Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 8 ■ USING THE COMMAND LINE BETTERYou can also write your own completion function. Here’s a very basic function you can add to/etc/bash_completion that looks up a partial hostname in LDAP:01 _ldapcomplete() {02 COMPREPLY=()03 cur=${COMP_WORDS[COMP_CWORD]}04 output=`ldapsearch -Q "(&(cn=$cur*) (objectClass=ipHost))" cn | grep ^cn:`05 name=${output#* }06 COMPREPLY=( ${COMPREPLY[@]} $name )07 return 008 }0910 complete -F _ldapcomplete sshLine 02 sets up the array variable that will be used for the completion return (COMPREPLY). Line 03sets $cur to the value that’s been passed into the function, that is, what’s already been input on thecommand line. The COMP_WORDS variable is set up earlier in /etc/bash_completion for use by all functions.The ldapsearch at line 04 looks for an entry in the LDAP directory, which is a host-type object with aname that begins with the existing input, and then it returns only the cn value of any suitable LDAP entryit finds. The output is piped into grep to strip out all the extraneous LDAP information (the -Q switch isused on the ldapsearch to make the output as quiet as possible). $output will be as follows:cn: myhostSo, line 05 splits on whitespace and takes the second half of $output to give just myhost. This value isput into COMPREPLY at line 06, and the function finishes. In this case, you’ll get only one value, so the linecould be this:COMPREPLY=$nameBut to match the rest of the file and to allow for further improvement, you treat it as an array.■ Note This function does not deal properly with multiple return possibilities (it autocompletes only when LDAPreturns a single value). To deal properly with multiple returns, COMPREPLY would have to be treated as an array.Line 10 allows you to actually use the function. It tells the shell that when using ssh, the_ldapcomplete function should be used for hostname completion.■ Note The documentation on the bash man page is pretty good on completion if you want to investigate further.178Download at WoweBook.Com
CHAPTER 8 ■ USING THE COMMAND LINE BETTER8-4. Using findlocate is a useful tool for quickly finding files. You can manually update the database with sudoupdatedb, although you should use cron to run updatedb regularly for it to be really useful. find issignificantly slower, since it searches the directory tree instead of using a constructed database as withlocate, but it is more reliable since it doesn’t need that database to be up-to-date, and it’s far moreflexible.It can, however, be a little confusing to use at first, especially since its error messages aren’t alwaysvery helpful. This recipe is a quick reference for some of the most helpful find options.The basic usage is as follows:find [-H|-L|-P] [path] [options] [expression]where [path] is the root directory to start the search from and [expression] is the criteria by which youwant to search. Without any other options besides [path], find will keep iterating further into thedirectory from which the search began, until it runs out of subdirectories and files.-H, -L, and -P control how find will deal with symbolic links. -P is the default and sets them to beignored. -L sets them to be followed. -H sets them to be ignored, unless the path given on the commandline is a symbolic link. In this case, the link will be followed. So, if you wanted to start from the directory/local/bin, which was a symlink to /usr/bin, and used this command:find -P /local/bin --name=fooyou would be unsuccessful. Instead, use this:find -H /local/bin --name fooOptionsThe most useful of these is likely to be -maxdepth:find / -maxdepth 2 -name fooThis limits the search to go only two levels below the path given on the command line. So, thiswould find /usr/bin/foo but not /usr/local/bin/foo.-mount is also useful, because it sets find to ignore directories on other filesystems; if you have / and/home on different filesystems, you can search just one or the other. For example, you can use it to checkhow many .bk files you have lying around in the / filesystem but not to look for those in /home:find / -mount -name '*.bk'■ Note If you’re searching an MS-DOS file tree or a CD-ROM, use the -noleaf option to avoid an optimizationthat doesn’t work on these filesystems.179Download 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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C H A P T E R 3■ ■ ■Monitorin
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CHAPTER 3 ■ MONITORING AND UPDATI
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C H A P T E R 4■ ■ ■Taking Ba
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CHAPTER 4 ■ TAKING BACKUPS AND MA
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C H A P T E R 5■ ■ ■Working w
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CHAPTER 5 ■ WORKING WITH FILESYST
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Page 157 and 158: CHAPTER 6 ■ SECURING YOUR SYSTEMS
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Page 191 and 192: C H A P T E R 8■ ■ ■Making Be
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Page 223 and 224: C H A P T E R 10■ ■ ■Things G
Page 225 and 226: CHAPTER 10 ■ THINGS GO IN, THINGS
Page 233 and 234: C H A P T E R 11■ ■ ■Tracking
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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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