Re: How to compute sha256sum

[Eric Smith <spacewar@xxxxxxxxx>]

The problem is that when you read the CD-ROM as a raw device, it will return more data than the length of the ISO image; there are almost always some additional sectors of padding beyond the end of the image.  Even dd'ing from the CD-ROM into shasum won't work unless you tell dd the number of blocks to copy, so that you don't include the padding.

Try something like
        dd if=/dev/sr0 of=foo.img bs=2k count=`isosize -d 2048 /dev/sr0` | sha256sum -

Note the backquotes for command substitution of the output of isosize.

I haven't tried this just now, so it's possible that I've got the details wrong.

Eric

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