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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 appropri‐
       ate 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 compressed
       streams with no container format headers are also supported.

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

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

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

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

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

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

       ·  File  is not a regular file.  Symbolic links are not followed, and thus they are not considered to be regu‐
          lar files.

       ·  File has more than one hard link.

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

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

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

       After successfully compressing or decompressing the file, xz copies  the  owner,  group,  permissions,  access
       time,  and modification time from the source file to the target file.  If copying the group fails, the permis‐
       sions are modified so that the target file doesn't become accessible to users who didn't  have  permission  to
       settings.  The settings used when compressing a file determine the memory requirements  of  the  decompressor.
       Typically  the decompressor needs 5 % to 20 % of the amount of memory that the compressor needed when creating
       the file.  For example, decompressing a file created with xz -9 currently requires 65 MiB of  memory.   Still,
       it is possible to have .xz files that require several gigabytes of memory to decompress.

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

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

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

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

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

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

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

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

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

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

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

              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 used.

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

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

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

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

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

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

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

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

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

              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  addi‐
              tional  conditions are met to make it safe.  Creating sparse files may save disk space and speed up the
              decompression by reducing the amount of disk I/O.

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

              When decompressing, recognize files with the suffix .suf in addition  to  files  with  the  .xz,  .txz,

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

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

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

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

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

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

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

              Supported check types:

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

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

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

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

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

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

              Do not use this option unless you know what you are doing.  Possible reasons to use this option:

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

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

                     These are somewhat fast presets.  -0 is sometimes faster than gzip  -9  while  compressing  much
                     better.   The higher ones often have speed comparable to bzip2(1) with comparable or better com‐
                     pression 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 distributing files that
                     need to be decompressible even on systems with only 16 MiB RAM.  (-5e or -6e may be  worth  con‐
                     sidering too.  See --extreme.)

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

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

              The following table summarises the features of the presets:

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

              Column descriptions:

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

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

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

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

       -e, --extreme

                      -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, respectively.  These are provided only for back‐
              wards 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 limited random-
              access decompression possible.  This option is typically used to override the  default  block  size  in
              multi-threaded mode, but this option can be used in single-threaded mode too.

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

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

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

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

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

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

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

              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

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

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

              The limit can be specified in multiple ways:

              ·  The limit can be an absolute value in bytes.  Using an integer suffix like MiB can be useful.  Exam‐
                 ple: --memlimit-compress=80MiB

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

              ·  The  limit  can be reset back to its default value by setting it to 0.  This is currently equivalent
                 to setting the limit to max (no memory usage limit).  Once multithreading support  has  been  imple‐
                 mented, 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, (old alias --memory=limit)
              This is equivalent to specifying --memlimit-compress=limit --memlimit-decompress=limit.

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

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

              Currently  the  only threading method is to split the input into blocks and compress them independently
              from each other.  The default block size depends on the compression level and can be 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 information in block headers.  All files compressed in multi-threaded mode  meet  this
              condition, but files compressed in single-threaded mode don't even if --block-size=size is used.

   Custom compressor filter chains

       filter in the chain, some only as a non-last filter, and some work in any position in the chain.  Depending on
       the filter, this limitation is either inherent to the filter design or exists to prevent security issues.

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

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

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

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

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

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

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

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

                     All bytes that cannot be encoded as matches are encoded as literals.  That is, literals are sim‐

              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

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

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

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

                     The following match finders are supported.  The memory usage formulas below are rough approxima‐
                     tions, 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:

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

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

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

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

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

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

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

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

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

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

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

              ·  Applying a BCJ filter on an archive containing multiple similar executables can make the compression
                 ratio worse than not using a BCJ filter.  This is because the BCJ filter doesn't detect  the  bound‐
                 aries 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  mem‐
              Since  the  BCJ-filtered  data  is usually compressed with LZMA2, the compression ratio may be improved
              slightly if the LZMA2 options are set to match the alignment of the selected BCJ filter.  For  example,
              with the IA-64 filter, it's good to set pb=4 with LZMA2 (2^4=16).  The x86 filter is an exception; it's
              usually good to stick to LZMA2's default four-byte alignment when compressing x86 executables.

              All BCJ filters support the same options:

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

              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

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

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

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

              The progress indicator shows the following information:

              ·  Completion percentage is shown if the size of the input file is known.  That is, the percentage can‐
                 not be shown in pipes.

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

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

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

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

              interruption, also the completion percentage is printed if the size of the input file is known.

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

              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 mem‐
              ory usage limits for compression and decompression, and exit successfully.

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

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

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

       The  robot mode is activated with the --robot option.  It makes the output of xz easier to parse by other pro‐
       grams.  Currently --robot is supported 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 development releases.

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

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

       Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

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

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

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

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

       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 file.

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

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

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

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

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

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

       If --verbose was specified twice, additional columns are included on the totals line:
              10. Maximum amount of memory (in bytes) required to decompress the files with this xz version
              11. yes or no indicating if all block headers have both compressed size and uncompressed size stored in
              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 exist‐
       ing columns won't be changed.

       0      All is good.

       1      An error occurred.

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

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

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

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

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

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

              Scripts may use XZ_OPT e.g. to set script-specific default compression options.   It  is  still  recom‐

       The numbering of the compression level presets is not identical in xz and LZMA Utils.  The most important dif‐
       ference  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

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

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

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

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

       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 better com‐
       pression) without affecting the file format.  The output can vary even between different builds of the same XZ
       Utils version, if different build options are used.

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

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

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

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

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

              xz foo

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

              xz -dk bar.xz

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

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

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

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

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

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

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

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

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

              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 preset.  This can be useful, because the pre‐
       sets 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  com‐
       press it quicker than xz -8 would do, a preset with a low CompCPU value (e.g. 1) can be modified to use a big‐
       ger 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.   How‐
       ever, 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 individ‐
       ual 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  sev‐
       eral  hundred  megabytes,  it  may be useful to use an even bigger dictionary than the 64 MiB that xz -9 would

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

       Using -vv (--verbose --verbose) like in the above example can be useful to see the memory requirements of  the
       compressor  and  decompressor.  Remember that using a dictionary bigger than the size of the uncompressed file
       so something like the following might give slightly (like 0.1 %) smaller file than xz -6e  (try  also  without

              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 filters than simple delta but uses Deflate for the actual compression.

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