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I am switching an old Gentoo machine over to Kubuntu for my father to use, and since I had a 500Gb external drive available to me at the time, I decided to use dd to make a complete copy of his harddisk first. I used the following command:
dd if=/dev/hda of=dbackup.img bs=1M
The copy went just fine, with dd reporting no errors.
I then checksummed both the harddisk I had just imaged and the backup image. The checksums were different!
I did md5sum /dev/hda > disk.txt for the harddisk, and md5sum dbackup.img > backup.txt for the image.
Thinking it to be a fluke, I ran md5sum again with ">>" in place of ">" to append to the checksum files I already had.
Lo and behold, the harddisk returned a DIFFERENT CHECKSUM! But the backup image reported the same checksum as before.
I tried this twice more, and each time the backup image came out with the same checksum, and the HDD came out with a different one!
What on earth could this be? I ran badblocks on the harddisk, and it reported no problems in non-destructive read-only mode, and I know it can't be a memory problem or the checksum of the image wouldn't come out the same each time.
The behavior is the same in binary mode, in case you are wondering.
doing the same thing with cksum instead of md5sum gives me cksum checksums which differ only in the first half of the checksum. The second half is the same.
Now I'm really confused.
I'm burning a brand new knoppix CD, rebooting the machine to ensure it has no errors (memory/hdd), and starting this process over once I can "see" my HDD partitions on the desktop in knoppix. If none of this helps, I'm going to make a dd image and hope its good, then install Kubuntu anyway. There isn't much in the way of critical data on this machine anyhow.
Still, any hypotheses as to why I'm seeing this strange behavior are appreciated.
I never did figure out what it was...I notice the same problems when imaging the same CD on different computer systems. Perhaps it is a file system/architecture dependent thing? One machine is x86_64 and the other is x86. Both have ext3 root partitions though... Strange indeed.