Provided by: xz-utils_5.2.5-2_amd64 bug

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 compressed  streams  with  no  container  format  headers  are  also
       supported.

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

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

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

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

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

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

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

       •  File has more than one hard link.

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

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

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

       After successfully compressing or decompressing the file,  xz  copies  the  owner,  group,
       permissions,  access  time, and modification time from the source file to the target file.
       If copying the group fails, the permissions are modified so that the target  file  doesn't
       become  accessible  to  users  who  didn't  have permission to access the source file.  xz
       doesn't support copying other metadata like access control lists  or  extended  attributes
       yet.

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

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

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

       Especially users of older systems may find the possibility  of  very  large  memory  usage
       annoying.   To  prevent  uncomfortable  surprises, xz has a built-in memory usage limiter,
       which is disabled by default.  While some operating systems  provide  ways  to  limit  the
       memory usage of processes, relying on it wasn't deemed to be flexible enough (for example,
       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, for example, XZ_DEFAULTS=--memlimit=150MiB.  It is possible  to  set
       the limits separately for compression and decompression by using --memlimit-compress=limit
       and --memlimit-decompress=limit.  Using these two options outside  XZ_DEFAULTS  is  rarely
       useful  because  a  single  run  of  xz  cannot  do both compression and decompression and
       --memlimit=limit (or -M limit) is shorter to type on the command line.

       If the specified memory usage limit is exceeded when decompressing,  xz  will  display  an
       error and decompressing the file will fail.  If the limit is exceeded when compressing, xz
       will try to scale the settings down so that the limit is no longer exceeded  (except  when
       using --format=raw or --no-adjust).  This way the operation won't fail unless the limit is
       very small.  The scaling of the settings is done in steps that don't match the compression
       level  presets,  for  example, if the limit is only slightly less than the amount required
       for xz -9, the settings will be scaled down only a little, not all the way down to xz -8.

   Concatenation and padding with .xz files
       It is possible to concatenate .xz files as is.  xz will decompress such files as  if  they
       were a single .xz file.

       It  is  possible  to insert padding between the concatenated parts or after the last part.
       The padding must consist of null bytes and the size of the padding must be a  multiple  of
       four  bytes.   This can be useful, for example, if the .xz file is stored on a medium that
       measures file sizes in 512-byte blocks.

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

OPTIONS

   Integer suffixes and special values
       In most places where an integer argument is expected, an optional suffix is  supported  to
       easily  indicate  large  integers.   There  must  be  no space between the integer and the
       suffix.

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

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

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

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

   Operation mode
       If multiple operation mode options are given, the last one takes effect.

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

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

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

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

              The default listing shows basic information about files, one file per line.  To get
              more   detailed  information,  use  also  the  --verbose  option.   For  even  more
              information, use --verbose twice, but note that this may be slow,  because  getting
              all the extra information requires many seeks.  The width of verbose output exceeds
              80 characters, so piping the output to, for example, 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.

              Since xz 5.4.0, this option also makes xz 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.  In earlier versions this was only done with --force.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Supported check types:

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

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

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

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

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

       --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.  Possible reasons to use
              this option:

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

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

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

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

              -0 ... -3
                     These are somewhat fast presets.  -0 is sometimes faster than gzip -9  while
                     compressing  much  better.   The  higher ones often have speed comparable to
                     bzip2(1) with comparable or better compression ratio, although  the  results
                     depend a lot on the type of data being 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 for distributing files that need to be decompressible even on systems
                     with only 16 MiB RAM.  (-5e or  -6e  may  be  worth  considering  too.   See
                     --extreme.)

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

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

              The following table summarises the features of the presets:

                     Preset   DictSize   CompCPU   CompMem   DecMem
                       -0     256 KiB       0        3 MiB    1 MiB
                       -1       1 MiB       1        9 MiB    2 MiB

                       -2       2 MiB       2       17 MiB    3 MiB
                       -3       4 MiB       3       32 MiB    5 MiB
                       -4       4 MiB       4       48 MiB    5 MiB
                       -5       8 MiB       5       94 MiB    9 MiB
                       -6       8 MiB       6       94 MiB    9 MiB
                       -7      16 MiB       6      186 MiB   17 MiB
                       -8      32 MiB       6      370 MiB   33 MiB
                       -9      64 MiB       6      674 MiB   65 MiB

              Column descriptions:

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

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

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

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

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

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

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

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

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

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

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

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

       --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 commas) is a shorthand to use the size of
              the previous block.

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

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

              In  multi-threaded  mode  the  sizes of the blocks are stored in the block headers.
              This isn't done in single-threaded mode, so the encoded output won't  be  identical
              to that of the multi-threaded 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 specified more  than  once,
              the  last  one  takes  effect.   The  special  timeout  value  of  0 can be used to
              explicitly disable this feature.

              This feature is not available on non-POSIX systems.

              This feature is still experimental.  Currently xz is unsuitable  for  decompressing
              the stream in real time due to how xz does 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 integer suffix  like  MiB
                 can be useful.  Example: --memlimit-compress=80MiB

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

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

              For  32-bit  xz  there  is a special case: if the limit would be over 4020 MiB, the
              limit is set to 4020 MiB.  (The values 0  and  max  aren't  affected  by  this.   A
              similar  feature  doesn't  exist  for  decompression.)   This can be helpful when a
              32-bit executable has access to 4 GiB address space while hopefully doing  no  harm
              in other situations.

              See also the section Memory usage.

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

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

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

       -T threads, --threads=threads
              Specify the number of worker threads to use.  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 overridden with the --block-size=size option.

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

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

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

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

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

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

       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 consist of  an  integer,
                     which may be followed by single-letter preset modifiers.  The integer can be
                     from 0 to 9, matching  the  command  line  options  -0  ...  -9.   The  only
                     supported modifier is currently e, which matches --extreme.  If no preset is
                     specified, the default values of LZMA1 or LZMA2 options are taken  from  the
                     preset 6.

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

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

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

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

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

                     The  literal  coding  makes  an  assumption  that the highest lc bits of the
                     previous uncompressed byte correlate with the next byte.   For  example,  in
                     typical English text, an upper-case letter is often followed by a lower-case
                     letter, and a lower-case letter is usually followed  by  another  lower-case
                     letter.   In  the US-ASCII character set, the highest three bits are 010 for
                     upper-case letters and 011 for lower-case letters.  When lc is at  least  3,
                     the  literal  coding can take advantage of this property in the uncompressed
                     data.

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

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

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

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

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

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

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

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

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

              mode=mode
                     Compression  mode  specifies  the method to analyze the data produced by the
                     match finder.  Supported modes are fast and normal.  The default is fast for
                     presets 0-3 and normal for presets 4-9.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Different instruction sets have different alignment:

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

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

              All BCJ filters support the same options:

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

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

              Currently  only  simple byte-wise delta calculation is supported.  It can be useful
              when compressing, for example,  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, for example, with flac(1).

              Supported options:

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

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

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

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

              The progress indicator shows the following information:

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

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

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

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

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

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

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

              When standard error is not a terminal, --verbose will make xz print  the  filename,
              compressed  size, uncompressed size, compression ratio, and possibly also the speed
              and elapsed  time  on  a  single  line  to  standard  error  after  compressing  or
              decompressing  the  file.   The  speed  and elapsed time are included only when the
              operation took at least a  few  seconds.   If  the  operation  didn't  finish,  for
              example, due to user interruption, also the completion percentage is printed if the
              size of the input file is known.

       -Q, --no-warn
              Don't set the exit status to 2 even if a condition worth a  warning  was  detected.
              This  option  doesn't  affect  the verbosity level, thus both --quiet and --no-warn
              have to be used to not display warnings and to not alter the exit status.

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

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

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

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

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

ROBOT MODE

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

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

       XZ_VERSION=XYYYZZZS
       LIBLZMA_VERSION=XYYYZZZS

       X      Major version.

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

       ZZZ    Patch level for stable releases or just a counter for development releases.

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

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

       Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

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

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

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

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

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

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

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

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

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

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

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

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

       The columns of the file lines:
              2.  Number of streams in the file
              3.  Total number of blocks in the stream(s)
              4.  Compressed size of the file
              5.  Uncompressed size of the file
              6.  Compression ratio, for example, 0.123.  If ratio is over  9.999,  three  dashes
                  (---) are displayed instead of the ratio.
              7.  Comma-separated  list of integrity check names.  The following strings are used
                  for the known check types: None, CRC32, CRC64, and SHA-256.  For unknown  check
                  types,  Unknown-N  is used, where N is the Check ID as a decimal number (one or
                  two digits).
              8.  Total size of stream padding in the file

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

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

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

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

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

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

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

EXIT STATUS

       0      All is good.

       1      An error occurred.

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

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

ENVIRONMENT

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

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

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

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

              Scripts  may  use  XZ_OPT,  for example, to set script-specific default compression
              options.  It is still recommended to allow users to  override  XZ_OPT  if  that  is
              reasonable.  For example, in sh(1) scripts one may use something like this:

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

LZMA UTILS COMPATIBILITY

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

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

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

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

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

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

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

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

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

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

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

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

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

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

NOTES

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

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

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

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

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

EXAMPLES

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

              xz foo

       Decompress bar.xz into bar and don't remove bar.xz even if decompression is successful:

              xz -dk bar.xz

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              Preset   CompCPU
               -0         0
               -1         1
               -2         2
               -3         3
               -4         4
               -5         5
               -6         6
               -5e        7
               -6e        8

       If you know that a file requires somewhat big dictionary (for example, 32 MiB) to compress
       well, but you want to compress it quicker than xz -8 would do, a preset with a low CompCPU
       value (for example, 1) can be modified to use a bigger dictionary:

              xz --lzma2=preset=1,dict=32MiB foo.tar

       With  certain  files,  the  above  command  may  be  faster  than  xz -6 while compressing
       significantly better.  However, it must be emphasized that only some files benefit from  a
       big  dictionary  while keeping the CompCPU value low.  The most obvious situation, where a
       big dictionary can help a lot, is an archive containing very similar files of at  least  a
       few  megabytes  each.   The  dictionary  size  has  to  be  significantly  bigger than any
       individual file to allow  LZMA2  to  take  full  advantage  of  the  similarities  between
       consecutive files.

       If  very  high  compressor  and  decompressor  memory  usage  is  fine, and the file being
       compressed is at least several hundred megabytes, it may be useful to use an  even  bigger
       dictionary than the 64 MiB that xz -9 would use:

              xz -vv --lzma2=dict=192MiB big_foo.tar

       Using  -vv (--verbose --verbose) like in the above example can be useful to see the memory
       requirements of the compressor and decompressor.  Remember that using a dictionary  bigger
       than  the  size  of  the  uncompressed file is waste of memory, so the above command isn't
       useful for small files.

       Sometimes the compression time doesn't matter, but the decompressor memory usage has to be
       kept  low,  for example, 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.  For example, 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.
       For example, to compress a x86-32 or x86-64 shared library using the x86 BCJ filter:

              xz --x86 --lzma2 libfoo.so

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

       The Delta filter together with LZMA2 can give good results with bitmap images.  It  should
       usually beat PNG, which has a few more advanced filters than simple delta but uses Deflate
       for the actual compression.

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