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)