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After writing an ISO image using Brasero, I discovered that the md5sum of the target DVD is different than the ISO image, despite no readability errors.

What has caused that difference?

  • 3
    Your ISO image is smaller than the capacity of DVD? The rest might be read as zero, which might be reason cause the hashsum difference. – 炸鱼薯条德里克 Mar 11 at 2:15
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    Maybe brasero created another image, with the iso as a file contained in it? I've always used growisofs and cdrecord directly, and the checksum always matched, unless there was some error. – Uncle Billy Mar 11 at 8:54
  • @炸鱼薯条德里克 have you actually tried that? your comment is completely off. – Uncle Billy Mar 11 at 9:02
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    In cases like this, I run cmp -l known-good.iso /dev/sr1 . It's OK if there's an error message saying the first file is shorter. To be more thorough, you could try (cat known-good.iso /dev/zero) | cmp -l - /dev/sr1 and see if the error output by cmp is about the second file being shorter. – Mark Plotnick Mar 11 at 18:49
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    @neverMind9 maybe it's trying to close/finalize (or unclose) the last session? (that results in the TOC on the disc being different from the TOC part of the iso image). Unfortunately, I'm not able to test anything right now. – Uncle Billy Mar 11 at 19:39
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When you do this kind of verification , md5sum or sha1sum you must be sure that your reading the same amount of data .

stat --printf '%s\n'  file.iso

blockdev --getsize64 /dev/sr1

if the data does have the size , you must compute on the smallest size . to do this :

dd if=file.iso bs=2k count=9000 | md5sum 

dd if=/dev/sr1 bs=2k count=9000 | md5sum
  • In that case, both have the same MD5. – neverMind9 Mar 11 at 20:24

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