At 7:38 PM -0700 1/1/07, Charles Curley wrote:
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On Tue, Jan 02, 2007 at 01:17:24PM +1100, Danny Yee wrote:
> Peter Gordon wrote:
> > Each ISOs directory contains a file called SHA1SUM that contains the
> > SHA-1 hashes of the images. You can use a tool called sha1sum to
> > calculate this hash from the image and compare it to the content of the
> > SHA1SUM file.
>
> I wanted to check the burn, not the download. But your message gave
> me half what I wanted.
>
> I ended up doing the following
>
> * looked at how big the iso image was and divided that by 512 to get
> the number of blocks in it
> * dd if=/dev/dvd of=check.iso count=blocks
> * sha1sum check.iso
> * compared that with the SHA1SUM file
"sha1sum /dev/dvd" would have saved you a step. In Unix or Linux,
everything is a file. Everything.
...
This gives a different checksum than the command below, which gives the
correct checksum. Checking extra 0's at the end of the DVD changes the sum.
[]# dd if=/dev/dvd bs=2048 count=`isosize -d 2048 /dev/dvd` | sha1sum
AIUI, even this can fail due to the kernel readahead bug. Sometimes it is
necessary to read the ISO into a file and trim it to the correct size. See
Paul Howarth's isograb script at
<
http://www.city-fan.org/tips/IsoImageFromMedia>.
--
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