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Date: Mon, 13 Apr 2009 10:16:27 +0100
From: Dave Korn <dave DOT korn DOT cygwin AT googlemail DOT com>
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Subject: Re: debian-live-500-i386-rescue.iso: FAILED
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David Christensen wrote:

>> When I attempt to verify the checksums related to the "rescue" disk,
>> the ISO image appears corrupt:
>>    2009-04-11 21:00:35 dpchrist AT p43400e /cygdrive/h/data/iso/debian
>>    $ md5sum -c MD5SUMS 2>&1 | grep 'rescue.iso'
>>    debian-live-500-i386-rescue.iso: FAILED
>>    debian-live-500-i386-rescue.iso.list: OK
>>    debian-live-500-i386-rescue.iso.log: OK
>>    debian-live-500-i386-rescue.iso.packages: OK
>> I've downloaded MD5SUMS and debian-live-500-i386-rescue.iso twice,
>> with the same results.

> I ran more some more tests:
> 
> 2009-04-12 08:13:07 dpchrist AT p43400e /cygdrive/h/data/iso/debian
> $ md5sum debian-live-500-i386-rescue.iso
> b02c3606a3f35f160a591fe1154aa362 *debian-live-500-i386-rescue.iso
> 
> 2009-04-12 08:13:39 dpchrist AT p43400e /cygdrive/h/data/iso/debian
> $ grep 'rescue.iso$' MD5SUMS
> b02c3606a3f35f160a591fe1154aa362  debian-live-500-i386-rescue.iso
> 
> 2009-04-12 08:42:26 dpchrist AT p43400e /cygdrive/h/data/iso/debian
> $ md5sum -c MD5SUMS 2>&1 | grep 'rescue\.iso'
> debian-live-500-i386-rescue.iso: FAILED
> debian-live-500-i386-rescue.iso.list: OK
> debian-live-500-i386-rescue.iso.log: OK
> debian-live-500-i386-rescue.iso.packages: OK
> 
> md5sum computes the same checksum as what is contained in MD5SUMS, but
> prepends an asterisk to the filename on output.  So, the *.iso file is
> okay, but "md5sum -c MD5SUMS" is somehow broken (?).

  The asterisk means that md5sum has detected the file is binary and opened it
in binary mode.  The lack of an asterisk on the other files means that md5sum
has identified them as text and opened and summed them in text mode.  This is
deliberate, it means that the same text document checksums the same regardless
of line-end style, which is generally what you want when verifying download
integrity - e.g. in case ftp text mode translation has been in effect.

  The reason this situation is causing surprise on the Debian list is because
in Linux, there's no distinction between text and binary mode.  I don't know
if it even supports binary mode, because I would have expected it to use
binary mode everywhere rather than nowhere.

  As to whether md5sum is right to fail, well I think it has to draw your
attention to the fact that the modes don't match even though the checksums do,
because that means "something weird is going on and I don't understand why".
I'm pretty sure your download is good though!

    cheers,
      DaveK


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