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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-15 09:41:35 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-15 09:41:35 +0000 |
| commit | 2ed1dcfa30b3967f7d6df74fba78ce23ed065497 (patch) | |
| tree | 8ff5a74b07bf976cd88df2460e1c9cafb27f050a /doc/man/txt/xz.txt | |
| parent | Releasing progress-linux version 5.6.1+really5.4.5-1~progress7.99u1. (diff) | |
| download | xz-utils-2ed1dcfa30b3967f7d6df74fba78ce23ed065497.tar.xz xz-utils-2ed1dcfa30b3967f7d6df74fba78ce23ed065497.zip | |
Merging upstream version 5.6.2.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/man/txt/xz.txt')
| -rw-r--r-- | doc/man/txt/xz.txt | 752 |
1 files changed, 421 insertions, 331 deletions
diff --git a/doc/man/txt/xz.txt b/doc/man/txt/xz.txt index 4fec85b..b543312 100644 --- a/doc/man/txt/xz.txt +++ b/doc/man/txt/xz.txt @@ -1,7 +1,5 @@ XZ(1) XZ Utils XZ(1) - - NAME xz, unxz, xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and .lzma files @@ -30,36 +28,36 @@ DESCRIPTION xz compresses or decompresses each file according to the selected oper- ation mode. If no files are given or file is -, xz reads from standard input and writes the processed data to standard output. xz will refuse - (display an error and skip the file) to write compressed data to stan- - dard output if it is a terminal. Similarly, xz will refuse to read + (display an error and skip the file) to write compressed data to stan- + dard output if it is a terminal. Similarly, xz will refuse to read compressed data from standard input if it is a terminal. - Unless --stdout is specified, files other than - are written to a new + Unless --stdout is specified, files other than - are written to a new file whose name is derived from the source file name: - o When compressing, the suffix of the target file format (.xz or - .lzma) is appended to the source filename to get the target file- + o When compressing, the suffix of the target file format (.xz or + .lzma) is appended to the source filename to get the target file- name. - o When decompressing, the .xz, .lzma, or .lz suffix is removed from - the filename to get the target filename. xz also recognizes the + o When decompressing, the .xz, .lzma, or .lz suffix is removed from + the filename to get the target filename. xz also recognizes the suffixes .txz and .tlz, and replaces them with the .tar suffix. - If the target file already exists, an error is displayed and the file + If the target file already exists, an error is displayed and the file is skipped. - Unless writing to standard output, xz will display a warning and skip + Unless writing to standard output, xz will display a warning and skip the file if any of the following applies: - o File is not a regular file. Symbolic links are not followed, and + o File is not a regular file. Symbolic links are not followed, and thus they are not considered to be regular files. o File has more than one hard link. o File has setuid, setgid, or sticky bit set. - o The operation mode is set to compress and the file already has a - suffix of the target file format (.xz or .txz when compressing to + o The operation mode is set to compress and the file already has a + suffix of the target file format (.xz or .txz when compressing to the .xz format, and .lzma or .tlz when compressing to the .lzma for- mat). @@ -71,7 +69,7 @@ DESCRIPTION owner, group, permissions, access time, and modification time from the source file to the target file. If copying the group fails, the per- missions are modified so that the target file doesn't become accessible - to users who didn't have permission to access the source file. xz + to users who didn't have permission to access the source file. xz doesn't support copying other metadata like access control lists or ex- tended attributes yet. @@ -85,8 +83,8 @@ DESCRIPTION cally updating progress indicator. Memory usage - The memory usage of xz varies from a few hundred kilobytes to several - gigabytes depending on the compression settings. The settings used + The memory usage of xz varies from a few hundred kilobytes to several + gigabytes depending on the compression settings. The settings used when compressing a file determine the memory requirements of the decom- pressor. Typically the decompressor needs 5 % to 20 % of the amount of memory that the compressor needed when creating the file. For example, @@ -101,7 +99,7 @@ DESCRIPTION processes, relying on it wasn't deemed to be flexible enough (for exam- ple, using ulimit(1) to limit virtual memory tends to cripple mmap(2)). - The memory usage limiter can be enabled with the command line option + The memory usage limiter can be enabled with the command line option --memlimit=limit. Often it is more convenient to enable the limiter by default by setting the environment variable XZ_DEFAULTS, for example, XZ_DEFAULTS=--memlimit=150MiB. It is possible to set the limits sepa- @@ -125,7 +123,7 @@ DESCRIPTION It is possible to concatenate .xz files as is. xz will decompress such files as if they were a single .xz file. - It is possible to insert padding between the concatenated parts or af- + It is possible to insert padding between the concatenated parts or af- ter the last part. The padding must consist of null bytes and the size of the padding must be a multiple of four bytes. This can be useful, for example, if the .xz file is stored on a medium that measures file @@ -153,34 +151,34 @@ OPTIONS supported by the option. Operation mode - If multiple operation mode options are given, the last one takes ef- + If multiple operation mode options are given, the last one takes ef- fect. -z, --compress - Compress. This is the default operation mode when no operation - mode option is specified and no other operation mode is implied + Compress. This is the default operation mode when no operation + mode option is specified and no other operation mode is implied from the command name (for example, unxz implies --decompress). -d, --decompress, --uncompress Decompress. -t, --test - Test the integrity of compressed files. This option is equiva- - lent to --decompress --stdout except that the decompressed data - is discarded instead of being written to standard output. No + Test the integrity of compressed files. This option is equiva- + lent to --decompress --stdout except that the decompressed data + is discarded instead of being written to standard output. No files are created or removed. -l, --list - Print information about compressed files. No uncompressed out- - put is produced, and no files are created or removed. In list - mode, the program cannot read the compressed data from standard + Print information about compressed files. No uncompressed out- + put is produced, and no files are created or removed. In list + mode, the program cannot read the compressed data from standard input or from other unseekable sources. - The default listing shows basic information about files, one - file per line. To get more detailed information, use also the - --verbose option. For even more information, use --verbose - twice, but note that this may be slow, because getting all the - extra information requires many seeks. The width of verbose + The default listing shows basic information about files, one + file per line. To get more detailed information, use also the + --verbose option. For even more information, use --verbose + twice, but note that this may be slow, because getting all the + extra information requires many seeks. The width of verbose output exceeds 80 characters, so piping the output to, for exam- ple, less -S may be convenient if the terminal isn't wide enough. @@ -206,19 +204,19 @@ OPTIONS o If the target file already exists, delete it before compress- ing or decompressing. - o Compress or decompress even if the input is a symbolic link - to a regular file, has more than one hard link, or has the - setuid, setgid, or sticky bit set. The setuid, setgid, and + o Compress or decompress even if the input is a symbolic link + to a regular file, has more than one hard link, or has the + setuid, setgid, or sticky bit set. The setuid, setgid, and sticky bits are not copied to the target file. - o When used with --decompress --stdout and xz cannot recognize - the type of the source file, copy the source file as is to - standard output. This allows xzcat --force to be used like + o When used with --decompress --stdout and xz cannot recognize + the type of the source file, copy the source file as is to + standard output. This allows xzcat --force to be used like cat(1) for files that have not been compressed with xz. Note that in future, xz might support new compressed file formats, - which may make xz decompress more types of files instead of - copying them as is to standard output. --format=format can - be used to restrict xz to decompress only a single file for- + which may make xz decompress more types of files instead of + copying them as is to standard output. --format=format can + be used to restrict xz to decompress only a single file for- mat. -c, --stdout, --to-stdout @@ -227,18 +225,18 @@ OPTIONS --single-stream Decompress only the first .xz stream, and silently ignore possi- - ble remaining input data following the stream. Normally such + ble remaining input data following the stream. Normally such trailing garbage makes xz display an error. - xz never decompresses more than one stream from .lzma files or - raw streams, but this option still makes xz ignore the possible + xz never decompresses more than one stream from .lzma files or + raw streams, but this option still makes xz ignore the possible trailing data after the .lzma file or raw stream. - This option has no effect if the operation mode is not --decom- + This option has no effect if the operation mode is not --decom- press or --test. --no-sparse - Disable creation of sparse files. By default, if decompressing + Disable creation of sparse files. By default, if decompressing into a regular file, xz tries to make the file sparse if the de- compressed data contains long sequences of binary zeros. It also works when writing to standard output as long as standard @@ -249,12 +247,12 @@ OPTIONS -S .suf, --suffix=.suf When compressing, use .suf as the suffix for the target file in- - stead of .xz or .lzma. If not writing to standard output and - the source file already has the suffix .suf, a warning is dis- + stead of .xz or .lzma. If not writing to standard output and + the source file already has the suffix .suf, a warning is dis- played and the file is skipped. - When decompressing, recognize files with the suffix .suf in ad- - dition to files with the .xz, .txz, .lzma, .tlz, or .lz suffix. + When decompressing, recognize files with the suffix .suf in ad- + dition to files with the .xz, .txz, .lzma, .tlz, or .lz suffix. If the source file has the suffix .suf, the suffix is removed to get the target filename. @@ -271,16 +269,16 @@ OPTIONS fore the filenames read from file. --files0[=file] - This is identical to --files[=file] except that each filename + This is identical to --files[=file] except that each filename must be terminated with the null character. Basic file format and compression options -F format, --format=format Specify the file format to compress or decompress: - auto This is the default. When compressing, auto is equiva- - lent to xz. When decompressing, the format of the input - file is automatically detected. Note that raw streams + auto This is the default. When compressing, auto is equiva- + lent to xz. When decompressing, the format of the input + file is automatically detected. Note that raw streams (created with --format=raw) cannot be auto-detected. xz Compress to the .xz file format, or accept only .xz files @@ -297,14 +295,14 @@ OPTIONS The .lz format version 0 and the unextended version 1 are supported. Version 0 files were produced by lzip 1.3 and - older. Such files aren't common but may be found from - file archives as a few source packages were released in - this format. People might have old personal files in - this format too. Decompression support for the format + older. Such files aren't common but may be found from + file archives as a few source packages were released in + this format. People might have old personal files in + this format too. Decompression support for the format version 0 was removed in lzip 1.18. - lzip 1.4 and later create files in the format version 1. - The sync flush marker extension to the format version 1 + lzip 1.4 and later create files in the format version 1. + The sync flush marker extension to the format version 1 was added in lzip 1.6. This extension is rarely used and isn't supported by xz (diagnosed as corrupt input). @@ -324,22 +322,22 @@ OPTIONS Supported check types: - none Don't calculate an integrity check at all. This is usu- - ally a bad idea. This can be useful when integrity of + none Don't calculate an integrity check at all. This is usu- + ally a bad idea. This can be useful when integrity of the data is verified by other means anyway. - crc32 Calculate CRC32 using the polynomial from IEEE-802.3 + crc32 Calculate CRC32 using the polynomial from IEEE-802.3 (Ethernet). crc64 Calculate CRC64 using the polynomial from ECMA-182. This is the default, since it is slightly better than CRC32 at - detecting damaged files and the speed difference is neg- + detecting damaged files and the speed difference is neg- ligible. - sha256 Calculate SHA-256. This is somewhat slower than CRC32 + sha256 Calculate SHA-256. This is somewhat slower than CRC32 and CRC64. - Integrity of the .xz headers is always verified with CRC32. It + Integrity of the .xz headers is always verified with CRC32. It is not possible to change or disable it. --ignore-check @@ -352,7 +350,7 @@ OPTIONS o Trying to recover data from a corrupt .xz file. - o Speeding up decompression. This matters mostly with SHA-256 + o Speeding up decompression. This matters mostly with SHA-256 or with files that have compressed extremely well. It's rec- ommended to not use this option for this purpose unless the file integrity is verified externally in some other way. @@ -383,13 +381,13 @@ OPTIONS memory usage reasonable even for old systems. -6 is the default, which is usually a good choice for distributing files that need to be decompressible even on systems with - only 16 MiB RAM. (-5e or -6e may be worth considering + only 16 MiB RAM. (-5e or -6e may be worth considering too. See --extreme.) -7 ... -9 - These are like -6 but with higher compressor and decom- - pressor memory requirements. These are useful only when - compressing files bigger than 8 MiB, 16 MiB, and 32 MiB, + These are like -6 but with higher compressor and decom- + pressor memory requirements. These are useful only when + compressing files bigger than 8 MiB, 16 MiB, and 32 MiB, respectively. On the same hardware, the decompression speed is approximately a @@ -415,40 +413,44 @@ OPTIONS Column descriptions: o DictSize is the LZMA2 dictionary size. It is waste of memory - to use a dictionary bigger than the size of the uncompressed - file. This is why it is good to avoid using the presets -7 - ... -9 when there's no real need for them. At -6 and lower, + to use a dictionary bigger than the size of the uncompressed + file. This is why it is good to avoid using the presets -7 + ... -9 when there's no real need for them. At -6 and lower, the amount of memory wasted is usually low enough to not mat- ter. o CompCPU is a simplified representation of the LZMA2 settings that affect compression speed. The dictionary size affects speed too, so while CompCPU is the same for levels -6 ... -9, - higher levels still tend to be a little slower. To get even + higher levels still tend to be a little slower. To get even slower and thus possibly better compression, see --extreme. - o CompMem contains the compressor memory requirements in the - single-threaded mode. It may vary slightly between xz ver- - sions. Memory requirements of some of the future multi- - threaded modes may be dramatically higher than that of the - single-threaded mode. + o CompMem contains the compressor memory requirements in the + single-threaded mode. It may vary slightly between xz ver- + sions. - o DecMem contains the decompressor memory requirements. That - is, the compression settings determine the memory require- + o DecMem contains the decompressor memory requirements. That + is, the compression settings determine the memory require- ments of the decompressor. The exact decompressor memory us- age is slightly more than the LZMA2 dictionary size, but the values in the table have been rounded up to the next full MiB. + Memory requirements of the multi-threaded mode are significantly + higher than that of the single-threaded mode. With the default + value of --block-size, each thread needs 3*3*DictSize plus Comp- + Mem or DecMem. For example, four threads with preset -6 needs + 660-670 MiB of memory. + -e, --extreme Use a slower variant of the selected compression preset level (-0 ... -9) to hopefully get a little bit better compression ra- - tio, but with bad luck this can also make it worse. Decompres- - sor memory usage is not affected, but compressor memory usage + tio, but with bad luck this can also make it worse. Decompres- + sor memory usage is not affected, but compressor memory usage increases a little at preset levels -0 ... -3. - Since there are two presets with dictionary sizes 4 MiB and - 8 MiB, the presets -3e and -5e use slightly faster settings + Since there are two presets with dictionary sizes 4 MiB and + 8 MiB, the presets -3e and -5e use slightly faster settings (lower CompCPU) than -4e and -6e, respectively. That way no two presets are identical. @@ -487,50 +489,76 @@ OPTIONS whichever is more. Typically a good value is 2-4 times the size of the LZMA2 dictionary or at least 1 MiB. Using size less than the LZMA2 dictionary size is waste of RAM because then the LZMA2 - dictionary buffer will never get fully used. The sizes of the - blocks are stored in the block headers, which a future version - of xz will use for multi-threaded decompression. + dictionary buffer will never get fully used. In multi-threaded + mode, the sizes of the blocks are stored in the block headers. + This size information is required for multi-threaded decompres- + sion. In single-threaded mode no block splitting is done by default. Setting this option doesn't affect memory usage. No size infor- mation is stored in block headers, thus files created in single- threaded mode won't be identical to files created in multi- - threaded mode. The lack of size information also means that a - future version of xz won't be able decompress the files in - multi-threaded mode. + threaded mode. The lack of size information also means that xz + won't be able decompress the files in multi-threaded mode. + + --block-list=items + When compressing to the .xz format, start a new block with an + optional custom filter chain after the given intervals of uncom- + pressed data. + + The items are a comma-separated list. Each item consists of an + optional filter chain number between 0 and 9 followed by a colon + (:) and a required size of uncompressed data. Omitting an item + (two or more consecutive commas) is a shorthand to use the size + and filters of the previous item. + + If the input file is bigger than the sum of the sizes in items, + the last item is repeated until the end of the file. A special + value of 0 may be used as the last size to indicate that the + rest of the file should be encoded as a single block. - --block-list=sizes - When compressing to the .xz format, start a new block after the - given intervals of uncompressed data. + An alternative filter chain for each block can be specified in + combination with the --filters1=filters ... --filters9=filters + options. These options define filter chains with an identifier + between 1-9. Filter chain 0 can be used to refer to the default + filter chain, which is the same as not specifying a filter + chain. The filter chain identifier can be used before the un- + compressed size, followed by a colon (:). For example, if one + specifies --block-list=1:2MiB,3:2MiB,2:4MiB,,2MiB,0:4MiB then + blocks will be created using: - The uncompressed sizes of the blocks are specified as a comma- - separated list. Omitting a size (two or more consecutive com- - mas) is a shorthand to use the size of the previous block. + o The filter chain specified by --filters1 and 2 MiB input - If the input file is bigger than the sum of sizes, the last - value in sizes is repeated until the end of the file. A special - value of 0 may be used as the last value to indicate that the - rest of the file should be encoded as a single block. + o The filter chain specified by --filters3 and 2 MiB input + + o The filter chain specified by --filters2 and 4 MiB input + + o The filter chain specified by --filters2 and 4 MiB input - If one specifies sizes that exceed the encoder's block size (ei- - ther the default value in threaded mode or the value specified - with --block-size=size), the encoder will create additional - blocks while keeping the boundaries specified in sizes. For ex- + o The default filter chain and 2 MiB input + + o The default filter chain and 4 MiB input for every block un- + til end of input. + + If one specifies a size that exceeds the encoder's block size + (either the default value in threaded mode or the value speci- + fied with --block-size=size), the encoder will create additional + blocks while keeping the boundaries specified in items. For ex- ample, if one specifies --block-size=10MiB --block-list=5MiB,10MiB,8MiB,12MiB,24MiB and the input file is 80 MiB, one will get 11 blocks: 5, 10, 8, 10, 2, 10, 10, 4, 10, 10, and 1 MiB. In multi-threaded mode the sizes of the blocks are stored in the - block headers. This isn't done in single-threaded mode, so the - encoded output won't be identical to that of the multi-threaded + block headers. This isn't done in single-threaded mode, so the + encoded output won't be identical to that of the multi-threaded mode. --flush-timeout=timeout - When compressing, if more than timeout milliseconds (a positive - integer) has passed since the previous flush and reading more - input would block, all the pending input data is flushed from - the encoder and made available in the output stream. This can + When compressing, if more than timeout milliseconds (a positive + integer) has passed since the previous flush and reading more + input would block, all the pending input data is flushed from + the encoder and made available in the output stream. This can be useful if xz is used to compress data that is streamed over a network. Small timeout values make the data available at the receiving end with a small delay, but large timeout values give @@ -556,24 +584,24 @@ OPTIONS ceeded and display a notice that automatic adjustment was done. The adjustments are done in this order: reducing the number of threads, switching to single-threaded mode if even one thread in - multi-threaded mode exceeds the limit, and finally reducing the + multi-threaded mode exceeds the limit, and finally reducing the LZMA2 dictionary size. - When compressing with --format=raw or if --no-adjust has been - specified, only the number of threads may be reduced since it + When compressing with --format=raw or if --no-adjust has been + specified, only the number of threads may be reduced since it can be done without affecting the compressed output. - If the limit cannot be met even with the adjustments described - above, an error is displayed and xz will exit with exit status + If the limit cannot be met even with the adjustments described + above, an error is displayed and xz will exit with exit status 1. The limit can be specified in multiple ways: - o The limit can be an absolute value in bytes. Using an inte- - ger suffix like MiB can be useful. Example: --memlimit-com- + o The limit can be an absolute value in bytes. Using an inte- + ger suffix like MiB can be useful. Example: --memlimit-com- press=80MiB - o The limit can be specified as a percentage of total physical + o The limit can be specified as a percentage of total physical memory (RAM). This can be useful especially when setting the XZ_DEFAULTS environment variable in a shell initialization script that is shared between different computers. That way @@ -588,17 +616,17 @@ OPTIONS over 4020 MiB, the limit is set to 4020 MiB. On MIPS32 2000 MiB is used instead. (The values 0 and max aren't affected by this. A similar feature doesn't exist for decompression.) This can be - helpful when a 32-bit executable has access to 4 GiB address - space (2 GiB on MIPS32) while hopefully doing no harm in other + helpful when a 32-bit executable has access to 4 GiB address + space (2 GiB on MIPS32) while hopefully doing no harm in other situations. See also the section Memory usage. --memlimit-decompress=limit - Set a memory usage limit for decompression. This also affects - the --list mode. If the operation is not possible without ex- - ceeding the limit, xz will display an error and decompressing - the file will fail. See --memlimit-compress=limit for possible + Set a memory usage limit for decompression. This also affects + the --list mode. If the operation is not possible without ex- + ceeding the limit, xz will display an error and decompressing + the file will fail. See --memlimit-compress=limit for possible ways to specify the limit. --memlimit-mt-decompress=limit @@ -608,20 +636,20 @@ OPTIONS multi-threading, the limit is ignored and xz will continue in single-threaded mode. Note that if also --memlimit-decompress is used, it will always apply to both single-threaded and multi- - threaded modes, and so the effective limit for multi-threading - will never be higher than the limit set with --memlimit-decom- + threaded modes, and so the effective limit for multi-threading + will never be higher than the limit set with --memlimit-decom- press. - In contrast to the other memory usage limit options, --mem- - limit-mt-decompress=limit has a system-specific default limit. + In contrast to the other memory usage limit options, --mem- + limit-mt-decompress=limit has a system-specific default limit. xz --info-memory can be used to see the current value. - This option and its default value exist because without any - limit the threaded decompressor could end up allocating an in- - sane amount of memory with some input files. If the default + This option and its default value exist because without any + limit the threaded decompressor could end up allocating an in- + sane amount of memory with some input files. If the default limit is too low on your system, feel free to increase the limit but never set it to a value larger than the amount of usable RAM - as with appropriate input files xz will attempt to use that + as with appropriate input files xz will attempt to use that amount of memory even with a low number of threads. Running out of memory or swapping will not improve decompression perfor- mance. @@ -648,18 +676,18 @@ OPTIONS -T threads, --threads=threads Specify the number of worker threads to use. Setting threads to - a special value 0 makes xz use up to as many threads as the pro- - cessor(s) on the system support. The actual number of threads - can be fewer than threads if the input file is not big enough - for threading with the given settings or if using more threads - would exceed the memory usage limit. + a special value 0 makes xz use up to as many threads as the + processor(s) on the system support. The actual number of + threads can be fewer than threads if the input file is not big + enough for threading with the given settings or if using more + threads would exceed the memory usage limit. The single-threaded and multi-threaded compressors produce dif- ferent output. Single-threaded compressor will give the small- est file size but only the output from the multi-threaded com- pressor can be decompressed using multiple threads. Setting threads to 1 will use the single-threaded mode. Setting threads - to any other value, including 0, will use the multi-threaded + to any other value, including 0, will use the multi-threaded compressor even if the system supports only one hardware thread. (xz 5.2.x used single-threaded mode in this situation.) @@ -670,9 +698,9 @@ OPTIONS added in xz 5.4.0. If an automatic number of threads has been requested and no mem- - ory usage limit has been specified, then a system-specific de- - fault soft limit will be used to possibly limit the number of - threads. It is a soft limit in sense that it is ignored if the + ory usage limit has been specified, then a system-specific de- + fault soft limit will be used to possibly limit the number of + threads. It is a soft limit in sense that it is ignored if the number of threads becomes one, thus a soft limit will never stop xz from compressing or decompressing. This default soft limit will not make xz switch from multi-threaded mode to single- @@ -681,7 +709,7 @@ OPTIONS Currently the only threading method is to split the input into blocks and compress them independently from each other. The de- - fault block size depends on the compression level and can be + fault block size depends on the compression level and can be overridden with the --block-size=size option. Threaded decompression only works on files that contain multiple @@ -690,6 +718,9 @@ OPTIONS files compressed in single-threaded mode don't even if --block-size=size has been used. + The default value for threads is 0. In xz 5.4.x and older the + default is 1. + Custom compressor filter chains A custom filter chain allows specifying the compression settings in de- tail instead of relying on the settings associated to the presets. @@ -701,9 +732,9 @@ OPTIONS A filter chain is comparable to piping on the command line. When com- pressing, the uncompressed input goes to the first filter, whose output - goes to the next filter (if any). The output of the last filter gets - written to the compressed file. The maximum number of filters in the - chain is four, but typically a filter chain has only one or two fil- + goes to the next filter (if any). The output of the last filter gets + written to the compressed file. The maximum number of filters in the + chain is four, but typically a filter chain has only one or two fil- ters. Many filters have limitations on where they can be in the filter chain: @@ -712,20 +743,49 @@ OPTIONS pending on the filter, this limitation is either inherent to the filter design or exists to prevent security issues. - A custom filter chain is specified by using one or more filter options - in the order they are wanted in the filter chain. That is, the order - of filter options is significant! When decoding raw streams (--for- - mat=raw), the filter chain is specified in the same order as it was - specified when compressing. - - Filters take filter-specific options as a comma-separated list. Extra - commas in options are ignored. Every option has a default value, so - you need to specify only those you want to change. + A custom filter chain can be specified in two different ways. The op- + tions --filters=filters and --filters1=filters ... --filters9=filters + allow specifying an entire filter chain in one option using the liblzma + filter string syntax. Alternatively, a filter chain can be specified + by using one or more individual filter options in the order they are + wanted in the filter chain. That is, the order of the individual fil- + ter options is significant! When decoding raw streams (--format=raw), + the filter chain must be specified in the same order as it was speci- + fied when compressing. Any individual filter or preset options speci- + fied before the full chain option (--filters=filters) will be forgot- + ten. Individual filters specified after the full chain option will re- + set the filter chain. + + Both the full and individual filter options take filter-specific op- + tions as a comma-separated list. Extra commas in options are ignored. + Every option has a default value, so specify those you want to change. To see the whole filter chain and options, use xz -vv (that is, use --verbose twice). This works also for viewing the filter chain options used by presets. + --filters=filters + Specify the full filter chain or a preset in a single option. + Each filter can be separated by spaces or two dashes (--). fil- + ters may need to be quoted on the shell command line so it is + parsed as a single option. To denote options, use : or =. A + preset can be prefixed with a - and followed with zero or more + flags. The only supported flag is e to apply the same options + as --extreme. + + --filters1=filters ... --filters9=filters + Specify up to nine additional filter chains that can be used + with --block-list. + + For example, when compressing an archive with executable files + followed by text files, the executable part could use a filter + chain with a BCJ filter and the text part only the LZMA2 filter. + + --filters-help + Display a help message describing how to specify presets and + custom filter chains in the --filters and --filters1=filters ... + --filters9=filters options, and exit successfully. + --lzma1[=options] --lzma2[=options] Add LZMA1 or LZMA2 filter to the filter chain. These filters @@ -751,9 +811,9 @@ OPTIONS dict=size Dictionary (history buffer) size indicates how many bytes - of the recently processed uncompressed data is kept in - memory. The algorithm tries to find repeating byte se- - quences (matches) in the uncompressed data, and replace + of the recently processed uncompressed data is kept in + memory. The algorithm tries to find repeating byte se- + quences (matches) in the uncompressed data, and replace them with references to the data currently in the dictio- nary. The bigger the dictionary, the higher is the chance to find a match. Thus, increasing dictionary size @@ -763,16 +823,16 @@ OPTIONS Typical dictionary size is from 64 KiB to 64 MiB. The minimum is 4 KiB. The maximum for compression is cur- rently 1.5 GiB (1536 MiB). The decompressor already sup- - ports dictionaries up to one byte less than 4 GiB, which + ports dictionaries up to one byte less than 4 GiB, which is the maximum for the LZMA1 and LZMA2 stream formats. - Dictionary size and match finder (mf) together determine + Dictionary size and match finder (mf) together determine the memory usage of the LZMA1 or LZMA2 encoder. The same (or bigger) dictionary size is required for decompressing - that was used when compressing, thus the memory usage of - the decoder is determined by the dictionary size used - when compressing. The .xz headers store the dictionary - size either as 2^n or 2^n + 2^(n-1), so these sizes are + that was used when compressing, thus the memory usage of + the decoder is determined by the dictionary size used + when compressing. The .xz headers store the dictionary + size either as 2^n or 2^n + 2^(n-1), so these sizes are somewhat preferred for compression. Other sizes will get rounded up when stored in the .xz headers. @@ -791,7 +851,7 @@ OPTIONS ter, and a lower-case letter is usually followed by an- other lower-case letter. In the US-ASCII character set, the highest three bits are 010 for upper-case letters and - 011 for lower-case letters. When lc is at least 3, the + 011 for lower-case letters. When lc is at least 3, the literal coding can take advantage of this property in the uncompressed data. @@ -807,11 +867,11 @@ OPTIONS data is assumed when encoding literals. See pb below for more information about alignment. - pb=pb Specify the number of position bits. The minimum is 0 + pb=pb Specify the number of position bits. The minimum is 0 and the maximum is 4; the default is 2. - Pb affects what kind of alignment in the uncompressed - data is assumed in general. The default means four-byte + Pb affects what kind of alignment in the uncompressed + data is assumed in general. The default means four-byte alignment (2^pb=2^2=4), which is often a good choice when there's no better guess. @@ -820,7 +880,7 @@ OPTIONS files having one-byte alignment (US-ASCII, ISO-8859-*, UTF-8), setting pb=0 can improve compression slightly. For UTF-16 text, pb=1 is a good choice. If the alignment - is an odd number like 3 bytes, pb=0 might be the best + is an odd number like 3 bytes, pb=0 might be the best choice. Even though the assumed alignment can be adjusted with pb @@ -869,7 +929,7 @@ OPTIONS mode=mode Compression mode specifies the method to analyze the data - produced by the match finder. Supported modes are fast + produced by the match finder. Supported modes are fast and normal. The default is fast for presets 0-3 and nor- mal for presets 4-9. @@ -878,17 +938,17 @@ OPTIONS the presets do. nice=nice - Specify what is considered to be a nice length for a + Specify what is considered to be a nice length for a match. Once a match of at least nice bytes is found, the algorithm stops looking for possibly better matches. Nice can be 2-273 bytes. Higher values tend to give bet- - ter compression ratio at the expense of speed. The de- + ter compression ratio at the expense of speed. The de- fault depends on the preset. depth=depth - Specify the maximum search depth in the match finder. - The default is the special value of 0, which makes the + Specify the maximum search depth in the match finder. + The default is the special value of 0, which makes the compressor determine a reasonable depth from mf and nice. Reasonable depth for Hash Chains is 4-100 and 16-1000 for @@ -908,6 +968,7 @@ OPTIONS --powerpc[=options] --ia64[=options] --sparc[=options] + --riscv[=options] Add a branch/call/jump (BCJ) filter to the filter chain. These filters can be used only as a non-last filter in the filter chain. @@ -916,9 +977,9 @@ OPTIONS their absolute counterparts. This doesn't change the size of the data but it increases redundancy, which can help LZMA2 to produce 0-15 % smaller .xz file. The BCJ filters are always re- - versible, so using a BCJ filter for wrong type of data doesn't - cause any data loss, although it may make the compression ratio - slightly worse. The BCJ filters are very fast and use an in- + versible, so using a BCJ filter for wrong type of data doesn't + cause any data loss, although it may make the compression ratio + slightly worse. The BCJ filters are very fast and use an in- significant amount of memory. These BCJ filters have known problems related to the compression @@ -931,16 +992,16 @@ OPTIONS sion, which will make the compression worse with these files. o If a BCJ filter is applied on an archive, it is possible that - it makes the compression ratio worse than not using a BCJ - filter. For example, if there are similar or even identical - executables then filtering will likely make the files less - similar and thus compression is worse. The contents of non- - executable files in the same archive can matter too. In - practice one has to try with and without a BCJ filter to see + it makes the compression ratio worse than not using a BCJ + filter. For example, if there are similar or even identical + executables then filtering will likely make the files less + similar and thus compression is worse. The contents of non- + executable files in the same archive can matter too. In + practice one has to try with and without a BCJ filter to see which is better in each situation. - Different instruction sets have different alignment: the exe- - cutable file must be aligned to a multiple of this value in the + Different instruction sets have different alignment: the exe- + cutable file must be aligned to a multiple of this value in the input data to make the filter work. Filter Alignment Notes @@ -951,14 +1012,29 @@ OPTIONS PowerPC 4 Big endian only IA-64 16 Itanium SPARC 4 + RISC-V 2 - Since the BCJ-filtered data is usually compressed with LZMA2, - the compression ratio may be improved slightly if the LZMA2 op- + Since the BCJ-filtered data is usually compressed with LZMA2, + the compression ratio may be improved slightly if the LZMA2 op- tions are set to match the alignment of the selected BCJ filter. - For example, with the IA-64 filter, it's good to set pb=4 or - even pb=4,lp=4,lc=0 with LZMA2 (2^4=16). The x86 filter is an - exception; it's usually good to stick to LZMA2's default four- - byte alignment when compressing x86 executables. + Examples: + + o IA-64 filter has 16-byte alignment so pb=4,lp=4,lc=0 is good + with LZMA2 (2^4=16). + + o RISC-V code has 2-byte or 4-byte alignment depending on + whether the file contains 16-bit compressed instructions (the + C extension). When 16-bit instructions are used, + pb=2,lp=1,lc=3 or pb=1,lp=1,lc=3 is good. When 16-bit in- + structions aren't present, pb=2,lp=2,lc=2 is the best. read- + elf -h can be used to check if "RVC" appears on the "Flags" + line. + + o ARM64 is always 4-byte aligned so pb=2,lp=2,lc=2 is the best. + + o The x86 filter is an exception. It's usually good to stick + to LZMA2's defaults (pb=2,lp=0,lc=3) when compressing x86 ex- + ecutables. All BCJ filters support the same options: @@ -966,7 +1042,7 @@ OPTIONS Specify the start offset that is used when converting be- tween relative and absolute addresses. The offset must be a multiple of the alignment of the filter (see the ta- - ble above). The default is zero. In practice, the de- + ble above). The default is zero. In practice, the de- fault is good; specifying a custom offset is almost never useful. @@ -978,13 +1054,13 @@ OPTIONS It can be useful when compressing, for example, uncompressed bitmap images or uncompressed PCM audio. However, special pur- pose algorithms may give significantly better results than Delta - + LZMA2. This is true especially with audio, which compresses + + LZMA2. This is true especially with audio, which compresses faster and better, for example, with flac(1). Supported options: dist=distance - Specify the distance of the delta calculation in bytes. + Specify the distance of the delta calculation in bytes. distance must be 1-256. The default is 1. For example, with dist=2 and eight-byte input A1 B1 A2 B3 @@ -994,23 +1070,23 @@ OPTIONS -q, --quiet Suppress warnings and notices. Specify this twice to suppress errors too. This option has no effect on the exit status. That - is, even if a warning was suppressed, the exit status to indi- + is, even if a warning was suppressed, the exit status to indi- cate a warning is still used. -v, --verbose - Be verbose. If standard error is connected to a terminal, xz - will display a progress indicator. Specifying --verbose twice + Be verbose. If standard error is connected to a terminal, xz + will display a progress indicator. Specifying --verbose twice will give even more verbose output. The progress indicator shows the following information: - o Completion percentage is shown if the size of the input file + o Completion percentage is shown if the size of the input file is known. That is, the percentage cannot be shown in pipes. - o Amount of compressed data produced (compressing) or consumed + o Amount of compressed data produced (compressing) or consumed (decompressing). - o Amount of uncompressed data consumed (compressing) or pro- + o Amount of uncompressed data consumed (compressing) or pro- duced (decompressing). o Compression ratio, which is calculated by dividing the amount @@ -1032,12 +1108,12 @@ OPTIONS When standard error is not a terminal, --verbose will make xz print the filename, compressed size, uncompressed size, compres- - sion ratio, and possibly also the speed and elapsed time on a + sion ratio, and possibly also the speed and elapsed time on a single line to standard error after compressing or decompressing the file. The speed and elapsed time are included only when the - operation took at least a few seconds. If the operation didn't - finish, for example, due to user interruption, also the comple- - tion percentage is printed if the size of the input file is + operation took at least a few seconds. If the operation didn't + finish, for example, due to user interruption, also the comple- + tion percentage is printed if the size of the input file is known. -Q, --no-warn @@ -1075,63 +1151,9 @@ OPTIONS ROBOT MODE The robot mode is activated with the --robot option. It makes the out- put of xz easier to parse by other programs. Currently --robot is sup- - ported only together with --version, --info-memory, and --list. It - will be supported for compression and decompression in the future. - - Version - xz --robot --version prints the version number of xz and liblzma in the - following format: - - XZ_VERSION=XYYYZZZS - LIBLZMA_VERSION=XYYYZZZS - - X Major version. - - YYY Minor version. Even numbers are stable. Odd numbers are alpha - or beta versions. - - ZZZ Patch level for stable releases or just a counter for develop- - ment releases. - - S Stability. 0 is alpha, 1 is beta, and 2 is stable. S should be - always 2 when YYY is even. - - XYYYZZZS are the same on both lines if xz and liblzma are from the same - XZ Utils release. - - Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002. - - Memory limit information - xz --robot --info-memory prints a single line with multiple tab-sepa- - rated columns: - - 1. Total amount of physical memory (RAM) in bytes. - - 2. Memory usage limit for compression in bytes (--memlimit-compress). - A special value of 0 indicates the default setting which for sin- - gle-threaded mode is the same as no limit. - - 3. Memory usage limit for decompression in bytes (--memlimit-decom- - press). A special value of 0 indicates the default setting which - for single-threaded mode is the same as no limit. - - 4. Since xz 5.3.4alpha: Memory usage for multi-threaded decompression - in bytes (--memlimit-mt-decompress). This is never zero because a - system-specific default value shown in the column 5 is used if no - limit has been specified explicitly. This is also never greater - than the value in the column 3 even if a larger value has been - specified with --memlimit-mt-decompress. - - 5. Since xz 5.3.4alpha: A system-specific default memory usage limit - that is used to limit the number of threads when compressing with - an automatic number of threads (--threads=0) and no memory usage - limit has been specified (--memlimit-compress). This is also used - as the default value for --memlimit-mt-decompress. - - 6. Since xz 5.3.4alpha: Number of available processor threads. - - In the future, the output of xz --robot --info-memory may have more - columns, but never more than a single line. + ported only together with --list, --filters-help, --info-memory, and + --version. It will be supported for compression and decompression in + the future. List mode xz --robot --list uses tab-separated output. The first column of every @@ -1155,10 +1177,10 @@ ROBOT MODE summary This line type is used only when --verbose was specified twice. This line is printed after all block lines. Like the file line, - the summary line contains overall information about the .xz + the summary line contains overall information about the .xz file. - totals This line is always the very last line of the list output. It + totals This line is always the very last line of the list output. It shows the total counts and sizes. The columns of the file lines: @@ -1166,10 +1188,10 @@ ROBOT MODE 3. Total number of blocks in the stream(s) 4. Compressed size of the file 5. Uncompressed size of the file - 6. Compression ratio, for example, 0.123. If ratio is over - 9.999, three dashes (---) are displayed instead of the ra- + 6. Compression ratio, for example, 0.123. If ratio is over + 9.999, three dashes (---) are displayed instead of the ra- tio. - 7. Comma-separated list of integrity check names. The follow- + 7. Comma-separated list of integrity check names. The follow- ing strings are used for the known check types: None, CRC32, CRC64, and SHA-256. For unknown check types, Unknown-N is used, where N is the Check ID as a decimal number (one or @@ -1240,24 +1262,94 @@ ROBOT MODE 9. Number of files. This is here to keep the order of the ear- lier columns the same as on file lines. - If --verbose was specified twice, additional columns are included on + If --verbose was specified twice, additional columns are included on the totals line: - 10. Maximum amount of memory (in bytes) required to decompress + 10. Maximum amount of memory (in bytes) required to decompress the files with this xz version - 11. yes or no indicating if all block headers have both com- + 11. yes or no indicating if all block headers have both com- pressed size and uncompressed size stored in them Since xz 5.1.2alpha: 12. Minimum xz version required to decompress the file - Future versions may add new line types and new columns can be added to + Future versions may add new line types and new columns can be added to the existing line types, but the existing columns won't be changed. + Filters help + xz --robot --filters-help prints the supported filters in the following + format: + + filter:option=<value>,option=<value>... + + filter Name of the filter + + option Name of a filter specific option + + value Numeric value ranges appear as <min-max>. String value choices + are shown within < > and separated by a | character. + + Each filter is printed on its own line. + + Memory limit information + xz --robot --info-memory prints a single line with multiple tab-sepa- + rated columns: + + 1. Total amount of physical memory (RAM) in bytes. + + 2. Memory usage limit for compression in bytes (--memlimit-compress). + A special value of 0 indicates the default setting which for sin- + gle-threaded mode is the same as no limit. + + 3. Memory usage limit for decompression in bytes (--memlimit-decom- + press). A special value of 0 indicates the default setting which + for single-threaded mode is the same as no limit. + + 4. Since xz 5.3.4alpha: Memory usage for multi-threaded decompression + in bytes (--memlimit-mt-decompress). This is never zero because a + system-specific default value shown in the column 5 is used if no + limit has been specified explicitly. This is also never greater + than the value in the column 3 even if a larger value has been + specified with --memlimit-mt-decompress. + + 5. Since xz 5.3.4alpha: A system-specific default memory usage limit + that is used to limit the number of threads when compressing with + an automatic number of threads (--threads=0) and no memory usage + limit has been specified (--memlimit-compress). This is also used + as the default value for --memlimit-mt-decompress. + + 6. Since xz 5.3.4alpha: Number of available processor threads. + + In the future, the output of xz --robot --info-memory may have more + columns, but never more than a single line. + + Version + xz --robot --version prints the version number of xz and liblzma in the + following format: + + XZ_VERSION=XYYYZZZS + LIBLZMA_VERSION=XYYYZZZS + + X Major version. + + YYY Minor version. Even numbers are stable. Odd numbers are alpha + or beta versions. + + ZZZ Patch level for stable releases or just a counter for develop- + ment releases. + + S Stability. 0 is alpha, 1 is beta, and 2 is stable. S should be + always 2 when YYY is even. + + XYYYZZZS are the same on both lines if xz and liblzma are from the same + XZ Utils release. + + Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002. + EXIT STATUS 0 All is good. 1 An error occurred. - 2 Something worth a warning occurred, but no actual errors oc- + 2 Something worth a warning occurred, but no actual errors oc- curred. Notices (not warnings or errors) printed on standard error don't affect @@ -1266,16 +1358,16 @@ EXIT STATUS ENVIRONMENT xz parses space-separated lists of options from the environment vari- ables XZ_DEFAULTS and XZ_OPT, in this order, before parsing the options - from the command line. Note that only options are parsed from the en- - vironment variables; all non-options are silently ignored. Parsing is - done with getopt_long(3) which is used also for the command line argu- + from the command line. Note that only options are parsed from the en- + vironment variables; all non-options are silently ignored. Parsing is + done with getopt_long(3) which is used also for the command line argu- ments. XZ_DEFAULTS User-specific or system-wide default options. Typically this is set in a shell initialization script to enable xz's memory usage - limiter by default. Excluding shell initialization scripts and - similar special cases, scripts must never set or unset XZ_DE- + limiter by default. Excluding shell initialization scripts and + similar special cases, scripts must never set or unset XZ_DE- FAULTS. XZ_OPT This is for passing options to xz when it is not possible to set @@ -1293,16 +1385,16 @@ ENVIRONMENT export XZ_OPT LZMA UTILS COMPATIBILITY - The command line syntax of xz is practically a superset of lzma, un- - lzma, and lzcat as found from LZMA Utils 4.32.x. In most cases, it is - possible to replace LZMA Utils with XZ Utils without breaking existing - scripts. There are some incompatibilities though, which may sometimes + The command line syntax of xz is practically a superset of lzma, un- + lzma, and lzcat as found from LZMA Utils 4.32.x. In most cases, it is + possible to replace LZMA Utils with XZ Utils without breaking existing + scripts. There are some incompatibilities though, which may sometimes cause problems. Compression preset levels - The numbering of the compression level presets is not identical in xz - and LZMA Utils. The most important difference is how dictionary sizes - are mapped to different presets. Dictionary size is roughly equal to + The numbering of the compression level presets is not identical in xz + and LZMA Utils. The most important difference is how dictionary sizes + are mapped to different presets. Dictionary size is roughly equal to the decompressor memory usage. Level xz LZMA Utils @@ -1341,15 +1433,15 @@ LZMA UTILS COMPATIBILITY LZMA Utils does that when compressing regular files. The alternative is to mark that uncompressed size is unknown and use end-of-payload marker to indicate where the decompressor should stop. LZMA Utils uses - this method when uncompressed size isn't known, which is the case, for + this method when uncompressed size isn't known, which is the case, for example, in pipes. - xz supports decompressing .lzma files with or without end-of-payload - marker, but all .lzma files created by xz will use end-of-payload - marker and have uncompressed size marked as unknown in the .lzma - header. This may be a problem in some uncommon situations. For exam- - ple, a .lzma decompressor in an embedded device might work only with - files that have known uncompressed size. If you hit this problem, you + xz supports decompressing .lzma files with or without end-of-payload + marker, but all .lzma files created by xz will use end-of-payload + marker and have uncompressed size marked as unknown in the .lzma + header. This may be a problem in some uncommon situations. For exam- + ple, a .lzma decompressor in an embedded device might work only with + files that have known uncompressed size. If you hit this problem, you need to use LZMA Utils or LZMA SDK to create .lzma files with known un- compressed size. @@ -1360,13 +1452,13 @@ LZMA UTILS COMPATIBILITY with xz and with LZMA SDK. The implementation of the LZMA1 filter in liblzma requires that the sum - of lc and lp must not exceed 4. Thus, .lzma files, which exceed this + of lc and lp must not exceed 4. Thus, .lzma files, which exceed this limitation, cannot be decompressed with xz. LZMA Utils creates only .lzma files which have a dictionary size of 2^n (a power of 2) but accepts files with any dictionary size. liblzma ac- - cepts only .lzma files which have a dictionary size of 2^n or 2^n + - 2^(n-1). This is to decrease false positives when detecting .lzma + cepts only .lzma files which have a dictionary size of 2^n or 2^n + + 2^(n-1). This is to decrease false positives when detecting .lzma files. These limitations shouldn't be a problem in practice, since practically @@ -1385,11 +1477,11 @@ LZMA UTILS COMPATIBILITY NOTES Compressed output may vary - The exact compressed output produced from the same uncompressed input + The exact compressed output produced from the same uncompressed input file may vary between XZ Utils versions even if compression options are identical. This is because the encoder can be improved (faster or bet- - ter compression) without affecting the file format. The output can - vary even between different builds of the same XZ Utils version, if + ter compression) without affecting the file format. The output can + vary even between different builds of the same XZ Utils version, if different build options are used. The above means that once --rsyncable has been implemented, the result- @@ -1401,30 +1493,30 @@ NOTES Embedded .xz decompressors Embedded .xz decompressor implementations like XZ Embedded don't neces- sarily support files created with integrity check types other than none - and crc32. Since the default is --check=crc64, you must use + and crc32. Since the default is --check=crc64, you must use --check=none or --check=crc32 when creating files for embedded systems. - Outside embedded systems, all .xz format decompressors support all the - check types, or at least are able to decompress the file without veri- + Outside embedded systems, all .xz format decompressors support all the + check types, or at least are able to decompress the file without veri- fying the integrity check if the particular check is not supported. - XZ Embedded supports BCJ filters, but only with the default start off- + XZ Embedded supports BCJ filters, but only with the default start off- set. EXAMPLES Basics - Compress the file foo into foo.xz using the default compression level + Compress the file foo into foo.xz using the default compression level (-6), and remove foo if compression is successful: xz foo - Decompress bar.xz into bar and don't remove bar.xz even if decompres- + Decompress bar.xz into bar and don't remove bar.xz even if decompres- sion is successful: xz -dk bar.xz - Create baz.tar.xz with the preset -4e (-4 --extreme), which is slower - than the default -6, but needs less memory for compression and decom- + Create baz.tar.xz with the preset -4e (-4 --extreme), which is slower + than the default -6, but needs less memory for compression and decom- pression (48 MiB and 5 MiB, respectively): tar cf - baz | xz -4e > baz.tar.xz @@ -1443,7 +1535,7 @@ EXAMPLES The -P option to xargs(1) sets the number of parallel xz processes. The best value for the -n option depends on how many files there are to - be compressed. If there are only a couple of files, the value should + be compressed. If there are only a couple of files, the value should probably be 1; with tens of thousands of files, 100 or even more may be appropriate to reduce the number of xz processes that xargs(1) will eventually create. @@ -1452,14 +1544,14 @@ EXAMPLES cause xargs(1) is used to control the amount of parallelization. Robot mode - Calculate how many bytes have been saved in total after compressing + Calculate how many bytes have been saved in total after compressing multiple files: xz --robot --list *.xz | awk '/^totals/{print $5-$4}' - A script may want to know that it is using new enough xz. The follow- - ing sh(1) script checks that the version number of the xz tool is at - least 5.0.0. This method is compatible with old beta versions, which + A script may want to know that it is using new enough xz. The follow- + ing sh(1) script checks that the version number of the xz tool is at + least 5.0.0. This method is compatible with old beta versions, which didn't support the --robot option: if ! eval "$(xz --robot --version 2> /dev/null)" || @@ -1524,23 +1616,23 @@ EXAMPLES Using -vv (--verbose --verbose) like in the above example can be useful to see the memory requirements of the compressor and decompressor. Re- member that using a dictionary bigger than the size of the uncompressed - file is waste of memory, so the above command isn't useful for small + file is waste of memory, so the above command isn't useful for small files. - Sometimes the compression time doesn't matter, but the decompressor - memory usage has to be kept low, for example, to make it possible to - decompress the file on an embedded system. The following command uses - -6e (-6 --extreme) as a base and sets the dictionary to only 64 KiB. - The resulting file can be decompressed with XZ Embedded (that's why + Sometimes the compression time doesn't matter, but the decompressor + memory usage has to be kept low, for example, to make it possible to + decompress the file on an embedded system. The following command uses + -6e (-6 --extreme) as a base and sets the dictionary to only 64 KiB. + The resulting file can be decompressed with XZ Embedded (that's why there is --check=crc32) using about 100 KiB of memory. xz --check=crc32 --lzma2=preset=6e,dict=64KiB foo - If you want to squeeze out as many bytes as possible, adjusting the - number of literal context bits (lc) and number of position bits (pb) + If you want to squeeze out as many bytes as possible, adjusting the + number of literal context bits (lc) and number of position bits (pb) can sometimes help. Adjusting the number of literal position bits (lp) might help too, but usually lc and pb are more important. For example, - a source code archive contains mostly US-ASCII text, so something like + a source code archive contains mostly US-ASCII text, so something like the following might give slightly (like 0.1 %) smaller file than xz -6e (try also without lc=4): @@ -1552,7 +1644,7 @@ EXAMPLES xz --x86 --lzma2 libfoo.so - Note that the order of the filter options is significant. If --x86 is + Note that the order of the filter options is significant. If --x86 is specified after --lzma2, xz will give an error, because there cannot be any filter after LZMA2, and also because the x86 BCJ filter cannot be used as the last filter in the chain. @@ -1561,26 +1653,24 @@ EXAMPLES images. It should usually beat PNG, which has a few more advanced fil- ters than simple delta but uses Deflate for the actual compression. - The image has to be saved in uncompressed format, for example, as un- - compressed TIFF. The distance parameter of the Delta filter is set to - match the number of bytes per pixel in the image. For example, 24-bit - RGB bitmap needs dist=3, and it is also good to pass pb=0 to LZMA2 to + The image has to be saved in uncompressed format, for example, as un- + compressed TIFF. The distance parameter of the Delta filter is set to + match the number of bytes per pixel in the image. For example, 24-bit + RGB bitmap needs dist=3, and it is also good to pass pb=0 to LZMA2 to accommodate the three-byte alignment: xz --delta=dist=3 --lzma2=pb=0 foo.tiff - If multiple images have been put into a single archive (for example, - .tar), the Delta filter will work on that too as long as all images + If multiple images have been put into a single archive (for example, + .tar), the Delta filter will work on that too as long as all images have the same number of bytes per pixel. SEE ALSO - xzdec(1), xzdiff(1), xzgrep(1), xzless(1), xzmore(1), gzip(1), + xzdec(1), xzdiff(1), xzgrep(1), xzless(1), xzmore(1), gzip(1), bzip2(1), 7z(1) XZ Utils: <https://tukaani.org/xz/> XZ Embedded: <https://tukaani.org/xz/embedded.html> LZMA SDK: <https://7-zip.org/sdk.html> - - -Tukaani 2023-07-17 XZ(1) +Tukaani 2024-04-08 XZ(1) |