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
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
- 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 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.