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Gentoo install iso: different checksum after burning
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micmac
l33t
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Joined: 28 Nov 2003
Posts: 993

PostPosted: Sun Apr 06, 2014 5:32 pm    Post subject: Gentoo install iso: different checksum after burning Reply with quote

Hello all,

I wanted to verify the burned media and ended up with a checksum different to the original iso:

Step-by-step:

- downloaded the iso, checked with sha512sum, all OK
Code:
sha512sum -c install-amd64-minimal-20140403.iso.DIGESTS.asc
install-amd64-minimal-20140403.iso: OK

- burned to DVD+RW:
Code:
wodim -v -dao -eject fs=64m dev=/dev/sr0 install-amd64-minimal-20140403.iso

- checked block and volume size on the DVD afterward:
Code:
isoinfo -d -i /dev/cdrom | grep -i -E 'block size|volume size'
Logical block size is: 2048
Volume size is: 130584

- ripped the DVD:
Code:
dd if=/dev/cdrom of=test.iso bs=2048 count=130584

- compared the isos:
Code:
sha512sum *.iso
ddef2ef386ab6f9ddab9da8735d8671cfbe8c36a9ffce4b62ddde1f506b8672265c316f2e2cda21148f59133dc7fe4ce1ed3d840a6acd894910c5851f6eb01a1  install-amd64-minimal-20140403.iso
d7c8e8e05d1690af5c30cdbbf548df3659306e1794c31c7f924f3ab1aa69719a36417864ae80ba3c8dfe6e8a5db798517218c62dd98e7ca109b9a8fcedc757a6  test.iso

md5sum *.iso
5961618e379b8f25ca7e062b0a8c9d27  install-amd64-minimal-20140403.iso
cf027815a72d42588cf7c68b38916e87  test.iso


I burned to CDR as well because I got curious. Same issue (same checksum also). Any idea what this is about? Until now it always worked fine and the checksums matched (last time with a Debian installation iso).

Kind regards
B
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chithanh
Developer
Developer


Joined: 05 Aug 2006
Posts: 2152
Location: Berlin, Germany

PostPosted: Sun Apr 06, 2014 7:31 pm    Post subject: Reply with quote

You can play a bit with the dd count= or skip= parameters to find out whether the difference is at the beginning or at the end, or somewhere in between.

Also you can try
Code:
$ growisofs -Z /dev/sr0=foo.iso
to see if that gives you a different result.
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micmac
l33t
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Joined: 28 Nov 2003
Posts: 993

PostPosted: Sun Apr 06, 2014 7:57 pm    Post subject: Reply with quote

Hey!

Thanks for your reply. I tried it, it generates the same burn - which is a good thing :)

In the meantime I found an explanation on the web. It's all good after all. Sorry for the noise!

In case anybody wonders, here are some links:

http://askubuntu.com/a/177625
http://riceissa.bitbucket.org/computing/wodim.html
https://wiki.archlinux.org/index.php/DVD_Burning#Verifying_the_burnt_ISO_image
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