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
   compressed streams with no container format headers are also supported.

   xz  compresses  or  decompresses  each  file  according to the selected
   operation 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 standard 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:

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

   ·  When  decompressing,  the  .xz  or  .lzma 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:

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

   ·  File has more than one hard link.

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

   ·  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

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

   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
   permissions 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 extended attributes yet.

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

   Sending  SIGINFO  or  SIGUSR1 to the xz process makes it print progress
   information to standard error.  This has only limited  use  since  when
   standard   error  is  a  terminal,  using  --verbose  will  display  an
   automatically 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
   decompressor.   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 (e.g.
   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,   e.g.
   XZ_DEFAULTS=--memlimit=150MiB.   It  is  possible  to  set  the  limits
   separately    for    compression    and    decompression    by    using
   --memlimit-compress=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
   --format=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, e.g. 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
   after 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 e.g. 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
   suffix  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

   -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
          equivalent 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
          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  information  requires  many  seeks.  The width of verbose
          output exceeds 80 characters,  so  piping  the  output  to  e.g.
          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

   Operation modifiers
   -k, --keep
          Don't delete the input files.

   -f, --force
          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.  --format=format can
             be used to restrict xz  to  decompress  only  a  single  file

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

          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.

          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
          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
          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, or .tlz suffix.  If
          the  source  file  has the suffix .suf, the suffix is removed to
          get the target filename.

          When compressing or decompressing  raw  streams  (--format=raw),
          the  suffix  must always be specified unless writing to standard
          output, because there is no default suffix for raw streams.

          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.

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

          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

          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 container headers.

   -C check, --check=check
          Specify  the  type  of  the  integrity  check.   The  check   is
          calculated  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

          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

          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

          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
          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.

   -0 ... -9
          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  depend  a  lot  on  the  type  of   data   being

          -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  e.g.  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 requirements.  These are useful only
                 when compressing files bigger  than  8 MiB,  16 MiB,  and
                 32 MiB, respectively.

          On the same hardware, the decompression speed is approximately a
          constant number of bytes of  compressed  data  per  second.   In
          other   words,  the  better  the  compression,  the  faster  the
          decompression 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:

          ·  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

          ·  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.

          ·  CompMem contains the compressor memory  requirements  in  the
             single-threaded  mode.   It  may  vary  slightly  between  xz
             versions.   Memory  requirements  of  some  of   the   future
             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  decompressor
             memory usage is slightly more than the LZMA2 dictionary size,
             but the values in the table have been rounded up to the  next
             full MiB.

   -e, --extreme
          Use  a  slower  variant of the selected compression preset level
          (-0 ... -9) to hopefully get a  little  bit  better  compression
          ratio,   but  with  bad  luck  this  can  also  make  it  worse.
          Decompressor 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,
          respectively.    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
          limited  random-access  decompression  possible.  This option is
          typically 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.

          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
          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 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
          (either  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  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

          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 disable
          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

          Set a memory usage limit for compression.   If  this  option  is
          specified multiple times, the last one takes effect.

          If the compression settings exceed the limit, xz will adjust the
          settings downwards so that the limit is no longer  exceeded  and
          display  a  notice  that  automatic  adjustment  was done.  Such
          adjustments are not made when compressing with  --format=raw  or
          if  --no-adjust has been specified.  In those cases, an error is
          displayed and xz will exit with exit status 1.

          The limit can be specified in multiple ways:

          ·  The limit can be  an  absolute  value  in  bytes.   Using  an
             integer   suffix   like   MiB   can   be   useful.   Example:

          ·  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
             memory.  Example: --memlimit-compress=70%

          ·  The  limit  can be reset back to its default value by setting
             it to 0.  This is currently equivalent to setting  the  limit
             to  max (no memory usage limit).  Once multithreading support
             has been implemented, there may be a difference between 0 and
             max for the multithreaded case, so it is recommended to use 0
             instead of max until the details have been decided.

          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
          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.

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

          Display an error and exit if the compression settings exceed the
          memory usage limit.  The  default  is  to  adjust  the  settings
          downwards  so  that  the  memory  usage  limit  is not exceeded.
          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 as many threads as there are  CPU
          cores  on  the system.  The actual number of threads can be less
          than threads if the input file is not big enough  for  threading
          with  the  given  settings or if using more threads would exceed
          the memory usage limit.

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

          Threaded  decompression  hasn't  been  implemented yet.  It will
          only work on  files  that  contain  multiple  blocks  with  size
          information  in  block  headers.  All files compressed in multi-
          threaded mode meet  this  condition,  but  files  compressed  in
          single-threaded mode don't even if --block-size=size is used.

   Custom compressor filter chains
   A  custom  filter  chain  allows specifying the compression settings in
   detail 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
   option  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
   compressing, 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

   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.
   Depending  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
   (--format=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
          issues 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
                 consist  of  an integer, which may be followed by single-
                 letter 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
                 --extreme.  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
                 sequences (matches) in the uncompressed data, and replace
                 them  with  references  to  the  data  currently  in  the
                 dictionary.  The bigger the dictionary, the higher is the
                 chance to find a match.  Thus, increasing dictionary size
                 usually  improves  compression  ratio,  but  a dictionary
                 bigger 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
                 currently 1.5 GiB (1536 MiB).  The  decompressor  already
                 supports  dictionaries  up  to  one byte less than 4 GiB,
                 which is the maximum  for  the  LZMA1  and  LZMA2  stream

                 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
                 addition, 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.  E.g. in typical English text, an upper-
                 case letter is often followed by a lower-case letter, and
                 a lower-case letter is usually followed by another 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
                 maximum  compression,  test  lc=4.   Sometimes it helps a
                 little, and sometimes it makes compression worse.  If  it
                 makes it worse, test e.g. lc=2 too.

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

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

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

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

                 When the aligment is known, setting  pb  accordingly  may
                 reduce  the  file  size  a  little.  E.g. 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
                 compressed 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
                 normal 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
                 better compression ratio at the expense  of  speed.   The
                 default 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
                 setting the depth over 1000 unless you  are  prepared  to
                 interrupt  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
          reversible, so using a BCJ filter for wrong type of data doesn't
          cause any data loss, although it may make the compression  ratio
          slightly worse.

          It  is fine to apply a BCJ filter on a whole executable; there's
          no need to apply it only on the executable section.  Applying  a
          BCJ  filter on an archive that contains both executable and non-
          executable files may  or  may  not  give  good  results,  so  it
          generally  isn't  good  to  blindly  apply  a  BCJ  filter  when
          compressing binary packages for distribution.

          These BCJ filters are very fast and use insignificant amount  of
          memory.   If  a BCJ filter improves compression ratio of a file,
          it can improve decompression speed at the same  time.   This  is
          because,  on the same hardware, the decompression speed of LZMA2
          is roughly a fixed  number  of  bytes  of  compressed  data  per

          These BCJ filters have known problems related to the compression

          ·  Some types of files containing executable code  (e.g.  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 conversion, which
             will make the compression worse with these files.

          ·  Applying a BCJ  filter  on  an  archive  containing  multiple
             similar executables can make the compression ratio worse than
             not using a BCJ filter.   This  is  because  the  BCJ  filter
             doesn't  detect  the  boundaries of the executable files, and
             doesn't  reset  the  address  conversion  counter  for   each

          Both  of the above problems will be fixed in the future in a new
          filter.  The old BCJ filters will still be  useful  in  embedded
          systems,  because  the  decoder of the new filter will be bigger
          and use more memory.

          Different instruction sets have have different alignment:

                 Filter      Alignment   Notes
                 x86             1       32-bit or 64-bit x86
                 PowerPC         4       Big endian only
                 ARM             4       Little endian only
                 ARM-Thumb       2       Little endian only
                 IA-64          16       Big or little endian
                 SPARC           4       Big or little endian

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

          All BCJ filters support the same options:

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

          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  e.g. uncompressed bitmap
          images or uncompressed  PCM  audio.   However,  special  purpose
          algorithms  may  give  significantly better results than Delta +
          LZMA2.  This is true especially  with  audio,  which  compresses
          faster and better e.g. 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
          indicate 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:

          ·  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

          ·  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,
             e.g. 2 min 30 s.

          When standard error is not a terminal, --verbose  will  make  xz
          print   the   filename,   compressed  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, e.g. due to user interruption, also the
          completion  percentage  is printed if the size of the input file
          is known.

   -Q, --no-warn
          Don't set the exit status to 2  even  if  a  condition  worth  a
          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.

          Print  messages  in a machine-parsable format.  This is intended
          to ease writing  frontends  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
          releases.  See the section ROBOT MODE for details.

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

   -h, --help
          Display  a  help  message  describing  the  most  commonly  used
          options, 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
   output of xz easier to parse by other programs.  Currently  --robot  is
   supported  only together with --version, --info-memory, and --list.  It
   will be supported for compression and decompression in the future.

   xz --robot --version will print 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
          development releases.

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

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

   Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

   Memory limit information
   xz  --robot --info-memory prints a single line with three tab-separated

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

   2.  Memory usage limit for compression in bytes.  A  special  value  of
       zero  indicates the default setting, which for single-threaded mode
       is the same as no limit.

   3.  Memory usage limit for decompression in bytes.  A special value  of
       zero  indicates the default setting, which for single-threaded mode
       is the same as no limit.

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

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

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

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

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

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

          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
          7.  Comma-separated   list   of   integrity  check  names.   The
              following 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,
   because 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
              excludes 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
              compression time cannot be known, because only  the  options
              that  are  needed  for  decompression  are stored in the .xz

   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
              compressed 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
              earlier 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
              compressed 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

   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
   variables  XZ_DEFAULTS  and  XZ_OPT,  in this order, before parsing the
   options from the command line.  Note that only options are parsed  from
   the  environment  variables;  all  non-options  are  silently  ignored.
   Parsing is done with getopt_long(3) which is used also for the  command
   line arguments.

          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_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
          e.g. when xz is run by a script or tool, e.g. GNU tar(1):

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

          Scripts  may  use  XZ_OPT  e.g.  to  set script-specific default
          compression options.  It is still recommended to allow users  to
          override XZ_OPT if that is reasonable, e.g. 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,
   unlzma,  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
   example,  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
   uncompressed 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
   accepts  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
   obscure 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
   better  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
   resulting 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
   rsyncable output stable across xz versions.

   Embedded .xz decompressors
   Embedded  .xz  decompressor  implementations  like  XZ  Embedded  don't
   necessarily 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
   verifying the integrity check if the particular check is not supported.

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


   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 e.g. 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 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
   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 -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,
   because 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
   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 "$(xz --robot --version 2> /dev/null)" ||
                  [ "$XZ_VERSION" -lt 50000002 ]; then
              echo "Your xz is too old."

   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
   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  --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 (e.g. 32  MiB)
   to  compress well, but you want to compress it quicker than xz -8 would
   do, a preset with a low CompCPU value (e.g. 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.
   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 e.g. 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.  E.g. 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.  E.g. 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
   filters than simple delta but uses Deflate for the actual compression.

   The  image has to be saved in uncompressed format, e.g. as uncompressed
   TIFF.  The distance parameter of the Delta filter is set to  match  the
   number  of  bytes per pixel in the image.  E.g. 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 (e.g. .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: <http://tukaani.org/xz/>
   XZ Embedded: <http://tukaani.org/xz/embedded.html>
   LZMA SDK: <http://7-zip.org/sdk.html>


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