CODEWITHSUNDEEP
linuxddext2
SpyderDriver
SpyderDriver

Reputation:

DD img different MD5's?

We have a smart media card with a linux install on it that we need to duplicate. We created an img with DD and then used dd to write the img back to a couple of new smart media cards. We have compared the MD5 checksum of both the original and the new copies and they are different.

Here is what we used:

dd if=/dev/sdb of=myimage.img

dd if=myimage.img of=/dev/sdb

dd if=/dev/sdb of=newimage.img

Anyone have any ideas of why these come out different?

Upvotes: 4

Views: 809

Answers (3)

Martin Thurau
Martin Thurau

Reputation: 7654

If you mounted /dev/sdb in between it would be an answer. If I remember correctly ext2 and ext3 have a "mount counter".

Upvotes: 1

Joe Koberg
Joe Koberg

Reputation: 26769

If the cards are different sizes, dd'ing the smaller image to a larger card will not "fill it up", and zeros will remain at the end of the card. An image made from this card will be different than the original image.

It's also always possible that data was mis-written, mis-read, or otherwise corrupted in-transit.

Upvotes: 2

Liudvikas Bukys
Liudvikas Bukys

Reputation: 5870

The card capacities differ? Running 'ls -l myimage.img newimage.img' might tell you something. Running 'cmp -l myimage.img newimage.img' might tell you something.

Upvotes: 1

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