Linux System Administration Recipes: A Problem-Solution Approach

282 Pages·2009·4.29 MB·English

by  Juliet Kemp

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Books for professionaLs By professionaLs® The experT’s Voice® in Linux
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Linux System Administration Recipes:
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A Problem-Solution Approach
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Dear Reader, n

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I decided to write this book based on my own experience as a sysadmin, having
to deal with the wide variety of challenges, bugs, and problems that come up on x
a daily basis. The sheer scope of the job is both its biggest joy and its biggest chal-
lenge. S
Linux sysadmins can use any number of tools in their jobs—as the Perl maxim
y
says, “There’s more than one way to do it.” This book covers many of those tools
s
in a fast, accessible format. It’s aimed at the busy sysadmin who wants quick tips
to solve problems (and avoid future problems) now. It’ll be particularly helpful if t
you are, as I have been, a solo admin who is responsible for support and setup e
System Administration
across all levels of your network (from user-facing to back-end systems). m
In Linux System Administration Recipes, you’ll find a quick-start guide for
several networking and provisioning technologies (LDAP, Kerberos, Nagios, and
A
Puppet), as well as tips to help out with common and not-so-common problems.
This book is designed so that you can flip through the pages, find the stand-alone d
recipe you need, and use it right away. Recipes
m
If you already know which end of a server is which but want to improve your
abilities, increase the options in your toolbox, and have a useful reference in hand
i
the next time you encounter a problem, this book is for you. n
i
Juliet Kemp s
t
r
a
THE APRESS ROADMAP A Problem-Solution Approach
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Automating Linux and Unix System Pro Bash Programming:
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See last page for details i
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Linux System
Administration Recipes
A Problem-Solution Approach

■ ■ ■
Juliet Kemp

i
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Linux System Administration Recipes: A Problem-Solution Approach
Copyright © 2009 by Juliet Kemp
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or by any information storage or retrieval
system, without the prior written permission of the copyright owner and the publisher.
ISBN-13 (pbk): 978-1-4302-2449-5
ISBN-13 (electronic): 978-1-4302-2450-1
Printed and bound in the United States of America 9 8 7 6 5 4 3 2 1
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occurrence of a trademarked name, we use the names only in an editorial fashion and to the benefit of
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Lead Editor: Frank Pohlmann
Technical Reviewer: Sean Purdy
Editorial Board: Clay Andres, Steve Anglin, Mark Beckner, Ewan Buckingham, Tony Campbell, Gary
Cornell, Jonathan Gennick, Jonathan Hassell, Michelle Lowman, Matthew Moodie, Jeffrey
Pepper, Frank Pohlmann, Douglas Pundick, Ben Renow-Clarke, Dominic Shakeshaft, Matt
Wade, Tom Welsh
Project Manager: Kylie Johnston, Sofia Marchant
Copy Editor: Kim Wimpsett
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Artist: April Milne
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Contents at a Glance
■ About the Author................................................................................................xiv
■ About the Technical Reviewer.............................................................................xv
■ Acknowledgments..............................................................................................xvi
■ Introduction.......................................................................................................xvii
■ Chapter 1: Saving Yourself Effort..........................................................................1
■ Chapter 2: Centralizing Your Network: Kerberos, LDAP, and NFS.......................21
■ Chapter 3: Monitoring and Updating...................................................................63
■ Chapter 4: Taking Backups and Managing Data..................................................95
■ Chapter 5: Working with Filesystems................................................................119
■ Chapter 6: Securing Your Systems....................................................................135
■ Chapter 7: Working with Apache.......................................................................157
■ Chapter 8: Using the Command Line Better.......................................................171
■ Chapter 9: Working with Text in Files ...............................................................185
■ Chapter 10: Things Going In, Things Going Out.................................................203
■ Chapter 11: Tracking Down Bugs......................................................................213
■ Chapter 12: Managing Time and People............................................................231
■ Appendix: Perl Tips............................................................................................247
■ Index..................................................................................................................253
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Contents
■ About the Author................................................................................................xiv
■ About the Technical Reviewer.............................................................................xv
■ Acknowledgments..............................................................................................xvi
■ Introduction.......................................................................................................xvii
■ Chapter 1: Saving Yourself Effort..........................................................................1
1-1. Documentation: Knowing It’s a Good Thing............................................................1
1-2. Documentation: Keeping Track of What You’re Doing.............................................1
1-3. Documentation: Using a Wiki..................................................................................2
1-4. Documentation: Running Multiple Independent Wikis on the Same Install.............3
1-5. Scripting: Setting the Display Style.........................................................................7
1-6. Dealing with Variables in Perl.................................................................................7
1-7. Testing Scripts Fully................................................................................................9
1-8. Version Control: Using Subversion Aliases............................................................10
1-9. Version Control: Adding Labels to Subversion Log Messages...............................11
1-10. Version Control: Adding Multiple Files to Subversion..........................................11
1-11. Version Control: Telling Subversion to Ignore Files.............................................13
1-12. Subversion: Dividing Repositories.......................................................................14
1-13. Subversion: Branching Repositories...................................................................15
1-14. Subversion: Merging Repositories......................................................................16
1-15. Testing: Knowing It’s a Good Thing.....................................................................16
1-16. Reinventing the Wheel........................................................................................18
■ Chapter 2: Centralizing Your Network: Kerberos, LDAP, and NFS.......................21
2-1. Setting Up Kerberos Authentication......................................................................21
How Kerberos Works.......................................................................................21
2-1a. Server Installation and Configuration....................................................22
2-1b. Kerberos Client Setup............................................................................26
2-2. Setting Up Kerberos SSH and Logon.....................................................................26
Troubleshooting..............................................................................................28
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■ CONTENTS
2-3. Setting Up an LDAP Server....................................................................................28
2-3a. OpenSSL................................................................................................29
2-3b. LDAP Server...........................................................................................30
2-4. Finishing the LDAP Setup: Authenticating with Kerberos......................................32
Setting Up the Database.................................................................................33
Testing!...........................................................................................................34
Troubleshooting..............................................................................................35
2-5. Populating the LDAP Database..............................................................................35
2-6. Setting Up the LDAP Client....................................................................................38
Troubleshooting..............................................................................................39
2-7. Using LDAP............................................................................................................40
ldapsearch......................................................................................................40
ldapadd...........................................................................................................41
ldapmodify......................................................................................................41
ldapdelete.......................................................................................................42
2-8. Setting Up a Slave LDAP Server............................................................................42
Troubleshooting..............................................................................................45
2-9. Setting Up Kerberos Replication............................................................................47
Troubleshooting..............................................................................................48
2-10. Adding a New User to LDAP with a Script...........................................................49
2-11. Modifying and Deleting Using LDAP Scripts........................................................52
Deleting Entries...............................................................................................53
2-12. Querying LDAP with a Script...............................................................................55
2-13. Adding Your Own Fields to LDAP.........................................................................57
2-14. Using NFS and automount...................................................................................59
2-15. Connecting Macs to a Linux NFS Server.............................................................60
2-16. Improving NFS Performance...............................................................................60
■ Chapter 3: Monitoring and Updating...................................................................63
3-1. Nagios: Setting Up Centralized Monitoring............................................................63
3-2. Adding Another Host to Nagios.............................................................................67
3-3. Using Templates in Nagios....................................................................................67
3-4. Using Hostgroups and Services in Nagios.............................................................68
3-5. Setting Up Nagios Alerts.......................................................................................69
3-6. Defining Nagios Commands..................................................................................71
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■ CONTENTS
3-7. Writing a Nagios Plug-In........................................................................................71
3-8. Setting Up the NRPE Plug-in for Nagios................................................................73
3-9. Enabling External Commands in Nagios................................................................76
3-10. Synchronizing Your Root Setup...........................................................................78
3-11. Setting Up Puppet................................................................................................79
Setting Up a Client...........................................................................................80
Setting Up Your Site Manifest.........................................................................81
3-12. Creating Puppet and Resource Dependencies....................................................83
3-13. Puppet: Managing Other Types...........................................................................83
3-14. Setting Up Nodes in Puppet.................................................................................85
3-15. Defining Your Puppet Nodes in LDAP..................................................................86
3-16. Puppet: Using Facter and Templates..................................................................88
Custom Facts..................................................................................................90
Other Variables................................................................................................90
3-17. Using ClusterSSH................................................................................................91
■ Chapter 4: Taking Backups and Managing Data..................................................95
4-1. Calculating Your Network’s Total Disk Size and Current Usage...........................96
4-2. Finding Out How Often Your Files Change.............................................................99
4-3. Backing Up Your Wiki..........................................................................................100
4-4. Backing Up MySQL..............................................................................................102
4-5. Backing Up Kerberos and LDAP..........................................................................103
4-6. Performing a Rapid Restore with Automated rsync............................................104
4-7. Using rsync with SSH Keys.................................................................................108
4-8. Creating an Off-Site Backup via E-mail...............................................................110
4-9. Using anacron for Laptop Backups.....................................................................112
4-10. Performing Basic Data Recovery: fsck and dd..................................................113
4-11. Using Foremost to Retrieve Data.......................................................................116
4-12. Rescuing Data: Autopsy....................................................................................116
4-13. Securely Wiping Data........................................................................................118
■ Chapter 5: Working with Filesystems................................................................119
5-1. Changing ext2 to ext3 with tune2fs....................................................................119
5-2. Making Changes to Automatic fsck Checking.....................................................120
5-3. Saving Space on Large Filesystems and Directories..........................................121
5-4. Working with Disks, UUID, and Labels................................................................121
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■ CONTENTS
5-5. Resizing Partitions on the Fly..............................................................................123
With a Nearly Full Disk..................................................................................126
5-6. Using RAID Arrays and mdadm...........................................................................128
mdadm..........................................................................................................129
5-7. Using rsnapshot..................................................................................................130
5-8. Working with Other Filesystems.........................................................................132
ext4...............................................................................................................133
XFS................................................................................................................134
■ Chapter 6: Securing Your Systems....................................................................135
6-1. Using and Limiting SSH Keys..............................................................................135
6-2. Managing Keys with Keychain............................................................................137
6-3. Limiting rsync Over ssh.......................................................................................138
6-4. ssh Options: Keeping Your Connection Alive.......................................................140
6-5. ssh Options: Minimizing Typing..........................................................................141
6-6. Transferring Files Over an Existing ssh Connection............................................142
6-7. Kerberizing Your SSH Setup................................................................................143
6-8. Setting and Enforcing a Password Policy with Kerberos....................................144
6-9. Setting and Enforcing Password Policy with pam_cracklib................................146
6-10. Checking the Password Policy..........................................................................147
6-11. Limiting sudo.....................................................................................................148
6-12. sudo: Figuring Out Which Password to Use......................................................149
6-13. Stopping Brute-Force Attacks with iptables.....................................................151
6-14. Monitoring for Break-ins with chkrootkit..........................................................152
6-15. Using cron-apt to Keep Updated.......................................................................154
■ Chapter 7: Working with Apache.......................................................................157
7-1. Using the apache2 Command Line......................................................................157
7-2. Apache2: Dealing with Modules..........................................................................160
7-3. Setting Up an SSL Certificate for Apache2..........................................................162
7-4. Compiling and Configuring Apache with SSL......................................................164
Testing..........................................................................................................166
Troubleshooting............................................................................................166
7-5. Securing Your Web Site with htaccess...............................................................167
7-6. Securing Your Web Site: Apache with Kerberos.................................................169
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