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XZ(1)                              XZ Utils                              XZ(1)

       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:

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

       o  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:

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

       o  File has more than one hard link.

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

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

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

       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:

              o  If   the   target  file  already  exists,  delete  it  before
                 compressing or decompressing.

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

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

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

              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.

       -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:

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

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

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

              o  DecMem  contains  the decompressor memory requirements.  That
                 is,   the   compression   settings   determine   the   memory
                 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.

       --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.

              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:

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

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

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

              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.  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

       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.

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

                     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

              o  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.

              o  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:

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

              o  Amount  of compressed data produced (compressing) or consumed

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

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

              o  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.

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

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

       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 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

       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.  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 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

       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."
              unset XZ_VERSION LIBLZMA_VERSION

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

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

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

       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: <>
       XZ Embedded: <>
       LZMA SDK: <>

Tukaani                           2010-10-04                             XZ(1)