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XZ(1)				   XZ Utils				 XZ(1)

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

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

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

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

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

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

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

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

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

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

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

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

       o  File has more	than one hard link.

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

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

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

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

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

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

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

       Especially  users  of  older  systems  may find the possibility of very
       large memory usage annoying.  To	prevent	 uncomfortable	surprises,  xz
       has  a  built-in	 memory	 usage	limiter, which is disabled by default.
       While some operating systems provide ways to limit the memory usage  of
       processes,  relying on it wasn't	deemed to be flexible enough (e.g. us-
       ing ulimit(1) to	limit virtual memory tends to cripple mmap(2)).

       The memory usage	limiter	can be enabled with the	 command  line	option
       --memlimit=limit.  Often	it is more convenient to enable	the limiter by
       default by setting the environment variable  XZ_DEFAULTS,  e.g.	XZ_DE-
       FAULTS=--memlimit=150MiB.   It is possible to set the limits separately
       for compression and decompression  by  using  --memlimit-compress=limit
       and  --memlimit-decompress=limit.   Using  these	 two  options  outside
       XZ_DEFAULTS is rarely useful because a single run of xz cannot do  both
       compression  and	 decompression	and  --memlimit=limit (or -M limit) is
       shorter to type on the command line.

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

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

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

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

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

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

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

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

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

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

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

       -d, --decompress, --uncompress

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      Supported	check types:

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

	      crc32  Calculate CRC32  using  the  polynomial  from  IEEE-802.3

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

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

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

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

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

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

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

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

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

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

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

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

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

	      The following table summarises the features of the presets:

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

	      Column descriptions:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      This feature is not available on non-POSIX systems.

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

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

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

	      The limit	can be specified in multiple ways:

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

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

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

	      See also the section Memory usage.

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

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

	      Display an error and exit	if the compression settings exceed the
	      memory usage limit.  The default is to adjust the	settings down-
	      wards so that the	memory usage limit is not exceeded.  Automatic
	      adjusting	 is  always disabled when creating raw streams (--for-

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

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

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

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

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

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

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

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

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

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

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

	      LZMA1 and	LZMA2 share the	same set of options:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      These BCJ	filters	have known problems related to the compression

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

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

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

	      Different	instruction sets have have different alignment:

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

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

	      All BCJ filters support the same options:

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

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

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

	      Supported	options:

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

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

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

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

	      The progress indicator shows the following information:

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

	      o	 Amount	of compressed data produced (compressing) or  consumed

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

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

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

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

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

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

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

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

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

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

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

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

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

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


       X      Major version.

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

       ZZZ    Patch level for stable releases or just a	counter	 for  develop-
	      ment releases.

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

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

       Examples: 4.999.9beta is	49990091 and 5.0.0 is 50000002.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       0      All is good.

       1      An error occurred.

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

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

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

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

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

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

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

		     export XZ_OPT

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      xz foo

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

	      xz -dk bar.xz

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	      Preset   CompCPU
	       -0	  0
	       -1	  1

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

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

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

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

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

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

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

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

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

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

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

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

	      xz --x86 --lzma2

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

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

       The image has to	be saved in uncompressed format, e.g. as  uncompressed
       TIFF.   The  distance parameter of the Delta filter is set to match the
       number of bytes per pixel in the	image.	E.g. 24-bit RGB	 bitmap	 needs
       dist=3,	and  it	 is also good to pass pb=0 to LZMA2 to accommodate the
       three-byte alignment:

	      xz --delta=dist=3	--lzma2=pb=0 foo.tiff

       If multiple images have been put	into a single archive (e.g. .tar), the
       Delta  filter will work on that too as long as all images have the same
       number of bytes per pixel.

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

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

Tukaani				  2017-04-19				 XZ(1)


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