[plug] CD read errors

Jim Householder nofixed at westnet.com.au
Tue May 17 18:33:15 WST 2005

Matt Kemner wrote:
> On Mon, 16 May 2005, quoth Cameron Patrick:
>>Also, if you find that your image _is_ missing a bit, using the
>>command-line tool `readcd` with the option to read one sector at a
>>time will often (slowly!) extract data off discs which are otherwise
>>hard to read, or which dd conks out on at the end.
> Another thing I can suggest, when dealing with things like Linux ISO
> images (and other things which are freely available via rsync) is to use
> readcd (or even dd) to read as much as you can from the CD (usually only
> the last few sectors give errors) and then use rsync against one of the
> public mirrors to "fix" the image - which will only take a few minutes,
> and will use negligible bandwidth.

Thanks all.

Assuming that any errors in the directory structure would be reported,
I used the following to check the discs:

mount the disc
cd to it
find -type f > ~/tmp/cd.ls
change each line  in cd.ls to compare (cmp) the original file (in
    /mnt/cdrom2) with the copy.
       ./file  -->  cmp {/mnt/cdrom2,/loop1}/file
mount the copy loopback
run the compares.

No errors or differences were reported for any of the 4 discs, so I
will assume the copies are good.


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