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mailto(bugs-rzip@tridgell.net)
manpage(rzip)(1)(October 2003)()()
manpagename(rzip)(a large-file compression program)
manpagesynopsis()
rzip [OPTIONS] <files...>
manpagedescription()
rzip is a file compression program designed to do particularly
well on very large files containing long distance redundancy.
manpagesection(OPTIONS SUMMARY)
Here is a summary of the options to rzip.
verb(
-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
)
manpageoptions()
startdit()
dit(bf(-h --help)) Print an options summary page
dit(bf(-V --version)) Print the rzip version number
dit(bf(-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 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.
dit(bf(-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.
dit(bf(-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.
dit(bf(-S --suffix)) Set the compression suffix. The default is '.rz'.
dit(bf(-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.
dit(bf(-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.
dit(bf(-P --progress)) If this option is specified then rzip will show
the percentage progress while compressing.
enddit()
manpagesection(INSTALLATION)
Just install rzip in your search path.
manpagesection(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.
manpagesection(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.
manpagesection(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.
manpagesection(CREDITS)
Thanks to the following people for their contributions to rzip
itemize(
it() Paul Russell for many suggestions and the debian packaging
it() The authors of bzlib for an excellent library
)
manpageauthor()
rzip was written by Andrew Tridgell
url(http://samba.org/~tridge/)(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.
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