Description

Lunzip is a decompressor for the lzip format written in C. Its small size
makes it well suited for embedded devices or software installers that need
to decompress files but don't need compression capabilities. Lunzip is
compatible with lzip 1.4 or newer.

Lzip is a lossless data compressor with a user interface similar to the one
of gzip or bzip2. Lzip uses a simplified form of the 'Lempel-Ziv-Markov
chain-Algorithm' (LZMA) stream format to maximize interoperability. The
maximum dictionary size is 512 MiB so that any lzip file can be decompressed
on 32-bit machines. Lzip provides accurate and robust 3-factor integrity
checking. Lzip can compress about as fast as gzip (lzip -0) or compress most
files more than bzip2 (lzip -9). Decompression speed is intermediate between
gzip and bzip2. Lzip is better than gzip and bzip2 from a data recovery
perspective. Lzip has been designed, written, and tested with great care to
replace gzip and bzip2 as the standard general-purpose compressed format for
Unix-like systems.

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

   * The lzip format provides very safe integrity checking and some data
     recovery means. The program lziprecover 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 source 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 the lzip reference implementation 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.

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

Lunzip provides a 'low memory' mode able to decompress any file using as
little memory as 50 kB, irrespective of the dictionary size used to
compress the file. To activate it, specify the size of the output buffer
with the option '--buffer-size' and lunzip will use the decompressed
file as dictionary for distances beyond the buffer size. Of course, the
larger the difference between the buffer size and the dictionary size, the
more accesses to disk are needed and the slower the decompression is.
This 'low memory' mode only works when decompressing to a regular file
and is intended for systems without enough memory (RAM + swap) to keep
the whole dictionary at once. It has been tested on a laptop with a 486
processor and 4 MiB of RAM.

The option '--buffer-size' may help to decompress a file erroneously created
with a dictionary size much larger than the uncompressed size. (Lzip adjusts
the dictionary size to the uncompressed size, but third-party tools may not).

The amount of memory required by lunzip to decompress a file is about 46 kB
larger than the dictionary size used to compress that file, unless
'--buffer-size' is specified.

Lunzip 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

Decompressing a file is much like copying or moving it. Therefore lunzip
preserves the access and modification dates, permissions, and, if you have
appropriate privileges, 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).

Lunzip is able to read from some types of non-regular files if either the
option '-c' or the option '-o' is specified.

If no file names are specified, lunzip decompresses from standard input to
standard output. In this case, lunzip refuses to read compressed input from
a terminal, as this might leave the terminal in an abnormal state.

Lunzip correctly decompresses a file which is the concatenation of two or
more compressed files. The result is the concatenation of the corresponding
decompressed files. Integrity testing of concatenated compressed files is
also supported.

The ideas embodied in lunzip are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrei Markov (for the
definition of Markov chains), G.N.N. Martin (for the definition of range
encoding), Igor Pavlov (for putting all the above together in LZMA), and
Julian Seward (for bzip2's CLI).

LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never have
been compressed. Decompressed is used to refer to data which have undergone
the process of decompression.


Copyright (C) 2010-2024 Antonio Diaz Diaz.

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

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