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tar cvf 1.tar tmp
md5sum 1.tar

rm 1.tar
cd tmp
touch test.txt
rm test.txt
cd ..

tar cvf 1.tar tmp
md5sum 1.tar

i dont understand why these two check sums are different. how does adding a file and then removing it from the tmp directory create a "different" tar file?

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If you want to checksum a directory (or rather all files in it), using cfv will give better results. – Hubert Kario Jan 5 '11 at 13:43
up vote 7 down vote accepted

When you create and delete the test.txt file the modification time of the directory is updated. That's the difference in the tar file that causes the checksum to be different.

You can see the affect by doing ls -ld tmp before and after touching and removing the file. You can also see it if you do tar tvf before and after.


As LatinSuD mentioned in a comment, tar files contain date, owner and permission information about the files and directories contained within.

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Mention that tar files not only contain the files but also information about them like dates, owner, permission, etc. – LatinSuD Jan 5 '11 at 9:01
@LatinSuD: Done. Thanks. – Dennis Williamson Jan 5 '11 at 15:29

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