Re: tar giving different results for same command, trying to test cdrom device integrity

[Paul E Condon <pecondon@quiknet.com>]

Walter Tautz wrote:

> I am curious if anyone can clear up the following phenomena
> for gnu tar on testing:
>
> # tar --version
> tar (GNU tar) 1.13.25
> Copyright (C) 2001 Free Software Foundation, Inc.
> This program comes with NO WARRANTY, to the extent permitted by law.
> You may redistribute it under the terms of the GNU General Public License;
> see the file named COPYING for details.
> Written by John Gilmore and Jay Fenlason.
>
> basically I have  cdrom mounted under a directory
>
> and i ran
>
> tar zcvf win2k.tgz /mnt
>
> and
>
> tar zcvf win2k-2.tgz /mnt
>
> Perhaps I should be using different options to get the
> same files:
>
> # cmp -version
> cmp - GNU diffutils version 2.7
>
> cmp -l on the files yields:
>
> # cmp -l *
>      5  35 362
>          6   4   2
>
> I also did a dd on the raw device and that at least gave no differences.
>
> I am trying to determine whether the cdrom drive is faulty. Does anyone know
> of good ways to test such a thing.
>
> -walter

I have had some success with the following procedure:
1> use dd to create an image copy of the cd on hard disk;
       e.g. dd if=/dev/cdrom of=/tmp/cdcpy1
2> mount a loop back view of cdcpy1
       e.g. mount -t iso9660 -o ro,loop=/dev/loop0 /tmp/cdcpy1 /your/mount/point

3> use diff to compare /your/mount/point to /cdrom

Paul