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3 Lzip is a lossless data compressor with a user interface similar to the one
4 of gzip or bzip2. Lzip uses a simplified form of the 'Lempel-Ziv-Markov
5 chain-Algorithm' (LZMA) stream format, chosen to maximize safety and
6 interoperability. Lzip can compress about as fast as gzip (lzip -0) or
7 compress most files more than bzip2 (lzip -9). Decompression speed is
8 intermediate between gzip and bzip2. Lzip is better than gzip and bzip2 from
9 a data recovery perspective. Lzip has been designed, written, and tested
10 with great care to replace gzip and bzip2 as the standard general-purpose
11 compressed format for unix-like systems.
13 For compressing/decompressing large files on multiprocessor machines plzip
14 can be much faster than lzip at the cost of a slightly reduced compression
17 For creation and manipulation of compressed tar archives tarlz can be more
18 efficient than using tar and plzip because tarlz is able to keep the
19 alignment between tar members and lzip members.
21 The lzip file format is designed for data sharing and long-term archiving,
22 taking into account both data integrity and decoder availability:
24 * The lzip format provides very safe integrity checking and some data
25 recovery means. The program lziprecover can repair bit flip errors
26 (one of the most common forms of data corruption) in lzip files, and
27 provides data recovery capabilities, including error-checked merging
28 of damaged copies of a file.
30 * The lzip format is as simple as possible (but not simpler). The lzip
31 manual provides the source code of a simple decompressor along with a
32 detailed explanation of how it works, so that with the only help of the
33 lzip manual it would be possible for a digital archaeologist to extract
34 the data from a lzip file long after quantum computers eventually
35 render LZMA obsolete.
37 * Additionally the lzip reference implementation is copylefted, which
38 guarantees that it will remain free forever.
40 A nice feature of the lzip format is that a corrupt byte is easier to repair
41 the nearer it is from the beginning of the file. Therefore, with the help of
42 lziprecover, losing an entire archive just because of a corrupt byte near
43 the beginning is a thing of the past.
45 Lzip uses the same well-defined exit status values used by bzip2, which
46 makes it safer than compressors returning ambiguous warning values (like
47 gzip) when it is used as a back end for other programs like tar or zutils.
49 Lzip will automatically use for each file the largest dictionary size that
50 does not exceed neither the file size nor the limit given. Keep in mind that
51 the decompression memory requirement is affected at compression time by the
52 choice of dictionary size limit.
54 The amount of memory required for compression is about 1 or 2 times the
55 dictionary size limit (1 if input file size is less than dictionary size
56 limit, else 2) plus 9 times the dictionary size really used. The option '-0'
57 is special and only requires about 1.5 MiB at most. The amount of memory
58 required for decompression is about 46 kB larger than the dictionary size
59 really used.
61 When compressing, lzip replaces every file given in the command line
62 with a compressed version of itself, with the name "original_name.lz".
63 When decompressing, lzip attempts to guess the name for the decompressed
64 file from that of the compressed file as follows:
66 filename.lz becomes filename
67 filename.tlz becomes filename.tar
68 anyothername becomes anyothername.out
70 (De)compressing a file is much like copying or moving it; therefore lzip
71 preserves the access and modification dates, permissions, and, when
72 possible, ownership of the file just as 'cp -p' does. (If the user ID or
73 the group ID can't be duplicated, the file permission bits S_ISUID and
74 S_ISGID are cleared).
76 Lzip is able to read from some types of non-regular files if either the
77 option '-c' or the option '-o' is specified.
79 If no file names are specified, lzip compresses (or decompresses) from
80 standard input to standard output. Lzip will refuse to read compressed data
81 from a terminal or write compressed data to a terminal, as this would be
82 entirely incomprehensible and might leave the terminal in an abnormal state.
84 Lzip will correctly decompress a file which is the concatenation of two or
85 more compressed files. The result is the concatenation of the corresponding
86 decompressed files. Integrity testing of concatenated compressed files is
87 also supported.
89 Lzip can produce multimember files, and lziprecover can safely recover the
90 undamaged members in case of file damage. Lzip can also split the compressed
91 output in volumes of a given size, even when reading from standard input.
92 This allows the direct creation of multivolume compressed tar archives.
94 Lzip is able to compress and decompress streams of unlimited size by
95 automatically creating multimember output. The members so created are large,
96 about 2 PiB each.
98 In spite of its name (Lempel-Ziv-Markov chain-Algorithm), LZMA is not a
99 concrete algorithm; it is more like "any algorithm using the LZMA coding
100 scheme". For example, the option '-0' of lzip uses the scheme in almost the
101 simplest way possible; issuing the longest match it can find, or a literal
102 byte if it can't find a match. Inversely, a much more elaborated way of
103 finding coding sequences of minimum size than the one currently used by lzip
104 could be developed, and the resulting sequence could also be coded using the
105 LZMA coding scheme.
107 Lzip currently implements two variants of the LZMA algorithm; fast
108 (used by option '-0') and normal (used by all other compression levels).
110 The high compression of LZMA comes from combining two basic, well-proven
111 compression ideas: sliding dictionaries (LZ77/78) and markov models (the
112 thing used by every compression algorithm that uses a range encoder or
113 similar order-0 entropy coder as its last stage) with segregation of
114 contexts according to what the bits are used for.
116 The ideas embodied in lzip are due to (at least) the following people:
117 Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for the
118 definition of Markov chains), G.N.N. Martin (for the definition of range
119 encoding), Igor Pavlov (for putting all the above together in LZMA), and
120 Julian Seward (for bzip2's CLI).
122 LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never have
123 been compressed. Decompressed is used to refer to data which have undergone
124 the process of decompression.
127 Copyright (C) 2008-2021 Antonio Diaz Diaz.
129 This file is free documentation: you have unlimited permission to copy,
130 distribute, and modify it.
132 The file Makefile.in is a data file used by configure to produce the
133 Makefile. It has the same copyright owner and permissions that configure