Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 4 ■ TAKING BACKUPS AND MANAGING DATA16 attrs => [ 'dn', 'cn', 'automountInformation' ],17 );18 my @entries = $mesg->entries;1920 foreach my $entry ( @entries ) {21 my $cn = $entry->get_value( 'cn' );22 $mesg = $ldap->modify( $entry, replace => { 'automountInformation' =>'-fstype=nfs,rw $newhome$cn' } );23 }2425 $mesg = ldap->unbindLines 05–08 set up the names for your old and new servers and the directories; edit this asappropriate for your network. Lines 09–12 open the connection to the LDAP server (see recipe 2-9 formore details on the Net::LDAPS Perl module). Lines 14–18 search for any automount entries with the oldserver name.Lines 20–23 are the ones that do the work. For each entry, the value of the directory name isretrieved ($cn; this would be jkemp for user jkemp, for example), and then the map is modified to changehomeserver:/homedisk/jkemp to newserver:/new/home/jkemp for each entry. See recipe 2-13 for a discussion of the other options in theautomountInformation line. Line 25 tidies up the LDAP connection when you’re done.After this, log in to newserver, and check that /etc/exports has this line:/new/home*.example.com(rw)Then restart the NFS server on that machine with sudo /etc/init.d/nfs-kernel-server restart,and restart autofs on all other machines across the network (sudo /etc/init.d/autofs restart).ClusterSSH (see recipe 3-20) may be useful for this. All should be well again. You can now fix homeserverin a bit less of a rush, since everyone can carry on working while you do it!4-7. Using rsync with SSH KeysYou can use the method in the previous recipe for off-site backup, as well, if you have shell access to anoff-site machine. Simply give the machine’s full name:rsync -avuz /dir/to/backup offsite.example2.com:/shared/backupdir■ Note This is probably not something you want to do for your full-site home directory, unless you have a veryfast connection to the off-site machine. However, it may be useful for some key directories.However, at this point, it still requires an ssh password, which is no good from an automation pointof view. The final stage is to set up a password-free ssh key.108Download at WoweBook.Com
CHAPTER 4 ■ TAKING BACKUPS AND MANAGING DATA■ Note See recipe 6-1 for further discussion of ssh and keys.To create your private key, enter this into a terminal window on your home machine:ssh-keygen -t rsa -f ~/.ssh/rsyncThis will generate an RSA key and save it in ~/.ssh/rsync.■ Note You can also generate DSA keys. DSA is a slightly older standard than RSA. It’s quicker for someoperations (notably for key generation), but RSA is quicker overall. It’s sometimes suggested that RSA is strongerthan DSA, but there’s some debate about the details of this. The default key length for RSA is 2,048 bits, whereasDSA keys must be 1,024 bits long. Since longer keys are in general stronger, this is a significant advantage forRSA, which is also more flexible. Unless you have a specific reason for using DSA, stick with RSA.You will be prompted for a passphrase. Hit Enter to leave this blank. You will now have files rsyncand rsync.pub in your ~/.ssh directory.With a passworded key, all you would need to do here is add the contents of ~/.ssh/rsync.pub to thefile ~/.ssh/authorized_keys2 on offsite.example.com. However, with a passphraseless key, that’s a badidea, since then if an attacker gained access to your home machine, they would also immediately haveunlimited access to your account on offsite.example.com.Instead, it’s possible to reduce the security risk by restricting what this particular key can do. In thiscase, let’s restrict it to a single command, using the ~/.ssh/authorized_keys2 file onoffsite.example.comCopy ~/.ssh/rsync.pub to tmpfile, and edit tmpfile so that it’s a single line (this single line is thepublic half of your key, which will look like a big block of random characters, with an English identifier atthe end). Then add this at the start of that line:command="rsync -avuz -e "ssh -i /home/user/.ssh/rsync" /test user@offsite.example.com:/home/user/backup", no-port-forwarding,no-X11-forwarding,no-agent-forwarding ■ Note There are line breaks here for printing reasons only; your version should not include any line breaks. Itmust be a single line, including both the previous code and your private key.Now add the contents of tmpfile to ~/.ssh/authorized_keys2 on offsite.example.com (using cutand paste, or cat). Again, ensure that it remains as a single line.109Download 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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Page 77 and 78: CHAPTER 2 ■ CENTRALIZING YOUR NET
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CHAPTER 7 ■ WORKING WITH APACHEOn
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CHAPTER 7 ■ WORKING WITH APACHEdi
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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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