XZ(1)                              XZ Utils                              XZ(1)



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

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

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

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

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

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

         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:

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

         File has more than one hard link.

         File has setuid, setgid, or sticky bit set.

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

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

       After successfully compressing or decompressing the file, xz copies the
       owner, group, permissions, access time, and modification time from  the
       source  file  to the target file.  If copying the group fails, the 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
       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 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.
       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 sepa-
       rately for  compression  and  decompression  by  using  --memlimit-com-
       press=limit  and  --memlimit-decompress=limit.  Using these two options
       outside XZ_DEFAULTS is rarely useful because a single run of xz  cannot
       do  both  compression  and  decompression  and  --memlimit=limit (or -M
       limit) is shorter to type on the command line.

       If the specified memory usage limit is exceeded when decompressing,  xz
       will  display  an  error  and decompressing the file will fail.  If the
       limit is exceeded when compressing, xz will try to scale  the  settings
       down  so that the limit is no longer exceeded (except when using --for-
       mat=raw or --no-adjust).  This way the operation won't fail unless  the
       limit is very small.  The scaling of the settings is done in steps that
       don't match the compression level presets, 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 use-
       ful e.g. if the .xz file is stored on a medium that measures file sizes
       in 512-byte blocks.

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

OPTIONS
   Integer suffixes and special values
       In most places where an integer argument is expected, an optional  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
       effect.

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

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

       -t, --test
              Test the integrity of compressed files.  This option is  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
              locales.   For machine-readable output, --robot --list should be
              used.

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

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

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

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

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

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

       --single-stream
              Decompress only the first .xz stream, and silently ignore 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.

       --no-sparse
              Disable creation of sparse files.  By default, if  decompressing
              into  a  regular  file,  xz tries to make the file sparse if the
              decompressed data contains long sequences of binary  zeros.   It
              also  works  when writing to standard output as long as standard
              output is connected to a regular  file  and  certain  additional
              conditions  are  met to make it safe.  Creating sparse files may
              save disk space and speed up the decompression by  reducing  the
              amount of disk I/O.

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

              When decompressing, recognize files  with  the  suffix  .suf  in
              addition to files with the .xz, .txz, .lzma, or .tlz suffix.  If
              the source file has the suffix .suf, the suffix  is  removed  to
              get the target filename.

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

       --files[=file]
              Read  the  filenames  to  process from file; if file is omitted,
              filenames are read from standard input.  Filenames must be  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
              before the filenames read from file.

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

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

              auto   This  is  the default.  When compressing, auto is 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
                     Utils.

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

              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
                     (Ethernet).

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

              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.

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

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

                Trying to recover data from a corrupt .xz file.

                Speeding up decompression.  This matters mostly with  SHA-256
                 or with files that have compressed extremely well.  It's 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
              using  a  too  high preset level might make it painful to decom-
              press 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,
                     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  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:


                     tab(;); c c c c  c  n  n  n  n  n.   Preset;DictSize;Com-
                     pCPU;CompMem;DecMem -0;256 KiB;0;3 MiB;1 MiB -1;1 MiB;1;9
                     MiB;2 MiB -2;2 MiB;2;17 MiB;3 MiB -3;4 MiB;3;32 MiB;5 MiB
                     -4;4  MiB;4;48  MiB;5  MiB  -5;8  MiB;5;94 MiB;9 MiB -6;8
                     MiB;6;94 MiB;9  MiB  -7;16  MiB;6;186  MiB;17  MiB  -8;32
                     MiB;6;370 MiB;33 MiB -9;64 MiB;6;674 MiB;65 MiB

              Column descriptions:

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

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

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

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

       -e, --extreme
              Use  a  slower  variant of the selected compression preset level
              (-0 ... -9) to hopefully get a  little  bit  better  compression
              ratio,  but  with  bad luck this can also make it worse.  Decom-
              pressor 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.


                     tab(;); c c c c  c  n  n  n  n  n.   Preset;DictSize;Com-
                     pCPU;CompMem;DecMem   -0e;256  KiB;8;4  MiB;1  MiB  -1e;1
                     MiB;8;13  MiB;2  MiB  -2e;2  MiB;8;25  MiB;3  MiB   -3e;4
                     MiB;7;48   MiB;5  MiB  -4e;4  MiB;8;48  MiB;5  MiB  -5e;8
                     MiB;7;94  MiB;9  MiB  -6e;8  MiB;8;94  MiB;9  MiB  -7e;16
                     MiB;8;186  MiB;17  MiB -8e;32 MiB;8;370 MiB;33 MiB -9e;64
                     MiB;8;674 MiB;65 MiB

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

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

       --block-size=size
              When compressing to the .xz format, split the  input  data  into
              blocks  of  size bytes.  The blocks are compressed independently
              from each other, 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
              allocated in each thread for buffering input  and  output.   The
              default  size is three times the LZMA2 dictionary size or 1 MiB,
              whichever is more.  Typically a good value is 2-4 times the size
              of the LZMA2 dictionary or at least 1 MiB.  Using size less than
              the LZMA2 dictionary size is waste of RAM because then the LZMA2
              dictionary  buffer  will never get fully used.  The sizes of the
              blocks are stored in the block headers, which a  future  version
              of xz will use for multi-threaded decompression.

              In  single-threaded  mode no block splitting is done by default.
              Setting this option doesn't affect memory usage.  No size 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.

       --block-list=sizes
              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
              (either the default value in threaded mode or the  value  speci-
              fied with --block-size=size), the encoder will create additional
              blocks while keeping the boundaries  specified  in  sizes.   For
              example,      if      one      specifies      --block-size=10MiB
              --block-list=5MiB,10MiB,8MiB,12MiB,24MiB and the input  file  is
              80  MiB, one will get 11 blocks: 5, 10, 8, 10, 2, 10, 10, 4, 10,
              10, and 1 MiB.

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

       --flush-timeout=timeout
              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-
              ture.

              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
              buffering.

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

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

              The limit can be specified in multiple ways:

                The  limit can be an absolute value in bytes.  Using an inte-
                 ger suffix like MiB can be useful.  Example:  --memlimit-com-
                 press=80MiB

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

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

              See also the section Memory usage.

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

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

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

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

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

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

       A filter chain is comparable to piping on the command line.  When  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-
       ters.

       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 fil-
       ter 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.

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

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

              LZMA1 and LZMA2 share the same set of options:

              preset=preset
                     Reset  all LZMA1 or LZMA2 options to preset.  Preset 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
                     --extreme.  If no preset is specified, the default values
                     of LZMA1 or LZMA2 options are taken from the preset 6.

              dict=size
                     Dictionary (history buffer) size indicates how many bytes
                     of the recently processed uncompressed data  is  kept  in
                     memory.   The  algorithm  tries  to  find  repeating byte
                     sequences (matches) in the uncompressed data, and replace
                     them with references to the data currently in the 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
                     choice.

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

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

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

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

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

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

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

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

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

              It is fine to apply a BCJ filter on a whole executable;  there's
              no  need to apply it only on the executable section.  Applying a
              BCJ filter on an archive that contains both executable and  non-
              executable  files may or may not give good results, so it 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-
              ond.

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

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

                Applying a BCJ filter on an archive containing multiple 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:


                     tab(;); l n l l n l.  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 fil-
              ter.  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 usu-
              ally good to stick to LZMA2's default four-byte  alignment  when
              compressing x86 executables.

              All BCJ filters support the same options:

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

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

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

              Supported options:

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

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

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

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

                Amount of compressed data produced (compressing) or  consumed
                 (decompressing).

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

                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.

                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.

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

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

              When  standard  error  is not a terminal, --verbose will make xz
              print the filename, compressed size, uncompressed size, 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.

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

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

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

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

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

ROBOT MODE
       The robot mode is activated with the --robot option.  It makes the 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.

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

       XZ_VERSION=XYYYZZZS
       LIBLZMA_VERSION=XYYYZZZS

       X      Major version.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

EXIT STATUS
       0      All is good.

       1      An error occurred.

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

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

ENVIRONMENT
       xz parses space-separated lists of options from the  environment  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
       environment  variables;  all non-options are silently ignored.  Parsing
       is done with getopt_long(3) which is used also  for  the  command  line
       arguments.

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

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

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

              Scripts  may use XZ_OPT e.g. to set script-specific default 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:

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

LZMA UTILS COMPATIBILITY
       The command line syntax of  xz  is  practically  a  superset  of  lzma,
       unlzma,  and  lzcat as found from LZMA Utils 4.32.x.  In most cases, it
       is possible to replace LZMA Utils with XZ Utils without breaking exist-
       ing  scripts.  There are some incompatibilities though, which may some-
       times 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.


              tab(;);  c  c  c c n n.  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:


              tab(;); c c c c n n.  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
       uncompressed size.

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

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

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

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

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

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

NOTES
   Compressed output may vary
       The exact compressed output produced from the same  uncompressed  input
       file may vary between XZ Utils versions even if compression options are
       identical.  This is because the encoder can be improved (faster or 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-
       set.

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

              xz foo

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

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

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

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


              tab(;);  c  c n n.  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 uncom-
       pressed file is waste of memory, so the above command isn't useful  for
       small files.

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

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

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

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

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

              xz --x86 --lzma2 libfoo.so

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

       The  Delta filter together with LZMA2 can give good results with bitmap
       images.  It should usually beat PNG, which has a few more advanced 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.

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

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



Tukaani                           2014-12-16                             XZ(1)

You can also request any man page by name and (optionally) by section:

Command: 
Section: 
Architecture: 
Collection: 
 

Use the DEFAULT collection to view manual pages for third-party software.


©1994 Man-cgi 1.15, Panagiotis Christias <christia@softlab.ntua.gr>
©1996-2015 Modified for NetBSD by Kimmo Suominen