Provided by: xz-utils_5.1.1alpha+20120614-2ubuntu2_i386 bug

NAME

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

SYNOPSIS

       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.

DESCRIPTION

       xz is a general-purpose data compression tool with command line  syntax
       similar  to  gzip(1)  and  bzip2(1).  The native file format is the .xz
       format, but the  legacy  .lzma  format  used  by  LZMA  Utils  and  raw
       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
          filename.

       ·  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
          format).

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

       After successfully compressing or decompressing the file, xz copies the
       owner, group, permissions, access time, and modification time from  the
       source  file  to  the  target  file.   If  copying the group fails, the
       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
       streams.

OPTIONS

   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
       effect.

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

       -d, --decompress, --uncompress
              Decompress.

       -t, --test
              Test   the  integrity  of  compressed  files.   This  option  is
              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
              used.

   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
                 format.

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

       --single-stream
              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.

       --no-sparse
              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.

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

       --files0[=file]
              This  is  identical  to --files[=file] except that each filename
              must be terminated with the null character.

   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-
                     detected.

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

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

              raw    Compress or uncompress a raw stream (no  headers).   This
                     is meant for advanced users only.  To decode raw streams,
                     you need use  --format=raw  and  explicitly  specify  the
                     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
              decompressed.

              Supported check types:

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

              crc32  Calculate  CRC32  using  the  polynomial  from IEEE-802.3
                     (Ethernet).

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

              sha256 Calculate  SHA-256.   This  is somewhat slower than CRC32
                     and CRC64.

              Integrity of the .xz headers is always verified with CRC32.   It
              is not possible to change or disable it.

       -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
                     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  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
                 matter.

              ·  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 slighly 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.

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

       --block-size=size
              When compressing to the .xz format, split the  input  data  into
              blocks  of  size bytes.  The blocks are compressed independently
              from each other.

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

              If the compression settings exceed the limit, xz will adjust the
              settings downwards so that the limit is no longer  exceeded  and
              display  a  notice  that  automatic  adjustment  was done.  Such
              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:
                 --memlimit-compress=80MiB

              ·  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.

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

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

       --no-adjust
              Display an error and exit if the compression settings exceed the
              memory usage limit.  The  default  is  to  adjust  the  settings
              downwards  so  that  the  memory  usage  limit  is not exceeded.
              Automatic adjusting is always disabled when creating raw streams
              (--format=raw).

       -T threads, --threads=threads
              Specify  the number of worker threads to use.  The actual number
              of threads can be less than threads if using more threads  would
              exceed the memory usage limit.

              Multithreaded  compression and decompression are not implemented
              yet, so this option has no effect for now.

              As of writing (2010-09-27), it hasn't been  decided  if  threads
              will  be  used  by default on multicore systems once support for
              threading has been  implemented.   Comments  are  welcome.   The
              complicating factor is that using many threads will increase the
              memory usage dramatically.  Note that if multithreading will  be
              the  default,  it  will probably be done so that single-threaded
              and multithreaded modes produce the same output, so  compression
              ratio  won't  be  significantly  affected  if  threading will be
              enabled by default.

   Custom compressor filter chains
       A custom filter chain allows specifying  the  compression  settings  in
       detail  instead  of  relying  on  the settings associated to the preset
       levels.  When a custom  filter  chain  is  specified,  the  compression
       preset level options (-0 ... -9 and --extreme) are silently ignored.

       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
       filters.

       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.

       --lzma1[=options]
       --lzma2[=options]
              Add LZMA1 or LZMA2 filter to the filter  chain.   These  filters
              can be used only as the last filter in the chain.

              LZMA1  is  a legacy filter, which is supported almost solely due
              to the legacy .lzma file  format,  which  supports  only  LZMA1.
              LZMA2  is  an  updated  version  of  LZMA1 to fix some practical
              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:

              preset=preset
                     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.   The  default  preset  is  6,  from which the
                     default values for the rest of the LZMA1 or LZMA2 options
                     are taken.

              dict=size
                     Dictionary (history buffer) size indicates how many bytes
                     of the recently processed uncompressed data  is  kept  in
                     memory.   The  algorithm  tries  to  find  repeating byte
                     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
                     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
                     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
                     choice.

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

              mode=mode
                     Compression mode specifies the method to analyze the data
                     produced by the match finder.  Supported modes  are  fast
                     and  normal.   The  default  is  fast for presets 0-3 and
                     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.

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

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

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

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

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

       --x86[=options]
       --powerpc[=options]
       --ia64[=options]
       --arm[=options]
       --armthumb[=options]
       --sparc[=options]
              Add a branch/call/jump (BCJ) filter to the filter chain.   These
              filters  can  be  used  only  as a non-last filter in the filter
              chain.

              A BCJ filter converts relative addresses in the machine code  to
              their  absolute  counterparts.   This doesn't change the size of
              the data, but it increases redundancy, which can help  LZMA2  to
              produce  0-15 %  smaller  .xz  file.  The BCJ filters are always
              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
              second.

              These BCJ filters have known problems related to the compression
              ratio:

              ·  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
                 executable.

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

              Different instruction sets have 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:

              start=offset
                     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.

       --delta[=options]
              Add the Delta filter to the filter chain.  The Delta filter  can
              be only used as a non-last filter in the filter chain.

              Currently  only simple byte-wise delta calculation is supported.
              It can be  useful  when  compressing  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:

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

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

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

              ·  Amount   of   uncompressed  data  consumed  (compressing)  or
                 produced (decompressing).

              ·  Compression ratio, which is calculated by dividing the amount
                 of  compressed  data  processed  so  far  by  the  amount  of
                 uncompressed data processed so far.

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

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

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

       --robot
              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.

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

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

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

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

ROBOT MODE

       The robot mode is activated with the  --robot  option.   It  makes  the
       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  normal  compression  and decompression in the
       future.

   Version
       xz --robot --version will print the version number of xz and liblzma in
       the following format:

       XZ_VERSION=XYYYZZZS
       LIBLZMA_VERSION=XYYYZZZS

       X      Major version.

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

       ZZZ    Patch  level  for  stable  releases  or  just  a   counter   for
              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
       columns:

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

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

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

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

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

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

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

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

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

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

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

       The columns of the file lines:
              2.  Number of streams in the file
              3.  Total number of blocks in the stream(s)
              4.  Compressed size of the file
              5.  Uncompressed size of the file
              6.  Compression  ratio,  for  example  0.123.   If ratio is over
                  9.999, three dashes  (---)  are  displayed  instead  of  the
                  ratio.
              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
                  file
              6.  Uncompressed  start  offset relative to the beginning of the
                  file
              7.  Total compressed size of the block (includes headers)
              8.  Uncompressed size
              9.  Compression ratio
              10. Name of the integrity check

       If --verbose was specified twice, additional columns  are  included  on
       the  block  lines.   These  are  not displayed with a single --verbose,
       because getting this information requires many seeks and  can  thus  be
       slow:
              11. Value of the integrity check in hexadecimal
              12. Block header size
              13. Block  flags:  c  indicates that compressed size is present,
                  and u indicates that uncompressed size is present.   If  the
                  flag  is  not  set,  a dash (-) is shown instead to keep the
                  string length fixed.  New flags may be added to the  end  of
                  the string in the future.
              14. Size  of  the  actual  compressed  data  in  the block (this
                  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
                  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
                  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.

EXIT STATUS

       0      All is good.

       1      An error occurred.

       2      Something  worth  a  warning  occurred,  but  no  actual  errors
              occurred.

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

ENVIRONMENT

       xz  parses  space-separated  lists  of  options  from  the  environment
       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.

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

       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:

                     XZ_OPT=${XZ_OPT-"-7e"}
                     export XZ_OPT

LZMA UTILS COMPATIBILITY

       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
       files.

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

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

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

NOTES

   Compressed output may vary
       The exact compressed output produced from the same  uncompressed  input
       file may vary between XZ Utils versions even if compression options are
       identical.  This is because the encoder  can  be  improved  (faster  or
       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 implementing --rsyncable to create rsyncable .xz
       files is not going to happen without freezing a  part  of  the  encoder
       implementation, which can then be used with --rsyncable.

   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
       offset.

EXAMPLES

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

              xz foo

       Decompress  bar.xz  into  bar  and  don't   remove   bar.xz   even   if
       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."
              fi
              unset XZ_VERSION LIBLZMA_VERSION

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

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

   Custom compressor filter chains
       The simplest use for  custom  filter  chains  is  customizing  a  LZMA2
       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.

SEE ALSO

       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>