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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.

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

	      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
	      overridden with the --block-size=size option.

	      Threaded	decompression  hasn't  been  implemented yet.  It will
	      only work	on files that contain multiple blocks with size	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 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				  2020-02-01				 XZ(1)


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