Search backward for word under cursor. Matches only exact words. {vim}
g* Search backward for word under cursor. Matches the characters of this word
when embedded in a longer word. {vim}
g# Search backward for word under cursor. Matches the characters of this word
when embedded in a longer word. {vim}
% Find match of current parenthesis, brace, or bracket.
fx Move cursor forward tox on current line.
Fx Move cursor backward tox on current line.
tx Move cursor forward to character beforex in current line.
Tx Move cursor backward to character afterx in current line.
, Reverse search direction of lastf,F,t, orT.
; Repeat lastf,F,t, orT.
Command Action
Ctrl-G Display current line number.
gg Move to first line in file. {vim}
numG Move to line numbernum.
G Move to last line in file.
:num Move to line numbernum.
Command Action
mx Place markx at current position.
`x (backquote) Move cursor to markx.
'x (apostrophe) Move to start of line containingx.
`` (backquotes) Return to position before most recent jump.
" (apostrophes) Like preceding, but return to start of line.
'" (apostrophe quote) Move to position when last editing the file. {vim}
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686 | Chapter9: The vi, ex, and vim Editors
Insert Commands
The following commands work in insert mode.
`[,`] (backquote bracket) Move to beginning/end of previous text operation. {vim}
'[,'] (apostrophe bracket) Like preceding, but return to start of line where opera-
tion occurred. {vim}
`. (backquote period) Move to last change in file. {vim}
'. (apostrophe period) Like preceding, but return to start of line. {vim}
`0 Position where you last exitedvim. {vim}
:marks List active marks. {vim}
Command Action
a Append after cursor.
A Append to end of line.
c Begin change operation.
C Change to end of line.
gI Insert at beginning of line. {vim}
i Insert before cursor.
I Insert at beginning of line.
o Open a line below cursor.
O Open a line above cursor.
R Begin overwriting text.
s Substitute a character.
S Substitute entire line.
ESC Terminate insert mode.
Command Action
Backspace Delete previous character.
Delete Delete current character.
Tab Insert a tab.
Ctrl-A Repeat last insertion. {vim}
Ctrl-D Shift line left to previous shift width. {vim}
Ctrl-E Insert character found just below cursor. {vim}
Ctrl-H Delete previous character (same as Backspace).
Ctrl-I Insert a tab.
Ctrl-K Begin insertion of multi-keystroke character.
Ctrl-N Insert next completion of the pattern to the left of the cursor. {vim}
Ctrl-P Insert previous completion of the pattern to the left of the cursor. {vim}
Ctrl-T Shift line right to next shift width. {vim}
Ctrl-U Delete current line.
Ctrl-V Insert next character verbatim.
Command Action
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vi Commands | 687
vi, ex, and vim
Some of the control characters listed in the previous table are set by stty. Your
terminal settings may differ.
Edit Commands
Recall that c, d, and y are the basic editing operators.
Changing and deleting text
The following table is not exhaustive, but it illustrates the most common
operations.
Ctrl-W Delete previous word.
Ctrl-Y Insert character found just above cursor. {vim}
Ctrl-[ (Escape) Terminate insert mode.
Command Action
cw Change word.
cc Change line.
c$ Change text from current position to end of line.
C Same asc$.
dd Delete current line.
numdd Deletenum lines.
d$ Delete text from current position to end of line.
D Same asd$.
dw Delete a word.
d} Delete up to next paragraph.
d^ Delete back to beginning of line.
d/pat Delete up to first occurrence of pattern.
dn Delete up to next occurrence of pattern.
dfa Delete up to and includinga on current line.
dta Delete up to (but not including)a on current line.
dL Delete up to last line on screen.
dG Delete to end of file.
gqap Reformat current paragraph totextwidth. {vim}
g~w Switch case of word. {vim}
guw Change word to lowercase. {vim}
gUw Change word to uppercase. {vim}
p Insert last deleted or yanked text after cursor.
gp Same asp, but leave cursor at end of inserted text. {vim}
]p Same asp, but match current indention. {vim}
[p Same asP, but match current indention. {vim}
P Insert last deleted or yanked text before cursor.
gP Same asP, but leave cursor at end of inserted text. {vim}
Command Action
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688 | Chapter9: The vi, ex, and vim Editors
Copying and moving
Register names are the letters a–z. Uppercase names append text to the corre-
sponding register.
Saving and Exiting
Writing a file means overwriting the file with the current text.
rx Replace character withx.
Rtext Replace with newtext (overwrite), beginning at cursor. Escape ends replace
mode.
s Substitute character.
4s Substitute four characters.
S Substitute entire line.
u Undo last change.
Ctrl-R Redo last change. {vim}
U Restore current line.
x Delete current cursor position.
X Delete back one character.
5X Delete previous five characters.
. Repeat last change.
~ Reverse case and move cursor right.
Ctrl-A Increment number under cursor. {vim}
Ctrl-X Decrement number under cursor. {vim}
Command Action
Y Copy current line.
yy Copy current line.
"xyy Copy current line to registerx.
ye Copy text to end of word.
yw Likeye, but include the whitespace after the word.
y$ Copy rest of line.
"xdd Delete current line into registerx.
"xd Delete into registerx.
"xp Put contents of registerx.
y]] Copy up to next section heading.
ye Copy to end of word.
"xp Put contents of registerx.
J Join current line to next line.
gJ Same asJ, but without inserting a space. {vim}
:j Same asJ.
:j! Same asgJ.
Command Action
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vi Commands | 689
vi, ex, and vim
Accessing Multiple Files
Window Commands
The following table lists common commands for controlling windows in vim. See
also the split, vsplit, and resize commands in the “Alphabetical Summary of ex
Commands” on page 697. For brevity, control characters are marked in the
following list by ^.
Command Action
ZZ Quitvi, writing the file only if changes were made.
:x Same asZZ.
:wq Write file and quit.
:w Write file.
:wfile Save copy tofile.
:n,mwfile Write linesn tom to newfile.
:n,mw >>file Append linesn tom to existingfile.
:w! Write file (overriding protection).
:w!file Overwritefile with current text.
:w %.new Write current buffer namedfile asfile.new.
:q Quitvi (fails if changes were made).
:q! Quitvi (discarding edits).
Q Quitvi and invokeex.
:vi Return tovi afterQ command.
% Replaced with current filename in editing commands.
# Replaced with alternate filename in editing commands.
Command Action
:efile Edit anotherfile; current file becomes alternate.
:e! Return to version of current file at time of last write.
:e +file Begin editing at end offile.
:e +numfile Openfile at linenum.
:e # Open to previous position in alternate file.
:tatag Edit file at locationtag.
:n Edit next file in the list of files.
:n! Force next file.
:nfiles Specify new list offiles.
:rewind Edit first file in the list.
Ctrl-G Show current file and line number.
:args Display list of files to be edited.
:prev Edit previous file in the list of files.
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690 | Chapter9: The vi, ex, and vim Editors
Interacting with the System
Command Action
:new Open a new window.
:newfile Openfile in a new window.
:sp [file] Split the current window. Withfile, edit that file in the new window.
:sv [file] Same as:sp, but make new window read-only.
:sn [file] Edit next file in file list in new window.
:vsp [file] Like:sp, but split vertically instead of horizontally.
:clo Close current window.
:hid Hide current window, unless it is the only visible window.
:on Make current window the only visible one.
:resnum Resize window tonum lines.
:wa Write all changed buffers to file.
:qa Close all buffers and exit.
^W s Same as:sp.
^W n Same as:new.
^W ^ Open new window with alternate (previously edited) file.
^W c Same as:clo.
^W o Same as:only.
^W j,^W k Move cursor to next/previous window.
^W p Move cursor to previous window.
^W h,^W l Move cursor to window on left/right.
^W t,^W b Move cursor to window on top/bottom of screen.
^W K,^W B Move current window to top/bottom of screen.
^W H,^W L Move current window to far left/right of screen.
^W r,^W R Rotate windows down/up.
^W +,^W - Increase/decrease current window size.
^W = Make all windows same height.
Command Action
:rfile Read in contents offile after cursor.
:r !command Read in output fromcommand after current line.
:numr !command Like above, but place after linenum (0 for top of file).
:!command Runcommand, then return.
!motion command Send the text covered bymotion to Unixcommand; replace with output.
:n,m!command Send linesn-m tocommand; replace with output.
num!!command Sendnum lines to Unixcommand; replace with output.
:!! Repeat last system command.
:sh Create subshell; return to file withEOF.
Ctrl-Z Suspend editor, resume withfg.
:sofile Read and executeex commands fromfile.
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vi Commands | 691
vi, ex, and vim
Macros
In vi, the following characters are unused in command mode and can be mapped
as user-defined commands:
Letters
g K q V v
Control keys
^A ^K ^O ^W ^X ^_ ^\
Symbols
_ * \ = #
The = is used by vi if Lisp mode is set. Different versions of vi may
use some of these characters, so test them before using.
vim does not use ^K, ^_, _, or \.
Miscellaneous Commands
Command Action
:abin out Usein as abbreviation forout in insert mode.
:unabin Remove abbreviation forin.
:ab List abbreviations.
:mapstring sequence Map charactersstring assequence of commands. Use#1,#2, etc., for the func-
tion keys.
:unmapstring Remove map for charactersstring.
:map List character strings that are mapped.
:map!string sequence Map charactersstring to input modesequence.
:unmap!string Remove input mode map (you may need to quote the character withCtrl-V).
:map! List character strings that are mapped for input mode.
qx Recordtypedcharactersintoregisterspecifiedbyletterx.Ifletterisuppercase,
append to register. {vim}
q Stop recording. {vim}
@x Execute the register specified by letterx. Use@@ to repeat the last@
command.
Command Action
< Shift text described by following motion command left by one shiftwidth.
{vim}
> Shift text described by following motion command right by one shiftwidth.
{vim}
<< Shift line left one shift width (default is eight spaces).
>> Shift line right one shift width (default is eight spaces).
>} Shift right to end of paragraph.
<% Shift left until matching parenthesis, brace, or bracket. (Cursor must be on the
matching symbol.)
= = Indent line in C-style, or using program specified inequalprg option. {vim}
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692 | Chapter9: The vi, ex, and vim Editors
vi Configuration
This section describes the following:
• The :set command
• Options available with :set
• Sample .exrc file
The :set Command
The :set command allows you to specify options that change characteristics of
your editing environment. Options may be put in the ~/.exrc file or set during a vi
session.
The colon does not need to be typed if the command is put in .exrc:
Options Used by :set
Table 9-1 contains brief descriptions of the important set command options. In
the first column, options are listed in alphabetical order; if the option can be
abbreviated, that abbreviation is shown in parentheses. The second column shows
the default setting. The last column describes what the option does, when enabled.
This table lists set options for vi, with the addition of important vim options.
Other versions of vi may have more or fewer or different options. See your local
documentation, or use :set all to see the full list. Options that receive a value are
marked with an =.
g Start many multiple character commands invim.
K Lookupwordundercursorinmanpages(orprogramdefinedinkeywordprg).
{vim}
^O Return to previous jump. {vim}
q Record keystrokes. {vim}
^Q Same as^V. {vim} (On some terminals, resume data flow.)
^T Return to the previous location in the tag stack. (vim)
^] Perform a tag lookup on the text under the cursor.
^\ Enterex line-editing mode.
^^ (Caret key with Ctrl key pressed) Return to previously edited file.
Command Action
:setx Enable Boolean optionx, show value of other options.
:set nox Disable optionx.
:setx=value Givevalue to optionx.
:set Show changed options.
:set all Show all options.
:setx? Show value of optionx.
Command Action
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vi Configuration | 693
vi, ex, and vim
Table 9-1 . :set options
Option Default Description
autoindent (ai) noai In insert mode, indent each line to the same level as the
line above or below. Use with theshiftwidth option.
autoprint (ap) ap Display changes after each editor command. (For global
replacement, display last replacement.)
autowrite (aw) noaw Automatically write (save) the file if changed before
opening another file with a command such as:n, or
before giving Unix command with:!.
background (bg) Describe the background so the editor can choose appro-
priate highlighting colors. Default value ofdark orlight
depends on the environment in which the editor is
invoked. {vim}
backup (bk) nobackup Create a backup file when overwriting an existing file.
{vim}
backupdir= (bdir) .,~/tmp/,~/ Namedirectoriesinwhichtostorebackupfilesifpossible.
The list of directories is comma-separated and in order of
preference. {vim}
beautify (bf) nobf Ignore all control characters during input (except tab,
newline, or formfeed).
backupext= (bex) ~ String to append to filenames for backup files. {vim}
cindent (cin) nocindent In insert mode, indent each line relative to the one above
it, as is appropriate for C or C++ code. {vim}
compatible (cp) cp Makevim behave more likevi. Default isnocp when a~/
.vimrc file is found. {vim}
directory (dir) /tmp Name of directory in whichex/vi stores buffer files.
(Directory must be writable.) This can be a comma-
separated list forvim.
edcompatible noedcompatible Remembertheflagsusedwiththemostrecentsubstitute
command (global, confirming) and use them for the next
substitute command. Despite the name, no version ofed
actually does this.
equalprg= (ep) Usethespecifiedprogramforthe=command.Whenthe
option is blank (the default), the key invokes the internal
C indention function or the value of theindentexpr
option. {vim}
errorbells (eb) errorbells Sound bell when an error occurs.
exrc (ex) noexrc Allow the execution of.exrc files that reside outside the
user’s home directory.
formatprg= (fp) Thegq command will invoke the named external
program to format text. It will call internal formatting
functions when this option is empty (the default). {vim}
gdefault (gd) nogdefault Set theg flag on for substitutions by default. {vim}
hardtabs= (ht) 8 Define boundaries for terminal hardware tabs.
hidden (hid) nohidden Hide buffers rather than unload them when they are
abandoned. {vim}
hlsearch (hls) hlsearch Highlight all matches of most recent search pattern. Use
:nohlsearch to remove highlighting. {vim}
history= (hi) 20 Number ofex commands to store in the history table.
{vim}
ignorecase (ic) noic Disregard case during a search.
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694 | Chapter9: The vi, ex, and vim Editors
incsearch (is) noincsearch Highlight matches to a search pattern as it is typed. {vim}
lisp nolisp InsertindentsinappropriateLispformat.(),{},[[,and]]
are modified to have meaning for Lisp.
list nolist Printtabsas^I;markendsoflineswith$.(Uselisttotell
if end character is a tab or a space.)
magic magic Wildcardcharacters;.(dot),*(asterisk),and[](brackets)
have special meaning in patterns.
mesg mesg Permit system messages to display on terminal while
editing invi.
mousehide (mh) mousehide Whencharactersaretyped,hidethemousepointer.{vim}
novice nonovice Requiretheuseoflongexcommandnames,suchascopy
orread.
number (nu) nonu Display line numbers on left of screen during editing
session.
open open Allowentrytoopenorvisualmodefromex.Althoughnot
invim, this option has traditionally been invi, and may
be in your version ofvi.
optimize (opt) noopt Abolish carriage returns at the end of lines when printing
multiple lines; speed output on dumb terminals when
printing lines with leading whitespace (spaces or tabs).
paragraphs (para) IPLPPPQPP LIpplpipnpbp Define paragraph delimiters for movement by{ or}. The
pairs of characters in the value are the names oftroff
macros that begin paragraphs.
paste nopaste Change the defaults of various options to make pasting
text into a terminal window work better. All options are
returned to their original value when thepaste option is
reset. {vim}
prompt prompt Displaytheexprompt(:)whenvi‘sQcommandisgiven.
readonly (ro) noro Any writes (saves) of a file fail unless you use! after the
write (works withw,ZZ, orautowrite).
redraw (re) vi redraws the screen whenever edits are made.nore-
draw is useful at slow speeds on a dumb terminal: the
screen isn’t fully updated until you press Escape. Default
depends on line speed and terminal type.
remap remap Allow nested map sequences.
report= 5 Display a message on the status line whenever you make
an edit that affects at least a certain number of lines. For
example,6dd reports the message “6 lines deleted.”
ruler (ru) ruler Show line and column numbers for the current cursor
position. {vim}
scroll= [ 1 / 2 window] Number of lines to scroll with^D and^U commands.
sections= (sect) SHNHH HUnhsh+c Define section delimiters for[ [ and] ] movement. The
pairs of characters in the value are the names oftroff
macros that begin sections.
shell= (sh) /bin/sh Pathname of shell used for shell escape (:!) and shell
command (:sh). Default value is derived from shell envi-
ronment, which varies on different systems.
shiftwidth= (sw) 8 Define number of spaces used when the indent in
increased or decreased.
Table 9-1 . :set options (continued)
Option Default Description
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vi Configuration | 695
vi, ex, and vim
showmatch (sm) nosm Invi, when) or} is entered, cursor moves briefly to
matching( or{. (If no match, rings the error message bell.)
Very useful for programming.
showmode noshowmode Ininsertmode,displayamessageonthepromptlineindi-
cating the type of insert you are making. For example,
“OPEN MODE” or “APPEND MODE.”
slowopen (slow) Hold off display during insert. Default depends on line
speed and terminal type.
smartcase (scs) nosmartcase Override theignorecase option when a search pattern
contains uppercase characters. {vim}
tabstop= (ts) 8 Define number of spaces a tab indents during editing
session. (Printer still uses system tab of 8.)
taglength= (tl) 0 Define number of characters that are significant for tags.
Default (zero) means that all characters are significant.
tags= tags/usr/lib/tags Define pathname of files containing tags. (See the Unix
ctags command.) (By default,vi searches the filetags in
the current directory and/usr/lib/tags.)
tagstack tagstack Enablestackingoftaglocationsonastack.(Solarisviand
vim.)
term= Set terminal type.
terse noterse Display shorter error messages.
textwidth= (tw) 0 The maximum width of text to be inserted; longer lines
are broken after whitespace. Default (zero) disables this
feature, in which casewrapmargin is used. {vim}
timeout (to) timeout Keyboard maps timeout after 1 second. a
timeoutlen= (tm) 1000 Number of milliseconds after which keyboard maps
timeout. Default value of 1000 provides traditionalvi
behavior. {vim}
ttytype= Set terminal type. This is just another name forterm.
undolevels= (ul) 1000 Number of changes that can be undone. {vim}
warn warn Display the warning message, “No write since last
change.”
window (w) Show a certain number of lines of the file on the screen.
Default depends on line speed and terminal type.
wrap When on, long lines wrap on the screen. When off, only
the first part of the line is displayed. {vim}
wrapmargin (wm) 0 Definerightmargin.Ifgreaterthanzero,viautomatically
inserts carriage returns to break lines.
wrapscan (ws) ws Searches wrap around either end of file.
writeany (wa) nowa Allow saving to any file.
writebackup (wb) wb Back up files before attempting to overwrite them.
Remove the backup when the file has been successfully
written, unless thebackup option is set. {vim}
a Whenyouhavemappingsofseveralkeys(forexample,:mapzzz3dw),youprobablywanttousenotimeout.Otherwise,youneedtotype
zzzwithin1second.Whenyouhaveaninsertmodemappingforacursorkey(forexample,:map!^[OB^[ja),youshouldusetimeout.
Otherwise,vi won’t react to Escape until you type another key.
Table 9-1 . :set options (continued)
Option Default Description
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696 | Chapter9: The vi, ex, and vim Editors
Sample .exrc File
The following lines of code are an example of a customized .exrc file:
set nowrapscan " Searches don't wrap at end of file
set wrapmargin=7 " Wrap text at 7 columns from right margin
set sections=SeAhBhChDh nomesg " Set troff macros, disallow message
map q :w^M:n^M " Alias to move to next file
map v dwElp " Move a word
ab ORA O'Reilly Media, Inc. " Input shortcut
The q alias isn’t needed for vim, which has the :wn command. The
v alias would hide the vim command v, which enters character-at-a-
time visual-mode operation.
ex Basics
The ex line editor serves as the foundation for the screen editor vi. Commands in
ex work on the current line or on a range of lines in a file. Most often, you use ex
from within vi. In vi, ex commands are preceded by a colon and entered by
pressing Enter.
You can also invoke ex on its own—from the command line—just as you would
invoke vi. (You could execute an ex script this way.) You can also use the vi
command Q to quit the vi editor and enter ex.
Syntax of ex Commands
To enter an ex command from vi, type:
:[address]command[options]
An initial : indicates an ex command. As you type the command, it is echoed on
the status line. Execute the command by pressing the Enter key. address is the line
number or range of lines that are the object of command. options and addresses are
described below. ex commands are described in the next section “Alphabetical
Summary of ex Commands” on page 697.
You can exit ex in several ways:
:x Exit (save changes and quit).
:q! Quit without saving changes.
:vi Switch to the vi editor on the current file.
Addresses
If no address is given, the current line is the object of the command. If the address
specifies a range of lines, the format is:
x,y
where x and y are the first and last addressed lines (x must precede y in the
buffer). x and y may each be a line number or a symbol. Using ; instead of , sets
the current line to x before interpreting y. The notation 1,$ addresses all lines in
the file, as does %.
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abbreviate | 697
vi, ex, and vim
Address Symbols
See Chapter 7 for more information on using patterns.
Options
! Indicates a variant form of the command, overriding the normal behavior.
The ! must come immediately after the command.
count
The number of times the command is to be repeated. Unlike in vi commands,
count cannot precede the command, because a number preceding an ex
command is treated as a line address. For example, d3 deletes three lines
beginning with the current line; 3d deletes line 3.
file
The name of a file that is affected by the command. % stands for the current
file; # stands for the previous file.
Alphabetical Summary of ex Commands
ex commands can be entered by specifying any unique abbreviation. In this
listing, the full name appears in the margin, and the shortest possible abbrevia-
tion is used in the syntax line. Examples are assumed to be typed from vi, so they
include the : prompt.
abbreviate ab [string text]
Define string when typed to be translated into text. If string and
text are not specified, list all current abbreviations.
Symbol Meaning
1,$ All lines in the file.
x,y Linesx throughy.
x;y Linesx throughy, with current line reset tox.
0 Top of file.
. Current line.
num Absolute line numbernum.
$ Last line.
% All lines; same as1,$.
x-n n lines beforex.
x+n n lines afterx.
-[num] One ornum lines previous.
+[num] One ornum lines ahead.
'x Line marked withx.
" Previous mark.
/pattern/ Forward to line matchingpattern.
?pattern? Backward to line matchingpattern.
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698 | Chapter9: The vi, ex, and vim Editors
Examples
Note: ^M appears when you type ^V followed by Enter.
:ab ora O'Reilly Media, Inc.
:ab id Name:^MRank:^MPhone:
append [address] a[!]
text
.
Append new text at specified address, or at present address if none
is specified. Add a ! to toggle the autoindent setting that is used
during input. That is, if autoindent was enabled, ! disables it. Enter
new text after entering the command. Terminate input of new text
by entering a line consisting of just a period.
Example
:a Begin appending to current line.
Append this line
and this line too.
. Terminate input of text to append.
args ar
argsfile ...
Print the members of the argument list (files named on the
command line), with the current argument printed in brackets ([ ]).
The second syntax is for vim, which allows you to reset the list of
files to be edited.
bdelete [num] bd[!] [num]
Unload buffer num and remove it from the buffer list. Add a ! to
force removal of an unsaved buffer. The buffer may also be speci-
fied by filename. If no buffer is specified, remove the current buffer.
{vim}
buffer [num] b[!] [num]
Begin editing buffer num in the buffer list. Add a ! to force a switch
from an unsaved buffer. The buffer may also be specified by file-
name. If no buffer is specified, continue editing the current buffer.
{vim}
buffers buffers[!]
Print the members of the buffer list. Some buffers (e.g., deleted
buffers) will not be listed. Add ! to show unlisted buffers. ls is
another abbreviation for this command. {vim}
cd cddir
chdirdir
Change current directory within the editor to dir.
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edit | 699
vi, ex, and vim
center [address] ce [width]
Center line within the specified width. If width is not specified, use
textwidth. {vim}
change [address] c[!]
text
.
Replace the specified lines with text. Add a ! to switch the autoindent
setting during input of text. Terminate input by entering a line
consisting of just a period.
close clo[!]
Close current window unless it is the last window. If buffer in
window is not open in another window, unload it from memory.
This command will not close a buffer with unsaved changes, but
you may add ! to hide it instead. {vim}
copy [address] codestination
Copy the lines included in address to the specified destination
address. The command t (short for “to”) is a synonym for copy.
Example
:1,10 co 50 Copy first 10 lines to just after line 50
delete [address] d [register]
Delete the lines included in address. If register is specified, save or
append the text to the named register. Register names are the
lowercase letters a–z. Uppercase names append text to the corre-
sponding register.
Examples
:/Part I/,/Part II/-1d Delete to line above "Part II"
:/main/+d Delete line below "main"
:.,$d x Delete from this line to last line into register x
edit e[!] [+num] [filename]
Begin editing on filename. If no filename is given, start over with a
copy of the current file. Add a ! to edit the new file even if the
current file has not been saved since the last change. With the +num
argument, begin editing on line num. Or num may be a pattern, of
the form /pattern.
Examples
:e file Edit file in current editing buffer
:e +/^Index # Edit alternate file at pattern match
:e! Start over again on current file
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700 | Chapter9: The vi, ex, and vim Editors
file f [filename]
Change the filename for the current buffer to filename. The next time
the buffer is written, it will be written to file filename. When the
name is changed, the buffer’s “not edited” flag is set, to indicate
you are not editing an existing file. If the new filename is the same
as a file that already exists on the disk, you will need to use :w! to
overwrite the existing file. When specifying a filename, the % char-
acter can be used to indicate the current filename. A # can be used
to indicate the alternate filename. If no filename is specified, print
the current name and status of the buffer.
Example
:f%.new
fold address fo
Fold the lines specified by address. A fold collapses several lines on
the screen into one line, which later can be unfolded. It doesn’t
affect the text of the file. {vim}
foldclose [address] foldc[!]
Close folds in specified address, or at present address if none is
specified. Add a ! to close more than one level of folds. {vim}
foldopen [address] foldo[!]
Open folds in specified address, or at present address if none is
specified. Add a ! to open more than one level of folds. {vim}
global [address] g[!]/pattern/[commands]
Execute commands on all lines which contain pattern or, if address
is specified, on all lines within that range. If commands are not
specified, print all such lines. Add a ! to execute commands on all
lines not containing pattern. See also v.
Examples
:g/Unix/p Print all lines containing "Unix"
:g/Name:/s/tom/Tom/ Change "tom" to "Tom" on all lines
containing "Name:"
hide hid
Close current window unless it is the last window, but do not
remove the buffer from memory. This is a safe command to use on
an unsaved buffer. {vim}
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map | 701
vi, ex, and vim
insert [address] i[!]
text
.
Insert text at line before the specified address, or at present address
if none is specified. Add a ! to switch the autoindent setting during
input of text. Terminate input of new text by entering a line
consisting of just a period.
join [address] j[!] [count]
Place the text in the specified range on one line, with whitespace
adjusted to provide two space characters after a period (.), no space
characters before a ), and one space character otherwise. Add a ! to
prevent whitespace adjustment.
Example
:1,5j! Join first five lines, preserving whitespace
jumps ju
Print jump list used with Ctrl-I and Ctrl-O commands. The jump
list is a record of most movement commands that skip over
multiple lines. It records the position of the cursor before each
jump. {vim}
k [address] kchar
Same as mark; see mark, later in this list.
left [address] le [count]
Left-align lines specified by address, or current line if no address is
specified. Indent lines by count spaces. {vim}
list [address] l [count]
Print the specified lines so that tabs display as ^I, and the ends of
lines display as $. l is like a temporary version of :set list.
map map[!] [string commands]
Define a keyboard macro named string as the specified sequence of
commands. string is usually a single character, or the sequence
#num, representing a function key on the keyboard. Use a ! to
create a macro for input mode. With no arguments, list the
currently defined macros.
Examples
:map K dwwP Transpose two words
:map q :w^M:n^M Write current file; go to next
:map! + ^[bi(^[ea) Enclose previous word in parentheses
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702 | Chapter9: The vi, ex, and vim Editors
vim has K and q commands, which the above aliases
would hide.
mark [address] machar
Mark the specified line with char, a single lowercase letter. Return
later to the line with 'x (where x is the same as char). vim also uses
uppercase and numeric characters for marks. Lowercase letters
work the same as in vi. Uppercase letters are associated with file-
names and can be used between multiple files. Numbered marks,
however, are maintained in a special viminfo file and cannot be set
using this command. Same as k.
marks marks [chars]
Print list of marks specified by chars, or all current marks if no
chars specified. {vim}
Example
:marks abc Print marks a, b and c.
mkexrc mk[!]file
Create an .exrc file containing set commands for changed ex
options and key mappings. This saves the current option settings,
allowing you to restore them later.
move [address] mdestination
Move the lines specified by address to the destination address.
Example
:.,/Note/m /END/ Move text block to after line containing "END"
new [count] new
Create a new window count lines high with an empty buffer. {vim}
next num[!] [[+num]filelist]
Edit the next file from the command-line argument list. Use args to
list these files. If filelist is provided, replace the current argument
list with filelist and begin editing on the first file. With the +num
argument, begin editing on line num. Or num may be a pattern, of
the form /pattern.
Example
:n chap* Start editing all "chapter" files
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qall | 703
vi, ex, and vim
nohlsearch noh
Temporarily stop highlighting all matches to a search when using
the hlsearch option. Highlighting is resumed with the next search.
{vim}
number [address] nu [count]
Print each line specified by address, preceded by its buffer line
number. Use # as an alternate abbreviation for number. count
specifies the number of lines to show, starting with address.
only on [!]
Make the current window be the only one on the screen. Windows
open on modified buffers are not removed from the screen
(hidden), unless you also use the ! character. {vim}
open [address] o [/pattern/]
Enter open mode (vi) at the lines specified by address, or at the
lines matching pattern. Exit open mode with Q. Open mode lets
you use the regular vi commands, but only one line at a time. It can
be useful on slow dial-up lines (or on very distant Internet ssh
connections).
preserve pre
Save the current editor buffer as though the system were about to
crash.
previous prev[!]
Edit the previous file from the command-line argument list. {vim}
print [address] p [count]
Print the lines specified by address. count specifies the number of
lines to print, starting with address. P is another abbreviation.
Example
:100;+5p Show line 100 and the next five lines
put [address] pu [char]
Restore previously deleted or yanked lines from named register
specified by char, to the line specified by address. If char is not
specified, the last deleted or yanked text is restored.
qall qa[!]
Close all windows and terminate current editing session. Use ! to
discard changes made since the last save. {vim}
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704 | Chapter9: The vi, ex, and vim Editors
quit q[!]
Terminate current editing session. Use ! to discard changes made
since the last save. If the editing session includes additional files in
the argument list that were never accessed, quit by typing q! or by
typing q twice. vim only closes the editing window if there are still
other windows open on the screen.
read [address] rfilename
Copy the text of filename after the line specified by address. If file-
name is not specified, the current filename is used.
Example
:0r $HOME/data Read file in at top of current file
read [address] r !command
Read the output of shell command into the text after the line speci-
fied by address.
Example
:$r !spell % Place results of spell checking at end of file
recover rec [file]
Recover file from the system save area.
redo red
Restore last undone change. Same as Ctrl-R. {vim}
resize res [[±]num]
Resize current window to be num lines high. If + or - is specified,
increase or decrease the current window height by num lines.
{vim}
rewind rew[!]
Rewind argument list and begin editing the first file in the list. Add
a ! to rewind even if the current file has not been saved since the
last change.
right [address] ri [width]
Right-align lines specified by address, or current line if no address is
specified, to column width. Use textwidth option if no width is
specified. {vim}
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split | 705
vi, ex, and vim
sbnext [count] sbn [count]
Split the current window and begin editing the count’th next buffer
from the buffer list. If no count is specified, edit the next buffer in
the buffer list. {vim}
sbuffer [num] sb [num]
Split the current window and begin editing buffer num from the
buffer list in the new window. The buffer to be edited may also be
specified by filename. If no buffer is specified, open the current
buffer in the new window. {vim}
set separameter1parameter2 ...
Set a value to an option with each parameter, or, if no parameter is
supplied, print all options that have been changed from their
defaults. For Boolean options, each parameter can be phrased as
option or nooption; other options can be assigned with the syntax
option=value. Specify all to list current settings. The form set
option? displays the value of option. See the list of set options in the
section “The :set Command” on page 692.
Examples
:set nows wm=10
:set all
shell sh
Create a new shell. Resume editing when the shell terminates.
snext [count] sn [[+num]filelist]
Split the current window and begin editing the next file from the
command-line argument list. If count is provided, edit the count’th
next file. If filelist is provided, replace the current argument list
with filelist and begin editing the first file. With the +n argument,
begin editing on line num. Alternately, num may be a pattern of the
form /pattern. {vim}
source sofile
Read (source) and execute ex commands from file.
Example
:so $HOME/.exrc
split [count] sp [+num] [filename]
Split the current window and load filename in the new window, or
the same buffer in both windows if no file is specified. Make the
new window count lines high, or, if count is not specified, split the
window into equal parts. With the +n argument, begin editing on
line num. num may also be a pattern of the form /pattern. {vim}
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706 | Chapter9: The vi, ex, and vim Editors
sprevious [count] spr [+num]
Split the current window and begin editing the previous file from the
command-line argument list in the new window. If count is speci-
fied, edit the count’th previous file. With the +num argument, begin
editing on line num. num may also be a pattern of the form /pattern.
{vim}
stop st
Suspend the editing session. Same as Ctrl-Z. Use the shell fg
command to resume the session.
substitute [address] s [/pattern/replacement/] [options] [count]
Replace the first instance of pattern on each of the specified lines
with replacement. If pattern and replacement are omitted, repeat last
substitution. count specifies the number of lines on which to substi-
tute, starting with address. See additional examples in Chapter 7.
Options
c Prompt for confirmation before each change.
g Substitute all instances of pattern on each line (global).
p Print the last line on which a substitution was made.
Examples
:1,10s/yes/no/g Substitute on first 10 lines
:%s/[Hh]ello/Hi/gc Confirm global substitutions
:s/Fortran/\U&/ 3 Uppercase "Fortran" on next three lines
:g/^[0-9][0-9]*/s//Line &:/ For every line beginning with
one or more digits, add "Line" and a colon
suspend su
Suspend the editing session. Same as Ctrl-Z. Use the shell fg
command to resume the session.
sview [count] sv [+num] [filename]
Same as the split command, but set the readonly option for the
new buffer. {vim}
t [address] tdestination
Copy the lines included in address to the specified destination
address. t is equivalent to copy.
Example
:%t$ Copy the file and add it to the end
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view | 707
vi, ex, and vim
tag [address] tatag
In the tags file, locate the file and line matching tag, and start
editing there.
Example
Run ctags, then switch to the file containing myfunction:
:!ctags *.c
:tag myfunction
tags tags
Print list of tags in the tag stack. {vim}
unabbreviate unaword
Remove word from the list of abbreviations.
undo u
Reverse the changes made by the last editing command. In vi, the
undo command will undo itself, redoing what you undid. vim
supports multiple levels of undo. Use redo to redo an undone
change in vim.
unhide [count] unh
Split screen to show one window for each active buffer in the buffer
list. If specified, limit the number of windows to count. {vim}
unmap unm[!]string
Remove string from the list of keyboard macros. Use ! to remove a
macro for input mode.
v [address] v/pattern/[command]
Execute command on all lines not containing pattern. If command is
not specified, print all such lines. v is equivalent to g!. See global.
Example
:v/#include/d Delete all lines except "#include" lines
version ve
Print the editor’s current version number and date of last change.
view vie[[+num]filename]
Same as edit, but set file to readonly. When executed in ex mode,
return to normal or visual mode. {vim}
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708 | Chapter9: The vi, ex, and vim Editors
visual [address] vi [type] [count]
Enter visual mode (vi) at the line specified by address. Return to ex
mode with Q. type can be one of -, ^, or . (see the z command).
count specifies an initial window size.
visual vi [+num]file
Begin editing file in visual mode (vi), optionally at line num.
vsplit [count] vs [+num] [filename]
Same as the split command, but split the screen vertically. The
count argument can be used to specify a width for the new window.
{vim}
wall wa[!]
Write all changed buffers with filenames. Add ! to force writing of
any buffers marked readonly. {vim}
wnext [count] wn[!] [[+num]filename]
Write current buffer and open next file in argument list, or the
count’th next file if specified. If filename is specified, edit it next.
With the +num argument, begin editing on line num. num may also
be a pattern of the form /pattern. {vim}
write [address] w[!] [[>>]file]
Write lines specified by address to file, or write full contents of
buffer if address is not specified. If file is also omitted, save the
contents of the buffer to the current filename. If >> file is used,
append lines to the end of the specified file. Add a ! to force the
editor to write over any current contents of file.
Examples
:1,10w name_list Copy first 10 lines to file name_list
:50w >> name_list Now append line 50
write [address] w !command
Write lines specified by address to command.
Example
:1,66w !pr -h myfile | lp Print first page of file
wq wq[!]
Write and quit the file in one movement. The file is always written.
The ! flag forces the editor to write over any current contents of
file.
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! | 709
vi, ex, and vim
wqall wqa[!]
Write all changed buffers and quit the editor. Add ! to force writing
of any buffers marked readonly. xall is another alias for this
command. {vim}
X X
Prompt for an encryption key. This command can be preferable to
:set key, as typing the key is not echoed to the console. To remove
an encryption key, just reset the key option to an empty value. {vim}
xit x
Write the file if it was changed since the last write, then quit.
yank [address] y [char] [count]
Place lines specified by address in named register char. Register
names are the lowercase letters a-z. Uppercase names append text
to the corresponding register. If no char is given, place lines in
general register. count specifies the number of lines to yank,
starting with address.
Example
:101,200 ya a Copy lines 100–200 to register "a"
z [address] z [type] [count]
Print a window of text with the line specified by address at the top.
count specifies the number of lines to be displayed.
Type
+ Place specified line at the top of the window (default).
- Place specified line at the bottom of the window.
. Place specified line in the center of the window.
^ Print the previous window.
= Place specified line in the center of the window and leave the
current line at this line.
! [address] !command
Execute Unix command in a shell. If address is specified, use the
lines contained in address as standard input to command, and
replace the lines with the output and error output. (This is called
filtering the text through the command.)
Examples
:!ls List files in the current directory
:11,20!sort –f Sort lines 11–20 of current file
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710 | Chapter9: The vi, ex, and vim Editors
= [address] =
Print the line number of the line indicated by address. Default is
line number of the last line.
< > [address] < [count]
[address] > [count]
Shift lines specified by address either left (<) or right (>). Only
leading spaces and tabs are added or removed when shifting lines.
count specifies the number of lines to shift, starting with address.
The shiftwidth option controls the number of columns that are
shifted. Repeating the < or > increases the shift amount. For
example, :>>> shifts three times as much as :>.
address address
Print the lines specified in address.
Enter Print the next line in the file. (For ex only; not from the : prompt
in vi.)
@ [address] @ [char]
Execute contents of register specified by char. If address is given,
move cursor to the specified address first. If char is @, repeat the
last @ command.
& [address] & [options] [count]
Repeat the previous substitute (s) command. count specifies the
number of lines on which to substitute, starting with address.
options are the same as for the substitute command.
Examples
:s/Overdue/Paid/ Substitute once on current line
:g/Status/& Redo substitution on all "Status" lines
~ [address] ~ [count]
Replace the last-used regular expression (even if from a search, and
not from an s command) with the replacement pattern from the
most recent s (substitute) command. This is rather obscure; see
Chapter 6 of Learning the vi and Vim Editors by Arnold Robbins
et al. (O’Reilly) for details.
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711
Chapter 10sed
10
The sed Editor
The sed “stream editor” is one of the most prominent text-processing tools on
Unix and Linux. It is most often used for performing simple substitutions on data
streams going through pipelines, but sed scripts can be written to do much more.
This chapter presents the following topics:
• Conceptual overview of sed
• Command-line syntax
• Syntax of sed commands
• Group summary of sed commands
• Alphabetical summary of sed commands
The version of sed provided with Linux systems is the GNU version written by the
Free Software Foundation; its home page is http://www.gnu.org/software/sed/sed.
html. For more information on sed, see Dale Dougherty and Arnold Robbins’s
sed & awk (O’Reilly).
Conceptual Overview
The stream editor, sed, is a noninteractive editor. It interprets a script and
performs the actions in the script. sed is stream-oriented because, like many Unix
programs, input flows through the program and is directed to standard output.
For example, sort is stream-oriented; vi is not. sed’s input typically comes from a
file or pipe, but it can also be taken from the keyboard. Output goes to the screen
by default, but it can be captured in a file or sent through a pipe instead. GNU sed
can edit files that use multibyte character sets.
Typical Uses of sed
• Editing one or more files automatically.
• Simplifying repetitive edits to multiple files.
• Writing conversion programs.
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712 | Chapter10: The sed Editor
sed Operation
sed operates as follows:
• Each line of input is copied into a pattern space, an internal buffer where editing
operations are performed.
• All editing commands in a sed script are applied, in order, to each line of
input.
• Editing commands are applied to all lines (globally) unless line addressing
restricts the lines affected.
• If a command changes the input, subsequent commands and address tests are
applied to the current line in the pattern space, not the original input line.
• The original input file is unchanged because the editing commands modify an
in-memory copy of each original input line. The copy is sent to standard out-
put (but can be redirected to a file).
• sed also maintains the hold space, a separate buffer that can be used to save
data for later retrieval.
Command-Line Syntax
The syntax for invoking sed has two forms:
sed [-n] [-e] 'command'file(s)
sed [-n] -f scriptfile file(s)
The first form allows you to specify an editing command on the command line,
surrounded by single quotes. The second form allows you to specify a scriptfile, a
file containing sed commands. Both forms may be used together, and they may be
used multiple times. If no file (s) is specified, sed reads from standard input.
Standard Options
The following options are recognized:
-n Suppress the default output; sed displays only those lines specified with the p
command or with the p flag of the s command.
-e cmd
Next argument is an editing command. Necessary if multiple scripts or
commands are specified.
-f file
Next argument is a file containing editing commands.
If the first line of the script is #n, sed behaves as if -n had been specified.
Multiple -e and -f options may be provided, and they may be mixed. The final
script consists of the concatenation of all the script and file arguments.
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Syntax of sed Commands | 713
sed
GNU sed Options
GNU sed accepts a number of additional command-line options, as well as long-
option equivalents for the standard options. The GNU sed options are:
-e cmd, --expression cmd
Use cmd as editing commands.
-f file, --file file
Obtain editing commands from file.
--help
Print a usage message and exit.
-i[suffix], --in-place[=suffix]
Edit files in place, overwriting the original file. If optional suffix is supplied,
use it for renaming the original file as a backup file. See the GNU sed online
Info documentation for the details.
-l len, --line-length len
Set the line length for the l command to len characters.
-n, --quiet, --silent
Suppress the default output; sed displays only those lines specified with the p
command or with the p flag of the s command.
--posix
Disable all GNU extensions. Setting POSIXLY_CORRECT in the environ-
ment merely disables those extensions that are incompatible with the POSIX
standard.
-r, --regex-extended
Use Extended Regular Expressions instead of Basic Regular Expressions. See
Chapter 7 for more information.
-s, --separate
Instead of considering the input to be one long stream consisting of the
concatenation of all the input files, treat each file separately. Line numbers
start over with each file, the address $ refers to the last line of each file, files
read by the R command are rewound, and range addresses (/x/,/y/) may not
cross file boundaries.
-u, --unbuffered
Buffer input and output as little as possible. Useful for editing the output of
tail -f when you don’t want to wait for the output.
--version
Print the version of GNU sed and a copyright notice, and then exit.
Syntax of sed Commands
sed commands have the general form:
[address[,address]][!]command[arguments]
commands consist of a single letter or symbol; they are described later, by group
and alphabetically. arguments include the label supplied to b or t, the filename
supplied to r or w, and the substitution flags for s. addresses are described next.
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714 | Chapter10: The sed Editor
Pattern Addressing
A sed command can specify zero, one, or two addresses. In POSIX sed, an address has
one of the forms in the following table. Regular expressions are described in Chapter7.
Additionally, \n can be used to match any newline in the pattern space (resulting
from the N command), but not the newline at the end of the pattern space.
GNU sed allows additional address forms:
Pattern Addressing Examples
Braces ({ }) are used in sed to nest one address inside another or to apply multiple
commands at a single matched address:
[/pattern/[,/pattern/]]{
command1
command2
}
Address Meaning
/pattern/ Lines that matchpattern.
\;pattern; Like previous, but use semicolon as the delimiter instead of slash. Any char-
actermaybeused.Thisisusefulifpatterncontainsmultipleslashcharacters.
n Line numbern.
$ The last input line.
If the command specifies: Then the command is applied to:
No address Each input line.
One address Anylinematchingtheaddress.Somecommandsacceptonlyoneaddress:a,
i,r,q, and=.
Two comma-separated addresses First matching line and all succeeding lines up to and including a line
matching the second address.
An address followed by! All lines that donot match the address.
Address Meaning
/pattern/i Match pattern, ignoring case.I may be used instead ofi.
/pattern/m Matchpattern,allowing^and$tomatcharoundanembeddednewline.M
may be used instead ofm.
0,/pattern/ Similar to1,/pattern/, but if line 1 matchespattern, it will end the range.
address,+n Matches line matchingaddress, and then following lines.
address~incr Matches line matchingaddress and everyincr lines after it. For example,
42~3 matches 42, 45, 48, and so on.
Command Action performed
s/xx/yy/g Substitute on all lines (all occurrences).
/BSD/d Delete lines containingBSD.
/^BEGIN/,/^END/p Print betweenBEGIN andEND, inclusive.
/SAVE/!d Delete any line that doesn’t containSAVE.
/BEGIN/,/END/!s/xx/yy/g Substitute on all lines, except betweenBEGIN andEND.
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Group Summary of sed Commands | 715
sed
The opening curly brace must end its line, and the closing curly brace must be on
a line by itself. Be sure there are no spaces after the braces.
GNU sed Regular Expression Extensions
With the -r option, GNU sed uses Extended Regular Expressions instead of Basic
Regular expressions. (See Chapter 7 for more information.) However, even
without -r, you can use additional escape sequences for more powerful text
matching. The following escape sequences are valid only in regular expressions:
\b Matches on a word boundary, where of the two surrounding characters
(x\by), one is a word-constituent character and the other is not.
\B Matches on a nonword boundary, where both of the two surrounding charac-
ters (x\by) are either word-constituent or not word-constituent.
\w Matches any word-constituent character (i.e., a letter, digit, or underscore).
\W Matches any nonword-constituent character (i.e., anything that is not a letter,
digit, or underscore).
\' Matches the beginning of the pattern space. This is different from ^ when the
m modifier is used for a pattern or the s command.
\’ Matches the end of the pattern space. This is different from $ when the m
modifier is used for a pattern or the s command.
The following escape sequences may be used anywhere.
\a The ASCII BEL character.
\f The ASCII formfeed character.
\n The ASCII newline character.
\r The ASCII carriage-return character.
\v The ASCII vertical tab character.
\dnn
The character whose ASCII decimal value is nn.
\onn
The character whose ASCII octal value is nn.
\xnn
The character whose ASCII hexadecimal value is nn.
Group Summary of sed Commands
In the lists that follow, the sed commands are grouped by function and are
described tersely. Full descriptions, including syntax and examples, can be found
afterward in the “Alphabetical Summary of sed Commands” on page 717.
Commands marked with a † are specific to GNU sed.
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716 | Chapter10: The sed Editor
Basic Editing
Line Information
Input/Output Processing
Yanking and Putting
Command Action
a\ Append text after a line.
c\ Replace text (usually a text block).
i\ Insert text before a line.
d Delete lines.
s Make substitutions.
y Translate characters (like Unixtr).
Command Action
= Display line number of a line.
l Display control characters in ASCII.
p Display the line.
Command Action
e† Execute commands.
n Skip current line and go to the next line.
r Read another file’s contents into the output stream.
R † Read one line from a file into the output.
w Write input lines to another file.
W † Write first line in pattern space to another file.
q Quit thesed script (no further output).
Q † Quit without printing the pattern space.
v † Require a specific version of GNUsed to run the script.
Command Action
h Copy into hold space; wipe out what’s there.
H Copy into hold space; append to what’s there.
g Get the hold space back; wipe out the destination line.
G Get the hold space back; append to the pattern space.
x Exchange contents of the hold and pattern spaces.
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= | 717
sed
Branching Commands
Multiline Input Processing
Alphabetical Summary of sed Commands
GNU sed lets you use the filenames /dev/stdin, /dev/stdout and /dev/stderr to refer
to standard input, output, and error, respectively, for the r, R, w, and W
commands and the w flag to the s command.
GNU-specific commands or extensions are noted with {G} in the command
synopsis. When the GNU version allows a command to have two addresses, the
command is performed for each input line within the range.
# #
Begin a comment in a sed script. Valid only as the first character of
the first line. (Some versions, including GNU sed, allow comments
anywhere, but it is better not to rely on this.) If the first line of the
script is #n, sed behaves as if -n had been specified.
: :label
Label a line in the script for the transfer of control by b or t.
According to POSIX, sed must support labels that are unique in the
first eight characters. GNU sed has no limit, but some older
versions support up to only seven characters.
= [/pattern/]=
[address1[,address2]]={G}
Write to standard output the line number of each line addressed by
pattern.
Command Action
b Branch tolabel or to end of script.
t Same asb, but branch only after substitution.
T † Same ast, but branch only if no successful substitutions.
:label Label branched to byt orb.
Command Action
N Read another line of input (creates embedded newline).
D Delete up to the embedded newline.
P Print up to the embedded newline.
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718 | Chapter10: The sed Editor
a [address]a\
text
[address1[,address2]]a \{G}
text
Append text following each line matched by address. If text goes
over more than one line, newlines must be “hidden” by preceding
them with a backslash. The text is terminated by the first newline
that is not hidden in this way. The text is not available in the
pattern space, and subsequent commands cannot be applied to it.
The results of this command are sent to standard output when the
list of editing commands is finished, regardless of what happens to
the current line in the pattern space.
The GNU version accepts two addresses and allows you to put the
first line of text on the same line as the a command.
Example
$ a\
This goes after the last line in the file\
(marked by $). This text is escaped at the\
end of each line, except for the last one.
b [address1[,address2]]b[label]
Unconditionally transfer control to :label elsewhere in script. That
is, the command following the label is the next command applied
to the current line. If no label is specified, control falls through to
the end of the script, so no more commands are applied to the
current line.
Example
# Ignore HTML tables; resume script after </table>:
/<table/,/<\/table>/b
c [address1[,address2]]c\
text
Replace (change) the lines selected by the address(es) with text.
(See a for details on text.) When a range of lines is specified, all
lines are replaced as a group by a single copy of text. The contents
of the pattern space are, in effect, deleted, and no subsequent
editing commands can be applied to the pattern space (or to text).
Example
# Replace first 100 lines in a file:
1,100c\
\
<First 100 names to be supplied>
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G | 719
sed
d [address1[,address2]]d
Delete the addressed line (or lines) from the pattern space. Thus,
the line is not passed to standard output. A new line of input is
read, and editing resumes with the first command in the script.
Example
# Delete all empty lines, including lines with just
whitespace:
/^[#tab]*$/d
D [address1[,address2]]D
Delete the first part (up to embedded newline) of a multiline
pattern space created by the N command, and resume editing with
the first command in the script. If this command empties the
pattern space, then a new line of input is read, as if the d command
had been executed.
Example
# Strip multiple blank lines, leaving only one:
/^$/{
N
/^\n$/D
}
e [address1[,address2]]e [command]{G}
With command, execute the command and send the result to stan-
dard output. Without command, execute the contents of the
pattern space as a command, and replace the pattern space with
the results.
g [address1[,address2]]g
Paste the contents of the hold space (see h and H) back into the
pattern space, wiping out the previous contents of the pattern
space. The Example shows a simple way to copy lines.
Example
This script collects all lines containing the word Item: and copies
them to a place marker later in the file. The place marker is
overwritten:
/Item:/H
/<Replace this line with the item list>/g
G [address1[,address2]]G
Same as g, except that a newline and the hold space are pasted to
the end of the pattern space instead of overwriting it. The Example
shows a simple way to “cut and paste” lines.
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720 | Chapter10: The sed Editor
Example
This script collects all lines containing the word Item: and moves
them after a place marker later in the file. The original Item: lines
are deleted.
/Item:/{
H
d
}
/Summary of items:/G
h [address1[,address2]]h
Copy the pattern space into the hold space, a special temporary
buffer. The previous contents of the hold space are obliterated. You
can use h to save a line before editing it.
Example
# Edit a line; print the change; replay the original
/Linux/{
h
s/.* Linux \(.*\) .*/\1:/
p
x
}
Sample input:
This describes the Linux ls command.
This describes the Linux cp command.
Sample output:
ls:
This describes the Linux ls command.
cp:
This describes the Linux cp command.
H [address1[,address2]]H
Append a newline and then the contents of the pattern space to the
contents of the hold space. Even if the hold space is empty, H still
appends a newline. H is like an incremental copy. See Examples
under g and G.
i [address]i\
text
[address1[,address2]]i \{G}
text
Insert text before each line matched by address. (See a for details on
text.)
The GNU version accepts two addresses and allows you to put the
first line of text on the same line as the i command.
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N | 721
sed
Example
/Item 1/i\
The five items are listed below:
l [address1[,address2]]l
[address1[,address2]]l [len]{G}
List the contents of the pattern space, showing nonprinting charac-
ters as ASCII codes. Long lines are wrapped. With GNU sed, len is
the character position at which to wrap long lines. A value of 0
means to never break lines.
n [address1[,address2]]n
Read the next line of input into pattern space. The current line is
sent to standard output, and the next line becomes the current line.
Control passes to the command following n instead of resuming at
the top of the script.
Example
In DocBook/XML, titles follow section tags. Suppose you are using
a convention where each opening section tag is on a line by itself,
with the title on the following line. To print all the section titles,
invoke this script with sed -n:
/<sect[1-4]/{
n
p
}
N [address1[,address2]]N
Append the next input line to contents of pattern space; the new
line is separated from the previous contents of the pattern space by
a newline. (This command is designed to allow pattern matches
across two lines.) By using \n to match the embedded newline, you
can match patterns across multiple lines. See the Example under D.
Examples
Like the Example in n, but print the section tag line as well as
header title:
/<sect[1-4]/{
N
p
}
Join two lines (replace newline with space):
/<sect[1-4]/{
N
s/\n/ /
p
}
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722 | Chapter10: The sed Editor
p [address1[,address2]]p
Print the addressed line(s). Note that this can result in duplicate
output unless default output is suppressed by using #n or the -n
command-line option. Typically used before commands that
change control flow (d, n, b), which might prevent the current line
from being output. See the Examples under h, n, and N.
P [address1[,address2]]P
Print first part (up to embedded newline) of multiline pattern space
created by N command. Same as p if N has not been applied to a
line.
Example
Suppose you have function references in two formats:
function(arg1, arg2)
function(arg1,
arg2)
The following script changes argument arg2, regardless of whether
it appears on the same line as the function name:
s/function(arg1, arg2)/function(arg1, XX)/
/function(/{
N
s/arg2/XX/
P
D
}
q [address]q
[address]q [value]{G}
Quit when address is encountered. The addressed line is first
written to the output (if default output is not suppressed), along
with any text appended to it by previous a or r commands. GNU
sed allows you to provide value, which is used as the exit status.
Examples
Delete everything after the addressed line:
/Garbled text follows:/q
Print only the first 50 lines of a file:
50q
Q [address]Q [value]{G}
Quits processing, but without printing the pattern space. If value is
provided, it is used as sed’s exit status.
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s | 723
sed
r [address]rfile
[address1[,address2]]rfile{G}
Read contents of file and append to the output after the contents of
the pattern space. There must be exactly one space between the r
and the filename. The GNU version accepts two addresses.
Example
/The list of items follows:/r item_file
R [address1[,address2]]Rfile{G}
Read one line of file and append to the output after the contents of
the pattern space. Successive R commands read successive lines
from file.
s [address1[,address2]]s/pattern/replacement/[flags]
Substitute replacement for pattern on each addressed line. If pattern
addresses are used, the pattern // represents the last pattern address
specified. Any delimiter may be used. Use \ within pattern or
replacement to escape the delimiter. The following flags can be
specified (those marked with a † are specific to GNU sed):
n Replace nth instance of pattern on each addressed line. n is
any number in the range 1 to 512, and the default is 1.
e† If the substitution was made, execute the contents of the
pattern space as a shell command and replaces the pattern
space with the results.
g Replace all instances of pattern on each addressed line, not
just the first instance.
i or I†
Do a case-insensitive regular expression match.
m or M†
Allow ^ and $ to match around a newline embedded in the
pattern space.
p Print the line if the substitution is successful. If several
successful substitutions are successful, sed prints multiple
copies of the line.
w file
Write the line to file if a replacement was done. In the tradi-
tional Unix sed, a maximum of 10 different files can be opened.
GNU sed allows you to use the special filenames /dev/stdout
and /dev/stderr to write to standard output or standard error,
respectively.
Within the replacement, GNU sed accepts special escape
sequences, with the following meanings:
\L Lowercase the replacement text until a terminating \E or \U.
\l Lowercase the following character only.
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724 | Chapter10: The sed Editor
\U Uppercase the replacement text until a terminating \E or \L.
\u Uppercase the following character only.
\E Terminate case conversion from \L or \U.
Examples
Here are some short, commented scripts:
# Change third and fourth quote to ( and ):
/function/{
s/"/)/4
s/"/(/3
}
# Remove all quotes on a given line:
/Title/s/"//g
# Remove first colon and all quotes; print resulting lines:
s/://p
s/"//gp
# Change first "if" but leave "ifdef" alone:
/ifdef/!s/if/ if/
t [address1[,address2]]t [label]
Test if successful substitutions have been made on addressed lines,
and if so, branch to the line marked by :label. (See b and : .) If label
is not specified, control branches to the bottom of the script. The t
command is like a case statement in the C programming language
or the various shell programming languages. You test each case;
when it’s true, you exit the construct.
Example
Suppose you want to fill empty fields of a database. You have this:
ID: 1 Name: greg Rate: 45
ID: 2 Name: dale
ID: 3
You want this:
ID: 1 Name: greg Rate: 45 Phone: ??
ID: 2 Name: dale Rate: ?? Phone: ??
ID: 3 Name: ???? Rate: ?? Phone: ??
You need to test the number of fields already there. Here’s the
script (fields are tab-separated):
#n
/ID/{
s/ID: .* Name: .* Rate: .*/& Phone: ??/p
t
s/ID: .* Name: .*/& Rate: ?? Phone: ??/p
t
s/ID: .*/& Name: ???? Rate: ?? Phone: ??/p
}
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y | 725
sed
T [address1[,address2]]T [label]{G}
Like t, but only branches to label if there not any successful substi-
tutions. (see b, t, and : ). If label is not specified, control branches
to the bottom of the script.
v [address1[,address2]]v [version]{G}
This command doesn’t do anything. You use it to require GNU sed
for your script. This works, because non-GNU versions of sed
don’t implement the command at all, and will therefore fail. If you
supply a specific version, GNU sed fails if the required version is
newer than the one executing the script.
w [address1[,address2]]wfile
Append contents of pattern space to file. This action occurs when
the command is encountered rather than when the pattern space is
output. Exactly one space must separate the w and the filename.
This command will create the file if it does not exist; if the file
exists, its contents will be overwritten each time the script is
executed. Multiple write commands that direct output to the same
file append to the end of the file.
GNU sed allows you to use the special filenames /dev/stdout and
/dev/stderr to write to standard output or standard error,
respectively.
Example
# Store HTML tables in a file
/<table/,/<\/table>/w tables.html
W [address1[,address2]]Wfile
Like w, but only writes the contents of the first line in the pattern
space to the file.
x [address1[,address2]]x
Exchange the contents of the pattern space with the contents of the
hold space. See h for an example.
y [address1[,address2]]y/abc/xyz/
Translate characters. Change every instance of a to x, b to y, c to z,
etc.
Example
# Change item 1, 2, 3 to Item A, B, C ...
/^item [1-9]/y/i123456789/IABCDEFGHI/
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726
Chapter 11gawk
11
The gawk Programming
Language
gawk is the GNU version of awk, a powerful utility often used for text and string
manipulation within shell scripts, particularly when input data may be viewed as
records and fields. awk is also an elegant and capable programming language that
allows you to accomplish a lot with very little work.
This chapter presents the following topics:
• Conceptual overview
• Command-line syntax
• Patterns and procedures
• Built-in variables
• Operators
• Variables and array assignment
• User-defined functions
• gawk-specific facilities
• Implementation limits
• Group listing of awk functions and commands
• Alphabetical summary of awk functions and commands
• Source code
Conceptual Overview
awk is a pattern-matching program for processing files, especially when each line
has a simple field-oriented layout. Linux provides the GNU version of awk, called
gawk, which provides a number of additional features. This utility can be invoked
either through the standard name awk or through gawk.
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Command-Line Syntax | 727
gawk
This chapter describes functionality that is found in gawk. Most of this discus-
sion applies to all versions of awk, but items marked “gawk-specific” or as an
“extension” may not apply to versions of awk other than GNU’s. If portability to
older, non-Linux systems is important, do not use gawk-specific features.
With gawk, you can:
• Think of a text file as made up of records and fields in a textual database.
• Perform arithmetic and string operations.
• Use programming constructs, such as loops and conditionals.
• Produce formatted reports.
• Define your own functions.
• Execute Unix commands from a script.
• Process the results of Unix commands.
• Process command-line arguments gracefully.
• Work easily with multiple input streams.
• Flush open output files and pipes.
• Sort arrays.
• Retrieve and format system time values.
• Do bit manipulation.
• Internationalize your gawk programs, allowing strings to be translated into a
local language at runtime.
• Perform two-way I/O to a coprocess.
• Open a two-way TCP/IP connection to a socket.
• Dynamically add built-in functions.
• Profile your gawk programs.
Command-Line Syntax
The syntax for invoking awk has two forms:
awk [options] 'script' var=value file(s)
awk [options] -fscriptfile var=value file(s)
You can specify a script directly on the command line, or you can store a script in
a scriptfile and specify it with -f. gawk allows multiple -f scripts. Variables can be
assigned a value on the command line. The value can be a string or numeric
constant, a shell variable ($name), or a command substitution (`cmd`), but the
value is available only after the BEGIN statement is executed.
awk operates on one or more files. If none are specified (or if - is specified), awk
reads from standard input.
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728 | Chapter11: The gawk Programming Language
Standard Options
The standard options are:
-Ffs
Set the field separator to fs. This is the same as setting the built-in variable FS.
gawk allows fs to be a regular expression. Each input line, or record, is divided
into fields by whitespace (spaces or tabs) or by some other user-definable field
separator. Fields are referred to by the variables $1, $2,..., $n. $0 refers to the
entire record.
-v var=value
Assign a value to variable var. This allows assignment before the script begins
execution.
For example, to print the first three (colon-separated) fields of each record on
separate lines:
awk -F: '{ print $1; print $2; print $3 }' /etc/passwd
Numerous examples are shown in “Simple Pattern-Procedure Examples” on
page 730.
Important gawk Options
Besides the standard command line options, gawk has a large number of addi-
tional options. This section lists those of most value in day-to-day use. Any
unique abbreviation of these options is acceptable.
--dump-variables[=file]
When the program has finished running, print a sorted list of global variables,
their types, and their final values to file. The default file is awkvars.out.
--gen-po
Read the awk program and print all strings marked as translatable to stan-
dard output in the form of a GNU gettext Portable Object file. See the section
“Internationalization” on page 736 for more information.
--help
Print a usage message to standard error and exit.
--lint[=fatal]
Enable checking of nonportable or dubious constructs, both when the
program is read and as it runs. With an argument of fatal, lint warnings
become fatal errors.
--non-decimal-data
Allow octal and hexadecimal data in the input to be recognized as such. This
option is not recommended; use strtonum() in your program, instead.
--profile[=file]
With gawk, put a “prettyprinted” version of the program in file. Default is
awkprof.out. With pgawk (see “Profiling” on page 735), put the profiled
listing of the program in file.
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Patterns and Procedures | 729
gawk
--posix
Turn on strict POSIX compatibility, in which all common and gawk-specific
extensions are disabled.
--source='program text'
Use program text as the awk source code. Use this option with -f to mix
command-line programs with awk library files.
--traditional
Disable all gawk-specific extensions, but allow common extensions (e.g., the
** operator for exponentiation).
--version
Print the version of gawk on standard error and exit.
Patterns and Procedures
awk scripts consist of patterns and procedures:
pattern {procedure }
Both pattern and { procedure } are optional. If pattern is missing, { procedure } is
applied to all lines. If { procedure } is missing, the matched line is printed.
Patterns
A pattern can be any of the following:
general expression
/regular expression/
relational expression
pattern-matching expression
BEGIN
END
• General expressions can be composed of quoted strings, numbers, operators,
function calls, user-defined variables, or any of the predefined variables
described in “Built-in Variables” on page 731.
• Regular expressions use the extended set of metacharacters, as described in
Chapter 7.
• The ^ and $ metacharacters refer to the beginning and end of a string (such
as the fields), respectively, rather than the beginning and end of a line. In par-
ticular, these metacharacters will not match at a newline embedded in the
middle of a string.
• Relational expressions use the relational operators listed in “Operators” on
page 732. For example, $2 > $1 selects lines for which the second field is
greater than the first. Comparisons can be either string or numeric. Thus,
depending upon the types of data in $1 and $2, awk will do either a numeric
or a string comparison. This can change from one record to the next.
• Pattern-matching expressions use the operators ~ (match) and !~ (don’t
match). See “Operators” on page 732.
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730 | Chapter11: The gawk Programming Language
• The BEGIN pattern lets you specify procedures that will take place before the
first input line is processed. (Generally, you process the command line and
set global variables here.)
• The END pattern lets you specify procedures that will take place after the last
input record is read.
• BEGIN and END patterns may appear multiple times. The procedures are
merged as if there had been one large procedure.
Except for BEGIN and END, patterns can be combined with the Boolean opera-
tors || (or), && (and), and ! (not). A range of lines can also be specified using
comma-separated patterns:
pattern,pattern
Procedures
Procedures consist of one or more commands, function calls, or variable assign-
ments, separated by newlines or semicolons, and are contained within curly braces.
Commands fall into five groups:
• Variable or array assignments
• Input/Output commands
• Built-in functions
• Control-flow commands
• User-defined functions
Simple Pattern-Procedure Examples
Print first field of each line:
{ print $1 }
Print all lines that contain pattern:
/pattern/
Print first field of lines that contain pattern:
/pattern/{ print $1 }
Select records containing more than two fields:
NF > 2
Interpret input records as a group of lines up to a blank line. Each line is a single field:
BEGIN { FS = "\n"; RS = "" }
Print fields 2 and 3 in switched order, but only on lines whose first field matches
the string URGENT:
$1 ~ /URGENT/ { print $3, $2 }
Count and print the number of pattern found:
/pattern/{ ++x }
END { print x }
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Built-in Variables | 731
gawk
Add numbers in second column and print the total:
{ total += $2 }
END { print "column total is", total}
Print lines that contain less than 20 characters:
length($0) < 20
Print each line that begins with Name: and that contains exactly seven fields:
NF = = 7 && /^Name:/
Print the fields of each record in reverse order, one per line:
{
for (i = NF; i >= 1; i--)
print $i
}
Built-in Variables
All awk variables are included in gawk.
Version Variable Description
awk ARGC Number of arguments on the command line.
ARGV Anarraycontainingthecommand-linearguments,indexedfrom0
toARGC -1.
ENVIRON An associative array of environment variables.
FILENAME Current filename.
FNR LikeNR, but relative to the current file.
FS Field separator (a space).
NF Number of fields in current record.
NR Number of the current record.
OFMT Output format for numbers ("%.6g").
OFS Output field separator (a space).
ORS Output record separator (a newline).
RLENGTH Length of the string matched bymatch() function.
RS Record separator (a newline).
RSTART First position in the string matched bymatch() function.
SUBSEP Separator character for array subscripts ("\034").
$0 Entire input record.
$n nth field in current record; fields are separated byFS.
gawk ARGIND Index inARGV of current input file.
BINMODE Controls binary I/O for input and output files. Use values of1,2, or
3 for input, output, or both kinds of files, respectively. Set it on the
command line to affect standard input, standard output, and stan-
dard error.
ERRNO Astringindicatingtheerrorwhenaredirectionfailsforgetlineorif
close() fails.
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732 | Chapter11: The gawk Programming Language
Operators
The following table lists the operators, in order of increasing precedence, that are
available in awk.
While ** and **= are common extensions, they are not part of
POSIX awk.
Variable and Array Assignment
Variables can be assigned a value with an equals sign. For example:
FS = ","
Expressions using the operators +, -, /, and % (modulo) can be assigned to
variables.
FIELDWIDTHS A space-separated list of field widths to use for splitting up the
record, instead ofFS.
IGNORECASE Whentrue,allregularexpressionmatches,stringcomparisons,and
index() ignore case.
LINT Dynamicallycontrolsproductionof“lint”warnings.Withavalueof
"fatal", lint warnings become fatal errors.
PROCINFO Anarraycontaininginformationabouttheprocess,suchasrealand
effective UID numbers, process ID number, and so on.
RT The text matched byRS, which can be a regular expression in
gawk.
TEXTDOMAIN Thetextdomain(applicationname)forinternationalizedmessages
("messages").
Symbol Meaning
= += -= *= /= %= ^= **= Assignment.
?: C conditional expression.
|| Logical OR (short-circuit).
&& Logical AND (short-circuit).
in Array membership.
~ !~ Match regular expression and negation.
< <= > >= != == Relational operators.
(blank) Concatenation.
+ - Addition, subtraction.
* / % Multiplication, division, and modulus (remainder).
+ - ! Unary plus and minus, and logical negation.
^ ** Exponentiation.
++ -- Increment and decrement, either prefix or postfix.
$ Field reference.
Version Variable Description
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Variable and Array Assignment | 733
gawk
Arrays can be created with the split() function (described later), or they can
simply be named in an assignment statement. Array elements can be subscripted
with numbers (array[1], ..., array[n]) or with strings. Arrays subscripted by
strings are called associative arrays. * For example, to count the number of widgets
you have, you could use the following script:
/widget/ { count["widget"]++ } Count widgets
ND { print count["widget"] } Print the count
You can use the special for loop to read all the elements of an associative array:
for (item in array)
process array[item]
The index of the array is available as item, while the value of an element of the
array can be referenced as array[item].
You can use the operator in to test that an element exists by testing to see if its
index exists. For example:
if (index in array)
...
tests that array[index] exists, but you cannot use it to test the value of the
element referenced by array[index].
You can also delete individual elements of the array using the delete statement.
(See also the delete entry in “Alphabetical Summary of awk Functions and
Commands” on page 738.)
Escape sequences
Within string and regular-expression constants, the following escape sequences
may be used.
The \x escape sequence is a common extension; it is not part of
POSIX awk.
*In fact, all arrays in awk are associative; numeric subscripts are converted to strings before being
used as array subscripts. Associative arrays are one of awk’s most powerful features.
Sequence Meaning Sequence Meaning
\a Alert (bell) \v Vertical tab
\b Backspace \\ Literal backslash
\f Form feed \nnn Octal valuennn
\n Newline \xnn Hexadecimal valuenn
\r Carriage return \” Literal double quote (in strings)
\t Tab \/ Literal slash (in regular expressions)
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734 | Chapter11: The gawk Programming Language
Octal and Hexadecimal Constants in gawk
gawk allows you to use octal and hexadecimal constants in your program source
code. The form is as in C: octal constants start with a leading 0, and hexadecimal
constants with a leading 0x or 0X. The hexadecimal digits a–f may be in either
uppercase or lowercase.
$gawk 'BEGIN { print 042, 42, 0x42 }'
34 42 66
Use the strtonum() function to convert octal or hexadecimal input data into
numerical values.
User-Defined Functions
gawk allows you to define your own functions. This makes it easy to encapsulate
sequences of steps that need to be repeated into a single place and reuse the code
from anywhere in your program.
The following function capitalizes each word in a string. It has one parameter,
named input, and five local variables, which are written as extra parameters:
# capitalize each word in a string
function capitalize(input, result, words, n, i, w)
{
result = ""
n = split(input, words, " ")
for (i = 1; i <= n; i++) {
w = words[i]
w = toupper(substr(w, 1, 1)) substr(w, 2)
if (i > 1)
result = result " "
result = result w
}
return result
}
# main program, for testing
{ print capitalize($0) }
With this input data:
A test line with words and numbers like 12 on it.
This program produces:
A Test Line With Words And Numbers Like 12 On It.
For user-defined functions, no space is allowed between the func-
tion name and the left parenthesis when the function is called.
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gawk-Specific Features | 735
gawk
gawk-Specific Features
This section describes features unique to gawk.
Coprocesses and Sockets
gawk allows you to open a two-way pipe to another process, called a coprocess.
This is done with the |& operator used with getline and print or printf.
printdatabase command |& "db_server"
"db_server" |& getline response
If the command used with |& is a filename beginning with /inet/, gawk opens a
TCP/IP connection. The filename should be of the following form:
/inet/protocol/lport/hostname/rport
The parts of the filename are:
protocol
One of tcp, udp or raw, for TCP, UDP, or raw IP sockets, respectively. Note:
raw is currently reserved but unsupported.
lport
The local TCP or UPD port number to use. Use 0 to let the operating system
pick a port.
hostname
The name or IP address of the remote host to connect to.
rport
The port (application) on the remote host to connect to. A service name (e.g.,
tftp) is looked up using the C getservbyname() function.
Profiling
When gawk is built and installed, a separate program named pgawk (profiling
gawk) is built and installed with it. The two programs behave identically;
however, pgawk runs more slowly because it keeps execution counts for each
statement as it runs. When it is done, it automatically places an execution profile
of your program in a file named awkprof.out. (You can change the filename with
the --profile option.)
The execution profile is a “prettyprinted” version of your program, with execu-
tion counts listed in the left margin. For example, after running this program:
$pgawk '/bash$/ { nusers++ }
>END { print nusers, "users use Bash." }' /etc/passwd
16 users use Bash.
the execution profile looks like this:
# gawk profile, created Mon Nov 1 14:34:38 2004
# Rule(s)
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736 | Chapter11: The gawk Programming Language
35 /bash$/ { # 16
16 nusers++
}
# END block(s)
END {
1 print nusers, "users use Bash."
}
If sent SIGUSR1, pgawk prints the profile and an awk function call stack trace,
and then keeps going. Multiple SIGUSR1 signals may be sent; the profile and
trace will be printed each time. This facility is useful if your awk program appears
to be looping and you want to see if something unexpected is being executed.
If sent SIGHUP, pgawk prints the profile and stack trace, and then exits.
File Inclusion
The igawk program provides a file-inclusion facility for gawk. You invoke it the
same way you do gawk: it passes all command line arguments on to gawk.
However, igawk processes source files and command-line programs for special
statements of the form:
@include file.awk
Such files are searched for along the list of directories specified by the AWKPATH
environment variable. When found, the @include line is replaced with the text of
the corresponding file. Included files may themselves include other files with
@include.
The combination of the AWKPATH environment variable and igawk makes it
easy to have and use libraries of awk functions.
Internationalization
You can internationalize your programs if you use gawk. This consists of choosing
a text domain for your program, marking strings that are to be translated, and, if
necessary, using the bindtextdomain(), dcgettext(), and dcngettext() functions.
Localizing your program consists of extracting the marked strings, creating trans-
lations, and compiling and installing the translations in the proper place. Full
details are given in sed & awk by Dale Dougherty and Arnold Robbins (O’Reilly).
The internationalization features in gawk use GNU gettext. You may need to
install the GNU gettext tools to create translations if your system doesn’t already
have them. Here is a very brief outline of the steps involved:
1. Set TEXTDOMAIN to your text domain in a BEGIN block:
BEGIN { TEXTDOMAIN = "whizprog" }
2. Mark all strings to be translated by prepending a leading underscore:
printf(_"whizprog: can't open /dev/telepath (%s)\n",
dcgettext(ERRNO)) > "/dev/stderr"
3. Extract the strings with the --gen-po option:
$gawk --gen-po -f whizprog.awk > whizprog.pot
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Group Listing of awk Functions and Commands | 737
gawk
4. Copy the file for translating, and make the translations:
$cp whizprog.pot esperanto.po
$ed esperanto.po
5. Use the msgfmt program from GNU gettext to compile the translations. The
binary format allows fast lookup of the translations at runtime. The default
output is a file named messages:
$msgfmt esperanto.po
$mv messages esperanto.mo
6. Install the file in the standard location. This is usually done at program instal-
lation. The location can vary from system to system.
That’s it! gawk will automatically find and use the translated messages, if they exist.
Implementation Limits
Many versions of awk have various implementation limits, on things such as:
• Number of fields per record
• Number of characters per input record
• Number of characters per output record
• Number of characters per field
• Number of characters per printf string
• Number of characters in literal string
• Number of characters in character class
• Number of files open
• Number of pipes open
• The ability to handle 8-bit characters and characters that are all zero (ASCII
NUL)
gawk does not have limits on any of the above items, other than those imposed by
the machine architecture and/or the operating system.
Group Listing of awk Functions and Commands
The following table classifies awk functions and commands.
Function type Functions or commands
Arithmetic atan2 cos exp int log
rand sin sqrt srand
String asort a asorti a gensub a gsub index
length match split sprintf strtonum a
sub substr tolower toupper
Control flow break continue do/while exit for
if/else return while
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738 | Chapter11: The gawk Programming Language
The following functions are specific to gawk.
Alphabetical Summary of awk Functions and
Commands
The following alphabetical list of keywords and functions includes all that are
available in POSIX awk and gawk. Extensions that aren’t part of POSIX awk but
that are in both gawk and the Bell Laboratories awk are marked as {E}. Cases
where gawk has extensions are marked as {G}. Items that aren’t marked with a
symbol are available in all versions.
# #
Ignore all text that follows on the same line. # is used in awk
scripts as the comment character and is not really a command.
and and(expr1,expr2) {G}
Return the bitwise AND of expr1 and expr2, which should be
values that fit in a C unsigned long.
asort asort(src [,dest]) {G}
Sort the array src based on the element values, destructively
replacing the indices with values from one to the number of
elements in the array. If dest is supplied, copy src to dest and sort
dest, leaving src unchanged. Returns the number of elements in src.
asorti asorti(src [,dest]) {G}
Like asort(), but the sorting is done based on the indices in the
array, not based on the element values. For gawk 3.1.2 and later.
I/O close fflush b getline next nextfile b
print printf
Programming extension a delete function system
a Available ingawk.
b Available in Bell Labsawk andgawk.
Function type Functions or commands
Bit
manipulation
and compl lshift or rshift
xor
Time mktime strftime systime
Translation bindtext-
domain
dcgettext dcngettext
Function type Functions or commands
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dcngettext | 739
gawk
atan2 atan2(y,x)
Return the arctangent of y/x in radians.
bindtextdomain bindtextdomain(dir [,domain]) {G}
Look in directory dir for message translation files for text domain
domain (default: value of TEXTDOMAIN). Returns the directory
where domain is bound.
break break
Exit from a while, for, or do loop.
close close(expr)
close(expr,how) {G}
In most implementations of awk, you can only have up to ten files
and one pipe open simultaneously. Therefore, POSIX awk provides
a close() function that allows you to close a file or a pipe. It takes
the same expression that opened the pipe or file as an argument.
This expression must be identical, character by character, to the
one that opened the file or pipe—even whitespace is significant.
In the second form, close one end of either a TCP/IP socket or a
two-way pipe to a coprocess. how is a string, either “from” or “to”.
Case does not matter.
compl compl(expr) {G}
Return the bitwise complement of expr, which should be a value
that fits in a C unsigned long.
continue continue
Begin next iteration of while, for, or do loop.
cos cos(x)
Return the cosine of x, an angle in radians.
dcgettext dcgettext(str [,dom [,cat]]) {G}
Return the translation of str for the text domain dom in message
category cat. Default text domain is value of TEXTDOMAIN.
Default category is "LC_MESSAGES".
dcngettext dcngettext(str1,str2,num [,dom [,cat]]) {G}
If num is one, return the translation of str1 for the text domain dom
in message category cat. Otherwise, return the translation of str2.
Default text domain is value of TEXTDOMAIN. Default category
is "LC_MESSAGES". For gawk 3.1.1 and later.
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740 | Chapter11: The gawk Programming Language
delete deletearray[element]
deletearray {E}
Delete element from array. The brackets are typed literally. The
second form is a common extension, which deletes all elements of
the array in one shot.
do do
statement
while (expr)
Looping statement. Execute statement, then evaluate expr and if
true, execute statement again. A series of statements must be put
within braces.
exit exit [expr]
Exit from script, reading no new input. The END procedure, if it
exists, will be executed. An optional expr becomes awk’s return
value.
exp exp(x)
Return exponential of x (ex).
extension extension(lib,init) {G}
Dynamically load the shared object file lib, calling the function init
to initialize it. Return the value returned by the init function. This
function allows you to add new built-in functions to gawk. See
Arnold Robbins’s Effective awk Programming (O’Reilly) for the
details.
fflush fflush([output-expr]) {E}
Flush any buffers associated with open output file or pipe output-expr.
gawk extends this function. If no output-expr is supplied, it flushes
standard output. If output-expr is the null string (""), it flushes all
open files and pipes.
for for (init-expr;test-expr;incr-expr)
statement
C-style looping construct. init-expr assigns the initial value of a
counter variable. test-expr is a relational expression that is evalu-
ated each time before executing the statement. When test-expr is
false, the loop is exited. incr-expr is used to increment the counter
variable after each pass. All of the expressions are optional. A
missing test-expr is considered to be true. A series of statements
must be put within braces.
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gsub | 741
gawk
for for (item inarray)
statement
Special loop designed for reading associative arrays. For each
element of the array, the statement is executed; the element can be
referenced by array [item]. A series of statements must be put
within braces.
function functionname(parameter-list) {
statements
}
Create name as a user-defined function consisting of awk state-
ments that apply to the specified list of parameters. No space is
allowed between name and the left parenthesis when the function
is called.
gensub gensub(regex,str,how [,target]) {G}
General substitution function. Substitute str for matches of the
regular expression regex in the string target. If how is a number,
replace the howth match. If it is "g" or "G", substitute globally. If
target is not supplied, $0 is used. Return the new string value. The
original target is not modified. (Compare with gsub and sub.) Use
& in the replacement string to stand for the text matched by the
pattern.
getline getline
getline [var] [<file]
command | getline [var]
command |& getline [var] {G}
Read next line of input.
The second form reads input from file, and the third form reads the
output of command. All forms read one record at a time, and each
time the statement is executed, it gets the next record of input. The
record is assigned to $0 and is parsed into fields, setting NF, NR
and FNR. If var is specified, the result is assigned to var and $0 and
NF are not changed. Thus, if the result is assigned to a variable, the
current record does not change. getline is actually a function, and
it returns 1 if it reads a record successfully, 0 if end-of-file is
encountered, and -1 if for some reason it is otherwise unsuccessful.
The fourth form reads the output from coprocess command. See the
section “Coprocesses and Sockets” on page 735 for more information.
gsub gsub(regex,str [,target])
Globally substitute str for each match of the regular expression
regex in the string target. If target is not supplied, defaults to $0.
Return the number of substitutions. Use & in the replacement
string to stand for the text matched by the pattern.
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742 | Chapter11: The gawk Programming Language
if if (condition)
statement1
[else
statement2]
If condition is true, do statement1; otherwise do statement2 in
optional else clause. The condition can be an expression using any
of the relational operators <, <=, = =, !=, >=, or >, as well as the
array membership operator in, and the pattern-matching operators
~ and !~ (e.g., if ($1 ~ /[Aa].*/)). A series of statements must be put
within braces. Another if can directly follow an else in order to
produce a chain of tests or decisions.
index index(str,substr)
Return the position (starting at 1) of substr in str, or zero if substr is
not present in str.
int int(x)
Return integer value of x by truncating any fractional part.
length length([arg])
Return length of arg, or the length of $0 if no argument.
log log(x)
Return the natural logarithm (base e) of x.
lshift lshift(expr,count) {G}
Return the result of shifting expr left by count bits. Both expr and
count should be values that fit in a C unsigned long.
match match(str,regex)
match(str,regex [,array]) {G}
Function that matches the pattern, specified by the regular expres-
sion regex, in the string str and returns either the position in str
where the match begins, or 0 if no occurrences are found. Sets the
values of RSTART and RLENGTH to the start and length of the
match, respectively.
If array is provided, gawk puts the text that matched the entire
regular expression in array[0], the text that matched the first
parenthesized subexpression in array[1], the second in array[2],
and so on.
mktime mktime(timespec) {G}
Turns timespec (a string of the form YYYY MM DD HH MM
SS[DST] representing a local time) into a time-of-day value in
seconds since midnight, January 1, 1970, UTC.
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rand | 743
gawk
next next
Read next input line and start new cycle through pattern/procedures
statements.
nextfile nextfile {E}
Stop processing the current input file and start new cycle through
pattern/procedures statements, beginning with the first record of
the next file.
or or(expr1,expr2) {G}
Return the bitwise OR of expr1 and expr2, which should be values
that fit in a C unsigned long.
print print [output-expr[ , ...]] [dest-expr ]
Evaluate the output-expr and direct it to standard output followed
by the value of ORS. Each comma-separated output-expr is sepa-
rated in the output by the value of OFS. With no output-expr, print
$0. The output may be redirected to a file or pipe via the dest-expr,
which is described in “Output Redirections” on page 746.
printf printf(format [,expr-list ]) [dest-expr ]
An alternative output statement borrowed from the C language. It
has the ability to produce formatted output. It can also be used to
output data without automatically producing a newline. format is a
string of format specifications and constants. expr-list is a list of
arguments corresponding to format specifiers. As for print, output
may be redirected to a file or pipe. See “printf Formats” on
page 746 for a description of allowed format specifiers.
Like any string, format can also contain embedded escape sequences:
\n (newline) or \t (tab) being the most common. Spaces and literal
text can be placed in the format argument by quoting the entire
argument. If there are multiple expressions to be printed, there
should be multiple formats specified.
Examples
Using the script:
{ printf("The sum on line %d is %.0f.\n", NR, $1+$2) }
The following input line:
5 5
produces this output, followed by a newline:
The sum on line 1 is 10.
rand rand()
Generate a random number between 0 and 1. This function returns
the same series of numbers each time the script is executed, unless
the random number generator is seeded using srand().
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744 | Chapter11: The gawk Programming Language
return return [expr]
Used within a user-defined function to exit the function, returning
the value of expr. The return value of a function is undefined if expr
is not provided.
rshift rshift(expr,count) {G}
Return the result of shifting expr right by count bits. Both expr and
count should be values that fit in a C unsigned long.
sin sin(x)
Return the sine of x, an angle in radians.
split split(string,array [,sep])
Split string into elements of array array[1],...,array[n]. Return the
number of array elements created. The string is split at each occur-
rence of separator sep. If sep is not specified, FS is used.
sprintf sprintf(format [,expressions])
Return the formatted value of one or more expressions, using the
specified format. Data is formatted but not printed. See “printf
Formats” on page 746 for a description of allowed format
specifiers.
sqrt sqrt(arg)
Return the square root of arg.
srand srand([expr])
Use optional expr to set a new seed for the random number gener-
ator. Default is the time of day. Return value is the old seed.
strftime strftime([format [,timestamp]]) {G}
Format timestamp according to format. Return the formatted
string. The timestamp is a time-of-day value in seconds since
midnight, January 1, 1970, UTC. The format string is similar to
that of sprintf. If timestamp is omitted, it defaults to the current
time. If format is omitted, it defaults to a value that produces
output similar to that of the Unix date command. See the date
entry in Chapter 3 for a list.
strtonum strtonum(expr) {G}
Return the numeric value of expr, which is a string representing an
octal, decimal, or hexadecimal number in the usual C notations.
Use this function for processing nondecimal input data.
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tolower | 745
gawk
sub sub(regex,str [,target])
Substitute str for first match of the regular expression regex in the
string target. If target is not supplied, defaults to $0. Returns 1 if
successful, 0 otherwise. Use & in the replacement string to stand
for the text matched by the pattern.
substr substr(string,beg [,len])
Return substring of string at beginning position beg (counting from
1), and the characters that follow to maximum specified length len.
If no length is given, use the rest of the string.
system system(command)
Function that executes the specified command and returns its exit
status. The status of the executed command typically indicates
success or failure. A value of 0 means that the command executed
successfully. A nonzero value indicates a failure of some sort. The
documentation for the command will give you the details.
awk does not make the output of the command available for
processing within the awk script. Use command | getline to read
the output of a command into the script.
systime systime() {G}
Return a time-of-day value in seconds since midnight, January 1,
1970, UTC.
Examples
Log the start and end times of a data-processing program:
BEGIN {
now = systime()
mesg = strftime("Started at %m/%d/%Y %H:%M:%S",
now)
print mesg
}
process data ...
END {
now = systime()
mesg = strftime("Ended at %m/%d/%Y %H:%M:%S",
now)
print mesg
}
tolower tolower(str)
Translate all uppercase characters in str to lowercase and return the
new string. *
*Very early versions of nawk don’t support tolower() and toupper(). However, they are now part
of the POSIX specification for awk.
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746 | Chapter11: The gawk Programming Language
toupper toupper(str)
Translate all lowercase characters in str to uppercase and return the
new string.
while while (condition)
statement
Do statement while condition is true (see if for a description of
allowable conditions). A series of statements must be put within
braces.
xor xor(expr1,expr2) {G}
Return the bitwise XOR of expr1 and expr2, which should be
values that fit in a C unsigned long.
Output Redirections
For print and printf, dest-expr is an optional expression that directs the output to
a file or pipe.
> file
Direct the output to a file, overwriting its previous contents.
>> file
Append the output to a file, preserving its previous contents. In both this case
and the > file case, the file will be created if it does not already exist.
| command
Direct the output as the input to a system command.
|& command
Direct the output as the input to a coprocess. gawk only.
Be careful not to mix > and >> for the same file. Once a file has been opened with
>, subsequent output statements continue to append to the file until it is closed.
Remember to call close() when you have finished with a file, pipe, or coprocess. If
you don’t, eventually you will hit the system limit on the number of simulta-
neously open files.
printf Formats
Format specifiers for printf and sprintf have the following form:
%[posn$][flag][width][.precision]letter
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xor | 747
gawk
The control letter is required. The format-conversion control letters are given in
the following table.
gawk allows you to provide a positional specifier after the % (posn$). A positional
specifier is an integer count followed by a $. The count indicates which argument
to use at that point. Counts start at one and don’t include the format string. This
feature is primarily for use in producing translations of format strings. For example:
$gawk 'BEGIN { printf "%2$s, %1$s\n", "world", "hello" }'
hello, world
The optional flag is one of the following.
The optional width is the minimum number of characters to output. The result
will be padded to this size if it is smaller. The 0 flag causes padding with zeros;
otherwise, padding is with spaces.
Character Description
c ASCII character.
d Decimal integer.
i Decimal integer (added in POSIX).
e Floating-point format ([-]d.precisione[+-]dd).
E Floating-point format ([-]d.precisionE[+-]dd).
f Floating-point format ([-]ddd.precision).
g e orf conversion, whichever is shortest, with trailing zeros removed.
G E orf conversion, whichever is shortest, with trailing zeros removed.
o Unsigned octal value.
s String.
u Unsigned decimal value.
x Unsigned hexadecimal number. Usesa-f for 10 to 15.
X Unsigned hexadecimal number. UsesA-F for 10 to 15.
% Literal%.
Character Description
- Left-justify the formatted value within the field.
space Prefix positive values with a space and negative values with a minus.
+ Always prefix numeric values with a sign, even if the value is positive.
# Useanalternateform:%ohasapreceding0;%xand%Xareprefixedwith0xand0X,
respectively;%e,%E and%f always have a decimal point in the result; and%g and
%G do not have trailing zeros removed.
0 Pad output with zeros, not spaces. This only happens when the field width is wider
than the converted result. This flag applies to all output formats, even nonnumeric
ones.
‘ gawk 3.1.4 and later only. For numeric formats, in locales that support it, supply a
thousands-separator charater.
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748 | Chapter11: The gawk Programming Language
The precision is optional. Its meaning varies by control letter, as shown in the
following table.
Conversion Precision means
%d, %i, %o, %u, %x, %X The minimum number of digits to print.
%e, %E, %f The number of digits to the right of the decimal point.
%g, %G The maximum number of significant digits.
%s The maximum number of characters to print.
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749
Chapter 12Source Code Management
12
Source Code Management:
AnOverview
Chapters 13 and 14 describe two popular source code management systems for
Linux: Subversion (SVN) and Git. This chapter introduces the major concepts
involved with using these systems for users who may never have used one. If
you’re already familiar with source code management, feel free to skip ahead to
the particular software suite that interests you.
This chapter covers the following topics:
• Introduction and terminology
• Usage models
• Source code management systems
• Other source code management systems
Introduction and Terminology
Source code management systems let you store and retrieve multiple versions of a
file. While originally designed for program source code, they can be used for any
kind of file: source code, documentation, configuration files, and so on. Modern
systems allow you to store binary files as well, such as image or audio data.
Source code management systems let you compare different versions of a file, as
well as do “parallel development.” In other words, you can work on two different
versions of a file at the same time, with the source code management system
storing both versions. You can then merge changes from two versions into a third
version. This will become more clear shortly. We’ll start by defining some terms:
Repository
A repository is where the source code management system stores its copy of
your file. Usually one file in the source code management system is used to
hold all the different versions of a source file. Each source code management
system uses its own format to allow it to retrieve different versions easily and
to track who made what changes, and when.
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750 | Chapter12: Source Code Management: AnOverview
Sandbox
A sandbox is your personal, so-called “working copy” of the program or set of
documents under development. You edit your private copy of the file in your
own sandbox, returning changes to the source code management system
when you’re satisfied with the new version.
Check in, check out
You “check out” files from the repository, edit them, and then “check them
in” when you’re satisfied with your changes. Other developers working
against the same repository will not see your changes until after you check
them back in. Another term used for check-in is commit.
Log message
Every time you check in a file, you are prompted for a message describing the
changes you made. You should do so in a concise fashion. If your software
development practices include the use of a bug tracking system, you might
also wish to include the bug number or problem report (PR) number that
your change resolves.
Keyword substitutions
When you check out a file, the source code management system can replace
special keywords with values representing such things as the file’s version
number, the name of the user who made the most recent change, the date
and time the file was last changed, the file’s name, and so on. Each of the
systems described in this book uses an overlapping set of keywords. Some
systems always do keyword substitution, while others require that you explic-
itly enable the feature for each file.
Branch
A branch is a separate development path. For example, once you’ve released
version 1.0 of whizprog, you will wish to proceed with the development for
version 2.0. The main line of development is often called the trunk.
Now consider what happens when you wish to make a bug-fix release to
whizprog 1.0, to be named version 1.1. You create a separate branch, based
on the original 1.0 code, in a new sandbox. You perform all your develop-
ment there, without disturbing the development being done for the 2.0 release.
Tag
A tag is a name you give to a whole group of files at once, at whatever version
each individual file may be, in order to identify those files as being part of a
particular group. For example, you might create tags WHIZPROG-1_0-
ALPHA, WHIZPROG-1_0-BETA, WHIZPROG-1_0-RELEASE and so on.
This is a powerful facility that should be used well, since it allows you to
retrieve a “snapshot” of your entire development tree as it existed at different
points in time.
Merging
Most typically, when development along a branch is completed, it becomes
necessary to merge the changes from that branch back into the main line of
development. In our hypothetical example, all the bugs fixed in whizprog 1.0
to create version 1.1 should also be fixed in the ongoing 2.0 development.
Source code management systems can help you automate the process of
merging.
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Usage Models | 751
Source Code
Management
Conflict
A conflict occurs when two developers make inconsistent changes to the same
partof a source file. Modern source code management systems detect the
conflict, usually marking the conflicting parts of the file in your working copy
using special markers. You first discuss the conflict with the other developer,
in order to arrive at a correct resolution of the conflict. Once that’s done, you
then resolve the conflict manually (by making the appropriate changes) and
check in the new version of the file.
Client/Server
As with other “client/server” networking models, the idea here is that the
repository is stored on one machine, the server, and that different developers
may access the repository from multiple client systems. This powerful feature
facilitates distributed development, allowing developers to work easily on
their local systems, with the repository kept in a central place where it can be
easily accessed and administered.
Usage Models
Different systems have different conceptual “models” as to how they’re used.
Older systems such as SCCS and RCS use a “check out with locking” model.
These systems were developed before client/server computing, when software
development was done on centralized minicomputers and mainframes. In this
model, the repository is a central directory on the same machine where the devel-
opers work, and each developer checks out a private copy into their own sandbox.
In order to avoid two developers making conflicting changes to a file, the file must
be locked when it’s checked out. Only one user may lock a particular version of a
file at a time. When that user has checked in their changes, they unlock the file so
that the next user can check in changes. If necessary, the second user may “break”
the first user’s lock, in which case the first user is notified via electronic mail.
This model works well for small projects where developers are co-located and can
communicate easily. As long as one developer locks a file when she checks it out,
another developer wishing to work with the file will know that he can’t until the
first one is done. The drawback is that such locking can slow down development
significantly.
Newer systems, such as CVS and Subversion, use a “copy, modify, merge” model.
In practice, when two developers wish to work on the same file, they usually end
up changing different, unrelated parts of the file. Most of the time, each devel-
oper can make changes without adversely affecting the other. Thus, files are not
locked upon checkout into a sandbox. Instead, the source code management
system detects conflicts and disallows a check-in when conflicts exist.
For example, consider two developers, dangermouse and penfold, who are both
working on whizprog.c. They each start with version 1.4 of the file. dangermouse
commits his changes, creating version 1.5. Before penfold can commit his
changes, the source code management system notices that the file has changed in the
repository. penfold must first merge dangermouse’s changes into his working copy.
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752 | Chapter12: Source Code Management: AnOverview
If there are no conflicts, he can then commit his changes, creating version 1.6. On
the other hand, if there are conflicts, he must first resolve them (they’ll be marked
in the working copy), and only then may he commit his version.
The combination of the “copy, modify, merge” model with a networked client/
server facility creates a powerful environment for doing distributed development.
Developers no longer have to worry about file locks. Because the source code
management system enforces serialization (making sure that new changes are
based on the latest version in the repository), development can move more
smoothly, with little danger of miscommunication or that successive changes will
be lost.
Source Code Management Systems
There are several source code management systems used in the Unix community:
SCCS
The Source Code Control System. SCCS is the original Unix source code
management system. It was developed in the late 1970s for the Programmer’s
Workbench (PWB) Unix systems within Bell Labs. It is still in use at a few
large longtime Unix sites. However, for a long time it was not available as a
standard part of most commercial or BSD Unix systems, and it did not
achieve the widespread popularity of other, later systems. (It is still available
with Solaris.) SCCS uses a file storage format that allows it to retrieve any
version of a source file in constant time.
RCS
The Revision Control System. RCS was developed in the early 1980s at
Purdue University by Walter F. Tichy. It became popular in the Unix world
when it was shipped with 4.2 BSD in 1983. At the time, Berkeley Unix was
the most widely used Unix variant, even though to get it, a site had to have a
Unix license from AT&T.
RCS is easier to use than SCCS. Although it has a number of related
commands, only three or four are needed for day-to-day use, and they are
quickly mastered. A central repository is easy to use: you first create a direc-
tory for the sandbox. In the sandbox, you make a symbolic link to the
repository named RCS, and then all the developers can share the repository.
RCSuses a file format that is optimized for retrieving the most recent version
of a file.
CVS
The Concurrent Versions System. CVS was initially built as a series of shell
scripts sitting atop RCS. Later it was rewritten in C for robustness, although
still using RCS commands to manage the storage of files. However, for quite
some time, CVS has had the RCS functionality built into it, and it no longer
requires that RCS be available. The file format continues to be the same. CVS
was the first distributed source code management system and was until
recently the standard one for Unix systems—in particular for collaborative,
distributed, free and open source development projects.
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Other Source Code Management Systems | 753
Source Code
Management
The repository is named when you create a sandbox and is then stored in the
files in the sandbox, so that it need not be provided every time you run a CVS
command. Unlike SCCS and RCS, which provide multiple commands, CVS has
one main command (named cvs), which you use for just about every operation.
Subversion
With increasing use, it became clear that CVS lacked some fundamental
capabilities. The Subversion project was started by several longtime CVS
users and developers with the explicit goal to “build a better CVS,” not neces-
sarily to explore uncharted territory in source code management systems.
Subversion is thus intentionally easy to learn for CVS users. Subversion uses
its own format for data storage, based on the Berkeley DB in-process data
library. Distributed use was designed in from day one, providing useful facili-
ties that leverage the capabilities of the well-known Apache HTTP server.
Git
Git is a source control system originally developed by Linus Torvalds as the
source control system to manage the Linux kernel. Today, it is maintained by
a community of developers and used for many diverse projects. Unlike the
previous source control systems, Git is distributed. A distributed system
differs from a centralized one such as CVS in several ways. The most notable
is that in distributed systems, individual check outs of the source tree, called
clones in distributed systems, are themselves complete and fully functioning
repositories. Instead of submitting changes to a centralized server, changes
are pushed and pulled among repositories.
RCS, CVS, and Subversion represent a progression, each one building on the
features of its predecessors. For example, all three share a large subset of the same
keyword substitutions, and command names are similar or identical in all three.
They also demonstrate the progression from locking-based development to
conflict-resolution-based development. Git is a radical departure from the central-
ized model.
Other Source Code Management Systems
Besides the source code management systems covered in this book, several other
systems are worth knowing about. The following list, though, is by no means
exhaustive:
Arch
GNU Arch is a distributed source code management system similar to CVS
and Subversion. One of its significant strengths is that you can do offline
development with it, working on multiple versions even on systems that are
not connected to the Internet and that cannot communicate with the central
repository. For more information, see http://www.gnu.org/software/gnu-arch/.
Codeville
Codeville is a distributed version-control system in the early stages of devel-
opment. It is written in Python, is easy to set up and use, and shows a lot of
promise. For more information, see http://codeville.org/.
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754 | Chapter12: Source Code Management: AnOverview
CSSC
CSSC is a free clone of SCCS. It intends to provide full compatibility with
SCCS, including file format, command names and options, and “bug for bug”
compatible behavior. If you have an existing SCCS repository, you should be
able to drop CSSC into your environment, in place of SCCS. CSSC can be
used to migrate from a commercial Unix system to a freely available clone,
such as GNU/Linux or a BSD system. For more information, see http://
directory.fsf.org/project/cssc.
Monotone
The web page for monotone describes it well:
monotone is a free distributed version control system. It provides a
simple, single-file transactional version store, with fully disconnected
operation and an efficient peer-to-peer synchronization protocol. It under-
stands history-sensitive merging, lightweight branches, integrated code
review, and third party testing. It uses cryptographic version naming and
client-side RSA certificates. It has good internationalization support, has
no external dependencies, runs on [Linux, Solaris, Mac OS X, NetBSD,
and Windows], and is licensed under the GNU GPL.
For more information, see http://monotone.ca.
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755
Chapter 13Subversion
13
The Subversion Version
Control System
The Subversion version control system is a powerful, open source system for
management of file and directory versions. Designed from the ground up to
support distributed development, it offers many leading-edge features.
This chapter covers the following topics:
• Conceptual overview
• Using Subversion: a quick tour
• The Subversion command line client: svn
• Repository administration: svnadmin
• Examining the repository: svnlook
• Providing remote access: svnserve
Version control was introduced in Chapter 12, which contains a comparison of
Subversion, GIT, and other popular systems. The material in the current chapter
is adapted from Version Control with Subversion, Second Edition, by C. Michael
Pilato et al. (O’Reilly). See that book for much more information on Subversion.
Conceptual Overview
Subversion is a version-control system. It lets you track changes to an entire
project directory tree. Every change made to the tree is recorded and can be
retrieved.
Basic Version-Control Operations
Project data is kept in a repository, a set of directories and files managed by
Subversion. Users use the svn client program to access the repository and make
changes to it.
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Subversion uses the copy-modify-merge development model. You make a private
copy of a given project in a sandbox. (This is often called checking out a copy.)
This private copy is not locked in the repository. You then make all the changes
you like to the copy within the sandbox, without having to worry about what
other developers are doing. As you work, you can compare your changes to the
version you started with, as well as the version currently in the repository. Once
you’re satisfied with the changes, you commit them, sometimes referred to as a
check-in.
In the event that another developer has modified part of a file that you were
working on and checked it in, when you commit your changes, Subversion notices
and indicates that a conflict exists. Conflicts are marked as such in the file, and
Subversion creates pristine copies of the file as it exists in the repository and of the
file as you modified it, so that you can do full comparisons. Once you have
resolved the conflict, you tell Subversion about it, and then commit the final
version.
Subversion lets you create a development branch, a separate stream of develop-
ment versions. You can periodically merge changes from the main development
stream (the trunk) into your branch, and also merge changes from your branch
back into the trunk.
Finally, you can tag a particular copy of the project. For instance, when a project
is ready for a release, you can create a snapshot of the project and give it a descrip-
tive tag that allows you to re-create the project tree exactly as it was for the
release. This is particularly valuable when you need to produce a bug fix for an
older version of the project, or when you have to attempt to retrofit a fix or
feature from current development into an older version.
Key Features
Directory versioning
Subversion implements a virtual versioned filesystem that tracks changes to
whole directory trees over time. Files and directories are versioned. Because it
tracks the history of the directory tree rather than just the files, you can add,
delete, copy, and rename both files and directories. Every newly added file
begins with a fresh, clean history all its own, even if the filename was previ-
ously used.
Atomic commits
A collection of modifications either goes into the repository completely, or
not at all. This allows developers to construct and commit changes as logical
chunks, and prevents problems that can occur when only a portion of a set of
changes is successfully sent to the repository.
Versioned metadata
Each file and directory has a set of properties—keys and their values—associated
with it. You can create and store any arbitrary key/value pairs. Properties are
versioned over time, just like file contents.
Choice of network layers
Subversion has an abstracted notion of repository access, making it easy for
people to implement new network mechanisms. Subversion can plug into the
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Conceptual Overview | 757
Subversion
Apache HTTP Server as an extension module. A more lightweight, stand-
alone Subversion server process is also available. This server speaks a custom
protocol that can be easily tunneled over SSH.
Consistent data handling
Subversion expresses file differences using a binary differencing algorithm,
which works identically on both text (human-readable) and binary (human-
unreadable) files. Both types of files are stored equally compressed in the
repository, and only the differences are transmitted in both directions across
the network.
Efficient branching and tagging
The cost of branching and tagging need not be proportional to the project
size. Subversion creates branches and tags by simply copying the project, using
a mechanism similar to a hard link. Thus these operations take only a very
small, constant amount of time.
Hackability
Subversion is implemented as a collection of shared C libraries with well-
defined APIs. This makes Subversion extremely maintainable and usable by
other applications and languages. Subversion is an open source project as
well. You can contribute to its development.
Special File Properties
Subversion allows you to associate properties with files or directories. A property is
just a keyword/value pair associated with the file. Subversion reserves property names
starting with svn: for its own use. The special properties in Subversion 1.5.4are:
svn:author
The username of the person who committed a particular revision.
svn:date
The server time when the transaction for a revision was created.
svn:eol-style
Different operating systems use different conventions to mark the end of lines
in text files. It should be set to one of the following values:
CR Clients should always use carriage return (CR) line terminators, no
matter what the native format is.
CRLF
Clients should always use carriage return and line feed (CR-LF) line
terminators, no matter what the native format is.
LF Clients should always use linefeed (LF) line terminators, no matter what
the native format is.
native
Clients should use the native format when checking out files.
Subversion always stores files in normalized, LF-only format in the repository.
svn:executable
Valid only for files. It indicates that the file should be made executable when
it’s checked out or updated from the repository. It has no effect on filesystems,
such as FAT-32 or NTFS, that don’t have the concept of an execute bit.
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svn:externals
This property, when set on a directory under version control, allows you to
specify other, external repositories to use for particular local subdirectories.
You set this property with svnpropset or svnpropedit (see “svn Subcommands”
on page 766). The value is a multiline table of directories and fully qualified
Subversion URLs. For example:
$svn propget svn:externals calc
third-party/sounds http://sounds.red-bean.com/repos
third-party/skins http://skins.red-bean.com/repositories/
skinproj
third-party/skins/toolkit -r21 http://svn.red-bean.com/repos/skin-maker
Once set, anyone else who checks out a working copy will also get the third
party files checked out automatically.
svn:ignore
Used to tell Subversion to not place certain file types under version control.
This property is set on a directory and should contain a list of file patterns
that certain Subversion operations (like svn status, svn add, and svn import.)
will ignore.
svn:keywords
A list of keywords for which Subversion should perform keyword expansion
when checking out the file. The valid keywords are listed below.
svn:log
The log message associated with the commit of a particular revision.
svn:mime-type
An indication of the type of data stored in the file. This prevents an attempt
to perform a “merge” on data that can’t be merged. This property also influ-
ences how the Subversion Apache module sets the HTTP Content-type:
header. In general, if it does not begin with text/, Subversion assumes that
the file contains binary data. For updates, this causes Subversion to rename a
modified working copy of the file with a .orig extension and replace the file
with the current version from the repository.
svn:realmstring
A specialized property that describes the “authentication realm” for a file in
Subversion’s cached copy of the authentication credentials. See Chapter 6 of
Version Control with Subversion for more information.
Valid subversion keywords
Subversion defines the list of keywords available for substitution. That list
contains the following five keywords, some of which have shorter aliases that you
can also use:
Date
This keyword describes the last time the file was changed in the repository
and looks like $Date: 2009-02-23 21:42:37 -0700 (Mon, 23 Feb 2009) $. It
may also be given as LastChangedDate.
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Subversion
Revision
This keyword describes the last revision in which this file changed in the
repository and looks like $Revision$. It may also be given as LastChanged-
Revision or abbreviated as Rev.
Author
This keyword describes the last user to change this file in the repository, and
looks like $Author$. It may be given as LastChangedBy.
HeadURL
This keyword describes the full URL to the latest version of the file in the
repository. It looks like $HeadURL: http://svn.collab.net/repos/trunk/
README $. It may be abbreviated as URL.
Id This keyword is a compressed combination of the other keywords. Its substi-
tution looks like $Id$: ch14.xml,v 1.5 2005/08/12 21:21:32 sally Exp sally $,
and is interpreted to mean that the file calc.c was last changed in revision 148
on the evening of July 28, 2005 by the user sally.
Obtaining Subversion
The Subversion project website is http://subversion.tigris.org. It contains links to
project documentation, Frequently Asked Questions (FAQs), and project source
code.
Most GNU/Linux systems come with Subversion available on the installation
CDs. Thus, you may be able to install a prebuilt binary for your system or use a
package manager to download and install it.
Using Subversion: A Quick Tour
This section provides a very quick tour of using Subversion for version control.
We start with the initial version of a project for importing into Subversion:
$find /tmp/hello -print Show directory layout
/tmp/hello
/tmp/hello/branches Directory for branch development
/tmp/hello/tags Directory for tagged releases
/tmp/hello/trunk
/tmp/hello/trunk/hello.c Mainline development is done on the trunk
/tmp/hello/trunk/Makefile
/tmp/hello/trunk/README
The next steps are to create the repository and then to import the project into it:
$svnadmin create /path/to/svnrepos
$svn import /tmp/hello file:///path/to/svnrepos -m "initial import"
Adding /tmp/hello/trunk
Adding /tmp/hello/trunk/hello.c
Adding /tmp/hello/trunk/Makefile
Adding /tmp/hello/trunk/README
Adding /tmp/hello/branches
Adding /tmp/hello/tags
Committed revision 1.
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Now that the project exists in Subversion, we check out a working copy into a
sandbox underneath our home directory and start making changes:
$cd Move to home directory
$svn checkout file:///path/to/svnrepos hello Check out working copy
A hello/trunk
A hello/trunk/hello.c
A hello/trunk/README
A hello/trunk/Makefile
A hello/branches
A hello/tags
Checked out revision 1.
$cd hello/trunk Change to sandbox
$vi message.c hello.c Makefile Make changes
3 files to edit
$cat message.c Show newly created file
const char message[ ] = "hello, world!";
$make Compile program and test it
cc -c -o hello.o hello.c
cc -c -o message.o message.c
cc -O hello.o message.o -o hello
$hello
hello, world!
One of the most common operations is to compare the changed copy with the
original. The result is in unified diff format, the equivalent of the regular diff -u
command:
$svn diff hello.c
Index: hello.c
===============================================================
====
--- hello.c (revision 1)
+++ hello.c (working copy)
@@ -1,7 +1,9 @@
#include <stdio.h>
+extern const char message[ ];
+
int main(void)
{
- printf("hello, world!\n");
+ printf("%s\n", message);
return 0;
}
Now that we’re comfortable with the changes, we schedule the new file, message.c,
for addition to the repository, and then we actually commit our changes:
$svn add message.c Schedule message.c for addition
A message.c
$svn commit Commit all the changes
Sending trunk/Makefile
Sending trunk/hello.c
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Subversion
Adding trunk/message.c
Transmitting file data ...
Committed revision 2.
Finally, we can view all our changes relative to the initial revision:
$svn diff -r 1
Index: hello.c
===================================================================
--- hello.c (revision 1)
+++ hello.c (working copy)
@@ -1,7 +1,9 @@
#include <stdio.h>
+extern const char message[ ];
+
int main(void)
{
- printf("hello, world!\n");
+ printf("%s\n", message);
return 0;
}
Index: Makefile
=================================================================
==
--- Makefile (revision 1)
+++ Makefile (working copy)
@@ -1,2 +1,2 @@
-hello: hello.c
- $(CC) -O $< -o $@
+hello: hello.o message.o
+ $(CC) -O hello.o message.o -o $@
Index: message.c
=================================================================
==
--- message.c (revision 0)
+++ message.c (revision 2)
@@ -0,0 +1 @@
+const char message[ ] = "hello, world!";
The Subversion Command Line Client: svn
The syntax for the Subversion command line client, svn, consists of options and a
subcommand. svn’s options and subcommand may be provided in any order.
Common svn Options
While Subversion subcommands have different valid options, all options mean the
same thing regardless of the subcommand you use it with. For example, --verbose
(-v) always means verbose output, regardless of the subcommand you use it with.
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--accept arg
Specify action for automatic conflict resolution. Possible actions are post-
pone, base, mine-full, theirs-full, edit, and launch.
--auto-props
Automatically set properties an newly added or imported files, overriding the
enable-auto-props directive in the config file. By default this is disabled.
--change arg, -c arg
Apply subcommand to specified change (a.k.a. revision.) This can be used as
shorthand for "-r arg-1:arg".
--changelist name, -cl name
Limit subcommand to files belonging to changelist name. You use the
changelist subcommand to name the set of files to which you are making
changes. A file can only belong to one changelist at a time. Changelists are
local and are not saved in the repository. The name is usually discarded after
committing. This option can be repeated to include more than one set of
files.
--config-dir dir
Read configuration information from the specified directory instead of the
default location (.subversion in the user’s home directory).
--depth arg
Control the tree-depth to which the subcommand should be recursively
applied. When used with the checkout command this will set the depth prop-
erty of the checked out files as well, affecting what you receive and what
future commands will affect in the repository. To change this “ambient
depth” use the --set-depth option. This option replaces the --recursive and
--non-recursive options. arg may be one of the following:
empty
Apply to specified target only.
files
Apply to the immediate file children of the target.
immediates
Apply to the immediate file and directory children of target.
infinity
Apply recursively to all file and directory children of target.
--diff-cmd cmd
Use cmd as the external program to show differences between files instead of
Subversion’s internal diff engine. (Use --extensions to pass options to the
external diff program.)
--diff3-cmd cmd
Use cmd as the external program to merge files.
--dry-run
Run a command, but make no actual changes—either on disk or in the
repository.
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Subversion
--editor-cmd cmd
Use cmd as the program for editing a log message or a property value. If not
set, Subversion checks the environment variable SVN_EDITOR, the runtime
configuration (usually ~/.subversion/config), then environment variables
VISUAL and EDITOR for the name of the editor to use.
--encoding enc
Use enc as the encoding for the commit message. The default encoding is
your operating system’s native locale, and you should specify the encoding if
your commit message is in any other encoding.
--extensions args, -x args
Pass args to an external diff command when providing differences between
files. To pass multiple arguments, enclose all of them in quotes (for example,
svn diff --diff-cmd /usr/bin/diff -x "-b -E"). This option can be used only if
you also pass the --diff-cmd option.
--file filename, -F filename
Use the contents of filename for the specified subcommand. How it’s used
depends on the subcommand.
--force
Force a particular command or operation to run. There are some operations
that Subversion prevents you from doing in normal usage, but you can pass
this option to tell Subversion that you know what you’re doing, as well as the
possible repercussions of doing it, so do it anyway. Use with caution.
--force-log
Force a suspicious parameter passed to the --message (-m) or --file (-F)
options to be accepted as valid. This can be used to pass a versioned file as
the source for the commit log message, something Subversion would usually
consider a mistake and reject.
--help, -h, -?
If used with one or more subcommands, show the built-in help text for each
subcommand. If used alone, display the general client help text.
--ignore-ancestry
Ignore ancestry when calculating differences (i.e., rely on path contents
alone).
--ignore-externals
Ignore external definitions and external working copies managed by them.
--incremental
Print output in a format suitable for concatenation.
--keep-changelists
Don’t delete the changelist association after committing.
--keep-local
Keep the local copy of a file when using the delete subcommand to remove a
file from the repository.
--limit num, -l num
Only show the first num log messages.
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--message message, -m message
Use message as the commit message. For example:
$svn commit -m "They don't make Sunday."
--native-eol format
Used with the export subcommand sets the end of line marker to use for all
files with the svn:eol-style property set to native. You can specify LR, CR or
CRLF for format.
--new arg
Use arg as the newer target when producing a diff.
--no-auth-cache
Do not cache authentication information (e.g., username and password) in
the Subversion administrative directories.
--no-auto-props
Disable auto-props, overriding the enable-auto-props directive in the config file.
--no-diff-deleted
Do not print differences for deleted files. The default behavior when you
remove a file is for svn diff to print the same differences that you would see if
you had left the file but removed all the content.
--no-ignore
Show files in the status listing that would normally be omitted because they
match a pattern in the svn:ignore property.
--no-unlock
Do not unlock files on commit.
--non-interactive
In the case of an authentication failure, or insufficient credentials, do not
prompt for credentials (e.g., username or password). This is useful if you’re
running Subversion inside of an automated script where it’s better to have
Subversion fail instead of trying to prompt for more information.
--non-recursive, -N
Stop a subcommand from recursing into subdirectories. Most subcommands
recurse by default, but some subcommands—usually those that have the
potential to remove or undo your local modifications—do not. This
command is deprecated. You should use --depth instead.
--notice-ancestry
Pay attention to ancestry when calculating differences.
--old arg
Use arg as the older target when producing a diff.
--parents
Create and add nonversioned parent directories to the working copy or the
repository. Useful for creating directories on commit.
--password pass
Use pass as the password for authentication on the command line; otherwise,
if it is needed, Subversion prompts you for it.
--quiet, -q
Print only essential information while performing an operation.
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Subversion
--record-only
Mark a revision as merged.
--reintegrate
Used with the svn merge subcommand, merges changes in a specified source
URL into the working copy. This can be used to merge changes from a
branch back into its original line.
--recursive, -R
Make a subcommand recurse into subdirectories. Most subcommands
recurse by default. This option is deprecated. Use --depth instead.
--relocate from to [path ...]
Used with the svn switch subcommand to change the location of the reposi-
tory that your working copy references. This is useful if the location of your
repository changes and you have an existing working copy that you’d like to
continue to use. See svn switch in “svn Subcommands” on page 766 for an
example.
--revision rev, -r rev
Use rev as the revision (or range of revisions) for a particular operation. You
can provide revision numbers, revision keywords, or dates (in curly braces) as
arguments to the revision option. To provide a range of revisions, provide
two revisions separated by a colon. For example:
$svn log -r 1729
$svn log -r 1729:HEAD
$svn log -r 1729:1744
$svn log -r {2001-12-04}:{2002-02-17}
$svn log -r 1729:{2002-02-17}
The acceptable revision keywords for --revision are:
BASE
The original, unmodified version of the working copy. This keyword
cannot refer to a URL.
COMMITTED
The last revision, before or at BASE, at which an item actually changed.
This keyword cannot refer to a URL.
HEAD
The most recent revision in the repository.
PREV
The revision just before that at which an item changed. Equivalent to
COMMITED - 1. This keyword cannot refer to a URL.
Revision Date
A date specification enclosed in curly braces, { and }, such as {2002-02-
17}, {15:30}, {"2002-02-17 15:30"}, {2002-02-17T15:30}, or
{20020217T1530-0500}. See Version Control with Subversion for full
details.
--revprop
Operate on a revision property instead of a Subversion property specific to
a file or directory. This option requires that you also pass a revision with
the --revision (-r) option.
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--set-depth arg
Use arg as the new recursive depth for the target. This accepts the same
values as the --depth command.
--show-revs arg
Used with svn mergeinfo, specifies which collection of merge information to
display. arg may be either merged or eligible.
--show-updates, -u
Display information about which files in your working copy are out of date.
This doesn’t actually update any of your files; it just shows you which files
will be updated if you run svn update.
--stop-on-copy
Cause a Subversion subcommand that is traversing the history of a versioned
resource to stop harvesting that historical information when it encounters a
copy—that is, a location in history where that resource was copied from
another location in the repository.
--strict
Use strict semantics. See Version Control with Subversion for more information.
--summarize
Use with diff to get a summary of changes without a list of the changes
themselves.
--targets filename
Retrieve the list of files to operate on from filename instead of listing all the
files on the command line.
--username name
Use name as the username for authentication; otherwise, if it is needed,
Subversion prompts you for it.
--verbose, -v
Print out as much information as possible while running any subcommand.
This may result in Subversion printing out additional fields, detailed informa-
tion about every file, or additional information regarding its actions.
--version
Print the client version info. This information not only includes the version
number of the client, but also a listing of all repository access modules that
the client can use to access a Subversion repository.
--with-revprop property
Set a revision property when writing to the repository (specify in
NAME=VALUE format). When used with svn log –xml, display the value of
the specified property name in the log output.
--xml
Prints output in XML format.
svn Subcommands
The svn command is the main user interface to Subversion. It works by accepting
subcommands with arguments. Five of the previous options are global in version 1.5.
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Subversion
All subcommands will accept --config-dir, --no-auth-cache, --non-interactive,
--password, and --username. Even commands for which these are meaningless
will accept these options without fail. This is intended to make scripting easier.
Because all subcommands accept these, we don’t list them in options the below.
The general form of a subcommand is:
svn subcommand [ options ] arguments
add svn addpath ...
Add files and directories to your working copy and schedule them
for addition to the repository. They will be uploaded and added to
the repository on your next commit. If you add something and
change your mind before committing, you can unschedule the
addition using svn revert.
Alternate names: none
Changes: working copy
Accesses repository: no
Options
--auto-props
--depth arg
--no-auto-props
--no-ignore
--no-parents
--non-recursive (-N)
--quiet (-q)
--targets filename
Examples
To add a file to your working copy:
$svn add foo.c
A foo.c
You can add a directory without adding its contents:
$svn add –depth empty otherdir
A otherdir
blame svn blametarget ...
Show author and revision information inline for the specified files
or URLs. Each line of text is annotated at the beginning with the
author (username) and the revision number for the last change to
that line.
Alternate names: praise, annotate, ann
Changes: nothing
Accesses repository: yes
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Options
--extensions args, -x args
--force
--incremental
--revision rev, -r rev
--use-merge-history, -g
--verbose, -v
--xml
cat svn cattarget ...
Output the contents of the specified files or URLs. For listing the
contents of directories, see svn list.
Alternate names: none
Changes: nothing
Accesses repository: yes
Options
--revision rev, -r rev
Examples
To view readme.txt in your repository without checking it out:
$svn cat http://svn.red-bean.com/repos/test/readme.txt
This is a README file.
You should read this.
If your working copy is out of date (or if you have local
modifications) and you want to see the HEAD revision of
a file in your working copy, svn cat automatically fetches
the HEAD revision when you give it a path.
$cat foo.c
This file is in my local working copy
and has changes that I've made.
$svn cat foo.c
Latest revision fresh from the repository!
changelist svn changelistname target...
svn changelist --removename target...
Group files for operations into named collections. This makes it
easier to work or multiple groups of files.
Alternate names: cl
Changes: working copy
Accesses repository: no
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Subversion
Options
--changelist name, -cl name
--depth arg
--quiet (-q)
--remove
--targets filename
Examples
Edit three files, add them to a changelist, then commit only files in
that changelist.:
$svn changelist issue1729 foo.c bar.c baz.c
Path "foo.c" is now a member of changelist 'issue1729'.
Path "bar.c" is now a member of changelist 'issue1729'.
Path "baz.c" is now a member of changelist 'issue1729'.
$svn status
A someotherfile.c
A test/sometest.c
--Changelist 'issue1729':
A foo.c
A bar.c
A baz.c
$svn commit --changelist issue1729 -m "Fixing Issue 1729"
Adding foo.c
Adding bar.c
Adding baz.c
Transmitting file data...
Committed revision 2
$svn status
A someotherfile.c
A test/sometest.c
checkout svn checkoutURL ... [path]
Check out a working copy from a repository. If path is omitted, the
basename of the URL is used as the destination. If multiple URLs
are given, each one is checked out into a subdirectory of path, with
the name of the subdirectory being the basename of the URL.
Alternate names: co
Changes: creates a working copy
Accesses repository: yes
Options
--depth arg
--force
--ignore-externals
--quiet (-q)
--revision rev, -r rev
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770 | Chapter13: The Subversion Version Control System
Examples
Check out a working copy into a directory called mine:
$svn checkout file:///tmp/repos/test mine
A mine/a
A mine/b
Checked out revision 2.
$ls
mine
If you interrupt a checkout (or something else interrupts your
checkout, such as loss of connectivity, etc.), you can restart it either
by issuing the identical checkout command again or by updating
the incomplete working copy:
$svn checkout file:///tmp/repos/test test
A test/a
A test/b
^C
svn: The operation was interrupted
svn: caught SIGINT
$svn checkout file:///tmp/repos/test test
A test/c
A test/d
^C
svn: The operation was interrupted
svn: caught SIGINT
$cd test
$svn update
A test/e
A test/f
Updated to revision 3.
cleanup svn cleanup [path ...]
Recursively clean up the working copy, removing locks and
resuming unfinished operations. If you ever get a working-copy-
locked error, run this command to remove stale locks and get your
working copy into a usable state again.
If, for some reason, an svn update fails due to a problem running
an external diff program (e.g., user input or network failure), pass
the --diff3-cmd option to allow cleanup to complete any merging
with your external diff program. You can also specify any configu-
ration directory with the --config-dir option, but you should need
these options extremely infrequently.
Alternate names: none
Changes: working copy
Accesses repository: no
Options:
--diff3-cmd cmd
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commit | 771
Subversion
commit svn commit [path ...]
Send changes from your working copy to the repository. If you do
not supply a log message with your commit by using either the --file
or --message option, svn starts your editor for you to compose a
commit message.
If you begin a commit and Subversion starts your editor
to compose the commit message, you can still abort with-
out committing your changes. To cancel your commit,
just quit your editor without saving your commit mes-
sage and Subversion prompts you to abort the commit,
continue with no message, or edit the message again.
Alternate names: ci (short for check in—not co, which is short for
checkout)
Changes: working copy, repository
Accesses repository: yes
Options
--changelist name, -cl name
--deptharg
--editor-cmdcmd
--encoding enc
--file file, -F file
--force-log
--keep-changelists
--message text, -m text
--no-unlock
--quiet (-q)
--targets filename
--with-revprop property
Examples
Commit a simple modification to a file with the commit message on
the command line and an implicit target of your current directory (.):
$svn commit -m "added howto section."
Sending a
Transmitting file data.
Committed revision 3.
To commit a file scheduled for deletion:
$svn commit -m "removed file 'c'."
Deleting c
Committed revision 7.
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772 | Chapter13: The Subversion Version Control System
copy svn copysrc dst
Copy a file in a working copy or in the repository. src and dst can
each be either a working-copy (WC) path or a URL:
WC→WC
Copy and schedule an item for addition (with history).
WC→URL
Immediately commit a copy of WC to URL.
URL→WC
Check out URL into WC, and schedule it for addition.
URL→URL
Complete server-side copy. This is usually used to branch and
tag.
You can only copy files within a single repository. Subver-
sion does not support cross-repository copying.
Alternate names: cp
Changes: repository if destination is a URL; working copy if desti-
nation is a WC path
Accesses repository: if source or destination is in the repository, or
if needed to look up the source revision number
Options
--editor-cmd editor
--encoding enc
--file file, -F file
--force-log
--message text, -m text
--parents
--quiet (-q)
--revision rev, -r rev
--with-revprop property
Examples
Copy an item within your working copy (just schedules the copy;
nothing goes into the repository until you commit):
$svn copy foo.txt bar.txt
A bar.txt
$svn status
A + bar.txt
Copy an item from the repository to your working copy (just
schedules the copy; nothing goes into the repository until you
commit):
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delete | 773
Subversion
$svn copy file:///tmp/repos/test/far-away near-here
A near-here
This is the recommended way to resurrect a dead file in
your repository!
And finally, copying between two URLs:
$svn copy file:///tmp/repos/test/far-away \
>file:///tmp/repos/test/over-there -m "remote copy."
Committed revision 9.
This is the easiest way to tag a revision in your reposi-
tory; just svn copy that revision (usually HEAD) into
your tags directory.
$svn copy file:///tmp/repos/test/trunk \
> file:///tmp/repos/test/tags/0.6.32-prerelease \
> -m "tag tree"
Committed revision 12.
delete svn deletepath ...
svn deleteURL ...
Items specified by path are scheduled for deletion upon the next
commit. Files (and directories that have not been committed) are
immediately removed from the working copy. The command will
not remove any unversioned or modified items; use the --force
option to override this behavior.
Items specified by URL are deleted from the repository via an
immediate commit. Multiple URLs are committed atomically.
Alternate names: del, remove, rm
Changes: working copy if operating on files; repository if operating
on URLs
Accesses repository: only if operating on URLs
Options
--editor-cmd editor
--encoding enc
--file file, -F file
--force
--force-log
--keep-local
--message text, -m text
--quiet (-q)
--targets filename
--with-revprop property
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774 | Chapter13: The Subversion Version Control System
diff svn diff [-rN[:M]] [--oldold-tgt] [--newnew-tgt] [path ...]
svn diff -rN:M URL
svn diff [-rN[:M]]URL1[@N]URL2[@M]
Display the differences between two paths. The three different
ways you can use svn diff are:
svn diff [ -r N [ :M ]] [ --old old-tgt ] [ --new new-tgt ] [ path ... ]
Display the differences between old-tgt and new-tgt. If paths
are given, they are treated as relative to old-tgt and new-tgt,
and the output is restricted to differences in only those paths.
old-tgt and new-tgt may be working copy paths or URL[@rev].
old-tgt defaults to the current working directory, and new-tgt
defaults to old-tgt. N defaults to BASE or, if old-tgt is a URL,
to HEAD. M defaults to the current working version or,
if new-tgt is a URL, to HEAD. svn diff -r N sets the revision
of old-tgt to N, whereas svn diff -r N:M also sets the revision of
new-tgt to M.
svn diff -r N:M URL
A shorthand for svn diff -r N:M --old=URL --new=URL.
svn diff [ -r N [ :M ]] URL1 [ @N ] URL2 [ @M ]
A shorthand for svn diff [-r N[:M]] --old=URL1 --new=URL2.
If target is a URL, then revisions N and M can be given either via
the --revision option or by using @ notation as described earlier.
If target is a working copy path, then the --revision option means:
--revision N:M
The server compares target@N and target@M.
--revision N
The client compares target@N against the working copy.
No --revision option
The client compares the base and working copies of target.
If the alternate syntax is used, the server compares URL1 and
URL2 at revisions N and M respectively. If either N or M are
omitted, a value of HEAD is assumed.
By default, svn diff ignores the ancestry of files and merely
compares the contents of the two files being compared. If you use
--notice-ancestry, the ancestry of the paths in question is taken into
consideration when comparing revisions. (That is, if you run svn
diff on two files with identical contents but different ancestry you
will see the entire contents of the file as having been removed and
added again.)
Alternate names: di
Changes: nothing
Accesses repository: for obtaining differences against anything but
the BASE revision in your working copy.
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export | 775
Subversion
Options
--change args, -c args
--changelist name, -cl name
--depth arg
--diff-cmd cmd
--extensions args, -x args
--force
--new new-target
--no-diff-deleted
--notice-ancestry
--old old-target
--revision rev, -r rev
--summarize
--xml
Examples
Compare BASE and your working copy:
$svn diff COMMITTERS
Index: COMMITTERS
=================================================
==================
--- COMMITTERS (revision 4404)
+++ COMMITTERS (working copy)
...
See how your working copy’s modifications compare against an
older revision:
$svn diff -r 3900 COMMITTERS
Index: COMMITTERS
=================================================
==================
--- COMMITTERS (revision 3900)
+++ COMMITTERS (working copy)
...
Use --diff-cmd cmd and -x to pass arguments directly to the
external diff program:
$svn diff --diff-cmd /usr/bin/diff -x "-i -b" COMMITTERS
Index: COMMITTERS
=================================================
==================
0a1,2
> This is a test
>
export svn export [-rrev]URL [path]
svn exportpath1 path2
The first form exports a clean directory tree into path from the
repository specified by URL, at revision rev if it is given—otherwise at
HEAD. If path is omitted, the last component of the URL is used
for the local directory name.
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776 | Chapter13: The Subversion Version Control System
The second form exports a clean directory tree from the working
copy specified by path1 into path2. All local changes are preserved,
but files not under version control are not copied.
This command will also take the unique --native-eoloption.
Alternate names: none
Changes: local disk
Accesses repository: only if exporting from a URL
Options
--deptharg
--force
--ignore-externals
--native-eol format
--quiet (-q)
--revision rev, -r rev
help svn help [subcommand ...]
Provide a quick usage summary. With subcommand, provide infor-
mation about the given subcommand.
Alternate names: ?, h
Changes: nothing
Accesses repository: no
import svn import [path]URL
Recursively commit a copy of path to URL. If path is omitted, . is
assumed. Parent directories are created in the repository as
necessary.
Alternate names: none
Changes: repository
Accesses repository: yes
Options
--auto-props
--depth arg
--editor-cmd editor
--encoding enc
--file file, -F file
--force
--force-log
--message text, -m text
--no-auto-props
--no-ignore
Examples
Import the local directory myproj into the root of your repository:
$svn import -m "New import" myproj \
>http://svn.red-bean.com/repos/test
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info | 777
Subversion
Adding myproj/sample.txt
...
Transmitting file data .........
Committed revision 16.
Import the local directory myproj into trunk/vendors in your reposi-
tory. The directory trunk/vendors need not exist before you import
into it; svn import will recursively create directories for you:
$svn import -m "New import" myproj \
>http://svn.red-bean.com/repos/test/trunk/vendors/myproj
Adding myproj/sample.txt
...
Transmitting file data .........
Committed revision 16.
After importing data, note that the original tree is not under version
control. To start working, you still need to svn checkout a fresh
working copy of the tree.
info svn info [path ...]
svn infoURL
Print information about paths in your working copy or specified
URLs, including:
•Path
•Name
• URL
•Repository root
•Repostiory UUID
•Revision
•Node kind
•Last changed author
•Last changed revision
•Last changed date
•Last token
•Lock owner
•Lock created (date)
•Lock expires (date)
•Schedule
•Copied from URL
•Copied from rev
•Text last updated
•Properties last updated
•Checksum
Alternate names: none
Changes: nothing
Accesses repository: no
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778 | Chapter13: The Subversion Version Control System
Options
--changelistname, -cl name
--depth arg
--incremental
--revisionrev, -rrev
--targets filename
--xml
list svn list [target ...]
List each target file and the contents of each target directory as they
exist in the repository. If target is a working copy path, the corre-
sponding repository URL is used. The default target is . , meaning
the repository URL of the current working-copy directory.
With --verbose, the following fields show the status of the item:
• Revision number of the last commit
• Author of the last commit
• Size (in bytes)
• Date and time of the last commit
Alternate names: ls
Changes: nothing
Accesses repository: yes
Options
--depth arg
--incremental
--revision rev, -r rev
--verbose (-v)
--xml
Examples
To see what files a repository has without downloading a working
copy:
$svn list http://svn.red-bean.com/repos/test/support
README.txt
INSTALL
examples/
...
Pass the --verbose option for additional information:
$svn list --verbose file:///tmp/repos
16 sally 28361 Jan 16 23:18 README.txt
27 sally 0 Jan 18 15:27 INSTALL
24 harry Jan 18 11:27 examples/
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log | 779
Subversion
lock svn lockpath ...
svn lockURL
Set a lock token on a specified file to prevent other users or even
the same user on another system from updating the file. Only the
system with the lock token may commit changes. Locks are useful
when working on binary files that cannot be merged. By default,
Subversion’s locks are not strict, however. Locks can be broken or
taken over by other users by using the --force option.
Alternate names: none
Changes: working copy; repository
Accesses repository: yes
Options
--encodingenc
--file file, -F file
--force
--force-log
--messagetext, -mtext
--targets filename
log svn log [path]
svn logURL [path ...]
The default target is the path of your current directory. If no argu-
ments are supplied, svn log shows the log messages for all files and
directories inside of (and including) the current working directory
of your working copy. You can refine the results by specifying a
path, one or more revisions, or any combination of the two. The
default revision range for a local path is BASE:1.
If you specify a URL alone, the command prints log messages for
everything that the URL contains. If you add paths past the URL,
only messages for those paths under that URL are printed. The
default revision range for a URL is HEAD:1.
With --verbose, svn log also prints all affected paths with each log
message. With --quiet, svn log does not print the log message body
itself (this is compatible with --verbose).
Each log message is printed just once, even if more than one of the
affected paths for that revision were explicitly requested. Logs
follow copy history by default. Use --stop-on-copy to disable this
behavior, which can be useful for determining branch points.
Alternate names: none
Changes: nothing
Accesses repository: yes
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780 | Chapter13: The Subversion Version Control System
Options
--changearg, -c arg
--incremental
--limit num, -l num
--quiet (-q)
--revision rev, -r rev
--stop-on-copy
--targets filename
--use-merge-history, -g
--verbose (-v)
--with-all-revprops
--with-revpropproperty
--xml
Examples
To see the log messages for all the paths that changed in your
working copy, run svn log from the top:
$svn log
----------------------------------------------------------
--------------
r20 | harry | 2003-01-17 22:56:19 -0600 (Fri, 17 Jan 2003)
| 1 line
Tweak.
----------------------------------------------------------
--------------
r17 | sally | 2003-01-16 23:21:19 -0600 (Thu, 16 Jan 2003)
| 2 lines
...
If you don’t have a working copy handy, you can log a URL:
$svn log http://svn.red-bean.com/repos/test/foo.c
----------------------------------------------------------
--------------
r32 | sally | 2003-01-13 00:43:13 -0600 (Mon, 13 Jan 2003)
| 1 line
Added defines.
----------------------------------------------------------
--------------
r28 | sally | 2003-01-07 21:48:33 -0600 (Tue, 07 Jan 2003)
| 3 lines
...
If you run svn log on a specific path and provide a specific revision
and get no output at all:
$svn log -r 20 http://svn.red-bean.com/untouched.txt
----------------------------------------------------------
--------------
That just means that the path was not modified in that revision. If
you log from the top of the repository, or know the file that
changed in that revision, you can specify it explicitly:
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merge | 781
Subversion
$svn log -r 20 touched.txt
----------------------------------------------------------
--------------
r20 | sally | 2003-01-17 22:56:19 -0600 (Fri, 17 Jan 2003)
| 1 line
Made a change.
----------------------------------------------------------
--------------
merge svn mergesourceURL1[@N]sourceURL2[@M] [wcpath]
svn mergesourceWCPATH1@NsourceWCPATH2@M [wcpath]
svn merge -rN:M source [path]
In the first form, the source URLs are specified at revisions N and
M. These are the twosources to be compared. The revisions default
to HEAD if omitted.
In the second form, the URLs corresponding to the source working
copy paths define the sources to be compared. The revisions must
be specified.
In the third form, source can be a URL or working-copy item, in
which case the corresponding URL is used. This URL, at revisions
N and M, defines the two sources to be compared.
wcpath is the working-copy path that will receive the changes. If
wcpath is omitted, a default value of "." is assumed, unless the
sources have identical basenames that match a file within ".", in
which case, the differences are applied to that file.
Unlike svn diff, this command takes the ancestry of a file into
consideration when performing a merge operation. This is very
important when you’re merging changes from one branch into
another and you’ve renamed a file on one branch but not the other.
Alternate names: none
Changes: working copy
Accesses repository: only if working with URLs
Options
--accept arg
--changearg, -c arg
--depth arg
--diff3-cmd cmd
--dry-run
--extensions args, -x args
--force
--ignore-ancestry
--quiet (-q)
--record-only
--reintegrate
--revision rev, -r rev
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782 | Chapter13: The Subversion Version Control System
Examples
Merge a branch back into the trunk (assuming that you have a
working copy of the trunk and that the branch was created in revi-
sion 250):
$svn merge -r 250:HEAD \
>http://svn.red-bean.com/repos/branches/my-branch
U myproj/tiny.txt
U myproj/thhgttg.txt
U myproj/win.txt
U myproj/flo.txt
If you branched at revision 23, and you want to merge changes
from the trunk into your branch, you could do this from inside the
working copy of your branch:
$svn merge -r 23:30 file:///tmp/repos/trunk/vendors
U myproj/thhgttg.txt
...
To merge changes to a single file:
$cd myproj
$svn merge -r 30:31 thhgttg.txt
U thhgttg.txt
mergeinfo svn mergeinfosourceURL[@rev] [target ...]
Query information about merges or potential merges between
sourceURL and target . By default it shows merged information. The
option --show-revs can be used to get information about eligible
merges.
Alternate names: none
Changes: nothing
Accesses repository: yes
Options
--revisionrev, -rrev
--show-revs arg
Examples
Find out which changesets your trunk directory has already
received as well as what changesets it’s still eligible to receive:
$svn mergeinfo branches/test
Path: branches/test
Source path: /trunk
Merged ranges: r2:13
Eligible ranges: r13:15
mkdir svn mkdirpath ...
svn mkdirURL ...
Create a directory with a name given by the final component of the
path or URL. A directory specified by a working copy path is sched-
uled for addition in the working copy. A directory specified by a
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move | 783
Subversion
URL is created in the repository via an immediate commit.
Multiple directory URLs are committed atomically. In both cases,
all the intermediate directories must already exist.
Alternate names: none
Changes: working copy; repository if operating on a URL
Accesses repository: only if operating on a URL
Options
--editor-cmd editor
--encoding enc
--file file, -F file
--force-log
--message text, -m text
--parents
--quiet (-q)
--with-revprop property
move svn movesrc dst
This command moves (renames) a file or directory in your working
copy or in the repository.
This command is equivalent to an svn copy followed by
svn delete.
WC→WC
Move and schedule a file or directory for addition (with history).
URL→URL
Complete server-side rename.
Subversion does not support moving between working
copies and URLs. In addition, you can move files only
within a single repository; Subversion does not support
cross-repository moving.
Alternate names: mv, rename, ren
Changes: working copy; repository if operating on a URL
Accesses repository: only if operating on a URL
Options
--editor-cmd editor
--encoding enc
--file file, -F file
--force
--force-log
--message text, -m text
--revision rev, -r rev
--revprop
--with-revprop property
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784 | Chapter13: The Subversion Version Control System
propdel svn propdelpropname [path ...]
svn propdelpropname --revprop -rrev [URL]
This removes properties from files, directories, or revisions. The
first form removes versioned properties in your working copy,
while the second removes unversioned remote properties on a
repository revision.
Alternate names: pdel, pd
Changes: working copy; repository only if operating on a URL
Accesses repository: only if operating on a URL
Options
--changelist name, -cl name
--depth arg
--quiet (-q)
--revision rev, -r rev
--revprop
Examples
Delete a property from a file in your working copy:
$svn propdel svn:mime-type some-script
property 'svn:mime-type' deleted from 'some-script'.
Delete a revision property:
$svn propdel --revprop -r 26 release-date
property 'release-date' deleted from repository revision
'26'
propedit svn propeditpropname path ...
svn propeditpropname --revprop -rrev [URL]
Edit one or more properties using your favorite editor. The first
form edits versioned properties in your working copy, while the
second edits unversioned remote properties on a repository revision.
Alternate names: pedit, pe
Changes: working copy; repository only if operating on a URL
Accesses repository: only if operating on a URL
Options
--editor-cmd editor
--encoding enc
--force
--force-log
--password pass
--revision rev, -r rev
--revprop
--with-revprop property
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proplist | 785
Subversion
propget svn propgetpropname [path ...]
svn propgetpropname --revprop -rrev [URL]
Print the value of a property on files, directories, or revisions. The
first form prints the versioned property of an item or items in your
working copy, while the second prints the unversioned remote
property on a repository revision.
Alternate names: pget, pg
Changes: working copy; repository only if operating on a URL
Accesses repository: only if operating on a URL
Options
--changelistname, -cl name
--deptharg
--revision rev, -r rev
--revprop
--strict
--xml
proplist svn proplist [path ...]
svn proplist --revprop -rrev [URL]
List all properties on files, directories, or revisions. The first form
lists versioned properties in your working copy, while the second
lists unversioned remote properties on a repository revision.
Alternate names: plist, pl
Changes: working copy; repository only if operating on a URL
Accesses repository: only if operating on a URL
Options
--changelistname, -cl name
--depth arg
--quiet (-q)
--revision rev, -r rev
--revprop
--verbose (-v)
--xml
Examples
You can use svn proplist to see the properties on an item in your
working copy:
$svn proplist foo.c
Properties on 'foo.c':
svn:mime-type
svn:keywords
owner
Download at WoweBook.Com
786 | Chapter13: The Subversion Version Control System
But with the --verbose flag, svn proplist is extremely handy, as it
also shows you the values for the properties:
$svn proplist --verbose foo.c
Properties on 'foo.c':
svn:mime-type : text/plain
svn:keywords : Author Date Rev
owner : sally
propset svn propsetpropname [propval]path ...
svn propsetpropname --revprop -rrev [propval] [URL]
Set propname to propval on files, directories, or revisions. The first
example creates a versioned, local property change in the working
copy, and the second creates an unversioned, remote property
change on a repository revision. The new property value, propval,
may be provided literally, or using the -F valfile option.
Alternate names: pset, ps
Changes: working copy; repository only if operating on a URL
Accesses repository: only if operating on a URL
Options
--changelistname, -cl name
--deptharg
--encoding enc
--file file, -F file
--force
--quiet (-q)
--revision rev, -r rev
--revprop
--targets filename
Examples
Set the mimetype on a file:
$svn propset svn:mime-type image/jpeg foo.jpg
property 'svn:mime-type' set on 'foo.jpg'
On a Unix system, if you want a file to have the executable permis-
sion set:
$svn propset svn:executable ON somescript
property 'svn:executable' set on 'somescript'
By default, you cannot modify revision properties in a
Subversion repository. Your repository administrator
must explicitly enable revision property modifications by
creating a hook named pre-revprop-change.
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resolved | 787
Subversion
resolve svn resolvepath ...
Remove the conflicted state on working-copy files or directories.
This command does not semantically resolve conflict markers;
instead it replaces path and then removes conflict-related artifact
files. Use the --accept argument to specify what version to use
when replacing path. This command allows path to be committed
again by telling Subversion that the conflicts have been resolved.
Use it after you have resolved the conflict in the file. You can pass
the following arguments to the --accept option:
Alternate names: none
Changes: working copy
Accesses repository: no
Options
--accept arg
--depth arg
--quiet (-q)
--recursive, -R
--targets filename
Example
If you get a conflict on an update, your working copy will contain
three additional files:
$svn update
Conflict discovered in 'foo.c'.
Select: (p) postpone, (df) diff-full, (e) edit,
(h) help for more options: p
C foo.c
Updated to revision 31
$svn resolve --accept mine-full foo.c
Resolved conflicted state of 'foo.c'
You can just remove the conflict files and commit, but
svn resolve fixes up some bookkeeping data in the
working-copy administrative area in addition to remov-
ing the conflict files, so you should use this command.
resolved svn resolvedpath ...
Deprecated. Remove the conflicted state on working-copy files or
directories. Symantically it is the same as ' svn resolve --accept
working path ', which you should now use instead.
Alternate names: none
Changes: working copy
Accesses repository: no
Download at WoweBook.Com
788 | Chapter13: The Subversion Version Control System
Options
--depth arg
--quiet (-q)
--recursive (-R)
--targets filename
revert svn revertpath ...
Revert any local changes to a file or directory, and resolve any
conflicted states. svn revert reverts not only the contents of an item
in your working copy, but also any property changes. Finally, you
can use it to undo any scheduling operations that you may have
done (e.g., files scheduled for addition or deletion can be unscheduled).
Alternate names: none
Changes: working copy
Accesses repository: no
Options
--changelistname, -cl name
--deptharg
--quiet (-q)
--recursive (-R)
--targets filename
Examples
Discard changes to a file:
$svn revert foo.c
Reverted foo.c
If you want to revert a whole directory of files, use the
--depth=infinity flag:
$svn revert --depth=infinity .
Reverted newdir/afile
Reverted foo.c
Reverted bar.txt
If you provide no targets to svn revert, it does nothing; to
protect you from accidentally losing changes in your
working copy, svn revert requires you to provide at least
one target.
status svn status [path ...]
Print the status of working-copy files and directories. With no
arguments, it prints only locally modified items (no repository
access). With --show-updates, add working revision and server
out-of-date information. With --verbose, print full revision infor-
mation on every item.
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status | 789
Subversion
The first five columns in the output are each one character wide,
and each column gives you information about different aspects of
each working-copy item.
The first column indicates that an item was added, deleted, or
otherwise changed:
space
No modifications.
A Item is scheduled for addition.
D Item is scheduled for deletion.
M Item has been modified.
R Item has been replaced in your working copy. This means the
file was scheduled for deletion, and then a new file with the
same name was scheduled for addition in its place.
C The contents of the item conflicts with updates received from
the repository.
X Item is related to an externals definition.
I Item is being ignored (e.g., with the svn:ignore property).
? Item is not under version control.
! Item is missing (e.g., you moved or deleted it without using
svn). This also indicates that a directory is incomplete (a
checkout or update was interrupted).
~ Item is versioned as a directory but has been replaced by a file,
or vice versa.
The second column tells the status of a file’s or directory’s
properties:
space
No modifications.
M Properties for this item have been modified.
C Properties for this item are in conflict with property updates
received from the repository.
The third column is populated only if the working copy directory is
locked:
space
Item is not locked.
L Item is locked.
The fourth column is populated only if the item is scheduled for
addition-with-history:
space
No history scheduled with commit.
+ History scheduled with commit.
The fifth column is populated only if the item is switched relative
to its parent:
space
Item is a child of its parent directory.
S Item is switched.
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790 | Chapter13: The Subversion Version Control System
The sixth column is populated with lock information:
space
When --show-updates is used, the file is not locked. Other-
wise, it merely means that the file is not locked in this working
copy.
K File is locked in this working copy.
O File is locked by another user or in another working copy.
This will only appear when --show-updates is used.
T File is locked in this working copy, but the lock has been
stolen and is invalid. The file is locked in the repository. This
will only appear when --show-updates is used.
B File is locked in this working copy, but the lock has been
broken and is invalid. The file is no longer locked. This will
only appear when --show-updates is used.
If you pass the --show-updates option, then out-of-date information
appears in the seventh column:
space
The item in your working copy is up to date.
* A newer revision of the item exists on the server.
The remaining fields are variable width and delimited by spaces. The
working revision is the next field if the --show-updates or --verbose
options are passed.
If the --verbose option is passed, the last committed revision and
last committed author are displayed next.
The working-copy path is always the final field, so it can include
spaces.
Alternate names: stat, st
Changes: nothing
Accesses repository: only if using --show-updates
Options
--changelistname, -cl name
--deptharg
--ignore-externals
--incremental
--no-ignore
--non-recursive (-N)
--quiet (-q)
--show-updates (-u)
--no-ignore
--xml
Examples
To find out what changes you have made to your working copy:
$svn status wc
M wc/bar.c
A + wc/qax.c
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switch | 791
Subversion
To find out what files in your working copy are out of date, pass
the --show-updates option (this does not make any changes to your
working copy). Here you can see that wc/foo.c has changed in the
repository since we last updated our working copy:
$svn status --show-updates wc
M 965 wc/bar.c
* 965 wc/foo.c
A + 965 wc/qax.c
Status against revision: 981
--show-updates places an asterisk only next to items that
are out of date (that is, items that will be updated from
the repository if you run svn update). --show-updates
does not cause the status listing to reflect the repository’s
version of the item.
And finally, the most information you can get out of the status
subcommand:
$svn status --show-updates --verbose wc
M 965 938 sally wc/bar.c
* 965 922 harry wc/foo.c
A + 965 687 harry wc/qax.c
965 687 harry wc/zig.c
Head revision: 981
switch svn switchURL [path]
This subcommand updates your working copy to mirror a new
URL—usually a URL that shares a common ancestor with your
working copy, although not necessarily. This is the Subversion way
to move a working copy to a new branch.
As with most subcommands, you can limit the scope of the switch
operation to a particular tree depth using the --depth option. Alter-
natively, you can use the --set-depth option to set a new “sticky”
working copy depth on the switch target. Currently, the depth of a
working copy directory can only be increased (telescoped more
deeply); you cannot make a directory more shallow.
Alternate names: sw
Changes: working copy
Accesses repository: yes
Options
--acceptarg
--deptharg
--diff3-cmd cmd
--force
--ignore-externals
--quiet (-q)
--relocate
--revision rev, -r rev
--set-depth arg
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792 | Chapter13: The Subversion Version Control System
Examples
If you’re currently inside the directory vendors, which was branched
to vendors-with-fix, and you’d like to switch your working copy to
that branch:
$svn switch http://svn.red-bean.com/repos/branches/ \
>vendors-with-fix .
U myproj/foo.txt
U myproj/bar.txt
U myproj/baz.c
U myproj/qux.c
Updated to revision 31.
And to switch back, just provide the URL to the location in the
repository from which you originally checked out your working
copy:
$svn switch http://svn.red-bean.com/repos/trunk/vendors .
U myproj/foo.txt
U myproj/bar.txt
U myproj/baz.c
U myproj/qux.c
Updated to revision 31.
You can just switch part of your working copy to a
branch if you don’t want to switch your entire working
copy.
Sometimes an administrator might change the “base location” of
your repository; in other words, the contents of the repository
don’t change, but the main URL used to reach the root of the
repository does. For example, the hostname may change, or the
URL schema, or perhaps just the path that leads to the repository.
Rather than checking out a new working copy, you can have
the svn switch command “rewrite” the beginnings of all the URLs
in your working copy. Use the --relocate command to do the substitu-
tion. No file contents are changed, nor is the repository contacted.
It’s similar to running a sed script over your working copy .svn/
directories, which runs s/OldRoot/NewRoot/:
$cd /tmp
$svn checkout file:///tmp/repos test
A test/a
A test/b
...
$mv repos newlocation
$cd test/
$svn update
svn: Unable to open an ra_local session to URL
svn: Unable to open repository 'file:///tmp/repos'
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update | 793
Subversion
$svn switch --relocate file:///tmp/repos file:///tmp/
newlocation .
$svn update
At revision 3.
unlock svn unlockpath ...
svn unlockURL
Remove the lock token from the specified files. This command will
print a warning if the target is locked by another user or no lock
token exists, but will continue to unlock files it can unlock. Use the
--force option to break a lock belonging to another user or working
copy.
Alternate names: none
Changes: working copy; repository
Accesses repository: yes
Options
--force
--targets filename
update svn update [PATH ...]
svn update brings changes from the repository into your working
copy. If no revision is given, it brings your working copy up to date
with the HEAD revision. Otherwise, it synchronizes the working
copy to the revision given by the --revision option.
For each updated item Subversion prints a line starting with a
specific character reporting the action taken. These characters have
the following meaning:
A Added
B Broken lock (third column only)
D Deleted
U Updated
C Conflicted
G Merged
E Existed
A character in the first column signifies an update to the actual file,
while updates to the file’s properties are shown in the second
column. Lock information is printed in the third column.
If you want to examine an older revision of a single file,
you may want to use svn cat.
Alternate names: up
Changes: working copy
Accesses repository: yes
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794 | Chapter13: The Subversion Version Control System
Options
--accept arg
--changelist name, -cl name
--depth arg
--diff3-cmd cmd
--editor-cmd editor
--force
--ignore-externals
--quiet (-q)
--revision rev, -r rev
--set-depth arg
Repository Administration: svnadmin
svnadmin is the administrative tool for monitoring and repairing your Subversion
repository.
Common svnadmin Options
--bdb-log-keep
(Berkeley DB specific) Disable automatic log removal of database logfiles.
--bdb-txn-nosync
(Berkeley DB specific) Disable use of fsync() when committing database
transactions.
--bypass-hooks
Bypass the repository hook system.
--clean-logs
Remove unused Berkeley DB logs.
--force-uuid
By default, when loading data into a repository that already contains revisions,
svnadmin ignores the UUID from the dump stream. This option causes the
repository’s UUID to be set to the UUID from the stream.
--ignore-uuid
By default, when loading an empty repository, svnadmin uses the UUID from
the dump stream. This option causes that UUID to be ignored.
--incremental
Dump a revision only as a diff against the previous revision, instead of the
usual full text.
--parent-dir dir
When loading a dumpfile, root paths at dir instead of /.
--quiet
Do not show normal progress; show only errors.
--revision rev, -r rev
Specify a particular revision to operate on.
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dump | 795
Subversion
Common svnadmin Subcommands
The svnadmin command creates and administers the repository. As such, it
always operates on local paths, not on URLs.
create svnadmin createrepos_path
Create a new, empty repository at the path provided. If the
provided directory does not exist, it is created for you.
Options
--bdb-log-keep
--bdb-txn-nosync
Example
Creating a new repository is just this easy:
$svnadmin create /usr/local/svn/repos
deltify svnadmin deltify [-rlower[:upper]]repos_path
svnadmin deltify only exists in 1.0.x due to historical reasons. This
command is deprecated and no longer needed.
It dates from a time when Subversion offered administrators greater
control over compression strategies in the repository. This turned
out to be a lot of complexity for very little gain, and the feature was
deprecated.
Options
--quiet
--revision rev, -r rev
dump svnadmin dumprepos_path [-rlower[:upper]] [--incremental]
Dump the contents of filesystem to standard output in a dumpfile
portable format, sending feedback to standard error. Dump revi-
sions lower rev through upper rev. If no revisions are given, dump
all revision trees. If only lower is given, dump that one revision tree.
Options
--incremental
--quiet
--revision rev, -r rev
Examples
Dump your whole repository:
$svnadmin dump /usr/local/svn/repos
SVN-fs-dump-format-version: 1
Revision-number: 0
* Dumped revision 0.
Prop-content-length: 56
Content-length: 56
...
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796 | Chapter13: The Subversion Version Control System
Incrementally dump a single transaction from your repository:
$svnadmin dump /usr/local/svn/repos -r 21 --incremental
* Dumped revision 21.
SVN-fs-dump-format-version: 1
Revision-number: 21
Prop-content-length: 101
Content-length: 101
...
help svnadmin help [subcommand ...]
Provide a quick usage summary. With subcommand, provide infor-
mation about the given subcommand.
Alternate names: ?, h
hotcopy svnadmin hotcopyold_repos_path new_repos_path
This subcommand makes a full hot backup of your repository,
including all hooks, configuration files, and, of course, database
files. If you pass the --clean-logs option, svnadmin performs a
hotcopy of your repository, and then removes unused Berkeley DB
logs from the original repository. You can run this command at any
time and make a safe copy of the repository, regardless of whether
other processes are using the repository.
Option
--clean-logs
list-dblogs svnadmin list-dblogsrepos_path
List Berkeley DB logfiles. Berkeley DB creates logs of all changes to
the repository, which allow it to recover in the face of catastrophe.
Unless you enable DB_LOGS_AUTOREMOVE, the logfiles accu-
mulate, although most are no longer used and can be deleted to
reclaim disk space.
list-unused-
dblogs
svnadmin list-unused-dblogsrepos_path
List unused Berkeley DB logfiles (see svnlook list-dblogs).
Example
Remove all unused logfiles from a repository:
$svnadmin list-unused-dblogs /path/to/repos | xargs rm
## disk space reclaimed!
load svnadmin loadrepos_path
Read a dumpfile-formatted stream from standard input, commit-
ting new revisions into the repository’s filesystem. Send progress
feedback to standard output.
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rmtxns | 797
Subversion
Options
--force-uuid
--ignore-uuid
--parent-dir
--quiet (-q)
Examples
This shows the beginning of loading a repository from a backup file
(made, of course, with svn dump):
$svnadmin load /usr/local/svn/restored < repos-backup
<<< Started new txn, based on original revision 1
* adding path : test ... done.
* adding path : test/a ... done.
...
Or, to load into a subdirectory:
$svnadmin load --parent-dir new/subdir/for/project \
> /usr/local/svn/restored < repos-backup
<<< Started new txn, based on original revision 1
* adding path : test ... done.
* adding path : test/a ... done.
...
lslocks svnadmin lslocksrepos_path[path]
Print descriptions of all locks in repository repos_path underneath
path . If path isn’t given it defaults to the root directory of the
repository.
lstxns svnadmin lstxnsrepos_path
Print the names of all uncommitted transactions.
recover svnadmin recoverrepos_path
Run this command if you get an error indicating that your reposi-
tory needs to be recovered. This command requires a database
lock. Normally failure to obtain a lock will cause an error. Use the
--wait option to cause the command to wait indefinitely for a data-
base lock.
Options
--wait
rmlocks svnadmin rmlocksrepos_path locked_path...
Unconditionally remove locks from each locked path.
rmtxns svnadmin rmtxnsrepos_path txn_name ...
Delete outstanding transactions from a repository.
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798 | Chapter13: The Subversion Version Control System
Options
--quiet (-q)
Examples
Remove all uncommitted transactions from your repository, using
svn lstxns to provide the list of transactions to remove:
$svnadmin rmtxns /usr/local/svn/repos/ \
>`svnadmin lstxns /usr/local/svn/repos/`
setlog svnadmin setlogrepos_path –rrevision file
Set the log message on revision revision to the contents of file.
This is similar to using svn propset --revprop to set the svn:log prop-
erty on a revision, except that you can also use the option --bypass-
hooks to avoid running any pre- or post-commit hooks, which is
useful if the modification of revision properties has not been enabled
in the pre-revprop-change hook.
Revision properties are not under version control, so
this command permanently overwrites the previous log
message.
Options
--bypass-hooks
--revision rev, -r rev
Example
Set the log message for revision 19 to the contents of the file msg:
$svnadmin setlog /usr/local/svn/repos/ -r 19 msg
setrevprop svnadmin setrevproprepos_path –rrevision name file
Set the property name on revision revision to the contents of file.
Options
--revision rev, -r rev
Example
Set the revision property repository-photo to the contents of the file
repo.png:
$svnadmin setrevprop /var/svn/repos/ -r 0 repository-
photo repo.png
setuuid svnadmin setuuidrepos_path [new_uuid]
Reset the repository UUID to new_uuid. If no new uuid is given
generate a new one.
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Subversion
verify svnadmin verifyrepos_path
Run this command to verify the integrity of your repository. This
iterates through all revisions in the repository by internally
dumping all revisions and discarding the output.
Examining the Repository: svnlook
svnlook is a command-line utility for examining different aspects of a Subversion
repository. It does not make any changes to the repository. svnlook is typically
used by the repository hooks, but a repository administrator might find it useful
for diagnostic purposes.
Since svnlook works via direct repository access (and thus can only be used on
the machine that holds the repository), it refers to the repository with a path, not
a URL.
If no revision or transaction is specified, svnlook defaults to the youngest (most
recent) revision of the repository.
svnlook Options
Options in svnlook are global, just as in svn and svnadmin; however, most
options apply to only one subcommand because the functionality of svnlook is
(intentionally) limited in scope.
--copy-info
Used with the changed command to show detailed copy source information.
--no-diff-deleted
Do not print differences for deleted files. The default behavior when a file is
deleted in a transaction/revision is to print the same differences that you
would see if you had left the file but removed all the content.
--no-diff-added
Do not print differences for added files. The default behavior is to print the
same differences that you would see if you added the entire contents of an
existing but empty file.
--revision rev, -r rev
Examine revision number rev.
--revprop
Operate on a revision property rather than the property of a file or directory.
You must also specify a revision using --revision when using this option.
--show-ids
Show the filesystem node revision IDs for each path in the filesystem tree.
--transaction tid, -t tid
Examine transaction ID tid.
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800 | Chapter13: The Subversion Version Control System
svnlook Subcommands
author svnlook authorrepos_path
Print the author of a revision or transaction in the repository.
Options
--revision rev, -r rev
--transaction tid, -t tid
cat svnlook catrepos_path path_in_repos
Print the contents of a file.
Options
--revision rev, -r rev
--transaction tid, -t tid
changed svnlook changedrepos_path
Print the paths that were changed in a particular revision or trans-
action, as well as an svn update-style status letter in the first
column: A for added, D for deleted, and U for updated (modified).
Options
--copy-info
--revision rev, -r rev
--transaction tid, -t tid
Example
Show a list of all the changed files in revision 39 of a test
repository:
$svnlook changed -r 39 /usr/local/svn/repos
A trunk/vendors/deli/
A trunk/vendors/deli/chips.txt
A trunk/vendors/deli/sandwich.txt
A trunk/vendors/deli/pickle.txt
date svnlook daterepos_path
Print the datestamp of a revision or transaction in a repository.
Options
--revision rev, -r rev
--transaction tid, -t tid
diff svnlook diffrepos_path
Print GNU-style differences of changed files and properties in a
repository. If a file has a nontextual svn:mime-type property, the
differences are explicitly not shown.
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info | 801
Subversion
Options
--no-diff-added
--no-diff-deleted
--revision rev, -r rev
--transaction tid, -t tid
dirs-changed svnlook dirs-changedrepos_path
Print the directories that were themselves changed (property edits)
or whose file children were changed.
Options
--revision rev, -r rev
--transaction tid, -t tid
help svnlook help [subcommand]
svnlook -h [subcommand]
svnlook -? [subcommand]
Provide a quick usage summary. With subcommand, provide infor-
mation about the given subcommand.
Alternate names: ?, h
history svnlook historyrepos_path [path_in_repos]
Print information about the history of a path in the repository (or
the root directory if no path is supplied).
Options
--limitnum, -lnum
--revision rev, -r rev
--show-ids
Example
This shows the history output for the path /tags/1.0, as of revision
20 in our sample repository.
$svnlook history -r 20 /usr/local/svn/repos /tags/1.0 \
>--show-ids
REVISION PATH <ID>
-------- ---------
19 /tags/1.0 <1.2.12>
17 /branches/1.0-rc2 <1.1.10>
16 /branches/1.0-rc2 <1.1.x>
14 /trunk <1.0.q>
...
info svnlook inforepos_path
Print the author, datestamp, log message size, and log message.
Options
--revision rev, -r rev
--transaction tid, -t tid
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802 | Chapter13: The Subversion Version Control System
lock svnlook lockrepos_path path_in_repos
Print available information about existing lock for path_in_repos.
If no lock exists, print nothing.
log svnlook logrepos_path
Print the log message.
Options
--revision rev, -r rev
--transaction tid, -t tid
propget svnlook propgetrepos_path propname path_in_repos
List the value of a property on a path in the repository.
Alternate names: pg, pget
Options
--revision rev, -r rev
--transaction tid, -t tid
Example
Show the value of the seasonings property on the file /trunk/
sandwich in the HEAD revision:
$svnlook pg /usr/local/svn/repos seasonings /trunk/
sandwich
mustard
proplist svnlook proplistrepos_path path_in_repos
List the properties of a path in the repository. With --verbose,
show the property values too.
Alternate names: pl, plist
Options
--revision rev, -r rev
--revprop
--transaction tid, -t tid
--verbose (-v)
Examples
Show the names of properties set on the file /trunk/README in the
HEAD revision:
$svnlook proplist /usr/local/svn/repos /trunk/README
original-author
svn:mime-type
This is the same command as in the previous example, but this
time it shows the property values as well:
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Providing Remote Access: svnserve | 803
Subversion
$svnlook proplist --verbose /usr/local/svn/repos \
>/trunk/README
original-author : fitz
svn:mime-type : text/plain
tree svnlook treerepos_path[path_in_repos]
Print the tree, starting at path_in_repos (if supplied; at the root of
the tree otherwise), optionally showing node revision IDs.
Options
--full-paths
--non-recursive, -N
--revision rev, -r rev
--show-ids
--transaction tid, -t tid
Example
This shows the tree output (with node IDs) for revision 40 in our
sample repository:
$svnlook tree -r 40 /usr/local/svn/repos --show-ids
/ <0.0.2j>
trunk/ <p.0.2j>
vendors/ <q.0.2j>
deli/ <1g.0.2j>
egg.txt <1i.e.2j>
soda.txt <1k.0.2j>
sandwich.txt <1j.0.2j>
uuid svnlook uuidrepos_path
Print the UUID for the repository. The UUID is the repository’s
Universal Unique IDentifier. The Subversion client uses this identi-
fier to differentiate between one repository and another.
youngest svnlook youngestrepos_path
Print the youngest revision number of a repository.
Providing Remote Access: svnserve
svnserve allows access to Subversion repositories using the svn network protocol.
You can run svnserve either as a standalone server process, or by having another
process—such as inetd, xinetd, or sshd—start it for you.
Once the client has selected a repository by transmitting its URL, svnserve reads a
file named conf/svnserve.conf in the repository directory to determine repository-
specific settings, such as what authentication database to use and what authoriza-
tion policies to apply. The details are provided in Version Control with Subversion.
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804 | Chapter13: The Subversion Version Control System
svnserve Options
Unlike the previous commands we’ve described, svnserve has no subcommands;
svnserve is controlled exclusively by options.
--daemon, -d
Run in daemon mode. svnserve backgrounds itself, and accepts and serves
TCP/IP connections on the svn port (3690, by default).
--foreground
When used together with -d, this option causes svnserve to stay in the fore-
ground. This option is mainly useful for debugging.
--help, -h
Display a usage summary and exit.
--inetd, -i
Use the standard input/standard output file descriptors, as appropriate for a
server running out of inetd.
--listen-host=host
Listen on the interface specified by host, which may be either a hostname or
an IP address.
--listen-once, -X
Accept one connection on the svn port, serve it, and exit. This option is
mainly useful for debugging.
--listen-port=port
Listen on port when run in daemon mode.
--pid-filefilename
Write process ID to filename.
--root=root, -r=root
Set the virtual root for repositories served by svnserve to root. The pathname
in URLs provided by the client are interpreted relative to this root and are not
allowed to escape this root.
--threads, -T
When running in daemon mode, spawn a thread instead of a process for each
connection. The svnserve process still backgrounds itself at startup time.
--tunnel, -t
Run in tunnel mode, which is just like the inetd mode of operation (serve one
connection over standard input/standard output), except that the connection
is considered to be pre-authenticated with the username of the current UID.
This flag is selected by the client when running over a tunnelling agent such
as ssh.
--tunnel-userusername
Used with –tunnel to specify an alternate username for pre-authentication.
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805
Chapter 14Git
14
The Git Version Control
System
Git is a powerful, open source, distributed version control system (DVCS). It is
not considered as user-friendly as Subversion but has many advanced features,
including elegant merges of contributions from multiple independent sources and
the ability to access the entire project history, even when not connected to a
central server.
This chapter covers the following topics:
• Conceptual overview
• Using Git: a quick tour
• The Git command line client: git
Version control was introduced in Chapter 12, which contains a comparison of
Subversion, Git, and other popular systems. A more thorough discussion on Git
can be found in Jon Loeliger’s Version Control with Git (O’Reilly).
Conceptual Overview
Git was originally created in 2005 by Linus Torvalds as a system for managing
changes to the Linux kernel. Although it is used for many of the same tasks as
other version control systems like Subversion, Git’s internal workings are very
different. It’s important to understand some of these concepts in order to use Git
successfully.
Git maintains a repository; a directory structure that tracks the historical contents
of a set of files. Generally, the repository is stored in a .git directory (or another
directory named by $GIT_DIR) along with the files themselves.
Unlike other version control systems, Git does not enforce the concept of a
“central repository.” Instead, every set of files tracked by Git has its own .git
repository, and revisions can be easily pushed and pulled from one repository to
another.
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806 | Chapter14: The Git Version Control System
The set of files currently being tracked by Git is called the working tree. The
working tree is where most of your daily work takes place. By default, the working
tree starts in the parent directory of the .git directory. (You can override this by
setting $GIT_WORK_TREE.) The operation of creating a working tree from a
repository is called checking out the files, which is done by git checkout. After
modifying the files in the working tree, you save the changes back to the reposi-
tory by committing them with git commit (this is also called checking in).
Unlike other systems, Git introduces an extra, intermediate state between the
repository and the working tree called the index. (You might see the index called
the cache in a few places, but this terminology is obsolete and should be avoided.)
Initially, the index tracks the set of files as they were at checkout time. As you
become confident that changes you made to the working tree are correct, you add
them to the index using git add. Then, when the set of changes forms a coherent
batch, you commit the index into the repository (along with a log message) using
gitcommit. The main advantage of this two-step process is it’s easy to limit a commit
to only some of the changes you’ve been working on, which leads to more coherent
individual commits. Git’s working style—including the index—encourages many
small commits instead of large batches.
Git Repository Format
The set of commits in a Git repository is stored in the form of a directed acyclic
graph, or DAG. This simply means that each commit can reference one or more
earlier “parent” commits, and more than one commit can refer to the same
parents. The word “acyclic” refers to the fact that the structure is not allowed to
contain loops; no parent commit can refer back to a commit that lists it as a
parent.
The structure of the DAG defines the repository’s history. Normally, each commit
has exactly one parent, which describes the repository exactly as it was before the
new commit was made. By comparing a commit to its parent, you can produce a
diff, which is a precise set of changes that were applied to the parent in order to
produce the new version.
Some commits have more than one parent. These commits are called merge
commits because they express a merging of two separate branches of history. If
two people have a copy of a particular repository and start making commits, those
two histories will start to diverge, which is called forking. Eventually, someone
will need to rejoin the two histories into one, which is called merging. (As with
other version control systems, you can also create additional named branches in
each repository if you want. For example, you might create a maintenance branch
for each major release of your software.)
Referring to Commits
Each commit in Git can be uniquely identified by its commitid, a SHA-1 hash code
made up of 40 hexadecimal digits. Unlike revisions in centralized systems like
Subversion, Git revision numbers cannot be sequential, since there’s no central
server to assign the sequential IDs. Because it’s impossible for a human to
remember strings of 40 digits, Git provides several more convenient ways to refer
to commits.
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Conceptual Overview | 807
Git
Any Git command that can accept a revision can accept any of the following forms:
Full 40-digit hash
You can always simply supply the full 40-digit hash code, such as
da87b5990c03a799ae7a581c2edb1287dba08a43.
Abbreviated hash
Since the 40 digits of a hash code are effectively random, it’s very unlikely
(though not impossible) that there will be more than one commit with the
same hash. Thus, you can refer to any commit by the first few digits of its
name, as long as only one commit starts with those digits. People often
choose seven digits as a reasonably safe length. For example, da87b59.
Tags
Using the git tag command, you can create user-friendly names for individual
commits. For example, if you released version v1.1 of your software after
making commit da87b59, you could run git tag v1.1 da87b59 so that in the
future, you can always refer to a commit named v1.1. Tag names can be
shared between repositories, but you have to do it explicitly using git push
and git pull.
Local branches
Branches are similar to tags, in that they name a particular commit. However,
branches are special because if you check out a branch and make a new
commit, the branch advances automatically to point at the new commit.
Unlike with other version control systems, branch names in Git are main-
tained locally for every copy of a repository. That means if you clone
someone else’s repository, you take a copy of the branch called master (the
default Git branch name). They may continue committing to their master
branch, and you might commit to yours, and then there will exist two
branches called master, each with different contents. You can resync them
using git push and git pull.
Remote tracking branches
When you clone a central repository, you will frequently want to keep track
of the branches as they exist in that respository, even as you make changes to
them in your own repository. Git helps do this by naming repositories using
the git remote command. After that, a particular branch on a particular
remote would be named remotename/branchname. (Git automatically creates
a remote named origin to identify the repository you originally cloned from,
and the default branch in a repository is usually master. So you might have a
local branch called master corresponding to a remote tracking branch called
origin/master.)
HEAD
HEAD is a special name that always refers to the currently checked-out
commit.
FETCH_HEAD
FETCH_HEAD is a special name that refers to the most recent commit
retrieved by git fetch.
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808 | Chapter14: The Git Version Control System
commit^n notation
For any commit, you can refer to its n-th direct parent by giving its name
(using any acceptable form of a commit name, such as a branch name, tag, or
hash), followed by ^, followed by the parent number you want. Most
commits (other than merge commits) have only one parent, so if n is omitted,
the immediate parent is returned. For example, da87b59^ is the first parent
of da87b59; HEAD^2^1 is the first parent of the second parent of HEAD;
origin/master^^^^ is four parents up from origin/master, taking the first
parent at each step.
commit~n notation
You can refer to a parent n steps up the tree using commit~n notation. For
example, HEAD~4 is four parents up from HEAD, and is equivalent to
HEAD^^^^. Note that you can combine ~ and ^ notation, so HEAD^2~4 is
four steps up the tree from the second direct parent of HEAD.
branch@{n} notation
Because branch names can be retargeted at any time to refer to a different
commit, you run the risk of accidentally losing a lot of work if you change or
delete a branch name incorrectly. branch@{n} notation is designed to fix this;
it refers to the commit branch referred to n commits ago. For example, if you
use git reset or git merge and then change your mind, you can refer to the
commit before the most recent change using HEAD@{1}.
Unlike ^ and ~ notation, the name here must really be a branch name, not an
arbitrary commit, since it makes no sense to refer to the old meaning of a
particular commit. However, you can use ^ and ~ on the output of
commit@{n}, however. For example, HEAD@{1}^2~4.
You can see the history of a branch name in a format suitable for use with
commit@{n}, using git reflog.
Using Git: A Quick Tour
Git permits a staggering number of different workflow styles, from “almost
centralized” (everyone frequently pushes and pulls to the same central server) to
entirely email-based (people exchange patches using a mailing list). It would be
impossible to explain all the different Git workflows here, so we’ll focus on just
one: a simple push/pull workflow with a single shared repository.
Before You Start
Before you start using Git for the first time, you need to set two global configura-
tion values, user.email and user.name, or else you won’t be able to make new
commits. Here’s how:
$git config --global user.name 'John Smith'
$git config --global user.email 'jsmith@example.com'
These settings will remain in place across all your repositories, so you don’t have
to reset them every time. You can also override them on a per-repository basis
if you want, by running the commands in a particular repository and omitting the
--global option.
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Using Git: A Quick Tour | 809
Git
Example: The Linux Kernel Repository
As our first example, let’s clone a copy of the Linux kernel into /tmp/linux-2.6:
$cd /tmp
$git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux-2.6.git linux-2.6
Initialized empty Git repository in /tmp/linux-2.6/.git/
remote: Counting objects: 1177432, done.
remote: Compressing objects: 100% (189064/189064), done.
remote: Total 1177432 (delta 982454), reused 1176803 (delta 981879)
Receiving objects: 100% (1177432/1177432), 288.00 MiB | 406 KiB/s, done.
Resolving deltas: 100% (982454/982454), done.
Checking out files: 100% (27842/27842), done.
Now you have a copy of the entire Linux kernel and its development history,
including many different tags and branches. You’ve started out on branch master,
which is the latest version. Check out the v2.6.20 tag to get an older version:
$cd linux-2.6
$git checkout v2.6.20
Checking out files: 100% (33554/33554), done.
Note: moving to 'v2.6.20' which isn't a local branch
If you want to create a new branch from this checkout, you may do so
(now or later) by using -b with the checkout command again. Example:
git checkout -b <new_branch_name>
HEAD is now at 62d0cfc... Linux 2.6.20
You can’t make changes to tags, and you haven’t created a local branch for your
work, so Git has given you what it calls a disconnected HEAD. You can make
commits, but they won’t be attached to any branch at all. That’s a bit dangerous,
since it’s easy to lose track of your work that way. Let’s name our work so it
doesn’t get lost:
$git checkout -b my-test-branch
Switched to a new branch "my-test-branch"
And look at the list of local branches:
$git branch
master
* my-test-branch
You can make a test commit:
$echo 'hello world' >hello.txt
$git add hello.txt
$git commit -m 'my first hello commit'
Created commit 22b0a19: my first hello commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 hello.txt
Remember, this new commit hasn’t been shared with anyone; you’ve only
committed it to your local repository.
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810 | Chapter14: The Git Version Control System
Try pulling in the changes from v2.6.20 to v2.6.21:
$git pull origin v2.6.21
Merge made by recursive.
...
$ls hello.txt
hello.txt
All the changes from v2.6.21 have been merged into your branch, but your new
hello.txt is still there too. Success! If you had permission to push your new branch
back to the central kernel repository, which you probably don’t, you could do it
now:
$git push origin my-test-branch
Counting objects: 228, done.
Delta compression using 2 threads.
Compressing objects: 100% (165/165), done.
Writing objects: 100% (228/228), 38.66 KiB, done.
Total 228 (delta 142), reused 77 (delta 60)
To git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
linux-2.6
* [new branch] my-test-branch -> my-test-branch
Someone could then pull your branch into theirs and receive your hello.txt
changes.
Creating and Sharing a New Repository
If you have a project that isn’t already in Git, you will need to first create a local
repository for it. Let’s say you have a directory called my-project in which you
already have a set of files. You want to keep it under version control. Here’s what
you do:
$cd my-project
$git init
Initialized empty Git repository in .git/
$git add .
$git commit -m 'Initial commit'
(The git add command above won’t work unless there is at least one file to add,
and git commit won’t work until you’ve git added at least one file.)
For personal projects, that might be all you need; you can now create commits,
branches, and tags, compare differences, and so on.
If you want to share your project with someone else, however, you will need to
create a bare repository (i.e., one with no work tree of its own) and give other
people access to it. In this example, we’ll create a new bare repository in /home/
git/my-project.git, copied from /tmp/my-project, and give access to everyone in the
mygroup Unix group:
$git clone --bare /tmp/my-project /home/git/my-project.git
Initialized empty Git repository in .git/
$cd /home/git/my-project.git
$git config core.sharedRepository group
$chgrp -R mygroup .
$chmod -R g+rwX .
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The Git Command Line Client: git | 811
Git
By convention, bare repositories have pathnames that end in a .git suffix. This is
because they don’t contain a .git subdirectory—the .git subdirectory contents are
in the root of the bare repository, since there’s no work tree.
People in mygroup can now git clone /home/git/my-project.git and push and pull
from it.
If you want to host an open source project that everyone on the Internet can
share, you have several options:
git daemon
You can run the Git daemon on your server. The git daemon command is
beyond the scope of this book, but you can find instructions in git help
daemon.
Gitosis
Gitosis is a separate tool that lets you create a single SSH account and give
multiple people access to a Git repository through that.
git shell
The git shell command (see git help shell) is included with Git and does a
similar job to Gitosis. Most people prefer Gitosis.
http://github.com
A commercial service, github.com, offers free hosting services for open source
projects and reasonably priced hosting of proprietary projects.
Gitorious
Gitorious is an open source tool similar to github.com. You can use it to
create your own github.com-like hosting service.
http://repo.or.cz
repo.or.cz was the original public Git hosting service. It provides basic push/
pull access, although it isn’t as user friendly as the other alternatives.
Because Git repositories are fully distributed, you can choose to host your project
in more than one place at a time for added reliability, in case a server is unavail-
able or loses its data.
The Git Command Line Client: git
The git Command
Everything you do with Git is accomplished using the git command. The git main
program doesn’t actually do anything itself; instead, it runs subcommands based
on the first word on the command line, often executing a subprogram based on
that name. For example, if you run git add, Git might end up executing a program
called git-add. In fact, if you create additional git-* commands in your $PATH, Git
will add them to its repertoire automatically.
Git contains a daunting number of subcommands—well over 100 of them. Most
of these commands are meant to be used internally to create other subcommands.
We’ll cover only the most important commands in this book.
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812 | Chapter14: The Git Version Control System
Accessing Git’s Online Help
You can ask the git command for help using the git help command. By default, it
just gives a list of the most common commands:
$git help
The most commonly used git commands are:
add Add file contents to the index
apply Apply a patch on a git index file and a working tree
archive Create an archive of files from a named tree
...
You can also get a complete list of all the commands:
$git help -a
git commands available in '/usr/bin'
------------------------------------------
add gui reflog
add--interactive hash-object relink
am http-fetch remote
...
Finally, you can get the Unix manpage for a particular command (every Git
command, even the obscure ones, has a manpage). For example, to get help for
the git add command:
$git help add
git Subcommands
add git addfilename ...
Add or update a file in the index so its changes will be committed
upon the next call to git commit. This is called staging the change.
Unlike other systems, Git commits only the exact file contents that
you have added, so if you make further changes to a file, you will
need to add it again before running git commit.
With the -p option, Git lets you stage individual changes (“hunks”)
interactively, even inside a particular file. You can use this to help
break your commits into smaller, more understandable pieces.
Options
-n (no-op)
-v (verbose)
-f(force)
-p (partial)
Examples
To stage a new or updated file in the index:
$git add myfile.c
To stage all the files in the current directory, except the ones
ignored by .gitignore:
$git add.
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archive | 813
Git
To add a file even though it is ignored by .gitignore:
$git add myfile.o
The following paths are ignored by one of your .gitignore
files:
myfile.o
Use -f if you really want to add them.
fatal: no files added
$git add -f myfile.o
To add only part of a file:
$git add -p README
diff --git a/README b/README
index 42644cd..e2ad5c3 100644
--- a/README
+++ b/README
@@ -1 +1,2 @@
...
Stage this hunk [y,n,q,a,d,/,e,?]? y
archive git archive [--remote=repository-path] [--format=zip]revision
-- [path ...] >outputfile
Create a tar or zip format archive from the current repository or
from the repository at repository-path if --remote is specified. The
default output file format is (uncompressed) tar, but git archive
can also produce a zip file instead if you specify --format=zip.
git archive always writes the new archive to standard output, so
you should redirect or pipe its output somewhere.
You must specify the revision from which to take the files. If you
want to use the current revision, use HEAD.
If you specify one or more paths, only those paths are included in
the produced archive.
Options
--list
--remote
--format=tar|zip
Examples
To list the available options for --format:
$git archive --list
tar
zip
To create a tar.gz file of the currently checked-out revision:
$git archive HEAD | gzip >my-release.tar.gz
To create a zip file of tag v1.2 in a repository from another computer
named myserver (where you have Unix shell access via ssh):
$ git archive --format=zip --remote=myserver:src/myapp.git
v1.2 >myapp-1.2.zip
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814 | Chapter14: The Git Version Control System
bisect git bisect start [bad-commit [good-commit...]] -- [path ...]
git bisect bad [commit ...]
git bisect good [commit ...]
git bisect skip [commit ...]
git bisect reset
git bisect view
git bisect runcmd [args ...]
Go back in history to find the first commit that introduced a
problem. git bisect uses a binary search algorithm to narrow down
which commit caused a problem using as few steps as possible. If
there are n commits to consider, git bisect can find the exact culprit
with approximately log2 n attempts. For example, with 100
commits, it will take about 7 tries; with 1,000 commits, it will take
about 10 tries.
git bisect start[bad-commit [good-commit ...] --[path ...]
Use this command to start the bisection. You can optionally
specify one known bad-commit (which exhibits the problem)
and one or more known good-commits (which do not exhibit
the problem). If you know the bug is in a particular set of files
or directory, specify them as paths to further narrow the set of
commits to consider.
git bisect bad[commit ...]
Mark the given commit(s) as bad and check out the next candi-
date. If no commits are provided, the default is the currently
checked-out HEAD.
git bisect good[commit...]
Mark the given commit(s) as good and check out the next
candidate. If no commits are provided, the default is the
currently checked-out HEAD.
git bisect skip[commit...]
Mark the given commit(s) as untestable and check out the next
candidate. You need this if some other bug exists in the
current commit that prevents you from testing the bug you’re
looking for. If no commits are provided, the default is the
currently checked-out HEAD.
git bisect reset
Abort the bisection and check out the commit you were using
when you ran git bisect start.
git bisect view
Show the current bisection status using gitk.
git bisect runcmd[args ...]
Continue the bisection automatically by running the given
cmd on each candidate. If the command returns an error, the
commit is considered bad; otherwise, it is considered good.
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branch | 815
Git
Examples
To look for a problem when you know revisions v2.0 and v1.1 are
good, but the current version is bad, and the bug is probably in the
mymodule subdirectory:
$git bisect start HEAD v2.0 v1.1 -- mymodule
Bisecting: 100 revisions left to test after this (roughly
7 steps)
[fa16ab36ad014bcc03acc4313bb0918fb241b54d] Fix the widget
$make test
...
$git bisect bad
Bisecting: 50 revisions left to test after this (roughly
6steps)
[49cf82288aac5f0dcb152e2d75cd340e48d9e760] Change some
bits
$make test
...
$git bisect good
fa16ab36ad014bcc03acc4313bb0918fb241b54d is first bad
commit
To find a bug that was introduced somewhere between v1.1 and
v2.0, and that could be in any file:
$git bisect start
$git bisect good v1.1
$git bisect bad v2.0
Bisecting: 97 revisions left to test after this (roughly
7steps)
[fa16ab36ad014bcc03acc4313bb0918fb241b54d] Fix the widget
$git bisect run make test
...
1f73862f3b63bbc9f0a8a8a12dd58e1a39a3355f is first bad commit
bisect run success
branch git branch [-r] [-a] [--containscommit]
git branch [-f] [--track]branchname [commit]
git branch -moldnamenewname
git branch -d|-D [-r]branchname
List, create, rename, and delete branches.
git branch [-r] [-a] [--containscommit]
List the existing branches. By default, lists only local branches
(.git/refs/heads/*). With -r, list remote tracking branches
instead (.git/refs/remotes/*/*). With -a, list all local and remote
tracking branches. With --contains, list only the branches that
contain the given commit.
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816 | Chapter14: The Git Version Control System
git branch [-f] [--track|--no-track]branchname [commit]
Create a new branch, branchname, that points at the given
commit. The default for commit is HEAD. If branchname
already exists, the operation will fail unless -f is specified. If
you specify --track (the default in newer versions of Git) and
commit is a remote tracking branch, you will be able to type
simply git merge or git pull in the future to merge remote
changes into your branch.
This command does not check out your new branch. If
you want to create a new branch and check it out in one
step, use git checkout -b.
git branch -m|-Moldnamenewname
Rename a branch from oldname to newname. If newname
already exists, -m will fail while -M will overwrite it.
git branch -d|-D [-r]branchname
Delete branchname. If -r is specified, branchname is a remote
tracking branch (.git/refs/remotes/*/*); otherwise it is a local
branch (.git/refs/heads/*). If you use -d, the branch will only be
deleted if your current HEAD already includes everything in
branchname; otherwise, it will fail. If you use -D, this safety
check doesn’t occur.
Examples
To get the list of all branches:
$git branch -a
To create a new branch that starts off pointing at your current
HEAD:
$git branch savepoint1
To later delete the savepoint1 branch:
$git branch -d savepoint1
To create and check out a new branch test based on remote
tracking branch origin/master:
$git branch --track test origin/master
$git checkout test
Switched to branch 'test'
checkout git checkout [revision]path...
Copy files from the repository into your working tree and possibly
switch branches. git checkout does one of four different things,
depending on which options are provided:
revision but no path
Switch branches to the one named by revision. If files are
modified in the working tree and also changed in the new
branch, the operation will fail. The next commit will be in the
new branch.
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cherry-pick | 817
Git
If revision is a valid commit but not the name of a local branch,
Git still switches HEAD to the given commit but does not give
the new branch a name. This is called a detached HEAD. You
can later name the new branch with git checkout -b.
In either case, if the -b option is given, a new branch is created
from the given revision, and Git switches to that branch.
path(s) but no revision
Destroys all working tree changes in the named files or direc-
tories, replacing them with their contents from the index.
revision and path(s)
Destroys all working tree changes in the named files or direc-
tories, replacing them with their contents from the given
revision. This does not switch branches; instead, it replaces
contents of the given files in the index. The next git commit,
will affect the same branch as before, but the named paths will
be considered modified.
no revision and no path(s)
No changes. Prints a list of files that have been modified in the
working tree.
Options
-q(quiet)
-f(force)
-bnew_branch_name
--track(-t)
--no-track
-m(merge)
Examples
To revert all the files in directory docs to their version from the
index:
$git checkout docs
To switch to the branch called new-feature, which must already
exist:
$git checkout new-feature
Switched to branch "new-feature"
To switch to the remote branch origin/master, creating a new
branch called new-feature:
$git checkout -b new-feature origin/master
Branch new-feature set up to track remote branch refs/
remotes/origin/master.
Switched to a new branch "new-feature"
cherry-pick git cherry-pickcommit
Take the changes from an individual commit (usually one from
another branch) and apply it to the current branch. Note that
unlike git merge, git cherry-pick applies only a single change, not
all the history leading up to that change.
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818 | Chapter14: The Git Version Control System
The newly created commit is completely independent of the orig-
inal, although it has the same commit message by default. git
cherry-pick commit is the rough equivalent of git show commit |
patch -p1
Options
-e, --edit
-x (extend commit message)
-m parent-number
-n, --no-commit
-s, --signoff
Examples
To cherry-pick commit 1a48191 onto the current branch and edit
the commit message:
$git cherry-pick -e 1a48191
Finished one cherry-pick.
clean git clean -n|-f [-d] [-x]
Removes files from the work tree that are not in the Git index. By
default, it only removes files that are not listed in .gitignore and
does not remove directories. (To undo work tree changes to files
that are in the index, use git checkout.)
You must provide one of -n or -f.
Options
-n (print only, do not remove)
-f (force removal of files)
-d (also remove extra directories)
-x (also remove files skipped by .gitignore)
-X (only remove files skipped by .gitignore)
-q (quiet)
Examples
To remove all extra files in the work tree so the only files remaining
are ones that would be there after a fresh git clone:
$git clean -f -d -x
Removing foo
To see what would happen if you ran the above command:
$git clean -n -d -x
Would remove foo
clone git clonerepository [local-directory]
Make a copy of repository (which can be a local or remote Git
repository) in local-directory. By default, if repository is on the
local filesystem, Git will use hardlinks to copy the .git/objects folder
to minimize disk space waste.
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commit | 819
Git
Available forms for repository are:
/path/repo.git
rsync://hostname/path/repo.git
http://hostname/path/repo.git
https://hostname/path/repo.git
git://host/path/repo.git
ssh://host/path/repo.git
ssh://user@host:port/path/repo.git
host:path/repo.git
user@host:path/repo.git
Options
-s, --shared
--no-hardlinks
--referenceother-parent-repository
-q, --quiet
-n, --no-checkout
--bare
-oorigin-name, --originorigin-name
--depthshallow-clone-depth
Examples
To clone the Linux kernel repository:
$git clone git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git linux-2.6
commit git commit [--file ...]
Commit the changes that have already been staged in the index,
updating HEAD.
If -a is given, all changed files in the work tree—not only staged
changes—will be committed. (-a is the common behavior in
systems like Subversion.)
If files are specified, exactly those files are committed, regardless of
the state of the index.
You cannot commit a file for the first time, even with -a, unless it
has first been added with git add.
Options
-a(all files, not just added ones)
--amend
-mcommit-message, --message=commit-message
-Fcommit-message-file
-q, --quiet
-s, --signoff
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820 | Chapter14: The Git Version Control System
Examples
To commit changes only to files in the mylib directory:
$git commit -- mylib
Created commit 90716b6: my new commit
1 files changed, 13 insertions(+), 0 deletions(-)
create mode 100644 test-file
config git config [--global] --list
git config [--global]name
git config [--global]namevalue
List, get, or set configuration values. If --global is given, uses your
account-wide default settings (in ~/.gitconfig); otherwise uses the
settings for the current repository (in .git/config). Instead of using
git config, you can also just view or edit these files directly.
The most important settings are:
core.autocrlf
If true, converts LF line endings to CRLF on files when checking
out and converts the line endings back to LF when committing.
core.bare
Makes this repository a bare repository, which means it has no
work tree. (Public shared repositories are usually bare.)
core.sharedRepository
Set to either all, group, or false. If group, the files in .git will
be group readable and writable. If all, the files will also be
readable (but not writable) by everyone.
core.editor
The path of your favourite text editor, for editing commit
messages. The $EDITOR environment variable overrides this.
gc.autopacklimit
Controls how frequently Git will automatically run git gc after
common operations. To disable it completely, use 0.
rerere.enabled
When committing a conflicted merge, Git will remember how
you resolved the conflict and attempt to reuse the recorded
resolution if it encounters it again in the future.
user.email
Your email address. This will be attached to commit messages
automatically. The $EMAIL environment variable overrides
this.
user.name
You full name. This will be attached to commit messages
automatically. The $GIT_COMMITTER_NAME and $GIT_
AUTHOR_NAME environment variables override this.
Options
--unset
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diff | 821
Git
Examples
To set your email address and name for future commits:
$git config --global user.name 'John Smith'
$git config --global user.email 'jsmith@example.com'
To list all your global settings:
$git config --global --list
user.name=John Smith
user.email=jsmith@example.com
gc.autopacklimit=0
diff git difffirst-commit [second-commit] [--path ...]
git diff --cached [first-commit] [--path ...]
Show the differences between two revisions. If paths are specified,
restricts the comparison to only the given files or directories.
The default first-commit is HEAD.
The default second-commit is normally the work tree. With --cached,
the default second-commit is the index.
Options
--name-only
--name-status
--stat(show diffstat instead of patch)
-a, --text
-M(detect renames)
-C(detect copies and renames)
--find-copies-harder
-R(reverse patch)
-w, --ignore-all-space
--exit-code
-Un, --unified=n
Examples
To see which changes are already staged in the index:
$git diff --cached
To see which changes are in the work tree but not yet staged:
$git diff
To see a summary of changes between two tags (v1.1 and v2.0):
$git diff --stat v1.1 v2.0
To see the changes between v1.1 and the current work tree:
$git diff v1.1
To see the changes between v1.1 and HEAD:
$git diff v1.1 HEAD
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822 | Chapter14: The Git Version Control System
fetch git fetch [remote-name]
git fetchrepository [remoteref[:localref]]
Fetch commits from a remote Git repository and adds it to the
local one.
In the first form, fetch all branches and tags from the given remote-
name (a remote repository set up using git remote). The default
remote name is origin.
In the second form, fetch a particular remoteref from repository
and store it as local branch localref. The default localref is FETCH_
HEAD. The default remoteref is HEAD.
Options
-f, --force
-n, --no-tags
-t, --tags
Examples
To fetch the latest Linux kernel release and compare it against your
current work tree:
$git fetch git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git linux-2.6 master
From git://git.kernel.org/...
* branch master -> FETCH_HEAD
$git diff FETCH_HEAD
To update all the remote tracking branches attached to the remote
named origin:
$git fetch origin
remote: Counting objects: 15, done.
remote: Compressing objects: 100% (10/10), done.
remote: Total 10 (delta 8), reused 0 (delta 0)
Unpacking objects: 100% (10/10), done.
From git://git.kernel.org/...
6544ab2..e3498f3 master -> origin/master
To retrieve the branch test1 from someone’s repository and save it
as the local branchmytest1:
$git fetch git://git.kernel.org/... test1:mytest1
gc git gc [--prune] [--aggressive]
Pack the .git/objects directory to save disk space and increase speed.
git gc is run automatically from time to time, so it is rarely needed
unless you want to use the --prune or --aggressive options or want
to force packing to happen at a particular time (such as before
making a backup).
Options
--aggressive (take extra time to save even more space)
--prune (delete unused objects)
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grep | 823
Git
Examples
To aggressively repack the current repository and save as much
space as possible:
$git gc --aggressive --prune
Generating pack...
Done counting 3299 objects.
Deltifying 3299 objects...
100% (3299/3299) done
Writing 3299 objects...
100% (3299/3299) done
Total 3299 (delta 2225), reused 0 (delta 0)
Pack pack-4eb8f89a145f826ef93923fe97c4ab23bd8abb62
created.
Removing unused objects 100%...
Done.
gitk gitk [git-log options...]
Display a graphical browser showing the Git history. gitk takes all
the same options as git log.
Examples
To show the history of all changes to the mylib directory on
branches test1 and test2, but leave out all changes that are included
in v1.1:
$gitk test1 test2 ^v1.1 -- mylib
grep git grep [-e]pattern [--cached|commit ...] [--path ...]
Search the given commits for the given regular expression
pattern(s).
If no commits are specified, normally searches the current work
tree. With --cached, searches the index instead. If paths are speci-
fied, restricts the search to the given files or directories.
The main advantage of git grep over plain grep is that it ignores
files (such as compiler output and editor backups) that have not
been added with git add.
When multiple patterns are specified (using -e), the default combi-
nation is --or, unless --and or --not is specified.
Options
-epattern
--and
--or
--not
(
)
-E (act like egrep)
-F(act like fgrep)
-i, --ignore-case
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824 | Chapter14: The Git Version Control System
-v, --invert-match
-w, --word-regexp
-l, --files-with-matches
-L, --files-without-matches
Examples
To search the work tree for lines containing chicken without
considering case:
$git grep -i chicken
To search the top of branches test1 and test2 for lines containing
alpha and either beta or gamma:
$git grep -e alpha --and \( -e beta -e gamma \) test1
test2
To search only the mylib directory for files starting with the word
chicken:
$git grep '^chicken' -- mylib
init git init [-q] [--bare] [--shared=false|group|all]
Create a new Git repository in the current directory.
Options
-q, --quiet
--bare
--shared=false|group|all
Examples
To create a new repository with default settings:
$git init
To create a new bare repository that will be shared with everyone
in your Unix group:
$git init –bare --shared=group
log git [revision ...] [--path ...]
Show the commit history. If paths are specified, show only the
history related to the given files or directories. If revisions are speci-
fied, show the history starting from the given revisions. The default
revision is HEAD. With --all, the default is to show all revisions in
all local branches.
Each revision can be specified in one of the following formats:
commit
Include the history for the given commit.
^commit
Exclude the history starting at the given commit.
a..b
Includes all commits in b that are not in a. Equivalent to b ^a.
a...b
Includes all commits in a and b that are not in both.
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log | 825
Git
Options
--all
-p (show patch)
-Un, --unified=n
-a, --text
--raw
--stat
-M (detect renames)
-C (detect copies)
--find-copies-harder
-R (reverse patch)
-w, --ignore-all-space
-n, --max-count=n (show up to onlyn commits)
--pretty=(oneline|short|medium|full|fuller|email|raw|
format:...)
--abbrev-commit
--full-history
--no-merges
--first-parent
--parents
--left-right
--graph
--author=regex
--committer=regex
--grep=regex
--reverse
Examples
To show the commits on this branch, starting with the most recent:
$git log
commit 3ad3a1c1866bef36461d549d87fe39babe412d61
Author: John Smith <jsmith@example.com>
Date: Sun Jan 18 18:41:32 2009 -0500
Make some changes.
commit 529fc80df85a5ec7c88552bcb27bc0770a84e336
Author: John Smith <jsmith@example.com>
Date: Sun Jan 17 12:13:06 2009 -0500
Do the first thing.
...
To show what was changed by the most recent commit:
$git log -1 -p
diff --git a/server/hello.html b/server/hello.html
index 63ede62..e26d280 100644
--- a/server/hello.html
+++ b/server/hello.html
@@ -1,17 +1 @@
...
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826 | Chapter14: The Git Version Control System
To show all commits in all local branches where the commit
message contains the word hello:
$git log --grep=hello --all
commit 3ad3a1c1866bef36461d549d87fe39babe412d61
Author: John Smith <jsmith@example.com>
Date: Sun Jan 18 18:41:32 2009 -0500
Undo changes to hello.html.
...
merge git mergecommit ...
Merge one or more other branches into the current HEAD. For
each specified commit, Git calculates the set of changes on that
branch that are not currently in HEAD and attempts to apply those
changes to the current HEAD. If the changes cannot be applied
successfully, Git will leave conflicts in the index, which you will
need to resolve by hand (using an editor, git add, and git commit).
Almost always, you will supply exactly one commit. In some situa-
tions, you may wish to merge more than one branch at the same
time; this is called an octopus merge and is allowed only if none of
the merges cause any conflicts. It is equivalent to merging the given
commits one by one, except that the merged result produces only
one new commit.
You can override the merge strategy to be used, but this is almost
never necessary. When more than one commit is specified, the only
allowed strategy is octopus.
Normally, Git combines the branch histories so git log will show
all the commits from all branches that have been merged. With
--squash, it eliminates the history of the branches other than
HEAD. This simplifies the git log output, but prevents successful
merges from that branch in the future, so it is usually a bad idea.
Options
--no-commit
--squash
--log
--no-ff
-s (resolve|recursive|octopus|ours|subtree)
-mmsg
Examples
To merge feature branches feature1 and feature2 into your current
branch using an octopus merge:
$git merge feature1 feature2
Already up-to-date with
aa871d4ef9657e03b2ef7053dc13a16777955499
Trying simple merge with
bdd84225b4f7c282731aed540171e7cbe392c00d
Merge made by octopus.
58 files changed, 1371 insertions(+), 195 deletions(-)
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pull | 827
Git
To merge the branch production into the current HEAD, resulting
in a conflict:
$git merge production
Auto-merging testfile.c
Auto-merging server/hello.html
CONFLICT (content): Merge conflict in server/hello.html
Auto-merging test2.c
Recorded preimage for 'server/hello.html'
Automatic merge failed; fix conflicts and then commit the
result.
To resolve the conflict above and commit the completed merge:
(edit server/hello.html)
$git add server/hello.html
$git commit
mv git mvoldfilenewfile
git mvoldfiles ...newdir
Rename oldfile to newfile or move a series of oldfiles into the direc-
tory newdir, which must already exist. git mv updates both the
work tree and the index.
There is no need for a git cp (copy) command. Just copy
the file using Unix cp and git add. Git is still able to track
the history of files moved and copied in this way.
Options
-f (overwrite even if newfile exists)
-n, --dry-run
Examples
To rename file1.c to file1b.c:
$git mv file1.c file1b.c
To move file1.c and file2.c into the mylib directory:
$git mv file1.c file2.c mylib/
pull git pull
git pullrepositorybranch
Fetch the given branch then merge it into HEAD. git pull is just a
short form for git fetch followed by git merge.
If no repository or branch is specified, git pull attempts to pull from
the remote tracking branch associated with your current branch, if
any. (Associations are set up using the --track option when creating
a branch with git branch. You can also add them later with git
config.)
The repository can be a local repository path, a repository URL (see
git clone), or a remote name (see git remote). The branch must be a
valid branch or tag name in the remote repository.
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828 | Chapter14: The Git Version Control System
For more information about how pull works, see git fetch and git
merge.
Options
--no-commit
--squash
--log
--no-ff
-s (resolve|recursive|octopus|ours|subtree)
--tags
--no-tags
Examples
To pull the latest Linux kernel changes into your current branch:
$git pull git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git master
From git://git.kernel.org/...
* branch master -> FETCH_HEAD
Merge made by recursive.
21 files changed, 932 insertions(+), 66 deletions(-)
push git push [--all] [--tags] [repository [localref][:remoteref]]
Push changes from one or more branches or tags into the specified
remote repository.
Repository can be a local repository path, a repository URL (see git
clone), or a remote name (see git remote). If repository is omitted,
it defaults to origin.
If localref is omitted, it defaults to pushing all the refs that currently
exist on the remote. For example, if you have local branches named
A, B, C, and D, and the remote has branches named A, C, and E,
then Git will push branches A and C unless you specify a specific
localref.
As an alternative to providing localref, you can provide --all or --tags.
With --all, Git pushes all the local branches. With --tags, Git
pushes all the local tags.
If remoteref is omitted, it defaults to the same name as localref. If
you supply remoteref, it needs to be the full refname, such as refs/
heads/master, not just the base branch name.
If you supply a remoteref without a localref, Git deletes remoteref in
the remote repository. This is useful if the remote end refuses to
update a ref because it is not a fast forward; you can delete the
remote ref, and then re-create it.
Options
--all
--tags
--dry-run
--thin
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rebase | 829
Git
Examples
To push the current branch (master) to the remote named origin:
$git push origin master
To push all local branches to the default remote (origin), as long as
they already exist there:
$git push
To push all the local branches to a particular remote repository:
$git push --all server:/git/myrepo.git
To delete the branch test1 on a remote named myremote:
$git push myremote :test1
To push the current HEAD to a branch named test1 on myremote:
$git push myremote HEAD:refs/heads/test1
rebase git rebase [-i] [--onto onto-commit] base-commit [switch-branch]
git rebase --continue | --skip | --abort
Automatically cherry-pick a series of commits between base-
commit and switch-branch onto onto-commit, leaving the result in
switch-branch.
If switch-branch is omitted, the default is HEAD. If onto-commit is
omitted, the default is base-commit.
Using git rebase can completely disrupt future merges to
and from the rebased branch. Use git rebase only for
changing commits that have never been shared with others,
such as before a new branch has been pushed to a shared
repository.
git rebase is a powerful alternative to git merge. You can use it to
simplify and rewrite the history of your changes in order to make
them easier to review, audit, and share. However, because git
rebase rewrites the history of your repository, misuse can cause
hard-to-resolve errors, including duplicate commits and merge
conflicts.
You can imagine git rebase as a series of commands that looks
something like this:
git checkout switch-branch
git reset --hard onto-commit
for commit in base-commit..switch-branch
git cherry-pick commit
done
The end result is a new branch that contains onto-branch plus a
linear series of commits (i.e., with no merges). The new commits
consist of all the commits that were previously part of switch-
branch but not base-commit.
With -i, git rebase opens an interactive editor before the rebase
operation starts. The editor contains a list of all the commits in
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830 | Chapter14: The Git Version Control System
base-commit..switch-branch. You can rearrange the list, add/delete
individual entries, or merge (squash) multiple commits into a single
one, thus allowing you to produce a set of commits that is easier
for others to review.
During a rebase operation, cherry-picking a particular commit may
result in a conflict. In that case, you need to do one of the
following:
•Resolve the conflict, commit it with git commit, and then run
git rebase --continue.
• Run git rebase --skip to skip this commit entirely.
• Run git rebase --abort to cancel the rebase operation and
change the Git history back to the way it started.
Options
-i, --interactive
--ontoonto-commit
-p, --preserve-merges
Examples
To take all the patches in HEAD that are not in origin/master, and
apply them on top of the current origin/master:
$git rebase origin/master
To do the same as the above, but interactively reorder, edit, and
squash the patches:
$git rebase -i origin/master
To take all the patches in the feature1 branch that are not in origin/
master, and add them on top of feature2, resulting in a new
feature1:
$git rebase --onto feature2 origin/master feature1
To do the same as the above in two steps for clarity:
$git checkout feature1
$git rebase --onto feature2 origin/master
To resolve a conflict that arose during the rebase operation:
(edit test1.c)
$git add test1.c
$git commit
$git rebase --continue
reflog git reflog show [branch]
Show entries from the reflog, which tracks changes to local refs
(branches). If branch is omitted, shows the reflog for HEAD.
The reflog tracks the “history of history.” Although commands like
git reset can be used to undo a commit, the old commit still stays
around in the reflog until it eventually expires. This allows you to
undo many Git operations you might have performed by accident.
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remote | 831
Git
You can refer to entries in the reflog using branch@{n} notation.
For example, HEAD@{5} means to use HEAD as it existed five
changes ago.
Examples
To list all the recent changes to HEAD:
$git reflog
To undo the most recent merge operation:
$git reset HEAD@{1}
remote git remote add [-f]namerepository-url
git remote rmname
git remote showname
git remote prune [--dry-run]name
git remote update [name ...]
Manipulate remotes, which act as short forms for tracking reposi-
tory URLs and branches. This command takes one of several
forms:
git remote addnamerepository-url
Register a new remote name at repository-url. With -f, also git
fetch the set of remote branches from the new remote.
git remote rmname
Unregister the remote name.
git remote showname
Show information about the given remote name.
git remote prunename
Delete remote tracking branches that no longer exist on the
remote name. To prevent accidental data loss, remote tracking
branches in the local repository are never deleted unless you
run this command.
git remote update[name...]
Equivalent to running git fetch name for each of the names
individually. If no names are provided, fetches all the regis-
tered remotes.
Examples
To show information about the remote named origin (which is
created automatically by git clone):
$git remote show origin
* remote origin
URL: git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git
HEAD branch: master
Remote branches:
master tracked
production tracked
Local branches configured for 'git pull':
master merges with remote master
production merges with remote production
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832 | Chapter14: The Git Version Control System
Local refs configured for 'git push':
master pushes to master (up to date)
production pushes to production (local out of date)
To replace origin with a pointer to a new server and fetch the
branches on the new server:
$git remote rm origin
$git remote add -f origin myserver:/git/myproj.git
Updating origin
From myserver:/git/myproj.git
* [new branch] master -> origin/master
* [new branch] production -> origin/production
To update all registered remotes:
$git remote update
Updating origin
reset git reset [--soft|--hard] [commit] [--path ...]
If no paths are given, update HEAD to point at the given commit.
This can be used to undo one or more commits as if they had never
happened. If paths are given, HEAD is not changed; only the listed
files and directories are modified.
git reset is extremely dangerous and can cause you to lose
track of portions of your repository’s history. Use it only
on branches that have never been shared with anyone
else. If you make a mistake with git reset, you can usu-
ally undo it using git reflog.
With --soft, neither the index nor the work tree are modified, and
only the HEAD pointer is changed. Thus, the difference between
HEAD and the index is the set of changes needed to convert the
new HEAD into the original HEAD. If you then run git commit, a
new commit will be created that changes the files back to the way
they were before you ran git reset.
With --hard, both the index and the work tree are modified to
match the given commit; any changes from the given commit to
HEAD are lost.
If neither --soft nor --hard is specified, then the index is updated,
but not the work tree.
Examples
To undo the most recent commit without losing the changes to the
files themselves (so they can be committed again):
$git reset HEAD^
To change the current branch to point at the same place as origin/
master, destroying anything else that might have happened in the
current branch previously:
$git reset --hard origin/master
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rm | 833
Git
To undo the above git reset operation by recovering the previous
HEAD from the reflog:
$git reset --hard HEAD@{1}
To undo the most recent five commits and recommit their changes
as a single commit:
$git reset --soft HEAD~5
$git commit
revert git revert [-n] commit
Create a new commit that reverses the effect of commit.
Options
-n, --no-commit
-s, --signoff
Examples
To undo the most recent commit:
$git revert HEAD
[master ae3f932] Revert "Say hello."
1 files changed, 0 insertions(+), 50 deletions(-)
To undo commit ae3f932, even if it is not the most recent commit:
$git revert ae3f932
[master ae3f932] Revert "Say hello."
1 files changed, 0 insertions(+), 50 deletions(-)
rm git rm [-f] [-r] --path ...
Remove files from the work tree and index. They will be perma-
nently removed when you run git commit.
With -f, forces removal of a file even if it doesn’t match HEAD.
With -r, removes entire directories and all their contained files.
Options
-f (force)
-r (recursive)
--cached (ignore work tree)
-n, --dry-run
Examples
To remove the mylib directory:
$git rm -r mylib
rm 'mylib/test1.c'
rm 'mylib/test2.c'
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834 | Chapter14: The Git Version Control System
stash git stash
git stash list
git stash show [stashid]
git stash apply [stashid]
Save, list, or reapply the set of uncommitted changes from a work
tree and index.
This command takes one of four forms:
git stash
Save the current set of uncommitted changes and undo them.
The index and work tree are reset to match HEAD.
git stash list
Show the list of all stashes that have previously been saved.
git stash show [stashid]
Show the exact set of changes that are saved as stashid. If
stashid is omitted, uses the most recently saved changes.
git stash apply [stashid]
Brings back the changes from the given stashid and applies
them to the current index and work tree. If stashid is omitted,
uses the most recently saved changes.
Examples
To save the current set of uncommitted changes, switch branches,
and apply those changes to the new branch:
$git stash
Saved working directory and index state "WIP on master:
44951b7... Say hello"
(To restore them type "git stash apply")
HEAD is now at 44951b7 Say hello
$git checkout feature1
Switched to a new branch "feature1"
$git stash apply
Removed test1.c
status git status [path ...]
Check what would happen if you ran git commit. If paths are speci-
fied, check what would happen if you ran git commitpaths.
Examples
To check the status of the current branch:
$git status
# On branch master
# Changed but not updated:
# (use "git add <file>..." to update what will be
committed)
#
# modified: test1.c
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tag | 835
Git
# modified: test2.c
#
no changes added to commit (use "git add" and/or "git
commit -a")
To see what would happen if you ran git commit test1.c:
$git status test1.c
# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
#
# modified: test1.c
#
# Changed but not updated:
# (use "git add <file>..." to update what will be
committed)
#
# modified: test2.c
#
tag git tag [-a|-s|-ugpg-key-id] [-f] [-mmsg | -Fmsg-file]
tagnamecommit
git tag -dtagname
git tag -l [glob-pattern]
git tag -vtagname ...
Manipulate tags. A tag is simply a user-friendly name for a partic-
ular commit. The command takes one of four forms:
git tag [-a|-s|-ugpg-key-id] [-mmsg | -Fmsg-file]tagnamecommit
Create a new tag named tagname based on the given commit.
With -a, the tag is annotated (i.e., it has a commit message
attached) but not signed. With -s or -u, the tag is annotated
and signed with the default or specified gpg private key,
respectively. With -m or -F, use the given commit message or
filename containing the commit message, respectively. If none
of -a, -s, or -u is specified, the tag has no annotation. (Tags
you shared with other people should always have an annota-
tion and should usually be gpg signed.)
git tag -dtagname
Delete the given tagname from the local repository. Note that
if the tag has already been pushed to a remote repository,
there is no way to make sure everyone erases it.
git tag -l [glob-pattern]
List all the tags matching the glob-pattern. If glob-pattern is
omitted, lists all the tags.
git tag -vtagname...
Verifies the gpg signature of each requested tag.
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836 | Chapter14: The Git Version Control System
Examples
To mark the current version with a v1.1 tag and sign it with your
gpg key:
$git tag -s v1.1 HEAD
To delete the v1.1 tag (only useful if it has never been pushed):
$git tag -d v1.1
To list all tags for version 1.x:
$git tag -l 'v1.*'
Download at WoweBook.Com
837
Chapter 15Virtualization
15
Virtualization
Command-LineTools
This chapter covers common tools used with Linux to run many virtual servers on
a single physical server. We cover the two dominant hypervisors used with Linux:
Xen and KVM. We also cover libvirt-based tools used to manage both Xen and
KVM. Although it isn’t strictly a Linux solution, VMware uses a Linux operating
system for the Service Console of their ESX server and recent vSphere products, so
we have included basic console commands they provide.
This chapter covers the following topics:
• Conceptual overview
• Basic virtualization operations
• The Xen Hypervisor
• The KVM Hypervisor
• The libvirt virtualization API
• VMware command line interface
We do not provide a tutorial or in-depth information on virtualization here. This
is meant as a quick reference to virtualization concepts, commands, and utilities.
Refer to the following locations for more in-depth coverage on each of these
technologies.
The Xen hypervisor http://www.xen.org/
The KVM hypervisor http://www.linux-kvm.org/
libvirt virtualization API http://libvirt.org/
VMware Documentation http://www.vmware.com/support/pubs/
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Conceptual Overview
All of the virtualization programs we cover in this chapter provide full system
virtualization. They use a software layer to present a virtualized hardware
system. This layer, called the virtual machine monitor (VMM) or hypervisor,
makes it possible to run multiple operating systems simultaneously. The oper-
ating system at the base—running directly on the hardware and interacting with it
directly—is called the host, and the software instances that run on top of it—
interacting only indirectly with hardware—are called the guests.
Virtualization isn’t a new topic. As a means to divide a computer’s resources into
multiple running environments, virtualization has been around since the 60s.
Back then, IBM used it to partition mainframe computers into separate virtual
machines, allowing it to run multiple applications and processes simultaneously.
Although low-cost PC hardware generally replaced mainframe hardware virtual-
ization in the 80s and 90s, virtual machines were still commonly used to provide a
virtualized environment for a process: e.g., creating a security sandbox or
providing greater portability. The Java Virtual Machine (JVM) is a good example
of process virtualization. This kind of virtualization also includes tools like chroot
and virtfs.
Another popular type of virtualization creates a new instance of the same oper-
ating system on top of the host. This technology is often called containers. It
typically includes such projects as Solaris Zones and User Mode Linux (UML).
We don’t cover containers in this chapter.
Here, we cover the tools of industrial-strength server virtualization. The solutions
in this chapter offer environments that look like complete, independent hardware
computers even though they are just software instances running on a common
hardware base. While hardware costs for PCs remain fairly low, systems with
multiple CPUs or CPU cores can easily handle the task of running dozens of
highly available virtualized servers simultaneously. Businesses use virtualization to
reduce deployment and administration costs. Many businesses also use virtual-
ized-desktop systems to replace physical desktops, simplifying management tasks
throughout the company.
Configuring virtualization requires administrative access to systems, CPUs with
built-in virtualization technology, or even modified operating systems. The tools
covered here are intended for large-scale server deployments. Although these
tools might allow you to run an alternative operating system on your desktop or
notebook, if you are just looking to run a single guest you will find that easier to do
with another kind of tool. VMware Player or VirtualBox, for example, both run in
user space, require no kernel modifications or special CPU, and are available for free.
System Requirements
To run the tools covered in this chapter you should have at minimum:
• A processor that supports virtualization technology (Intel VT or AMD-V).
Support should be enabled in the system BIOS.
• At least 2 GB of memory.
• At least 6 GB of disk space.
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Virtualization
Xen can run paravirtualized guests without virtualization technology in the CPU, but
it requires it for full virtualization. You can check whether your existing CPU
supports virtualization by grepping /proc/cpuinfo as follows:
$ egrep '(vmx|svm)' /proc/cpuinfo
If nothing shows up, your CPU does not support virtualization. If something does
appear, you may still need to enable it in BIOS to use it.
Each solution has additional requirements or limitations. Before making a hard-
ware purchase you should check the requirements and supported hardware for
the solution you plan to use.
If you want to support migration (moving a running guest from one host to
another) you will also want some kind of shared-storage solution. That might be
an iSCSI or SAN volume to which all servers have access. You don’t need that to
get started though.
Virtualization Technology
In full virtualization, the guest operating system doesn’t need to be aware that it is
running in a virtual environment. It interacts with the virtual hardware in the
same way it would physical hardware. Some tasks in a fully virtualized environ-
ment, however, are computationally expensive. One way to handle the expensive
tasks is to use a modified processor that performs these tasks for the hypervisor.
Paravirtualization provides another way to handle these expensive tasks. In
paravirtualization the guest operating system is modified to hand these expensive
tasks to the hypervisor, which can handle the task without having to emulate
hardware.
Network Concepts
For your virtual server to connect to the Internet it must have a way to use the
physical connection of the host. Xen, KVM, and VMware will all create a default
bridge interface to handle mapping the virtual systems to the physical interface. A
virtual machine could also be assigned directly to a physical device, but for most
situations a bridge is what you want. More complex network configurations can
be made by defining a kind of virtual switch or router. We will cover some
commands that can do this here.
libvirt Tools and Terminology
Xen, KVM, and other Linux-based hypervisors support a single generic API called
libvirt. For most tasks, it doesn’t matter which Linux hypervisor you are using.
You can use the same basic tools. libvirt has its own terminology which will be
helpful to know when reading the libvirt section.
• A node is a single physical machine.
• A hypervisor is a layer of software that virtualizes a node, providing a set of
virtual machines that may differ from the node itself.
• A domain is an instance of an operating system running on a virtualized
machine provided by the hypervisor.
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840 | Chapter15: Virtualization Command-LineTools
Throughout this chapter, though, we’ll stick to more common industry termi-
nology, referring to a domain as a guest and the node running the guest as a host.
Basic Virtualization Operations
The complexity of virtualization prevents us from covering everything in a small
chapter within this book. Fortunately, developers have written tools that handle
much of the complexity for you. They have worked hard to make the defaults do
the right thing for your system and have written scripts to simplify the tasks. Here
we cover the higher-order tools that will help you create and manage virtual
systems and networks.
Creating Virtual Systems
For VMware you will use the VI Client GUI interface to create your virtual
systems. We won’t cover that task here. With Xen and KVM you can use virt-
manager’s virt-install to install a new guest. At minimum you must tellvirt-install:
• the name of the new guest domain
• whether the guest will be paravirtualized or fully virtualized (-p or -v)
• the amount of RAM to give to the new system (-r)
• what to use as a system disk and if creating a disk, how large it should be
(-f and -s)
• whether to support graphics or not (--vnc or --nographics)
• where to find the installation files (-c, -l, or --pxe)
virt-install will prompt for any values you do not provide to it on the command
line. The name should be a short unique identifier; whatever helps you distinguish it
from other virtual machines controlled by the same hypervisor. Paravirtualization
or full virtualization depends on what your OS supports. If you do not have an
installation already prepared for virtualization, you need full virtualization.
The system disk can be stored anywhere in your filesystem. Use a full path to
specify where, or just a filename to have it stored in the default location for your
hypervisor.
You will need a way to connect to the new system. See the section “Graphic and
Console Interfaces” on page 842. If you are installing a fully virtualized system,
use the --vnc option. If you aren’t installing on a system running X Window
System, you may need to connect to your guest remotely from a system that does.
If you are installing a paravirtualized system and the guest system supports it, you
can use either --vnc or --nographics. If using --nographics fails, you may need to use
virsh to destroy the domain and start over as you will have no way to connect to it.
What you use for installation files will depend on what kind of virtualization you
are using. For a fully virtualized system you may want to install from a CDROM
drive or an installation disk ISO. You can use the -c option to point to a physical
device on the host (/dev/cdrom) or to an ISO file.
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To install a paravirtualized Linux or UNIX system, you will instead use the -l
option with virt-install to point to the location of the initial boot image. For some
distributions, youcan point this to an ISO image, but the -l option does not
configure a virtual CDROM, so after the boot you will need to tell the install
program where to find a mirror of the installation media. You can use HTTP,
NFS, or FTP to connect to that media. This means you will have already had to
have set up a server to provide these files. You can quickly prepare an installation
ISO for this by mounting it via the loop back device and either exporting the
directory via NFS or serving the files through HTTP. We’ll provide examples.
virt-install has many other options that can help you customize your virtual
server. If you are using KVM, you might want to use the --accelerate option to
better take advantage of the hypervisor. You might want to use --os-type option
to optimize guest configuration. You can provide more detailed information on
how to configure the network interface (without any options, it just connects the
guest to the default bridge interface). See virt-install’s entry in this chapter for
further information.
Some distributions come with wrapper-scripts that call virt-install with default
options to install a basic Linux operating system. Ubuntu, for example, provides a
vm-builder script that will install a stripped-down version of Ubuntu, ready to run.
Examples
Mounting a Red Hat ISO for export via NFS:
# mkdir /mount/rhel5.3
# mount -o ro,loop RHEL-5.3.iso /mount/jeos-8
# exportfs *:/mount/rhel5.3/
Mounting a Red Hat ISO for HTTP access:
# mkdir /var/www/html/rhel5.3
# mount -o ro,loop RHEL-5.3.iso /var/www/html/rhel5.3
Full virtualization install from an installation iso:
# virt-install -name rhel-fv -v -r 256 -f /images/rhel-fv.img -s 8 –vnc \
-c RHEL-5.3.iso
Paravirtual installation via HTTP using a serial console:
# virt-install -name rhel-pv -p -r 256 -f /images/rhel-pv.img -s 6 \
-–nographics -lhttp://example.com/rhel-5.3/
Managing Virtual Systems
While hypervisors can control the starting and stopping of virtual machines, they
can’t always shut them down gracefully. You may want to power off your systems by
connecting to each system and initiating a shutdown in the normal way. Sometimes
you can’t do that, though, and you need to do the virtual equivalent of pulling the
plug on a system that isn’t responding. The commands listed here cover these
basic operations.
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Xen and KVM virtual guests can be managed with virsh commands. Use virsh list
--all to get a list of all managed domains. The start, shutdown, reboot, and
destroy commands are your virtual power and reset buttons. From the service
console in Vmware’s ESX server you can do similar things with vmware-cmd.
Graphic and Console Interfaces
You need some way to interact with the virtual systems. Generally, you will use a
VNC or SDL graphic interface set up by your guest installation tool. VMware
provides its own client software to handle this. For Xen and KVM you will likely
use the VNC client virt-viewer or the GUI management tool virt-manager to
connect to a virtual system. As an alternative, you could interact with a virtual
system through a text-based console connected to a virtual system’s serial device.
The virt-install command has a --nographics option that will attempt to set this
console up for you, but it works only with paravirtualized guests. If your guest
system has a properly functioning network connection, you may also be able to
use ssh to connect to it.
Configuring Networks
Your basic network options are to use bridging or Network Address Translation
(NAT). In bridging, a special bridge interface transparently connects your virtual
interfaces to your host’s physical interface(s). Your virtual servers will share the
physical interface.
Using NAT, your virtual servers are assigned private network IP addresses, and
another interface then provides the NAT for your system. This NAT interface is
essentially a bridge as well. A bridge is really any interface used to hook your
virtual interfaces up to your physical interfaces. Still, these two approaches are
commonly referred to as bridging and NAT.
VMware uses a third option. It creates a virtual switch to which you connect your
guests’ interfaces. The default switch, however, simply bridges the switch to the
server’s network interface card. Neither Xen or KVM come with a ready-made
virtual switch solution, although some vendors may offer virtual switch solutions
you could add to your system.
Upon installation of the hypervisor and libvirt, most distributions will automati-
cally configure basic networking support. They will likely configure both a NAT
and bridge interface. Xen’s tools will use the bridge interface by default, but virt-
manager’s tools will likely use NAT.
The approach you want to use will depend on the kind of system on which you
have installed the host operating system. If you are installing on a system that
might frequently change networks (for example, a notebook you move between
home and work) or want to keep your virtual systems separate from your physical
network, you will probably want NAT. If you are using a wireless card, you must
use NAT. Bridging will not work with wireless interfaces because wireless chipsets
reject foreign MAC addresses. If you are installing on a server and want your
virtual systems to interact with your network the way any physical system would,
you want to use bridging.
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Virtualization
While we don’t cover it in this chapter, the Net:Bridge or (bridge-utils) package
contains the brctl command. This command can help you build and manage
more complex bridges. You can find more information on this package at:
http://www.linuxfoundation.org/en/Net:Bridge
We highly recommend you read that page and explore the tool if you want to dig
any deeper into configuring your bridges.
The basic concept to keep in mind for virtual networking is that your host systems
will have interfaces for physical devices, virtual devices, and bridge devices. What
they are named by default depends on your distribution and hypervisor. The
following are the interfaces you might find running if you used ifconfig on a
CentOS system running Xen.
vifX.Y
A vif interface on the host connects to the virtual interface on a guest domain.
Consider it the server’s representation of that virtual Network Interface Card
(NIC). vif0.0 is Domain-0’s first interface. vif0.1 would be its second. vif1.0 is
the first interface on the first running guest (Domain 1).
eth0
The virtual interface for Domain-0, which is connected to vif0.0.
peth0
This device performs packet distribution for guest systems, including
Domain-0. It is bound to the bridge device, the physical network card. It has
no IP address of its own, but instead acts as a simple switch. This is how
packets get to the appropriate vif device.
xenbr0
Xen’s default bridge device that connects vif interfaces to the physical inter-
face (peth0).
virbr0
An interface providing NAT. This is the default bridge device for virt-
manager tools. You may need to enable packet forwarding in Domain-0 to
make this device work.
You will likely find these devices on an Ubuntu system running KVM:
eth0
The physical interface for the host. Note that it doesn’t have an IP address.
The host’s interface is bridged to this device.
vnet0
An interface providing NAT. The default bridge device for virt-manager.
vnetX
Interfaces connected to a guest’s virtual interface, where X is numbered 1 or
higher. These are bridged through vnet0 by default.
br0
The host system’s bridge device. This one has the host’s IP address and
connects to the physical interface, eth0.
You can set the interface to be used by a virtual domain when using virt-install
with the --network option.
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MAC Addresses
You may want to set a MAC address on a virtual interface manually. This is a
special hexadecimal number that uniquely identifies your interface card. If not set,
your configuration tool will generate a random number for it, but knowing what it
will be ahead of time can help you configure DHCP or a PXE boot. With virt-install
you can set it with the --mac option. VMware’s VI Client provides an option as well.
There are some restrictions. The first three sets of numbers in a MAC address
identify the vendor. When setting them, use the following vendor addresses:
Making Changes to Virtual Machines
VMware’s VI Client can be used to edit virtual machine configurations. Making
changes to a virtual machine under Xen or KVM can be a little trickier. You can
make some changes (such as memory settings) using xm or virsh. For more
complex changes with Xen, you could change the configuration files located
under /etc/xen/. These are in a text format, and most of the settings you will want
to change will be easy to figure out.
virsh provides one common way to make complex changes:
1. Run virsh dumpxml to get an XML configuration file for the domain you
wish to change.
2. Use a text editor to edit the XML file.
3. Shut down the virtual system if it is still running.
4. Run virsh define to remove the old configuration from the hypervisor and
replace it with the configuration in your edited XML file.
You can now start the domain with your new configuration.
Creating and Manipulating Disk Image Files
Tools such as virt-install will create disks as needed when installing a new virtual
server, but you might want to add a disk to an existing server. One common form
of disk image for virtual machines is a sparse file. The simplest tool for creating
this is the dd command documented in Chapter 3. For instance, to create a
10,000 MB sparse file suitable for use as a disk image you can use the following
command:
# dd if=/dev/zero of=newdisk.img bs=1M seek=10000 count=1
Change the system’s configuration file to add the new drive. You can use the
guest’s system tools (such as fdisk) to configure the new disk.
You can easily increase the size of a sparse file by using dd to create a new sparse
file then append the existing file with the new file. Don’t try this with an image file
Xen 00:16:3e
KVM/Qemu 54:52:00
VMware 12:50:56 AM
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Xen | 845
Virtualization
currently in use by a running guest, though: shut down the guest system first.
Here we use dd and cat to add a 5000 MB extension to the original image.
# dd if=/dev/zero of=diskextension.img bs=1M seek=5000 count=1
# cat diskextension.img >> newdisk.img
You will need to use a tool appropriate to the guest operating system to take
advantage of the new space. For example, resize2fs makes the space available to
an ext3 filesystem.
For more advanced features on a disk image, you can use qemu-img, a tool we
don’t document here. It can create and convert disk images to a several different
formats, including to VMware’s .vmdk format. If you are using KVM you should
already have it installed on your system. If you do not, you can install it via the
qemu package.
Xen
Xen is the most common hypervisor used on Red Hat Advanced Server 5, Fedora,
and distributions based on these, such as CentOS 5. Assuming you are using one
of these, to use Xen you must install the xen and kernel-xen packages from your
package repository:
# yum install xen kernel-xen
Other operating systems will probably have similar packages. Some offer a
groupinstall that will include all the necessary packages:
# yum groupinstall Virtualization
Once installed, reboot your system using the Xen kernel. You may want to modify
your /boot/grub/grub.conf file to boot the Xen kernel by default. Usually this
means changing the default= entry to default=0, where 0 refers to the first boot
configuration described by the file. See Chapter 4 for details on configuring grub
and modifying the grub.conf file.
The installation of the previously mentioned packages should also configure two
services to run: the Xen daemon (xend) and the xendomains script that the
system uses to automatically start and stop your guest domains.
Once the new kernel and xend service is running, you should be able to run the
command
# xm list
to list your current nodes. At first you will have one domain running, Domain-0.
To understand Domain-0, it helps to know that your system is not really running
Linux directly. It’s running Xen’s own kernel, a virtual machine monitor based on
the Nemesis microkernel. Xen’s kernel doesn’t provide an administrative inter-
face; it depends on a modified operating system running as a guest to do this. This
privileged guest also provides guest domains access to hardware devices. In our
case, Domain-0 is running a modified version of Linux. Your OS is actually the
controlling domain in a cluster of guest domains.
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In Xen, these other guest domains are referred to as unprivileged domains, or
DomU (the U stands for unprivileged). Domain-0 can also delegate control of
hardware devices to other privileged domains, but that’s a more advanced topic
we won’t cover here.
Paravirtualization and Architecture
Xen supports paravirtualized guests that run on the same architecture as Domain-0.
Thus, if Domain-0 is running X86_64, paravirtualized guests must be X86_64 as
well. To run a 32-bit guest on a 64-bit system, you must run it fully virtualized.
Like Domain-0, paravirtualized Linux guests run the Xen kernel instead of the
regular kernel.
Xen Networking
Mixing libvirt and Xm tools can lead to some confusion when it comes to
networking. Guest domains installed using Xen’s tools bridge to device xenbr0 by
default. Those installed by libvirt’s virt-install bridge to device virbr0. To cut
down on confusion and take full advantage of libvirt, you may want to disable
Xen’s bridge networking altogether. Details on how to configure networking for
Xen using libvirt can be found on the libvirt wiki: http://wiki.libvirt.org/page/
Networking. Altertnatively you can tell virt-install to bridge to device xenbr0
using the -w option (-w bridge:xenbr0).
Xen Commands
Xen has its own special commands for installing and managing domains, but for
most things you can use the libvirt tools documented in this chapter. Here, we
will cover the most commonly used xm subcommands and the xentop command.
xm xm [ options ] command
Xen hypervisor management interface. Generally you will use virsh
to control VMs, but there are a few useful functions you can get from
xm but not virsh. We cover the most common commands here.
xm can be used to configure virtual machine access rights and secu-
rity policies. Policies are given labels and the labels applied to
domains. This is an advanced topic we do not cover in this book.
Commands
console domain
Connect to serial console on domain, if available. Use ctrl-] to
exit a console.
create [-c] configfile [settings]
Start the guest domain described in configfile. This command
is generally used to start a previously installed domain that is
not currently running. By default, a domain will have a config-
uration file of the same name in /etc/xen/. You can specify
the configfile with a full path, or a path relative to /etc/xen/.
The configuration file, a Python executable file, largely consists
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of name=value pairs. These can also be given in a space-separated
list on the command line. The manpage for xmdomain.cfg
contains details on configuration file format and valid entries.
The -c option causes xm to connect to the console as soon as
the machine starts.
destroy domain
Immediately kill any running instance of the domain and free
its resources to the hypervisor. (You usually want to use
shutdown instead.)
dmesg [-c]
Print the Xen message buffer. This buffer contains informa-
tional, warning, and error messages. The -c option clears the
message buffer.
help[--long]
Print a list of xm commands. If --long is given, print all
commands grouped by function.
info
Print information about host system.
list [options] [domains]
List information about one or more domains (a space-separated
list of domain names, ids or UUIDs). This is a more verbose
listing than that provided by libvirt. It includes resource allo-
cation and running time information.
Options
-l, --long
Print detailed information about domains in a format that
can easily be consumed by external programs.
--label
Include security label information.
log
Print the contents of the xend log. This log is also found at /var/
log/xen/xend.log.
top
Run the xentop command (described next).
list [options] [domains]
List information about one or more domains (a space-separated
list of domain names, ids or UUIDs). This is a more verbose
listing than that provided by libvirt. It includes resource
allocation and running time information as well as state. There
are six possible states: running, blocked, paused, shutdown,
crashed, and dying.
Options
-l, --long
Print detailed information about domains in a format that
can easily be consumed by external programs.
--label
Include security label information.
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pause domain
Cease hypervisor scheduling for domain.
shutdown [options] domain
Begin a graceful shutdown on domain. For guests that support
this, it is the same as running shutdown on the guest. It may
not succeed. By default, the command does not wait for the
shutdown to complete. xm list will reveal the guest’s current
state.
Options
-a Print detailed information about domains in a format that can
easily be consumed by external programs.
-w Wait for domain to complete shutdown before exiting.
unpause domain
Resume hypervisor scheduling for domain.
xentop xentop [ options ]
Provide frequently updated information about current domains.
This program performs a function similar to the Linux top
command, only with information about the hypervisor and
domains instead of processes. Its various options change what
information is displayed. Like top, xentop also has some interactive
commands to change what information xentop displays as it runs.
Options
-b, --batch
Run in batch mode; don’t accept command-line input. Useful
for sending output to another command or to a file.
-d seconds, --delay=seconds
Set the delay between refreshes. Default is 3.
-i num, --iterations=num
Update display num times, then exit.
-n, --networks
Show network information.
-r, --repeat-header
Repeat the table header before each domain.
-v, --vcpus
Show virtual CPU information.
-x, --vbds
Show virtual block device information.
Interactive commands
All interactive commands are case-insensitive.
B Toggle display of virtual block device information.
D Prompt for a new delay setting.
N Toggle display of network information.
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Q, Esc
Quit.
R Toggle display of table header before each domain.
S Change sort order by cycling through the available columns.
V Toggle display of virtual CPU information.
Up, Down
Scroll through displayed domains.
KVM
The Kernel-based Virtual Machine (KVM) is a full virtualization hypervisor for
Linux. The work of the KVM hypervisor is handled by the Linux kernel. Each
guest in KVM runs as a process and can be managed by Linux tools such as top
and kill.
KVM isn’t a complete virtualization solution. It depends on both the libvirt tools
for management and the open source processor emulator QEMU for hardware
emulation. Therefore, you will need those installed as well.
KVM is the most popular hypervisor on Ubuntu distributions. Assuming you are
using Ubuntu, you can use apt-get to install the necessary packages:
$ sudo apt-get install kvm libvirt-bin ubuntu-vm-builder qemu bridge-utils
You may alsowant the virt-viewer and virt-manager packages, though these will
require the X Window System as well. As of Ubuntu version 8.10 (Intrepid) you
can install the meta package ubuntu-virt-server for the basic tools mentioned
previously and ubuntu-virt-mgmt for the GUI management tools.
You will likely want to provide your controlling user account with access to
network devices created by libvirt. Use usermod to add your account to the
libvirtd user group.
Restart your system. If all goes well, you should be able to run the following
command without error:
$ virsh -c qemu:///system list
Also check to make sure KVM is working:
sudo kvm
This will confirm that you have enabled virtualization support in BIOS properly.
QEMU
QEMU is really its own virtualization solution that works in user space.
Combining it with KVM speeds it up considerably, providing a robust hypervisor
running at the kernel level. QEMU comes with some of its own commands for the
installation and launching of virtual systems. Some older tutorials show how to
use them. We won’t cover those here; instead use libvirt tools to handle these tasks.
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Ubuntu Builder Scripts
Ubuntu comes with tools to help you quickly build guest systems. In older systems
these tools are in the ubuntu-vm-builder package; in newer systems, they are in
the python-vm-builder package. These tools handle the defaults for installing a
simple Ubuntu guest. In most cases all you need to provide is a name for your new
domain.
libvirt and Red Hat Virtual Machine Manager
The libvirt virtualization API provides an open source programming interface to
hypervisors like Xen and KVM. It comes with virsh, a management interface for
controlling hypervisors. A closely related project, the Red Hat Virtual Machine
Manager application, is a collection of tools built using libvirt. This includes a few
command-line tools as well as the GUI virt-manager application.
Whether you are using Xen or KVM, these libvirt based tools will handle most of
the tasks of creating and managing your guests. Except for some minor differ-
ences in what each hypervisor supports and the connection string used to get to
the hypervisor, these commands work the same regardless of what hypervisor you
choose. You’ll want to know these tools well.
XML Configuration Files
libvirt uses XML files to define or describe the capabilities and configuration of
domains, networks, and hardware devices. Many of the command tools expect to
receive information from an XML file. You don’t have to know the XML tags to get
started, as the tools will build the required files for you, but you may want to edit
an XML file directly to change the configuration of a guest.
The XML formats, as well as more in-depth information on virsh and the API, can
be found on the libvirt website: http://libvirt.org.
Connection URIs
To control a hypervisor, libvirt tools must first connect to it. You will use a URI
to specify the location of the hypervisor. For KVM use a qemu:// URI and for Xen
use xen://. For backwards compatibility virsh will also accept just plain xen,
which it will treat as xen:///. If no connection option is given, virsh will try to
connect to the URI given in the environment variable LIBVIRT_DEFAULT_URI.
If none exists, it will probe the defaults in whatever hypervisor drivers it has
available.
You can also make a connection to a remote server. For security reasons you will
usually use SSH to do this by using an xen+ssh:// or qemu+ssh:// URI.
Connection URI Examples
Connect to the local Xen hypervisor:
xen:///
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Use SSH to connect to the Xen hypervisor running on xenhost.yoyodyne.com:
xen+ssh://xenhost.yoyodyne.com/
Connect as root to the local KVM hypervisor:
qemu:///system
Connect as an unprivileged user to the local KVM hypervisor:
qemu:///session
Use SSH to connect as user john to the KVM hypervisor onkvmhost.yoyodyne.com.
ssh+qemu://john@kvmhost.yoyodyne.com/system
Remote GUI control
Installing the X Window System on your server nodes will consume resources you
might rather give to a virtual machine, as well as increase the security risk to your
servers. Instead, consider creating a server to control your nodes. That system can
be a desktop system with a full X Window installation. Install the libvirt tools and
virt-manager to that system and use a URI connection string to connect to your
client. Using SSH will keep the connection secure. Use the VIRSH_DEFAULT_
CONNECT_URI environment variable to hold the connection string. virsh will
look there before trying the default connection URIs.
You may have problems connecting with virt-manager over SSH. If you launch
virt-manager as an unprivileged user, it will usually try to switch you to the root
user. This will clear environment settings like your ssh-agent settings. If prompted
for the root password, select the “run unprivileged” option. This will preserve
your current SSH settings. You don’t need to run as root because you aren’t control-
ling a hypervisor on the local system. For privileged access you will connect to a
privileged user on the remote node.
At this time, virt-manager does not support creating new guests on remote
systems. But you can manage your system just fine.
IP Forwarding and libvirt Networking
libvirt’s default network configures an isolated bridge device to be used by guest
domains. This default bridge creates a private network for the virtual machines,
but does not connect that private network to your physical network. The simplest
way to complete that connection is to enable IP Forwarding in the kernel. You can
quickly enable IP Forwarding using sysctl like so:
# sysctl -w net.ipv4.ip_forward=1
To set your system to enable IP forwarding upon bootup, edit the net.ipv4.ip_
forward setting in /etc/sysctl.conf.
While IP forwarding can get you running quickly, for production environments
you probably want to configure a more robust bridge network. Information on
creating bridge networks for libvirt can be found on the libvirt wiki at:
http://wiki.libvirt.org/page/Networking
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852 | Chapter15: Virtualization Command-LineTools
libvirt and Virtual Machine Manager Commands
virsh virsh [ options ] [ command [ command-options ]]
libvirt management interface. virsh uses the libvirt API to connect
to a hypervisor and manipulate the configuration and state of
virtual machines controlled by that hypervisor. If invoked with a
command, it will execute the command and then exit. If invoked
without a command, virsh enters a shell mode from which you can
execute commands.
This manager will work with any hypervisor that has libvirt
support. However, not all virsh commands are supported by all
hypervisors. Nor will they work on all guests. Still, if a hypervisor
can do something, you can generally use virsh to do it. Some
hypervisors, including Xen, come with their own tools for
managing virtual machines, but we still recommend you use virsh
instead.
Most virsh commands expect a domain option. A domain refers to
a virtual machine. You can use the virtual machine’s name or
UUID. If the machine is running, it should also have an ID number
within the hypervisor, and you can use this for the domain option
as well. Use the list command to see names and IDs of domains
managed by the hypervisor.
Options
--curi, --connect=uri
Connect to a hypervisor specified by uri.
-d level, --debug=level
Set the level of debugging information to be printed to stan-
dard output. Accepted values are 0–5. 0 disables debugging
messages and is the default. 5 prints all debugging messages.
-h, --help
Print a brief description of options and commands.
-l file, --log=file
Log debugging information and errors to the specified file.
-q, --quiet
Quiet mode. Do not print informational messages to standard
out.
-r, --readonly
Connect to hypervisor in read-only mode.
-t, --timing
Print timing information.
-v, --version
Print version information, and exit.
Commands
attach-devicedomain xmlfile
Attach device defined in xmlfile to domain.
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attach-diskdomain source target[options]
Attach disk device to domain. source and target are paths for
the files and devices.
Options
--driver name
Set the driver name attribute. Valid values include file,
tap (network tap), or phy (physical).
--subdriver type
Set the driver type attribute. The valid values depend on
the driver. It’s common to use aio with the tap driver.
--mode mode
Set the mode of device. Valid values include readonly and
shareable.
--type type
Set the type of device. Valid values include cdrom and
floppy.
attach-interfacedomain type source[options]
Attach interface device to domain. Usually type will be either
network or bridge. The source is the host’s network or bridge
device to which the virtual network should connect, or
default, to use the default gateway.
Options
--mac macaddress
Assign an address to the virtual interface.
--target name
Assign the target interface name to use in the guest.
--script path
Provide the path to a script to handle the bridge.
autostart[--disable]domain
Automatically start domain at system boot.
capabilities
Print hypervisor capabilities in XML format.
connect [uri] [--readonly]
Connect or reconnect to a hypervisor.
console domain
If a serial console is available on domain, connect to it. Use
ctrl-] to exit a console.
create xmlfile
Start a domain described in the specified xmlfile.
start domain
Start an inactive domain.
destroy domain
Immediately kill any running instance of the domain and free
its resources to the hypervisor. (You usually want to use shut-
down instead.)
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define xmlfile
Add persistent domain information described in the specified
XML file. The domain is added but not started.
detach-devicedomain file
Detach device defined in file.
detach-diskdomain target
Detach disk device target from domain.
detach-interfacedomain type [--mac macaddress]
Detach network interface from domain. Use macaddress to
distinguish between multiple interfaces of the specified type.
domblkstat domain device
Print basic stats for block device on domain.
domid domain
Given the domain name, print the domain’s ID.
domifstat domain interface
Print basic stats for network interface device on domain.
dominfo domain
Print basic information on domain.
domuuid domain
Print the domain’s UUID.
domname domain
Given the domain ID, print the domain’s name.
domstate domain
Print the domain’s state.
dump domain file
Dump domain’s core to file.
dumpxml domain
Print the domain’s information in XML. Output is suitable for
use with the create and define commands.
freecell [number]
Print available memory on the machine, or if specified, available
memory in Non-Uniform Memory Access (NUMA) cell number.
help [command]
Print a list of available commands or information on a speci-
fied command.
hostname
Print the hypervisor’s hostname.
list [option]
Print a list of active domains and their current state. Use
option --inactive to list inactive domains, or --all to list both
active and inactive domains. There are six possible states:
running, blocked, paused, shutdown, crashed, and dying.
migrate [--live] domain destination [transport]
Migrate a domain to a new destination host. The destination
should be given as a connection URI. If the transport method
differs it can be given as a separate URI, though this isn’t
usually necessary. Use --live to migrate an active domain
without interruption.
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net-autostart[--disable]network
Automatically start network at system boot.
net-create xmlfile
Create and activate a network described in the specified xmlfile.
net-define xmlfile
Define a network described in the specified xmlfile but don’t
start it.
net-destroy network
Immediately stop an active network.
net-dumpxml network
Print the network’s information in XML.
net-list [option]
Print a list of active networks. Use option --inactive to list
inactive networks, or --all to list both active and inactive
networks.
net-name uuid
Print the name of the network specified by uuid.
net-start network
Start a previously defined but inactive network.
net-undefine network
Remove network’s definition.
net-uuid name
Print the UUID of the network specified by name.
nodeinfo
Print basic information about the physical system.
quit
Exit virsh’s interactive terminal.
reboot domain
Reboot the domain as if a reboot command was run from the
console.
restore file
Restore a domain from a domain state saved in file by the save
command.
resume domain
Resume execution of a suspended domain.
save domain file
Save a domain’s state to file. This will suspend the domain,
similar to hibernating a system.
schedinfo [options] domain
Set or show CPU scheduler settings.
Options
--weight n
Set scheduler weight. Valid values of n are between 1 and
65535.
--cap percent
Set the maximum percent that any one physical CPU
domain can consume.
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setmem domain size
Change domain’s current memory allocation to the size given
in kilobytes.
setmaxmem domain size
Change domain’s maximum memory allocation to the size
given in kilobytes. The new size can’t be larger than was speci-
fied when the virtual machine was created.
setvcpus domain n
Change the number of active virtual CPUs. n cannot exceed
the number of CPUs specified in domain’s configuration file at
boot time.
shutdown domain
Shut down the domain as ifthe shutdown command was run
from the console.
suspend domain
Pause execution of domain.
ttyconsole domain
Print domain’s tty console device if it has one.
undefine domain
Remove domain’s definition.
uri
Print hypervisor’s URI.
vcpuinfo domain
Print information about domain’s virtual CPU.
vcpupin domain vcpu cpulist
Control domain virtual CPU affinity. Assign the given vcpu
number to the physical cpulist given as a comma-separated list
of numbers or number ranges: e.g., 0,2 or 0–2,5,6.
version
Print library API version number and the hypervisor URI.
vncdisplay domain
Print the IP address and port number of domain’s display, if
available.
virt-clone virt-clone [ options ]
Clone a virtual machine. virt-clone copies hard drives and dupli-
cates the virtual hardware configuration of an existing virtual
machine. Elements that must be unique, such as the MAC address
of a virtualized network interfaces, are updated so as to avoid
conflicts with the old system. This system to be cloned must be
shut off, as an active system cannot be safely cloned.
If no options are given, virt-clone will query for the needed
information.
virt-clone writes debugging information to $HOME/.virtinst/virt-
clone.log.
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Options
--connect=uri
The hypervisor connection uri.
-d, --debug
Print debugging information to standard output.
-fpath, --file=path
The path to the file, disk partition, or logical volume to use to
store the new guests virtual disk. If the original system has
multiple disks, this option should be run once per disk.
--force
Run without prompting. Assume a yes response to any yes/no
prompt. For all other prompts, exit.
-nname, --name=name
The new domain name for the copied system.
-odomain, --original=domain
The name or UUID of the original domain to copy.
--preserve-data
Preserves any data that exists on the target of an -f option.
-maddress, --mac=address
The new hardware MAC address for the network interface on
the copied system.
-uuuid, --uuid=uuid
The new uuid for the copied system. This is a 32-digit hexa-
decimal number. If not specified, a random UUID is used.
virt-image virt-image [ options ] xmlfile
Create a guest machine from the image descriptor in xmlfile.
Attributes for the new guest are taken from the descriptor file,
although some missing information can be provided on the
command line. Command-line options supersede information in
the image descriptor file.
Options
--boot=n
If image has multiple boot descriptors, use descriptor n. The
first descriptor is descriptor 0. When omitted, the one that
best fits the current hypervisor is chosen.
--check-cpu
Warn if the number of virtual CPUs for the guest exceeds the
number of physical CPUs in the host system.
--connect=uri
The hypervisor connection uri.
-d, --debug
Print debugging information to standard output.
-h, --help
Print information on the command and options, then exit.
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-kmap, --keymap=map
Set the map to use for the graphical console. By default, an
English keymap is used.
-maddress, --mac=address
The hardware MAC address for the network interface on the
copied system. If none is specified or the address is given as
RANDOM, assign a random address.
-nname, --name=name
The domain name for the new guest.
--noacpi
Disable Advanced Configuration and Power Interface (ACPI).
--noapic
Disable Advanced Programmable Interrupt Controller (APIC).
--nographics
Do not set up graphic support.
-rsize, --ram=size
Allocate size in megabytes of memory for guest.
--sdl
Use Simple DirectMedia Layer for graphic access.
-uuuid, --uuid=uuid
The uuid for the new guest system. This is a 32-digit hexa-
decimal number. If not specified, a random UUID is used.
--vnc
Use permanent port n for VNC instead of a random port.
Note that specifying a port may cause clashes with other guests.
--vncport=n
Use port n for VNC. Note that s pecifying a port may cause
clashes with other guests.
--vcpusn
Configure the new system with n virtual CPUs.
-wtype[:name], --network=type[:name]
Configure the guest’s network connection. The type of
network may be bridge, network, or user. For bridge and
network you should also provide the network name as config-
ured in the hypervisor. (Use virsh net-list to see configured
network names.) user is supported by qemu’s unprivileged
mode. It provides limited NAT by way of SliRP, a SLIP/PPP
emulator.
virt-install virt-install [ options ]
Create a guest machine completely from the command line. Virt-
install does not require an XML image descriptor file. virt-install
will prompt for any required information not provided on the
command line. Following is the required information.
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Options
--accelerate
Use KVM or KQEMU kernel acceleration if available. Recom-
mended when the guest OS is compatible.
--boot=n
If an image has multiple boot descriptors, use descriptor n.
The first descriptor is descriptor 0. When omitted, the one
that best fits the current hypervisor is chosen.
-cpath, --cdrom=path
File to use for virtual CDROM device. The file may be an ISO
file, CDROM device, or a URL that refers to an ISO image to
fetch.
--check-cpu
Warn if the number of virtual CPUs for the guest exceeds the
number of physical CPUs in the host system.
--connect=uri
The hypervisor connection uri.
--cpuset=set
Allow guest to use only the given set of CPUs. A set is a
comma-separated list of numbers or number ranges: e.g., 0,2
or 0–2,5,6.
-d, --debug
Print debugging information to standard output.
-fpath, --file=path
Required. The path to the file, disk partition, or logical
volume to use to store the new guest’s virtual disk. If the orig-
inal system has multiple disks, this option should be given
once per disk.
-h, --help
Print information on the command and options, then exit.
-kmap, --keymap=map
Set the keymap to use for the virtual console. By default, an
English keymap is used.
-lpath, --location=path
Specify the location of the installation source. path may be
given as a URI. Use this instead of -c when installing from a
kernel/initrd pair instead of a CDROM. Required for installing
paravirtualized guests.
--livecd
The guest will always use a live CDROM image. Configure
guest to boot from CDROM drive by default. Commonly used
with --nodisks option.
-maddress, --mac=address
The hardware MAC address for the network interface on the
copied system. If none is specified or address is given as
RANDOM, assign a random address.
-nname, --name=name
Required. The domain name for the new guest.
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--noacpi
Disable Advanced Configuration and Power Interface (ACPI).
--noapic
Disable Advanced Programmable Interrupt Controller (APIC).
--noautoconsole
Don’t automatically launch a console for the installation. By
default, virt-install launches a VNC client or virsh console to
connect to the guest.
--nodisks
Guest is being created without disks. Do not prompt for disk
setup.
--nographics
Don’t prompt for virtual console setup if neither--sdl nor --vnc is
specified. Set up a text based console on the first serial port (or
equivalent console device) instead.
--nonsparse
Fully allocate space for the virtual disk. This takes longer to
initialize, but results in a faster disk and ensures you don’t run
out of space. Recommended.
--os-type=type
Optimize guest for the specified guest OS type. Valid values
for type include linux, windows, unix, and other.
-p, --paravirt
Guest will be a paravirtualized system.
--pxe
Use PXE boot protocol to load initial kernel.
-rsize, --ram=size
Required. Allocate size in megabytes of memory for guest.
-ssize, --file-size=size
Required when creating a new file. Create a file of size in
gigabytes. Size may be given as a decimal, for example: 2.5. By
default, virt-install creates a sparse file. The full size will be
allocated, though, if used with the --nonsparse option.
--sdl
Set up a virtual console and export it using Simple Direct-
Media Layer (SDL).
-uuuid, --uuid=uuid
The uuid for the new guest system. This is a 32-digit hexa-
decimal number. If not specified, a random UUID is used.
-v, --hvm
Configure guest with full virtualization. Don’t use paravirtual-
ization if available.
--vnc
Set up a virtual console and export it using VNC.
--vncport=n
Use permanent port n for VNC instead of a random port.
Note that specifying a port may cause clashes with other guests.
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Virtualization
--vcpusn
Configure new system with n virtual CPUs.
-wtype[:name], --network=type[:name]
Configure guest’s network connection. The type of network
may be bridge, network, or user. For bridge and network you
should also provide the network name as configured in the
hypervisor. (Use virshnet-list to see configured network names.)
user is supported by qemu’s unprivileged mode. It provides
limited NAT by way of SliRP, a SLIP/PPP emulator. If this
option is omitted, a single NIC is created to a bridge device or
to the default network. Specify the option multiple times to set
up multiple network interfaces.
-x kernelargs, --extra-args=kernelargs
Pass additional kernel arguments to a Linux kernel. Used with the
-l option. Commonly used to pass a Kickstart file to the kernel.
virt-viewer virt-viewer [ options ] domain
Use VNC to open the console of a virtual machine. The domain
may be given by name, ID, or UUID.
Options
--curi, --connect=uri
Connect to a hypervisor specified by uri.
--d, --direct
Don’t tunnel the VNC connection over SSH, even if the
connection URI uses SSH.
--v, --verbose
Print information about the connection to standard output.
--w, --wait
Wait for the domain to start up before connecting to the console.
virt-manager virt-manager [ options ]
Launch GUI virtual machine manager. This manager visually
displays domain and hypervisor stats. Like virsh, it can manage
domains, and when run on the same system as the hypervisor, it
can even be used to configure new systems. It has a couple of useful
options for controlling how it starts.
Options
--curi, --connect=uri
Connect to a hypervisor specified by uri.
--no-fork
Run without forking a new process. This can be useful for
debugging connection problems.
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VMware ESX 3.5
While VMware isn’t exactly a Linux product and isn’t free, it does provide access
to a Service Console, which is something like Xen’s Domain-0. The Service Console
runs a modified version of Red Hat Enterprise Server 3.0. So even though it is a
commercial product, we want to include some information on it in this chapter.
Here, we will cover useful Service Console commands for administrators using the
commercial ESX 3.5 product. VMware has also provided a free version of ESX,
named ESXi. ESXi does not technically have a Service Console, though you can
launch an unsupported Linux interface similar to the Service Console that has
many of the same commands. Many of the commands listed in this section will
work in the unsupported console, although in keeping with the unsupported
nature of this console, nothing is guaranteed. VMware also provides a remote
command line interface (rCLI), which is a collection of Perl utilities that mostly
mimic the Service Console commands.
As we are writing this, VMware is preparing to release vSphere, the new version of
ESX. It too, has a Service Console and remote CLI, the vCLI. VMware has depre-
cated some commands in vSphere moving functionality to the vCLI. still, they
continue to provide the Service Console for troubleshooting and technical support
sessions. Most of what we document here still works in vSphere.
You will need to install ESX or ESXi on a bare system. Its installation is nearly
identical to an older Red Hat installation. Given your network information, it
should be able to configure a default network switch that will provide your guest
systems with network access.
ESX Management Client
While we cover some of the common commands below, you won’t use these for
most of your management tasks. Once installed and booted, the initial screen will
give you a URL you can connect to in order to perform some basic configuration.
That URL will also direct you to where you can find a Virtual Infrastructure Client
(VI Client) to manage your ESX server. It’s that client you will use to manage your
servers. VI Client runs on Microsoft Windows.
Virtual Center
If you are using VMware servers, you are probably going to use multiple servers to
take advantage of the High Availability features VMware offers, such as Vmotion.
To coordinate those servers you will need to run a Microsoft Windows Server
system with VMware’s virtual center installed. It’s rumored that vSphere will have
a Linux-based Virtual Center, but this has not been announced for the initial
release. It still requires Microsoft Windows.
VMware is GUI driven and VMware expects you will primarily use VI Client to
interact with your systems. You will need to run at least one windows system
to manage VMware ESX servers. The Service Console won’t let you get around
this requirement. However, when your network stops working right or you need
to take a closer look at a system’s performance, you will be glad to have the
service console available.
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VMware Networking
When configuring a virtual network switch, you will configure three different
network connection types: Virtual Machine, VMkernel, and Service Console.
VMware refers to these as different kinds of port groups. A port group specifies
port configuration options, such as VLAN tagging or bandwidth limitations for
devices assigned to that group. The switch handles the mapping of virtual devices
to physical devices. In a default installation of ESX you should have a Service
Console and Virtual Machine port group.
The Service Console port group provides network access to the service console
and is used by the virtual center or VI Client to control the server. The Virtual
Machine port group is a default port group that will bridge your virtual machines
to your physical network devices. Each network card on a virtual machine must
be assigned to a virtual machine port group. For a high availability cluster of ESX
servers, you will need to add a VMkernel port group as well. This is the port
group the hypervisors will use to speak with each other and for moving virtual
machines between servers.
Physical interfaces on a server are given a name beginning with vmnic. The service
console’s interfaces are given names beginning with vswif. Both of these will show
up if you run ifconfig from the service console.
We won’t cover virtual switch configuration further, but these terms will help you
better understand the network and switch-related commands.
Shared Disks
To run multiple ESX servers, you need a shared data store. It can be SAN-based
block storage (e.g., Fibre Channel or iSCSI) or a NAS connection (NFS), but you
need some place the servers can all access the same data. For block storage,
VMware uses a shared filesystem, vmfs, which is designed to handle multiple
systems reading and writing to the same drive.
Snapshots
ESX can take snapshots of a running system. This process essentially freezes
machine state and begins tracking changes to the system in a separate file. Later
you can apply those changes or discard them to revert your system to the state it
had when you took the snapshot. This is commonly used to test a configuration
change or system update.
Because it preserves a system’s state at a specific time, you want your virtual
machine doing as little as possible when taking the snapshot. Activity such as
network file transfers and database transactions will fail if you decide to revert to
the snapshot. Depending on virtual machine configuration, some disk activity
may not be included in the snapshot.
The file tracking changes can grow quickly, so you will need sufficient space to
hold the file, and you will probably not want to keep snapshots for very long.
Having a snapshot may also limit your ability to migrate a system between servers.
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Restoring the snapshot on a new system may not work. VMware will generate
warnings when you try to migrate a system with a snapshot. Generally you want
to remove all snapshots before migration.
VMware Tools
Paravirtualization on ESX depends on VMware tools. This is a collection of
drivers and daemons that allow the hypervisor to communicate with the guest
system. VMware tools can synchronize the guests clock with the ESX server’s
clock, initiate graceful shutdowns when needed, provide better access to an X
Window System running on a guest, and more. You almost always want to install
these.
ESX Server Commands
Most commands for ESX server begin with either vm or esx. Commands that
begin with vm all have something to do with manipulating virtual machines.
Commands that begin with esx manipulate the server and its configuration. The
commands may have more options than those we document here. Here, we focus
on the most useful commands and command options.
esxcfg-firewall esxcfg-firewall [ options ]
Configure a firewall for the service console. ESX uses iptables to
provide the firewall. Don’t use the iptables command to configure
it, though; use this command instead. In its default configuration,
it denies all incoming or outgoing connections except for the ports
required for the server to function:
--allowIncoming
Allow incoming connections by default.
--allowOutgoing
Allow outgoing connections by default.
--blockIncoming
Block incoming connections by default.
--blockOutgoing
Block outgoing connections by default.
-c port type direction, --close port,type,direction
Close a port. The type may be tcp or udp, The direction may
be in or out.
-d [service], --disableService [service]
Close the ports required by the specified service.
-e [service], --enableService [service]
Open the ports required by the specified service.
-h, --help
Print a usage message. This is the default if no options are
given.
-l, --load
Load current firewall settings into iptables.
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-q [service], --query [service]
Print all current settings or the state of a service specified by
name. Instead of a service you can query the default settings
for incoming or outgoing packets.
-o port type direction name, --open port,type,direction,name
Open a port. The type may be tcp or udp, The direction may
be in or out. You must give the service you have opened a
name.
-r, --resetDefaults
Reset all parameters to the installed defaults.
-s, --services
List known service names.
Example
Allow vmware-cmd to connect to remote hosts by opening
outgoing connections to port 443:
#esxcfg-firewall -o 443,tcp,out,vmware-cmd
esxcfg-vswif esxcfg-vswif options [ interface ]
Configure the service console network interface. Don’t use ifconfig
or manipulate /etc/sysconfig/network-script files directly; use this
command instead. Service console interface names start with vswif
followed by a number. For example: vswif0 or vswif1.
Options
-a, --add
Add a service console interface. Requires the --ip and --port-
group options.
-baddress, --broadcastaddress
Set the broadcast address.
-d, --del
Remove a service console interface.
-D, --disable-all
Disable all service console interfaces.
-e, --enable
Enable a disabled interface.
-E, --enable-all
Enable all service console interfaces.
-iaddress, --ipaddress
Set the IP address for the interface. You can also specify
DHCP for address.
-l, --list
List service console interfaces along with current configura-
tion and state.
-nmask, --netmaskmask
Set the netmask.
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866 | Chapter15: Virtualization Command-LineTools
-pname, --portgroupname
Set the interface’s portgroup name.
-s, --disable
Disable an interface.
esxcfg-vswitch esxcfg-vswitch options [ switch ]
Configure a virtual switch. The virtual switch handles port groups and
VLAN tagging, and sets the uplink for virtual port groups. By default,
there is a single virtual switch: vSwitch0. You can add additional
switches and assign them to different physical network interfaces.
Options
-a, --add
Add a new virtual switch. You must provide a switch name.
-A name, --add-pg name
Add port group name to the switch.
-b, --get-cdp
Print the current Cisco Discovery Protocol (CDP) for the switch.
-B status, --set-cdp status
Set the CDP status for the switch. This may be down, listen,
advertise, or both.
-d, --delete
Delete a virtual switch. If the switch has any ports in use, this
will fail.
-D name, --del-pg name
Remove port group name from the switch.
-l, --list
List switches and their port groups.
-L interface, --link interface
Attach an uplink interface to a virtual switch. This should be
an unused physical interface or vmnic.
-m size, --mtu size
Set the size of the Maximum Transfer Unit (MTU) for the
switch. This will affect all interfaces attached to the virtual switch.
-M interface, --add-pg-uplink interface
Add an uplink interface to a port group.
-N interface, --del-pg-uplink interface
Remove an uplink interface from a port group.
-p name, --pg name
Specify name of the port group to use with the --vlan option.
Specify ALL to apply to all port groups on the switch.
-U interface, --unlink interface
Remove an uplink interface from a virtual switch.
-v id, --vlan id
Set the VLAN id for a port group. Use with the --pg option.
Setting id to 0 disables VLAN tagging for the port group.
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Virtualization
esxcfg-nics esxcfg-nics options [ interface ]
Display information about physical network interfaces and manage
some interface settings.
Options
-a, --auto
Set the interface to auto-negotiate speed and duplex settings.
-d mode, --duplex mode
Set duplex mode for the interface. Value may be full or half.
-l, --list
Print current configuration of all network interfaces on the
system.
-s n, --speed n
Set the speed of the interface to n. Valid values are 10, 100,
1000, or 10000 and are measured in megabits per second.
esxtop esxtop [ options ]
Provide frequently updated information about resource usage on
the ESX server. This program performs a function similar to the
Linux top command. Where top shows information on processes
and process IDs, esxtop shows information on hypervisor resource
pools, and resource pool groups. A resource pool is any item the
hypervisor must schedule. For example, each virtual CPU, has a
resource pool ID, and each virtual processor on a single virtual
machine belongs to the same resource pool group.
esxtop’s various options change what information is displayed.
Like top, esxtop also offers interactive commands to change what
information it displays as it runs. esxtop has more interactive
commands than we’ll show here. We are just covering the basic
screens and common commands. The h command, however, will
always show you the currently valid interactive commands.
Options
-a Override configuration file settings and show all statistics.
-b Run in batch mode; don’t accept command-line input. Useful
for sending output to another command or to a file.
-c file
Use alternative configuration file. This also becomes the
default file for the interactive command W.
-d seconds
Set the delay between refreshes. Default is 3.
-n num
Update display num times, then exit.
-s Secure mode. Disable the interactive command s.
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868 | Chapter15: Virtualization Command-LineTools
Interactive commands
# Prompt for number of rows to show.
c Switch to CPU resource screen.
d Switch to storage device screen.
f, F
Add or remove fields.
h Show information on currently available commands.
m Switch to memory resource screen.
o, O
Change field order.
Q, Esc
Quit.
s Prompt for a new delay setting.
n Switch to network resource usage screen.
v Switch to virtual machine disk usage screen.
W Write a configuration file matching current setup to ~/.esxtop3rc.
vmware-cmd vmware-cmd [ options ][ vmxpath command ]
Console-based virtual machine manager. This command can work
on the local system, or connect to a remote system using the Simple
Object Access Protocol (SOAP). To connect to a remote system
you may need to alter your firewall settings on the system issuing
the commands so that it will allow outgoing connections to port
443. See the example in esxcfg-firewall.
The guest you want to work on is identified by the full path to its
.vmx configuration file (vmxpath). The path must include the
UUID of the vmfs volume and so can be quite long. Use the -l
option to get the correct path for all registered virtual machines.
While vmware-cmd has options for getting and setting virtual
machine configuration values, we don’t cover those here.
Options
-h Print basic usage and commands.
-H host
Connect to remote host. This can be given as a domain name
or IP address.
-s[un]registerconfigfile
Add or remove the guest described in .vmx file found at path
from server control.
-l List virtual machines registered with server.
-O port
Connect to alternative port, specified by port number. The
default is port 443.
-P password
Provide password for the user specified in the -U option.
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Virtualization
-q Quiet mode. Minimize output.
-U username
Connect with the given username.
-v Verbose mode.
Command
Return values for the command generally show the command func-
tion and whether they succeed (value 1) or fail (value 0.) Power-
related commands generally take an option power operation mode
of soft, hard, or trysoft. soft power operations use vmware-tools
to generally do the right thing to the guest, such as gracefully shut-
ting it down before pulling the virtual plug, or running special
scripts to prepare the system for suspension. hard operations just
perform the requested action immediately. trysoft operations will
attempt to use vmware-tools for its operations, but if that fails, will
force the operation without using tools.
connectdevice name
Connect device name to system. Valid device names can be
found in the system’s .vmx configuration file.
createsnapshot name description quiesce memory
Take a snapshot of the system, setting the new snapshot’s
name and description. If these values contain spaces, enclose
them in quotes. You can quiesce drive activity and save
memory state while taking the snapshot. quiesce and memory
should be 0 for false or 1 for true. You usually will want both
to be 1.
getstate
Report whether the virtual machine is off, on, suspended, or
stuck.
getuptime
Report how long, in minutes, a machine has been running.
hassnapshot
Report whether virtual machine has a snapshot.
reset[mode]
Restart virtual machine.
removesnapshots
Apply saved changes and delete all snapshots.
revertsnapshot
Discard changes and restore virtual machine to most recent
snapshot. Begin tracking changes again from the snapshot
state.
start[mode]
Power up virtual machine.
stop [mode]
Power off virtual machine.
suspend
Save virtual machine’s state and suspend its operation.
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870 | Chapter15: Virtualization Command-LineTools
Examples
List registered virtual machines:
vmware-cmd -l
Register the yoyodyne system with the hypervisor:
vmware-cmd -s register /vmfs/volumes/uuid/yoyodyne/
yoyodyne.vmx
Start a registered virtual machine:
vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx start
Create a snapshot of the yoyodyne system:
vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx \
createsnapshot beforeupdate "state before system update" 1 1
Connect a virtual IDE CDROM to yoyodyne system:
vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx \
connectdevice ide0:0
vmkfstools vmkfstools options [target]
Manipulate disk images and vmfs filesystems. As with other
commands, you generally use VI Client to perform these tasks. But
you must use the command line when importing a disk from another
VMware product, such as VMware Workstation. Use this command
to create or extend a VMFS system or to extend, rename, or remove a
disk image. It can also set or query disk image properties. Use vmkfs-
tools instead of mv and cp to move and copy virtual disks.
You generally do not want to perform virtual disk operations on
disks currently in use by a virtual machine. Shut down virtual
machines first. Changes in a virtual disk will often require changes
in a virtual machine’s configuration or changes in the virtual machine’s
operating system. One example is changing virtual machine partition
information to take advantage of an extended disk.
Targets
The target will be a device, partition, or file, depending on what you
intend to do.
device
A device target will begin with /vmfs/devices/, the mount point
of the device filesystem. This will include SAN-based disks,
logical volumes, and SCSI devices attached to the ESX server.
partition
A partition target begins with vmhba followed by numbers
that signify adapter:target: LUN:partition[:filepath]. For example,
vmhba0:1:14:2 would be the 2nd partition of LUN 14 on
target 1 HBA 0. You can also target a file on a partition by
appending the filepath.
path
A path target is simply a path to a .vmdk virtual disk file. This
path can be given relative to the /vmfs directory. The path to
the file target isn’t required if it is in the current working
directory.
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Virtualization
Options
We have grouped options that are commonly used together, gener-
ally following the order used in the manpages.
VMFS options:
-b size, --blocksize size
Set new VMFS volume block size. Default is 1m for 1 mega-
byte. Other valid options are 2m, 4m and 8m. Used with the -C
option.
-Ctype, --createfs type
Create a VMFS filesystem on a partition target. In ESX 3.5, the
only valid type is vmfs3.
-S label, -setfsname label
Set the label for a new VMFS filesystem. This is used only with
the -C option.
-Z partition, --extendfs partition
Extend existing vmfs3 filesystem by adding the specified parti-
tion to it. vmfs3 filesystems can have at most 32 partitions.
-P, --queryfs
List attributes of a VMFS filesystem. The target of this command
may be the path to any directory or file on a VMFS filesystem.
-h, --human-readable
Used in conjunction with the -P option. Print sizes in a more
easily read form.
Virtual disk options:
-c size, --createvirtualdisk size
Create a new virtual disk of the specified size in bytes (by
default). You can also append g, m, or k to give numbers in
gigabytes, megabytes, or kilobytes, respectively. For example:
8g for 8 gigabytes.
-a [type], --adaptertype [type]
Specify adapter type to use with the virtual disk. The only
valid types are buslogic or lsilogic. Default is buslogic, but for
Linux you probably want lsilogic.
-d format, --diskformat format
Set virtual disk format. This option is used when creating and
cloning virtual disks (-c and -i options). See later options for
valid virtual disk formats. When cloning, this option can be
used to specify the format of the target disk; for example,
when cloning a VMFS virtual disk file to a 2 GB sparse file
useable by other VMware products.
-U, --deletevirtualdisk
Delete a virtual disk and any associated files.
-E source, --renamevirtualdisk source
Rename source virtual disk and associated files to target.
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872 | Chapter15: Virtualization Command-LineTools
-i source, --clonevirtualdisk source
Clone source virtual disk and associated files to target. This is
commonly used to import disks from other VMware prod-
ucts. You can use -d to specify the format of the source.
-X size, --extendvirtualdisk size
Extend an existing disk to the specified size in bytes (by
default). You can also append g, m, or k to give numbers in
gigabytes, megabytes, or kilobytes respectively. This action will
break snapshots and the guest will need some way to recog-
nize and take advantage of the new disk size (such as by
resizing a partition with resize2fs).
-rdevice, --createrdmdevice
Create a virtual raw device mapping. (See the following
section, “Virtual disk formats.”) Give device as the full path to
a device under /vmfs/devices.
-q, --queryrdm
Print attributes of an existing raw disk mapping.
-zdevice, --createrdmpassthroughdevice
Create a physical raw device mapping. (See the following
section, “Virtual disk formats.”) Give device as the full path to
a device under /vmfs/devices.
-g, --geometry
Print geometry information for a virtual disk.
-w, --writezeroes
Initialize a virtual disk with zeroes. This will wipe any existing
data from the disk.
-j, --inflatedisk
Convert a thin virtual disk to a preallocated virtual disk,
preserving existing data and zeroing out unallocated blocks.
Virtual disk formats
This section lists the valid target disk formats to use with the -d
option when creating or cloning a virtual disk. Created disks may
be in any of the ESX vmdk formats. When cloning a disk, use -d if
you need to export to an alternate format or target a raw device.
ESX vmdk formats:
zeroedthick
Allocate all space and wipe any previous contents of that space
during virtual machine read and write operations. This is the
default format.
eagerzeroedthick
Like zeroedthick, only the allocated space is wiped at creation
time.
thick
Allocate all space, but don’t bother cleaning any existing
content on the disk.
thin
Supply and zero out space for the filesystem as it is used by the
virtual machine.
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Virtualization
VMware compatible formats:
2gbsparse
Sparse disk with 2 GB maximum extent size (the Virtual disk
will be split into 2 GB sections). This is a useful format when
writing to disks that don’t support files larger than 2 GB.
monosparse
One monolithic disk file.
monoflat
One monolithic flat file.
Raw device mappings:
rdm:device
Virtual raw device mapping. These are treated by a guest as
any other virtual disk.
rdmp:device
Physical raw device mapping. A virtual machine is given direct
access to a physical raw device and interacts with it as it would
any SCSI device. LUN listing requests are virtualized,
however, so only the system that owns the virtual device can
access it.
raw:device
A raw SCSI device, like a tape archive or an unmapped LUN.
Examples
Export a VMFS virtual disk to 2 GB sparse file:
# vmkfstools -i original.vmdk -d 2gbsparse new.vmdk
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875
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Chapter 16
16
Index
Symbols
& (ampersand)
background execution, 601, 602
command redirection, 603
repeat substitute command in ex, 710
reuse text matched by pattern, 657
&& (ampersand, double)
AND operator for commands, 602
AND operator, in expressions, 620,
732
< or > (angle brackets)
command redirection, 601, 602–604
shift commands in ex, 710
* (asterisk)
match multiple instances of a
character, 655
in filename, 599
multiplication operator, 732
** (asterisk, double) exponentiation
operator, 732
*= (asterisk, equals sign) assignment
operator, 732
*() (asterisk, parentheses) in
filename, 600
**= (asterisks, equals sign) assignment
operator, 732
@ (at sign) execute register command in
ex, 710
@() (at sign, parentheses) in
filename, 600
` (backtick) command
substitution, 601, 602
\ (backslash)
escape character, Bash shell, 601
escape character, pattern
matching, 657
escape character, prompt
strings, 612
\< or \> (backslash, angle brackets)
match beginning or end of
word, 656
\' (backslash, apostrophe) escape
character, pattern
matching, 656
\` (backslash, backtick) escape
character, pattern
matching, 656
\{...\} (backslash, braces) enclosing range
of characters to match, 655
\(...\) (backslash parentheses) save
enclosed subpattern, 656
\;...; (backslash, semicolon) enclosing
pattern address in sed, 714
{...} (braces)
enclosing command grouping, 602
enclosing nested pattern address in
sed, 714
enclosing procedures in gawk, 729
enclosing range of characters to
match, 655
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876 | Index
[...] (brackets)
enclosing array elements, 611
enclosing characters to match, 655
enclosing expressions, 647–650
in filename, 599
[[...]] (brackets, double) enclosing
expressions, 620
^ (caret)
match at beginning of line or
string, 655
exponentiation operator, 732
^= (caret, equals sign) assignment
operator, 732
: (colon)
null command, 620
preceding ex commands, 696
preceding label, sed, 717
$ (dollar sign)
field reference, 732
last input line as pattern address in
sed, 714
match at end of line or string, 655
preceding built-in variables, 607
preceding macros in ftp, 149
variable substitution, 601
${...} (dollar sign, braces)
enclosing arrays, 611
enclosing variable substitution, 606
$(()) (dollar sign, double parentheses)
arithmetic substitution, 602,
613
$() (dollar sign, parentheses) command
substitution, 602
. (dot)
end message, mailx, 267
match single character, 655
read and execute file command, 620
"..." (double quotes) enclosing special
characters, 601
= (equals sign)
assignment operator, 732
print line number command in
ex, 710
command in sed, 716, 717
! (exclamation point)
execute command in ex, 709
execute command, mailx, 269
history expansion character, 614
logical negation operator, 732
negating pipeline, 619
NOT operator for commands, 602
preceding commands in ftp, 149
!= (exclamation point, equal) not equal
operator, 732
!() (exclamation point, parentheses) in
filename, 600
!~ (exclamation point, tilde) match
negation of regular
expression, 732
# (hash sign)
preceding comments in gawk, 738
preceding comments in LILO
configuration file, 507
preceding comments in sed
scripts, 717
preceding comments in shell
scripts, 619
- (hyphen)
previous command, mailx, 269
subtraction operator, 732
unary minus operator, 732
-- (hyphen, double) decrement
operator, 732
-= (hyphen, equals sign) assignment
operator, 732
- or -- (hyphen(s)) preceding command
options, 33
< (left angle bracket) less than
operator, 620, 732
<= (left angle bracket, equals sign) less
than or equal operator, 732
(...) (parentheses)
enclosing group of commands, 601,
602
enclosing group of regular
expressions, 656
% (percent sign)
preceding job ID in commands, 617
reuse previous replacement
pattern, 657
modulus operator, 732
%= (percent sign, equals sign)
assignment operator, 732
+ (plus sign)
addition operator, 732
match one or more instances, 656
unary plus operator, 732
++ (plus sign, double) increment
operator, 732
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Index | 877
+= (plus sign, equals sign) assignment
operator, 732
+() (plus sign, parentheses) in
filename, 600
? (question mark)
in filename, 599
help command, mailx, 269
match zero or one instance, 656
?: (question mark, colon) conditional
expression, 732
?() (question mark, parentheses) in
filename, 600
> (right angle bracket)
greater than operator, 620, 732
output redirection, 746
>> (right angle bracket, double) append
output, 746
>= (right angle bracket, equals sign)
greater than or equal
operator, 732
> or >> (right angle brackets) in cat
command, 68
; (semicolon) command separator, 601,
602
'...' (single quotes) enclosing special
characters, 601
/ (slash) division operator, 732
/= (slash, equals sign) assignment
operator, 732
/.../ (slashes) enclosing pattern address
in sed, 714
~ (tilde)
in filename, 599
match regular expression, 732
tilde escape commands, mailx, 268
replace regular expression command
in ex, 710
reuse previous replacement
pattern, 657
~- (tilde, hyphen) in filename, 599
~+ (tilde, plus sign) in filename, 599
| (vertical bar)
match either one or the other, 656
output directed to next
command, 746
pipe character, 601, 602
|& (vertical bar, ampersand) output
directed to coprocess, 735, 746
|| (vertical bar, double)
OR operator for commands, 602
OR operator, in expressions, 620, 732
A
\a alert escape sequence, 601, 715, 733,
612
a command, sed, 716, 718
\A time escape sequence, 612
abbreviate command, ex, 697
accept command, 34
access command, 34
access mode for files, checking, 34
access permissions, changing, 80
account command, ftp, 149
account command, mailx, 269
aclocal command, 34
aconnect command, 35
ACPI (Advanced Configuration and
Power Interface)
displaying information about, 35
eventsfrom,informinguserprograms
of, 36
acpi command, 35
acpid daemon, 36
add command, git, 812
add command, svn, 767
addition operator (+), 732
addr add command, ip, 212
addr del command, ip, 212
addr show command, ip, 212
addr2line command, 37
Address Resolution Protocol (ARP), 22,
49
addresses of lines, ex, 696, 710
addresses, program, translating to
filenames and line
numbers, 37
Advanced Configuration and Power
Interface (see ACPI)
Advanced Linux Sound Architecture (see
ALSA)
Advanced Package Tool (see APT)
Advanced Power Management (APM)
hardware, handling events
from, 45
agetty command, 38
alias command, Bash, 620
alias command, lftp, 245
alias command, mailx, 269
aliases
assigning, 620
removing, 653
aliases database, rebuilding, 308
alnum character class, 600, 656
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878 | Index
alpha character class, 600, 656
ALSA (Advanced Linux Sound
Architecture)
MIDI files
playing, 44
recording, 48
mixer
connecting to one or more sound
cards, 40
controlling, 41
ports, reading and writing MIDI files
to, 40
sound cards, advanced configuration
settings for, 39
sound files
playing, 43
recording, 48
alsactl command, 39
alsamixer command, 40
alternates (alt) command, mailx, 269
amidi command, 40
amixer command, 41
ampersand (&)
background execution, 601, 602
command redirection, 603
repeat substitute command in ex, 710
reuse text matched by pattern, 657
ampersand, double (&&)
AND operator, in expression, 620
AND operator, in expressions, 732
for commands, 602
anacron command, 43
and() function, gawk, 738
AND operator (&&)
for commands, 602
in expression, 620
angle brackets (< or >)
command redirection, 601, 602–604
shift commands in ex, 710
(see also left angle bracket; right
angle bracket)
anon command, lftp, 245
ANSI/VT100 terminal
emulation, 379–384
Apache web server
benefits of using with Linux, 3
user authentication files for, creating
or updating, 199
aplay command, 43
aplaymidi command, 44
APM (Advanced Power Management)
hardware, handling events
from, 45
apmd command, 45
append command, ex, 698
append command, ftp, 149
apropos command, 46
APT (Advanced Package Tool), 46, 544
(see also aptitude command, Debian;
synaptic command, Debian)
apt command, 46
apt-cache command, Debian, 569–571
apt-cdrom command, Debian, 571
apt-config command, Debian, 572
apt-extracttemplates command,
Debian, 573
apt-file script, Debian, 568
apt-ftparchive command, Debian, 574
apt-get command, Debian, 575–579
aptitude command, Debian, 544,
579–583
apt-rdepends script, Debian, 568
apt-sortpkgs command, Debian, 579
ar command, 47
arch command, 48
Arch system, 753
architecture for package, 543
architecture type, printing, 48
archive command, git, 813
archives
copying files to or from tape or
disk, 89–92
copying files to or restoring
from, 431–437
of Debian packages, 566
index for, generating, 347
maintaining, 47
of RPM packages, 552
(see also packages)
arecord command, 48
arecordmidi command, 48
args command, ex, 698
arguments on command-line
checking, 633
printing, 494
shifting, 643
arithmetic expressions, 602, 613, 636
arithmetic for loop, 632
ARP (Address Resolution Protocol), 22,
49
arp command, 49
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Index | 879
arrays
Bash, 611, 637
gawk, 733
AS (autonomous system), 25
as command, 50
ASCII codes of keys, printing, 399
ascii command, ftp, 149
ASCII format, displaying files in, 196
asort() function, gawk, 738
asorti() function, gawk, 738
assembly source files, generating object
files from, 50
assignment operators, gawk, 732
associative arrays
Bash, 611
gawk, 733
asterisk (*)
in filename, 599
match multiple instances of a
character, 655
multiplication operator, 732
asterisk, double (**) exponentiation
operator, 732
asterisk, equals sign (*=) assignment
operator, 732
asterisk, parentheses (*()) in
filename, 600
asterisks, equals sign (**=) assignment
operator, 732
at command, 51
at command, lftp, 245
at sign (@) execute register command in
ex, 710
at sign, parentheses (@()) in
filename, 600
atan2() function, gawk, 739
atd command, 53
atq command, 53
atrm command, 53
audio files
playing, 43
recording, 48
recording to CDs, 69–71, 75,
484–488
recording to DVDs, 125, 484–488
authentication
adding RSA or DSA identities to
agent, 409
gathering keys from multiple
hosts, 411
hold private keys for public key
authentication, 410
keys, managing, 410
author command, svnlook, 800
autoconf command, 34, 53
autoheader command, 54
automake command, 55
autonomous system (AS), 25
autoreconf command, 56
auto_resume built-in variable, 611
autoscan command, 57
autoupdate command, 58
awk, GNU (see gawk language)
AWKPATH environment variable,
gawk, 736
B
\b backspace escape sequence, 601, 733
b command, sed, 717, 718
\B escape sequence, 656, 715
\b escape sequence, 656, 715
background execution of
commands, 601, 602, 621,
653
backing up files, 122–123
backslash (\)
escape character, Bash shell, 601
escape character, pattern
matching, 657
escape character, prompt
strings, 612
backslash, angle brackets (\< or \>)
match beginning or end of
word, 656
backslash, apostrophe (\') escape
character, pattern
matching, 656
backslash, backtick (\`) escape
character, pattern
matching, 656
backslash, braces (\{...\}) enclosing
range of characters to
match, 655
backslash parentheses (\(...\)) save
enclosed subpattern, 656
backslash, semicolon (\;...;) enclosing
pattern address in sed, 714
backtick (`) command
substitution, 601, 602
backup files, restoring, 357–359
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880 | Index
badblocks command, 58
base64 command, 59
basename command, 59
BASH built-in variable, 608
Bash shell, 60, 596–653
arguments for, 599
arithmetic expressions, 602, 613, 636
arrays, 611
background execution, 601, 621
built-in commands, executing
bypassing functions, 622
built-in variables, 607–611
character classes, 600
command execution, 618
command forms, 602
command history, 614–617, 631,
634
command redirection, 601, 602–604
command substitution, 601, 602
command-line options for, 598
commands, enabling or
disabling, 629
commands, list of, 619–653
coprocesses,604
debugger, 608
escape character, 601
filenames, metacharacters for, 599
functions, 605
help on commands for, 634
home directories for, 599
invoking, 597–599
job control, 617
line-edit mode, 614
options for, setting or
unsetting, 643–647
POSIX notation in, 600
programmable
completion, 615–617,
624–626
prompt strings, 612
quoting special characters in, 600
restricted shells, 619
startup files for, 599
suspending, 647
variable substitution, 601, 606
version of, covered in this book, 596
websites about, 597
BASH_ARGC built-in variable, 608
BASH_ARGV built-in variable, 608
BASH_COMMAND built-in
variable, 608
BASH_EXECUTION_STRING built-in
variable, 608
BASH_LINENO built-in variable, 608
BASH_REMATCH built-in
variable, 608
BASH_SOURCE built-in variable, 608
BASH_SUBSHELL built-in variable, 608
BASH_VERSINFO built-in
variable, 608
BASH_VERSION built-in variable, 608
batch command, 60
Bautts, Tony (Linux Network
Administrator’s Guide), xvii,
23, 29
bc compiler, 60–64
bdelete command, ex, 698
Beebe, Nelson H.F. (Classic Shell
Scripting), 597
bell command, ftp, 149
Berkeley C shell, 596
Berkeley Internet Name Domain
(BIND), 26
Berkeley Software Distribution
(BSD), 4, 7
bg command, Bash, 621
BGP (Border Gateway Protocol), 25
binary command, ftp, 149
BIND (Berkeley Internet Name
Domain), 26
bind command, Bash, 621
BIND DNS server, sending commands
to, 363
binder process, NIS, 494
bindtextdomain() function, gawk, 739
biod daemon, 30
bisect command, git, 814–815
bison command, 64
blame command, svn, 767
blank character class, 600, 656
block files, creating, 292
blocklist command, GRUB, 530
blocks group, printing information
about, 124
bookmark command, lftp, 245
books and publications
Building Internet Firewalls (Zwicky;
Cooper; Chapman), 29
Classic Shell Scripting (Robbins;
Beebe), 597
GNU Emacs Pocket Reference
(Cameron), 654
Download at WoweBook.Com
Index | 881
Internetworking with TCP/IP
(Comer), 23
Learning GNU Emacs (Cameron
et al.), 654, 662
Learning Red Hat Enterprise Linux
and Fedora (McCarty), 5
Learning the bash Shell
(Newham), 597
Learning the Unix Operating System
(Peek; Todino-Gonguet;
Strang), xvii
Linux iptables Pocket Reference
(Purdy), 29
Linux Journal, xviii
Linux Magazine, xviii
Linux Network Administrator’s
Guide (Bautts; Dawson;
Purdy), xvii, 23, 29
Managing Projects with GNU Make
(Mecklenburg), 275
Mastering Regular Expressions
(Friedl), 654
Perl 5 Pocket Reference
(Vromans), 654
Perl in a Nutshell (Patwardhan
et al.), 654
Regular Expression Pocket Reference
(Stubblebine), 654
Running Linux (Dalheimer;
Welsh), xvii, 4
TCP/IP Network Administration
(Hunt), 23
Version Control with Subversion
(Pilato et al.), 755
boot command, GRUB, 530
boot loader, 505
boot sector, 505
booting, 504–541
dual booting, 504, 505, 536–539
GRUB, 504, 516–536
kernel options during, 539–541
LILO, 504, 506–516
virtualization for, 504
bootp command, GRUB, 526
Border Gateway Protocol (BGP), 25
Bourne shell, 596
Bourne-Again SHell (see Bash shell)
braces ({...})
enclosing command grouping, 602
enclosing nested pattern address in
sed, 714
enclosing procedures in gawk, 729
enclosing range of characters to
match, 655
brackets ([...])
enclosing array elements, 611
enclosing characters to match, 655
enclosing expressions, 647–650
in filename, 599
brackets, double ([[...]]) enclosing
expressions, 620
branch command, git, 815
branches, for source code management
system, 750, 756
branches, in Git, 806, 815
merging, 826, 827
pushing, 828
tracking changes to, 830
brctl command, 843
break command, Bash, 622
break command, gawk, 739
break command, gdb, 164
bridge-utils package, 843
bridging, 842
BSD (Berkeley Software
Distribution), 4, 7
bt command, gdb, 164
buffer command, ex, 698
buffer-manipulation commands,
Emacs, 666
buffers command, ex, 698
Building Internet Firewalls (Zwicky;
Cooper; Chapman), 29
builtin command, Bash, 622
built-in commands (see commands,
Bash)
built-in variables, 607–611
built-in variables, gawk, 731
bunzip2 command, 65
bye command, ftp, 149
bzcat command, 65
bzcmp command, 65
bzdiff command, 65
bzgrep command, 65
bzip2 command, 65
bzip2 files, 65–67
(see also compressed files)
bzip2recover command, 65
bzless command, 67
bzmore command, 67
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882 | Index
C
c command, gdb, 164
c command, sed, 716, 718
c++ compiler (see g++ compiler)
\c control character escape
sequence, 601
C language
generating from RPC code, 366
preprocessor for, 92–98
cache command, lftp, 245
cache command, mailx, 269
cal command, 68
calendar, printing, 68
caller command, Bash, 622
cameras, reading images from, 376
Cameron, Debra
GNU Emacs Pocket Reference, 654
Learning GNU Emacs, 654, 662
capitalization commands, Emacs, 666
caret (^)
exponentiation operator, 732
match at beginning of line or
string, 655
caret, equals sign (^=) assignment
operator, 732
case command, Bash, 622
case command, ftp, 149
cat command, 68
cat command, GRUB, 531
cat command, svn, 768
cat command, svnlook, 800
cc compiler (see gcc compiler)
cd command, Bash, 623
cd command, ex, 698
cd command, ftp, 149
cd command, gdb, 164
CDDA (Compact Disc Digital Audio)
converting to WAV, 69
converting to WAV format, 200–203
cdda2wav command, 69
cdparanoia command, 69–71
CDPATH built-in variable, 609
cdrdao command, 71–75
cdrecord command, 75
CD-Rs, writing in DAO mode, 71–75
CDs
commands for, list of, 9
converting from CDDA to WAV
format, 200–203
ejecting, 128
reading and writing, 350, 352
recording audio files to, 69–71, 75
recording data files to, 75
recording data or audio to, 484–488
cdup command, ftp, 149
center command, ex, 699
centering commands, Emacs, 668
cfdisk command, 75
c++filt command, 67
C-h command (help), Emacs, 663
chage command, 76
chainloader, 517
chainloader command, GRUB, 531
chains, 29
change command, ex, 699
changed command, svnlook, 800
changelist command, svn, 768
Chapman, D. Brent (Building Internet
Firewalls), 29
character classes
Bash, 600
pattern matching, 656
character files, creating, 292
chattr command, 77
chdir (c) command, mailx, 269
checkout command, git, 816
checkout command, svn, 769
checksums, calculating and
printing, 427
check-update command, yum, 547
cherry-pick command, git, 817
chfn command, 78
chgrp command, 78
chkconfig command, 79
chmod command, 80
chmod command, ftp, 149
chown command, 82
chpasswd command, 83
chroot command, 83
chrt command, 83
chsh command, 84
chvt command, 84
CIDR (Classless Inter-Domain
Routing), 24
cksum command, 84
Classic Shell Scripting (Robbins;
Beebe), 597
classify command, mailx, 270
Classless Inter-Domain Routing
(CIDR), 24
clean command, git, 818
clean command, yum, 548
Download at WoweBook.Com
Index | 883
cleanup command, svn, 770
clear command, 84
clear command, gdb, 164
clearing screen, 356
client, NIS, 32
client/server model, for source code
management system, 751
clocks
commands for, list of, 14
reading or setting, 200
clone command, git, 818
close command, ex, 699
close command, ftp, 150
close command, lfpt, 246
close() function, gawk, 739
cmp command, 85
cmp command, GRUB, 531
cntrl character class, 600, 656
code examples in this book, using, xix
Codeville system, 753
col command, 85
colcrt command, 86
colon (:)
null command, 620
preceding ex commands, 696
preceding label, sed, 717
color command, GRUB, 526
colrm command, 86
column command, 86
columns
formatting input into, 86
removing from file, 86, 102
COLUMNS built-in variable, 609
Comer, Douglas E. (Internetworking
with TCP/IP), 23
comm command, 86
command command, Bash, 623
command command, lftp, 246
command mode, vi, 678, 681
command-line arguments
checking, 633
printing, 494
shifting, 643
commands, 3, 5
Bash, 619–653
aliases for, assigning, 620
aliases for, removing, 653
conditional execution of, 622,
635
coprocessing, 604
enabling or disabling, 629
executing, 618
executing based on signals, 650
executing, bypassing aliases or
functions, 622, 623
executing in current process, 630
forms of, 602
hash table for, 633
history of, 614–617, 631, 634
programmable completion
for, 624–626
redirection of, 601, 602–604
substitution of, 601, 602
type of, determining, 651
for clocks, 14
for communications, 7
for comparisons, 8
for daemons, 14
deleting queued jobs of, 53
displaying manual pages for, 283
Emacs, 663, 669–676
buffer-manipulation, 666
capitalization, 666
centering, 668
completions for, 662
deletion, 664
file-handling, 663
help, 663, 668
indentation, 667
jobs, 667
listing, 663
macro, 668
paragraph, 665
region, 665
search, 665
shell, 667
stopping, 665
transposition, 665
undoing, 665
windows, 666
word-abbreviation, 666
ex, 697–710
line addresses in, 696, 710
options for, 697
syntax for, 696
executing and timing the
execution, 445
executing as superuser, 426
executing at scheduled times, 98
executing at specific time and
date, 51
executing even after logging out, 311
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884 | Index
commands (continued)
executing in a new session, 395
executing in batch from standard
input, 60
executing on remote host, 367
executing periodically, 43
executing queued jobs of, 53
executing remotely, 359
executing repeatedly, 472
executing with arguments from
standard input, 488–489
executing with lower priority, 309
executing with specific options, 119
executing within ftp, 149
for file management, 8
for filesystems, 17
full pathnames for execution of, 481
GRUB, 525–536
for hardware, 15
help on, 33
for host information, 15
for installation, 16
for kernel, 17
list of, by category, 7–13
listing queued jobs of, 53
locating files for, 480
for mail, 16
for media, 9
for networking, 18
for NFS administration, 22
for NIS administration, 22
for NIS maps, 31
options for, entering, 33
output from, sending to both
standard output and files, 440
for printing, 9, 18
for process management, 19
for program maintenance, 10
for programming, 9
scheduling, 20
for searching, 10
for security, 18
sending to BIND DNS server, 363
for shell programming, 11
for storage, 11
for system administration, 14–20
for system integrity, 18
for system logging, 20
for system status, 11
for TCP/IP administration, 21
for TCP/IP troubleshooting, 28
for text processing, 12
tracing system calls and signals
for, 416–418
for user management, 20
vi, 683–692
copy and move, 688
edit, 687
insert, 686
macros, 691
movement, 683–686
multiple files, accessing, 689
saving files, 688
:set command, 692–696
system access, 690
window, 690
waiting before execution of, 403
(see also specific commands)
commands command, gdb, 164
comments
in bc, 63
in C, nested, warnings for, 96, 161
in database map input file, 282
in DNS update requests, 311
in file containing format strings, 197
in gawk, 738
in GRUB configuration file, 521
in history expansion, 611
in LILO configuration files, 507
in MAC address input file, 305
in makefiles, 276
in RPM package manifest file, 557
in sed scripts, 717
in shell scripts, 619
in xinetd input, 491
commit command, git, 819
commit command, svn, 771
communications, commands for, 7
Compact Disc Digital Audio (see
CDDA)
comparison operators, 620
comparisons, commands for, 8
COMP_CWORD built-in variable, 608
compgen command, Bash, 624
compl() function, gawk, 739
complete command, Bash, 615,
624–626
completion, programmable, 615–617,
624–626
COMP_LINE built-in variable, 608
COMP_POINT built-in variable, 608
COMPREPLY built-in variable, 609
Download at WoweBook.Com
Index | 885
compress command, logrotate, 253
compresscmd command, logrotate, 253
compressed files
bzip2 files, 65–67
comparing, 501
compressing executable files, 190
compressing files with Lempel-Ziv
coding, 191
reading and then writing to standard
output, 501
renaming, 501
uncompressing and searching, 502
uncompressing and then paging
through, 502
uncompressing and then
recompressing in .gz
format, 503
uncompressing files, 190
compressext command, logrotate, 253
compressoptions command,
logrotate, 253
COMP_WORDBREAKS built-in
variable, 608
COMP_WORDS built-in variable, 608
concatenation operator, 732
Concurrent Versions System (CVS), 752
conditional execution of commands
case command, 622
if command, 635
short-circuit operations for, 602
config command, git, 820
configfile command, GRUB, 531
configuration of vi editor, 692–696
configuration script
generating from m4 macros, 53
updating, 56
conflict, in source code management
system, 751
console command, xm, 846
contact information for this book, xxi
containers technology, 838
context-free grammar, converting to
tables, 493
continue command, Bash, 626
continue command, gawk, 739
conventions used in this book, xx
Cooper, Simon (Building Internet
Firewalls), 29
coproc reserved word, 604
coprocesses, Bash, 604
coprocesses, gawk, 735
copy and move commands, vi, 688
copy (co) command, mailx, 270
copy command, ex, 699
copy command, logrotate, 254
copy command, svn, 772
copyleft (see GPL)
copy-modify-merge model,
Subversion, 756
copytruncate command, logrotate, 254
cos() function, gawk, 739
cp command, 87–89
cpio command, 89–92
cpp command, 92–98
cr command, ftp, 150
CRC (cyclic redundancy check)
checksum, computing, 84
create command, logrotate, 254
create command, svnadmin, 795
create command, xm, 846
cron command, 545
crond command, 98
crontab command, 98
csh shell, 596
csplit command, 99
CSSC system, 754
ctags command, 100
Ctrl key (C-), Emacs, 662
CUPS printer queues, configuring, 256
cupsd command, 101
current working directory
changing, 623
printing, 638
cursor (point) location, Emacs, 662
cursor-movement commands,
Emacs, 664
cut and paste (kill and yank),
Emacs, 662
cut command, 102
cut-and-paste utility for Linux
console, 178–180
CVS (Concurrent Versions System), 752
cyclic redundancy check (CRC)
checksum, computing, 84
D
D command, sed, 717, 719
d command, sed, 716, 719
\D date escape sequence, 612
\d date escape sequence, 612
\d decimal escape sequence, 715
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886 | Index
daemons, 21
commands for, list of, 14
nfsd daemons, 30
routing daemons, 25
daily command, logrotate, 254
Dalheimer, Matthias Kalle (Running
Linux), xvii, 4
DAO (disk-at-once) mode, 71
database maps for sendmail,
creating, 282
database of files, searching, 250
databases, searching for a specific
key, 173
date and time
current date and time,
printing, 103–105
retrieving from specific host(s) on
network, 348
date command, 103–105
date command, svnlook, 800
Dawson, Terry (Linux Network
Administrator’s Guide), xvii,
23, 29
dbm database files, 31
dbm file, NIS, creating or dumping, 281
dcgettext() function, gawk, 739
dcngettext() function, gawk, 739
dd command, 105, 844
dd command, GRUB, 519
deallocv command, 107
Debian Package Manager, 544, 565–569
commands for, 569–595
files used by, 565
interactive frontend for (see dselect
command, Debian)
lower-level packaging tool for (see
dpkg-deb command, Debian)
naming conventions for, 543, 565
package flags, 567
package priorities, 566
package states, 567
scripts for, 568
debug command, ftp, 150
debug command, GRUB, 531
debugfs command, 107–110
debugger
Bash, 608
gdb, 163–165
debuginfo-install plugin, yum, 551
decimal format, displaying files in, 196
declare command, Bash, 626
decoding, base64, 59
decrement operator (--), 732
decryption (see encryption and
decryption)
default command, GRUB, 522
#define statements, generating template
of, 54
delaycompress command,
logrotate, 254
delete command, ex, 699
delete command, ftp, 150
delete command, gawk, 740
delete command, gdb, 164
delete command, svn, 773
delete (d) command, mailx, 270
deletion commands, Emacs, 664
deltify command, svnadmin, 795
dependencies for packages, 542, 543
dependency file, creating, 110
deplist command, yum, 548
depmod command, 110
desktop environments, 4
desktop system, Linux as, 3
destroy command, xm, 847
devdump command, 111
device command, GRUB, 526
device map, GRUB, 518
devices
assigning interfaces to, 305
displaying contents of, 111
formatting, 287
formatting as ext2
filesystem, 288–290
paging, turning off, 427
paging, turning on, 427
swapping, turning off, 427
swapping, turning on, 427
volume name for, determining, 471
df command, 112
dhcp command, GRUB, 527
diff command, 113–115
diff command, git, 821
diff command, svn, 774–775
diff command, svnlook, 800
diff3 command, 115–116
dig command, 26, 116
digit character class, 600, 656
dir command, 118
dir command, ftp, 150
Download at WoweBook.Com
Index | 887
dircolors command, 118
directories
adding to stack, 638
contents of, listing verbosely, 468
creating, 287
deleting, 362
listing contents of, 118, 260–263
lost+found directory, creating, 292
moving or renaming, 302–303
printing stack for, 627
printing top directory from
stack, 637
removing from path, 59
Dired (Directory Editor) mode,
Emacs, 662
dirname command, 119
dirs command, Bash, 627
dirs-changed command, svnlook, 801
DIRSTACK built-in variable, 609
disaster recovery data, storing, 126
disconnect command, ftp, 150
disk image files, for virtualization, 844
disk usage
auditing, 345
available space, determining, 112
printing, 120, 344
quota statistics for, printing, 347
reporting on, 355
disk-at-once (DAO) mode, 71
disown command, Bash, 628
display command, gdb, 164
displayapm command, GRUB, 531
displaymem command, GRUB, 531
distributions of Linux, 3
division operator (/), 732
dmesg command, 119
dmesg command, xm, 847
DNS (Domain Name System), 26
DNS servers, querying, 116
do command, gawk, 740
do reserved word, Bash, 628
document formatting (see groff
command)
document processing, gs command
for, 189
doexec command, 119
dollar sign ($)
field reference, 732
last input line as pattern address in
sed, 714
match at end of line or string, 655
preceding built-in variables, 607
preceding macros in ftp, 149
variable substitution, 601
dollar sign, braces (${...})
enclosing arrays, 611
enclosing variable substitution, 606
dollar sign, double parentheses ($(()))
arithmetic substitution, 602,
613
dollar sign, parentheses ($()) command
substitution, 602
Domain Name System (DNS), 26
domain names
contact for, finding, 483
definition of, 26
domain nameserver
querying, 311
updating, 311
domainname command, 120
domains
definition of, 26
NIS, 31
done reserved word, Bash, 628
dosfsck command, 120
dot (.)
end message, mailx, 267
match single character, 655
read and execute file command, 620
double quotes ("...") enclosing special
characters, 601
down command, gdb, 164
downloading files from
Internet, 474–480
dp (dt) command, mailx, 270
dpkg command, Debian, 583–588
(see also Debian Package Manager)
dpkg-architecture script, Debian, 568
dpkg-buildpackage script, Debian, 568
dpkg-checkbuilddeps script,
Debian, 568
dpkg-deb command, Debian, 544,
588–590
dpkg-distaddfile script, Debian, 568
dpkg-divert script, Debian, 568
dpkg-genchanges script, Debian, 568
dpkg-gencontrol script, Debian, 568
dpkg-name script, Debian, 568
dpkg-parsechangelog script,
Debian, 568
dpkg-preconfigure script, Debian, 568
dpkg-query command, Debian, 590
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888 | Index
dpkg-reconfigure script, Debian, 568
dpkg-scanpackages script, Debian, 568
dpkg-shlibdeps script, Debian, 568
dpkg-source script, Debian, 569
dpkg-split command, Debian, 591
dpkg-statoverride script, Debian, 569
DSA identities, adding to authentication
agent, 409
dselect command, Debian, 544,
592–594
du command, 120
dual booting, 504, 505, 536–539
dump command, 122–123
dump command, GRUB, 531
dump command, svnadmin, 795
dumpe2fs command, 124
dumpiso command, 124
dumpkeys command, 124
dvdrecord command, 125
DVDs
commands for, list of, 9
ejecting, 128
recording, 125, 484–488
E
e command, sed, 716, 719
\E escape character, pattern
matching, 657
\E escape sequence, 601
\e escape character, pattern
matching, 657
\e escape sequence, 601, 612
e2fsck command, 125
e2image command, 126
e2label command, 127
EasyBCD software, 536
echo command, 127
echo command, Bash, 628
ed editor, metacharacters supported
by, 657
edit command, ex, 699
edit commands, vi, 687
edit (e) command, mailx, 270
EDITOR built-in variable, 609
editors (see ed editor; Emacs editor; ex
editor; sed editor; vi editor;
vim editor)
edquota command, 127
EGP (Exterior Gateway Protocol), 25
egrep command, 128, 657
eject command, 128
elevator algorithm, setting latency
for, 130
ELF (Executable and Linking Format)
object files, 351
elvis editor, 677
elvtune command, 130
EMACS built-in variable, 609
emacs command, 663
Emacs editor, 130, 661–676
commands
buffer-manipulation, 666
capitalization, 666
centering, 668
completions for, 662
cursor-movement, 664
deletion, 664
file-handling, 663
help, 663, 668, 669
indentation, 667
jobs, 667
list of, alphabetic by
keystroke, 669–672
list of, alphabetic by
name, 672–676
list of, most important, 663
listing, 663
macro, 668
paragraph, 665
region, 665
search, 665
shell, 667
stopping, 665
transposition, 665
undoing, 665
windows, 666
word-abbreviation, 666
Ctrl key notation (C-), 662
file buffers in, 662
invoking, 663
kill and yank (cut and paste) in, 662
mark location in, 662
Meta key notation (M-), 662
modes in, 661
point (cursor) location in, 662
windows in, 662
embed command, GRUB, 532
embedded versions of Linux, 3
enable command, 130
enable command, Bash, 629
encoding, base64, 59
Download at WoweBook.Com
Index | 889
encryption and decryption with GNU
Privacy Guard, 173–177
(see also security)
endscript command, logrotate, 254
Enter key, print next line command in
ex, 710
ENV built-in variable, 609
env command, 130
environment, displaying, 130
environment variables
printing, 334
setting, 130
substituting in shell string or
script, 131
envsubst command, 131
equals sign (=)
assignment operator, 732
command in sed, 716, 717
print line number command in
ex, 710
esac reserved word, Bash, 629
escape sequences, 601
gawk, 733
pattern matching, 656
ESX management client, for
VMware, 862
ESX server commands, for
VMware, 864–873
esxcfg-firewall command, VMware, 864
esxcfg-nics command, VMware, 867
esxcfg-vswif command, VMware, 865
esxcfg-vswitch command, VMware, 866
esxtop command, VMware, 867
etags command, 131
EUID built-in variable, 609
eval command, Bash, 629
ex editor, 132, 677, 678–680, 696–710
command options, 697
command syntax, 696
command-line options, 678–680
commands, 697–710
exiting, 681
invoking, 680, 696
line addresses in, 696, 710
pattern matching metacharacters
supported by, 657
examples in this book, using, xix
exclamation point (!)
execute command in ex, 709
execute command, mailx, 269
history expansion character, 614
logical negation operator, 732
negating pipeline, 619
NOT operator for commands, 602
preceding commands in ftp, 149
exclamation point, equal (!=) not equal
operator, 732
exclamation point, parentheses (!()) in
filename, 600
exclamation point, tilde (!~) match
negation of regular
expression, 732
exec command, Bash, 630
Executable and Linking Format (ELF)
object files, 351
executable files, compressing, 190
exit command, Bash, 630
exit command, gawk, 740
exit (ex, x) command, mailx, 270
exp() function, gawk, 740
expand command, 132
exponentiation operator (^ or **), 732
export command, Bash, 630
export command, svn, 775
expr command, 133–135
expressions, evaluating, 133–135, 443,
620, 647–650
ext2 filesystem
checking and repairing, 125
debugging, 107–110
formatting devices as, 288–290
label for, displaying, 127
printing block and superblock
information, 124
resizing, 356
storing disaster recovery data
for, 126
tuning parameters of, 457–460
ext3 filesystem, 16
debugging, 107–110
formatting devices as, 291
printing block and superblock
information, 124
extended Internet services
daemon, 490–493
extended regular expressions, searching
with, 128
Extensible Filesystem (see XFS)
extension command, logrotate, 254
extension() function, gawk, 740
Exterior Gateway Protocol (EGP), 25
eXternal Data Representation (XDR), 32
Download at WoweBook.Com
890 | Index
F
\f form feed escape sequence, 715, 733,
601
factor command, 135
fallback command, GRUB, 522
false command, 135
false command, Bash, 631
Fast Lexical Analyzer Generator, 143
FAT filesystem, 16
fc command, Bash, 614, 631
fc-cache command, 135
FCEDIT built-in variable, 609
fc-list command, 136
fdisk command, 136
fetch command, git, 822
fflush() function, gawk, 740
fg command, Bash, 631
fgconsole command, 137
fgrep command, 137
fi reserved word, Bash, 632
field reference ($), gawk, 732
FIFO pipes, creating, 292
FIGNORE built-in variable, 609
file command, 137
file command, ex, 700
file (fi) command, mailx, 270
file inclusion, gawk, 736
filenames
checking validity of, 326
database of, searching, 250
metacharacters for, 599
temporary, 293
validity and portability of, 326
files
access mode for, checking, 34
access permissions for, changing, 80
attributes of, changing, 77
attributes of, listing, 263
backing up, 122–123
base64 encoding or decoding, 59
byte count for, 473
classifying, 137
columns in, removing, 86
comparing, 85, 113–116
comparing and finding differences
between, 384
comparing lines common to, 86
compressing, 191
compressing and decompressing, 65
computing or checking MD5
checksums for, 285
concatenating, 68
conditions of, testing for, 647
converting into tables for parsing, 64
converting to alternate character
encoding, 203
converting to tables, 493
copying, 87–89
copying and converting format
of, 105
copying or restoring from
archives, 431–437
copying securely, 378
copying to or from remote
systems, 347
creation mask for, displaying or
setting, 652
deleting, 361
deleting files older than a specific
access time, 447
displaying in hex, octal, decimal, or
ASCII, 196
displaying one screen at a
time, 235–242, 295
downloading from Internet, 474–480
dumping, in octal format by
default, 319–322
executable, compressing, 190
formatting into columns, 86
group for, changing, 78
line count for, 473
linking, 247
locating, 480
maintaining in archives, 47
management of, commands for, 8,
663
merging, 286
merging corresponding lines of, 323
moving or renaming, 302–303
overwriting, to make contents
unrecoverable, 400
ownership of, changing, 82
paginating, suitable for
printing, 332–334
paging through, 235–242, 295
paging, turning off, 427
printing, 258
printing first few lines of, 196
printing last ten lines of, 430
printing lines in reverse order, 429
processes using, identifying, 154
Download at WoweBook.Com
Index | 891
recompiling and relinking based on
dependencies, 275–281
reformatting to a specific width, 144,
145
remote file distribution, 348–350
removing by unlinking, 464
removing columns or fields
from, 102
removing duplicate adjacent lines
in, 463
renaming, 354
restoring from backup, 357–359
reversing characters in each line
of, 359
searching, 137
searching for files meeting specific
conditions, 139–143
searching for printable strings
in, 418
searching for strings at beginning of
lines, 256
searching with extended regular
expressions, 128
separating into context-based
sections, 99
sorted, joining, 226
sorting lines of, 404
sorting strings in, 457
splitting into equal-sized
segments, 405
swapping, turning off, 427
transferring to and from remote
sites, 148–153, 244–247, 398
unchanged, verifying, 285
uncompressing, 190
updating access and modification
times to current time, 452
updating across a network, 368–374
word count for, 473
(see also directories; paths)
filesystem checker, for MS-DOS
filesystems, 120
filesystem types, 16
filesystems, 16
checking and repairing, 125, 147
commands for, list of, 17
creating on a device, 291
debugging, 107–110
displaying contents of, 111
ISO9660/Joliet/HFS,
generating, 165–173, 292
mounting, 297–299, 300
quotas, editing, 127
quotas for, enforcing, 346
quotas for, turning off enforcement
of, 347
unmounting, 461
writing buffers to disk, 428
(see also NFS)
find command, 139–143
find command, GRUB, 532
firewalls, 28
book about, 29
rules, printing, 223
rules, restoring, 222
firstaction command, logrotate, 254
fixmbr command, 506
flex command, 143
floppy disks, ejecting, 128
fmt command, 144
fold command, 145
fold command, ex, 700
foldclose command, ex, 700
folder (fold) command, mailx, 270
folders command, mailx, 270
foldopen command, ex, 700
font conventions used in this book, xx
font information caches, creating, 135
fonts, listing, 136
for command, Bash, 632
for command, gawk, 740, 741
foreground, moving job to, 631
form command, ftp, 150
formail command, 145–147
forward (fwd) command, mailx, 270
frame command, gdb, 164
free command, 147
free disk space, determining, 112
Free Software Foundation (see FSF)
Friedl, Jeffrey E.F. (Mastering Regular
Expressions), 654
from (f) command, mailx, 270
fsck command, 147
fsck.ext2 command, 125
FSF (Free Software Foundation), 6
fstest command, GRUB, 532
ftp command, 148–153
(see also sftp command)
ftpd command, 153
FUNCNAME built-in variable, 609
function command, Bash, 633
function command, gawk, 741
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892 | Index
functions, 605
declaring, 633
defining, 637
deleting, 653
exiting and returning status
from, 640
listing for source file, 131
overloading, decoding symbols
for, 67
source and line number for, 622
user-defined, gawk, 734
fuser command, 154
G
G command, sed, 716, 719
g command, sed, 716, 719
g++ compiler, 155
gateways, 25
gawk command, 155
gawk language, 726–747
array assignment, 733
built-in variables, 731
command-line options for, 728–729
command-line syntax for, 727
commands for, 737–746
coprocesses,735
escape sequences, 733
file inclusion for, 736
functions for, 737–746
hexadecimal constants in, 734
implementation limits of, 737
internationalization for, 736
invoking, 727
octal constants in, 734
operators, 732
output redirection, 746
pattern matching metacharacters
supported by, 657
patterns in, 729, 730
procedures in, 729, 730
profiling, 735
sockets, 735
user-defined functions, 734
variable assignment, 732
gc command, git, 822
gcc compiler, 156–163
gdb debugger, 163–165
General Public License (see GPL)
genisoimage command, 165–173
gensub() function, gawk, 741
geometry command, GRUB, 532
get command, ftp, 150
getent command, 173
getkeycodes command, 173
getline command, gawk, 741
getopts command, Bash, 633
getpwnam() function, 599
getpwuid() function, 599
gettext, GNU, 736
GhostScript, 189
git command, 811–836
add subcommand, 812
archive subcommand, 813
bisect subcommand, 814–815
branch subcommand, 815
checkout subcommand, 816
cherry-pick subcommand, 817
clean subcommand, 818
clone subcommand, 818
commit subcommand, 819
config subcommand, 820
diff subcommand, 821
fetch subcommand, 822
gc subcommand, 822
gitk subcommand, 823
grep subcommand, 823
help subcommand, 812
init subcommand, 824
log subcommand, 824
merge subcommand, 826
mv subcommand, 827
pull subcommand, 827
push subcommand, 828
rebase subcommand, 829
reflog subcommand, 830
remote subcommand, 831
reset subcommand, 832
revert subcommand, 833
rm subcommand, 833
stash subcommand, 834
status subcommand, 834
tag subcommand, 835
git daemon, 811
git shell, 811
Git version control system, 753,
805–836
branches in, 806, 815
merging, 826, 827
pushing, 828
tracking changes to, 830
Download at WoweBook.Com
Index | 893
checking in (committing) files, 806,
809, 819
cherry-picking commits, 817, 829
finding problem in, 814–815
referring to commits, 806–808
remotely, 822
reversing, 833
searching commits, 823
testing results of, 834
undoing, 832
checking out files, 806, 809, 816
command line for, 811
configuring, 820
differences, generating, 821
help for, 812
history, displaying, 823, 824
hosting projects, 811
index for, 806
adding or updating files in, 812
removing files from, 833
remotes for, 831
repositories for, 805, 806
cloning, 818
creating, 810, 824
creating archive from, 813
packing, 822
subcommands for, 812–836
tags for, 807, 835
uncommitted changes, working
with, 834
user name and email for, 808
working tree for, 806
cleaning, 818
removing files from, 833
github.com service, 811
gitk command, git, 823
Gitorious tool, 811
Gitosis tool, 811
glob command, ftp, 150
global command, ex, 700
GLOBIGNORE built-in variable, 609
GNOME desktop, 7
GNU Arch system, 753
GNU awk (see gawk language)
GNU Emacs Pocket Reference
(Cameron), 654
GNU Emacs (see Emacs editor)
GNU gettext, 736
GNU makefiles, creating from template
files, 55
GNU Privacy Guard
application, 173–177
GNU project, 3
GNU sed editor (see sed editor)
GNU utilities documentation, website
for, xvii
GNU/Linux, 1
(see also Linux)
good (go) command, mailx, 270
gpasswd command, 173
gpg command, 173–177
gpgsplit command, 177
gpgv command, 178
GPL (General Public License), 6
gpm command, 178–180
gprof command, 181–182
GRand Unified Bootloader (see GRUB)
graph character class, 600, 656
graphical desktop environments for
Linux, 4
graphical tools for Linux, 4
greater than (>) operator, 620
grep command, 182–185, 657
grep command, git, 823
groff command, 185–187
group ID, displaying information
about, 204
groupadd command, 187
groupdel command, 188
groupinfo command, yum, 548
groupinstall command, yum, 548
grouplist command, yum, 548
groupmod command, 188
groupremove command, yum, 548
groups
changing for files, 78
changing for user, 308
creating, 187
creating shadowed groups from, 189
listing for users, 188
managing, 173
modifying, 188
removing, 188
removing corrupt and duplicate
entries in, 188
space allowed on disk for, 344
GROUPS built-in variable, 609
groups command, 188
grpck command, 188
grpconv command, 189
grub command, GRUB, 519, 523
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894 | Index
GRUB (GRand Unified
Bootloader), 504, 516–536
boot CD for, 519
boot floppy for, 519
commands for, 525–536
configuration file, 521–523, 539, 541
device map, 518
installation stages, 517
installing, 518–521
menu interface, 523
naming conventions, 517
shell, 523–525
grub-install shell script, 518, 520
grub-md5-crypt command, GRUB, 522
gs command, 189
gsub() function, gawk, 741
gunzip command, 190
gzexe command, 190
gzip command, 191
H
H command, sed, 716, 720
h command, sed, 716, 720
H hostname escape sequence, 612
\h hostname escape sequence, 612
halt command, 192
halt command, GRUB, 532
hard drive
parameters for, reading or
setting, 192–195
partitioning, 75, 136
hard links, 248
hardware
commands for, list of, 15
performance improvements on, 3
supported by Linux, 3
hardware clock, reading or setting, 200
hash command, Bash, 633
hash command, ftp, 150
hash sign (#)
preceding comments, 619
preceding comments in gawk, 738
preceding comments in LILO
configuration file, 507
preceding comments in sed
scripts, 717
hdparm command, 192–195
head command, 196
header for packages, 552
headers (h) command, mailx, 270
headers+ (h+) command, mailx, 270
headers- (h-) command, mailx, 270
Hello Protocol, 25
help command, Bash, 634
help command (C-h), Emacs, 663
help command, ftp, 150
help command, git, 812
help command, GRUB, 532
help command, ip, 212
help command, mailx, 270
help command, svn, 776
help command, svnadmin, 796
help command, svnlook, 801
help command, xm, 847
help command, yum, 549
help commands, Emacs, 663, 668, 669
hexadecimal constants, gawk, 734
hexadecimal format
displaying files in, 196
printing host ID in, 198
hexdump command, 196
HFS filesystem, generating, 165–173,
292
hiddenmenu command, GRUB, 522
hide command, ex, 700
hide command, GRUB, 527
histchars built-in variable, 611
HISTCMD built-in variable, 607, 609
HISTCONTROL built-in variable, 610
HISTFILE built-in variable, 610
HISTFILESIZE built-in variable, 610
HISTIGNORE built-in variable, 610
history command, Bash, 634
history command, svnlook, 801
history expansion character (!), 614
history of commands, 614–617, 631,
634
HISTSIZE built-in variable, 610
HISTTIMEFORMAT built-in
variable, 610
hoclock command, 200
hold (ho) command, mailx, 270
hold space, sed, 712
HOME built-in variable, 610
home directories, determining, 599
host command, 26, 197
host ID, printing in hexadecimal
format, 198
HOSTFILE built-in variable, 610
hostid command, 198
HOSTNAME built-in variable, 609
hostname command, 198
Download at WoweBook.Com
Index | 895
hosts
information about, commands
for, 15
name of, displaying or setting, 198
printing information about, 197
HOSTTYPE built-in variable, 609
hotcopy command, svnadmin, 796
htdigest command, 199
hunspell command, 199
Hunt, Craig (TCP/IP Network
Administration), 23
hypervisor, 838, 839
(see also virtualization tools)
hyphen (-)
previous command, mailx, 269
subtraction operator, 732
unary minus operator, 732
hyphen, double (--) decrement
operator, 732
hyphen, equals sign (-=) assignment
operator, 732
hyphen(s) (- or --) preceding command
options, 33
I
i command, sed, 716, 720
IANA (Internet Assigned Numbers
Authority), 25
IBM Journaled Filesystem (see JFS)
ICANN (Internet Corporation for
Assigned Names and
Numbers), 27
icedax command, 200–203
ICMP (Internet Control Message
Protocol), 23
iconv command, 203
id command, 204
idle command, ftp, 150
IEEE 1394 packets, dumping, 124
if command, Bash, 635
if command, gawk, 742
ifconfig command, 27, 204–206
ifconfig command, GRUB, 527
ifempty command, logrotate, 254
IFS built-in variable, 610
igawk (inclusion gawk), 736
ignore command, mailx, 271
IGNOREEOF built-in variable, 610
image command, ftp, 149
imap command, mailx, 271
IMAP (Interactive Mail Access Protocol)
server daemon, 207
imapd command, 207
import command, svn, 776
impsprobe command, GRUB, 532
in operator, for array membership, 732
include command, logrotate, 254
@include directive, gawk, 736
inclusion gawk (igawk), 736
InCrEdible Digital Audio eXtractor (see
icedax command)
increment operator (++), 732
indentation commands, Emacs, 667
index, for Git, 806
adding or updating files in, 812
removing files from, 833
index() function, gawk, 742
inetd command, 207
info command, 207
info command, gdb, 164
info command, svn, 777
info command, svnlook, 801
info command, xm, 847
info command, yum, 549
init command, git, 824
init daemon, Upstart, 208
init program, 19
initctl command, 208
initrd command, GRUB, 522, 533, 541
inode, printing contents of, 413–416
input command, ftp, 151
INPUTRC built-in variable, 610
insert command, ex, 701
insert commands, vi, 686
insert mode, vi, 678, 681
insmod command, 209
install command, 210
install command, GRUB, 533
install command, yum, 549
installation, commands for, 16
int() function, gawk, 742
integer comparisons, testing for, 649
Intel Multiprocessor Specification, 532
Interactive Mail Access Protocol (IMAP)
server daemon, 207
interfaces, assigning to a device, 305
internationalization, gawk, 736
Internet Assigned Numbers Authority
(IANA), 25
Internet Control Message Protocol
(ICMP), 23
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896 | Index
Internet Corporation for Assigned
Names and Numbers
(ICANN), 27
Internet protocols, 21
Internet services daemon, 207
Internetworking with TCP/IP
(Comer), 23
interprocess communication (see IPC)
I/O latency for elevator algorithm, 130
I/O scheduling class, setting, 211
ionice command, 211
ioprobe command, GRUB, 534
IP address
contact for, finding, 483
definition of, 23–25
ip command, 27, 211–215
IP ports, mapping to RPC program
numbers, 329
IPC (interprocess communication)
removing message queues, 215
removing semaphore arrays, 215
removing shared memory
segments, 215
reporting on, 216
ipcrm command, 215
ipcs command, 216
iptables command, 29, 216–222
iptables (see netfilter)
iptables-restore command, 29, 222
iptables-save command, 29, 223
IPv4 addresses, 23
IPv6 addresses, 24
ISO9660 images
displaying content of, 223
displaying information about, 223
displaying length of, 224
verifying integrity of, 224
ISO9660/Joliet/HFS filesystem,
generating, 165–173, 292
isodump command, 223
isoinfo command, 223
isosize command, 224
isovfy command, 224
ispell command, 224
J
\j jobs escape sequence, 612
JFS (Journaled Filesystem), 16
job control, 617
Emacs commands for, 667
listing jobs, 635
moving job to foreground, 631
removing job from job list, 628
terminating jobs, 636
waiting for background jobs to
finish, 653
jobs command, Bash, 635
join command, 226
join command, ex, 701
Journaled Filesystem (see JFS)
jump command, gdb, 164
jumps command, ex, 701
junk (j) command, mailx, 271
K
k command, ex, 701
kbd_mode command, 227
kbdrate command, 227
kernel, 1
commands for, list of, 17
loading modules into, 209
messages, displaying, prioritizing,
and logging, 229
parameters, displaying or
modifying, 428
kernel command, GRUB, 522, 523, 534
Kernel-based Virtual Machine (see KVM
hypervisor)
keyboard
assigning keycode events to
scancodes, 393
driver translation tables, printing
information about, 124
mode for, printing or setting, 227
printing keycodes, scancodes, or
ASCII codes of keys
pressed, 399
rate, setting, 227
Unicode mode for, 463
keycodes
mapping table for, 173
printing, 399
keymaps, loading, 248
keys, authentication
gathering public and private keys
from multiple, 411
generating, managing, and
converting, 410
holding private keys for public
authentication, 410
keyword substitutions, in source code
management system, 750
Download at WoweBook.Com
Index | 897
kill and yank (cut and paste),
Emacs, 662
kill command, 227
kill command, Bash, 636
kill command, gdb, 164
killall command, 228
klogd command, 229
Korn shell, 596
ksh shell, 596
KVM hypervisor, 849
building guest systems, 850
changing virtual machine
configurations, 844
device interfaces for, 843
graphic interface for, 842
installing, 849
libvirt used with (see libvirt
virtualization API)
managing virtual systems, 842
QEMU used with, 849
website for, 837
L
\l basename escape sequence, 612
l command, sed, 716, 721
\L escape character, pattern
matching, 657
\l escape character, pattern
matching, 657
LANG built-in variable, 610
last command, 230
lastaction command, logrotate, 254
lastb command, 230
lastlog command, 231
latency in elevator algorithm,
setting, 130
LC_ALL built-in variable, 610
LC_COLLATE built-in variable, 610
LC_CTYPE built-in variable, 610
lcd command, ftp, 150
LC_MESSAGES built-in variable, 610
LC_NUMERIC built-in variable, 610
ld command, 231–234
ldconfig command, 234
ldd command, 235
Learning GNU Emacs (Cameron
et al.), 654, 662
Learning Red Hat Enterprise Linux and
Fedora (McCarty), 5
Learning the bash Shell (Newham), 597
Learning the Unix Operating System
(Peek; Todino-Gonguet;
Strang), xvii
LED flag settings, displaying or
changing, 393
left angle bracket (<) less than
operator, 620, 732
left angle bracket, equals sign (<=) less
than or equal operator, 732
left command, ex, 701
Lempel-Ziv coding (LZ77), compressing
files using, 191
length() function, gawk, 742
less command, 235–244
less than operator (<), 620
lesskey command, 242–244
let command, Bash, 613, 636
lexical analysis program,
generating, 143
lftp command, 244–247
lftpget command, 247
libraries
examining and updating, 234
shared, displaying program
requirements for, 235
libvirt virtualization API, 839, 850–861
connection URIs for hypervisor, 850
networking for, 851
remote GUI control for, 851
virsh commands, 852–856
virt-clone command, 856
virt-image command, 857
virt-install command, 858–861
virt-manager command, 861
virt-viewer command, 861
website for, 837, 850
XML configuration files for, 850
licenses for Linux, 6
(see also GPL)
lilo command, 506, 514–516
LILO (Linux Loader), 504, 506–516
boot errors, 516
configuration file, 506, 507–514,
539, 541
global options, 508–511
image options, 512
kernel options, 513
rescue CD for, making, 506
line-edit mode, Bash, 614
LINENO built-in variable, 607
LINES built-in variable, 610
Download at WoweBook.Com
898 | Index
link command, 247
link set command, ip, 212
link show command, ip, 212
Linux
benefits of, 2
commands, 3, 5
compared to Unix, 1
as desktop system, 3
distributions of, 3
embedded versions of, 3
hardware supported by, 3
history of, 1
installing, book about, xvii
licenses for, 6
performance improvements by, 3
source code for, 6
starting, 19
stopping, 19
support for, xviii, 3
(see also shells)
Linux Documentation Project
website, xvii
Linux Gazette website, xvii
Linux Insider website, xvii
Linux iptables Pocket Reference
(Purdy), 29
Linux Journal, xviii
Linux Loader (see LILO)
Linux Magazine, xviii
Linux Network Administrator’s Guide
(Bautts; Dawson; Purdy), xvii,
23, 29
Linux Second Extended Filesystem (see
ext2 filesystem)
Linux Security website, xvii
Linux Third Extended Filesystem (see
ext3 filesystem)
Linux Today website, xvii
Linux Weekly News website, xvii
list command, ex, 701
list command, gdb, 164
list command, mailx, 271
list command, svn, 778
list command, xm, 847
list command, yum, 549
list-dblogs command, svnadmin, 796
list-unused-dblogs command,
svnadmin, 796
ln command, 247
load command, svnadmin, 796
loaded modules, listing, 264
loadkeys command, 248
local command, Bash, 636
local variables, Bash, 636
locale command, 249
locale settings, printing, 249
localinstall command, yum, 549
localizing gawk programs, 736
localupdate command, yum, 550
locate command, 250
lock command, GRUB, 522, 534
lock command, svn, 779
lock command, svnlook, 802
lockfile command, 251
log command, git, 824
log command, svn, 779
log command, svnlook, 802
log command, xm, 847
log() function, gawk, 742
log message, for source code
management system, 750
logger command, 252
logging in
to remote host, 360
to remote system, securely, 406–409
to tty port, 38
logging (see system logging)
logical AND operator (&&), 620
logical negation operator (!), 732
logical operators, 620
logical OR operator (||), 620
login shell
changing, 84
exiting, 636
logins
bad attempts at, displaying, 230
for system accounts, displaying times
of, 231
most recent, printing, 230
printing list of, 467
printing summary of, 471
logout command, Bash, 636
logrotate command, 253–256
look command, 256
loop devices, setting up and
controlling, 256
loops
exiting from, 622
for command, 632
skipping remaining commands in, 626
until command, 653
while command, 653
Download at WoweBook.Com
Index | 899
losetup command, 256
lost+found directory, creating, 292
lower character class, 600, 656
lpadmin command, 256
lpinfo command, 258
lpmove command, 258
lpq command, 258
lpr command, 258
lprm command, 259
lpstat command, 260
ls command, 118, 260–263
ls command, ftp, 150
lsattr command, 263
lshift() function, gawk, 742
lslocks command, svnadmin, 797
lsmod command, 264
lspci command, 263
lstxns command, svnadmin, 797
lsusb command, 264
LZ77 (Lempel-Ziv coding), compressing
files using, 191
M
m4 command, 264
m4 macros
combining into one file, 34
generating configuration script
from, 53
generating template of #define
statements from, 54
MAC address, for virtualization, 844
macdef command, ftp, 150
MACHTYPE built-in variable, 609
macro commands, Emacs, 668
macro commands, vi, 691
macro processor, 264
macros
executing in ftp, 149
in package spec file, 553
listing for source file, 131
magnetic tape drive, controlling, 300
mail
aliases database, rebuilding, 308
aliases, printing, 334
commands for, list of, 16
reading or sending, 265, 266–275
remote mail, receiving, 362
sendmail queue, listing messages
in, 265
sendmail statistics, reporting, 266
MAIL built-in variable, 610
mail command, 265
mail command, logrotate, 254
mail (m) command, mailx, 271
mail transfer agent (MTA), 385–392
mailbox format, filtering input
into, 145–147
MAILCHECK built-in variable, 610
mailfirst command, logrotate, 254
maillast command, logrotate, 254
MAILPATH built-in variable, 610
mailq command, 265
mailstats command, 266
mailx command, 266–275
make command, 275–281
makeactive command, GRUB, 534
makecache command, yum, 550
makedbm command, 281
makefiles
creating from template files, 55
executing, 275–281
makemap command, 282
man command, 283
Managing Projects with GNU Make
(Mecklenburg), 275
manpath command, 285
manual pages
displaying, 283
path to, determining, 285
searching for keyword, 480
searching short descriptions for
strings, 46
map command, ex, 701
map command, GRUB, 534
mapfile command, Bash, 637
maps, NIS, 31
mark command, ex, 702
mark location, Emacs, 662
marks command, ex, 702
masquerading, 29
master boot record (see MBR)
Mastering Regular Expressions
(Friedl), 654
match() function, gawk, 742
mbox command, mailx, 271
MBR (master boot record), 505
installing GRUB boot loader
on, 518, 520, 521
installing LILO boot loader on, 506
restoring, 506
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900 | Index
McCarty, Bill (Learning Red Hat
Enterprise Linux and
Fedora), 5
MD5 checksums for files, computing or
checking, 285
md5crypt command, GRUB, 522, 534
md5sum command, 285
mdelete command, ftp, 151
mdir command, ftp, 151
Mecklenburg, Robert (Managing
Projects with GNU
Make), 275
media (see CDs; DVDs)
memory maps, displaying for a
process, 329
memory usage, statistics about, 147
menu items, providing to user, 640
merge command, 286
merge command, git, 826
merge command, svn, 781
mergeinfo command, svn, 782
mesg command, 286
message queues, IPC, removing, 215
Meta key handling, displaying or
setting, 394
Meta key (M-), Emacs, 662
metacharacters in pattern
matching, 654–658
mget command, ftp, 151
MIDI files
playing, 44
reading and writing to ALSA
ports, 40
recording, 48
MIDI ports, connecting to route
events, 35
mirror command, lftp, 246
missingok command, logrotate, 254
mixer, ALSA
connecting to ALSA sound
card(s), 40
controlling, 41
mkdir command, 287
mkdir command, ftp, 151
mkdir command, svn, 782
mkdosfs command, 287
mke2fs command, 288–290
mkexrc command, ex, 702
mkfifo command, 291
mkfs command, 291
mkfs.ext3 command, 291
mkisofs command, 292
mkisofs command, GRUB, 519
mklost+found command, 292
mknod command, 292
mkrescue command, 506
mkswap command, 293
mktemp command, 293
mktime() function, gawk, 742
mls command, ftp, 151
mode command, ftp, 151
modinfo command, 294
modprobe command, 294
modtime command, ftp, 151
module command, GRUB, 534
modulenounzip command, GRUB, 534
modules
loading, 294
loading into kernel, 209
printing information about, 294
unloading, 362
modulus operator (%), 732
monotone system, 754
monthly command, logrotate, 254
more command, 295
mount command, 30, 297–299
mountd command, 300
mountd daemon, 30
mouse server for Linux
console, 178–180
move command, ex, 702
move command, svn, 783
move (mv) command, mailx, 271
movement commands, vi, 683–686
mt command, 300
MTA (mail transfer agent), 385–392
Multiboot Specification, 516
multiplication operator (*), 732
mv command, 302–303
mv command, git, 827
M-x Tab (command names list)
command, Emacs, 663
N
N command, sed, 717, 721
n command, sed, 716, 721
\n escape character, pattern
matching, 656, 657
\n newline escape sequence, 601, 715,
733, 612
name command, Bash, 637
Download at WoweBook.Com
Index | 901
name service, 26
named daemon, 26
named pipes (FIFO), making, 291
namei command, 304
nameif command, 305
nameserver, 26, 311
naming conventions
GRUB, 517
packages, 543
NAT (Network Address
Translation), 842
nc command, 305–306
neigh add command, ip, 212
neigh chg command, ip, 213
neigh del command, ip, 213
neigh flush command, ip, 213
neigh list command, ip, 213
neigh repl command, ip, 213
Net:Bridge package, 843
netcat command (see nc command)
netfilter (iptables), 29
books about, 29
filtering rules, configuring, 216–222
netstat command, 306
network, 21–22
administration, book about, xvii
commands for, list of, 18
configuring for virtualization, 842
confirming response of remote hosts
on, 327
devices, manipulating, 211–215
dumping headers and packets of
network traffic, 437–439
interface, configuring, 27, 204–206
packet capture files for, reading and
manipulating, 439
reading and writing data
across, 305–306
serial lines, attaching as network
interfaces, 403
status of, displaying, 306
TCP/IP administration, 21, 22–28
updating files across, 368–374
Windows-based, Linux server
supporting, 3
(see also NFS; NIS)
Network Address Translation
(NAT), 842
Network File System (see NFS)
Network Information System (see NIS)
new command, ex, 702
newaliases command, 308
newer command, ftp, 151
newgrp command, 308
Newham, Cameron (Learning the bash
Shell), 597
newline character, as word
separator, 601
newsgroups, xviii
newusers command, 308
next command, ex, 702
next command, gawk, 743
next command, gdb, 164
next (n) command, mailx, 271
nextfile command, gawk, 743
NFS (Network File System), 29
administering, 30
commands for, list of, 22
daemons, 30
exporting filesystems, 30
module, launching threads for, 308
mounting filesystems, 30
server, displaying information
about, 400
statistics on, printing, 309
nfsd command, 308
nfsd daemons, 30
nfstat command, 309
NIC names, finding contact for, 483
nice command, 309
NIS+, 31
NIS binder process, 494
NIS database
creating, 495
printing specific values in, 495
NIS dbm file, creating or dumping, 281
NIS map
forcing propagation of, 497
printing values of keys, 496
transferring from server to local
host, 500, 501
version of, determining, 497
NIS (Network Information System), 31
administering, 32
client, setting up, 32
commands for, list of, 22, 31
domain, setting or displaying name
of, 120
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902 | Index
NIS (continued)
domains, 31
login password for, changing, 496
maps, 31
password file, modifying, 496
server, setting up, 32
servers, 31
services, checking configuration
for, 499
user accounts, 32
NIS server, 498
hostname of, determining, 500
setting for ypbind command, 499
nlist command, ftp, 151
nm command, 310
nmap command, ftp, 151
nocompress command, logrotate, 255
nocopy command, logrotate, 255
nocopytruncate command,
logrotate, 255
nocreate command, logrotate, 255
nodelaycompress command,
logrotate, 255
nohlsearch command, ex, 703
nohup command, 311
nomail command, logrotate, 255
nomissingok command, logrotate, 255
noolddir command, logrotate, 255
nosharedscripts command,
logrotate, 255
NOT operator (!) for commands, 602
notifempty command, logrotate, 255
nroff command, formatting output
from, 85, 86
nslookup command, 311
nsupdate command, 311
ntrans command, ftp, 151
null command (:), 620
number command, ex, 703
numbers, printing in sequence, 393
nvi editor, 677
O
\o octal escape sequence, sed, 715
objcopy command, 313–317
objdump command, 317–319
object files
combining into executable object
module, 231–234
copying, 313–317
displaying information
about, 317–319
generating from assembly source
files, 50
removing symbols from, 419
size of, printing, 402
octal constants, gawk, 734
octal format, displaying files in, 196
od command, 319–322
olddir command, logrotate, 255
OLDPWD built-in variable, 607
online documentation, displaying, 207
only command, ex, 703
open command, ex, 703
open command, ftp, 152
OpenPGP-format messages, splitting
into packets, 177
OpenPGP-signed files, checking
signature of, 178
openvt command, 322
operating system, printing information
about, 461
operators
arithmetic, 613
comparison, 620
gawk, 732
logical, 620
OPTARG built-in variable, 607
OPTERR built-in variable, 610
OPTIND built-in variable, 607
or() function, gawk, 743
OR operator (||)
for commands, 602
for expressions, 620, 732
OSTYPE built-in variable, 609
output redirection, gawk, 746
ownership of files, changing, 82
P
P command, sed, 716, 717, 722
p command, sed, 722
package managers, 542–545
(see also APT; Debian Package
Manager; RPM; yum program)
Download at WoweBook.Com
Index | 903
package-cleanup plugin, yum, 551
packages, 542–595
Debian, 565–595
archive of, 566
cache for, managing, 569–571
files used by, 565
flags for, 567
generating, 574
managing, 575–590, 592–594
naming conventions for, 565
priorities of, 566
querying, 590
sorting records in, 579
sources for, adding, 571
splitting, 591
states of, 567
dependencies for, 543
naming conventions for, 543
RPM, 545–565
archive of, 552
building, 564–565
header for, 552
managing with rpm
command, 553–563
managing with yum, 545–552
repository of, 545
signature verification for, 552
spec file for, 552
signature verification for, 543
user privileges required for, 543
packets
IEEE394, dumping, 124
tracing path to host taken by, 454,
455
pager command, GRUB, 527
paragraph commands, Emacs, 665
paravirtualization, 839, 846, 864
parentheses ((...))
enclosing group of commands, 601,
602
enclosing group of regular
expressions, 656
partnew command, GRUB, 527
parttype command, GRUB, 528
passwd command, 322
password command, GRUB, 522, 528
passwords
changing, 83
created shadowed entries for, 344
creating or changing, 322
expirations for, changing, 76
information stored with,
changing, 78
removing corrupt or duplicate
entries, 343
paste command, 323
paste (yank), Emacs, 662
patch command, 324–326
patches, applying, 324–326
PATH built-in variable, 610
pathchk command, 326
paths
checking validity of, 326
following to terminal point, 304
for current working directory,
printing, 344
printing only leading directory
components from, 119
removing leading directory
components from, 59
pattern addressing, sed, 714–715
pattern matching, 155, 654–660
character classes in, 656
escape sequences in, 656
metacharacters in, 654–658
replacement patterns, 656
search patterns, 655
searching and replacing, examples
of, 659
searching, examples of, 658
searching files with extended regular
expressions, 128
searching files with regular
expressions, 182–185
pattern space, sed, 712
patterns, gawk, 729, 730
Patwardhan, Nathan (Perl in a
Nutshell), 654
pause command, GRUB, 535
pause command, xm, 848
pccardctl command, 327
PCI (Peripheral Component
Interconnect) devices,
listing, 263
PCMCIA sockets, controlling, 327
PDF (Portable Document Format)
language, interpreter for, 189
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904 | Index
Peek, Jerry (Learning the Unix
Operating System), xvii
percent sign (%)
modulus operator, 732
preceding job ID in commands, 617
reuse previous replacement
pattern, 657
percent sign, equals sign (%=)
assignment operator, 732
performance, Linux improving, 3
Peripheral Component Interconnect
(PCI) devices, listing, 263
Perl 5 Pocket Reference (Vromans), 654
Perl in a Nutshell (Patwardhan
et al.), 654
permuted indexes, 342
pgawk (profiling gawk), 735
pidof command, 327
Pilato, C. Michael (Version Control with
Subversion), 755
ping command, 327
pipe character (|), 601, 602
pipe (pi) command, mailx, 271
pipes
named pipes (FIFO), making, 291
negating result of, 619
PIPESTATUS built-in variable, 609
plugins for yum program, 551
plus, equals sign (+=) assignment
operator, 732
plus sign (+)
addition operator, 732
match one or more instances, 656
unary plus operator, 732
plus sign, double (++) increment
operator, 732
plus sign, parentheses (+()) in
filename, 600
pmap command, 329
PNM (Portable aNyMap) format,
writing images to, 376
point (cursor) location, Emacs, 662
Point-to-Point Protocol (PPP), 23, 28,
330–332
popd command, Bash, 637
Portable aNyMap (PNM) format,
writing images to, 376
Portable Document Format (PDF)
language, interpreter for, 189
portmap command, 329
portmap daemon, 30
POSIX notation, in Bash, 600, 602
POSIXLY_CORRECT built-in
variable, 610
postrotate command, logrotate, 255
PostScript language, interpreter for, 189
poweroff command, 330
PPID built-in variable, 607
PPP (Point-to-Point Protocol), 23, 28,
330–332
pppd command, 330–332
pppd daemon, 28
pr command, 332–334
#pragma implementation directive, 163
#pragma interface directive, 162
praliases command, 334
prerotate command, logrotate, 255
preserve command, ex, 703
preserve (pre) command, mailx, 271
previous command, ex, 703
prime factors, calculating, 135
print character class, 600, 656
print command, ex, 703
print command, gawk, 743, 746
print command, gdb, 164
print jobs
cancelling, 259
moving to a new destination, 258
Print (P) command, mailx, 271
print (p) command, mailx, 271
print queues
accepting, 34
CUPS, configuring, 256
displaying status of, 260
rejecting, 354
print scheduler, starting, 101
print spool queue, displaying
information about, 258
printenv command, 334
printer drivers, printing information
about, 258
printers
enabling, 130
printing information about, 258
tuning device parameters for, 460
printf command, 334
printf command, Bash, 638
printf() function, gawk, 743, 746
printing, commands for, 9, 18, 258
priority of processes, controlling, 355
privileges required for packages, 543
procedures, gawk, 729, 730
Download at WoweBook.Com
Index | 905
process IDs
determining for specific files or
filesystems, 154
displaying for programs, 327
processes
active, reporting on, 335–341
managing, commands for, 19
memory maps for, displaying, 329
most CPU-intensive, displaying
information about, 448–452
priority of, controlling, 355
real-time scheduling for,
changing, 83
terminating, 227, 636
terminating all processes, 228
processor affinity mask, retrieving or
setting, 437
profile data for an object,
displaying, 181–182
profiling, gawk, 735
program addresses, translating to
filenames and line
numbers, 37
programmable completion, 615–617,
624–626
programming
commands for, list of, 9
maintenance of, commands for, 10
(see also gawk language; source code
management systems)
prompt command, ftp, 152
prompt strings, 612
PROMPT_COMMAND built-in
variable, 610
propdel command, svn, 784–786
propedit command, svn, 784
properties, Subversion, 757
propget command, svn, 785
propget command, svnlook, 802
proplist command, svn, 785
proplist command, svnlook, 802
propset command, svn, 786
protocols, Internet, 21
provides command, yum, 550
proxy command, ftp, 152
ps command, 335–341
PS1 built-in variable, 610, 612
PS2 build-in variable, 612
PS2 built-in variable, 610
PS3 built-in variable, 610
PS4 built-in variable, 611, 612
pseudonyms (links) for files, 247
ptx command, 342
ptype command, gdb, 164
pull command, git, 827
punct character class, 600, 656
Purdy, Gregor
Linux iptables Pocket Reference, 29
Linux Network Administrator’s
Guide, xvii, 23, 29
push command, git, 828
pushd command, Bash, 638
put command, ex, 703
put command, ftp, 152
pwck command, 343
pwconv command, 344
PWD built-in variable, 607
pwd command, 344
pwd command, Bash, 638
pwd command, ftp, 152
pwd command, gdb, 164
python-vm-builder package, 850
Q
Q command, sed, 716, 722
q command, sed, 716, 722
qall command, ex, 703
QEMU, combining with KVM
hypervisor, 849
qemu-img tool, 845
question mark (?)
in filename, 599
help command, mailx, 269
match zero or one instance, 656
question mark, colon (?:) conditional
expression, 732
question mark, parentheses (?()) in
filename, 600
quit command, ex, 704
quit command, ftp, 149
quit command, gdb, 165
quit command, GRUB, 535
quit (q) command, mailx, 271
quota command, 344
quotacheck command, 345
quotaoff command, 347
quotaon command, 346
quotas
exceeding limit, sending messages to
users regarding, 472
setting, 394
Download at WoweBook.Com
906 | Index
quotastats command, 347
quote command, ftp, 152
quoting special characters in Bash, 600
R
\r carriage return escape sequence, 612,
715, 733
R command, sed, 716, 723
r command, sed, 716, 723
rand() function, gawk, 743
RANDOM built-in variable, 608
ranlib command, 347
rarp command, GRUB, 528
RARP (Reverse Address Resolution
Protocol), 23
rcp command, 347
RCS (Revision Control System), 752
rdate command, 348
rdist command, 348–350
rdistd command, 350
read command, Bash, 639
read command, ex, 704
read command, GRUB, 535
readcd command, 350
readelf command, 351
readline library, managing, 621
readlink command, 352
readom command, 352
readonly command, Bash, 640
real-time scheduling for processes,
changing, 83
rebase command, git, 829
reboot command, 354
reboot command, GRUB, 535
recover command, ex, 704
recover command, svnadmin, 797
Red Hat Package Manager (see RPM)
Red Hat Virtual Machine
Manager, 850–851
redirection of commands, 602–604
redo command, ex, 704
reflog command, git, 830
reget command, ftp, 152
region commands, Emacs, 665
Regular Expression Pocket Reference
(Stubblebine), 654
regular expressions, 654
(see also pattern matching)
reinstall command, yum, 550
reject command, 354
relational operators, gawk, 732
release of package, 543
remainder operator (%), 732
remote command, git, 831
remote file distribution, 348–350
remote host, logging in to, 360
remote hosts, confirming responses
of, 327
Remote Procedural Call (RPC) language,
generating C code from, 366
Remote Procedure Call (RPC), 32
remote procedure call (RPC) activity,
statistics on, 309
remote shell server, 367
remote systems, accessing, 441
remotehelp command, ftp, 152
remotestatus command, ftp, 152
remove command, yum, 550
remove (rem) command, mailx, 271
rename command, 354
rename command, ftp, 152
rename (ren) command, mailx, 271
renice command, 355
replacement patterns, metacharacters
for, 656
replacing, with pattern matching, 659
REPLY built-in variable, 608
Reply (R) command, mailx, 271
reply (r) command, mailx, 271
replyall command, mailx, 271
repoclosure plugin, yum, 551
repodiff plugin, yum, 551
repo-graph plugin, yum, 551
repolist command, yum, 550
repomanage plugin, yum, 551
repo.or.cz hosting service, 811
repoquery plugin, yum, 551
repo-rss plugin, yum, 551
repositories, for Git, 805, 806
cloning, 818
creating, 810, 824
creating archive from, 813
packing, 822
repository, for source code management
system, 749, 755
repository, of RPM packages, 545
reposync plugin, yum, 552
repotrack plugin, yum, 552
repquota command, 355
reset command, 356
reset command, ftp, 152
reset command, git, 832
Download at WoweBook.Com
Index | 907
resize command, ex, 704
resize2fs command, 356
resolve command, svn, 787
resolved command, svn, 787
resolvedep command, yum, 550
resolver, 26
resource limits, printing, 652
resources (see books and publications;
website resources)
respond command, mailx, 271
restart command, ftp, 152
restore command, 357–359
restricted shells, 619
retain command, mailx, 271
return command, Bash, 640
return command, gawk, 744
rev command, 359
Reverse Address Resolution Protocol
(RARP), 23
reverse-search command, gdb, 165
revert command, git, 833
revert command, svn, 788
Revision Control System (RCS), 752
revision of package, 543
rewind command, ex, 704
rexec command, 359
rexecd command, 360
right angle bracket (>)
greater than operator, 620, 732
output redirection, 746
right angle bracket, double (>>) append
output, 746
right angle bracket, equals sign (>=)
greater than or equal
operator, 732
right angle brackets (> or >>) in cat
command, 68
right command, ex, 704
RIP (Routing Information Protocol), 25
rlogin command, 360
rlogind command, 360
rm command, 361
rm command, git, 833
rmail command, 362
rmdir command, 362
rmdir command, ftp, 152
rmlocks command, svnadmin, 797
rmmod command, 362
rmtxns command, svnadmin, 797
rndc command, 363
Robbins, Arnold (Classic Shell
Scripting), 597
root command, GRUB, 535
root directory, changing, 83
rootnoverify command, GRUB, 535
rotate command, logrotate, 255
route add command, ip, 213
route chg command, ip, 213
route command, 364–365
route del command, ip, 213
route events, connecting MIDI ports
to, 35
route list command, ip, 213
route repl command, ip, 213
routed daemon, 26
routing, controlling, 211–215
routing daemons, 25
Routing Information Protocol (RIP), 25
routing tables, 26, 364–365
RPC (Remote Procedure Call), 32
activity of, statistics on, 309
generating C code from, 366
program numbers
mapping to IP ports, 329
mapping to universal
addresses, 365
reporting information for
programs, 366
rpcbind command, 365
rpcbind daemon, 30
rpcgen command, 366
rpcinfo command, 366
rpm command, 367, 552–563
RPM (Red Hat Package Manager), 544,
552–565
database rebuild options for, 562
examples of, 563
freshen options for, 555
install options for, 554
naming conventions for, 543
options for, 554–563
package-query options for, 559
package-selection options
for, 557–559
query options for, 557
rpm command syntax for, 553
rpmbuild command syntax and
options for, 564–565
signature-check options for, 562
uninstall options for, 560
upgrade options for, 554
verify options for, 560
rpmbuild command, RPM, 552,
564–565
Download at WoweBook.Com
908 | Index
RSA identities, adding to authentication
agent, 409
rsh command, 367
rshd command, 367
rshift() function, gawk, 744
rsync command, 368–374
rsyslogd command, 375
run command, gdb, 165
runique command, ftp, 152
runlevel command, 376
runlevels, 19
changing, 440
specifying services to be run at, 79
Running Linux (Dalheimer;
Welsh), xvii, 4
S
s command, sed, 716, 723
\s shell escape sequence, 612
sandbox, for source code management
system, 750, 756
SANE (Scanner Access Now Easy), 376
sane-find-scanner command, 376
save (s) command, mailx, 272
savedefault command, GRUB, 535
saveignore command, mailx, 272
saveretain command, mailx, 272
saving files, vi, 688
sbnext command, ex, 705
sbuffer command, ex, 705
scancodes, printing, 399
scancode-to-keycode mapping
table, 173
scanimage command, 376
Scanner Access Now Easy (SANE)
detecting scanners, 376
scanners
detecting by SANE, 376
reading images from, 376
SCCS (Source Code Control
System), 752
scheduling commands, 20
scp command, 378
screen command, 379–384
script command, 384
scripts in package spec file, 553
SCSI scanners, detecting by SANE, 376
sdiff command, 384
search command, gdb, 165
search command, yum, 550
search commands, Emacs, 665
search patterns, metacharacters for, 655
searching
commands for, list of, 10
with pattern matching, 658, 659
Second Extended Filesystem (see ext2
filesystem)
SECONDS built-in variable, 608
secure copying of files, 378
secure login to remote system, 406–409
security
commands for, list of, 18
encryption with GNU Privacy
Guard, 173–177
website about, xvii
(see also authentication; signature
verification)
sed command, 385
sed editor, 711–725
branching commands, 717
command syntax for, 713
editing commands, 716
hold space for, 712
input for, 711, 712, 716, 717
input/output commands, 716
invoking, 712
line information commands, 716
multiline input commands, 717
options for, 712
pattern addressing, 714–715
pattern matching metacharacters
supported by, 657
pattern space for, 712
yanking and putting commands, 716
seen command, mailx, 272
select command, Bash, 640
semaphore arrays, IPC, removing, 215
semaphore files, creating, 251
semicolon (;) command separator, 601,
602
sendmail command, 385–392
database maps for, creating, 282
mail aliases for, printing, 334
sendport command, ftp, 152
sensor chips, displaying readings and
configuring, 392
sensors command, 392
seq command, 393
serial command, GRUB, 528
Serial Line IP (SLIP), 28
serial lines, attaching as network
interfaces, 403
Download at WoweBook.Com
Index | 909
servers, NIS, 31, 32
services, managing runlevels for, 79
set command, Bash, 641–643
set command, ex, 705
set command, lftp, 247
:set command, vi, 692–696
set (se) command, mailx, 272
set variable command, gdb, 165
setkey command, GRUB, 529
setkeycodes command, 393
setleds command, 393
setlog command, svnadmin, 798
setmetamode command, 394
setquota command, 394
setrevprop command, svnadmin, 798
setsid command, 395
setterm command, 395–397
setup command, GRUB, 521, 535
setuuid command, svnadmin, 798
sftp command, 398
SGI Extensible Filesystem (see XFS)
sh shell, 399, 596, 597
SHA1 checksums, computing or
checking, 399
sha1sum command, 399
shadow files
creating or updating from
passwords, 344
removing corrupt and duplicate
entries in, 188, 343
shadowed groups, creating, 189
shared memory segments, IPC,
removing, 215
sharedscripts command, logrotate, 255
SHELL built-in variable, 611
shell command, ex, 705
shell command, yum, 550
shell commands, Emacs, 667
shell conditions, testing for, 649
#!shell directive, 620
shell scripts
comments in, 619
exiting, 630
shell (sh) command, mailx, 272
SHELLOPTS built-in variable, 609
shells, 5, 596
changing, 84
creating with effective user ID, 425
invoking in a script, 620
programming, commands for, 11
starting on remote host, 367
(see also Bash shell)
shift command, Bash, 643
SHLVL built-in variable, 609
shopt command, Bash, 643–647
show (Sh) command, mailx, 272
showkey command, 399
showmount command, 30, 400
shred command, 400
shutdown command, 401
shutdown command, xm, 848
shutting down the system, 192, 330,
354, 401
signal command, gdb, 165
signature verification
with GNU Privacy Guard, 173–177
of OpenPGP-signed files, 178
of packages, 543, 552
Simple Mail Transport Protocol
(SMTP), 23
Simple Network Management Protocol
(SNMP), 23
sin() function, gawk, 744
single quotes ('...') enclosing special
characters, 601
site command, ftp, 153
size command, 402
size command, ftp, 153
size command, logrotate, 255
size command, mailx, 272
slab cache information, displaying in
real time, 402
slabtop command, 402
slash (/) division operator, 732
slash, equals sign (/=) assignment
operator, 732
Slashdot website, xvii
slashes (/.../) enclosing pattern address
in sed, 714
slattach command, 403
sleep command, 403
sleep for a specified time, 467
SLIP (Serial Line IP), 28
SMTP (Simple Mail Transport
Protocol), 23
snext command, ex, 705
SNMP (Simple Network Management
Protocol), 23
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910 | Index
sockets, gawk language, 735
sort command, 404
sorted files, joining, 226
sorting strings in a file, 457
sound cards, ALSA
advanced configuration settings
for, 39
connecting to ALSA mixer, 40
sound files
playing, 43
recording, 48
recording to CDs, 69–71, 75,
484–488
recording to DVDs, 125, 484–488
Source Code Control System
(SCCS), 752
source code for Linux, 6
source code management
systems, 749–754
checking files in or out, 750
client/server model for, 751
Codeville, 753
copy, modify, merge model for, 751
CSSC, 754
CVS, 752
Git (see Git Version Control System)
GNU Arch, 753
locking model for, 751
merging changes in, 750
monotone system, 754
RCS, 752
SCCS, 752
Subversion (see Subversion Version
Control System)
source command, Bash, 647
source command, ex, 705
source command, mailx, 272
source files, listing function and macro
names in, 100, 131
space character, as word separator, 601
space character class, 600, 656
spec file for package, 552
spell checkers, 199, 224
splashimage command, GRUB, 529
split command, 405
split command, ex, 705
split() function, gawk, 733, 744
sprevious command, ex, 706
sprintf() function, gawk, 744, 746
sqrt() function, gawk, 744
srand() function, gawk, 744
ssh command, 406–409
ssh-add command, 409
ssh-agent command, 410
sshd command, 412
ssh-keygen command, 410
ssh-keyscan command, 411
Stallman, Richard (founder of FSF), 7
standard input
determining terminal connected
to, 457
reading a line from, 639
start command, logrotate, 255
starting the system, 19
startup files for Bash, 599
stash command, git, 834
stat command, 413–416
statd command, 416
status command, ftp, 153
status command, git, 834
status command, svn, 788–791
status line, vi, 683
step command, gdb, 165
stop command, ex, 706
stopping commands, Emacs, 665
stopping the system, 19
storage, commands for, 11
strace command, 416–418
Strang, John (Learning the Unix
Operating System), xvii
stream editor (see sed editor)
strftime() function, gawk, 744
string conditions, testing for, 648
strings
completions for, generating, 624
converting initial whitespace to
tabs, 462
printing with specific format, 334
sorting, 457
translating characters in, 453–454
writing to standard output, 628
strings command, 418
strip command, 419
strtonum() function, gawk, 734, 744
struct command, ftp, 153
stty command, 420–425
Stubblebine, Tony (Regular Expression
Pocket Reference), 654
su command, 425
sub() function, gawk, 745
subdomains, 26
substitute command, ex, 706
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Index | 911
substr() function, gawk, 745
subtraction operator (-), 732
Subversion version control system, 753,
755–804
atomic commits, 756
authors of files, showing, 767
book about, 755
branching in, 756, 757
checking in (committing)
changes, 756, 760, 771
checking out files, 760, 769
conflicts, handling of, 756, 787, 788
copying files, 772
copy-modify-merge model used
by, 756
differencing files, 757, 761, 774–775
directories, creating, 782
directory versioning, 756
displaying file contents, 768
help for, 776
keywords for, 758
locking files, 779, 793, 797
logging for, 779
merging files, 781, 782
moving (renaming) files, 783
networks used with, 756
obtaining, 759
projects
adding files and directories
to, 767
creating, 759
deleting files and directories
from, 773
grouping files into
collections, 768
properties (metadata) for, 756, 757,
784–786
remote access for, 803
repository for, 755, 794–803
exporting from, 775
importing to, 776
listing contents of, 778
sandbox for, 756
svn command line, 761–766
svn subcommands, 766–794
svnadmin command, 794
svnadmin subcommands, 795–799
svnlook command, 799
svnlook subcommands, 800–803
svnserv command, 803
tags in, 756, 757
working copy
cleaning, 770
printing information about, 777
status of, 788–791
updating, 791–792, 793
sudo command, 426
sum command, 427
Sun Yellow Pages (YP), 31
sunique command, ftp, 153
superblock, printing information
about, 124
supernetting, 24
superuser, executing commands as, 426
support for Linux, xviii, 3
suspend command, Bash, 647
suspend command, ex, 706
sview command, ex, 706
svn command, Subversion, 761–766
svn subcommands,
Subversion, 766–794
svnadmin command, Subversion, 794
svnadmin subcommands,
Subversion, 795–799
svnlook command, Subversion, 799
svnlook subcommands,
Subversion, 800–803
svnserv command, Subversion, 803
swapoff command, 427
swapon command, 427
swapspace, creating, 293
switch command, svn, 791–792
symbol table, printing in alphabetical
order, 310
symbolic links, 248, 352
synaptic command, Debian, 544, 594
sync command, 428
sysctl command, 428
sysklogd command, 428
syslogd command, 429
system access commands, vi, 690
system administration, commands
for, 14–20
system command, ftp, 153
system control messages,
displaying, 119
system() function, gawk, 745
system integrity, commands for, 18
system load
averages of, graphing, 447
averages of, printing, 464
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912 | Index
system logging
adding entries to log, 252
commands for, 20
manipulating logfiles, 253–256
system messages, 375, 428
system status
commands for, list of, 11
time running, printing, 464
usage, printing summary of, 471
System V init (SysVinit), 19
systime() function, gawk, 745
SysVinit (System V init), 19
T
t command, ex, 706
T command, sed, 717, 725
t command, sed, 717, 724
\t tab escape sequence, 601, 733
\T time escape sequence, 612
\t time escape sequence, 612
tabooext command, logrotate, 255
tabs
as word separator, 601
converting initial whitespace to, 462
converting to spaces, 132
tac command, 429
tag command, ex, 707
tag command, git, 835
tags, 750
Git, 807, 835
Subversion, 756
tags command, ex, 707
tail command, 430
tailf command, 431
talk command, 431
tape drive, controlling, 300
tapes, ejecting, 128
tar command, 431–437
taskset command, 437
tbl command, formatting output
from, 85, 86
tcpdump command, 437–439
TCP/IP, 22–28
books about, 23
commands for, list of, 21, 28
configuring, 27
gateways, 25
IP addresses, 23–25
name service, 26
routing daemons, 25
troubleshooting, 28
TCP/IP Network Administration
(Hunt), 23
tcpslice command, 439
tcsh shell, 596
tee command, 440
telinit command, 440
telnet command, 441
telnetd command, 442–443
temporary filename, generating, 293
tenex command, ftp, 153
TERM built-in variable, 611
terminal
as standard input, determining, 457
attributes, setting, 395–397
initializing, 456
I/O options, setting, 420–425
resetting, 356
terminal command, GRUB, 529
terminal emulation, 379–384
terminal session, typescript of, 384
test command, 443
test command, Bash, 647–650
testload command, GRUB, 536
testvbe command, GRUB, 536
text patterns (see pattern matching)
text processing, commands for, 12
TEXTDOMAIN environment variable,
gawk, 736
tftpserver command, GRUB, 530
Third Extended Filesystem (see ext3
filesystem)
thread (th) command, mailx, 272
threads, launching for NFS module, 308
tilde (~)
in filename, 599
match regular expression, 732
replace regular expression command
in ex, 710
reuse previous replacement
pattern, 657
tilde escape commands, mailx, 268
tilde, hyphen (~-) in filename, 599
tilde, plus sign (~+) in filename, 599
time command, 445
time command, Bash, 650
time (see date and time)
time system has been running,
printing, 464
TIMEFORMAT built-in variable, 611
timeout command, GRUB, 522
times command, Bash, 650
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Index | 913
title command, GRUB, 522
tload command, 447
TMOUT built-in variable, 611
tmpwatch command, 447
Todino-Gonguet, Grace (Learning the
Unix Operating System), xvii
tolower() function, gawk, 745
top command, 448–452
top command, mailx, 272
top command, xm, 847
Torvalds, Linus (developer of Linux), 1
touch command, 452
touch command, mailx, 272
toupper() function, gawk, 746
tr command, 453–454
trace command, ftp, 153
tracepath command, 454
traceroute command, 455
translating characters in a
string, 453–454
translation tables of keyboard
driver, 124
transposition commands, Emacs, 665
trap command, Bash, 650
tree command, svnlook, 803
trigger scriptlets in package spec
file, 553
troff command (see groff command)
true command, 456
true command, Bash, 651
tset command, 456
tsort command, 457
tty command, 457
tty port, logging in to, 38
tune2fs command, 457–460
tunelp command, 460
type command, Bash, 651
type command, ftp, 153
Type (T) command, mailx, 272
type (t) command, mailx, 272
typescript of terminal session, 384
U
\U escape character, pattern
matching, 657
\u escape character, pattern
matching, 657
\u username escape sequence, 612
ubuntu-virt-mgmt package, 849
ubuntu-virt-server package, 849
ubuntu-vm-builder package, 850
UDP (User Datagram Protocol), 23
UID built-in variable, 609
ul command, 460
ulimit command, Bash, 652
umask command, Bash, 652
umask command, ftp, 153
umount command, 30, 461
unabbreviate command, ex, 707
unalias command, Bash, 653
unalias command, mailx, 272
uname command, 461
unanswered command, mailx, 272
unary minus operator (-), 732
unary plus operator (+), 732
uncollapse (unc) command, mailx, 272
uncompresscmd command,
logrotate, 256
undelete (u) command, mailx, 272
underscores, translating to
underlining, 460
undisplay command, gdb, 165
undo command, ex, 707
undoing commands, Emacs, 665
unexpand command, 462
ungood command, mailx, 272
unhide command, ex, 707
unhide command, GRUB, 530
Unicode mode for keyboard, 463
unicode_start command, 463
unicode_stop command, 463
uniq command, 463
universal addresses, mapping RPC
program numbers to, 365
Universal Serial Bus (USB) devices,
listing, 264
Universal Unique Identifier (see UUID)
Unix, compared to Linux, 1
unjunk command, mailx, 272
unlink command, 464
unlock command, svn, 793
unmap command, ex, 707
unread (U) command, mailx, 272
unset command, Bash, 653
unset (uns) command, mailx, 273
until command, Bash, 653
until command, gdb, 165
up command, gdb, 165
up2date program, 544
update command, svn, 793
update command, yum, 551
upgrade command, yum, 551
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914 | Index
upper character class, 600, 656
uppermem command, GRUB, 536
Upstart, 19
Upstart init daemon, 208
uptime command, 464
URLs, fetching, 247
USB scanners, detecting by SANE, 376
USB (Universal Serial Bus) devices,
listing, 264
Usenet newsgroups, xviii
user accounts, NIS, 32
user authentication files, creating or
updating, 199
user command, ftp, 153
User Datagram Protocol (UDP), 23
user groups, xix
user ID, displaying information
about, 204
useradd command, 464–466
user-defined functions, gawk, 734
userdel command, 466
usermod command, 466
users
adding or updating, 464–466
changing groups for, 308
creating or updating, 308
current, printing ID of, 483
deleting, 466
interactive conversations with, 488
logged in, listing, 482
logged in, printing summary of, 471
mailing regarding exceeded
quotas, 472
modifying account information
for, 466
number of logged in, printing, 464
space allowed on disk for, 344
talking to another user, 431
writing a message to all users, 471
(see also groups)
users command, 467
usleep command, 467
uuid command, svnlook, 803
UUID (Universal Unique Identifier)
creating, 468
uuidgen command, 468
V
v command, ex, 707
v command, sed, 716, 725
\V release escape sequence, 612
\v version escape sequence, 612
\v vertical tab escape sequence, 601,
715, 733
variable substitution, 601, 606
variables
built-in, 607–611
declaring, 626
exporting to make global, 630
forcing expansion of, 629
gawk, 731, 732
local, 636
reading an input line and assigning
to, 639
readonly, 640
setting or printing, 641–643
unsetting, 653
vbeprobe command, GRUB, 536
vdir command, 468
verbose command, ftp, 153
verify command, svnadmin, 799
verify (verif) command, mailx, 273
version command, ex, 707
version control system (see source code
management system)
Version Control with Subversion (Pilato
et al.), 755
version of package, 543
vertical bar (|)
match either one or the other, 656
output directed to next
command, 746
pipe character, 601, 602
vertical bar, ampersand (|&) output
directed to coprocess, 735,
746
vertical bar, double (||)
OR operator for commands, 602
OR operator, in expressions, 620,
732
VFAT filesystem, 16
vi command, 468, 678
vi editor, 677–696
command-line options, 678–680
commands, 683–692
copy and move, 688
edit, 687
insert, 686
line numbering, 685
macros, 691
marks, 685
movement, 683–686
Download at WoweBook.Com
Index | 915
multiple files, accessing, 689
on status line, 683
saving files, 688
:set command, 692–696
syntax for, 681
system access, 690
window, 690
configuration of, 692–696
exiting, 680, 688
invoking, 678
modes, 678, 681
pattern matching metacharacters
supported by, 657
video mode, setting, 468
vidmode command, 468
view command, ex, 707
vile editor, 677
vim command, 469
vim editor, 677, 678
command-line options, 678–680
visual mode, 682
virsh commands, 842, 844, 850,
852–856
virt-clone command, 856
virt-image command, 857
virt-install command, 840, 842, 844,
846, 858–861
virt-manager command, 861
virt-manager package, 842, 849, 850,
851
virtual center, for VMware, 862
virtual console
deallocating, 107
determining number of, 137
virtual machine monitor (VMM), 838
virtual memory statistics,
printing, 469–471
Virtual PC, 504
virtual terminal
executing commands on, 322
Meta key handling for, 394
switching to, 84
virtualization method for booting, 504
virtualization tools, 838–873
connection to Internet, 839
console interface for, 842
creating virtual systems, 840
disk image files for, 844
graphic interface for, 842
KVM (see KVM hypervisor)
libvert tools, 839
libvirt (see libvirt virtualization API)
MAC address for, 844
managing virtual systems, 841
migration support for, 839
network configuration for, 842
paravirtualization, 839
for a single guest, 838
system requirements for, 838
VMware (see VMware)
Xen (see Xen hypervisor)
virt-viewer command, 861
virt-viewer package, 842, 849
VISUAL built-in variable, 611
visual command, ex, 708
visual mode, vim, 682
visual (v) command, mailx, 273
vmkfstools command,
VMware, 870–873
VMM (virtual machine monitor), 838
vmstat command, 469–471
VMware, 862–873
changing virtual machine
configurations, 844
ESX management client for, 862
ESX server commands, 864–873
graphic interface for, 842
managing virtual systems, 842
networking for, 863
paravirtualization with, 864
shared disks for, 863
snapshots, 863
virtual center for, 862
virtual switch for networking, 842
website for, 837
VMware server, 504
vmware-cmd command, VMware, 842,
868–870
volname command, 471
volume name for device,
determining, 471
Vromans, Johan (Perl 5 Pocket
Reference), 654
vSphere, 862
vsplit command, ex, 708
W
w command, 471
W command, sed, 716, 725
w command, sed, 716, 725
\W current directory escape
sequence, 612
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916 | Index
\w current directory escape
sequence, 612
\W escape character, pattern
matching, 656
\W escape sequence, 715
\w escape character, pattern
matching, 656
\w escape sequence, 715
wait command, Bash, 653
wait command, lftp, 247
wall command, 471
wall command, ex, 708
warnquota command, 472
watch command, 472
watch command, gdb, 165
WAV format, converting to CDDA, 69,
200–203
wc command, 473
website resources, xvii–xix
Arch system, 753
Bash debugger, 608
Bash shell, 597
Codeville system, 753
CSSC system, 754
for this book, xxi
GNU utilities documentation, xvii
libvirt virtualization API, 850
Linux Documentation Project, xvii
Linux Gazette, xvii
Linux Insider, xvii
Linux Security, xvii
Linux Today, xvii
Linux Weekly News, xvii
monotone system, 754
netfilter, 29
online support, xviii
Slashdot, xvii
Subversion, 759
Usenet newsgroups, xviii
user groups, xix
vim editor, 678
virtualization tools, 837
weekly command, logrotate, 256
Welsh, Matt (Running Linux), xvii, 4
wget command, 474–480
whatis command, 480
whatis command, gdb, 165
whereis command, 480
which command, 481
while command, Bash, 653
while command, gawk, 746
whitespace, converting to tabs, 462
who command, 482
whoami command, 483
whois command, 483
window commands, Emacs, 666
window commands, vi, 690
Windows
accessing files from Linux, 16
as host OS with Linux as guest, 504
booting with GRUB, 517
booting with LILO, 506
dual booting Linux with, 505,
536–539
Linux as challenge to, 2
networking on, Linux providing, 3
restoring original boot loader, 506
wnext command, ex, 708
wodim command, 484–488
word character class, 600
word-abbreviation commands,
Emacs, 666
working tree, for Git, 806
cleaning, 818
removing files from, 833
wq command, ex, 708
wqall command, ex, 709
write a message to all users, 471
write command, 488
write command, ex, 708
write messages, controlling receipt
of, 286
write (w) command, mailx, 273
X
X command, ex, 709
x command, mailx, 270
x command, sed, 716, 725
\x hexadecimal escape sequence, 715,
733, 601
X Window System, 4
xargs command, 488–489
xdigit character class, 600, 656
XDR (eXternal Data
Representation), 32
Xen hypervisor, 845–849
changing virtual machine
configurations, 844
device interfaces for, 843
graphic interface for, 842
installing, 845
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Index | 917
libvirt used with (see libvirt
virtualization API)
managing virtual systems, 842
networking for, 846
paravirtualization with, 846
website for, 837
xentop command, 848
xm command, 846–848
xentop command, 848
XFS (Extensible Filesystem), 16
xinetd command, 490–493
xit command, ex, 709
xit (x) command, mailx, 273
xm command, Xen, 846–848
xor() function, gawk, 746
Y
y command, sed, 716, 725
yacc command, 493
yank command, ex, 709
yank (paste), Emacs, 662
yes command, 494
youngest command, svnlook, 803
YP (Yellow Pages), 31
ypbind command, 494
ypcat command, 495
ypinit command, 495
ypmatch command, 496
yppasswd, 496
yppasswdd command, 496
yppoll command, 497
yppush command, 497
yps server, 31
ypserv command, 498
ypserv server, 31
ypset command, 499
yptest command, 499
ypwhich command, 500
ypxfr command, 500
ypxfrd command, 501
yum program, 544, 545–552
command syntax and options
for, 545–547
commands used in, 547–551
configuration for, 545
plugins for, 551
yum-builddep plugin, yum, 552
yum-complete-transaction plugin,
yum, 552
yumdownloader plugin, yum, 552
yup program, 545
Z
z command, ex, 709
z command, mailx, 273
Z Shell, 596
zcat command, 501
zcmp command, 501
zdiff command, 501
zforce command, 501
zgrep command, 502
zless command, 502
zmore command, 502
znew command, 503
zones, printing information about, 197
zsh shell, 596
Zwicky, Elizabeth D. (Building Internet
Firewalls), 29
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About the Authors
Ellen Siever is a writer and editor specializing in Linux and other open source
topics. In addition to Linux in a Nutshell, she coauthored O’Reilly’s Perl in a
Nutshell. She is a longtime Linux and Unix user and was a programmer for many
years until she decided that writing about computers was more fun.
Stephen Figgins honed many of his computer skills while working as O’Reilly’s
book answer guy. A lifelong learner with many interests, Stephen draws on many
resources to make difficult topics understandable and accessible.
Now living in Lawrence, Kansas, he administrates Linux servers for Sunflower
Broadband, a cable company. When not found working with computers, writing,
or spending time with his family, you will likely find him outdoors. Stephen
teaches wilderness awareness and living skills.
Robert Love has been a Linux user and hacker since the early days. He is active
in—and passionate about—the Linux kernel and GNOME desktop communi-
ties. His recent contributions to the Linux kernel include work on the kernel event
layer and inotify. GNOME-related contributions include Beagle, GNOME
Volume Manager, NetworkManager, and Project Utopia. Currently, Robert works
in the Open Source Program Office at Google.
Robert is the author of Linux Kernel Development (SAMS, 2005) and Linux System
Programming (O’Reilly, 2007). He is also a contributing editor at Linux Journal.
He is currently working on a new work for O’Reilly that will be the greatest book
ever written, give or take. Robert holds a BA in mathematics and a BS in computer
science from the University of Florida. A proud Gator, Robert was born in South
Florida but currently calls Cambridge, Massachusetts home.
Arnold Robbins, an Atlanta native, is a professional programmer and technical
author. He has worked with Unix systems since 1980, when he was introduced to
a PDP-11 running a version of Sixth Edition Unix. He has been a heavy AWK user
since 1987, when he became involved with gawk, the GNU project’s version of
AWK. As a member of the POSIX 1003.2 balloting group, he helped shape the
POSIX standard for AWK. He is currently the maintainer of gawk and its docu-
mentation. He is also coauthor of O’Reilly’s Learning the vi and Vim Editors. Since
late 1997, he and his family have been living happily in Israel.
Colophon
The animal featured on the cover of Linux in a Nutshell, Sixth Edition, is an
Arabian horse. Known for its grace and intelligence, the Arabian is one of the
oldest breeds of horse, with evidence of its existence dating back 5,000 years. The
Arabian was instrumental as an ancestor to other popular breeds, most notably
the Thoroughbred in the 17th and 18th centuries. One of the more distinctive
horse breeds, the typical Arabian has large, expressive eyes and nostrils; small
ears; and a short, sturdy back. Its stamina suits it particularly well for endurance
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riding, a sport dominated by the Arabian breed. Its wonderful temperament
makes the Arabian an all-around favorite riding horse in North America, although
it also can be found in more specialized competitions such as dressage, jumping,
and reining.
The cover image is from the Dover Pictorial Archive. The cover font is Adobe ITC
Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad
Condensed; and the code font is LucasFont’s TheSansMonoCondensed.
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