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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
       extended	attributes yet.

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

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

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

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

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

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

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

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

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

   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

       -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
	      locales.	 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
	      instead 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
	      decompressed data	contains long sequences	of binary  zeros.   It
	      also  works  when	writing	to standard output as long as standard
	      output is	connected to a regular	file  and  certain  additional
	      conditions  are  met to make it safe.  Creating sparse files may
	      save disk	space and speed	up the decompression by	 reducing  the
	      amount of	disk I/O.

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

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

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

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

	      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
	      decompressing.  The CRC32	values in the .xz headers  will	 still
	      be verified normally.

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

	      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
	      using  a	too  high preset level might make it painful to	decom-
	      press the	file on	an old system with little RAM.	 Specifically,
	      it's  not	 a  good idea to blindly use -9	for everything like it
	      often is with gzip(1) and	bzip2(1).

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

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

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

	      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
		 usage 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
	      ratio, but with bad luck this can	also make  it  worse.	Decom-
	      pressor  memory  usage  is  not  affected, but compressor	memory
	      usage increases a	little at preset levels	-0 ... -3.

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

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

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

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

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

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

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

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

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

	      The limit	can be specified in multiple ways:

	      o	 The limit can be an absolute value in bytes.  Using an	 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
	      exceeding	the limit, xz will display an error and	 decompressing
	      the  file	will fail.  See	--memlimit-compress=limit for possible
	      ways to specify the limit.

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

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

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

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

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

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

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

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

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

	      LZMA1 and	LZMA2 share the	same set of options:

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

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

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

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

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

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

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

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

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

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

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

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

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

		     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
		     default 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
		     interrupt	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
	      reversible, so using a BCJ filter	for wrong type of data doesn't
	      cause any	data loss, although it may make	the compression	 ratio
	      slightly worse.

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

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

	      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
	      options  are set to match	the alignment of the selected BCJ fil-
	      ter.  For	example, with the IA-64	filter,	it's good to set  pb=4
	      with  LZMA2 (2^4=16).  The x86 filter is an exception; it's usu-
	      ally good	to stick to LZMA2's default four-byte  alignment  when
	      compressing x86 executables.

	      All BCJ filters support the same options:

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

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

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

	      Supported	options:

		     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
	      liblzma, which may be the	case with various scripts.  The	output
	      with this	option	enabled	 is  meant  to	be  stable  across  xz
	      releases.	 See the section ROBOT MODE for	details.

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

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

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

       -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
	      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,
       because 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
		  excludes the block header, block padding, and	check fields)
	      15. Amount of memory (in	bytes)	required  to  decompress  this
		  block	with this xz version
	      16. Filter  chain.   Note	 that most of the options used at com-
		  pression time	cannot be known, because only the options that
		  are  needed for decompression	are stored in the .xz headers.

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

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

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

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

       0      All is good.

       1      An error occurred.

       2      Something	 worth	a  warning  occurred,  but  no	actual	errors

       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
       environment  variables;	all non-options	are silently ignored.  Parsing
       is done with getopt_long(3) which is used also  for  the	 command  line

	      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_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,
       unlzma,	and  lzcat as found from LZMA Utils 4.32.x.  In	most cases, it
       is possible to replace LZMA Utils with XZ Utils without breaking	exist-
       ing  scripts.  There are	some incompatibilities though, which may some-
       times cause problems.

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

	      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
       uncompressed size.

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

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

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

       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
       obscure 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
       decompression (48 MiB and 5 MiB,	respectively):

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

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

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

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

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

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

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

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

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

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

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

       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.
       Remember	that using a dictionary	bigger than the	 size  of  the	uncom-
       pressed	file is	waste of memory, so the	above command isn't useful for
       small files.

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

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

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

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

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

	      xz --x86 --lzma2

       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				  2015-05-11				 XZ(1)


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