rzip(1)                                                                                                                                    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, --worst            fastest (worst) compression
       -6                     default compression level
       -9, --best             slowest (best) compression
       -d, --decompress       decompress
       -f, --force            force overwrite of any existing files
       -o, --output FILENAME  specify the output file name
       -k, --keep             keep existing files
       -L, --level LEVEL      set compression level
       -P, --progress         show compression progress
       -S, --suffix SUFFIX    specify compressed suffix (default '.rz')
       -v, --verbose          increase verbosity
       -V, --version          show version

OPTIONS

       -h --help
              Print an options summary page

       -V --version
              Print the rzip version number

       -0 (or --worst) to -9 (or --best) --level
              Set  the  compression  level from 0 to 9. The default is to use level 6, which is a reasonable compromise between speed and compres-
              sion.  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
              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 --output
              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 --suffix
              Set the compression suffix. The default is '.rz'.

       -f --force
              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 --keep
              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 --progress
              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 redun-
       dency. 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 pro-
       grams won't be able to take advantage of this redundency, 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)