{
    "mode": "man",
    "parameter": "lzma",
    "section": "1",
    "url": "https://www.chedong.com/phpMan.php/man/lzma/1/json",
    "generated": "2026-09-17T06:01:40Z",
    "synopsis": "xz [option...]  [file...]",
    "sections": {
        "NAME": {
            "content": "xz, unxz, xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and .lzma files\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "xz [option...]  [file...]\n",
            "subsections": []
        },
        "COMMAND ALIASES": {
            "content": "unxz is equivalent to xz --decompress.\nxzcat is equivalent to xz --decompress --stdout.\nlzma is equivalent to xz --format=lzma.\nunlzma is equivalent to xz --format=lzma --decompress.\nlzcat is equivalent to xz --format=lzma --decompress --stdout.\n\nWhen  writing scripts that need to decompress files, it is recommended to always use the name\nxz with appropriate arguments (xz -d or xz -dc) instead of the names unxz and xzcat.\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "xz is a general-purpose data compression tool with command line syntax similar to gzip(1) and\nbzip2(1).  The native file format is the .xz format, but the legacy .lzma format used by LZMA\nUtils and raw compressed streams with no container format headers are also supported.  In ad‐\ndition, decompression of the .lz format used by lzip is supported.\n\nxz compresses or decompresses each file according to the  selected  operation  mode.   If  no\nfiles  are  given or file is -, xz reads from standard input and writes the processed data to\nstandard output.  xz will refuse (display an error and skip the  file)  to  write  compressed\ndata  to  standard  output if it is a terminal.  Similarly, xz will refuse to read compressed\ndata from standard input if it is a terminal.\n\nUnless --stdout is specified, files other than - are written to a new file whose name is  de‐\nrived from the source file name:\n\n•  When  compressing,  the suffix of the target file format (.xz or .lzma) is appended to the\nsource filename to get the target filename.\n\n•  When decompressing, the .xz, .lzma, or .lz suffix is removed from the filename to get  the\ntarget  filename.   xz  also recognizes the suffixes .txz and .tlz, and replaces them with\nthe .tar suffix.\n\nIf the target file already exists, an error is displayed and the file is skipped.\n\nUnless writing to standard output, xz will display a warning and skip the file if any of  the\nfollowing applies:\n\n•  File  is  not a regular file.  Symbolic links are not followed, and thus they are not con‐\nsidered to be regular files.\n\n•  File has more than one hard link.\n\n•  File has setuid, setgid, or sticky bit set.\n\n•  The operation mode is set to compress and the file already has a suffix of the target file\nformat (.xz or .txz when compressing to the .xz format, and .lzma or .tlz when compressing\nto the .lzma format).\n\n•  The operation mode is set to decompress and the file doesn't have a suffix of any  of  the\nsupported file formats (.xz, .txz, .lzma, .tlz, or .lz).\n\nAfter successfully compressing or decompressing the file, xz copies the owner, group, permis‐\nsions,  access time, and modification time from the source file to the target file.  If copy‐\ning the group fails, the permissions are modified so that the target file doesn't become  ac‐\ncessible  to  users who didn't have permission to access the source file.  xz doesn't support\ncopying other metadata like access control lists or extended attributes yet.\n\nOnce the target file has been successfully closed, the source file is removed  unless  --keep\nwas  specified.  The source file is never removed if the output is written to standard output\nor if an error occurs.\n\nSending SIGINFO or SIGUSR1 to the xz process makes it print progress information to  standard\nerror.   This  has  only limited use since when standard error is a terminal, using --verbose\nwill display an automatically updating progress indicator.\n",
            "subsections": [
                {
                    "name": "Memory usage",
                    "content": "The memory usage of xz varies from a few hundred kilobytes to several gigabytes depending  on\nthe compression settings.  The settings used when compressing a file determine the memory re‐\nquirements  of  the decompressor.  Typically the decompressor needs 5 % to 20 % of the amount\nof memory that the compressor needed when creating the file.  For  example,  decompressing  a\nfile  created  with xz -9 currently requires 65 MiB of memory.  Still, it is possible to have\n.xz files that require several gigabytes of memory to decompress.\n\nEspecially users of older systems may find the possibility of very large memory usage  annoy‐\ning.   To  prevent  uncomfortable surprises, xz has a built-in memory usage limiter, which is\ndisabled by default.  While some operating systems provide ways to limit the memory usage  of\nprocesses, relying on it wasn't deemed to be flexible enough (for example, using ulimit(1) to\nlimit virtual memory tends to cripple mmap(2)).\n\nThe memory usage limiter can be enabled with the command line option --memlimit=limit.  Often\nit  is  more  convenient to enable the limiter by default by setting the environment variable\nXZDEFAULTS, for example, XZDEFAULTS=--memlimit=150MiB.  It is possible to  set  the  limits\nseparately  for  compression  and decompression by using --memlimit-compress=limit and --mem‐\nlimit-decompress=limit.  Using these two options outside XZDEFAULTS is rarely useful because\na single run of xz cannot do both compression and decompression and --memlimit=limit  (or  -M\nlimit) is shorter to type on the command line.\n\nIf  the specified memory usage limit is exceeded when decompressing, xz will display an error\nand decompressing the file will fail.  If the limit is exceeded when compressing, xz will try\nto scale the settings down so that the limit is no longer exceeded (except when using  --for‐\nmat=raw  or  --no-adjust).  This way the operation won't fail unless the limit is very small.\nThe scaling of the settings is done in steps that don't match the compression level  presets,\nfor  example, if the limit is only slightly less than the amount required for xz -9, the set‐\ntings will be scaled down only a little, not all the way down to xz -8.\n"
                },
                {
                    "name": "Concatenation and padding with .xz files",
                    "content": "It is possible to concatenate .xz files as is.  xz will decompress such files as if they were\na single .xz file.\n\nIt is possible to insert padding between the concatenated parts or after the last part.   The\npadding  must  consist  of  null bytes and the size of the padding must be a multiple of four\nbytes.  This can be useful, for example, if the .xz file is stored on a medium that  measures\nfile sizes in 512-byte blocks.\n\nConcatenation and padding are not allowed with .lzma files or raw streams.\n"
                }
            ]
        },
        "OPTIONS": {
            "content": "",
            "subsections": [
                {
                    "name": "Integer suffixes and special values",
                    "content": "In most places where an integer argument is expected, an optional suffix is supported to eas‐\nily indicate large integers.  There must be no space between the integer and the suffix.\n\nKiB    Multiply  the  integer by 1,024 (2^10).  Ki, k, kB, K, and KB are accepted as synonyms\nfor KiB.\n\nMiB    Multiply the integer by 1,048,576 (2^20).  Mi, m, M, and MB are accepted  as  synonyms\nfor MiB.\n\nGiB    Multiply  the  integer by 1,073,741,824 (2^30).  Gi, g, G, and GB are accepted as syn‐\nonyms for GiB.\n\nThe special value max can be used to indicate the maximum integer value supported by the  op‐\ntion.\n"
                },
                {
                    "name": "Operation mode",
                    "content": "If multiple operation mode options are given, the last one takes effect.\n"
                },
                {
                    "name": "-z --compress",
                    "content": "Compress.   This is the default operation mode when no operation mode option is speci‐\nfied and no other operation mode is implied from the command name (for  example,  unxz\nimplies --decompress).\n",
                    "flag": "-z",
                    "long": "--compress"
                },
                {
                    "name": "-d --decompress --uncompress",
                    "content": "Decompress.\n",
                    "flag": "-d",
                    "long": "--uncompress"
                },
                {
                    "name": "-t --test",
                    "content": "Test  the  integrity  of  compressed files.  This option is equivalent to --decompress\n--stdout except that the decompressed data is discarded instead of  being  written  to\nstandard output.  No files are created or removed.\n",
                    "flag": "-t",
                    "long": "--test"
                },
                {
                    "name": "-l --list",
                    "content": "Print  information about compressed files.  No uncompressed output is produced, and no\nfiles are created or removed.  In list mode, the program cannot  read  the  compressed\ndata from standard input or from other unseekable sources.\n\nThe  default  listing  shows basic information about files, one file per line.  To get\nmore detailed information, use also the --verbose option.  For even more  information,\nuse --verbose twice, but note that this may be slow, because getting all the extra in‐\nformation  requires many seeks.  The width of verbose output exceeds 80 characters, so\npiping the output to, for example, less -S may be convenient  if  the  terminal  isn't\nwide enough.\n\nThe  exact  output  may  vary between xz versions and different locales.  For machine-\nreadable output, --robot --list should be used.\n",
                    "flag": "-l",
                    "long": "--list"
                },
                {
                    "name": "Operation modifiers",
                    "content": ""
                },
                {
                    "name": "-k --keep",
                    "content": "Don't delete the input files.\n\nSince xz 5.2.6, this option also makes xz compress or decompress even if the input  is\na  symbolic  link  to  a regular file, has more than one hard link, or has the setuid,\nsetgid, or sticky bit set.  The setuid, setgid, and sticky bits are not copied to  the\ntarget file.  In earlier versions this was only done with --force.\n",
                    "flag": "-k",
                    "long": "--keep"
                },
                {
                    "name": "-f --force",
                    "content": "This option has several effects:\n\n•  If the target file already exists, delete it before compressing or decompressing.\n\n•  Compress  or decompress even if the input is a symbolic link to a regular file, has\nmore than one hard link, or has the setuid, setgid, or sticky bit set.  The setuid,\nsetgid, and sticky bits are not copied to the target file.\n\n•  When used with --decompress --stdout and xz cannot recognize the type of the source\nfile, copy the source file as is to standard output.  This allows xzcat --force  to\nbe  used like cat(1) for files that have not been compressed with xz.  Note that in\nfuture, xz might support new compressed file formats, which may make xz  decompress\nmore  types  of  files  instead  of  copying them as is to standard output.  --for‐\nmat=format can be used to restrict xz to decompress only a single file format.\n",
                    "flag": "-f",
                    "long": "--force"
                },
                {
                    "name": "-c --stdout --to-stdout",
                    "content": "Write the compressed or decompressed data to standard output instead of a file.   This\nimplies --keep.\n",
                    "flag": "-c",
                    "long": "--to-stdout"
                },
                {
                    "name": "--single-stream",
                    "content": "Decompress  only  the  first  .xz stream, and silently ignore possible remaining input\ndata following the stream.  Normally such trailing garbage makes xz display an error.\n\nxz never decompresses more than one stream from .lzma files or raw streams,  but  this\noption  still  makes  xz ignore the possible trailing data after the .lzma file or raw\nstream.\n\nThis option has no effect if the operation mode is not --decompress or --test.\n",
                    "long": "--single-stream"
                },
                {
                    "name": "--no-sparse",
                    "content": "Disable creation of sparse files.  By default, if decompressing into a  regular  file,\nxz  tries  to make the file sparse if the decompressed data contains long sequences of\nbinary zeros.  It also works when writing to standard output as long as standard  out‐\nput  is  connected to a regular file and certain additional conditions are met to make\nit safe.  Creating sparse files may save disk space and speed up the decompression  by\nreducing the amount of disk I/O.\n",
                    "long": "--no-sparse"
                },
                {
                    "name": "-S _ --suffix=_",
                    "content": "When  compressing, use .suf as the suffix for the target file instead of .xz or .lzma.\nIf not writing to standard output and the source file already has the suffix  .suf,  a\nwarning is displayed and the file is skipped.\n\nWhen decompressing, recognize files with the suffix .suf in addition to files with the\n.xz,  .txz,  .lzma,  .tlz, or .lz suffix.  If the source file has the suffix .suf, the\nsuffix is removed to get the target filename.\n\nWhen compressing or decompressing raw streams (--format=raw), the suffix  must  always\nbe specified unless writing to standard output, because there is no default suffix for\nraw streams.\n\n--files[=file]\nRead  the  filenames to process from file; if file is omitted, filenames are read from\nstandard input.  Filenames must be terminated with the newline character.  A dash  (-)\nis  taken  as  a  regular  filename; it doesn't mean standard input.  If filenames are\ngiven also as command line arguments, they are processed  before  the  filenames  read\nfrom file.\n\n--files0[=file]\nThis  is identical to --files[=file] except that each filename must be terminated with\nthe null character.\n",
                    "flag": "-S",
                    "long": "--suffix",
                    "arg": "_"
                },
                {
                    "name": "Basic file format and compression options",
                    "content": ""
                },
                {
                    "name": "-F _ --format=_",
                    "content": "Specify the file format to compress or decompress:\n\nauto   This is the default.  When compressing, auto is equivalent to xz.  When  decom‐\npressing,  the  format  of the input file is automatically detected.  Note that\nraw streams (created with --format=raw) cannot be auto-detected.\n\nxz     Compress to the .xz file format, or accept only .xz files when decompressing.\n\nlzma, alone\nCompress to the legacy .lzma file format, or accept only .lzma files  when  de‐\ncompressing.   The alternative name alone is provided for backwards compatibil‐\nity with LZMA Utils.\n\nlzip   Accept only .lz files when decompressing.  Compression is not supported.\n\nThe .lz format version 0 and the unextended version 1 are supported.  Version 0\nfiles were produced by lzip 1.3 and older.  Such files aren't common but may be\nfound from file archives as a few source packages were released in this format.\nPeople might have old personal files in this format too.  Decompression support\nfor the format version 0 was removed in lzip 1.18.\n\nlzip 1.4 and later create files in the format version 1.  The sync flush marker\nextension to the format version 1 was added in lzip  1.6.   This  extension  is\nrarely used and isn't supported by xz (diagnosed as corrupt input).\n\nraw    Compress  or  uncompress a raw stream (no headers).  This is meant for advanced\nusers only.  To decode raw streams, you need use  --format=raw  and  explicitly\nspecify  the  filter  chain,  which normally would have been stored in the con‐\ntainer headers.\n",
                    "flag": "-F",
                    "long": "--format",
                    "arg": "_"
                },
                {
                    "name": "-C _ --check=_",
                    "content": "Specify the type of the integrity check.  The check  is  calculated  from  the  uncom‐\npressed  data  and  stored  in the .xz file.  This option has an effect only when com‐\npressing into the .xz format; the .lzma format doesn't support integrity checks.   The\nintegrity check (if any) is verified when the .xz file is decompressed.\n\nSupported check types:\n\nnone   Don't  calculate  an integrity check at all.  This is usually a bad idea.  This\ncan be useful when integrity of the data is verified by other means anyway.\n\ncrc32  Calculate CRC32 using the polynomial from IEEE-802.3 (Ethernet).\n\ncrc64  Calculate CRC64 using the polynomial from ECMA-182.  This is the default, since\nit is slightly better than CRC32 at detecting damaged files and the speed  dif‐\nference is negligible.\n\nsha256 Calculate SHA-256.  This is somewhat slower than CRC32 and CRC64.\n\nIntegrity  of  the  .xz  headers is always verified with CRC32.  It is not possible to\nchange or disable it.\n",
                    "flag": "-C",
                    "long": "--check",
                    "arg": "_"
                },
                {
                    "name": "--ignore-check",
                    "content": "Don't verify the integrity check of the compressed data when decompressing.  The CRC32\nvalues in the .xz headers will still be verified normally.\n\nDo not use this option unless you know what you are doing.  Possible  reasons  to  use\nthis option:\n\n•  Trying to recover data from a corrupt .xz file.\n\n•  Speeding  up  decompression.   This  matters mostly with SHA-256 or with files that\nhave compressed extremely well.  It's recommended to not use this option  for  this\npurpose unless the file integrity is verified externally in some other way.\n",
                    "long": "--ignore-check"
                },
                {
                    "name": "-0  -9",
                    "content": "Select  a compression preset level.  The default is -6.  If multiple preset levels are\nspecified, the last one takes effect.  If a custom filter chain was already specified,\nsetting a compression preset level clears the custom filter chain.\n\nThe differences between the  presets  are  more  significant  than  with  gzip(1)  and\nbzip2(1).   The selected compression settings determine the memory requirements of the\ndecompressor, thus using a too high preset level might make it painful  to  decompress\nthe  file  on  an  old  system with little RAM.  Specifically, it's not a good idea to\nblindly use -9 for everything like it often is with gzip(1) and bzip2(1).\n\n-0 ... -3\nThese are somewhat fast presets.  -0 is sometimes faster  than  gzip  -9  while\ncompressing  much  better.   The  higher  ones  often  have speed comparable to\nbzip2(1) with comparable or better compression ratio, although the results  de‐\npend a lot on the type of data being compressed.\n\n-4 ... -6\nGood  to  very good compression while keeping decompressor memory usage reason‐\nable even for old systems.  -6 is the default, which is usually a  good  choice\nfor distributing files that need to be decompressible even on systems with only\n16 MiB RAM.  (-5e or -6e may be worth considering too.  See --extreme.)\n\n-7 ... -9\nThese  are  like -6 but with higher compressor and decompressor memory require‐\nments.  These are useful only when compressing files bigger than 8 MiB, 16 MiB,\nand 32 MiB, respectively.\n\nOn the same hardware, the decompression speed is approximately a  constant  number  of\nbytes  of compressed data per second.  In other words, the better the compression, the\nfaster the decompression will usually be.  This also means that the amount  of  uncom‐\npressed output produced per second can vary a lot.\n\nThe following table summarises the features of the presets:\n\nPreset   DictSize   CompCPU   CompMem   DecMem\n-0     256 KiB       0        3 MiB    1 MiB\n-1       1 MiB       1        9 MiB    2 MiB\n-2       2 MiB       2       17 MiB    3 MiB\n-3       4 MiB       3       32 MiB    5 MiB\n-4       4 MiB       4       48 MiB    5 MiB\n-5       8 MiB       5       94 MiB    9 MiB\n-6       8 MiB       6       94 MiB    9 MiB\n-7      16 MiB       6      186 MiB   17 MiB\n-8      32 MiB       6      370 MiB   33 MiB\n-9      64 MiB       6      674 MiB   65 MiB\n\nColumn descriptions:\n\n•  DictSize  is  the LZMA2 dictionary size.  It is waste of memory to use a dictionary\nbigger than the size of the uncompressed file.  This is why it is good to avoid us‐\ning the presets -7 ... -9 when there's no real need for them.  At -6 and lower, the\namount of memory wasted is usually low enough to not matter.\n\n•  CompCPU is a simplified representation of the LZMA2 settings that  affect  compres‐\nsion  speed.   The  dictionary size affects speed too, so while CompCPU is the same\nfor levels -6 ... -9, higher levels still tend to be a little slower.  To get  even\nslower and thus possibly better compression, see --extreme.\n\n•  CompMem  contains  the  compressor memory requirements in the single-threaded mode.\nIt may vary slightly between xz versions.  Memory requirements of some of  the  fu‐\nture  multithreaded  modes  may  be  dramatically  higher  than that of the single-\nthreaded mode.\n\n•  DecMem contains the decompressor memory requirements.   That  is,  the  compression\nsettings  determine  the memory requirements of the decompressor.  The exact decom‐\npressor memory usage is slightly more than the LZMA2 dictionary size, but the  val‐\nues in the table have been rounded up to the next full MiB.\n",
                    "flag": "-9"
                },
                {
                    "name": "-e --extreme",
                    "content": "Use a slower variant of the selected compression preset level (-0 ... -9) to hopefully\nget  a  little  bit  better compression ratio, but with bad luck this can also make it\nworse.  Decompressor memory usage is not affected, but  compressor  memory  usage  in‐\ncreases a little at preset levels -0 ... -3.\n\nSince there are two presets with dictionary sizes 4 MiB and 8 MiB, the presets -3e and\n-5e use slightly faster settings (lower CompCPU) than -4e and -6e, respectively.  That\nway no two presets are identical.\n\nPreset   DictSize   CompCPU   CompMem   DecMem\n-0e     256 KiB       8        4 MiB    1 MiB\n-1e       1 MiB       8       13 MiB    2 MiB\n-2e       2 MiB       8       25 MiB    3 MiB\n-3e       4 MiB       7       48 MiB    5 MiB\n-4e       4 MiB       8       48 MiB    5 MiB\n-5e       8 MiB       7       94 MiB    9 MiB\n-6e       8 MiB       8       94 MiB    9 MiB\n-7e      16 MiB       8      186 MiB   17 MiB\n-8e      32 MiB       8      370 MiB   33 MiB\n-9e      64 MiB       8      674 MiB   65 MiB\n\nFor  example, there are a total of four presets that use 8 MiB dictionary, whose order\nfrom the fastest to the slowest is -5, -6, -5e, and -6e.\n",
                    "flag": "-e",
                    "long": "--extreme"
                },
                {
                    "name": "--fast",
                    "content": "--best These are somewhat misleading aliases for -0 and -9, respectively.  These are provided\nonly for backwards compatibility with LZMA Utils.  Avoid using these options.\n\n--block-size=size\nWhen compressing to the .xz format, split the input data into blocks  of  size  bytes.\nThe  blocks  are  compressed  independently  from  each other, which helps with multi-\nthreading and makes limited random-access decompression possible.  This option is typ‐\nically used to override the default block size in multi-threaded mode, but this option\ncan be used in single-threaded mode too.\n\nIn multi-threaded mode about three times size bytes will be allocated in  each  thread\nfor  buffering input and output.  The default size is three times the LZMA2 dictionary\nsize or 1 MiB, whichever is more.  Typically a good value is 2–4 times the size of the\nLZMA2 dictionary or at least 1 MiB.  Using size less than the LZMA2 dictionary size is\nwaste of RAM because then the LZMA2 dictionary buffer will never get fully used.   The\nsizes of the blocks are stored in the block headers, which a future version of xz will\nuse for multi-threaded decompression.\n\nIn  single-threaded  mode  no block splitting is done by default.  Setting this option\ndoesn't affect memory usage.  No size information is stored  in  block  headers,  thus\nfiles  created  in  single-threaded mode won't be identical to files created in multi-\nthreaded mode.  The lack of size information also means that a future  version  of  xz\nwon't be able decompress the files in multi-threaded mode.\n\n--block-list=sizes\nWhen compressing to the .xz format, start a new block after the given intervals of un‐\ncompressed data.\n\nThe  uncompressed  sizes of the blocks are specified as a comma-separated list.  Omit‐\nting a size (two or more consecutive commas) is a shorthand to use  the  size  of  the\nprevious block.\n\nIf the input file is bigger than the sum of sizes, the last value in sizes is repeated\nuntil  the end of the file.  A special value of 0 may be used as the last value to in‐\ndicate that the rest of the file should be encoded as a single block.\n\nIf one specifies sizes that exceed the encoder's block size (either the default  value\nin threaded mode or the value specified with --block-size=size), the encoder will cre‐\nate  additional  blocks while keeping the boundaries specified in sizes.  For example,\nif one specifies --block-size=10MiB --block-list=5MiB,10MiB,8MiB,12MiB,24MiB  and  the\ninput  file is 80 MiB, one will get 11 blocks: 5, 10, 8, 10, 2, 10, 10, 4, 10, 10, and\n1 MiB.\n\nIn multi-threaded mode the sizes of the blocks are stored in the block headers.   This\nisn't  done  in single-threaded mode, so the encoded output won't be identical to that\nof the multi-threaded mode.\n\n--flush-timeout=timeout\nWhen compressing, if more than timeout milliseconds (a positive  integer)  has  passed\nsince  the  previous  flush  and reading more input would block, all the pending input\ndata is flushed from the encoder and made available in the output stream.  This can be\nuseful if xz is used to compress data that is streamed over a network.  Small  timeout\nvalues  make  the  data  available  at the receiving end with a small delay, but large\ntimeout values give better compression ratio.\n\nThis feature is disabled by default.  If this option is specified more than once,  the\nlast  one takes effect.  The special timeout value of 0 can be used to explicitly dis‐\nable this feature.\n\nThis feature is not available on non-POSIX systems.\n\nThis feature is still experimental.  Currently xz is unsuitable for decompressing  the\nstream in real time due to how xz does buffering.\n\n--memlimit-compress=limit\nSet a memory usage limit for compression.  If this option is specified multiple times,\nthe last one takes effect.\n\nIf  the  compression settings exceed the limit, xz will attempt to adjust the settings\ndownwards so that the limit is no longer exceeded and display a notice that  automatic\nadjustment  was  done.  The adjustments are done in this order: reducing the number of\nthreads, switching to single-threaded mode if even one thread in  multi-threaded  mode\nexceeds the limit, and finally reducing the LZMA2 dictionary size.\n\nWhen compressing with --format=raw or if --no-adjust has been specified, only the num‐\nber  of  threads  may be reduced since it can be done without affecting the compressed\noutput.\n\nIf the limit cannot be met even with the adjustments described above, an error is dis‐\nplayed and xz will exit with exit status 1.\n\nThe limit can be specified in multiple ways:\n\n•  The limit can be an absolute value in bytes.  Using an integer suffix like MiB  can\nbe useful.  Example: --memlimit-compress=80MiB\n\n•  The  limit  can  be specified as a percentage of total physical memory (RAM).  This\ncan be useful especially when setting the XZDEFAULTS  environment  variable  in  a\nshell  initialization  script that is shared between different computers.  That way\nthe limit is automatically bigger on systems with  more  memory.   Example:  --mem‐\nlimit-compress=70%\n\n•  The  limit can be reset back to its default value by setting it to 0.  This is cur‐\nrently equivalent to setting the limit to max (no memory usage limit).\n\nFor 32-bit xz there is a special case: if the limit would be over 4020 MiB, the  limit\nis set to 4020 MiB.  On MIPS32 2000 MiB is used instead.  (The values 0 and max aren't\naffected  by  this.   A similar feature doesn't exist for decompression.)  This can be\nhelpful when a 32-bit executable has access to 4 GiB address space (2 GiB  on  MIPS32)\nwhile hopefully doing no harm in other situations.\n\nSee also the section Memory usage.\n\n--memlimit-decompress=limit\nSet  a  memory  usage limit for decompression.  This also affects the --list mode.  If\nthe operation is not possible without exceeding the limit, xz will  display  an  error\nand decompressing the file will fail.  See --memlimit-compress=limit for possible ways\nto specify the limit.\n\n--memlimit-mt-decompress=limit\nSet  a  memory usage limit for multi-threaded decompression.  This can only affect the\nnumber of threads; this will never make xz refuse to decompress a file.  If  limit  is\ntoo  low  to  allow  any multi-threading, the limit is ignored and xz will continue in\nsingle-threaded mode.  Note that if also --memlimit-decompress is used, it will always\napply to both single-threaded and multi-threaded modes, and so the effective limit for\nmulti-threading will never be higher than the limit set with --memlimit-decompress.\n\nIn contrast to the other memory usage  limit  options,  --memlimit-mt-decompress=limit\nhas  a system-specific default limit.  xz --info-memory can be used to see the current\nvalue.\n\nThis option and its default value exist because without any limit the threaded  decom‐\npressor  could end up allocating an insane amount of memory with some input files.  If\nthe default limit is too low on your system, feel free to increase the limit but never\nset it to a value larger than the amount of usable RAM as with appropriate input files\nxz will attempt to use that amount of memory even with a low number of threads.   Run‐\nning out of memory or swapping will not improve decompression performance.\n\nSee  --memlimit-compress=limit  for possible ways to specify the limit.  Setting limit\nto 0 resets the limit to the default system-specific value.\n",
                    "long": "--fast"
                },
                {
                    "name": "-M _ --memlimit=_ --memory=_",
                    "content": "This is equivalent to specifying --memlimit-compress=limit --memlimit-decompress=limit\n--memlimit-mt-decompress=limit.\n",
                    "flag": "-M",
                    "long": "--memory",
                    "arg": "_"
                },
                {
                    "name": "--no-adjust",
                    "content": "Display an error and exit if the memory usage limit cannot be  met  without  adjusting\nsettings  that affect the compressed output.  That is, this prevents xz from switching\nthe encoder from multi-threaded mode to single-threaded mode  and  from  reducing  the\nLZMA2 dictionary size.  Even when this option is used the number of threads may be re‐\nduced to meet the memory usage limit as that won't affect the compressed output.\n\nAutomatic adjusting is always disabled when creating raw streams (--format=raw).\n",
                    "long": "--no-adjust"
                },
                {
                    "name": "-T _ --threads=_",
                    "content": "Specify  the  number  of  worker threads to use.  Setting threads to a special value 0\nmakes xz use up to as many threads as the processor(s) on the system support.  The ac‐\ntual number of threads can be fewer than threads if the input file is not  big  enough\nfor threading with the given settings or if using more threads would exceed the memory\nusage limit.\n\nThe  single-threaded and multi-threaded compressors produce different output.  Single-\nthreaded compressor will give the smallest file size but  only  the  output  from  the\nmulti-threaded compressor can be decompressed using multiple threads.  Setting threads\nto 1 will use the single-threaded mode.  Setting threads to any other value, including\n0,  will  use the multi-threaded compressor even if the system supports only one hard‐\nware thread.  (xz 5.2.x used single-threaded mode in this situation.)\n\nTo use multi-threaded mode with only one thread, set threads to +1.  The + prefix  has\nno  effect with values other than 1.  A memory usage limit can still make xz switch to\nsingle-threaded mode unless --no-adjust is used.  Support for the + prefix  was  added\nin xz 5.4.0.\n\nIf  an  automatic  number  of threads has been requested and no memory usage limit has\nbeen specified, then a system-specific default soft limit will  be  used  to  possibly\nlimit  the  number  of threads.  It is a soft limit in sense that it is ignored if the\nnumber of threads becomes one, thus a soft limit will never stop xz  from  compressing\nor decompressing.  This default soft limit will not make xz switch from multi-threaded\nmode to single-threaded mode.  The active limits can be seen with xz --info-memory.\n\nCurrently  the  only  threading  method is to split the input into blocks and compress\nthem independently from each other.  The default block size depends on the compression\nlevel and can be overridden with the --block-size=size option.\n\nThreaded decompression only works on files that contain multiple blocks with size  in‐\nformation  in block headers.  All large enough files compressed in multi-threaded mode\nmeet this condition, but files  compressed  in  single-threaded  mode  don't  even  if\n--block-size=size has been used.\n",
                    "flag": "-T",
                    "long": "--threads",
                    "arg": "_"
                },
                {
                    "name": "Custom compressor filter chains",
                    "content": "A custom filter chain allows specifying the compression settings in detail instead of relying\non  the  settings associated to the presets.  When a custom filter chain is specified, preset\noptions (-0 ... -9 and --extreme) earlier on the command line are forgotten.  If a preset op‐\ntion is specified after one or more custom filter chain options, the new preset takes  effect\nand the custom filter chain options specified earlier are forgotten.\n\nA  filter  chain  is  comparable to piping on the command line.  When compressing, the uncom‐\npressed input goes to the first filter, whose output goes to the next filter (if  any).   The\noutput of the last filter gets written to the compressed file.  The maximum number of filters\nin the chain is four, but typically a filter chain has only one or two filters.\n\nMany filters have limitations on where they can be in the filter chain: some filters can work\nonly  as  the  last filter in the chain, some only as a non-last filter, and some work in any\nposition in the chain.  Depending on the filter, this limitation is either  inherent  to  the\nfilter design or exists to prevent security issues.\n\nA  custom filter chain is specified by using one or more filter options in the order they are\nwanted in the filter chain.  That is, the order of filter options is significant!   When  de‐\ncoding  raw streams (--format=raw), the filter chain is specified in the same order as it was\nspecified when compressing.\n\nFilters take filter-specific options as a comma-separated list.  Extra commas in options  are\nignored.   Every  option  has  a default value, so you need to specify only those you want to\nchange.\n\nTo see the whole filter chain and options, use xz -vv (that is, use --verbose  twice).   This\nworks also for viewing the filter chain options used by presets.\n\n--lzma1[=options]\n--lzma2[=options]\nAdd  LZMA1 or LZMA2 filter to the filter chain.  These filters can be used only as the\nlast filter in the chain.\n\nLZMA1 is a legacy filter, which is supported almost solely due  to  the  legacy  .lzma\nfile  format,  which supports only LZMA1.  LZMA2 is an updated version of LZMA1 to fix\nsome practical issues of LZMA1.  The .xz format uses LZMA2 and doesn't  support  LZMA1\nat all.  Compression speed and ratios of LZMA1 and LZMA2 are practically the same.\n\nLZMA1 and LZMA2 share the same set of options:\n\npreset=preset\nReset  all  LZMA1  or  LZMA2  options to preset.  Preset consist of an integer,\nwhich may be followed by single-letter preset modifiers.  The  integer  can  be\nfrom  0  to 9, matching the command line options -0 ... -9.  The only supported\nmodifier is currently e, which matches --extreme.  If no preset  is  specified,\nthe default values of LZMA1 or LZMA2 options are taken from the preset 6.\n\ndict=size\nDictionary  (history  buffer)  size  indicates  how  many bytes of the recently\nprocessed uncompressed data is kept in memory.  The algorithm tries to find re‐\npeating byte sequences (matches) in the uncompressed  data,  and  replace  them\nwith  references  to the data currently in the dictionary.  The bigger the dic‐\ntionary, the higher is the chance to find a match.  Thus, increasing dictionary\nsize usually improves compression ratio, but a dictionary bigger than  the  un‐\ncompressed file is waste of memory.\n\nTypical  dictionary  size is from 64 KiB to 64 MiB.  The minimum is 4 KiB.  The\nmaximum for compression is currently 1.5 GiB (1536 MiB).  The decompressor  al‐\nready  supports dictionaries up to one byte less than 4 GiB, which is the maxi‐\nmum for the LZMA1 and LZMA2 stream formats.\n\nDictionary size and match finder (mf) together determine the  memory  usage  of\nthe  LZMA1  or LZMA2 encoder.  The same (or bigger) dictionary size is required\nfor decompressing that was used when compressing, thus the memory usage of  the\ndecoder  is  determined  by the dictionary size used when compressing.  The .xz\nheaders store the dictionary size either as 2^n or  2^n  +  2^(n-1),  so  these\nsizes  are somewhat preferred for compression.  Other sizes will get rounded up\nwhen stored in the .xz headers.\n\nlc=lc  Specify the number of literal context bits.  The minimum is 0 and  the  maximum\nis 4; the default is 3.  In addition, the sum of lc and lp must not exceed 4.\n\nAll  bytes that cannot be encoded as matches are encoded as literals.  That is,\nliterals are simply 8-bit bytes that are encoded one at a time.\n\nThe literal coding makes an assumption that the highest lc bits of the previous\nuncompressed byte correlate with the next byte.  For example, in  typical  Eng‐\nlish text, an upper-case letter is often followed by a lower-case letter, and a\nlower-case letter is usually followed by another lower-case letter.  In the US-\nASCII  character set, the highest three bits are 010 for upper-case letters and\n011 for lower-case letters.  When lc is at least 3, the literal coding can take\nadvantage of this property in the uncompressed data.\n\nThe default value (3) is usually good.  If you want maximum  compression,  test\nlc=4.   Sometimes  it helps a little, and sometimes it makes compression worse.\nIf it makes it worse, test lc=2 too.\n\nlp=lp  Specify the number of literal position bits.  The minimum is 0 and the  maximum\nis 4; the default is 0.\n\nLp  affects what kind of alignment in the uncompressed data is assumed when en‐\ncoding literals.  See pb below for more information about alignment.\n\npb=pb  Specify the number of position bits.  The minimum is 0 and the  maximum  is  4;\nthe default is 2.\n\nPb  affects  what kind of alignment in the uncompressed data is assumed in gen‐\neral.  The default means four-byte alignment (2^pb=2^2=4),  which  is  often  a\ngood choice when there's no better guess.\n\nWhen  the alignment is known, setting pb accordingly may reduce the file size a\nlittle.  For example, with text  files  having  one-byte  alignment  (US-ASCII,\nISO-8859-*,  UTF-8), setting pb=0 can improve compression slightly.  For UTF-16\ntext, pb=1 is a good choice.  If the alignment is an odd number like  3  bytes,\npb=0 might be the best choice.\n\nEven  though  the  assumed  alignment can be adjusted with pb and lp, LZMA1 and\nLZMA2 still slightly favor 16-byte alignment.  It might be  worth  taking  into\naccount when designing file formats that are likely to be often compressed with\nLZMA1 or LZMA2.\n\nmf=mf  Match finder has a major effect on encoder speed, memory usage, and compression\nratio.   Usually  Hash  Chain  match  finders are faster than Binary Tree match\nfinders.  The default depends on the preset: 0 uses hc3, 1–3 use hc4,  and  the\nrest use bt4.\n\nThe following match finders are supported.  The memory usage formulas below are\nrough  approximations, which are closest to the reality when dict is a power of\ntwo.\n\nhc3    Hash Chain with 2- and 3-byte hashing\nMinimum value for nice: 3\nMemory usage:\ndict * 7.5 (if dict <= 16 MiB);\ndict * 5.5 + 64 MiB (if dict > 16 MiB)\n\nhc4    Hash Chain with 2-, 3-, and 4-byte hashing\nMinimum value for nice: 4\nMemory usage:\ndict * 7.5 (if dict <= 32 MiB);\ndict * 6.5 (if dict > 32 MiB)\n\nbt2    Binary Tree with 2-byte hashing\nMinimum value for nice: 2\nMemory usage: dict * 9.5\n\nbt3    Binary Tree with 2- and 3-byte hashing\nMinimum value for nice: 3\nMemory usage:\ndict * 11.5 (if dict <= 16 MiB);\ndict * 9.5 + 64 MiB (if dict > 16 MiB)\n\nbt4    Binary Tree with 2-, 3-, and 4-byte hashing\nMinimum value for nice: 4\nMemory usage:\ndict * 11.5 (if dict <= 32 MiB);\ndict * 10.5 (if dict > 32 MiB)\n\nmode=mode\nCompression mode specifies the method to analyze the data produced by the match\nfinder.  Supported modes are fast and normal.  The default is fast for  presets\n0–3 and normal for presets 4–9.\n\nUsually  fast is used with Hash Chain match finders and normal with Binary Tree\nmatch finders.  This is also what the presets do.\n\nnice=nice\nSpecify what is considered to be a nice length for a match.  Once a match of at\nleast nice bytes is found, the algorithm  stops  looking  for  possibly  better\nmatches.\n\nNice  can  be 2–273 bytes.  Higher values tend to give better compression ratio\nat the expense of speed.  The default depends on the preset.\n\ndepth=depth\nSpecify the maximum search depth in the match finder.  The default is the  spe‐\ncial  value  of 0, which makes the compressor determine a reasonable depth from\nmf and nice.\n\nReasonable depth for Hash Chains is 4–100 and 16–1000 for Binary Trees.   Using\nvery high values for depth can make the encoder extremely slow with some files.\nAvoid setting the depth over 1000 unless you are prepared to interrupt the com‐\npression in case it is taking far too long.\n\nWhen decoding raw streams (--format=raw), LZMA2 needs only the dictionary size.  LZMA1\nneeds also lc, lp, and pb.\n\n--x86[=options]\n--arm[=options]\n--armthumb[=options]\n--arm64[=options]\n--powerpc[=options]\n--ia64[=options]\n--sparc[=options]\nAdd  a  branch/call/jump  (BCJ) filter to the filter chain.  These filters can be used\nonly as a non-last filter in the filter chain.\n\nA BCJ filter converts relative addresses in the machine code to their  absolute  coun‐\nterparts.  This doesn't change the size of the data but it increases redundancy, which\ncan  help  LZMA2  to  produce 0–15 % smaller .xz file.  The BCJ filters are always re‐\nversible, so using a BCJ filter for wrong type of data doesn't cause  any  data  loss,\nalthough  it  may make the compression ratio slightly worse.  The BCJ filters are very\nfast and use an insignificant amount of memory.\n\nThese BCJ filters have known problems related to the compression ratio:\n\n•  Some types of files containing executable code (for example, object  files,  static\nlibraries,  and Linux kernel modules) have the addresses in the instructions filled\nwith filler values.  These BCJ filters will still do the address conversion,  which\nwill make the compression worse with these files.\n\n•  If a BCJ filter is applied on an archive, it is possible that it makes the compres‐\nsion ratio worse than not using a BCJ filter.  For example, if there are similar or\neven  identical  executables then filtering will likely make the files less similar\nand thus compression is worse.  The contents of non-executable files  in  the  same\narchive  can  matter too.  In practice one has to try with and without a BCJ filter\nto see which is better in each situation.\n\nDifferent instruction sets have different  alignment:  the  executable  file  must  be\naligned to a multiple of this value in the input data to make the filter work.\n\nFilter      Alignment   Notes\nx86             1       32-bit or 64-bit x86\nARM             4\nARM-Thumb       2\nARM64           4       4096-byte alignment is best\nPowerPC         4       Big endian only\nIA-64          16       Itanium\nSPARC           4\n\nSince  the  BCJ-filtered  data is usually compressed with LZMA2, the compression ratio\nmay be improved slightly if the LZMA2 options are set to match the  alignment  of  the\nselected  BCJ  filter.   For  example, with the IA-64 filter, it's good to set pb=4 or\neven pb=4,lp=4,lc=0 with LZMA2 (2^4=16).  The x86 filter is an exception; it's usually\ngood to stick to LZMA2's default four-byte alignment when compressing x86 executables.\n\nAll BCJ filters support the same options:\n\nstart=offset\nSpecify the start offset that is used when converting between relative and  ab‐\nsolute addresses.  The offset must be a multiple of the alignment of the filter\n(see the table above).  The default is zero.  In practice, the default is good;\nspecifying a custom offset is almost never useful.\n\n--delta[=options]\nAdd the Delta filter to the filter chain.  The Delta filter can be only used as a non-\nlast filter in the filter chain.\n\nCurrently only simple byte-wise delta calculation is supported.  It can be useful when\ncompressing,  for example, uncompressed bitmap images or uncompressed PCM audio.  How‐\never, special purpose algorithms may give significantly better results  than  Delta  +\nLZMA2.   This  is  true especially with audio, which compresses faster and better, for\nexample, with flac(1).\n\nSupported options:\n\ndist=distance\nSpecify the distance of the delta  calculation  in  bytes.   distance  must  be\n1–256.  The default is 1.\n\nFor example, with dist=2 and eight-byte input A1 B1 A2 B3 A3 B5 A4 B7, the out‐\nput will be A1 B1 01 02 01 02 01 02.\n"
                },
                {
                    "name": "Other options",
                    "content": ""
                },
                {
                    "name": "-q --quiet",
                    "content": "Suppress  warnings  and notices.  Specify this twice to suppress errors too.  This op‐\ntion has no effect on the exit status.  That is, even if a warning was suppressed, the\nexit status to indicate a warning is still used.\n",
                    "flag": "-q",
                    "long": "--quiet"
                },
                {
                    "name": "-v --verbose",
                    "content": "Be verbose.  If standard error is connected to a terminal, xz will display a  progress\nindicator.  Specifying --verbose twice will give even more verbose output.\n\nThe progress indicator shows the following information:\n\n•  Completion  percentage  is  shown if the size of the input file is known.  That is,\nthe percentage cannot be shown in pipes.\n\n•  Amount of compressed data produced (compressing) or consumed (decompressing).\n\n•  Amount of uncompressed data consumed (compressing) or produced (decompressing).\n\n•  Compression ratio, which is calculated by dividing the amount  of  compressed  data\nprocessed so far by the amount of uncompressed data processed so far.\n\n•  Compression or decompression speed.  This is measured as the amount of uncompressed\ndata  consumed  (compression)  or produced (decompression) per second.  It is shown\nafter a few seconds have passed since xz started processing the file.\n\n•  Elapsed time in the format M:SS or H:MM:SS.\n\n•  Estimated remaining time is shown only when the size of the input file is known and\na couple of seconds have already passed since xz started processing the file.   The\ntime  is  shown in a less precise format which never has any colons, for example, 2\nmin 30 s.\n\nWhen standard error is not a terminal, --verbose will make xz print the filename, com‐\npressed size, uncompressed size, compression ratio, and possibly also  the  speed  and\nelapsed time on a single line to standard error after compressing or decompressing the\nfile.  The speed and elapsed time are included only when the operation took at least a\nfew  seconds.   If the operation didn't finish, for example, due to user interruption,\nalso the completion percentage is printed if the size of the input file is known.\n",
                    "flag": "-v",
                    "long": "--verbose"
                },
                {
                    "name": "-Q --no-warn",
                    "content": "Don't set the exit status to 2 even if a condition worth a warning was detected.  This\noption doesn't affect the verbosity level, thus both --quiet and --no-warn have to  be\nused to not display warnings and to not alter the exit status.\n",
                    "flag": "-Q",
                    "long": "--no-warn"
                },
                {
                    "name": "--robot",
                    "content": "Print  messages  in a machine-parsable format.  This is intended to ease writing fron‐\ntends that want to use xz instead of liblzma, which  may  be  the  case  with  various\nscripts.   The  output  with  this  option enabled is meant to be stable across xz re‐\nleases.  See the section ROBOT MODE for details.\n",
                    "long": "--robot"
                },
                {
                    "name": "--info-memory",
                    "content": "Display, in human-readable format, how much physical memory (RAM) and how many proces‐\nsor threads xz thinks the system has and the memory usage limits for  compression  and\ndecompression, and exit successfully.\n",
                    "long": "--info-memory"
                },
                {
                    "name": "-h --help",
                    "content": "Display  a  help  message describing the most commonly used options, and exit success‐\nfully.\n",
                    "flag": "-h",
                    "long": "--help"
                },
                {
                    "name": "-H --long-help",
                    "content": "Display a help message describing all features of xz, and exit successfully\n",
                    "flag": "-H",
                    "long": "--long-help"
                },
                {
                    "name": "-V --version",
                    "content": "Display the version number of xz and liblzma in human readable  format.   To  get  ma‐\nchine-parsable output, specify --robot before --version.\n",
                    "flag": "-V",
                    "long": "--version"
                }
            ]
        },
        "ROBOT MODE": {
            "content": "The  robot  mode  is  activated with the --robot option.  It makes the output of xz easier to\nparse by other programs.  Currently  --robot  is  supported  only  together  with  --version,\n--info-memory, and --list.  It will be supported for compression and decompression in the fu‐\nture.\n",
            "subsections": [
                {
                    "name": "Version",
                    "content": "xz --robot --version prints the version number of xz and liblzma in the following format:\n\nXZVERSION=XYYYZZZS\nLIBLZMAVERSION=XYYYZZZS\n\nX      Major version.\n\nYYY    Minor version.  Even numbers are stable.  Odd numbers are alpha or beta versions.\n\nZZZ    Patch level for stable releases or just a counter for development releases.\n\nS      Stability.   0 is alpha, 1 is beta, and 2 is stable.  S should be always 2 when YYY is\neven.\n\nXYYYZZZS are the same on both lines if xz and liblzma are from the same XZ Utils release.\n\nExamples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.\n"
                },
                {
                    "name": "Memory limit information",
                    "content": "xz --robot --info-memory prints a single line with multiple tab-separated columns:\n\n1.  Total amount of physical memory (RAM) in bytes.\n\n2.  Memory usage limit for compression in bytes (--memlimit-compress).  A special value of  0\nindicates the default setting which for single-threaded mode is the same as no limit.\n\n3.  Memory  usage  limit for decompression in bytes (--memlimit-decompress).  A special value\nof 0 indicates the default setting which for single-threaded  mode  is  the  same  as  no\nlimit.\n\n4.  Since  xz  5.3.4alpha:  Memory  usage  for  multi-threaded decompression in bytes (--mem‐\nlimit-mt-decompress).  This is never zero because a system-specific default  value  shown\nin  the  column  5 is used if no limit has been specified explicitly.  This is also never\ngreater than the value in the column 3 even if a larger value  has  been  specified  with\n--memlimit-mt-decompress.\n\n5.  Since  xz  5.3.4alpha: A system-specific default memory usage limit that is used to limit\nthe number of threads when compressing with an automatic number of threads  (--threads=0)\nand no memory usage limit has been specified (--memlimit-compress).  This is also used as\nthe default value for --memlimit-mt-decompress.\n\n6.  Since xz 5.3.4alpha: Number of available processor threads.\n\nIn  the  future, the output of xz --robot --info-memory may have more columns, but never more\nthan a single line.\n"
                },
                {
                    "name": "List mode",
                    "content": "xz --robot --list uses tab-separated output.  The first column of every  line  has  a  string\nthat indicates the type of the information found on that line:\n\nname   This  is always the first line when starting to list a file.  The second column on the\nline is the filename.\n\nfile   This line contains overall information about  the  .xz  file.   This  line  is  always\nprinted after the name line.\n\nstream This  line  type  is used only when --verbose was specified.  There are as many stream\nlines as there are streams in the .xz file.\n\nblock  This line type is used only when --verbose was specified.  There  are  as  many  block\nlines  as  there  are blocks in the .xz file.  The block lines are shown after all the\nstream lines; different line types are not interleaved.\n"
                },
                {
                    "name": "summary",
                    "content": "This line type is used only when --verbose was specified twice.  This line is  printed\nafter all block lines.  Like the file line, the summary line contains overall informa‐\ntion about the .xz file.\n\ntotals This  line is always the very last line of the list output.  It shows the total counts\nand sizes.\n\nThe columns of the file lines:\n2.  Number of streams in the file\n3.  Total number of blocks in the stream(s)\n4.  Compressed size of the file\n5.  Uncompressed size of the file\n6.  Compression ratio, for example, 0.123.  If ratio is over 9.999, three dashes (---)\nare displayed instead of the ratio.\n7.  Comma-separated list of integrity check names.  The following strings are used for\nthe known check types: None, CRC32, CRC64, and SHA-256.  For unknown check  types,\nUnknown-N  is  used,  where N is the Check ID as a decimal number (one or two dig‐\nits).\n8.  Total size of stream padding in the file\n\nThe columns of the stream lines:\n2.  Stream number (the first stream is 1)\n3.  Number of blocks in the stream\n4.  Compressed start offset\n5.  Uncompressed start offset\n6.  Compressed size (does not include stream padding)\n7.  Uncompressed size\n8.  Compression ratio\n9.  Name of the integrity check\n10. Size of stream padding\n\nThe columns of the block lines:\n2.  Number of the stream containing this block\n3.  Block number relative to the beginning of the stream (the first block is 1)\n4.  Block number relative to the beginning of the file\n5.  Compressed start offset relative to the beginning of the file\n6.  Uncompressed start offset relative to the beginning of the file\n7.  Total compressed size of the block (includes headers)\n8.  Uncompressed size\n9.  Compression ratio\n10. Name of the integrity check\n\nIf --verbose was specified twice, additional columns are included on the block lines.   These\nare  not  displayed  with  a single --verbose, because getting this information requires many\nseeks and can thus be slow:\n11. Value of the integrity check in hexadecimal\n12. Block header size\n13. Block flags: c indicates that compressed size is present, and u indicates that un‐\ncompressed size is present.  If the flag is not set, a dash (-) is  shown  instead\nto  keep the string length fixed.  New flags may be added to the end of the string\nin the future.\n14. Size of the actual compressed data in the block (this excludes the  block  header,\nblock padding, and check fields)\n15. Amount of memory (in bytes) required to decompress this block with this xz version\n16. Filter  chain.   Note  that most of the options used at compression time cannot be\nknown, because only the options that are needed for decompression  are  stored  in\nthe .xz headers.\n\nThe columns of the summary lines:\n2.  Amount of memory (in bytes) required to decompress this file with this xz version\n3.  yes  or  no  indicating  if all block headers have both compressed size and uncom‐\npressed size stored in them\nSince xz 5.1.2alpha:\n4.  Minimum xz version required to decompress the file\n\nThe columns of the totals line:\n2.  Number of streams\n3.  Number of blocks\n4.  Compressed size\n5.  Uncompressed size\n6.  Average compression ratio\n7.  Comma-separated list of integrity check names that were present in the files\n8.  Stream padding size\n9.  Number of files.  This is here to keep the order of the earlier columns  the  same\nas on file lines.\n\nIf --verbose was specified twice, additional columns are included on the totals line:\n10. Maximum  amount of memory (in bytes) required to decompress the files with this xz\nversion\n11. yes or no indicating if all block headers have both  compressed  size  and  uncom‐\npressed size stored in them\nSince xz 5.1.2alpha:\n12. Minimum xz version required to decompress the file\n\nFuture  versions  may  add  new  line types and new columns can be added to the existing line\ntypes, but the existing columns won't be changed.\n"
                }
            ]
        },
        "EXIT STATUS": {
            "content": "0      All is good.\n\n1      An error occurred.\n\n2      Something worth a warning occurred, but no actual errors occurred.\n\nNotices (not warnings or errors) printed on standard error don't affect the exit status.\n",
            "subsections": []
        },
        "ENVIRONMENT": {
            "content": "xz parses space-separated lists of options from the  environment  variables  XZDEFAULTS  and\nXZOPT,  in this order, before parsing the options from the command line.  Note that only op‐\ntions are parsed from the environment variables; all non-options are silently ignored.  Pars‐\ning is done with getoptlong(3) which is used also for the command line arguments.\n\nXZDEFAULTS\nUser-specific or system-wide default options.  Typically this is set in a  shell  ini‐\ntialization  script  to  enable xz's memory usage limiter by default.  Excluding shell\ninitialization scripts and similar special cases, scripts  must  never  set  or  unset\nXZDEFAULTS.\n\nXZOPT This  is for passing options to xz when it is not possible to set the options directly\non the xz command line.  This is the case when xz is run by a script or tool, for  ex‐\nample, GNU tar(1):\n\nXZOPT=-2v tar caf foo.tar.xz foo\n\nScripts  may  use  XZOPT, for example, to set script-specific default compression op‐\ntions.  It is still recommended to allow users to override XZOPT if that  is  reason‐\nable.  For example, in sh(1) scripts one may use something like this:\n\nXZOPT=${XZOPT-\"-7e\"}\nexport XZOPT\n",
            "subsections": []
        },
        "LZMA UTILS COMPATIBILITY": {
            "content": "The  command  line syntax of xz is practically a superset of lzma, unlzma, and lzcat as found\nfrom LZMA Utils 4.32.x.  In most cases, it is possible to replace LZMA Utils  with  XZ  Utils\nwithout  breaking existing scripts.  There are some incompatibilities though, which may some‐\ntimes cause problems.\n",
            "subsections": [
                {
                    "name": "Compression preset levels",
                    "content": "The numbering of the compression level presets is not identical in xz and  LZMA  Utils.   The\nmost  important  difference is how dictionary sizes are mapped to different presets.  Dictio‐\nnary size is roughly equal to the decompressor memory usage.\n\nLevel     xz      LZMA Utils\n-0     256 KiB      N/A\n-1       1 MiB     64 KiB\n-2       2 MiB      1 MiB\n-3       4 MiB    512 KiB\n-4       4 MiB      1 MiB\n-5       8 MiB      2 MiB\n-6       8 MiB      4 MiB\n-7      16 MiB      8 MiB\n-8      32 MiB     16 MiB\n-9      64 MiB     32 MiB\n\nThe dictionary size differences affect the compressor memory usage too, but  there  are  some\nother differences between LZMA Utils and XZ Utils, which make the difference even bigger:\n\nLevel     xz      LZMA Utils 4.32.x\n-0       3 MiB          N/A\n-1       9 MiB          2 MiB\n-2      17 MiB         12 MiB\n-3      32 MiB         12 MiB\n-4      48 MiB         16 MiB\n-5      94 MiB         26 MiB\n-6      94 MiB         45 MiB\n-7     186 MiB         83 MiB\n-8     370 MiB        159 MiB\n-9     674 MiB        311 MiB\n\nThe default preset level in LZMA Utils is -7 while in XZ Utils it is -6, so both use an 8 MiB\ndictionary by default.\n"
                },
                {
                    "name": "Streamed vs. non-streamed .lzma files",
                    "content": "The  uncompressed  size  of the file can be stored in the .lzma header.  LZMA Utils does that\nwhen compressing regular files.  The alternative is to mark that uncompressed size is unknown\nand use end-of-payload marker to indicate where the decompressor  should  stop.   LZMA  Utils\nuses  this  method  when  uncompressed  size  isn't known, which is the case, for example, in\npipes.\n\nxz supports decompressing .lzma files with or without end-of-payload marker,  but  all  .lzma\nfiles  created  by xz will use end-of-payload marker and have uncompressed size marked as un‐\nknown in the .lzma header.  This may be a problem in some uncommon situations.  For  example,\na  .lzma decompressor in an embedded device might work only with files that have known uncom‐\npressed size.  If you hit this problem, you need to use LZMA Utils  or  LZMA  SDK  to  create\n.lzma files with known uncompressed size.\n"
                },
                {
                    "name": "Unsupported .lzma files",
                    "content": "The  .lzma format allows lc values up to 8, and lp values up to 4.  LZMA Utils can decompress\nfiles with any lc and lp, but always creates files with lc=3 and lp=0.  Creating  files  with\nother lc and lp is possible with xz and with LZMA SDK.\n\nThe implementation of the LZMA1 filter in liblzma requires that the sum of lc and lp must not\nexceed 4.  Thus, .lzma files, which exceed this limitation, cannot be decompressed with xz.\n\nLZMA  Utils  creates  only .lzma files which have a dictionary size of 2^n (a power of 2) but\naccepts files with any dictionary size.  liblzma accepts only .lzma files which have  a  dic‐\ntionary  size  of  2^n  or 2^n + 2^(n-1).  This is to decrease false positives when detecting\n.lzma files.\n\nThese limitations shouldn't be a problem in practice, since practically all .lzma files  have\nbeen compressed with settings that liblzma will accept.\n"
                },
                {
                    "name": "Trailing garbage",
                    "content": "When  decompressing,  LZMA Utils silently ignore everything after the first .lzma stream.  In\nmost situations, this is a bug.  This also means that LZMA Utils don't support  decompressing\nconcatenated .lzma files.\n\nIf  there  is data left after the first .lzma stream, xz considers the file to be corrupt un‐\nless --single-stream was used.  This may break obscure scripts which have assumed that trail‐\ning garbage is ignored.\n"
                }
            ]
        },
        "NOTES": {
            "content": "",
            "subsections": [
                {
                    "name": "Compressed output may vary",
                    "content": "The exact compressed output produced from the same uncompressed input file may  vary  between\nXZ Utils versions even if compression options are identical.  This is because the encoder can\nbe improved (faster or better compression) without affecting the file format.  The output can\nvary  even  between different builds of the same XZ Utils version, if different build options\nare used.\n\nThe above means that once --rsyncable has been implemented, the resulting files won't  neces‐\nsarily  be rsyncable unless both old and new files have been compressed with the same xz ver‐\nsion.  This problem can be fixed if a part of the encoder implementation is  frozen  to  keep\nrsyncable output stable across xz versions.\n"
                },
                {
                    "name": "Embedded .xz decompressors",
                    "content": "Embedded  .xz  decompressor  implementations like XZ Embedded don't necessarily support files\ncreated with integrity check  types  other  than  none  and  crc32.   Since  the  default  is\n--check=crc64,  you  must  use --check=none or --check=crc32 when creating files for embedded\nsystems.\n\nOutside embedded systems, all .xz format decompressors support all the  check  types,  or  at\nleast are able to decompress the file without verifying the integrity check if the particular\ncheck is not supported.\n\nXZ Embedded supports BCJ filters, but only with the default start offset.\n"
                }
            ]
        },
        "EXAMPLES": {
            "content": "",
            "subsections": [
                {
                    "name": "Basics",
                    "content": "Compress the file foo into foo.xz using the default compression level (-6), and remove foo if\ncompression is successful:\n\nxz foo\n\nDecompress bar.xz into bar and don't remove bar.xz even if decompression is successful:\n\nxz -dk bar.xz\n\nCreate  baz.tar.xz  with  the preset -4e (-4 --extreme), which is slower than the default -6,\nbut needs less memory for compression and decompression (48 MiB and 5 MiB, respectively):\n\ntar cf - baz | xz -4e > baz.tar.xz\n\nA mix of compressed and uncompressed files can be decompressed to standard output with a sin‐\ngle command:\n\nxz -dcf a.txt b.txt.xz c.txt d.txt.lzma > abcd.txt\n"
                },
                {
                    "name": "Parallel compression of many files",
                    "content": "On GNU and *BSD, find(1) and xargs(1) can be used to parallelize compression of many files:\n\nfind . -type f \\! -name '*.xz' -print0 \\\n| xargs -0r -P4 -n16 xz -T1\n\nThe -P option to xargs(1) sets the number of parallel xz processes.  The best value  for  the"
                },
                {
                    "name": "-n",
                    "content": "of files, the value should probably be 1; with tens of thousands of files, 100 or  even  more\nmay be appropriate to reduce the number of xz processes that xargs(1) will eventually create.\n\nThe  option -T1 for xz is there to force it to single-threaded mode, because xargs(1) is used\nto control the amount of parallelization.\n",
                    "flag": "-n"
                },
                {
                    "name": "Robot mode",
                    "content": "Calculate how many bytes have been saved in total after compressing multiple files:\n\nxz --robot --list *.xz | awk '/^totals/{print $5-$4}'\n\nA script may want to know that it is using new enough xz.  The following sh(1) script  checks\nthat the version number of the xz tool is at least 5.0.0.  This method is compatible with old\nbeta versions, which didn't support the --robot option:\n\nif ! eval \"$(xz --robot --version 2> /dev/null)\" ||\n[ \"$XZVERSION\" -lt 50000002 ]; then\necho \"Your xz is too old.\"\nfi\nunset XZVERSION LIBLZMAVERSION\n\nSet a memory usage limit for decompression using XZOPT, but if a limit has already been set,\ndon't increase it:\n\nNEWLIM=$((123 << 20))  # 123 MiB\nOLDLIM=$(xz --robot --info-memory | cut -f3)\nif [ $OLDLIM -eq 0 -o $OLDLIM -gt $NEWLIM ]; then\nXZOPT=\"$XZOPT --memlimit-decompress=$NEWLIM\"\nexport XZOPT\nfi\n"
                },
                {
                    "name": "Custom compressor filter chains",
                    "content": "The simplest use for custom filter chains is customizing a LZMA2 preset.  This can be useful,\nbecause the presets cover only a subset of the potentially useful combinations of compression\nsettings.\n\nThe  CompCPU  columns  of the tables from the descriptions of the options -0 ... -9 and --ex‐\ntreme are useful when customizing LZMA2 presets.  Here are the relevant parts collected  from\nthose two tables:\n\nPreset   CompCPU\n-0         0\n-1         1\n-2         2\n-3         3\n-4         4\n-5         5\n-6         6\n-5e        7\n-6e        8\n\nIf  you  know  that a file requires somewhat big dictionary (for example, 32 MiB) to compress\nwell, but you want to compress it quicker than xz -8 would do, a preset with  a  low  CompCPU\nvalue (for example, 1) can be modified to use a bigger dictionary:\n\nxz --lzma2=preset=1,dict=32MiB foo.tar\n\nWith  certain  files,  the  above command may be faster than xz -6 while compressing signifi‐\ncantly better.  However, it must be emphasized that only some files benefit from a  big  dic‐\ntionary while keeping the CompCPU value low.  The most obvious situation, where a big dictio‐\nnary  can help a lot, is an archive containing very similar files of at least a few megabytes\neach.  The dictionary size has to be significantly bigger than any individual file  to  allow\nLZMA2 to take full advantage of the similarities between consecutive files.\n\nIf  very high compressor and decompressor memory usage is fine, and the file being compressed\nis at least several hundred megabytes, it may be useful to use an even bigger dictionary than\nthe 64 MiB that xz -9 would use:\n\nxz -vv --lzma2=dict=192MiB bigfoo.tar\n\nUsing -vv (--verbose --verbose) like in the above example can be useful to see the memory re‐\nquirements of the compressor and decompressor.  Remember that using a dictionary bigger  than\nthe  size  of the uncompressed file is waste of memory, so the above command isn't useful for\nsmall files.\n\nSometimes the compression time doesn't matter, but the decompressor memory usage  has  to  be\nkept low, for example, to make it possible to decompress the file on an embedded system.  The\nfollowing  command  uses -6e (-6 --extreme) as a base and sets the dictionary to only 64 KiB.\nThe resulting file can be decompressed with XZ Embedded (that's why there  is  --check=crc32)\nusing about 100 KiB of memory.\n\nxz --check=crc32 --lzma2=preset=6e,dict=64KiB foo\n\nIf you want to squeeze out as many bytes as possible, adjusting the number of literal context\nbits  (lc) and number of position bits (pb) can sometimes help.  Adjusting the number of lit‐\neral position bits (lp) might help too, but usually lc and pb are more important.  For  exam‐\nple,  a  source  code  archive contains mostly US-ASCII text, so something like the following\nmight give slightly (like 0.1 %) smaller file than xz -6e (try also without lc=4):\n\nxz --lzma2=preset=6e,pb=0,lc=4 sourcecode.tar\n\nUsing another filter together with LZMA2 can improve compression  with  certain  file  types.\nFor example, to compress a x86-32 or x86-64 shared library using the x86 BCJ filter:\n\nxz --x86 --lzma2 libfoo.so\n\nNote  that  the  order  of  the  filter  options is significant.  If --x86 is specified after\n--lzma2, xz will give an error, because there cannot be any filter after LZMA2, and also  be‐\ncause the x86 BCJ filter cannot be used as the last filter in the chain.\n\nThe  Delta  filter  together  with LZMA2 can give good results with bitmap images.  It should\nusually beat PNG, which has a few more advanced filters than simple delta  but  uses  Deflate\nfor the actual compression.\n\nThe  image  has  to  be saved in uncompressed format, for example, as uncompressed TIFF.  The\ndistance parameter of the Delta filter is set to match the number of bytes per pixel  in  the\nimage.   For  example,  24-bit  RGB  bitmap needs dist=3, and it is also good to pass pb=0 to\nLZMA2 to accommodate the three-byte alignment:\n\nxz --delta=dist=3 --lzma2=pb=0 foo.tiff\n\nIf multiple images have been put into a single archive (for example, .tar), the Delta  filter\nwill work on that too as long as all images have the same number of bytes per pixel.\n"
                }
            ]
        },
        "SEE ALSO": {
            "content": "xzdec(1), xzdiff(1), xzgrep(1), xzless(1), xzmore(1), gzip(1), bzip2(1), 7z(1)\n\nXZ Utils: <https://tukaani.org/xz/>\nXZ Embedded: <https://tukaani.org/xz/embedded.html>\nLZMA SDK: <https://7-zip.org/sdk.html>\n\nTukaani                                      2023-07-17                                        XZ(1)",
            "subsections": []
        }
    },
    "summary": "xz, unxz, xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and .lzma files",
    "flags": [
        {
            "flag": "-z",
            "long": "--compress",
            "arg": null,
            "description": "Compress. This is the default operation mode when no operation mode option is speci‐ fied and no other operation mode is implied from the command name (for example, unxz implies --decompress)."
        },
        {
            "flag": "-d",
            "long": "--uncompress",
            "arg": null,
            "description": "Decompress."
        },
        {
            "flag": "-t",
            "long": "--test",
            "arg": null,
            "description": "Test the integrity of compressed files. This option is equivalent to --decompress --stdout except that the decompressed data is discarded instead of being written to standard output. No files are created or removed."
        },
        {
            "flag": "-l",
            "long": "--list",
            "arg": null,
            "description": "Print information about compressed files. No uncompressed output 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 in‐ formation requires many seeks. The width of verbose output exceeds 80 characters, so piping the output to, for example, less -S may be convenient if the terminal isn't wide enough. The exact output may vary between xz versions and different locales. For machine- readable output, --robot --list should be used."
        },
        {
            "flag": "-k",
            "long": "--keep",
            "arg": null,
            "description": "Don't delete the input files. Since xz 5.2.6, 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."
        },
        {
            "flag": "-f",
            "long": "--force",
            "arg": null,
            "description": "This option has several effects: • If the target file already exists, delete it before compressing or decompressing. • 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. • 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. --for‐ mat=format can be used to restrict xz to decompress only a single file format."
        },
        {
            "flag": "-c",
            "long": "--to-stdout",
            "arg": null,
            "description": "Write the compressed or decompressed data to standard output instead of a file. This implies --keep."
        },
        {
            "flag": "",
            "long": "--single-stream",
            "arg": null,
            "description": "Decompress only the first .xz stream, and silently ignore possible 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 --decompress or --test."
        },
        {
            "flag": "",
            "long": "--no-sparse",
            "arg": null,
            "description": "Disable creation of sparse files. By default, if decompressing into a regular file, xz tries to make the file sparse if the decompressed data contains long sequences of binary zeros. It also works when writing to standard output as long as standard out‐ put 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."
        },
        {
            "flag": "-S",
            "long": "--suffix",
            "arg": "_",
            "description": "When compressing, use .suf as the suffix for the target file instead of .xz or .lzma. If not writing to standard output and the source file already has the suffix .suf, a warning is displayed and the file is skipped. When decompressing, recognize files with the suffix .suf in addition 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. 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 terminated 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 before the filenames read from file. --files0[=file] This is identical to --files[=file] except that each filename must be terminated with the null character."
        },
        {
            "flag": "-F",
            "long": "--format",
            "arg": "_",
            "description": "Specify the file format to compress or decompress: auto This is the default. When compressing, auto is equivalent to xz. When decom‐ pressing, 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 de‐ compressing. The alternative name alone is provided for backwards compatibil‐ ity with LZMA Utils. lzip Accept only .lz files when decompressing. Compression is not supported. 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 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 was added in lzip 1.6. This extension is rarely used and isn't supported by xz (diagnosed as corrupt input). 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 filter chain, which normally would have been stored in the con‐ tainer headers."
        },
        {
            "flag": "-C",
            "long": "--check",
            "arg": "_",
            "description": "Specify the type of the integrity check. The check is calculated from the uncom‐ pressed data and stored in the .xz file. This option has an effect only when com‐ pressing into the .xz format; the .lzma format doesn't support integrity checks. The integrity check (if any) is verified when the .xz file is decompressed. Supported check types: none Don't calculate an integrity check at all. This is usually 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 dif‐ ference is negligible. 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."
        },
        {
            "flag": "",
            "long": "--ignore-check",
            "arg": null,
            "description": "Don't verify the integrity check of the compressed data when decompressing. The CRC32 values in the .xz headers will still be verified normally. Do not use this option unless you know what you are doing. Possible reasons to use this option: • Trying to recover data from a corrupt .xz file. • Speeding up decompression. This matters mostly with SHA-256 or with files that have compressed extremely well. It's recommended to not use this option for this purpose unless the file integrity is verified externally in some other way."
        },
        {
            "flag": "-9",
            "long": null,
            "arg": null,
            "description": "Select a compression preset level. The default is -6. If multiple preset levels are specified, the last one takes effect. If a custom filter chain was already specified, setting a compression 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 using 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 comparable or better compression ratio, although the results de‐ pend a lot on the type of data being compressed. -4 ... -6 Good to very good compression while keeping decompressor memory usage reason‐ able 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 decompressor memory require‐ ments. 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 decompression will usually be. This also means that the amount of uncom‐ pressed 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: • 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 us‐ ing 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 matter. • CompCPU is a simplified representation of the LZMA2 settings that affect compres‐ sion 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. • CompMem contains the compressor memory requirements in the single-threaded mode. It may vary slightly between xz versions. Memory requirements of some of the fu‐ ture multithreaded modes may be dramatically higher than that of the single- threaded mode. • DecMem contains the decompressor memory requirements. That is, the compression settings determine the memory requirements of the decompressor. The exact decom‐ pressor memory usage is slightly more than the LZMA2 dictionary size, but the val‐ ues in the table have been rounded up to the next full MiB."
        },
        {
            "flag": "-e",
            "long": "--extreme",
            "arg": null,
            "description": "Use a slower variant of the selected compression preset level (-0 ... -9) to hopefully get a little bit better compression ratio, but with bad luck this can also make it worse. Decompressor memory usage is not affected, but compressor memory usage in‐ creases 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."
        },
        {
            "flag": "",
            "long": "--fast",
            "arg": null,
            "description": "--best These are somewhat misleading aliases for -0 and -9, respectively. 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 limited random-access decompression possible. This option is typ‐ ically 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 allocated in each thread for buffering input and output. The default 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 information 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 un‐ compressed data. The uncompressed sizes of the blocks are specified as a comma-separated list. Omit‐ ting a size (two or more consecutive commas) 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 in‐ dicate that the rest of the file should be encoded as a single block. If one specifies sizes that exceed the encoder's block size (either the default value in threaded mode or the value specified with --block-size=size), the encoder will cre‐ ate additional blocks while keeping the boundaries specified in sizes. For example, 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 specified more than once, the last one takes effect. The special timeout value of 0 can be used to explicitly dis‐ able this feature. 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 attempt to adjust the settings downwards so that the limit is no longer exceeded 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 LZMA2 dictionary size. When compressing with --format=raw or if --no-adjust has been specified, only the num‐ ber 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 dis‐ played and xz will exit with exit status 1. The limit can be specified in multiple ways: • The limit can be an absolute value in bytes. Using an integer suffix like MiB can be useful. Example: --memlimit-compress=80MiB • The limit can be specified as a percentage of total physical memory (RAM). This can be useful especially when setting the XZDEFAULTS environment variable in a shell initialization script that is shared between different computers. That way the limit is automatically bigger on systems with more memory. Example: --mem‐ limit-compress=70% • The limit can be reset back to its default value by setting it to 0. This is cur‐ rently equivalent to setting the limit to max (no memory usage limit). For 32-bit xz there is a special case: if the limit would be 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 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 exceeding 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 Set a memory usage limit for multi-threaded decompression. This can only affect the number of threads; this will never make xz refuse to decompress a file. If limit is too low to allow any 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-decompress. In contrast to the other memory usage limit options, --memlimit-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 decom‐ pressor could end up allocating an insane 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 amount of memory even with a low number of threads. Run‐ ning out of memory or swapping will not improve decompression performance. See --memlimit-compress=limit for possible ways to specify the limit. Setting limit to 0 resets the limit to the default system-specific value."
        },
        {
            "flag": "-M",
            "long": "--memory",
            "arg": "_",
            "description": "This is equivalent to specifying --memlimit-compress=limit --memlimit-decompress=limit --memlimit-mt-decompress=limit."
        },
        {
            "flag": "",
            "long": "--no-adjust",
            "arg": null,
            "description": "Display an error and exit if the memory usage limit cannot be met without adjusting settings that affect the compressed output. That is, this prevents xz from switching the encoder from multi-threaded mode to single-threaded mode and from reducing the LZMA2 dictionary size. Even when this option is used the number of threads may be re‐ duced to meet the memory usage limit as that won't affect the compressed output. Automatic adjusting is always disabled when creating raw streams (--format=raw)."
        },
        {
            "flag": "-T",
            "long": "--threads",
            "arg": "_",
            "description": "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 processor(s) on the system support. The ac‐ tual 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 different output. Single- threaded compressor will give the smallest file size but only the output from the multi-threaded compressor 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 compressor even if the system supports only one hard‐ ware thread. (xz 5.2.x used single-threaded mode in this situation.) To use multi-threaded mode with only one thread, set threads to +1. The + prefix has no effect with values other than 1. A memory usage limit can still make xz switch to single-threaded mode unless --no-adjust is used. Support for the + prefix was added in xz 5.4.0. If an automatic number of threads has been requested and no memory usage limit has been specified, then a system-specific default 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-threaded mode. The active limits can be seen with xz --info-memory. Currently the only threading method is to split the input into blocks and compress them independently from each other. The default 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 blocks with size in‐ formation in block headers. All large enough files compressed in multi-threaded mode meet this condition, but files compressed in single-threaded mode don't even if --block-size=size has been used."
        },
        {
            "flag": "-q",
            "long": "--quiet",
            "arg": null,
            "description": "Suppress warnings and notices. Specify this twice to suppress errors too. This op‐ tion has no effect on the exit status. That is, even if a warning was suppressed, the exit status to indicate a warning is still used."
        },
        {
            "flag": "-v",
            "long": "--verbose",
            "arg": null,
            "description": "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: • Completion percentage is shown if the size of the input file is known. That is, the percentage cannot be shown in pipes. • Amount of compressed data produced (compressing) or consumed (decompressing). • Amount of uncompressed data consumed (compressing) or produced (decompressing). • Compression ratio, which is calculated by dividing the amount of compressed data processed so far by the amount of uncompressed data processed so far. • Compression or decompression speed. This is measured as the amount of uncompressed data consumed (compression) or produced (decompression) per second. It is shown after a few seconds have passed since xz started processing the file. • Elapsed time in the format M:SS or H:MM:SS. • 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, com‐ pressed size, uncompressed size, compression 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 completion percentage is printed if the size of the input file is known."
        },
        {
            "flag": "-Q",
            "long": "--no-warn",
            "arg": null,
            "description": "Don't set the exit status to 2 even if a condition worth a warning 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."
        },
        {
            "flag": "",
            "long": "--robot",
            "arg": null,
            "description": "Print messages in a machine-parsable format. This is intended to ease writing fron‐ tends that want to use xz instead of liblzma, 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."
        },
        {
            "flag": "",
            "long": "--info-memory",
            "arg": null,
            "description": "Display, in human-readable format, how much physical memory (RAM) and how many proces‐ sor threads xz thinks the system has and the memory usage limits for compression and decompression, and exit successfully."
        },
        {
            "flag": "-h",
            "long": "--help",
            "arg": null,
            "description": "Display a help message describing the most commonly used options, and exit success‐ fully."
        },
        {
            "flag": "-H",
            "long": "--long-help",
            "arg": null,
            "description": "Display a help message describing all features of xz, and exit successfully"
        },
        {
            "flag": "-V",
            "long": "--version",
            "arg": null,
            "description": "Display the version number of xz and liblzma in human readable format. To get ma‐ chine-parsable output, specify --robot before --version."
        }
    ],
    "examples": [
        "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 decompression 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 decompression (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 standard output with a sin‐",
        "gle command:",
        "xz -dcf a.txt b.txt.xz c.txt d.txt.lzma > abcd.txt",
        "On GNU and *BSD, find(1) and xargs(1) can be used to parallelize compression 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",
        "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, because xargs(1) is used",
        "to control the amount of parallelization.",
        "Calculate how many bytes have been saved in total after compressing multiple files:",
        "xz --robot --list *.xz | awk '/^totals/{print $5-$4}'",
        "A script may want to know that it is using new enough xz.  The following sh(1) script  checks",
        "that the version number of the xz tool is at least 5.0.0.  This method is compatible with old",
        "beta versions, which didn't support the --robot option:",
        "if ! eval \"$(xz --robot --version 2> /dev/null)\" ||",
        "[ \"$XZVERSION\" -lt 50000002 ]; then",
        "echo \"Your xz is too old.\"",
        "fi",
        "unset XZVERSION LIBLZMAVERSION",
        "Set a memory usage limit for decompression using XZOPT, but if a limit has already been set,",
        "don't increase it:",
        "NEWLIM=$((123 << 20))  # 123 MiB",
        "OLDLIM=$(xz --robot --info-memory | cut -f3)",
        "if [ $OLDLIM -eq 0 -o $OLDLIM -gt $NEWLIM ]; then",
        "XZOPT=\"$XZOPT --memlimit-decompress=$NEWLIM\"",
        "export XZOPT",
        "fi",
        "The simplest use for custom filter chains is customizing a LZMA2 preset.  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 --ex‐",
        "treme 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 signifi‐",
        "cantly better.  However, it must be emphasized that only some files benefit from a  big  dic‐",
        "tionary while keeping the CompCPU value low.  The most obvious situation, where a big dictio‐",
        "nary  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 bigfoo.tar",
        "Using -vv (--verbose --verbose) like in the above example can be useful to see the memory re‐",
        "quirements of the compressor and decompressor.  Remember 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 lit‐",
        "eral position bits (lp) might help too, but usually lc and pb are more important.  For  exam‐",
        "ple,  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 sourcecode.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  be‐",
        "cause 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 filters than simple delta  but  uses  Deflate",
        "for the actual compression.",
        "The  image  has  to  be saved in uncompressed format, for example, as uncompressed 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": [
        {
            "name": "xzdec",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/xzdec/1/json"
        },
        {
            "name": "xzdiff",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/xzdiff/1/json"
        },
        {
            "name": "xzgrep",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/xzgrep/1/json"
        },
        {
            "name": "xzless",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/xzless/1/json"
        },
        {
            "name": "xzmore",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/xzmore/1/json"
        },
        {
            "name": "gzip",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/gzip/1/json"
        },
        {
            "name": "bzip2",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/bzip2/1/json"
        },
        {
            "name": "7z",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/7z/1/json"
        }
    ],
    "tldr": {
        "source": "official",
        "description": "This command is an alias of `xz --format lzma`.",
        "examples": [
            {
                "description": "View documentation for the original command",
                "command": "tldr xz"
            }
        ]
    }
}