XZ(1) XZ Utils XZ(1)
NAME
 xz, unxz, xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and
 .lzma files
SYNOPSIS
 xz [option...] [file...]
COMMAND ALIASES
 unxz is equivalent to xz --decompress.
 xzcat is equivalent to xz --decompress --stdout.
 lzma is equivalent to xz --format=lzma.
 unlzma is equivalent to xz --format=lzma --decompress.
 lzcat is equivalent to xz --format=lzma --decompress --stdout.
 When writing scripts that need to decompress files, it is recommended
 to always use the name xz with appropriate arguments (xz -d or xz -dc)
 instead of the names unxz and xzcat.
DESCRIPTION
 xz is a general-purpose data compression tool with command line syntax
 similar to gzip(1) and bzip2(1). The native file format is the .xz
 format, but the legacy .lzma format used by LZMA Utils and raw com-
 pressed streams with no container format headers are also supported.
 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
 compressed data from standard input if it is a terminal.
 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-
 name.
 o When decompressing, the .xz or .lzma suffix is removed from the
 filename to get the target filename. xz also recognizes the suf-
 fixes .txz and .tlz, and replaces them with the .tar suffix.
 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
 the file if any of the following applies:
 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
 the .xz format, and .lzma or .tlz when compressing to the .lzma for-
 mat).
 o The operation mode is set to decompress and the file doesn't have a
 suffix of any of the supported file formats (.xz, .txz, .lzma, or
 .tlz).
 After successfully compressing or decompressing the file, xz copies the
 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
 doesn't support copying other metadata like access control lists or ex-
 tended attributes yet.
 Once the target file has been successfully closed, the source file is
 removed unless --keep was specified. The source file is never removed
 if the output is written to standard output.
 Sending SIGINFO or SIGUSR1 to the xz process makes it print progress
 information to standard error. This has only limited use since when
 standard error is a terminal, using --verbose will display an automati-
 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
 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,
 decompressing a file created with xz -9 currently requires 65 MiB of
 memory. Still, it is possible to have .xz files that require several
 gigabytes of memory to decompress.
 Especially users of older systems may find the possibility of very
 large memory usage annoying. To prevent uncomfortable surprises, xz
 has a built-in memory usage limiter, which is disabled by default.
 While some operating systems provide ways to limit the memory usage of
 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
 --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-
 rately for compression and decompression by using --memlimit-com-
 press=limit and --memlimit-decompress=limit. Using these two options
 outside XZ_DEFAULTS is rarely useful because a single run of xz cannot
 do both compression and decompression and --memlimit=limit (or -M
 limit) is shorter to type on the command line.
 If the specified memory usage limit is exceeded when decompressing, xz
 will display an error and decompressing the file will fail. If the
 limit is exceeded when compressing, xz will try to scale the settings
 down so that the limit is no longer exceeded (except when using --for-
 mat=raw or --no-adjust). This way the operation won't fail unless the
 limit is very small. The scaling of the settings is done in steps that
 don't match the compression level presets, for example, if the limit is
 only slightly less than the amount required for xz -9, the settings
 will be scaled down only a little, not all the way down to xz -8.
 Concatenation and padding with .xz files
 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-
 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
 sizes in 512-byte blocks.
 Concatenation and padding are not allowed with .lzma files or raw
 streams.
OPTIONS
 Integer suffixes and special values
 In most places where an integer argument is expected, an optional suf-
 fix is supported to easily indicate large integers. There must be no
 space between the integer and the suffix.
 KiB Multiply the integer by 1,024 (2^10). Ki, k, kB, K, and KB are
 accepted as synonyms for KiB.
 MiB Multiply the integer by 1,048,576 (2^20). Mi, m, M, and MB are
 accepted as synonyms for MiB.
 GiB Multiply the integer by 1,073,741,824 (2^30). Gi, g, G, and GB
 are accepted as synonyms for GiB.
 The special value max can be used to indicate the maximum integer value
 supported by the option.
 Operation mode
 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
 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
 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
 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
 output exceeds 80 characters, so piping the output to, for exam-
 ple, less -S may be convenient if the terminal isn't wide
 enough.
 The exact output may vary between xz versions and different lo-
 cales. For machine-readable output, --robot --list should be
 used.
 Operation modifiers
 -k, --keep
 Don't delete the input files.
 Since xz 5.4.0, this option also makes xz 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. In earlier versions this was only done with
 --force.
 -f, --force
 This option has several effects:
 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
 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
 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-
 mat.
 -c, --stdout, --to-stdout
 Write the compressed or decompressed data to standard output in-
 stead of a file. This implies --keep.
 --single-stream
 Decompress only the first .xz stream, and silently ignore possi-
 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
 trailing data after the .lzma file or raw stream.
 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
 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
 output is connected to a regular file and certain additional
 conditions are met to make it safe. Creating sparse files may
 save disk space and speed up the decompression by reducing the
 amount of disk I/O.
 -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-
 played and the file is skipped.
 When decompressing, recognize files with the suffix .suf in ad-
 dition to files with the .xz, .txz, .lzma, or .tlz suffix. If
 the source file has the suffix .suf, the suffix is removed to
 get the target filename.
 When compressing or decompressing raw streams (--format=raw),
 the suffix must always be specified unless writing to standard
 output, because there is no default suffix for raw streams.
 --files[=file]
 Read the filenames to process from file; if file is omitted,
 filenames are read from standard input. Filenames must be ter-
 minated with the newline character. A dash (-) is taken as a
 regular filename; it doesn't mean standard input. If filenames
 are given also as command line arguments, they are processed be-
 fore the filenames read from file.
 --files0[=file]
 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
 (created with --format=raw) cannot be auto-detected.
 xz Compress to the .xz file format, or accept only .xz files
 when decompressing.
 lzma, alone
 Compress to the legacy .lzma file format, or accept only
 .lzma files when decompressing. The alternative name
 alone is provided for backwards compatibility with LZMA
 Utils.
 raw Compress or uncompress a raw stream (no headers). This
 is meant for advanced users only. To decode raw streams,
 you need use --format=raw and explicitly specify the fil-
 ter chain, which normally would have been stored in the
 container headers.
 -C check, --check=check
 Specify the type of the integrity check. The check is calcu-
 lated from the uncompressed data and stored in the .xz file.
 This option has an effect only when compressing into the .xz
 format; the .lzma format doesn't support integrity checks. The
 integrity check (if any) is verified when the .xz file is decom-
 pressed.
 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
 the data is verified by other means anyway.
 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-
 ligible.
 sha256 Calculate SHA-256. This is somewhat slower than CRC32
 and CRC64.
 Integrity of the .xz headers is always verified with CRC32. It
 is not possible to change or disable it.
 --ignore-check
 Don't verify the integrity check of the compressed data when de-
 compressing. The CRC32 values in the .xz headers will still be
 verified normally.
 Do not use this option unless you know what you are doing. Pos-
 sible reasons to use this option:
 o Trying to recover data from a corrupt .xz file.
 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.
 -0 ... -9
 Select a compression preset level. The default is -6. If mul-
 tiple preset levels are specified, the last one takes effect.
 If a custom filter chain was already specified, setting a com-
 pression preset level clears the custom filter chain.
 The differences between the presets are more significant than
 with gzip(1) and bzip2(1). The selected compression settings
 determine the memory requirements of the decompressor, thus us-
 ing a too high preset level might make it painful to decompress
 the file on an old system with little RAM. Specifically, it's
 not a good idea to blindly use -9 for everything like it often
 is with gzip(1) and bzip2(1).
 -0 ... -3
 These are somewhat fast presets. -0 is sometimes faster
 than gzip -9 while compressing much better. The higher
 ones often have speed comparable to bzip2(1) with compa-
 rable or better compression ratio, although the results
 depend a lot on the type of data being compressed.
 -4 ... -6
 Good to very good compression while keeping decompressor
 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
 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,
 respectively.
 On the same hardware, the decompression speed is approximately a
 constant number of bytes of compressed data per second. In
 other words, the better the compression, the faster the decom-
 pression will usually be. This also means that the amount of
 uncompressed output produced per second can vary a lot.
 The following table summarises the features of the presets:
 Preset DictSize CompCPU CompMem DecMem
 -0 256 KiB 0 3 MiB 1 MiB
 -1 1 MiB 1 9 MiB 2 MiB
 -2 2 MiB 2 17 MiB 3 MiB
 -3 4 MiB 3 32 MiB 5 MiB
 -4 4 MiB 4 48 MiB 5 MiB
 -5 8 MiB 5 94 MiB 9 MiB
 -6 8 MiB 6 94 MiB 9 MiB
 -7 16 MiB 6 186 MiB 17 MiB
 -8 32 MiB 6 370 MiB 33 MiB
 -9 64 MiB 6 674 MiB 65 MiB
 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,
 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
 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 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.
 -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
 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
 (lower CompCPU) than -4e and -6e, respectively. That way no two
 presets are identical.
 Preset DictSize CompCPU CompMem DecMem
 -0e 256 KiB 8 4 MiB 1 MiB
 -1e 1 MiB 8 13 MiB 2 MiB
 -2e 2 MiB 8 25 MiB 3 MiB
 -3e 4 MiB 7 48 MiB 5 MiB
 -4e 4 MiB 8 48 MiB 5 MiB
 -5e 8 MiB 7 94 MiB 9 MiB
 -6e 8 MiB 8 94 MiB 9 MiB
 -7e 16 MiB 8 186 MiB 17 MiB
 -8e 32 MiB 8 370 MiB 33 MiB
 -9e 64 MiB 8 674 MiB 65 MiB
 For example, there are a total of four presets that use 8 MiB
 dictionary, whose order from the fastest to the slowest is -5,
 -6, -5e, and -6e.
 --fast
 --best These are somewhat misleading aliases for -0 and -9, respec-
 tively. These are provided only for backwards compatibility
 with LZMA Utils. Avoid using these options.
 --block-size=size
 When compressing to the .xz format, split the input data into
 blocks of size bytes. The blocks are compressed independently
 from each other, which helps with multi-threading and makes lim-
 ited random-access decompression possible. This option is typi-
 cally used to override the default block size in multi-threaded
 mode, but this option can be used in single-threaded mode too.
 In multi-threaded mode about three times size bytes will be al-
 located in each thread for buffering input and output. The de-
 fault size is three times the LZMA2 dictionary size or 1 MiB,
 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.
 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.
 --block-list=sizes
 When compressing to the .xz format, start a new block after the
 given intervals of uncompressed data.
 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.
 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.
 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-
 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
 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
 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
 better compression ratio.
 This feature is disabled by default. If this option is speci-
 fied more than once, the last one takes effect. The special
 timeout value of 0 can be used to explicitly disable this fea-
 ture.
 This feature is not available on non-POSIX systems.
 This feature is still experimental. Currently xz is unsuitable
 for decompressing the stream in real time due to how xz does
 buffering.
 --memlimit-compress=limit
 Set a memory usage limit for compression. If this option is
 specified multiple times, the last one takes effect.
 If the compression settings exceed the limit, xz will adjust the
 settings downwards so that the limit is no longer exceeded and
 display a notice that automatic adjustment was done. Such ad-
 justments are not made when compressing with --format=raw or if
 --no-adjust has been specified. In those cases, 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-
 press=80MiB
 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
 the limit is automatically bigger on systems with more mem-
 ory. Example: --memlimit-compress=70%
 o The limit can be reset back to its default value by setting
 it to 0. This is currently equivalent to setting the limit
 to max (no memory usage limit). Once multithreading support
 has been implemented, there may be a difference between 0 and
 max for the multithreaded case, so it is recommended to use 0
 instead of max until the details have been decided.
 For 32-bit xz there is a special case: if the limit would be
 over 4020 MiB, the limit is set to 4020 MiB. (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 exe-
 cutable has access to 4 GiB address space 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
 ways to specify the limit.
 -M limit, --memlimit=limit, --memory=limit
 This is equivalent to specifying --memlimit-compress=limit
 --memlimit-decompress=limit.
 --no-adjust
 Display an error and exit if the compression settings exceed the
 memory usage limit. The default is to adjust the settings down-
 wards so that the memory usage limit is not exceeded. Automatic
 adjusting is always disabled when creating raw streams (--for-
 mat=raw).
 -T threads, --threads=threads
 Specify the number of worker threads to use. Setting threads to
 a special value 0 makes xz use as many threads as there are CPU
 cores on the system. The actual number of threads can be less
 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.
 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
 overridden with the --block-size=size option.
 Threaded decompression hasn't been implemented yet. It will
 only work on files that contain multiple blocks with size infor-
 mation in block headers. All files compressed in multi-threaded
 mode meet this condition, but files compressed in single-
 threaded mode don't even if --block-size=size is used.
 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.
 When a custom filter chain is specified, preset options (-0 ... -9 and
 --extreme) earlier on the command line are forgotten. If a preset op-
 tion is specified after one or more custom filter chain options, the
 new preset takes effect and the custom filter chain options specified
 earlier are forgotten.
 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-
 ters.
 Many filters have limitations on where they can be in the filter chain:
 some filters can work only as the last filter in the chain, some only
 as a non-last filter, and some work in any position in the chain. De-
 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.
 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.
 --lzma1[=options]
 --lzma2[=options]
 Add LZMA1 or LZMA2 filter to the filter chain. These filters
 can be used only as the last filter in the chain.
 LZMA1 is a legacy filter, which is supported almost solely due
 to the legacy .lzma file format, which supports only LZMA1.
 LZMA2 is an updated version of LZMA1 to fix some practical is-
 sues of LZMA1. The .xz format uses LZMA2 and doesn't support
 LZMA1 at all. Compression speed and ratios of LZMA1 and LZMA2
 are practically the same.
 LZMA1 and LZMA2 share the same set of options:
 preset=preset
 Reset all LZMA1 or LZMA2 options to preset. Preset con-
 sist of an integer, which may be followed by single-let-
 ter preset modifiers. The integer can be from 0 to 9,
 matching the command line options -0 ... -9. The only
 supported modifier is currently e, which matches --ex-
 treme. If no preset is specified, the default values of
 LZMA1 or LZMA2 options are taken from the preset 6.
 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
 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
 usually improves compression ratio, but a dictionary big-
 ger than the uncompressed file is waste of memory.
 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
 is the maximum for the LZMA1 and LZMA2 stream formats.
 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
 somewhat preferred for compression. Other sizes will get
 rounded up when stored in the .xz headers.
 lc=lc Specify the number of literal context bits. The minimum
 is 0 and the maximum is 4; the default is 3. In addi-
 tion, the sum of lc and lp must not exceed 4.
 All bytes that cannot be encoded as matches are encoded
 as literals. That is, literals are simply 8-bit bytes
 that are encoded one at a time.
 The literal coding makes an assumption that the highest
 lc bits of the previous uncompressed byte correlate with
 the next byte. For example, in typical English text, an
 upper-case letter is often followed by a lower-case let-
 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
 literal coding can take advantage of this property in the
 uncompressed data.
 The default value (3) is usually good. If you want maxi-
 mum compression, test lc=4. Sometimes it helps a little,
 and sometimes it makes compression worse. If it makes it
 worse, test lc=2 too.
 lp=lp Specify the number of literal position bits. The minimum
 is 0 and the maximum is 4; the default is 0.
 Lp affects what kind of alignment in the uncompressed
 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
 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
 alignment (2^pb=2^2=4), which is often a good choice when
 there's no better guess.
 When the aligment is known, setting pb accordingly may
 reduce the file size a little. For example, with text
 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
 choice.
 Even though the assumed alignment can be adjusted with pb
 and lp, LZMA1 and LZMA2 still slightly favor 16-byte
 alignment. It might be worth taking into account when
 designing file formats that are likely to be often com-
 pressed with LZMA1 or LZMA2.
 mf=mf Match finder has a major effect on encoder speed, memory
 usage, and compression ratio. Usually Hash Chain match
 finders are faster than Binary Tree match finders. The
 default depends on the preset: 0 uses hc3, 1-3 use hc4,
 and the rest use bt4.
 The following match finders are supported. The memory
 usage formulas below are rough approximations, which are
 closest to the reality when dict is a power of two.
 hc3 Hash Chain with 2- and 3-byte hashing
 Minimum value for nice: 3
 Memory usage:
 dict * 7.5 (if dict <= 16 MiB);
 dict * 5.5 + 64 MiB (if dict > 16 MiB)
 hc4 Hash Chain with 2-, 3-, and 4-byte hashing
 Minimum value for nice: 4
 Memory usage:
 dict * 7.5 (if dict <= 32 MiB);
 dict * 6.5 (if dict > 32 MiB)
 bt2 Binary Tree with 2-byte hashing
 Minimum value for nice: 2
 Memory usage: dict * 9.5
 bt3 Binary Tree with 2- and 3-byte hashing
 Minimum value for nice: 3
 Memory usage:
 dict * 11.5 (if dict <= 16 MiB);
 dict * 9.5 + 64 MiB (if dict > 16 MiB)
 bt4 Binary Tree with 2-, 3-, and 4-byte hashing
 Minimum value for nice: 4
 Memory usage:
 dict * 11.5 (if dict <= 32 MiB);
 dict * 10.5 (if dict > 32 MiB)
 mode=mode
 Compression mode specifies the method to analyze the data
 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.
 Usually fast is used with Hash Chain match finders and
 normal with Binary Tree match finders. This is also what
 the presets do.
 nice=nice
 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-
 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
 compressor determine a reasonable depth from mf and nice.
 Reasonable depth for Hash Chains is 4-100 and 16-1000 for
 Binary Trees. Using very high values for depth can make
 the encoder extremely slow with some files. Avoid set-
 ting the depth over 1000 unless you are prepared to in-
 terrupt the compression in case it is taking far too
 long.
 When decoding raw streams (--format=raw), LZMA2 needs only the
 dictionary size. LZMA1 needs also lc, lp, and pb.
 --x86[=options]
 --powerpc[=options]
 --ia64[=options]
 --arm[=options]
 --armthumb[=options]
 --sparc[=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.
 A BCJ filter converts relative addresses in the machine code to
 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.
 It is fine to apply a BCJ filter on a whole executable; there's
 no need to apply it only on the executable section. Applying a
 BCJ filter on an archive that contains both executable and non-
 executable files may or may not give good results, so it gener-
 ally isn't good to blindly apply a BCJ filter when compressing
 binary packages for distribution.
 These BCJ filters are very fast and use insignificant amount of
 memory. If a BCJ filter improves compression ratio of a file,
 it can improve decompression speed at the same time. This is
 because, on the same hardware, the decompression speed of LZMA2
 is roughly a fixed number of bytes of compressed data per sec-
 ond.
 These BCJ filters have known problems related to the compression
 ratio:
 o Some types of files containing executable code (for example,
 object files, static libraries, and Linux kernel modules)
 have the addresses in the instructions filled with filler
 values. These BCJ filters will still do the address conver-
 sion, which will make the compression worse with these files.
 o Applying a BCJ filter on an archive containing multiple simi-
 lar executables can make the compression ratio worse than not
 using a BCJ filter. This is because the BCJ filter doesn't
 detect the boundaries of the executable files, and doesn't
 reset the address conversion counter for each executable.
 Both of the above problems will be fixed in the future in a new
 filter. The old BCJ filters will still be useful in embedded
 systems, because the decoder of the new filter will be bigger
 and use more memory.
 Different instruction sets have different alignment:
 Filter Alignment Notes
 x86 1 32-bit or 64-bit x86
 PowerPC 4 Big endian only
 ARM 4 Little endian only
 ARM-Thumb 2 Little endian only
 IA-64 16 Big or little endian
 SPARC 4 Big or little endian
 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 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 com-
 pressing x86 executables.
 All BCJ filters support the same options:
 start=offset
 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-
 fault is good; specifying a custom offset is almost never
 useful.
 --delta[=options]
 Add the Delta filter to the filter chain. The Delta filter can
 be only used as a non-last filter in the filter chain.
 Currently only simple byte-wise delta calculation is supported.
 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
 faster and better, for example, with flac(1).
 Supported options:
 dist=distance
 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
 A3 B5 A4 B7, the output will be A1 B1 01 02 01 02 01 02.
 Other 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-
 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
 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
 is known. That is, the percentage cannot be shown in pipes.
 o Amount of compressed data produced (compressing) or consumed
 (decompressing).
 o Amount of uncompressed data consumed (compressing) or pro-
 duced (decompressing).
 o Compression ratio, which is calculated by dividing the amount
 of compressed data processed so far by the amount of uncom-
 pressed data processed so far.
 o Compression or decompression speed. This is measured as the
 amount of uncompressed data consumed (compression) or pro-
 duced (decompression) per second. It is shown after a few
 seconds have passed since xz started processing the file.
 o Elapsed time in the format M:SS or H:MM:SS.
 o Estimated remaining time is shown only when the size of the
 input file is known and a couple of seconds have already
 passed since xz started processing the file. The time is
 shown in a less precise format which never has any colons,
 for example, 2 min 30 s.
 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
 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
 known.
 -Q, --no-warn
 Don't set the exit status to 2 even if a condition worth a warn-
 ing was detected. This option doesn't affect the verbosity
 level, thus both --quiet and --no-warn have to be used to not
 display warnings and to not alter the exit status.
 --robot
 Print messages in a machine-parsable format. This is intended
 to ease writing frontends that want to use xz instead of li-
 blzma, which may be the case with various scripts. The output
 with this option enabled is meant to be stable across xz re-
 leases. See the section ROBOT MODE for details.
 --info-memory
 Display, in human-readable format, how much physical memory
 (RAM) xz thinks the system has and the memory usage limits for
 compression and decompression, and exit successfully.
 -h, --help
 Display a help message describing the most commonly used op-
 tions, and exit successfully.
 -H, --long-help
 Display a help message describing all features of xz, and exit
 successfully
 -V, --version
 Display the version number of xz and liblzma in human readable
 format. To get machine-parsable output, specify --robot before
 --version.
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 will print 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 three tab-separated
 columns:
 1. Total amount of physical memory (RAM) in bytes
 2. Memory usage limit for compression in bytes. A special value of
 zero indicates the default setting, which for single-threaded mode
 is the same as no limit.
 3. Memory usage limit for decompression in bytes. A special value of
 zero indicates the default setting, which for single-threaded mode
 is the same as no limit.
 In the future, the output of xz --robot --info-memory may have more
 columns, but never more than a single line.
 List mode
 xz --robot --list uses tab-separated output. The first column of every
 line has a string that indicates the type of the information found on
 that line:
 name This is always the first line when starting to list a file. The
 second column on the line is the filename.
 file This line contains overall information about the .xz file. This
 line is always printed after the name line.
 stream This line type is used only when --verbose was specified. There
 are as many stream lines as there are streams in the .xz file.
 block This line type is used only when --verbose was specified. There
 are as many block lines as there are blocks in the .xz file.
 The block lines are shown after all the stream lines; different
 line types are not interleaved.
 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
 file.
 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:
 2. Number of streams in the file
 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-
 tio.
 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
 two digits).
 8. Total size of stream padding in the file
 The columns of the stream lines:
 2. Stream number (the first stream is 1)
 3. Number of blocks in the stream
 4. Compressed start offset
 5. Uncompressed start offset
 6. Compressed size (does not include stream padding)
 7. Uncompressed size
 8. Compression ratio
 9. Name of the integrity check
 10. Size of stream padding
 The columns of the block lines:
 2. Number of the stream containing this block
 3. Block number relative to the beginning of the stream (the
 first block is 1)
 4. Block number relative to the beginning of the file
 5. Compressed start offset relative to the beginning of the
 file
 6. Uncompressed start offset relative to the beginning of the
 file
 7. Total compressed size of the block (includes headers)
 8. Uncompressed size
 9. Compression ratio
 10. Name of the integrity check
 If --verbose was specified twice, additional columns are included on
 the block lines. These are not displayed with a single --verbose, be-
 cause getting this information requires many seeks and can thus be
 slow:
 11. Value of the integrity check in hexadecimal
 12. Block header size
 13. Block flags: c indicates that compressed size is present,
 and u indicates that uncompressed size is present. If the
 flag is not set, a dash (-) is shown instead to keep the
 string length fixed. New flags may be added to the end of
 the string in the future.
 14. Size of the actual compressed data in the block (this ex-
 cludes the block header, block padding, and check fields)
 15. Amount of memory (in bytes) required to decompress this
 block with this xz version
 16. Filter chain. Note that most of the options used at com-
 pression time cannot be known, because only the options that
 are needed for decompression are stored in the .xz headers.
 The columns of the summary lines:
 2. Amount of memory (in bytes) required to decompress this file
 with this xz version
 3. yes or no indicating if all block headers have both com-
 pressed size and uncompressed size stored in them
 Since xz 5.1.2alpha:
 4. Minimum xz version required to decompress the file
 The columns of the totals line:
 2. Number of streams
 3. Number of blocks
 4. Compressed size
 5. Uncompressed size
 6. Average compression ratio
 7. Comma-separated list of integrity check names that were
 present in the files
 8. Stream padding size
 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
 the totals line:
 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-
 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
 the existing line types, but the existing columns won't be changed.
EXIT STATUS
 0 All is good.
 1 An error occurred.
 2 Something worth a warning occurred, but no actual errors oc-
 curred.
 Notices (not warnings or errors) printed on standard error don't affect
 the 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-
 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-
 FAULTS.
 XZ_OPT This is for passing options to xz when it is not possible to set
 the options directly on the xz command line. This is the case
 when xz is run by a script or tool, for example, GNU tar(1):
 XZ_OPT=-2v tar caf foo.tar.xz foo
 Scripts may use XZ_OPT, for example, to set script-specific de-
 fault compression options. It is still recommended to allow
 users to override XZ_OPT if that is reasonable. For example, in
 sh(1) scripts one may use something like this:
 XZ_OPT=${XZ_OPT-"-7e"}
 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
 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 decompressor memory usage.
 Level xz LZMA Utils
 -0 256 KiB N/A
 -1 1 MiB 64 KiB
 -2 2 MiB 1 MiB
 -3 4 MiB 512 KiB
 -4 4 MiB 1 MiB
 -5 8 MiB 2 MiB
 -6 8 MiB 4 MiB
 -7 16 MiB 8 MiB
 -8 32 MiB 16 MiB
 -9 64 MiB 32 MiB
 The dictionary size differences affect the compressor memory usage too,
 but there are some other differences between LZMA Utils and XZ Utils,
 which make the difference even bigger:
 Level xz LZMA Utils 4.32.x
 -0 3 MiB N/A
 -1 9 MiB 2 MiB
 -2 17 MiB 12 MiB
 -3 32 MiB 12 MiB
 -4 48 MiB 16 MiB
 -5 94 MiB 26 MiB
 -6 94 MiB 45 MiB
 -7 186 MiB 83 MiB
 -8 370 MiB 159 MiB
 -9 674 MiB 311 MiB
 The default preset level in LZMA Utils is -7 while in XZ Utils it is
 -6, so both use an 8 MiB dictionary by default.
 Streamed vs. non-streamed .lzma files
 The uncompressed size of the file can be stored in the .lzma header.
 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
 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
 need to use LZMA Utils or LZMA SDK to create .lzma files with known un-
 compressed size.
 Unsupported .lzma files
 The .lzma format allows lc values up to 8, and lp values up to 4. LZMA
 Utils can decompress files with any lc and lp, but always creates files
 with lc=3 and lp=0. Creating files with other lc and lp is possible
 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
 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
 files.
 These limitations shouldn't be a problem in practice, since practically
 all .lzma files have been compressed with settings that liblzma will
 accept.
 Trailing garbage
 When decompressing, LZMA Utils silently ignore everything after the
 first .lzma stream. In most situations, this is a bug. This also
 means that LZMA Utils don't support decompressing concatenated .lzma
 files.
 If there is data left after the first .lzma stream, xz considers the
 file to be corrupt unless --single-stream was used. This may break ob-
 scure scripts which have assumed that trailing garbage is ignored.
NOTES
 Compressed output may vary
 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
 different build options are used.
 The above means that once --rsyncable has been implemented, the result-
 ing files won't necessarily be rsyncable unless both old and new files
 have been compressed with the same xz version. This problem can be
 fixed if a part of the encoder implementation is frozen to keep rsynca-
 ble output stable across xz versions.
 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
 --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-
 fying the integrity check if the particular check is not supported.
 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
 (-6), and remove foo if compression is successful:
 xz foo
 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-
 pression (48 MiB and 5 MiB, respectively):
 tar cf - baz | xz -4e > baz.tar.xz
 A mix of compressed and uncompressed files can be decompressed to stan-
 dard output with a single command:
 xz -dcf a.txt b.txt.xz c.txt d.txt.lzma > abcd.txt
 Parallel compression of many files
 On GNU and *BSD, find(1) and xargs(1) can be used to parallelize com-
 pression of many files:
 find . -type f \! -name '*.xz' -print0 \
 | xargs -0r -P4 -n16 xz -T1
 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
 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.
 The option -T1 for xz is there to force it to single-threaded mode, be-
 cause xargs(1) is used to control the amount of parallelization.
 Robot mode
 Calculate how many bytes have been saved in total after compressing
 multiple files:
 xz --robot --list *.xz | awk '/^totals/{print 5ドル-4ドル}'
 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)" ||
 [ "$XZ_VERSION" -lt 50000002 ]; then
 echo "Your xz is too old."
 fi
 unset XZ_VERSION LIBLZMA_VERSION
 Set a memory usage limit for decompression using XZ_OPT, but if a limit
 has already been set, don't increase it:
 NEWLIM=$((123 << 20)) # 123 MiB
 OLDLIM=$(xz --robot --info-memory | cut -f3)
 if [ $OLDLIM -eq 0 -o $OLDLIM -gt $NEWLIM ]; then
 XZ_OPT="$XZ_OPT --memlimit-decompress=$NEWLIM"
 export XZ_OPT
 fi
 Custom compressor filter chains
 The simplest use for custom filter chains is customizing a LZMA2 pre-
 set. This can be useful, because the presets cover only a subset of
 the potentially useful combinations of compression settings.
 The CompCPU columns of the tables from the descriptions of the options
 -0 ... -9 and --extreme are useful when customizing LZMA2 presets.
 Here are the relevant parts collected from those two tables:
 Preset CompCPU
 -0 0
 -1 1
 -2 2
 -3 3
 -4 4
 -5 5
 -6 6
 -5e 7
 -6e 8
 If you know that a file requires somewhat big dictionary (for example,
 32 MiB) to compress well, but you want to compress it quicker than xz
 -8 would do, a preset with a low CompCPU value (for example, 1) can be
 modified to use a bigger dictionary:
 xz --lzma2=preset=1,dict=32MiB foo.tar
 With certain files, the above command may be faster than xz -6 while
 compressing significantly better. However, it must be emphasized that
 only some files benefit from a big dictionary while keeping the CompCPU
 value low. The most obvious situation, where a big dictionary can help
 a lot, is an archive containing very similar files of at least a few
 megabytes each. The dictionary size has to be significantly bigger
 than any individual file to allow LZMA2 to take full advantage of the
 similarities between consecutive files.
 If very high compressor and decompressor memory usage is fine, and the
 file being compressed is at least several hundred megabytes, it may be
 useful to use an even bigger dictionary than the 64 MiB that xz -9
 would use:
 xz -vv --lzma2=dict=192MiB big_foo.tar
 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
 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
 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)
 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
 the following might give slightly (like 0.1 %) smaller file than xz -6e
 (try also without lc=4):
 xz --lzma2=preset=6e,pb=0,lc=4 source_code.tar
 Using another filter together with LZMA2 can improve compression with
 certain file types. For example, to compress a x86-32 or x86-64 shared
 library using the x86 BCJ filter:
 xz --x86 --lzma2 libfoo.so
 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.
 The Delta filter together with LZMA2 can give good results with bitmap
 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
 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
 have the same number of bytes per pixel.
SEE ALSO
 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: <http://7-zip.org/sdk.html>
Tukaani 2020年02月01日 XZ(1)