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cat : ignore I/O error

 
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# 1  
Old 04-10-2010
cat : ignore I/O error
Hello,

I have to backup some cds but I get an I/O error message when I hit a bad sector (using the command cat) and my question is : what can I do to force the system to ignore theses errors (or all kind of errors) and let the process keep going?

(sorry for any eventuals language errors, I am french)

Thanks.
# 2  
Old 04-10-2010
Use "dd" with the "noerror" and "sync" options instead of "cat".
# 3  
Old 04-10-2010
Thanks i will have a look at this.

If we consider to only use cat : is it possible to just modify the C code of the cat command in order to avoid the process to stop? Or is it something else that stop the process?
Last edited by Actraiser47; 04-10-2010 at 01:44 PM..
# 4  
Old 04-10-2010
Of course it's possible given the source code. However:
  • it'd be a ridiculous amount of work
  • it could break things you didn't expect -- imagine your modified cat reading a file that gets truncated, and going into an endless loop when it tries to "read past" the "bad block"
  • It might need to work differently than the way you imagine it -- it wouldn't merely need to "skip past" bad blocks, it'd have to write empty blocks to match the blocks it skipped or else your output would be smaller than your input. which'd mean knowing a block size. which would mean either reading that from the disk or getting from the commandline somehow. etc. etc. etc.
  • cat is really not meant for dealing with block devices, while dd really is designed for them
  • There's already a perfectly good command that does precisely what you want the exact way you want to do it. dd's easy once you know it, and available almost anywhere.
Code:
dd if=/path/to/input of=/path/to/output conv=noerror,sync

Last edited by Corona688; 04-10-2010 at 06:08 PM..
# 5  
Old 04-10-2010
Actually dd's cousin ddrescure may be more suitable for the job.
Last edited by binlib; 04-10-2010 at 09:55 PM..
# 6  
Old 04-11-2010
Quote:
Originally Posted by binlib
Actually dd's cousin ddrescure may be more suitable for the job.
  1. They both work fine
  2. They're not cousins
  3. He almost certainly has dd and doesn't have dd_rescue
# 7  
Old 04-11-2010
Thanks for your replies.

So I used dd (not ddrescue) with suggested options but the backup has not been done correctly. When I just open a movie or program, it just doesnt work and when I open a plain text file (even rtf), I get long lines of weird caracters.

Soooo it didnt work and I dont really know what to do now... anyway I will try again (it tooks 5 hours).

EDIT : What means "noerror" and "sync"?
EDIT2 : OOPS! I just looked at the history of the commands I used and I didnt used the option "sync", just "noerror". Well I am really gonna give another 'correct' try. Scuse me again... (anyway can someone tell me what for are these options?)

---------- Post updated at 04:19 PM ---------- Previous update was at 10:00 AM ----------

Hello again

Well, this time it worked... everything from the test disc has been retreived... thanks for your help!
Last edited by Actraiser47; 04-11-2010 at 05:10 AM..
 
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