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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 redundency.

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 ex-
	    isting files. If you set this option then rzip will  silently  over-
	    write 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 gi-
     gabyte)  in  the input file. The second stage is to use a standard compres-
     sion 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 redundency. 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  mag-
     nitude 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 directo-
     ries 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 dupli-
     cated 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 redundency, and thus might achieve a much lower	compres-
     sion 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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