rzip(1)

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)

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Free and Open Source Software