DragonFly On-Line Manual Pages

Search: Section:  

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
              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
       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 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 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)

Search: Section: