This is lzip.info, produced by makeinfo version 4.13 from lzip.texinfo. INFO-DIR-SECTION Data Compression START-INFO-DIR-ENTRY * Lzip: (lzip). Data compressor based on the LZMA algorithm END-INFO-DIR-ENTRY  File: lzip.info, Node: Top, Next: Introduction, Up: (dir) Lzip Manual *********** This manual is for Lzip (version 1.12, 30 April 2011). * Menu: * Introduction:: Purpose and features of lzip * Algorithm:: How lzip compresses the data * Invoking Lzip:: Command line interface * File Format:: Detailed format of the compressed file * Examples:: A small tutorial with examples * Lziprecover:: Recovering data from damaged compressed files * Invoking Lziprecover:: Command line interface * Problems:: Reporting bugs * Concept Index:: Index of concepts Copyright (C) 2008, 2009, 2010, 2011 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it.  File: lzip.info, Node: Introduction, Next: Algorithm, Prev: Top, Up: Top 1 Introduction ************** Lzip is a lossless data compressor based on the LZMA algorithm, with very safe integrity checking and a user interface similar to the one of gzip or bzip2. Lzip decompresses almost as fast as gzip and compresses better than bzip2, which makes it well suited for software distribution and data archiving. Lzip replaces every file given in the command line with a compressed version of itself, with the name "original_name.lz". Each compressed file has the same modification date, permissions, and, when possible, ownership as the corresponding original, so that these properties can be correctly restored at decompression time. Lzip is able to read from some types of non regular files if the `--stdout' option is specified. If no file names are specified, lzip compresses (or decompresses) from standard input to standard output. In this case, lzip will decline to write compressed output to a terminal, as this would be entirely incomprehensible and therefore pointless. Lzip 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. Lzip can produce multimember files and safely recover, with lziprecover, the undamaged members in case of file damage. Lzip can also split the compressed output in volumes of a given size, even when reading from standard input. This allows the direct creation of multivolume compressed tar archives. The amount of memory required for compression is about 5 MiB plus 1 or 2 times the dictionary size limit (1 if input file size is less than dictionary size limit, else 2) plus 8 times the dictionary size really used. The option `-0' is special and only requires about 1.5 MiB at most. The amount of memory required for decompression is only a few tens of KiB larger than the dictionary size really used. Lzip will automatically use the smallest possible dictionary size 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 decompressing, lzip 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 As a self-check for your protection, lzip stores in the member trailer the 32-bit CRC of the original data and the size of the original data, to make sure that the decompressed version of the data is identical to the original. This guards against corruption of the compressed data, and against undetected bugs in lzip (hopefully very unlikely). The chances of data corruption going undetected are microscopic, less than one chance in 4000 million for each member processed. Be aware, though, that the check occurs upon decompression, so it can only tell you that something is wrong. It can't help you recover the original uncompressed data. Return values: 0 for a normal exit, 1 for environmental problems (file not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid input file, 3 for an internal consistency error (eg, bug) which caused lzip to panic.  File: lzip.info, Node: Algorithm, Next: Invoking Lzip, Prev: Introduction, Up: Top 2 Algorithm *********** Lzip implements a simplified version of the LZMA (Lempel-Ziv-Markov chain-Algorithm) algorithm. The high compression of LZMA comes from combining two basic, well-proven compression ideas: sliding dictionaries (LZ77/78) and markov models (the thing used by every compression algorithm that uses a range encoder or similar order-0 entropy coder as its last stage) with segregation of contexts according to what the bits are used for. Lzip is a two stage compressor. The first stage is a Lempel-Ziv coder, which reduces redundancy by translating chunks of data to their corresponding distance-length pairs. The second stage is a range encoder that uses a different probability model for each type of data; distances, lengths, literal bytes, etc. The match finder, part of the LZ coder, is the most important piece of the LZMA algorithm, as it is in many Lempel-Ziv based algorithms. Most of lzip's execution time is spent in the match finder, and it has the greatest influence on the compression ratio. Here is how it works, step by step: 1) The member header is written to the output stream. 2) The first byte is coded literally, because there are no previous bytes to which the match finder can refer to. 3) The main encoder advances to the next byte in the input data and calls the match finder. 4) The match finder fills an array with the minimum distances before the current byte where a match of a given length can be found. 5) Go back to step 3 until a sequence (formed of pairs, repeated distances and literal bytes) of minimum price has been formed. Where the price represents the number of output bits produced. 6) The range encoder encodes the sequence produced by the main encoder and sends the produced bytes to the output stream. 7) Go back to step 3 until the input data is finished or until the member or volume size limits are reached. 8) The range encoder is flushed. 9) The member trailer is written to the output stream. 10) If there are more data to compress, go back to step 1. The ideas embodied in lzip are due to (at least) the following people: Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey 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 and the idea of unzcrash).  File: lzip.info, Node: Invoking Lzip, Next: File Format, Prev: Algorithm, Up: Top 3 Invoking Lzip *************** The format for running lzip is: lzip [OPTIONS] [FILES] Lzip supports the following options: `-h' `--help' Print an informative help message describing the options and exit. `-V' `--version' Print the version number of lzip on the standard output and exit. `-b SIZE' `--member-size=SIZE' Produce a multimember file and set the member size limit to SIZE bytes. Minimum member size limit is 100kB. Small member size may degrade compression ratio, so use it only when needed. The default is to produce single-member files. `-c' `--stdout' Compress or decompress to standard output. Needed when reading from a named pipe (fifo) or from a device. Use it to recover as much of the uncompressed data as possible when decompressing a corrupt file. `-d' `--decompress' Decompress. `-f' `--force' Force overwrite of output file. `-F' `--recompress' Force recompression of files whose name already has the `.lz' or `.tlz' suffix. `-k' `--keep' Keep (don't delete) input files during compression or decompression. `-m LENGTH' `--match-length=LENGTH' Set the match length limit in bytes. After a match this long is found, the search is finished. Valid values range from 5 to 273. Larger values usually give better compression ratios but longer compression times. `-o FILE' `--output=FILE' When reading from standard input and `--stdout' has not been specified, use `FILE' as the virtual name of the uncompressed file. This produces a file named `FILE' when decompressing, a file named `FILE.lz' when compressing, and several files named `FILE00001.lz', `FILE00002.lz', etc, when compressing and splitting the output in volumes. `-q' `--quiet' Quiet operation. Suppress all messages. `-s SIZE' `--dictionary-size=SIZE' Set the dictionary size limit in bytes. Valid values range from 4KiB to 512MiB. Lzip will use the smallest possible dictionary size for each member without exceeding this limit. Note that dictionary sizes are quantized. If the specified size does not match one of the valid sizes, it will be rounded upwards by adding up to (SIZE / 16) to it. For maximum compression you should use a dictionary size limit as large as possible, but keep in mind that the decompression memory requirement is affected at compression time by the choice of dictionary size limit. `-S SIZE' `--volume-size=SIZE' Split the compressed output into several volume files with names `original_name00001.lz', `original_name00002.lz', etc, and set the volume size limit to SIZE bytes. Each volume is a complete, maybe multimember, lzip file. Minimum volume size limit is 100kB. Small volume size may degrade compression ratio, so use it only when needed. `-t' `--test' Check integrity of the specified file(s), but don't decompress them. This really performs a trial decompression and throws away the result. Use it together with `-v' to see information about the file. `-v' `--verbose' Verbose mode. When compressing, show the compression ratio for each file processed. When decompressing or testing, further -v's (up to 4) increase the verbosity level, showing status, dictionary size, compression ratio, trailer contents (CRC, data size, member size), and up to 6 bytes of trailing garbage (if any). `-0 .. -9' Set the compression parameters (dictionary size and match length limit) as shown in the table below. Note that `-9' can be much slower than `-0'. These options have no effect when decompressing. The bidimensional parameter space of LZMA can't be mapped to a linear scale optimal for all files. If your files are large, very repetitive, etc, you may need to use the `--match-length' and `--dictionary-size' options directly to achieve optimal performance. Level Dictionary size Match length limit -0 64 KiB 16 bytes -1 1 MiB 5 bytes -2 1.5 MiB 6 bytes -3 2 MiB 8 bytes -4 3 MiB 12 bytes -5 4 MiB 20 bytes -6 8 MiB 36 bytes -7 16 MiB 68 bytes -8 24 MiB 132 bytes -9 32 MiB 273 bytes `--fast' `--best' Aliases for GNU gzip compatibility. Numbers given as arguments to options may be followed by a multiplier and an optional `B' for "byte". Table of SI and binary prefixes (unit multipliers): Prefix Value | Prefix Value k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024) M megabyte (10^6) | Mi mebibyte (2^20) G gigabyte (10^9) | Gi gibibyte (2^30) T terabyte (10^12) | Ti tebibyte (2^40) P petabyte (10^15) | Pi pebibyte (2^50) E exabyte (10^18) | Ei exbibyte (2^60) Z zettabyte (10^21) | Zi zebibyte (2^70) Y yottabyte (10^24) | Yi yobibyte (2^80)  File: lzip.info, Node: File Format, Next: Examples, Prev: Invoking Lzip, Up: Top 4 File Format ************* In the diagram below, a box like this: +---+ | | <-- the vertical bars might be missing +---+ represents one byte; a box like this: +==============+ | | +==============+ represents a variable number of bytes. A lzip file consists of a series of "members" (compressed data sets). The members simply appear one after another in the file, with no additional information before, between, or after them. Each member has the following structure: +--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size | +--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ All multibyte values are stored in little endian order. `ID string' A four byte string, identifying the lzip format, with the value "LZIP". `VN (version number, 1 byte)' Just in case something needs to be modified in the future. Valid values are 0 and 1. Version 0 files are deprecated. They can contain only one member and lack the `Member size' field. `DS (coded dictionary size, 1 byte)' Bits 4-0 contain the base 2 logarithm of the base dictionary size. Bits 7-5 contain the number of "wedges" to substract from the base dictionary size to obtain the dictionary size. The size of a wedge is (base dictionary size / 16). Valid values for dictionary size range from 4KiB to 512MiB. `Lzma stream' The lzma stream, finished by an end of stream marker. Uses default values for encoder properties. `CRC32 (4 bytes)' CRC of the uncompressed original data. `Data size (8 bytes)' Size of the uncompressed original data. `Member size (8 bytes)' Total size of the member, including header and trailer. This facilitates safe recovery of undamaged members from multimember files.  File: lzip.info, Node: Examples, Next: Lziprecover, Prev: File Format, Up: Top 5 A small tutorial with examples ******************************** WARNING! Even if lzip is bug-free, other causes may result in a corrupt compressed file (bugs in the system libraries, memory errors, etc). Therefore, if the data you are going to compress is important give the `--keep' option to lzip and do not remove the original file until you verify the compressed file with a command like `lzip -cd file.lz | cmp file -'. Example 1: Replace a regular file with its compressed version file.lz and show the compression ratio. lzip -v file Example 2: Like example 1 but the created file.lz is multimember with a member size of 1MiB. The compression ratio is not shown. lzip -b 1MiB file Example 3: Restore a regular file from its compressed version file.lz. If the operation is successful, file.lz is removed. lzip -d file.lz Example 4: Verify the integrity of the compressed file file.lz and show status. lzip -tv file.lz Example 5: Compress a whole floppy in /dev/fd0 and send the output to file.lz. lzip -c /dev/fd0 > file.lz Example 6: Decompress file.lz partially until 10KiB of decompressed data are produced. lzip -cd file.lz | dd bs=1024 count=10 Example 7: Create a multivolume compressed tar archive with a volume size of 1440KiB. tar -c some_directory | lzip -S 1440KiB -o volume_name Example 8: Extract a multivolume compressed tar archive. lzip -cd volume_name*.lz | tar -xf - Example 9: Create a multivolume compressed backup of a big database file with a volume size of 650MB, where each volume is a multimember file with a member size of 32MiB. lzip -b 32MiB -S 650MB big_db Example 10: Recover a compressed backup from two copies on CD-ROM (see the GNU ddrescue manual for details about ddrescue) ddrescue -b2048 /dev/cdrom cdimage1 logfile1 mount -t iso9660 -o loop,ro cdimage1 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued1.tar.lz umount /mnt/cdimage (insert second copy in the CD drive) ddrescue -b2048 /dev/cdrom cdimage2 logfile2 mount -t iso9660 -o loop,ro cdimage2 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued2.tar.lz umount /mnt/cdimage lziprecover -m -v -o rescued.tar.lz rescued1.tar.lz rescued2.tar.lz Example 11: Recover the first volume of those created in example 9 from two copies, `big_db1_00001.lz' and `big_db2_00001.lz', with member 00007 damaged in the first copy, member 00018 damaged in the second copy, and member 00012 damaged in both copies. (Indented lines are abridged error messages from lzip/lziprecover). Two correct copies are produced and compared. lziprecover -s big_db1_00001.lz lziprecover -s big_db2_00001.lz lzip -t rec*big_db1_00001.lz rec00007big_db1_00001.lz: crc mismatch rec00012big_db1_00001.lz: crc mismatch lzip -t rec*big_db2_00001.lz rec00012big_db2_00001.lz: crc mismatch rec00018big_db2_00001.lz: crc mismatch lziprecover -m -v rec00012big_db1_00001.lz rec00012big_db2_00001.lz Input files merged successfully cp rec00007big_db2_00001.lz rec00007big_db1_00001.lz cp rec00012big_db1_00001_fixed.lz rec00012big_db1_00001.lz cp rec00012big_db1_00001_fixed.lz rec00012big_db2_00001.lz cp rec00018big_db1_00001.lz rec00018big_db2_00001.lz cat rec*big_db1_00001.lz > big_db3_00001.lz cat rec*big_db2_00001.lz > big_db4_00001.lz zcmp big_db3_00001.lz big_db4_00001.lz  File: lzip.info, Node: Lziprecover, Next: Invoking Lziprecover, Prev: Examples, Up: Top 6 Lziprecover ************* Lziprecover is a data recovery tool for lzip compressed files able to repair slightly damaged files, recover badly damaged files from two or more copies, and extract undamaged members from multi-member files. Lziprecover takes as arguments the names of the damaged files and writes zero or more recovered files depending on the operation selected and whether the recovery succeeded or not. The damaged files themselves are never modified. If the files are too damaged for lziprecover to repair them, data from damaged members can be partially recovered writing it to stdout as shown in the following example (the resulting file may contain garbage data at the end): lzip -cd rec00001file.lz > rec00001file If the cause of file corruption is damaged media, the combination GNU ddrescue + lziprecover is the best option for recovering data from multiple damaged copies. *Note ddrescue-example::, for an example.  File: lzip.info, Node: Invoking Lziprecover, Next: Problems, Prev: Lziprecover, Up: Top 7 Invoking Lziprecover ********************** The format for running lziprecover is: lziprecover [OPTIONS] [FILES] Lziprecover supports the following options: `-h' `--help' Print an informative help message describing the options and exit. `-V' `--version' Print the version number of lziprecover on the standard output and exit. `-f' `--force' Force overwrite of output file. `-m' `--merge' Try to produce a correct file merging the good parts of two or more damaged copies. The copies must be single-member files. The merge will fail if the copies have too many damaged areas or if the same byte is damaged in all copies. If successful, a repaired copy is written to the file `FILE_fixed.lz'. To give you an idea of its possibilities, when merging two copies each of them with one damaged area affecting 1 percent of the copy, the probability of obtaining a correct file is about 98 percent. With three such copies the probability rises to 99.97 percent. For large files with small errors, the probability approaches 100 percent even with only two copies. `-o FILE' `--output=FILE' Place the output into `FILE' instead of into `FILE_fixed.lz'. If splitting, the names of the files produced are in the form `rec00001FILE', etc. `-q' `--quiet' Quiet operation. Suppress all messages. `-R' `--repair' Try to repair a small error, affecting only one byte, in a single-member FILE. If successful, a repaired copy is written to the file `FILE_fixed.lz'. `FILE' is not modified at all. `-s' `--split' Search for members in `FILE' and write each member in its own `.lz' file. You can then use `lzip -t' to test the integrity of the resulting files, decompress those which are undamaged, and try to repair or partially decompress those which are damaged. The names of the files produced are in the form `rec00001FILE.lz', `rec00002FILE.lz', etc, and are designed so that the use of wildcards in subsequent processing, for example, `lzip -cd rec*FILE.lz > recovered_data', processes the files in the correct order. `-v' `--verbose' Verbose mode. Further -v's increase the verbosity level.  File: lzip.info, Node: Problems, Next: Concept Index, Prev: Invoking Lziprecover, Up: Top 8 Reporting Bugs **************** There are probably bugs in lzip. There are certainly errors and omissions in this manual. If you report them, they will get fixed. If you don't, no one will ever know about them and they will remain unfixed for all eternity, if not longer. If you find a bug in lzip, please send electronic mail to . Include the version number, which you can find by running `lzip --version'.  File: lzip.info, Node: Concept Index, Prev: Problems, Up: Top Concept Index ************* [index] * Menu: * algorithm: Algorithm. (line 6) * bugs: Problems. (line 6) * examples: Examples. (line 6) * file format: File Format. (line 6) * getting help: Problems. (line 6) * introduction: Introduction. (line 6) * invoking lzip: Invoking Lzip. (line 6) * invoking lziprecover: Invoking Lziprecover. (line 6) * lziprecover: Lziprecover. (line 6) * options: Invoking Lzip. (line 6) * usage: Invoking Lzip. (line 6) * version: Invoking Lzip. (line 6)  Tag Table: Node: Top224 Node: Introduction1031 Node: Algorithm4439 Node: Invoking Lzip6957 Node: File Format12303 Node: Examples14295 Ref: ddrescue-example16049 Node: Lziprecover17848 Node: Invoking Lziprecover18901 Node: Problems21262 Node: Concept Index21796  End Tag Table