Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 5 ■ WORKING WITH FILESYSTEMS40 */4 * * * /usr/local/bin/rsnapshot hourly30 02 * * * /usr/local/bin/rsnapshot daily20 02 * * 7 /usr/local/bin/rsnapshot weeklyThe hourly/daily/weekly retain levels don’t actually have to be at hourly/daily/weekly rates; they’rejust labels. You can set them to run however often you like in the cronjob. What the value in the configfile does is to set how many of each are retained. So here, we’re running the “hourly” snapshot every 4hours, and thus we keep 6 past versions to make up 24 hours (at which point a “daily” snapshot will betaken and the “hourly” can restart).■ Note If you get lock error messages from the “hourly” backup occasionally, it may be that the “daily” still hasthe lock. Increase the ten-minute interval between the two in the crontab to solve this. Here’s an example:50 */4 * * * /usr/local/bin/rsnapshot hourlyMake sure you set /snapshots/ to be owned by root so that users can’t modify their own files:chown root:root /snapshots; chmod og-w /snapshotsTo set up rsnapshot so any user can pull their own backups, rather than relying on root access,simply give read/execute access to this directory:chmod a+rx /snapshotsand then export it read-only over NFS, with the following line in /etc/exports:/snapshots 192.168.0.0/255.255.0.0(ro)Restart nfs-kernel-server (/etc/init.d/nfs-kernel-server restart) when you’ve finished editing/etc/exports. The files should be saved with the appropriate ownership and permissions, so any usercan grab their own files but won’t be able to modify them, because the share is read-only.rsnapshot should run on nearly any Unix-type system (requiring only perl and rsync) and isavailable as a package for most of the major <strong>Linux</strong>es.5-8. Working with Other FilesystemsAs well as the standard ext2 and ext3 <strong>Linux</strong> filesystems, other filesystems are available that you may wantto investigate. You may have to recompile your kernel to use these (either as modules or built in to thekernel). Find out what filesystems your current kernel supports using this:> cat /proc/filesystems132Download at WoweBook.Com
CHAPTER 5 ■ WORKING WITH FILESYSTEMSCheck out /lib/modules/[kernelversion]/kernel/fs to see what further filesystem modules youhave available; these should be loaded automatically by mount if needed, or you can try using insmod/path/to/module.o as root if need be.■ Note Unless you have a particular reason to use ext2, you’re far better off with ext3, since it has a journalingsystem that minimizes data loss in the event of any problems. See recipe 5-1 for how to convert ext2 to ext3 onthe fly.ext4This has improvements intended to better manage large filesystems (including a doubling of thesubdirectory limit, to 64,000) and improve performance with large files. The maximum filesystem size is1EB, compared to 16TB with ext3. (But note that the standard partition table will allow only 2TB perpartition, although GNU parted can be used to make larger partitions.) It also has options for persistentpreallocation (where space is allotted ahead of time for files), which has benefits for media streamingand for databases. Extra timestamp bits defer the “year 2038” problem for another 500 years. It’sbackward compatible with ext2 and ext3, so it’s easy to experiment with if you want. Switch yourpartition with this command:umount /dev/sda1tune2fs -O extents,uninit_bg,dir_index /dev/sda1fsck -pf /dev/sda1mount -t ext4 /dev/sda1Edit /etc/fstab to set the partition type as ext4:/dev/sda1 /local ext4 errors=remount-ro 0 1If you’re doing this to a root partition, you’ll need to edit /boot/grub/menu.lst as well. Add this tothe end of the kernel line:rootfstype=ext4and then update grub:sudo update-grubAs ever, make sure you have an up-to-date backup before you start doing this! It is designed to be asafe process and should work cleanly, but it’s always possible to run into problems when messing withfilesystems.133Download 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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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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