NAME

       rzip - a large-file compression program

SYNOPSIS

       rzip [OPTIONS] <files...>

DESCRIPTION

       rzip  is  a  file compression program designed to do particularly well on very large files
       containing long distance redundancy.

OPTIONS SUMMARY

       Here is a summary of the options to rzip.

        -0            fastest (worst) compression
        -6            default compression
        -9            slowest (best) compression
        -d            decompress
        -o filename   specify the output file name
        -S suffix     specify compressed suffix (default '.rz')
        -f            force overwrite of any existing files
        -k            keep existing files
        -P            show compression progress
        -V            show version

OPTIONS

       -h     Print an options summary page

       -V     Print the rzip version number

       -0..9  Set the compression level from 0 to 9. The default is to use level 6,  which  is  a
              reasonable  compromise between speed and compression. The compression level is also
              strongly related to how much memory rzip uses, so if you  are  running  rzip  on  a
              machine  with  limited  amounts  of  memory then you will probably want to choose a
              smaller level.

       -d     Decompress. If this option is not used then rzip looks at the name used  to  launch
              the program. If it contains the string 'runzip' then the -d option is automatically
              set.

       -o     Set the output file name. If this option is not set then the output  file  name  is
              chosen based on the input name and the suffix. The -o option cannot be used if more
              than one file name is specified on the command line.

       -S     Set the compression suffix. The default is '.rz'.

       -f     If this option is not specified then rzip will not overwrite any existing files. If
              you set this option then rzip will silently overwrite any files as needed.

       -k     If  this  option  is  not  specified  then  rzip  will delete the source file after
              successful compression or decompression. When this option  is  specified  then  the
              source files are not deleted.

       -P     If  this  option  is  specified  then  rzip will show the percentage progress while
              compressing.

INSTALLATION

       Just install rzip in your search path.

COMPRESSION ALGORITHM

       rzip operates in two stages. The first stage finds and encodes large chunks of  duplicated
       data over potentially very long distances (up to nearly a gigabyte) in the input file. The
       second stage is to use a standard compression algorithm (bzip2) to compress the output  of
       the first stage.

       The key difference between rzip and other well known compression algorithms is its ability
       to take advantage of very long distance redundancy. The well known deflate algorithm  used
       in gzip uses a maximum history buffer of 32k. The block sorting algorithm used in bzip2 is
       limited to 900k of history. The history buffer in rzip can be up to  900MB  long,  several
       orders of magnitude larger than gzip or bzip2.

       It  is  quite  common  these  days  to  need  to compress files that contain long distance
       redundancies. For example, when compressing a set of home directories several users  might
       have  copies  of  the  same  file,  or of quite similar files. It is also common to have a
       single file that contains large duplicated chunks over long distances, such as  pdf  files
       containing  repeated  copies of the same image. Most compression programs won't be able to
       take advantage of this redundancy, and thus might achieve a much lower  compression  ratio
       than rzip can achieve.

HISTORY

       The  ideas  behind  rzip were first implemented in 1998 while I was working on rsync. That
       version was too slow to be practical, and was replaced by this version in 2003.

BUGS

       Unlike most Unix compression programs, rzip cannot  compress  or  decompress  to  or  from
       standard  input  or  standard output. This is due to the nature of the algorithm that rzip
       uses and cannot easily be fixed.

CREDITS

       Thanks to the following people for their contributions to rzip

       o      Paul Russell for many suggestions and the debian packaging

       o      The authors of bzlib for an excellent library

AUTHOR

       rzip was written by Andrew Tridgell http://samba.org/~tridge/

       If  you  wish  to  report  a  problem   or   make   a   suggestion   then   please   email
       bugs-rzip@tridgell.net

       rzip  is  released under the GNU General Public License version 2 or later. Please see the
       file COPYING for license details.

                                           October 2003                                   rzip(1)