Linux administration : a beginner's guide

667 Pages·2009·6.575 MB·English

by  Wale Soyinka

Linux Administration:
A Beginner’s Guide
Fifth Edition
WALE SOYINKA
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DOI: 10.1036/0071545883
“W ith the right knowledge, Linux can be clear and simple to understand. This
book presents the core fundamentals of Linux in a manner that is very logical
and easy to follow.”
—Greg Kurtzer, CTO, Infiscale, Inc.
“ Wale continues to do a great job explaining complex information in a straightfor-
ward manner. All newcomers should start their Linux library with this book.”
—Ron Hudson, Senior Field Support Engineer, Intervoice, Inc.
“ Wale Soyinka did a stellar job in the fourth edition and he was up for the chal-
lenge of making the fifth edition his own. It is with great pleasure I present the
fifth edition of Linux Administration: A Beginners Guide by Wale Soyinka. This
book barely resembles the 500-odd pages written nine years ago in the first edi-
tion, and it is without hesitation that I say his new words are for the better.”
—From the Foreword by Steve Shah, original author of
Linux Administration: A Beginner’s Guide
ABOUT THE AUTHOR
Wale Soyinka (Canada) is a systems/network engineering consultant with several years
experience in the field. He has written an extensive library of Linux administration train-
ing materials. In addition to being a co-author of the fourth edition of Linux Administration:
A Beginner’s Guide, he is the author of a projects lab manual—Microsoft Windows 2000 Man-
aging Network Environments, which is part of the Microsoft certification series published
by Prentice Hall. Wale participates in several open source discussions and projects. His
latest project is at caffe*nix (www.caffenix.com) where he usually hangs out. caffe*nix is
possibly the world’s first (or only existing) brick-and-mortar store committed and dedi-
cated to prompting and showcasing open source technologies and culture.
ABOUT THE CONTRIBUTING AUTHOR
Steve Shah (San Jose, California) is the chief technology officer (CTO) and co-founder
of Asyncast, where he leads the product strategy and engineering groups. Prior to start-
ing Asyncast, Steve was the founder and principal of RisingEdge Consulting where he
provided strategic marketing services for a number of Silicon Valley infrastructure com-
panies. To earn his chops, Steve grew to be a prominent player in network load balanc-
ing, application delivery controllers, and Secure Sockets Layer-virtual private network
(SSL-VPN) markets as the director of product management at NetScaler (acquired by
Citrix) and Array Networks. Before turning into a marketing droid who is eerily com-
fortable at a Unix command prompt, Steve was a senior software engineer and systems
administrator at numerous companies. Steve holds a bachelor of science (BS) in com-
puter science with a minor in creative writing and a master in science (MS) in computer
science from University of California Riverside.
ABOUT THE TECHNICAL EDITOR
Dr. Ibrahim Haddad is director of technology at Motorola, Inc. and is responsible for
defining and developing the requirements for Motorola’s open source initiatives. Prior
to Motorola, Dr. Haddad managed the carrier-grade Linux and Mobile Linux Initiatives
at the Open Source Development Lab (OSDL), which included promoting the develop-
ment and adoption of Linux and open source software in the communications industry.
Prior to joining OSDL, Dr. Haddad was a senior researcher at the Research & Innova-
tion Department of Ericsson’s Corporate Unit of Research. He is a contributing editor
for Linux Journal and Enterprise Open Source magazines. Haddad received his BS and
MS degrees in computer science from the Lebanese American University, and his PhD
in computer science from Concordia University in Montreal, Canada. In 2000, he was
awarded by Concordia University both the J.W. McConnell Memorial Graduate Fel-
lowship, and the Concordia University 25th Anniversary Fellowship, in recognition for
academic excellence. In 2007, he was the winner of the Big Idea Innovation Award in
Recognition of Leadership and Vision at Motorola, Inc.
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CONTENTS
Foreword ................... ..... .......... ... ...... xx
Acknowledgments................... ..... .......... .. xxi
Introduction ................... ..... .......... ... ... xxii
Part I
Installing Linux as a Server
▼
1 Technical Summary of Linux Distributions . . . . . . . . . . . . . . . . . . . . . . . . 3
Linux—The Operating System ....................... ..... 4
What Is Open Source Software and GNU All About? ...... 5
What Is the GNU Public License? ..................... 7
The Advantages of Open Source Software ................... 8
Understanding the Differences Between Windows and Linux ... 9
Summary ....................... ..... ......... ..... . 14
▼
2 Installing Linux in a Server Configuration . . . . . . . . . . . . . . . . . . . . . . . 15
Hardware and Environmental Considerations .............. 16
Server Design ....................... ..... ......... ... 16
Uptime....................... ..... ......... .... 18
Dual-Booting Issues ....................... ..... ....... 18
v
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Linux Administration: A Beginner’s Guide
Methods of Installation ....................... ..... ..... 19
Installing Fedora ....................... ..... ......... . 20
Project Prerequisites ....................... ..... ... 20
Carrying Out the Installation ....................... . 21
Initial System Configuration ....................... . 36
Installing Ubuntu Server ....................... ..... ... 37
Summary ....................... ..... ......... ..... . 41
▼
3 Managing Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
The RPM Package Manager ....................... ..... . 44
The Debian Package Management System .................. 47
APT .................. ..... ........... ..... .... 47
Managing Software Using RPM ....................... .... 48
Querying for Information the RPM Way
(Getting to Know One Another) ..................... 48
Installing with RPM (Moving In Together) ............. 51
Uninstalling Software with RPM (Ending the Relationship) .. 54
Other Things You Can Do with RPM ................. 55
Software Management in Ubuntu ....................... . 58
Querying for Information ....................... ... 58
Installing Software in Ubuntu ....................... 59
Removing Software in Ubuntu ...................... 59
GUI RPM Package Managers ....................... 60
Compile and Install GNU Software ....................... 62
Getting and Unpacking the Package .................. 62
Looking for Documentation
(Getting to Know Each Other—Again) ................ 64
Configuring the Package ....................... .... 64
Compiling the Package ....................... ..... 65
Installing the Package ....................... ..... . 66
Testing the Software ....................... ..... ... 66
Cleanup....................... ..... ......... ... 67
Common Problems when Building from Source Code ........ 67
Problems with Libraries ....................... ..... 68
When There Is No configure Script ................... 68
Broken Source Code ....................... ..... ... 68
Summary ....................... ..... ......... ..... . 69
Part II
Single-Host Administration
▼
4 Managing Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
What Exactly Constitutes a User?....................... .. 74
Where User Information Is Kept ..................... 74
The /etc/passwd File ....................... ..... . 75
vii
Contents
The /etc/shadow File ................. ........... . 79
The /etc/group File ................. ........... .. . 80
User Management Tools ................. ........... .. .. 81
Command-Line User Management ................... 81
GUI User Managers ....................... ..... ... 85
Users and Access Permissions ....................... .... 88
Understanding SetUID and SetGID Programs .......... 88
Pluggable Authentication Modules (PAM) ................. 89
How PAM Works ....................... ..... ..... 89
PAM’s Files and Their Locations ..................... 90
Configuring PAM ....................... ..... .... 90
The “Other” File....................... ..... ...... 95
“DOH! I Can’t Log In!” ....................... ..... 95
Debugging PAM ....................... ..... ..... 95
A Grand Tour ....................... ..... ......... ... 96
Creating Users with useradd ....................... . 96
Creating Groups with groupadd ..................... 97
Modifying User Attributes with usermod .............. 98
Modifying Group Attributes with groupmod ........... 99
Deleting Groups and Users with groupdel and userdel ... 99
Summary ....................... ..... ......... ..... 100
▼
5 The Command Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
An Introduction to BASH ................. ........... .. 102
Job Control ................. ........... .. ....... 103
Environment Variables ................. .......... 104
Pipes................. ........... .. ............ 106
Redirection ................. ........... .. ....... 107
Command-Line Shortcuts ................. ........... . 107
Filename Expansion ................. ........... .. 108
Environment Variables as Parameters ................ 108
Multiple Commands ....................... ..... . 108
Backticks ....................... ..... ......... . 109
Documentation Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
The man Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
The texinfo System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Files, File Types, File Ownership, and File Permissions . . . . . . . . 112
Normal Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Hard Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Symbolic Links. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Block Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Character Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Named Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
viii
Linux Administration: A Beginner’s Guide
Listing Files: ls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Change Ownership: chown . . . . . . . . . . . . . . . . . . . . . . . . . 115
Change Group: chgrp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Change Mode: chmod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
File Management and Manipulation . . . . . . . . . . . . . . . . . . . . . . 119
Copy Files: cp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Move Files: mv ....................... ..... ...... 120
Link Files: ln....................... ..... ........ 120
Find a File: find ....................... ..... ..... 121
File Compression: gzip ....................... .... 121
bzip2 ....................... ..... ......... .... 122
Create a Directory: mkdir ....................... .. 122
Remove a Directory: rmdir ....................... . 123
Show Present Working Directory: pwd ............... 123
Tape Archive: tar ....................... ..... .... 123
Concatenate Files: cat ....................... ..... . 125
Display a File One Screen at a Time: more............. 126
Disk Utilization: du ....................... ..... .. 126
Show the Directory Location of a File: which .......... 127
Locate a Command: whereis ....................... 127
Disk Free: df ....................... ..... ........ 127
Synchronize Disks: sync ....................... ... 128
Moving a User and Its Home Directory ................... 128
List Processes: ps ....................... ..... .... 131
Show an Interactive List of Processes: top ............. 133
Send a Signal to a Process: kill ...................... 134
Miscellaneous Tools ....................... ..... ...... 135
Show System Name: uname ....................... 135
Who Is Logged In: who ....................... .... 136
A Variation on who: w ....................... ..... 136
Switch User: su ....................... ..... ..... 136
Editors ....................... ..... ......... ..... .. 137
vi .................... ..... ........... ..... ... 137
emacs....................... ..... ......... .... 138
joe.................... ..... ........... ..... ... 138
pico ....................... ..... ......... ..... 139
Standards ....................... ..... ......... ..... 139
Summary ....................... ..... ......... ..... 140
▼
6 Booting and Shutting Down. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Boot Loaders ....................... ..... ......... ... 142
GRUB....................... ..... ......... .... 142
LILO....................... ..... ......... ..... 152
Bootstrapping ....................... ..... ...... 152
ix
Contents
The init Process ................. ........... .. ........ 153
rc Scripts ................. ........... .. ............ . 154
Writing Your Own rc Script ....................... . 155
Enabling and Disabling Services ....................... . 159
Disabling a Service ....................... ..... ... 162
Odds and Ends of Booting and Shutting Down ............. 162
fsck! ....................... ..... ......... ..... 163
Booting into Single-User (“Recovery”) Mode .......... 163
Summary ....................... ..... ......... ..... 164
▼
7 File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
The Makeup of File Systems ................. ........... 166
i-Nodes ................. ........... .. ......... 166
Superblocks................. ........... .. ...... 167
ext3 and ReiserFS ................. ........... .. .. 168
Which File System to Use? ....................... . 169
Managing File Systems ....................... ..... .... 169
Mounting and Unmounting Local Disks .............. 169
Using fsck ....................... ..... ......... 176
Adding a New Disk ....................... ..... ...... 177
Overview of Partitions ....................... ..... 178
Traditional Disk- and Partition-Naming Conventions ... 178
Volume Management ....................... ..... ..... 179
Creating Partitions and Logical Volumes ............. 180
Creating File Systems ....................... ..... ..... 190
Summary ....................... ..... ......... ..... 192
▼
8 Core System Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
The init Daemon ................. ........... .. ....... 194
upstart: Die init. Die Now! ................. ........ 195
The /etc/inittab File ................. ........... . 196
xinetd and inetd ................. ........... .. ....... 198
The /etc/xinetd.conf File ................. ........ 200
Examples: A Simple Service Entry and
Enabling/Disabling a Service ...................... 205
The Logging Daemon ....................... ..... ..... 208
Invoking rsyslogd ....................... ..... ... 208
Configuring the Logging Daemon ....................... 208
Log Message Classifications ....................... 210
Format of /etc/rsyslog.conf . . . . . . . . . . . . . . . . . . . . . . . . 211
The cron Program ....................... ..... ........ 216
The crontab File ....................... ..... ..... 216
Editing the crontab File ....................... .... 218
Summary ....................... ..... ......... ..... 218
x
Linux Administration: A Beginner’s Guide
▼
9 Compiling the Linux Kernel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
What Exactly Is a Kernel? ....................... ..... .. 222
Finding the Kernel Source Code ....................... .. 224
Getting the Correct Kernel Version .................. 224
Unpacking the Kernel Source Code .................. 225
Building the Kernel ....................... ..... ...... 225
Preparing to Configure the Kernel .................. 227
Kernel Configuration ....................... ..... . 228
Compiling the Kernel ....................... ..... 231
Installing the Kernel ....................... ..... . 233
Booting the Kernel ....................... ..... ... 235
The Author Lied—It Didn’t Work! .................. 235
Patching the Kernel ....................... ..... ...... 236
Downloading and Applying Patches ................. 237
Summary ....................... ..... ......... ..... 239
▼
10 Knobs and Dials: proc and SysFS File Systems . . . . . . . . . . . . . . . . . . 241
What’s Inside the /proc Directory? ...................... 242
Tweaking Files Inside of /proc ..................... 243
Some Useful /proc Entries ....................... ..... . 244
Enumerated /proc Entries ....................... .. 246
Common proc Settings and Reports ...................... 247
SYN Flood Protection ....................... ..... 248
Issues on High-Volume Servers ..................... 249
Debugging Hardware Conflicts ..................... 249
SysFS....................... ..... ......... ..... .... 249
Summary ....................... ..... ......... ..... 252
Part III
Security and Networking
▼
11 TCP/IP for System Administrators . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
The Layers ....................... ..... ......... .... 256
TCP/IP Model and the OSI Model .................. 259
Headers ....................... ..... ......... ..... . 263
Ethernet....................... ..... ......... .. 264
IP (IPv4) ....................... ..... ......... .. 265
TCP .................. ..... ........... ..... ... 268
UDP ........... ....... ..... ........... ..... ... 272
A Complete TCP Connection ....................... .... 273
Opening a Connection ....................... ..... 273
Transferring Data ....................... ..... .... 274
Closing the Connection ....................... .... 275