Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 4 ■ TAKING BACKUPS AND MANAGING DATA4-11. Using Foremost to Retrieve DataIf fsck and dd aren’t enough to retrieve your data, you’ll need to try a little harder. You’ll need to startlooking through the raw disk data. You can do this manually by grepping through the disk image or usingstrings (see recipe 9-6), but it’s very hard work and will get you somewhere only if you’re lucky and ifyou’re just looking for text files.An easier alternative is Foremost (http://foremost.sourceforge.net/, available as theDebian/Ubuntu package foremost). This software was originally developed by the U.S. government fordata recovery, and it searches through a disk image to look for file headers, file footers, and otherinternal data structures.■ Note It’s a better bet to run this on a disk image, produced with dd as in recipe 4-8, than on your bad disk.The default rescue is straightforward and will output to the directory from where you ran it:foremost image.ddOr you can search for all defined types. These include text files; .jpg and other image files; .doc files;OLE files (a format used by PowerPoint, Excel, and so on); zipped files; media files using .avi, .wmv, andother formats; and some source code files). Then write them to a specified output directory:foremost -t all -o /rescue/dir -i image.ddThe -i switch identifies the image, the -o switch identifies the output directory to write to, and the -t switch gives file types (here it’s all). You can use the specific file type options if you’re looking only forspecific file types or if you want to extract and deal with different file types separately.If Foremost works, your files will be extracted without correct ownership and permissions, so you’llneed to go over the data afterward to correct that.■ Note scalpel and magicrescue (both available as Debian/Ubuntu packages of the same names) do the samesort of data recovery but are a little less resource intensive. None of these will re-create your directory structure.4-12. Rescuing Data: AutopsyAutopsy/Sleuthkit (available at http://www.sleuthkit.org/autopsy/ or as a package for most distros,called autopsy and sleuthkit on Debian/Ubuntu) is a Perl disk forensic browser with which you can lookthrough a filesystem in detail. If the previous recipes haven’t got you anywhere, you can try this recipe.116Download at WoweBook.Com
CHAPTER 4 ■ TAKING BACKUPS AND MANAGING DATA■ Note Again, you should run this on a disk image (created as in recipe 4-8) rather than on the disk itself. Themore you use your damaged disk, the more you risk damaging it.Start Autopsy, and see whether you can read your copied filesystem. It is possible that even if thefilesystem itself is still unreadable, you may be able to get at some of the inode and metadatainformation.In this case, you can experiment with the Sleuthkit command-line tools:• ils lists inode information from the image.• ffind finds the file or directory name using the inode.• icat outputs the file content based on its inode number.So, you can get inode information, use ffind to get the file/directory name, and then output thecontent with icat once you establish whether you’re looking at a file or a directory.As an example of this process, the Sleuthkit fls command will list the files and directory names in aparticular image:fls hdaimage.dd -r -f ext3 -i rawSo, you might get some output from fls, which includes the following line:r/r * 10: myfile.txtThe r/r at the start of the line gives the directory entry type value and the file type (r means regularfile; d is a directory). As a rule, these will match. * indicates that it’s been deleted, and 10 is the inodenumber. The final field is of course the file name.Use this command to retrieve the contents of this file:icat -r -f ext3 -i raw hdaimage.dd 10 > myfile.txtThis uses file recovery techniques (-r) since the file has been deleted. -f ext3 specifies thefilesystem type, and -i raw uses the image type that you’re working from. hdaimage.dd is the path to theimage file, and 10 is the inode we want (as retrieved from the earlier fls command). The recoveredoutput is piped into the file name that was retrieved from fls.■ Note Use the sorter script to look for particular types of file (for example, images). To use the suppliedimages.sort file, this should work:# sorter -f ext3 -C /usr/local/sleuthkit/share/sort/images.sort -d data/sortedimages -h -s hdaimage.dd117Download 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 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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