Ubuntu Manpage: par2 - PAR 2.0 compatible file verification and repair tool.

NAME

       par2 - PAR 2.0 compatible file verification and repair tool.

SYNOPSIS

       par2 c(reate) [options] <par2 file> [files]
       par2 v(erify) [options] <par2 file> [files]
       par2 r(epair) [options] <par2 file> [files]

         Or:

       par2create [options] <par2 file> [files]
       par2verify [options] <par2 file> [files]
       par2repair [options] <par2 file> [files]

DESCRIPTION

       par2  is  a  program  for creating and using PAR2 files to detect damage in data files and
       repair them if necessary. It can be used with any kind of file.

OPTIONS

       -b<n>  Set the Block-Count

       -s<n>  Set the Block-Size (Don't use both -b and -s)

       -r<n>  Level of Redundancy (%)

       -c<n>  Recovery block count (don't use both -r and -c)

       -f<n>  First Recovery-Block-Number

       -u     Uniform recovery file sizes

       -l     Limit size of recovery files (Don't use both -u and -l)

       -n<n>  Number of recovery files (Don't use both -n and -l)

       -m<n>  Memory (in MB) to use

       -v [-v]
              Be more verbose

       -q [-q]
              Be more quiet (-qq gives silence)

       --     Treat all remaining CommandLine as filenames

EXAMPLES

With PAR 2.0 you can create PAR2 recovery files for as few as 1 or as many as 32768 files.
If you wanted to create PAR1 recovery files for a single file you are forced to split the
file into muliple parts and RAR is frequently used for this purpose. You do NOT need to
split files with PAR 2.0.

To create PAR 2 recovery files for a single data file (e.g. one called test.mpg), you can
use the following command:

par2 create test.mpg

If test.mpg is an 800 MB file, then this will create a total of 8 PAR2 files with the
following filenames (taking roughly 6 minutes on a PC with a 1500MHz CPU):

test.mpg.par2 - This is an index file for verification only
test.mpg.vol00+01.par2 - Recovery file with 1 recovery block
test.mpg.vol01+02.par2 - Recovery file with 2 recovery blocks
test.mpg.vol03+04.par2 - Recovery file with 4 recovery blocks
test.mpg.vol07+08.par2 - Recovery file with 8 recovery blocks
test.mpg.vol15+16.par2 - Recovery file with 16 recovery blocks
test.mpg.vol31+32.par2 - Recovery file with 32 recovery blocks
test.mpg.vol63+37.par2 - Recovery file with 37 recovery blocks

The test.mpg.par2 file is 39 KB in size and the other files vary in size from 443 KB to 15
MB.

These par2 files will enable the recovery of up to 100 errors totalling 40 MB of lost or
damaged data from the original test.mpg file when it and the par2 files are posted on
UseNet.

When posting on UseNet it is recommended that you use the "-s" option to set a blocksize
that is equal to the Article size that you will use to post the data file. If you wanted
to post the test.mpg file using an article size of 300 KB then the command you would type
is:

par2 create -s307200 test.mpg

This will create 9 PAR2 files instead of 8, and they will be capable of correcting up to
134 errors totalling 40 MB. It will take roughly 8 minutes to create the recovery files
this time.

In both of these two examples, the total quantity of recovery data created was 40 MB
(which is 5% of 800 MB). If you wish to create a greater or lesser quantity of recovery
data, you can use the "-r" option.

To create 10% recovery data instead of the default of 5% and also to use a block size of
300 KB, you would use the following command:

par2 create -s307200 -r10 test.mpg

This would also create 9 PAR2 files, but they would be able to correct up to 269 errors
totalling 80 MB. Since twice as much recovery data is created, it will take about 16
minutes to do so with a 1500MHz CPU.

The "-u" and "-n" options can be used to control exactly how many recovery files are
created and how the recovery blocks are distributed amoungst them. They do not affect the
total quantity of recovery data created.

The "-f" option is used when you create additional recovery data.

e.g. If you have already created 10% and want another 5% then you migh use the following
command:

par2 create -s307200 -r5 -f300 test.mpg

This specifies the same block size (which is a requirement for additional recovery files),
5% recovery data, and a first block number of 300.

The "-m" option controls how much memory par2 uses. It defaults to 16 MB unless you
override it.

CREATING PAR2 FILES FOR MULTIPLE DATA FILES

When creating PAR2 recovery files form multiple data files, you must specify the base
filename to use for the par2 files and the names of all of the data files.

If test.mpg had been split into multiple RAR files, then you could use:

par2 create test.mpg.rar.par2 test.mpg.part*.rar

The files filename "test.mpg.rar.par2" says what you want the par2 files to be called and
"test.mpg.part*.rar" should select all of the RAR files.

VERIFYING AND REPAIRING

When using par2 recovery files to verify or repair the data files from which they were
created, you only need to specify the filename of one of the par2 files to par2.

e.g.:

par2 verify test.mpg.par2

This tells par2 to use the information in test.mpg.par2 to verify the data files.

par2 will automatically search for the other par2 files that were created and use the
information they contain to determine the filenames of the original data files and then to
verify them.

If all of the data files are ok, then par2 will report that repair will not be required.

If any of the data files are missing or damaged, par2 will report the details of what it
has found. If the recovery files contain enough recovery blocks to repair the damage, you
will be told that repair is possible. Otherwise you will be told exactly how many recovery
blocks will be required in order to repair.

To carry out a repair use the following command:

par2 repair test.mpg.par2

This tells par2 to verify and if possible repair any damaged or missing files. If a repair
is carried out, then each file which is repaired will be re-verified to confirm that the
repair was successful.

MISSNAMED AND INCOMPLETE DATA FILES

If any of the recovery files or data files have the wrong filename, then par2 will not
automatically find and scan them.

To have par2 scan such files, you must include them on the command line when attempting to
verify or repair.

e.g.:

par2 r test.mpg.par2 other.mpg

This tells par2 to scan the file called other.mpg to see if it contains any data belonging
to the original data files.

If one of the extra files specified in this way is an exact match for a data file, then
the repair process will rename the file so that it has the correct filename.

Because par2 is designed to be able to find good data within a damaged file, it can do the
same with incomplete files downloaded from UseNet. If some of the articles for a file are
missing, you should still download the file and save it to disk for par2 to scan. If you
do this then you may find that you can carry out a repair in a situation where you would
not otherwise have sufficient recovery data.

You can have par2 scan all files that are in the current directory using a command such
as:

par2 r test.mpg.par2 *

WHAT TO DO WHEN YOU ARE TOLD YOU NEED MORE RECOVERY BLOCKS

If par2 determines that any of the data files are damaged or missing and finds that there
is insufficient recovery data to effect a repair, you will be told that you need a certain
number of recovery blocks. You can obtain these by downloading additional recovery files.

In order to make things easy, par2 files have filenames that tell you exactly how many
recovery blocks each one contains.

Assuming that the following command was used to create recovery data:

par2 c -b1000 -r5 test.mpg

Then the recovery files that are created would be called:

test.mpg.par2
test.mpg.vol00+01.par2
test.mpg.vol01+02.par2
test.mpg.vol03+04.par2
test.mpg.vol07+08.par2
test.mpg.vol15+16.par2
test.mpg.vol31+19.par2

The first file in this list does not contain any recovery data, it only contains
information sufficient to verify the data files.

Each of the other files contains a different number of recovery blocks. The number after
the '+' sign is the number of recovery blocks and the number preceding the '+' sign is the
block number of the first recovery block in that file.

If par2 told you that you needed 10 recovery blocks, then you would need
"test.mpg.vol01+02.par2" and "test.mpg.vol07+08.par". You might of course choose to fetch
"test.mpg.vol15+16.par2" instead (in which case you would have an extra 6 recovery blocks
which would not be used for the repair).

NOTES

       This version of par2 does not support recording path information for files. Whilst you can
       create recovery files for files from multiple locations, it will expect all files to be in
       the  current  directory when verifying and repairing. This limitation will be corrected in
       an update.

REED SOLOMON CODING

       PAR2 uses Reed Solomon Coding to perform its calculations.  For  details  of  this  coding
       technique try the following link:

       ``A   Tutorial   on   Reed-Solomon  Coding  for  Fault-Tolerance  in  RAID-like  Systems''
       <http://www.cs.utk.edu/~plank/plank/papers/CS-96-332.html>

AUTHOR

       par2 was written by Peter Brian Clements <peterbclements@users.sourceforge.net>.

       This man page was contributed  by  Andres  Salomon  <dilinger@voxel.net>  for  the  Debian
       GNU/Linux system (but may be used by others).

                                             May 2004                                     par2(1)