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  com-
       pressed streams with no container format headers are also supported.

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

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

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

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

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

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

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

       o  File has more than one hard link.

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

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

       o  The  operation mode is set to decompress and the file doesn't have a
          suffix of any of the supported file formats (.xz,  .txz,  .lzma,  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 per-
       missions are modified so that the target file doesn't become accessible
       to  users  who  didn't  have  permission to access the source file.  xz
       doesn't support copying other metadata like access control lists or ex-
       tended attributes yet.

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

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

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

       Especially  users  of  older  systems  may find the possibility of very
       large memory usage annoying.  To prevent  uncomfortable  surprises,  xz
       has  a  built-in  memory  usage  limiter, which is disabled by default.
       While some operating systems provide ways to limit the memory usage  of
       processes,  relying on it wasn't deemed to be flexible enough (e.g. us-
       ing 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_DE-
       FAULTS=--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 --for-
       mat=raw or --no-adjust).  This way the operation won't fail unless  the
       limit is very small.  The scaling of the settings is done in steps that
       don't match the compression level presets, 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 af-
       ter the last part.  The padding must consist of null bytes and the size
       of  the  padding  must be a multiple of four bytes.  This can be useful
       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  suf-
       fix  is  supported to easily indicate large integers.  There must be no
       space between the integer and the suffix.

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

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

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

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

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

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

       -d, --decompress, --uncompress

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              When  decompressing, recognize files with the suffix .suf in ad-
              dition to files with the .xz, .txz, .lzma, 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 ter-
              minated with the newline character.  A dash (-) is  taken  as  a
              regular  filename; it doesn't mean standard input.  If filenames
              are given also as command line arguments, they are processed be-
              fore the filenames read from file.

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

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

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

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

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

              raw    Compress  or  uncompress a raw stream (no headers).  This
                     is meant for advanced users only.  To decode raw streams,
                     you need use --format=raw and explicitly specify the fil-
                     ter chain, which normally would have been stored  in  the
                     container headers.

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

              Supported check types:

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

              crc32  Calculate CRC32  using  the  polynomial  from  IEEE-802.3

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

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

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

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

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

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

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

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

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

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

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

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

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

              The following table summarises the features of the presets:

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

              Column descriptions:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              This feature is not available on non-POSIX systems.

              This  feature is still experimental.  Currently xz is unsuitable
              for decompressing the stream in real time due  to  how  xz  does

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

              If the compression settings exceed the limit, xz will adjust the
              settings  downwards  so that the limit is no longer exceeded and
              display a notice that automatic adjustment was done.   Such  ad-
              justments  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 inte-
                 ger suffix like MiB can be useful.  Example:  --memlimit-com-

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

              o  The limit can be reset back to its default value  by  setting
                 it  to  0.  This is currently equivalent to setting the limit
                 to max (no memory usage limit).  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  ex-
              ceeding  the  limit,  xz will display an error and decompressing
              the file will fail.  See --memlimit-compress=limit for  possible
              ways to specify the limit.

       -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 down-
              wards so that the memory usage limit is not exceeded.  Automatic
              adjusting  is  always disabled when creating raw streams (--for-

       -T threads, --threads=threads
              Specify the number of worker threads to use.  Setting threads to
              a  special value 0 makes xz use as many threads as there are CPU
              cores on the system.  The actual number of threads can  be  less
              than  threads  if the input file is not big enough for threading
              with the given settings or if using more  threads  would  exceed
              the memory usage limit.

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

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

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

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

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

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

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

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

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

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

              LZMA1 and LZMA2 share the same set of options:

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

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

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

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

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

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

                     The  literal  coding makes an assumption that the highest
                     lc bits of the previous uncompressed byte correlate  with
                     the  next  byte.  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 uncom-
                     pressed data.

                     The default value (3) is usually good.  If you want maxi-
                     mum compression, test lc=4.  Sometimes it helps a little,
                     and sometimes it makes compression worse.  If it makes it
                     worse, test 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 hav-
                     ing one-byte  alignment  (US-ASCII,  ISO-8859-*,  UTF-8),
                     setting  pb=0  can  improve  compression  slightly.   For
                     UTF-16 text, pb=1 is a good choice.  If the alignment  is
                     an  odd  number  like  3  bytes,  pb=0  might be the best

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              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  gener-
              ally  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  sec-

              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 simi-
                 lar 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  op-
              tions are set to match the alignment of the selected BCJ filter.
              For example, with the IA-64 filter, it's good to set  pb=4  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  com-
              pressing x86 executables.

              All BCJ filters support the same options:

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

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

              Currently  only simple byte-wise delta calculation is supported.
              It can be useful when compressing e.g. uncompressed  bitmap  im-
              ages  or uncompressed PCM audio.  However, special purpose algo-
              rithms 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  indi-
              cate a warning is still used.

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

              The progress indicator shows the following information:

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

              o  Amount of compressed data produced (compressing) or  consumed

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

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

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

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

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

              When  standard  error  is not a terminal, --verbose will make xz
              print the filename, compressed size, uncompressed size, compres-
              sion  ratio,  and  possibly also the speed and elapsed time on a
              single line to standard error after compressing or decompressing
              the file.  The speed and elapsed time are included only when the
              operation took at least a few seconds.  If the operation  didn't
              finish,  e.g. due to user interruption, also the completion per-
              centage 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 warn-
              ing  was  detected.   This  option  doesn't affect the verbosity
              level, thus both --quiet and --no-warn have to be  used  to  not
              display warnings and to not alter the exit status.

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

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

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

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

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

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

       xz --robot --version 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  develop-
              ment releases.

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

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

       Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

   Memory limit information
       xz  --robot --info-memory prints a single line with 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  ra-
              7.  Comma-separated  list of integrity check names.  The follow-
                  ing strings are used for the known check types: None, CRC32,
                  CRC64,  and  SHA-256.  For unknown check types, Unknown-N is
                  used, where N is the Check ID as a decimal  number  (one  or
                  two digits).
              8.  Total size of stream padding in the file

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

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

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

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

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

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

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

       0      All is good.

       1      An error occurred.

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

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

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

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

       XZ_OPT This is for passing options to xz when it is not possible to set
              the  options  directly on the xz command line.  This is the case
              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  com-
              pression  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, un-
       lzma, and lzcat as found from LZMA Utils 4.32.x.  In most cases, it  is
       possible  to replace LZMA Utils with XZ Utils without breaking existing
       scripts.  There are some incompatibilities though, which may  sometimes
       cause problems.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              xz foo

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

              xz -dk bar.xz

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Preset   CompCPU
               -0         0
               -1         1

               -2         2
               -3         3
               -4         4
               -5         5
               -6         6
               -5e        7
               -6e        8

       If  you know that a file requires somewhat big dictionary (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.  Re-
       member that using a dictionary bigger than the size of the uncompressed
       file  is  waste  of memory, so the above command isn't useful for small

       Sometimes the compression time doesn't  matter,  but  the  decompressor
       memory  usage has to be kept low 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 re-
       sulting 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 fil-
       ters 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: <https://tukaani.org/xz/>
       XZ Embedded: <https://tukaani.org/xz/embedded.html>
       LZMA SDK: <http://7-zip.org/sdk.html>

Tukaani                           2017-04-19                             XZ(1)
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