cmd:par

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Usage

  par c(heck)   [options] <par file>         : Check parity archive
  par r(ecover) [options] <par file>         : Restore missing volumes
  par a(dd)     [options] <par file> [files] : Add files to parity archive
Advanced:
  par m(ix)    [options] : Try to restore from all parity files at once

Info

Par uses Reed-Solomon coding to make multiple parity volumes from the same set of files.

What this means is that you can recover as many files as you have recovery volumes. Any recovery volumes for that set will do.

Typical example of use

create

You are uploading a rar-archive, Archive.rar to a newsgroup, split into 40 files. You decide to make a parity archive with five recovery volumes:

1. >par add -n5 Archive.PAR Archive.r

1.	>par add -n5 Archive.PAR Archive.r
	You machine rattles for a minute or two, resulting in one (small) Archive.PAR file, and five files Archive.P01 - P05. You upload these.

check

People download your files, and the Archive.PAR file to check if they downloaded correctly. Someone runs par to check if he got all files:

>par check Archive.PAR

recover

It reports that three files are missing, and he would need three parity volumes to recover them. He tries to download these, and he gets Archive.P02, .P04 and .P05. Then he runs par to recover those files:

>par recover Archive.PAR

His machine rattles for a minute or two, and all his files are restored.

Work on corrupted files

$ par recover -m eBooks_collection.part139.par
Checking eBooks_collection.part139.par
 eBooks_collection.part001.rar            - OK
 eBooks_collection.part002.rar            - OK
 eBooks_collection.part003.rar            - OK
 ...
  eBooks_collection.part108.rar            - OK
 ERROR: eBooks_collection.part109.rar: Failed md5 sum
 eBooks_collection.part109.rar            - CORRUPT
 eBooks_collection.part110.rar            - OK
 ERROR: eBooks_collection.part111.rar: Failed md5 sum
 eBooks_collection.part111.rar            - CORRUPT
 eBooks_collection.part112.rar            - OK
 ...

Restoring:
    Rename: eBooks_collection.part109.rar -> eBooks_collection.part109.rar.bad
 Rename: eBooks_collection.part111.rar -> eBooks_collection.part111.rar.bad
 0%....10%....20%....30%....40%....50%....60%....70%....80%....90%....100%
 eBooks_collection.part109.rar            - RECOVERED
 eBooks_collection.part111.rar            - RECOVERED

This version of par never overwrites an existing file. It can, however, move files out of the way (with the -m flag)

$ par recover eBooks_collection.part139.par
 Checking eBooks_collection.part139.par
 eBooks_collection.part001.rar            - OK
 eBooks_collection.part002.rar            - OK
 eBooks_collection.part003.rar            - OK
 ...
  eBooks_collection.part108.rar            - OK
 ERROR: eBooks_collection.part109.rar: Failed md5 sum
 eBooks_collection.part109.rar            - CORRUPT
 eBooks_collection.part110.rar            - OK
 ERROR: eBooks_collection.part111.rar: Failed md5 sum
 eBooks_collection.part111.rar            - CORRUPT
 eBooks_collection.part112.rar            - OK
 ...

Restoring:
 ERROR: eBooks_collection.part109.rar: File exists
 eBooks_collection.part109.rar            - NOT RESTORED
 ERROR: eBooks_collection.part111.rar: File exists
 eBooks_collection.part111.rar            - NOT RESTORED
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