Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 5 ■ WORKING WITH FILESYSTEMS■ Note You can also do this the other way around, starting from the UUID to find the /dev/ reference:> findfs UUID=d40acb36-5f32-4832-bf1a-80c67833a618/dev/sda5Alternatively, use df to look at the devices you currently have mounted, and then look at/dev/disk/by_uuid/ to see how they match up:> ls -l /dev/disk/by-uuidtotal 0lrwxrwxrwx 1 root root 10 2008-10-13 13:41 178f2692-fef4-4485-b9c5-445c990b502e -> ../../sda2lrwxrwxrwx 1 root root 10 2008-10-13 13:41 5b67edaf-078d-4ac0-8b1b-f2119da85482 -> ../../sdb1lrwxrwxrwx 1 root root 10 2008-10-13 13:41 77cb9269-447a-45ce-b585-1c45ae3290bd -> ../../sda1lrwxrwxrwx 1 root root 10 2008-10-13 13:41 d40acb36-5f32-4832-bf1a-80c67833a618 -> ../../sda5Once you have the UUID of a device, you can use it in your /etc/fstab by putting UUID=uuid at thestart of the relevant line, instead of /dev/hdaX:UUID=d40acb36-5f32-4832-bf1a-80c67833a618 /local ext3 defaults 0 2A similar but more human-readable option is to give the disk a human-readable label using thetune2fs command:tune2fs -L localdata /dev/hda2Then edit /etc/fstab to use the label to mount the disk:LABEL=localdata /local ext3 defaults 0 2However, the advantage of using the UUID is that you can check what device name (for example,/dev/sda2) this is being translated to by looking at /dev/disk/by-uuid/ (see the earlier code snippet),whereas there’s no similar list by disk label.If you’ve cloned a disk, such as by using dd (see recipe 4-10), you might want to be able to mountboth the original and the clone at the same time. To make sure that the UUIDs don’t clash, first generatea new UUID, and then assign it to the new disk with tunefs:> uuidgen79fb806d-4350-4b8c-8bc3-f3bb0c6b56f2> tune2fs -U 79fb806d-4350-4b8c-8bc3-f3bb0c6b56f2 /dev/sdc1122Download at WoweBook.Com
CHAPTER 5 ■ WORKING WITH FILESYSTEMSNow mount the new disk:mount -U 79fb806d-4350-4b8c-8bc3-f3bb0c6b56f2 /mnt/clonedisk■ Note See some of the other things you can do to filesystems on the fly with tunefs in recipes 5-1 to 5-3.5-5. Resizing Partitions on the FlyIf you have old machines, you may find that you start running out of space on / after a while. It’s worthchecking that there’s not lots of space being wasted in /tmp and/or /var. Use the du command tosummarize disk usage in various directories. The -s option summarizes the disk space used by all therelevant subdirectories, and -h gives human-friendly output in megabytes/gigabytes rather than inkilobytes.du -sh /tmpdu -sh /var/*However, the bottom line is that software keeps getting bigger, as do distributions. It may be thatyou really do want everything you have installed in / but you’re still running into the size limits imposedby whatever size you set / to originally. One way to avoid this is simply to use a single nonswap partitionper disk, but that has other disadvantages; for example, separating the system/software files in / fromuser data (in /home or elsewhere) means that it’s easy to reinstall a system if you start having problemswith it.Instead, it’s useful to have options for resizing a partition when that becomes necessary. parted is avery useful utility that will resize your partition on the fly. It does have one important restriction: you canresize partitions only at their ends. You can’t move the start point of a partition. This means that youcan’t just take space from the front of the next partition along when you need to resize a partition.However, there is a way to get around this!■ Note It is strongly recommended that you read the parted manual before starting to do this and also that youhave backups of all your data (which you should have anyway, of course).Let’s say your disk setup looks like this (we’ll ignore the swap space for the moment):/dev/hda1 / 5GB 4.5GB used/dev/hda2 /local 105GB 40GB usedYou want to expand / by 5GB, which should give you enough breathing space for the immediatefuture. It requires some juggling around and may take a while (because you will need to copy largequantities of data around more than once), but this is how to do it.123Download 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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