"offline" media check of install DVD?

[Tony Nelson]

At 7:38 PM -0700 1/1/07, Charles Curley wrote:
>Content-Type: multipart/signed; micalg=pgp-sha1;
>	protocol="application/pgp-signature"; boundary="BghK6+krpKHjj+jk"
>Content-Disposition: inline
>
>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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