I just tried burning both a Debian CD and a Debian DVD from their .iso files and I've got a weird behavior: the checksum of the CD is correct but the one of the DVD ain't.
Here's what working:
- downloaded the two .iso files
- verified the checksum of the two .iso files
- burn the CD debian-7.1.0-amd64-CD-1.iso to a CD
verify that the CD is correct by issuing:
dd if=/dev/sr0 | md5sum (or sha-1 or sha-256)
And this works fine: the checksum(s) I get from the CD by using dd and piping into md5, sha-1 or sha-256 do match the official checksums.
Now what I don't get is that I did burn a DVD from the DVD .iso --and I know that the file has been correctly downloaded seen that the .iso file checksum is correct.
However if I put the DVD in the drive and issue the same:
dd if=/dev/sr0 | md5sum (or sha-1 or sha-256)
then I get a bogus checksum.
The DVD still looks correct in that the files all seem to be there.
So here's my question: can I verify that a DVD has been correctly burned by using dd and piping its output into md5sum (or sha-1 or sha-256) or is there something "special" that would make dd work for verifying burned CDs but not burned DVDs?
*(note that I used Disk Utility on OS X to burn both the CD and the DVD)*
dd
probably has nothing to do with the problem. It's not doing anything thatcat /dev/sr0 | md5sum
ormd5sum /dev/sr0
wouldn't do, except maybe use a different buffer size, and that won't change the hash. As long as you still have the image file around, you can also runcmp /dev/sr0 foo.iso
to get some more information on whether they are really different. If it reports EOF on the image file, then the burned disc just has some padding on the end.