Description

Plzip is a massively parallel (multi-threaded) lossless data compressor
based on the lzlib compression library, with a user interface similar to
the one of lzip, bzip2 or gzip.

Plzip can compress/decompress large files on multiprocessor machines
much faster than lzip, at the cost of a slightly reduced compression
ratio. Note that the number of usable threads is limited by file size;
on files larger than a few GB plzip can use hundreds of processors, but
on files of only a few MB plzip is no faster than lzip.

When compressing, plzip divides the input file into chunks and
compresses as many chunks simultaneously as worker threads are chosen,
creating a multi-member compressed file.

When decompressing, plzip decompresses as many members simultaneously as
worker threads are chosen. Files that were compressed with lzip will not
be decompressed faster than using lzip (unless the "-b" option was used)
because lzip usually produces single-member files, which can't be
decompressed in parallel.

Plzip uses the lzip file format; the files produced by plzip are fully
compatible with lzip-1.4 or newer, and can be rescued with lziprecover.

The lzip file format is designed for long-term data archiving, taking
into account both data integrity and decoder availability:

   * The lzip format provides very safe integrity checking and some data
     recovery means. The lziprecover program can repair bit-flip errors
     (one of the most common forms of data corruption) in lzip files,
     and provides data recovery capabilities, including error-checked
     merging of damaged copies of a file.

   * The lzip format is as simple as possible (but not simpler). The
     lzip manual provides the code of a simple decompressor along with a
     detailed explanation of how it works, so that with the only help of
     the lzip manual it would be possible for a digital archaeologist to
     extract the data from a lzip file long after quantum computers
     eventually render LZMA obsolete.

   * Additionally lzip is copylefted, which guarantees that it will
     remain free forever.

A nice feature of the lzip format is that a corrupt byte is easier to
repair the nearer it is from the beginning of the file. Therefore, with
the help of lziprecover, losing an entire archive just because of a
corrupt byte near the beginning is a thing of the past.

Plzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer than compressors returning ambiguous warning
values (like gzip) when it is used as a back end for other programs like
tar or zutils.

Plzip will automatically use the smallest possible dictionary size for
each file without exceeding the given limit. Keep in mind that the
decompression memory requirement is affected at compression time by the
choice of dictionary size limit.

When compressing, plzip replaces every file given in the command line
with a compressed version of itself, with the name "original_name.lz".
When decompressing, plzip attempts to guess the name for the decompressed
file from that of the compressed file as follows:

filename.lz    becomes   filename
filename.tlz   becomes   filename.tar
anyothername   becomes   anyothername.out

(De)compressing a file is much like copying or moving it; therefore plzip
preserves the access and modification dates, permissions, and, when
possible, ownership of the file just as "cp -p" does. (If the user ID or
the group ID can't be duplicated, the file permission bits S_ISUID and
S_ISGID are cleared).

Plzip is able to read from some types of non regular files if the
"--stdout" option is specified.

If no file names are specified, plzip compresses (or decompresses) from
standard input to standard output. In this case, plzip will decline to
write compressed output to a terminal, as this would be entirely
incomprehensible and therefore pointless.

Plzip will correctly decompress a file which is the concatenation of two
or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.


Copyright (C) 2009-2014 Antonio Diaz Diaz.

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

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