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rzip(1)								       rzip(1)

       rzip - a	large-file compression program

       rzip [OPTIONS] <files...>

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

       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

       -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 com-
	      pression.	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 'run-
	      zip' 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  suf-
	      fix.  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.

       Just install rzip in your search	path.

       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 algo-
       rithms 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 con-
       tains 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	 redundency,  and  thus	 might
       achieve a much lower compression	ratio than rzip	can achieve.

       The  ideas behind rzip were first implemented in	1998 while I was work-
       ing on rsync. That version was too slow to be practical,	 and  was  re-
       placed by this version in 2003.

       Unlike  most  Unix compression programs,	rzip cannot compress or	decom-
       press 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.

       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

       rzip was	written	by Andrew Tridgell

       If  you wish to report a	problem	or make	a suggestion then please email

       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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