Re: DVD 1 of squeeze 6.0.1.a not OK?
I confirm that I cannot mount test_mix.iso.
On Apr 13, 2011, at 10:39 PM, Thomas Schmitt wrote:
> Hi,
>
> i still ponder about the supposed MBR allergy of the Macs.
>
> Maybe one should make another test by transplanting the first 32 kB of
> the i386 image into the first 32 kB of the sparc image.
> If the allergy theory is right, then that should not mount any more:
>
> dd if=debian-6.0.1a-i386-DVD-1.iso bs=2K count=16 >test_mix.iso
> dd if=debian-6.0.1a-sparc-CD-1.iso bs=2K skip=16 >>test_mix.iso
>
> If it mounts nevertheless, then one would have to explore the subtle
> differences between genisoimage and xorriso in detail. I already
> made a little list of suspects. (None convincing, though.)
>
> ------------------------------------------------------------------------
>
> me:
>>> A simple solution might be little de-MBR programs [...]
>>> Seek byte 0, write 32 kB of zeros, keep all other bytes unaltered.
> Anne Bezemer:
>> dd with conv=notrunc should do the trick.
>
> I should read the dd man page more often.
>
>
>> Of course, that way you change the file in-place ("make a backup first,
>> if you want to keep the original").
>
> Yep. Plus the risk to patch the wrong file.
>
> The advantage of specialized programs would be that they could
> insist in file name patterns like "debian-*.iso" and check
> bytes 32768 to 32773 whether they are {0x01,'C','D','0','0','1'}.
> That's a magic number for ISO 9660 and would thus tell with some
> probability that patching the first 32 kB will not destroy directory
> tree or file data.
>
>
>> Also, publishing an official md5sum of the patched file would be a good
>> idea.
>
> Computable on the server side without actually patching an image:
>
> (dd bs=2K count=16 if=/dev/zero ; dd bs=2K skip=16 if=debian...iso) | md5sum
>
> Nevertheless, one could argue that verifying the checksums before
> patching should suffice if patching itself is trustworthy.
>
>
> Have a nice day :)
>
> Thomas
>
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