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XZ(1)					     XZ Utils					    XZ(1)

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

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

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

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

DESCRIPTION
       xz is a general-purpose data compression tool with command line syntax similar to  gzip(1)
       and  bzip2(1).  The native file format is the .xz format, but the legacy .lzma format used
       by LZMA Utils and raw compressed streams with no container format headers  are  also  sup-
       ported.

       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 com-
       pressed data to standard output if it is a terminal.  Similarly, xz will  refuse  to  read
       compressed data from standard input if it is a terminal.

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

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

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

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

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

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

       o  File has more than one hard link.

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

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

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

       After successfully compressing or decompressing the file, xz copies the owner, group, per-
       missions,  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  stan-
       dard output.

       Sending	SIGINFO or SIGUSR1 to the xz process makes it print progress information to stan-
       dard 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 mem-
       ory 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,  decom-
       pressing a file created with xz -9 currently requires 65 MiB of memory.	Still, it is pos-
       sible 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 mem-
       ory  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  lim-
       its  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 --mem-
       limit=limit (or -M limit) is shorter to type on the command line.

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

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

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

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

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

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

       MiB    Multiply	the  integer  by 1,048,576 (2^20).  Mi, m, M, and MB are accepted as syn-
	      onyms 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 exam-
	      ple, 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 com-
	      pressed 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 informa-
	      tion, 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:

	      o  If the target file already exists, delete it before compressing  or  decompress-
		 ing.

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

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

	      lzma, alone
		     Compress  to  the	legacy .lzma file format, or accept only .lzma files when
		     decompressing.  The alternative name alone is provided for backwards compat-
		     ibility 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  uncom-
	      pressed  data and stored in the .xz file.  This option has an effect only when com-
	      pressing into the .xz format; the .lzma format doesn't  support  integrity  checks.
	      The integrity check (if any) is verified when the .xz file is decompressed.

	      Supported check types:

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

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

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

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

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

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

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

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

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

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

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

	      The following table summarises the features of the presets:

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

	      Column descriptions:

	      o  DictSize  is  the LZMA2 dictionary size.  It is waste of memory to use a dictio-
		 nary 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.

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

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

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

       -e, --extreme
	      Use  a slower variant of the selected compression preset level (-0 ... -9) to hope-
	      fully 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, respec-
	      tively.  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 pro-
	      vided 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.

       --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.  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.

	      Currently  this  option  is badly broken if used together with --block-size or with
	      multithreading.

       --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 adjust-
	      ment was done.  Such adjustments are not made when compressing with --format=raw or
	      if --no-adjust has been specified.  In those cases, an error is  displayed  and  xz
	      will exit with exit status 1.

	      The limit can be specified in multiple ways:

	      o  The  limit  can be an absolute value in bytes.  Using an integer suffix like MiB
		 can be useful.  Example: --memlimit-compress=80MiB

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

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

	      See also the section Memory usage.

       --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, (old alias --memory=limit)
	      This   is  equivalent  to  specifying  --memlimit-compress=limit	--memlimit-decom-
	      press=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 num-
	      ber  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 compres-
	      sion level and can be overriden with the --block-size=size option.

	      It  is  possible	that  the details of this option change before the next stable XZ
	      Utils release.  This may include the meaning of the special value 0.

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

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

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

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

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

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

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

	      LZMA1 and LZMA2 share the same set of options:

	      preset=preset
		     Reset  all  LZMA1 or LZMA2 options to preset.  Preset consist of an integer,
		     which may be followed by single-letter preset modifiers.  The integer can be
		     from  0  to  9,  matching the command line options -0 ... -9.  The only sup-
		     ported modifier is currently e, which matches --extreme.  The default preset
		     is  6,  from  which  the  default	values for the rest of the LZMA1 or LZMA2
		     options are taken.

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

		     Typical dictionary size is from 64 KiB to 64 MiB.	 The  minimum  is  4 KiB.
		     The maximum for compression is currently 1.5 GiB (1536 MiB).  The decompres-
		     sor 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  com-
		     pressing.	 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 maxi-
		     mum 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  pre-
		     vious  uncompressed byte correlate with the next byte.  E.g. in typical Eng-
		     lish text, an upper-case letter is often followed by  a  lower-case  letter,
		     and  a  lower-case  letter is usually followed by another lower-case letter.
		     In the US-ASCII character set, the highest three bits are 010 for upper-case
		     letters  and 011 for lower-case letters.  When lc is at least 3, the literal
		     coding can take advantage of this property in the uncompressed data.

		     The default value (3) is usually good.  If  you  want  maximum  compression,
		     test  lc=4.  Sometimes it helps a little, and sometimes it makes compression
		     worse.  If it makes it worse, test e.g. lc=2 too.

	      lp=lp  Specify the number of literal position bits.  The minimum is 0 and the maxi-
		     mum is 4; the default is 0.

		     Lp  affects  what kind of alignment in the uncompressed data is assumed when
		     encoding literals.  See pb below for more information about alignment.

	      pb=pb  Specify the number of position bits.  The minimum is 0 and the maximum is 4;
		     the default is 2.

		     Pb  affects  what	kind  of alignment in the uncompressed data is assumed in
		     general.  The default means four-byte alignment (2^pb=2^2=4), which is often
		     a good choice when there's no better guess.

		     When  the aligment is known, setting pb accordingly may reduce the file size
		     a little.	 E.g.  with  text  files  having  one-byte  alignment  (US-ASCII,
		     ISO-8859-*,  UTF-8),  setting  pb=0  can  improve compression slightly.  For
		     UTF-16 text, pb=1 is a good choice.  If the alignment is an odd number  like
		     3 bytes, pb=0 might be the best choice.

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

	      mf=mf  Match finder has a major effect on encoder speed, memory usage, and compres-
		     sion  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 bet-
		     ter 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 redun-
	      dancy, 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:

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

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

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

	      Different instruction sets have have different alignment:

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

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

	      All BCJ filters support the same options:

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

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

	      Currently  only  simple byte-wise delta calculation is supported.  It can be useful
	      when compressing e.g. uncompressed bitmap images or uncompressed PCM  audio.   How-
	      ever, 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  sup-
	      pressed, the exit status to indicate a warning is still used.

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

	      The progress indicator shows the following information:

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

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

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

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

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

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

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

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

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

       --robot
	      Print  messages  in  a  machine-parsable	format.  This is intended to ease writing
	      frontends that want to use xz instead of liblzma, which may be the case with  vari-
	      ous  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 success-
	      fully.

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

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

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

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

       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 over-
	      all 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 ver-
		  sion
	      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  ver-
		  sion
	      3.  yes  or no indicating if all block headers have both compressed size and uncom-
		  pressed 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  uncom-
		  pressed size stored in them
	      Since xz 5.1.2alpha:
	      12. Minimum xz version required to decompress the file

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

EXIT STATUS
       0      All is good.

       1      An error occurred.

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

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

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

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

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

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

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

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

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

   Compression preset levels
       The numbering of the compression level presets is not identical in xz and LZMA Utils.  The
       most important difference is how dictionary sizes are mapped to different  presets.   Dic-
       tionary 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  decom-
       press  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 detect-
       ing .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 decom-
       pressing 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 differ-
       ent build options are used.

       The above means that implementing --rsyncable to create rsyncable .xz files is  not  going
       to  happen  without  freezing a part of the encoder implementation, which can then be used
       with --rsyncable.

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

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

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

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

	      xz foo

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

	      xz -dk bar.xz

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

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

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

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

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

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

       The -P option to xargs(1) sets the number of parallel xz processes.  The  best  value  for
       the  -n	option depends on how many files there are to be compressed.  If there are only a
       couple of files, the value should probably be 1; with tens of thousands of files,  100  or
       even more may be appropriate to reduce the number of xz processes that xargs(1) will even-
       tually 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  compati-
       ble 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 use-
       ful,  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 col-
       lected from those two tables:

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

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

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

       With certain files, the above command may be faster than xz -6 while compressing  signifi-
       cantly  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 com-
       pressed is at least several hundred megabytes, it may be useful to use an even bigger dic-
       tionary 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 use-
       ful 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 fol-
       lowing 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 con-
       text  bits (lc) and number of position bits (pb) can sometimes help.  Adjusting the number
       of literal position bits (lp) might help too, but usually lc and pb  are  more  important.
       E.g.  a source code archive contains mostly US-ASCII text, so something like the following
       might give slightly (like 0.1 %) smaller file than xz -6e (try also without lc=4):

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

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

	      xz --x86 --lzma2 libfoo.so

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

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

       The image has to be saved in uncompressed format, e.g. as uncompressed TIFF.  The distance
       parameter of the Delta filter is set to match the number of bytes per pixel in the  image.
       E.g. 24-bit RGB bitmap needs dist=3, and it is also good to pass pb=0 to LZMA2 to accommo-
       date 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 				    2012-07-03					    XZ(1)
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