XZ(1)                              XZ Utils                              XZ(1)

          Memory usage
          Concatenation and padding with .xz files
          Integer suffixes and special values
          Operation mode
          Operation modifiers
          Basic file format and compression options
          Custom compressor filter chains
          Other options
          Memory limit information
          List mode
          Compression preset levels
          Streamed vs. non-streamed .lzma files
          Unsupported .lzma files
          Trailing garbage
          Compressed output may vary
          Embedded .xz decompressors
          Parallel compression of many files
          Robot mode
          Custom compressor filter chains
       SEE ALSO

       xz,  unxz,  xzcat, lzma, unlzma, lzcat - Compress or decompress .xz and
       .lzma files

       xz [option...]  [file...]

       unxz is equivalent to xz --decompress.
       xzcat is equivalent to xz --decompress --stdout.
       lzma is equivalent to xz --format=lzma.
       unlzma is equivalent to xz --format=lzma --decompress.
       lzcat is equivalent to xz --format=lzma --decompress --stdout.

       When writing scripts that need to decompress files, it  is  recommended
       to  always use the name xz with appropriate arguments (xz -d or xz -dc)
       instead of the names unxz and xzcat.

       xz is a general-purpose data compression tool with command line  syntax
       similar  to  gzip(1)  and  bzip2(1).  The native file format is the .xz
       format, but the legacy .lzma format used by LZMA  Utils  and  raw  com-
       pressed  streams  with  no container format headers are also supported.
       In addition, decompression of the .lz format used by lzip is supported.

       xz compresses or decompresses each file according to the selected oper-
       ation mode.  If no files are given or file is -, xz reads from standard
       input and writes the processed data to standard output.  xz will refuse
       (display  an error and skip the file) to write compressed data to stan-
       dard output if it is a terminal.  Similarly, xz  will  refuse  to  read
       compressed data from standard input if it is a terminal.

       Unless  --stdout  is specified, files other than - are written to a new
       file whose name is derived from the source file name:

       o  When compressing, the suffix of  the  target  file  format  (.xz  or
          .lzma)  is  appended  to the source filename to get the target file-

       o  When decompressing, the .xz, .lzma, or .lz suffix  is  removed  from
          the  filename  to  get  the target filename.  xz also recognizes the
          suffixes .txz and .tlz, and replaces them with the .tar suffix.

       If the target file already exists, an error is displayed and  the  file
       is skipped.

       Unless  writing  to standard output, xz will display a warning and skip
       the file if any of the following applies:

       o  File is not a regular file.  Symbolic links are  not  followed,  and
          thus they are not considered to be regular files.

       o  File has more than one hard link.

       o  File has setuid, setgid, or sticky bit set.

       o  The  operation  mode  is  set to compress and the file already has a
          suffix of the target file format (.xz or .txz  when  compressing  to
          the .xz format, and .lzma or .tlz when compressing to the .lzma for-

       o  The operation mode is set to decompress and the file doesn't have  a
          suffix of any of the supported file formats (.xz, .txz, .lzma, .tlz,
          or .lz).

       After successfully compressing or decompressing the file, xz copies the
       owner,  group, permissions, access time, and modification time from the
       source file to the target file.  If copying the group fails,  the  per-
       missions are modified so that the target file doesn't become accessible
       to users who didn't have permission to  access  the  source  file.   xz
       doesn't support copying other metadata like access control lists or ex-
       tended attributes yet.

       Once the target file has been successfully closed, the source  file  is
       removed  unless --keep was specified.  The source file is never removed
       if the output is written to standard output or if an error occurs.

       Sending SIGINFO or SIGUSR1 to the xz process makes  it  print  progress
       information  to  standard  error.  This has only limited use since when
       standard error is a terminal, using --verbose will display an automati-
       cally updating progress indicator.

   Memory usage
       The  memory  usage of xz varies from a few hundred kilobytes to several
       gigabytes depending on the compression  settings.   The  settings  used
       when compressing a file determine the memory requirements of the decom-
       pressor.  Typically the decompressor needs 5 % to 20 % of the amount of
       memory that the compressor needed when creating the file.  For example,
       decompressing a file created with xz -9 currently  requires  65 MiB  of
       memory.   Still,  it is possible to have .xz files that require several
       gigabytes of memory to decompress.

       Especially users of older systems may  find  the  possibility  of  very
       large  memory  usage  annoying.  To prevent uncomfortable surprises, xz
       has a built-in memory usage limiter,  which  is  disabled  by  default.
       While  some operating systems provide ways to limit the memory usage of
       processes, relying on it wasn't deemed to be flexible enough (for exam-
       ple, using ulimit(1) to limit virtual memory tends to cripple mmap(2)).

       The  memory  usage  limiter can be enabled with the command line option
       --memlimit=limit.  Often it is more convenient to enable the limiter by
       default  by  setting the environment variable XZ_DEFAULTS, for example,
       XZ_DEFAULTS=--memlimit=150MiB.  It is possible to set the limits  sepa-
       rately  for  compression  and  decompression  by  using --memlimit-com-
       press=limit and --memlimit-decompress=limit.  Using these  two  options
       outside  XZ_DEFAULTS is rarely useful because a single run of xz cannot
       do both compression  and  decompression  and  --memlimit=limit  (or  -M
       limit) is shorter to type on the command line.

       If  the specified memory usage limit is exceeded when decompressing, xz
       will display an error and decompressing the file  will  fail.   If  the
       limit  is  exceeded when compressing, xz will try to scale the settings
       down so that the limit is no longer exceeded (except when using  --for-
       mat=raw  or --no-adjust).  This way the operation won't fail unless the
       limit is very small.  The scaling of the settings is done in steps that
       don't match the compression level presets, for example, if the limit is
       only slightly less than the amount required for  xz  -9,  the  settings
       will be scaled down only a little, not all the way down to xz -8.

   Concatenation and padding with .xz files
       It is possible to concatenate .xz files as is.  xz will decompress such
       files as if they were a single .xz file.

       It is possible to insert padding between the concatenated parts or  af-
       ter the last part.  The padding must consist of null bytes and the size
       of the padding must be a multiple of four bytes.  This can  be  useful,
       for  example,  if the .xz file is stored on a medium that measures file
       sizes in 512-byte blocks.

       Concatenation and padding are not  allowed  with  .lzma  files  or  raw

   Integer suffixes and special values
       In  most places where an integer argument is expected, an optional suf-
       fix is supported to easily indicate large integers.  There must  be  no
       space between the integer and the suffix.

       KiB    Multiply  the integer by 1,024 (2^10).  Ki, k, kB, K, and KB are
              accepted as synonyms for KiB.

       MiB    Multiply the integer by 1,048,576 (2^20).  Mi, m, M, and MB  are
              accepted as synonyms for MiB.

       GiB    Multiply  the integer by 1,073,741,824 (2^30).  Gi, g, G, and GB
              are accepted as synonyms for GiB.

       The special value max can be used to indicate the maximum integer value
       supported by the option.

   Operation mode
       If  multiple  operation  mode options are given, the last one takes ef-

       -z, --compress
              Compress.  This is the default operation mode when no  operation
              mode  option is specified and no other operation mode is implied
              from the command name (for example, unxz implies --decompress).

       -d, --decompress, --uncompress

       -t, --test
              Test the integrity of compressed files.  This option is  equiva-
              lent  to --decompress --stdout except that the decompressed data
              is discarded instead of being written to  standard  output.   No
              files are created or removed.

       -l, --list
              Print  information about compressed files.  No uncompressed out-
              put is produced, and no files are created or removed.   In  list
              mode,  the program cannot read the compressed data from standard
              input or from other unseekable sources.

              The default listing shows basic  information  about  files,  one
              file  per  line.  To get more detailed information, use also the
              --verbose option.  For  even  more  information,  use  --verbose
              twice,  but  note that this may be slow, because getting all the
              extra information requires many seeks.   The  width  of  verbose
              output exceeds 80 characters, so piping the output to, for exam-
              ple, less -S may  be  convenient  if  the  terminal  isn't  wide

              The  exact output may vary between xz versions and different lo-
              cales.  For machine-readable output, --robot  --list  should  be

   Operation modifiers
       -k, --keep
              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

       -f, --force
              This option has several effects:

              o  If the target file already exists, delete it before compress-
                 ing or decompressing.

              o  Compress  or  decompress even if the input is a symbolic link
                 to a regular file, has more than one hard link,  or  has  the
                 setuid,  setgid,  or sticky bit set.  The setuid, setgid, and
                 sticky bits are not copied to the target file.

              o  When used with --decompress --stdout and xz cannot  recognize
                 the  type  of  the source file, copy the source file as is to
                 standard output.  This allows xzcat --force to be  used  like
                 cat(1) for files that have not been compressed with xz.  Note
                 that in future, xz might support new compressed file formats,
                 which  may  make xz decompress more types of files instead of
                 copying them as is to standard output.   --format=format  can
                 be  used to restrict xz to decompress only a single file for-

       -c, --stdout, --to-stdout
              Write the compressed or decompressed data to standard output in-
              stead of a file.  This implies --keep.

              Decompress only the first .xz stream, and silently ignore possi-
              ble remaining input data following the  stream.   Normally  such
              trailing garbage makes xz display an error.

              xz  never  decompresses more than one stream from .lzma files or
              raw streams, but this option still makes xz ignore the  possible
              trailing data after the .lzma file or raw stream.

              This  option has no effect if the operation mode is not --decom-
              press or --test.

              Disable creation of sparse files.  By default, if  decompressing
              into a regular file, xz tries to make the file sparse if the de-
              compressed data contains long sequences  of  binary  zeros.   It
              also  works  when writing to standard output as long as standard
              output is connected to a regular  file  and  certain  additional
              conditions  are  met to make it safe.  Creating sparse files may
              save disk space and speed up the decompression by  reducing  the
              amount of disk I/O.

       -S .suf, --suffix=.suf
              When compressing, use .suf as the suffix for the target file in-
              stead of .xz or .lzma.  If not writing to  standard  output  and
              the  source  file already has the suffix .suf, a warning is dis-
              played and the file is skipped.

              When decompressing, recognize files with the suffix .suf in  ad-
              dition  to files with the .xz, .txz, .lzma, .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.

              Read  the  filenames  to  process from file; if file is omitted,
              filenames are read from standard input.  Filenames must be  ter-
              minated  with  the  newline character.  A dash (-) is taken as a
              regular filename; it doesn't mean standard input.  If  filenames
              are given also as command line arguments, they are processed be-
              fore the filenames read from file.

              This is identical to --files[=file] except  that  each  filename
              must be terminated with the null character.

   Basic file format and compression options
       -F format, --format=format
              Specify the file format to compress or decompress:

              auto   This  is  the default.  When compressing, auto is equiva-
                     lent to xz.  When decompressing, the format of the  input
                     file  is  automatically  detected.  Note that raw streams
                     (created with --format=raw) cannot be auto-detected.

              xz     Compress to the .xz file format, or accept only .xz files
                     when decompressing.

              lzma, alone
                     Compress  to the legacy .lzma file format, or accept only
                     .lzma files when  decompressing.   The  alternative  name
                     alone  is  provided for backwards compatibility with LZMA

              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 fil-
                     ter  chain,  which normally would have been stored in the
                     container headers.

       -C check, --check=check
              Specify the type of the integrity check.  The  check  is  calcu-
              lated  from  the  uncompressed  data and stored in the .xz file.
              This option has an effect only when  compressing  into  the  .xz
              format;  the .lzma format doesn't support integrity checks.  The
              integrity check (if any) is verified when the .xz file is decom-

              Supported check types:

              none   Don't  calculate an integrity check at all.  This is usu-
                     ally a bad idea.  This can be useful  when  integrity  of
                     the data is verified by other means anyway.

              crc32  Calculate  CRC32  using  the  polynomial  from IEEE-802.3

              crc64  Calculate CRC64 using the polynomial from ECMA-182.  This
                     is the default, since it is slightly better than CRC32 at
                     detecting damaged files and the speed difference is  neg-

              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.

              Don't verify the integrity check of the compressed data when de-
              compressing.  The CRC32 values in the .xz headers will still  be
              verified normally.

              Do not use this option unless you know what you are doing.  Pos-
              sible reasons to use this option:

              o  Trying to recover data from a corrupt .xz file.

              o  Speeding up decompression.  This matters mostly with  SHA-256
                 or with files that have compressed extremely well.  It's rec-
                 ommended to not use this option for this purpose  unless  the
                 file integrity is verified externally in some other way.

       -0 ... -9
              Select  a compression preset level.  The default is -6.  If mul-
              tiple preset levels are specified, the last  one  takes  effect.
              If  a  custom filter chain was already specified, setting a com-
              pression preset level clears the custom filter chain.

              The differences between the presets are  more  significant  than
              with  gzip(1)  and  bzip2(1).  The selected compression settings
              determine the memory requirements of the decompressor, thus  us-
              ing  a too high preset level might make it painful to decompress
              the file on an old system with little RAM.   Specifically,  it's
              not  a  good idea to blindly use -9 for everything like it often
              is with gzip(1) and bzip2(1).

              -0 ... -3
                     These are somewhat fast presets.  -0 is sometimes  faster
                     than  gzip  -9 while compressing much better.  The higher
                     ones often have speed comparable to bzip2(1) with  compa-
                     rable  or  better compression ratio, although the results
                     depend a lot on the type of data being compressed.

              -4 ... -6
                     Good to very good compression while keeping  decompressor
                     memory  usage reasonable even for old systems.  -6 is the
                     default, which is usually a good choice for  distributing
                     files that need to be decompressible even on systems with
                     only 16 MiB RAM.  (-5e or -6e may  be  worth  considering
                     too.  See --extreme.)

              -7 ... -9
                     These  are  like -6 but with higher compressor and decom-
                     pressor memory requirements.  These are useful only  when
                     compressing  files bigger than 8 MiB, 16 MiB, and 32 MiB,

              On the same hardware, the decompression speed is approximately a
              constant  number  of  bytes  of  compressed data per second.  In
              other words, the better the compression, the faster  the  decom-
              pression  will  usually  be.  This also means that the amount of
              uncompressed output produced per second can vary a lot.

              The following table summarises the features of the presets:

                     Preset   DictSize   CompCPU   CompMem   DecMem
                       -0     256 KiB       0        3 MiB    1 MiB
                       -1       1 MiB       1        9 MiB    2 MiB
                       -2       2 MiB       2       17 MiB    3 MiB
                       -3       4 MiB       3       32 MiB    5 MiB
                       -4       4 MiB       4       48 MiB    5 MiB
                       -5       8 MiB       5       94 MiB    9 MiB
                       -6       8 MiB       6       94 MiB    9 MiB
                       -7      16 MiB       6      186 MiB   17 MiB
                       -8      32 MiB       6      370 MiB   33 MiB
                       -9      64 MiB       6      674 MiB   65 MiB

              Column descriptions:

              o  DictSize is the LZMA2 dictionary size.  It is waste of memory
                 to  use a dictionary bigger than the size of the uncompressed
                 file.  This is why it is good to avoid using the  presets  -7
                 ...  -9 when there's no real need for them.  At -6 and lower,
                 the amount of memory wasted is usually low enough to not mat-

              o  CompCPU  is a simplified representation of the LZMA2 settings
                 that affect compression speed.  The dictionary  size  affects
                 speed too, so while CompCPU is the same for levels -6 ... -9,
                 higher levels still tend to be a little slower.  To get  even
                 slower and thus possibly better compression, see --extreme.

              o  CompMem  contains  the  compressor memory requirements in the
                 single-threaded mode.  It may vary slightly between  xz  ver-
                 sions.   Memory  requirements  of  some  of the future multi-
                 threaded modes may be dramatically higher than  that  of  the
                 single-threaded mode.

              o  DecMem  contains  the decompressor memory requirements.  That
                 is, the compression settings determine  the  memory  require-
                 ments of the decompressor.  The exact decompressor memory us-
                 age is slightly more than the LZMA2 dictionary size, but  the
                 values  in  the  table  have been rounded up to the next full

       -e, --extreme
              Use a slower variant of the selected  compression  preset  level
              (-0 ... -9) to hopefully get a little bit better compression ra-
              tio, but with bad luck this can also make it worse.   Decompres-
              sor  memory  usage  is not affected, but compressor memory usage
              increases a little at preset levels -0 ... -3.

              Since there are two presets  with  dictionary  sizes  4 MiB  and
              8 MiB,  the  presets  -3e  and  -5e use slightly faster settings
              (lower CompCPU) than -4e and -6e, respectively.  That way no two
              presets are identical.

                     Preset   DictSize   CompCPU   CompMem   DecMem
                      -0e     256 KiB       8        4 MiB    1 MiB
                      -1e       1 MiB       8       13 MiB    2 MiB
                      -2e       2 MiB       8       25 MiB    3 MiB
                      -3e       4 MiB       7       48 MiB    5 MiB
                      -4e       4 MiB       8       48 MiB    5 MiB
                      -5e       8 MiB       7       94 MiB    9 MiB
                      -6e       8 MiB       8       94 MiB    9 MiB
                      -7e      16 MiB       8      186 MiB   17 MiB
                      -8e      32 MiB       8      370 MiB   33 MiB
                      -9e      64 MiB       8      674 MiB   65 MiB

              For  example,  there  are a total of four presets that use 8 MiB
              dictionary, whose order from the fastest to the slowest  is  -5,
              -6, -5e, and -6e.

       --best These  are  somewhat  misleading  aliases for -0 and -9, respec-
              tively.  These are provided  only  for  backwards  compatibility
              with LZMA Utils.  Avoid using these options.

              When  compressing  to  the .xz format, split the input data into
              blocks of size bytes.  The blocks are  compressed  independently
              from each other, which helps with multi-threading and makes lim-
              ited random-access decompression possible.  This option is typi-
              cally  used to override the default block size in multi-threaded
              mode, but this option can be used in single-threaded mode too.

              In multi-threaded mode about three times size bytes will be  al-
              located  in each thread for buffering input and output.  The de-
              fault size is three times the LZMA2 dictionary size  or  1  MiB,
              whichever is more.  Typically a good value is 2-4 times the size
              of the LZMA2 dictionary or at least 1 MiB.  Using size less than
              the LZMA2 dictionary size is waste of RAM because then the LZMA2
              dictionary buffer will never get fully used.  The sizes  of  the
              blocks  are  stored in the block headers, which a future version
              of xz will use for multi-threaded decompression.

              In single-threaded mode no block splitting is done  by  default.
              Setting this option doesn't affect memory usage.  No size infor-
              mation is stored in block headers, thus files created in single-
              threaded  mode  won't  be  identical  to files created in multi-
              threaded mode.  The lack of size information also means  that  a
              future  version  of  xz  won't  be  able decompress the files in
              multi-threaded mode.

              When compressing to the .xz format, start a new block after  the
              given intervals of uncompressed data.

              The  uncompressed  sizes of the blocks are specified as a comma-
              separated list.  Omitting a size (two or more  consecutive  com-
              mas) is a shorthand to use the size of the previous block.

              If  the  input  file  is  bigger than the sum of sizes, the last
              value in sizes is repeated until the end of the file.  A special
              value  of  0  may be used as the last value to indicate that the
              rest of the file should be encoded as a single block.

              If one specifies sizes that exceed the encoder's block size (ei-
              ther  the  default value in threaded mode or the value specified
              with --block-size=size),  the  encoder  will  create  additional
              blocks while keeping the boundaries specified in sizes.  For ex-
              ample,      if      one       specifies       --block-size=10MiB
              --block-list=5MiB,10MiB,8MiB,12MiB,24MiB  and  the input file is
              80 MiB, one will get 11 blocks: 5, 10, 8, 10, 2, 10, 10, 4,  10,
              10, and 1 MiB.

              In multi-threaded mode the sizes of the blocks are stored in the
              block headers.  This isn't done in single-threaded mode, so  the
              encoded  output won't be identical to that of the multi-threaded

              When compressing, if more than timeout milliseconds (a  positive
              integer)  has  passed  since the previous flush and reading more
              input would block, all the pending input data  is  flushed  from
              the  encoder  and made available in the output stream.  This can
              be useful if xz is used to compress data that is streamed over a
              network.   Small  timeout  values make the data available at the
              receiving end with a small delay, but large timeout values  give
              better compression ratio.

              This  feature  is disabled by default.  If this option is speci-
              fied more than once, the last one  takes  effect.   The  special
              timeout  value  of 0 can be used to explicitly disable this fea-

              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

              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 ex-
              ceeded  and display a notice that automatic adjustment was done.
              The adjustments are done in this order: reducing the  number  of
              threads, switching to single-threaded mode if even one thread in
              multi-threaded mode exceeds the limit, and finally reducing  the
              LZMA2 dictionary size.

              When  compressing  with  --format=raw or if --no-adjust has been
              specified, only the number of threads may be  reduced  since  it
              can be done without affecting the compressed output.

              If  the  limit cannot be met even with the adjustments described
              above, an error is displayed and xz will exit with  exit  status

              The limit can be specified in multiple ways:

              o  The  limit can be an absolute value in bytes.  Using an inte-
                 ger suffix like MiB can be useful.  Example:  --memlimit-com-

              o  The  limit can be specified as a percentage of total physical
                 memory (RAM).  This can be useful especially when setting the
                 XZ_DEFAULTS  environment  variable  in a shell initialization
                 script that is shared between different computers.  That  way
                 the  limit  is automatically bigger on systems with more mem-
                 ory.  Example: --memlimit-compress=70%

              o  The limit can be reset back to its default value  by  setting
                 it  to  0.  This is currently equivalent to setting the limit
                 to max (no memory usage limit).

              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

              See also the section Memory usage.

              Set a memory usage limit for decompression.  This  also  affects
              the  --list  mode.  If the operation is not possible without ex-
              ceeding the limit, xz will display an  error  and  decompressing
              the  file will fail.  See --memlimit-compress=limit for possible
              ways to specify the limit.

              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-decom-

              In contrast to the other  memory  usage  limit  options,  --mem-
              limit-mt-decompress=limit  has  a system-specific default limit.
              xz --info-memory can be used to see the current value.

              This option and its default  value  exist  because  without  any
              limit  the  threaded decompressor could end up allocating an in-
              sane amount of memory with some input  files.   If  the  default
              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.  Running out
              of  memory  or  swapping  will not improve decompression perfor-

              See --memlimit-compress=limit for possible ways to  specify  the
              limit.   Setting limit to 0 resets the limit to the default sys-
              tem-specific value.

       -M limit, --memlimit=limit, --memory=limit
              This  is  equivalent  to  specifying   --memlimit-compress=limit
              --memlimit-decompress=limit --memlimit-mt-decompress=limit.

              Display  an  error  and exit if the memory usage limit cannot be
              met without adjusting settings that affect the  compressed  out-
              put.   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 reduced to meet the memory usage  limit
              as that won't affect the compressed output.

              Automatic adjusting is always disabled when creating raw streams

       -T threads, --threads=threads
              Specify the number of worker threads to use.  Setting threads to
              a special value 0 makes xz use up to as many threads as the pro-
              cessor(s) on the system support.  The actual number  of  threads
              can  be  fewer  than threads if the input file is not big enough
              for threading with the given settings or if using  more  threads
              would exceed the memory usage limit.

              The  single-threaded and multi-threaded compressors produce dif-
              ferent output.  Single-threaded compressor will give the  small-
              est  file  size but only the output from the multi-threaded com-
              pressor can be decompressed  using  multiple  threads.   Setting
              threads to 1 will use the single-threaded mode.  Setting threads
              to any other value, including 0,  will  use  the  multi-threaded
              compressor even if the system supports only one hardware 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 mem-
              ory  usage  limit has been specified, then a system-specific de-
              fault soft limit will be used to possibly limit  the  number  of
              threads.   It is a soft limit in sense that it is ignored if the
              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

              Currently the only threading method is to split the  input  into
              blocks and compress them independently from each other.  The de-
              fault block size depends on the compression  level  and  can  be
              overridden with the --block-size=size option.

              Threaded decompression only works on files that contain multiple
              blocks with size information 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.

   Custom compressor filter chains
       A custom filter chain allows specifying the compression settings in de-
       tail instead of relying on the  settings  associated  to  the  presets.
       When  a custom filter chain is specified, preset options (-0 ... -9 and
       --extreme) earlier on the command line are forgotten.  If a preset  op-
       tion  is  specified  after one or more custom filter chain options, the
       new preset takes effect and the custom filter chain  options  specified
       earlier are forgotten.

       A  filter chain is comparable to piping on the command line.  When com-
       pressing, the uncompressed input goes to the first filter, whose output
       goes  to  the next filter (if any).  The output of the last filter gets
       written to the compressed file.  The maximum number of filters  in  the
       chain  is  four,  but typically a filter chain has only one or two fil-

       Many filters have limitations on where they can be in the filter chain:
       some  filters  can work only as the last filter in the chain, some only
       as a non-last filter, and some work in any position in the chain.   De-
       pending on the filter, this limitation is either inherent to the filter
       design or exists to prevent security issues.

       A custom filter chain is specified by using one or more filter  options
       in  the  order they are wanted in the filter chain.  That is, the order
       of filter options is significant!  When decoding  raw  streams  (--for-
       mat=raw),  the  filter  chain  is specified in the same order as it was
       specified when compressing.

       Filters take filter-specific options as a comma-separated list.   Extra
       commas  in  options  are ignored.  Every option has a default value, so
       you need to specify only those you want to change.

       To see the whole filter chain and options, use xz  -vv  (that  is,  use
       --verbose twice).  This works also for viewing the filter chain options
       used by presets.

              Add LZMA1 or LZMA2 filter to the filter  chain.   These  filters
              can be used only as the last filter in the chain.

              LZMA1  is  a legacy filter, which is supported almost solely due
              to the legacy .lzma file  format,  which  supports  only  LZMA1.
              LZMA2  is  an updated version of LZMA1 to fix some practical is-
              sues of LZMA1.  The .xz format uses LZMA2  and  doesn't  support
              LZMA1  at  all.  Compression speed and ratios of LZMA1 and LZMA2
              are practically the same.

              LZMA1 and LZMA2 share the same set of options:

                     Reset all LZMA1 or LZMA2 options to preset.  Preset  con-
                     sist  of an integer, which may be followed by single-let-
                     ter preset modifiers.  The integer can be from  0  to  9,
                     matching  the  command  line options -0 ... -9.  The only
                     supported modifier is currently e,  which  matches  --ex-
                     treme.   If no preset is specified, the default values of
                     LZMA1 or LZMA2 options are taken from the preset 6.

                     Dictionary (history buffer) size indicates how many bytes
                     of  the  recently  processed uncompressed data is kept in
                     memory.  The algorithm tries to find repeating  byte  se-
                     quences  (matches)  in the uncompressed data, and replace
                     them with references to the data currently in the dictio-
                     nary.   The  bigger  the  dictionary,  the  higher is the
                     chance to find a match.  Thus, increasing dictionary size
                     usually improves compression ratio, but a dictionary big-
                     ger than the uncompressed file is waste of memory.

                     Typical dictionary size is from 64 KiB  to  64 MiB.   The
                     minimum  is  4 KiB.   The maximum for compression is cur-
                     rently 1.5 GiB (1536 MiB).  The decompressor already sup-
                     ports  dictionaries up to one byte less than 4 GiB, which
                     is the maximum for the LZMA1 and LZMA2 stream formats.

                     Dictionary size and match finder (mf) together  determine
                     the memory usage of the LZMA1 or LZMA2 encoder.  The same
                     (or bigger) dictionary size is required for decompressing
                     that  was used when compressing, thus the memory usage of
                     the decoder is determined by  the  dictionary  size  used
                     when  compressing.   The .xz headers store the dictionary
                     size either as 2^n or 2^n + 2^(n-1), so these  sizes  are
                     somewhat preferred for compression.  Other sizes will get
                     rounded up when stored in the .xz headers.

              lc=lc  Specify the number of literal context bits.  The  minimum
                     is  0  and  the maximum is 4; the default is 3.  In addi-
                     tion, the sum of lc and lp must not exceed 4.

                     All bytes that cannot be encoded as matches  are  encoded
                     as  literals.   That  is, literals are simply 8-bit bytes
                     that are encoded one at a time.

                     The literal coding makes an assumption that  the  highest
                     lc  bits of the previous uncompressed byte correlate with
                     the next byte.  For example, in typical English text,  an
                     upper-case  letter is often followed by a lower-case let-
                     ter, and a lower-case letter is usually followed  by  an-
                     other  lower-case letter.  In the US-ASCII character set,
                     the highest three bits are 010 for upper-case letters and
                     011  for  lower-case letters.  When lc is at least 3, the
                     literal coding can take advantage of this property in the
                     uncompressed data.

                     The default value (3) is usually good.  If you want maxi-
                     mum compression, test lc=4.  Sometimes it helps a little,
                     and sometimes it makes compression worse.  If it makes it
                     worse, test lc=2 too.

              lp=lp  Specify the number of literal position bits.  The minimum
                     is 0 and the maximum is 4; the default is 0.

                     Lp  affects  what  kind  of alignment in the uncompressed
                     data is assumed when encoding literals.  See pb below for
                     more information about alignment.

              pb=pb  Specify  the  number  of position bits.  The minimum is 0
                     and the maximum is 4; the default is 2.

                     Pb affects what kind of  alignment  in  the  uncompressed
                     data  is assumed in general.  The default means four-byte
                     alignment (2^pb=2^2=4), which is often a good choice when
                     there's no better guess.

                     When  the  alignment is known, setting pb accordingly may
                     reduce the file size a little.  For  example,  with  text
                     files  having  one-byte  alignment (US-ASCII, ISO-8859-*,
                     UTF-8), setting pb=0 can  improve  compression  slightly.
                     For UTF-16 text, pb=1 is a good choice.  If the alignment
                     is an odd number like 3 bytes, pb=0  might  be  the  best

                     Even though the assumed alignment can be adjusted with pb
                     and lp, LZMA1 and  LZMA2  still  slightly  favor  16-byte
                     alignment.   It  might  be worth taking into account when
                     designing file formats that are likely to be  often  com-
                     pressed with LZMA1 or LZMA2.

              mf=mf  Match  finder has a major effect on encoder speed, memory
                     usage, and compression ratio.  Usually Hash  Chain  match
                     finders  are  faster than Binary Tree match finders.  The
                     default depends on the preset: 0 uses hc3, 1-3  use  hc4,
                     and the rest use bt4.

                     The  following  match  finders are supported.  The memory
                     usage formulas below are rough approximations, which  are
                     closest to the reality when dict is a power of two.

                     hc3    Hash Chain with 2- and 3-byte hashing
                            Minimum value for nice: 3
                            Memory usage:
                            dict * 7.5 (if dict <= 16 MiB);
                            dict * 5.5 + 64 MiB (if dict > 16 MiB)

                     hc4    Hash Chain with 2-, 3-, and 4-byte hashing
                            Minimum value for nice: 4
                            Memory usage:
                            dict * 7.5 (if dict <= 32 MiB);
                            dict * 6.5 (if dict > 32 MiB)

                     bt2    Binary Tree with 2-byte hashing
                            Minimum value for nice: 2
                            Memory usage: dict * 9.5

                     bt3    Binary Tree with 2- and 3-byte hashing
                            Minimum value for nice: 3
                            Memory usage:
                            dict * 11.5 (if dict <= 16 MiB);
                            dict * 9.5 + 64 MiB (if dict > 16 MiB)

                     bt4    Binary Tree with 2-, 3-, and 4-byte hashing
                            Minimum value for nice: 4
                            Memory usage:
                            dict * 11.5 (if dict <= 32 MiB);
                            dict * 10.5 (if dict > 32 MiB)

                     Compression mode specifies the method to analyze the data
                     produced by the match finder.  Supported modes  are  fast
                     and normal.  The default is fast for presets 0-3 and nor-
                     mal for presets 4-9.

                     Usually fast is used with Hash Chain  match  finders  and
                     normal with Binary Tree match finders.  This is also what
                     the presets do.

                     Specify what is considered to be  a  nice  length  for  a
                     match.  Once a match of at least nice bytes is found, the
                     algorithm stops looking for possibly better matches.

                     Nice can be 2-273 bytes.  Higher values tend to give bet-
                     ter  compression  ratio at the expense of speed.  The de-
                     fault depends on the preset.

                     Specify the maximum search depth  in  the  match  finder.
                     The  default  is  the special value of 0, which makes the
                     compressor determine a reasonable depth from mf and nice.

                     Reasonable depth for Hash Chains is 4-100 and 16-1000 for
                     Binary  Trees.  Using very high values for depth can make
                     the encoder extremely slow with some files.   Avoid  set-
                     ting  the  depth over 1000 unless you are prepared to in-
                     terrupt the compression in case  it  is  taking  far  too

              When  decoding  raw streams (--format=raw), LZMA2 needs only the
              dictionary size.  LZMA1 needs also lc, lp, and pb.

              Add a branch/call/jump (BCJ) filter to the filter chain.   These
              filters  can  be  used  only  as a non-last filter in the filter

              A BCJ filter converts relative addresses in the machine code  to
              their  absolute  counterparts.   This doesn't change the size of
              the data but it increases redundancy, which can  help  LZMA2  to
              produce 0-15 % smaller .xz file.  The BCJ filters are always re-
              versible, so using a BCJ filter for wrong type of  data  doesn't
              cause  any data loss, although it may make the compression ratio
              slightly worse.  The BCJ filters are very fast and  use  an  in-
              significant amount of memory.

              These BCJ filters have known problems related to the compression

              o  Some types of files containing executable code (for  example,
                 object  files,  static  libraries,  and Linux kernel modules)
                 have the addresses in the  instructions  filled  with  filler
                 values.   These BCJ filters will still do the address conver-
                 sion, which will make the compression worse with these files.

              o  If a BCJ filter is applied on an archive, it is possible that
                 it  makes  the  compression  ratio worse than not using a BCJ
                 filter.  For example, if there are similar or even  identical
                 executables  then  filtering  will likely make the files less
                 similar and thus compression is worse.  The contents of  non-
                 executable  files  in  the  same  archive can matter too.  In
                 practice one has to try with and without a BCJ filter to  see
                 which is better in each situation.

              Different  instruction  sets  have different alignment: the exe-
              cutable file must be aligned to a multiple of this value in  the
              input data to make the filter work.

                     Filter      Alignment   Notes
                     x86             1       32-bit or 64-bit x86
                     ARM             4
                     ARM-Thumb       2
                     ARM64           4       4096-byte alignment is best
                     PowerPC         4       Big endian only
                     IA-64          16       Itanium
                     SPARC           4

              Since  the  BCJ-filtered  data is usually compressed with LZMA2,
              the compression ratio may be improved slightly if the LZMA2  op-
              tions are set to match the alignment of the selected BCJ filter.
              For example, with the IA-64 filter, it's good  to  set  pb=4  or
              even  pb=4,lp=4,lc=0  with LZMA2 (2^4=16).  The x86 filter is an
              exception; it's usually good to stick to LZMA2's  default  four-
              byte alignment when compressing x86 executables.

              All BCJ filters support the same options:

                     Specify the start offset that is used when converting be-
                     tween relative and absolute addresses.  The  offset  must
                     be a multiple of the alignment of the filter (see the ta-
                     ble above).  The default is zero.  In practice,  the  de-
                     fault is good; specifying a custom offset is almost never

              Add the Delta filter to the filter chain.  The Delta filter  can
              be only used as a non-last filter in the filter chain.

              Currently  only simple byte-wise delta calculation is supported.
              It can be useful when  compressing,  for  example,  uncompressed
              bitmap  images or uncompressed PCM audio.  However, special pur-
              pose algorithms may give significantly better results than Delta
              +  LZMA2.   This is true especially with audio, which compresses
              faster and better, for example, with flac(1).

              Supported options:

                     Specify the distance of the delta calculation  in  bytes.
                     distance must be 1-256.  The default is 1.

                     For example, with dist=2 and eight-byte input A1 B1 A2 B3
                     A3 B5 A4 B7, the output will be A1 B1 01 02 01 02 01 02.

   Other options
       -q, --quiet
              Suppress warnings and notices.  Specify this twice  to  suppress
              errors too.  This option has no effect on the exit status.  That
              is, even if a warning was suppressed, the exit status  to  indi-
              cate a warning is still used.

       -v, --verbose
              Be  verbose.   If  standard error is connected to a terminal, xz
              will display a progress indicator.  Specifying  --verbose  twice
              will give even more verbose output.

              The progress indicator shows the following information:

              o  Completion  percentage is shown if the size of the input file
                 is known.  That is, the percentage cannot be shown in pipes.

              o  Amount of compressed data produced (compressing) or  consumed

              o  Amount  of  uncompressed  data consumed (compressing) or pro-
                 duced (decompressing).

              o  Compression ratio, which is calculated by dividing the amount
                 of  compressed  data processed so far by the amount of uncom-
                 pressed data processed so far.

              o  Compression or decompression speed.  This is measured as  the
                 amount  of  uncompressed  data consumed (compression) or pro-
                 duced (decompression) per second.  It is shown  after  a  few
                 seconds have passed since xz started processing the file.

              o  Elapsed time in the format M:SS or H:MM:SS.

              o  Estimated  remaining  time is shown only when the size of the
                 input file is known and a  couple  of  seconds  have  already
                 passed  since  xz  started  processing the file.  The time is
                 shown in a less precise format which never  has  any  colons,
                 for example, 2 min 30 s.

              When  standard  error  is not a terminal, --verbose will make xz
              print the filename, compressed size, uncompressed size, compres-
              sion  ratio,  and  possibly also the speed and elapsed time on a
              single line to standard error after compressing or decompressing
              the file.  The speed and elapsed time are included only when the
              operation took at least a few seconds.  If the operation  didn't
              finish,  for example, due to user interruption, also the comple-
              tion percentage is printed if the size  of  the  input  file  is

       -Q, --no-warn
              Don't set the exit status to 2 even if a condition worth a warn-
              ing was detected.  This  option  doesn't  affect  the  verbosity
              level,  thus  both  --quiet and --no-warn have to be used to not
              display warnings and to not alter the exit status.

              Print messages in a machine-parsable format.  This  is  intended
              to  ease  writing  frontends  that want to use xz instead of li-
              blzma, which may be the case with various scripts.   The  output
              with  this  option  enabled  is meant to be stable across xz re-
              leases.  See the section ROBOT MODE for details.

              Display, in human-readable  format,  how  much  physical  memory
              (RAM)  and  how  many processor threads xz thinks the system has
              and the memory usage limits for compression  and  decompression,
              and exit successfully.

       -h, --help
              Display  a  help  message  describing the most commonly used op-
              tions, and exit successfully.

       -H, --long-help
              Display a help message describing all features of xz,  and  exit

       -V, --version
              Display  the  version number of xz and liblzma in human readable
              format.  To get machine-parsable output, specify --robot  before

       The robot mode is activated with the --robot option.  It makes the out-
       put of xz easier to parse by other programs.  Currently --robot is sup-
       ported  only  together  with  --version, --info-memory, and --list.  It
       will be supported for compression and decompression in the future.

       xz --robot --version prints the version number of xz and liblzma in the
       following format:


       X      Major version.

       YYY    Minor  version.  Even numbers are stable.  Odd numbers are alpha
              or beta versions.

       ZZZ    Patch level for stable releases or just a counter  for  develop-
              ment releases.

       S      Stability.  0 is alpha, 1 is beta, and 2 is stable.  S should be
              always 2 when YYY is even.

       XYYYZZZS are the same on both lines if xz and liblzma are from the same
       XZ Utils release.

       Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

   Memory limit information
       xz  --robot  --info-memory prints a single line with multiple tab-sepa-
       rated columns:

       1.  Total amount of physical memory (RAM) in bytes.

       2.  Memory usage limit for compression in bytes  (--memlimit-compress).
           A  special  value of 0 indicates the default setting which for sin-
           gle-threaded mode is the same as no limit.

       3.  Memory usage limit for decompression  in  bytes  (--memlimit-decom-
           press).   A  special value of 0 indicates the default setting which
           for single-threaded mode is the same as no limit.

       4.  Since xz 5.3.4alpha: Memory usage for multi-threaded  decompression
           in  bytes (--memlimit-mt-decompress).  This is never zero because a
           system-specific default value shown in the column 5 is used  if  no
           limit  has  been  specified explicitly.  This is also never greater
           than the value in the column 3 even if  a  larger  value  has  been
           specified with --memlimit-mt-decompress.

       5.  Since  xz  5.3.4alpha: A system-specific default memory usage limit
           that is used to limit the number of threads when  compressing  with
           an  automatic  number  of threads (--threads=0) and no memory usage
           limit has been specified (--memlimit-compress).  This is also  used
           as the default value for --memlimit-mt-decompress.

       6.  Since xz 5.3.4alpha: Number of available processor threads.

       In  the  future,  the  output of xz --robot --info-memory may have more
       columns, but never more than a single line.

   List mode
       xz --robot --list uses tab-separated output.  The first column of every
       line  has  a string that indicates the type of the information found on
       that line:

       name   This is always the first line when starting to list a file.  The
              second column on the line is the filename.

       file   This line contains overall information about the .xz file.  This
              line is always printed after the name line.

       stream This line type is used only when --verbose was specified.  There
              are as many stream lines as there are streams in the .xz file.

       block  This line type is used only when --verbose was specified.  There
              are as many block lines as there are blocks  in  the  .xz  file.
              The  block lines are shown after all the stream lines; different
              line types are not interleaved.

              This line type is used only when --verbose was specified  twice.
              This line is printed after all block lines.  Like the file line,
              the summary line contains  overall  information  about  the  .xz

       totals This  line  is always the very last line of the list output.  It
              shows the total counts and sizes.

       The columns of the file lines:
              2.  Number of streams in the file
              3.  Total number of blocks in the stream(s)
              4.  Compressed size of the file
              5.  Uncompressed size of the file
              6.  Compression ratio, for example, 0.123.   If  ratio  is  over
                  9.999,  three  dashes (---) are displayed instead of the ra-
              7.  Comma-separated list of integrity check names.  The  follow-
                  ing strings are used for the known check types: None, CRC32,
                  CRC64, and SHA-256.  For unknown check types,  Unknown-N  is
                  used,  where  N  is the Check ID as a decimal number (one or
                  two digits).
              8.  Total size of stream padding in the file

       The columns of the stream lines:
              2.  Stream number (the first stream is 1)
              3.  Number of blocks in the stream
              4.  Compressed start offset
              5.  Uncompressed start offset
              6.  Compressed size (does not include stream padding)
              7.  Uncompressed size
              8.  Compression ratio
              9.  Name of the integrity check
              10. Size of stream padding

       The columns of the block lines:
              2.  Number of the stream containing this block
              3.  Block number relative to the beginning of  the  stream  (the
                  first block is 1)
              4.  Block number relative to the beginning of the file
              5.  Compressed  start  offset  relative  to the beginning of the
              6.  Uncompressed start offset relative to the beginning  of  the
              7.  Total compressed size of the block (includes headers)
              8.  Uncompressed size
              9.  Compression ratio
              10. Name of the integrity check

       If  --verbose  was  specified twice, additional columns are included on
       the block lines.  These are not displayed with a single --verbose,  be-
       cause  getting  this  information  requires  many seeks and can thus be
              11. Value of the integrity check in hexadecimal
              12. Block header size
              13. Block flags: c indicates that compressed  size  is  present,
                  and  u  indicates that uncompressed size is present.  If the
                  flag is not set, a dash (-) is shown  instead  to  keep  the
                  string  length  fixed.  New flags may be added to the end of
                  the string in the future.
              14. Size of the actual compressed data in the  block  (this  ex-
                  cludes the block header, block padding, and check fields)
              15. Amount  of  memory  (in  bytes)  required to decompress this
                  block with this xz version
              16. Filter chain.  Note that most of the options  used  at  com-
                  pression time cannot be known, because only the options that
                  are needed for decompression are stored in the .xz headers.

       The columns of the summary lines:
              2.  Amount of memory (in bytes) required to decompress this file
                  with this xz version
              3.  yes  or  no  indicating  if all block headers have both com-
                  pressed size and uncompressed size stored in them
              Since xz 5.1.2alpha:
              4.  Minimum xz version required to decompress the file

       The columns of the totals line:
              2.  Number of streams
              3.  Number of blocks
              4.  Compressed size
              5.  Uncompressed size
              6.  Average compression ratio
              7.  Comma-separated list of  integrity  check  names  that  were
                  present in the files
              8.  Stream padding size
              9.  Number of files.  This is here to keep the order of the ear-
                  lier columns the same as on file lines.

       If --verbose was specified twice, additional columns  are  included  on
       the totals line:
              10. Maximum  amount  of memory (in bytes) required to decompress
                  the files with this xz version
              11. yes or no indicating if all block  headers  have  both  com-
                  pressed size and uncompressed size stored in them
              Since xz 5.1.2alpha:
              12. Minimum xz version required to decompress the file

       Future  versions may add new line types and new columns can be added to
       the existing line types, but the existing columns won't be changed.

       0      All is good.

       1      An error occurred.

       2      Something worth a warning occurred, but  no  actual  errors  oc-

       Notices (not warnings or errors) printed on standard error don't affect
       the exit status.

       xz parses space-separated lists of options from the  environment  vari-
       ables XZ_DEFAULTS and XZ_OPT, in this order, before parsing the options
       from the command line.  Note that only options are parsed from the  en-
       vironment  variables; all non-options are silently ignored.  Parsing is
       done with getopt_long(3) which is used also for the command line  argu-

              User-specific or system-wide default options.  Typically this is
              set in a shell initialization script to enable xz's memory usage
              limiter  by default.  Excluding shell initialization scripts and
              similar special cases, scripts must never set  or  unset  XZ_DE-

       XZ_OPT This is for passing options to xz when it is not possible to set
              the options directly on the xz command line.  This is  the  case
              when xz is run by a script or tool, for example, GNU tar(1):

                     XZ_OPT=-2v tar caf foo.tar.xz foo

              Scripts  may use XZ_OPT, for example, to set script-specific de-
              fault compression options.  It is  still  recommended  to  allow
              users to override XZ_OPT if that is reasonable.  For example, in
              sh(1) scripts one may use something like this:

                     export XZ_OPT

       The command line syntax of xz is practically a superset  of  lzma,  un-
       lzma,  and lzcat as found from LZMA Utils 4.32.x.  In most cases, it is
       possible to replace LZMA Utils with XZ Utils without breaking  existing
       scripts.   There are some incompatibilities though, which may sometimes
       cause problems.

   Compression preset levels
       The numbering of the compression level presets is not identical  in  xz
       and  LZMA Utils.  The most important difference is how dictionary sizes
       are mapped to different presets.  Dictionary size is roughly  equal  to
       the decompressor memory usage.

              Level     xz      LZMA Utils
               -0     256 KiB      N/A
               -1       1 MiB     64 KiB
               -2       2 MiB      1 MiB
               -3       4 MiB    512 KiB
               -4       4 MiB      1 MiB
               -5       8 MiB      2 MiB
               -6       8 MiB      4 MiB
               -7      16 MiB      8 MiB
               -8      32 MiB     16 MiB
               -9      64 MiB     32 MiB

       The dictionary size differences affect the compressor memory usage too,
       but there are some other differences between LZMA Utils and  XZ  Utils,
       which make the difference even bigger:

              Level     xz      LZMA Utils 4.32.x
               -0       3 MiB          N/A
               -1       9 MiB          2 MiB
               -2      17 MiB         12 MiB
               -3      32 MiB         12 MiB
               -4      48 MiB         16 MiB
               -5      94 MiB         26 MiB
               -6      94 MiB         45 MiB
               -7     186 MiB         83 MiB
               -8     370 MiB        159 MiB
               -9     674 MiB        311 MiB

       The  default  preset  level in LZMA Utils is -7 while in XZ Utils it is
       -6, so both use an 8 MiB dictionary by default.

   Streamed vs. non-streamed .lzma files
       The uncompressed size of the file can be stored in  the  .lzma  header.
       LZMA  Utils  does that when compressing regular files.  The alternative
       is to mark that uncompressed size is  unknown  and  use  end-of-payload
       marker to indicate where the decompressor should stop.  LZMA Utils uses
       this method when uncompressed size isn't known, which is the case,  for
       example, in pipes.

       xz  supports  decompressing  .lzma files with or without end-of-payload
       marker, but all .lzma files  created  by  xz  will  use  end-of-payload
       marker  and  have  uncompressed  size  marked  as  unknown in the .lzma
       header.  This may be a problem in some uncommon situations.  For  exam-
       ple,  a  .lzma  decompressor in an embedded device might work only with
       files that have known uncompressed size.  If you hit this problem,  you
       need to use LZMA Utils or LZMA SDK to create .lzma files with known un-
       compressed size.

   Unsupported .lzma files
       The .lzma format allows lc values up to 8, and lp values up to 4.  LZMA
       Utils can decompress files with any lc and lp, but always creates files
       with lc=3 and lp=0.  Creating files with other lc and  lp  is  possible
       with xz and with LZMA SDK.

       The implementation of the LZMA1 filter in liblzma requires that the sum
       of lc and lp must not exceed 4.  Thus, .lzma files, which  exceed  this
       limitation, cannot be decompressed with xz.

       LZMA Utils creates only .lzma files which have a dictionary size of 2^n
       (a power of 2) but accepts files with any dictionary size.  liblzma ac-
       cepts  only  .lzma  files  which have a dictionary size of 2^n or 2^n +
       2^(n-1).  This is to decrease  false  positives  when  detecting  .lzma

       These limitations shouldn't be a problem in practice, since practically
       all .lzma files have been compressed with settings  that  liblzma  will

   Trailing garbage
       When  decompressing,  LZMA  Utils  silently ignore everything after the
       first .lzma stream.  In most situations, this  is  a  bug.   This  also
       means  that  LZMA  Utils don't support decompressing concatenated .lzma

       If there is data left after the first .lzma stream,  xz  considers  the
       file to be corrupt unless --single-stream was used.  This may break ob-
       scure scripts which have assumed that trailing garbage is ignored.

   Compressed output may vary
       The exact compressed output produced from the same  uncompressed  input
       file may vary between XZ Utils versions even if compression options are
       identical.  This is because the encoder can be improved (faster or bet-
       ter  compression)  without  affecting  the file format.  The output can
       vary even between different builds of the same  XZ  Utils  version,  if
       different build options are used.

       The above means that once --rsyncable has been implemented, the result-
       ing files won't necessarily be rsyncable unless both old and new  files
       have  been  compressed  with  the same xz version.  This problem can be
       fixed if a part of the encoder implementation is frozen to keep rsynca-
       ble output stable across xz versions.

   Embedded .xz decompressors
       Embedded .xz decompressor implementations like XZ Embedded don't neces-
       sarily support files created with integrity check types other than none
       and   crc32.    Since  the  default  is  --check=crc64,  you  must  use
       --check=none or --check=crc32 when creating files for embedded systems.

       Outside embedded systems, all .xz format decompressors support all  the
       check  types, or at least are able to decompress the file without veri-
       fying the integrity check if the particular check is not supported.

       XZ Embedded supports BCJ filters, but only with the default start  off-

       Compress  the  file foo into foo.xz using the default compression level
       (-6), and remove foo if compression is successful:

              xz foo

       Decompress bar.xz into bar and don't remove bar.xz even  if  decompres-
       sion is successful:

              xz -dk bar.xz

       Create  baz.tar.xz  with the preset -4e (-4 --extreme), which is slower
       than the default -6, but needs less memory for compression  and  decom-
       pression (48 MiB and 5 MiB, respectively):

              tar cf - baz | xz -4e > baz.tar.xz

       A mix of compressed and uncompressed files can be decompressed to stan-
       dard output with a single command:

              xz -dcf a.txt b.txt.xz c.txt d.txt.lzma > abcd.txt

   Parallel compression of many files
       On GNU and *BSD, find(1) and xargs(1) can be used to  parallelize  com-
       pression of many files:

              find . -type f \! -name '*.xz' -print0 \
                  | xargs -0r -P4 -n16 xz -T1

       The  -P  option  to  xargs(1) sets the number of parallel xz processes.
       The best value for the -n option depends on how many files there are to
       be  compressed.   If there are only a couple of files, the value should
       probably be 1; with tens of thousands of files, 100 or even more may be
       appropriate  to  reduce  the  number of xz processes that xargs(1) will
       eventually create.

       The option -T1 for xz is there to force it to single-threaded mode, be-
       cause xargs(1) is used to control the amount of parallelization.

   Robot mode
       Calculate  how  many  bytes  have been saved in total after compressing
       multiple files:

              xz --robot --list *.xz | awk '/^totals/{print $5-$4}'

       A script may want to know that it is using new enough xz.  The  follow-
       ing  sh(1)  script  checks that the version number of the xz tool is at
       least 5.0.0.  This method is compatible with old beta  versions,  which
       didn't support the --robot option:

              if ! eval "$(xz --robot --version 2> /dev/null)" ||
                      [ "$XZ_VERSION" -lt 50000002 ]; then
                  echo "Your xz is too old."
              unset XZ_VERSION LIBLZMA_VERSION

       Set a memory usage limit for decompression using XZ_OPT, but if a limit
       has already been set, don't increase it:

              NEWLIM=$((123 << 20))  # 123 MiB
              OLDLIM=$(xz --robot --info-memory | cut -f3)
              if [ $OLDLIM -eq 0 -o $OLDLIM -gt $NEWLIM ]; then
                  XZ_OPT="$XZ_OPT --memlimit-decompress=$NEWLIM"
                  export XZ_OPT

   Custom compressor filter chains
       The simplest use for custom filter chains is customizing a  LZMA2  pre-
       set.   This  can  be useful, because the presets cover only a subset of
       the potentially useful combinations of compression settings.

       The CompCPU columns of the tables from the descriptions of the  options
       -0  ...  -9  and  --extreme  are useful when customizing LZMA2 presets.
       Here are the relevant parts collected from those two tables:

              Preset   CompCPU
               -0         0
               -1         1
               -2         2
               -3         3
               -4         4
               -5         5
               -6         6
               -5e        7
               -6e        8

       If you know that a file requires somewhat big dictionary (for  example,
       32 MiB)  to  compress well, but you want to compress it quicker than xz
       -8 would do, a preset with a low CompCPU value (for example, 1) can  be
       modified to use a bigger dictionary:

              xz --lzma2=preset=1,dict=32MiB foo.tar

       With  certain  files,  the above command may be faster than xz -6 while
       compressing significantly better.  However, it must be emphasized  that
       only some files benefit from a big dictionary while keeping the CompCPU
       value low.  The most obvious situation, where a big dictionary can help
       a  lot,  is  an archive containing very similar files of at least a few
       megabytes each.  The dictionary size has  to  be  significantly  bigger
       than  any  individual file to allow LZMA2 to take full advantage of the
       similarities between consecutive files.

       If very high compressor and decompressor memory usage is fine, and  the
       file  being compressed is at least several hundred megabytes, it may be
       useful to use an even bigger dictionary than the  64  MiB  that  xz  -9
       would use:

              xz -vv --lzma2=dict=192MiB big_foo.tar

       Using -vv (--verbose --verbose) like in the above example can be useful
       to see the memory requirements of the compressor and decompressor.  Re-
       member that using a dictionary bigger than the size of the uncompressed
       file is waste of memory, so the above command isn't  useful  for  small

       Sometimes  the  compression  time  doesn't matter, but the decompressor
       memory usage has to be kept low, for example, to make  it  possible  to
       decompress  the file on an embedded system.  The following command uses
       -6e (-6 --extreme) as a base and sets the dictionary  to  only  64 KiB.
       The  resulting  file  can  be decompressed with XZ Embedded (that's why
       there is --check=crc32) using about 100 KiB of memory.

              xz --check=crc32 --lzma2=preset=6e,dict=64KiB foo

       If you want to squeeze out as many bytes  as  possible,  adjusting  the
       number  of  literal  context bits (lc) and number of position bits (pb)
       can sometimes help.  Adjusting the number of literal position bits (lp)
       might help too, but usually lc and pb are more important.  For example,
       a source code archive contains mostly US-ASCII text, so something  like
       the following might give slightly (like 0.1 %) smaller file than xz -6e
       (try also without lc=4):

              xz --lzma2=preset=6e,pb=0,lc=4 source_code.tar

       Using another filter together with LZMA2 can improve  compression  with
       certain file types.  For example, to compress a x86-32 or x86-64 shared
       library using the x86 BCJ filter:

              xz --x86 --lzma2 libfoo.so

       Note that the order of the filter options is significant.  If --x86  is
       specified after --lzma2, xz will give an error, because there cannot be
       any filter after LZMA2, and also because the x86 BCJ filter  cannot  be
       used as the last filter in the chain.

       The  Delta filter together with LZMA2 can give good results with bitmap
       images.  It should usually beat PNG, which has a few more advanced fil-
       ters than simple delta but uses Deflate for the actual compression.

       The  image  has to be saved in uncompressed format, for example, as un-
       compressed TIFF.  The distance parameter of the Delta filter is set  to
       match  the number of bytes per pixel in the image.  For example, 24-bit
       RGB bitmap needs dist=3, and it is also good to pass pb=0 to  LZMA2  to
       accommodate the three-byte alignment:

              xz --delta=dist=3 --lzma2=pb=0 foo.tiff

       If  multiple  images  have been put into a single archive (for example,
       .tar), the Delta filter will work on that too as  long  as  all  images
       have the same number of bytes per pixel.

       xzdec(1),   xzdiff(1),   xzgrep(1),   xzless(1),   xzmore(1),  gzip(1),
       bzip2(1), 7z(1)

       XZ Utils: <https://xz.tukaani.org/xz-utils/>
       XZ Embedded: <https://xz.tukaani.org/xz-embedded/>
       LZMA SDK: <https://7-zip.org/sdk.html>


Tukaani                           2024-01-19                             XZ(1)