Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 4 ■ TAKING BACKUPS AND MANAGING DATAThis will treat the source image (using the -s option, which here is hdaimage.dd) as an ext3 filesystem (set withthe -f option). -C specifies the config file, and -d specifies the directory to output to. If you add the -h option,thumbnails of the image files will also be created. There are other config (rules) files supplied, or you can writeyour own.4-13. Securely Wiping DataIt’s quite common to find yourself replacing machines that are still functional but don’t match up to thespecs you now need. These days, a three-year practical life span is about the best case in mostenvironments, but a three-year-old computer should still be perfectly functional. Ideally, therefore, youshould give them a new home rather than just throwing them out. Take a look for charities or recyclingorganizations in your area, or even offer them around to your staff!However, before you send the machines off to begin their new life, you need to consider datasecurity. Just deleting old data isn’t enough. It’s possible, if you know what you’re doing, to retrievedeleted data from the disk.DBAN (which stands for Darik’s Boot And Nuke), available from http://www.dban.org/, is designedto fully and securely wipe your disk. It’s a downloadable self-contained boot disk, available for CD/DVD,floppy disk, or USB flash drive. Boot from it, and it will look for hard disks on the system and then giveyou the option of deleting any or all of them by just hitting Enter.■ Note For RAID arrays, you may need to manually disassemble the array first.Several wipe methods are available, from a quick erase to a full three-pass wipe, including a coupleof methods that are used by the U.S. Department of Defense! The autonuke option, which is the defaultfrom the first screen, will automatically run through all detected disks, securely wiping them, so becareful with it, and make sure that you really are done with the machine before you start.■ Note A full standard disk wipe, especially on an old or slow machine, can take a long time (three to four hoursis quoted as standard, but it can be much more than that on older machines). I usually leave it running overnight.DBAN is easy to use and very secure; it uses multiple methods (including the Gutmann method andthe Mersenne twister) to ensure that the data really is gone for good. It’s a handy program to keeparound on disk, but make sure you label it very clearly and don’t end up booting from it by accident! (Itwon’t run without input, but it’s still best to be careful with anything seriously destructive.)118Download at WoweBook.Com
C H A P T E R 5■ ■ ■Working with FilesystemsFilesystems are the backbone of a Linux system (after all, in Linux, absolutely everything is a file). Thischapter discusses how to tune and make changes to the default Linux filesystems, how to resize yourfilesystems when you find yourself running out of space (something that seems to happen howevermuch room you think you’ve given yourself!), RAID arrays, and alternative filesystems.5-1. Changing ext2 to ext3 with tune2fsThe ext2 and ext3 filesystems, which are the filesystems that you’re most likely to be using on your Linuxsystems, have various parameters set at the time of creation. (ext3 is the default on most modern distrosnow.) One of these is the journaling parameter, which is the fundamental difference between an ext2filesystem and an ext3 filesystem. tune2fs enables you to change these parameters on the fly.By turning an ext2 filesystem into an ext3 filesystem, you can add journaling to the filesystem on thefly. Journaling filesystems log changes to a journal area before committing them to the main disk, whichavoids potential data inconsistencies in the event of a crash. In general, disk operations in Linux willrequire more than one write event (for example, removing a file directory entry and then also markingthe space as free), so if there’s a power failure or other problem when only one part of a disk operationhas been completed, the filesystem will be in an inconsistent state. In a non-journaled filesystem, yourun fsck or a similar tool to walk the whole filesystem looking for (and ideally fixing) inconsistencies. Ina journaled filesystem, the journal is instead used to rerun all recent operations until the filesystem isconsistent again. This is much quicker and more reliable.The basic command to create a journal for an ext2 filesystem is as follows:tune2fs -j /dev/hda1This will create an immutable journal file (one whose state cannot be manually altered, so it’s safefrom accidental deletion) for the filesystem. On the next reboot, this file will be moved to a special inode.You may want to reboot sooner rather than later to make sure this happens (and thus that the journal filecan’t be accidentally lost).119Download 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 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 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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