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I have a ext3 filesystem on a .img file. After mounting and unmounting it, I noticed that the md5sum is changed, even if no file inside was changed!

md5sum myfilesystem.img
XXXX myfilesystem.img
mount -t ext3 myfilesystem.img temp/
umount temp/
md5sum myfilesystem.img
YYYY myfilesystem.img

Why does XXXX differs from YYYY? I clearly didn't touch anything inside myfilesystem.img.

share|improve this question
last mount date is stored :) – gasko peter Feb 15 '13 at 14:16
up vote 6 down vote accepted

Because, if you mount the ext3 in writable mode, there are a few things that get updated, like the last mount date. Try if this also happens when you mount with -o ro.

share|improve this answer
With -o ro the md5sum is not changed. – michelemarcon Feb 15 '13 at 14:58
Note that sometimes, even mounting with -o ro doesn't guarantee that nothing gets written. See the man page for mount under --read-only. – Michael Kjörling Feb 15 '13 at 15:35

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