Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 5 ■ WORKING WITH FILESYSTEMS■ Note If the filesystem you’re changing is the root filesystem, you may need to boot from a LiveCD or rescue discand then run e2fsck /dev/hda1 from there so that the journal file can be moved to its new inode. Then reboot asnormal. Debian, and some other distros, have a workaround that avoids having to do this.If your existing filesystem is too full to have space for the journal file (the normal default is about 5percent of the filesystem size), you can use -J to set various options to work around this problem. (Or seerecipe 5-5 for how to resize filesystems on the fly.) The following will create a journal of size 512MB:tune2fs -j -J size=512 /dev/hda1Alternatively, you can create a journal file on a different device (here, /dev/hdb2) with this:mke2fs -O journal_dev /dev/hdb2Then when you set up journaling on your overfull filesystem, you can set it to use this externaljournal file:tune2fs -j -J device=/dev/hdb2 /dev/hda15-2. Making Changes to Automatic fsck CheckingIf you’re running a nonjournaled filesystem, you will be familiar with the automatic e2fsck check forinconsistencies that is triggered after a certain number of mounts. (Journaled filesystems don’t need thisbecause the journal is what avoids inconsistencies.) This can be irritating if it happens at bootup whenyou need a machine to come up quickly. Using tune2fs, it’s possible to turn it off altogether:tune2fs -c 0 /dev/hda1-c 0 sets the number of mounts between checks to 0, thus turning it off.■ Note This means that your filesystem will never be checked unless you do it manually! This is a problemonly if you’re using a non-journaled filesystem such as ext2. Journaling means that there’s no need for regularautomatic fscks.More useful is setting the value to different numbers for different partitions so that they don’t all getchecked on the same bootup. This means that at least you’ll be checking only one partition on any givenboot, which will speed things up a little.tune2fs -c 13 /dev/hda1tune2fs -c 17 /dev/hda2120Download at WoweBook.Com
CHAPTER 5 ■ WORKING WITH FILESYSTEMSAlternatively, set the filesystem to be checked every so many days rather than every so manymounts:tune2fs -i 13d /dev/hda1-i 13d sets the interval between checks to 13 days. Use 13w for 13 weeks, or use 13m for 13 months.Again, you can set this to be different values for different partitions.To force a check at the next reboot, you can set the number of mounts that the filesystem has had:tune2fs -C 14 /dev/hda1-C 14 will set the mount count to 14, which if you’ve set the automatic check to happen every 13mounts, means that the next time the filesystem is mounted (most likely on system reboot), it’ll bechecked.5-3. Saving Space on Large Filesystems and DirectoriesIf you have a really large filesystem, you can save some space by limiting the number of backupsuperblocks (see recipe 4-10 for when backup superblocks can come in handy.) However, you don’tneed quite as many as the default setting gives you if your directory is very large.tune2fs -O sparse_super /dev/hda1Similarly, for large directories, you can use hashed b-trees to speed up directory lookups:tune2fs -O dir_index /dev/hda1To set two -O options at once, use a comma and no space between the options:tune2fs -O dir_index,sparse_super /dev/hda15-4. Working with Disks, UUID, and LabelsAs well as the standard /dev/hda1, /dev/sda2 notation that you’re probably used to for referring to disks,<strong>Linux</strong> also provides universal unique identifier (UUID) notation. The major advantage of this is that,unlike the /dev notation, it’s linked specifically to a particular piece of hardware. So, although /dev/notation can shift between disks depending on how they’re plugged in, if you use UUID, this shouldn’thappen. This avoids the possibility of a system reconfiguration causing disks to be renamed and thuscausing knock-on breakage of things that reference that disk.The first part of this is to find out the existing UUID of your disks; you can do this using the blkidcommand:> blkid /dev/hda1/dev/hda1: UUID="0ef96300-36c0-4575-8a1d-2d36ff4cd585" SEC_TYPE="ext2" TYPE="ext3"121Download 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 3 ■ MONITORING AND UPDATI
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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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