Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 3 ■ MONITORING AND UPDATING3-10. Synchronizing Your Root SetupIf you’re working on lots of machines, it can be enormously frustrating to realize that a shortcut or aliasthat you’re used to while working on machine A isn’t there on machine B. For your own personal setup,this is one of the reasons why centralized login and NFS-mounted directories are useful—your settings,aliases, preferences, and whatever else will follow you around from machine to machine.■ Note Puppet (see recipe 3-11) is another centralization option. If you’re centralizing a lot of files, it’s likely to bea better idea to use Puppet. However, if it’s just one or two, a method like this can be appropriate (avoiding the useof the proverbial nut-cracking sledgehammer).Unfortunately, you can’t directly do this with the root user on a machine, because you need to beable to log in as root even when something has gone wrong with the network.One possibility is to use ClusterSSH (see recipe 3-17) to copy /root/.bashrc to all the othermachines every time you change it. However, as a nonautomated solution, this is obviously suboptimal.Another option is to set up a centralized /root/.bashrc that will work almost all of the time.source /shared/config/root.bashrcMake sure this is owned by root and readable only by root!chown root:root /shared/config/root.bashrc; chmod og-rw /shared/config/root.bashrcThere will probably be a few vital aliases or settings that you can’t live without even temporarily;these will need to go in the main /root/.bashrc file on each machine.If you don’t like the possibility of being without any of your aliases, you could set up a cronjob so acentral file is copied out to the file on each machine at regular intervals.One final hack that will work either with the roll-your-own centralization or with Puppet (see thenext recipe) is automatically copying any changes you make locally to the central file for propagation.This script, run regularly on each machine as a cronjob, will back up the old file with the name of themachine from which the new file is taken and the date/time and then put the new file in its place. It’llneed to run as root for the permissions to be correct.01 #!/bin/bash02 export PATH=/usr/bin;/usr/sbin;/bin;/sbin03 hostname=`hostname`04 date=`date +%Y%m%d-%H%M`05 local="/root/.bashrc"06 central="/shared/config/root.bashrc"07 diff=`diff -q $local $central`08 if [ $diff != "" ] ; then09 cp $central $central.$date.$hostname10 cp $local $central11 fi78Download at WoweBook.Com
CHAPTER 3 ■ MONITORING AND UPDATING■ Note You need the quotes surrounding the diff command in line 7 because if the files are different, diffreturns a multiword string. Without the quotes, bash gets confused by this.3-11. Setting Up PuppetOne of the biggest sysadmin centralization problems is getting your configuration set up the same wayacross all your machines. Even if you have centralized install set up, configuration is changed over time,and eventually you end up with some machines working and some not, and you have little real idea whythe difference is and where to look for a cause.Puppet is a centralized configuration management system, which helps you avoid this and othersimilar problems. A central Puppet server—the puppetmaster—keeps track of the configuration files andoptions for all its client machines in a cross-platform language. On the client, you run a daemon thatchecks in with the puppetmaster at intervals and copies over any changes to the client.■ Note Remember that if you’re using Puppet and you make a change manually on a client machine, the nexttime the daemon checks in with the puppetmaster, the change will be reverted. To make the change permanent,you need to remember to make the changes centrally every time. If you need to test a change locally first, you caneither set up a “testing” machine configuration within Puppet or just turn off the Puppet daemon on the clientmachine when you’re testing. Remember to turn it back on when you’re done! Setting up a testing sandbox isprobably the more correct option, and if you have your Puppet files checked into Subversion, you have anautomatic backup you can revert to, but it is more time-consuming when bug fixing.Anything Puppet will manage is called a resource, and resources are categorized into the followingtypes:• Files (ownership, mode, content, and existence can all be managed)• Users and groups• Packages• Services• Commands and scripts (Puppet can execute these under particular conditions)• Crontabs• MountsPuppet is under very active development, and people are regularly adding more types—or you cancreate your own.79Download at WoweBook.Com
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Contents■About the Author .......
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■ CONTENTS3-7. Writing a Nagios P
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■ CONTENTS■Chapter 8: Using the
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■ CONTENTSAbout the Author■Juli
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■ CONTENTSAcknowledgmentsMany tha
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■ CONTENTSIntroductionThis book i
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■ INTRODUCTIONDownloading the Cod
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C H A P T E R 1■ ■ ■Saving Yo
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CHAPTER 1 ■ SAVING YOURSELF EFFOR
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C H A P T E R 2■ ■ ■Centraliz
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CHAPTER 2 ■ CENTRALIZING YOUR NET
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CHAPTER 2 ■ CENTRALIZING YOUR NET
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CHAPTER 5 ■ WORKING WITH FILESYST
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C H A P T E R 6■ ■ ■Securing
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CHAPTER 6 ■ SECURING YOUR SYSTEMS
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C H A P T E R 7■ ■ ■Working w
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CHAPTER 7 ■ WORKING WITH APACHEOn
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CHAPTER 7 ■ WORKING WITH APACHE4.
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CHAPTER 7 ■ WORKING WITH APACHE
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CHAPTER 7 ■ WORKING WITH APACHEAl
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CHAPTER 7 ■ WORKING WITH APACHE
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C H A P T E R 8■ ■ ■Making Be
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CHAPTER 8 ■ USING THE COMMAND LIN
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C H A P T E R 9■ ■ ■Working w
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CHAPTER 9 ■ WORKING WITH TEXT IN
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C H A P T E R 10■ ■ ■Things G
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CHAPTER 10 ■ THINGS GO IN, THINGS
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C H A P T E R 11■ ■ ■Tracking
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CHAPTER 11 ■ TRACKING DOWN BUGSTh
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CHAPTER 11 ■ TRACKING DOWN BUGS01
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CHAPTER 11 ■ TRACKING DOWN BUGS
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CHAPTER 11 ■ TRACKING DOWN BUGSTh
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CHAPTER 11 ■ TRACKING DOWN BUGSAn
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CHAPTER 11 ■ TRACKING DOWN BUGS#
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C H A P T E R 12■ ■ ■Managing
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CHAPTER 12 ■ MANAGING TIME AND PE
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APPENDIX■ ■ ■Perl TipsSee rec
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APPENDIX ■ PERL TIPS• Date::Par
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APPENDIX ■ PERL TIPSPerl Syntax N
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■ ■ ■Index■Symbols$CDPATH,
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■ INDEXenscript option (printing)
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■ INDEX■NNagiosadding hosts to,
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■ INDEXsyslogcentralized logging
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