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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

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

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

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

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

      +  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 applies:



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



      +  File is not a regular file.  Symbolic links are not followed, and
         thus they are not considered to be regular 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
      permissions are modified so that the target file doesn't become
      accessible to users who didn't have permission to access the source
      file.  xz doesn't support copying other metadata like access control
      lists or extended attributes yet.

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

    Memory usage
      The memory usage of xz varies from a few hundred kilobytes to several
      gigabytes depending on the compression settings.  The settings used
      when compressing a file determine the 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 flexible enough (e.g.
      using ulimit(1) to limit virtual memory tends to cripple mmap(2)).



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



      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
      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 compression level presets, e.g. if the
      limit is only slightly less than the amount required for xz -9, the
      settings will be scaled down only a little, not all the way down to xz
      -8.

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

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

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

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




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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



      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).

      -d, --decompress, --uncompress
           Decompress.

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

      -l, --list
           Print information about compressed files.  No uncompressed output
           is produced, and no files are created or removed.  In list mode,
           the program cannot read the 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
           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.




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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



           +  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.

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

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

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

      --no-sparse
           Disable creation of sparse files.  By default, if decompressing
           into a regular file, xz tries to make the file sparse if the
           decompressed data contains long sequences of binary zeros.  It
           also works when writing to standard output as long as standard
           output is connected to a regular file and certain additional
           conditions are met to make it safe.  Creating sparse files may
           save disk space and speed up the decompression by reducing the
           amount of disk I/O.

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



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



           the target filename.

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

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

      --files0[=file]
           This is identical to --files[=file] except that each filename
           must be terminated with the null character.

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

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

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

           Supported check types:



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

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

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

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

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

      --ignore-check
           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.

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

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



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

           -4 ... -6
                Good to very good compression while keeping decompressor
                memory usage 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
                considering too.  See --extreme.)

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

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

           The following table summarises the features of the presets:

                tab(;); c c c c c n n n n n.
                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



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



              slower and thus possibly better compression, see --extreme.

           +  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 MiB.

      -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.  Decompressor
           memory usage is not affected, but compressor memory usage
           increases a little at preset levels -0 ... -3.

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

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

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

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

      --block-size=size
           When compressing to the .xz format, split the input data into
           blocks of size bytes.  The blocks are compressed independently
           from each other, 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-



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



           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
           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.

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

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

           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.

      --flush-timeout=timeout



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 XZ Utils                                                           XZ Utils

                                 2015-05-11



           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 specified
           more than once, the last one takes effect.  The special timeout
           value of 0 can be used to explicitly disable this feature.

           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
           buffering.

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

           If the compression settings exceed the limit, xz will adjust the
           settings downwards so that the limit is no longer exceeded and
           display a notice that automatic 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.  Example:
              --memlimit-compress=80MiB

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

           +  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.



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 XZ(1)                             Tukaani                             XZ(1)
 XZ Utils                                                           XZ Utils

                                 2015-05-11



           See also the section Memory usage.

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

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

      --no-adjust
           Display an error and exit if the compression settings exceed the
           memory usage limit.  The default is to adjust the settings
           downwards so that the memory usage limit is not exceeded.
           Automatic adjusting is always disabled when creating raw streams
           (--format=raw).

      -T threads, --threads=threads
           Specify the number of worker threads to use.  Setting threads to
           a special value 0 makes xz use as many threads as there are CPU
           cores on the system.  The actual 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
      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



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 XZ Utils                                                           XZ Utils

                                 2015-05-11



      compressing, 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 filters.

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

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

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

      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.

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

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

           LZMA1 and LZMA2 share the same set of options:

           preset=preset
                Reset all LZMA1 or LZMA2 options to preset.  Preset consist
                of an integer, which may be followed by single-letter preset
                modifiers.  The integer can be from 0 to 9, matching the
                command line options -0 ... -9.  The only 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.




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 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

                Typical dictionary size is from 64 KiB to 64 MiB.  The
                minimum is 4 KiB.  The maximum for compression is currently
                1.5 GiB (1536 MiB).  The 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 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 uncompressed data.

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



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                                 2015-05-11



                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 having
                one-byte alignment (US-ASCII, ISO-8859-*, UTF-8), setting
                pb=0 can improve compression slightly.  For UTF-16 text,
                pb=1 is a good choice.  If the alignment is an odd number
                like 3 bytes, pb=0 might be the best choice.

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

           mf=mf
                Match finder has a major effect on encoder speed, memory
                usage, and 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)




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                                 2015-05-11



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

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

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

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

           mode=mode
                Compression mode specifies the method to analyze the data
                produced by the match finder.  Supported modes are fast and
                normal.  The default is fast for presets 0-3 and normal for
                presets 4-9.

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

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

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

                Reasonable depth for Hash Chains is 4-100 and 16-1000 for
                Binary Trees.  Using very high values for depth can make the
                encoder extremely slow with some files.  Avoid setting the



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                                 2015-05-11



                depth over 1000 unless you are prepared to interrupt the
                compression in case it is taking far too long.

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

      --x86[=options]
      --powerpc[=options]
      --ia64[=options]
      --arm[=options]
      --armthumb[=options]
      --sparc[=options]
           Add a branch/call/jump (BCJ) filter to the filter chain.  These
           filters can be used only as a non-last filter in the filter
           chain.

           A BCJ filter converts relative addresses in the machine code to
           their absolute counterparts.  This doesn't change the size of the
           data, but it increases 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
           generally isn't good to blindly apply a BCJ filter when
           compressing binary packages for distribution.

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

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

           +  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.

           +  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



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                                 2015-05-11



              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:

                tab(;); l n l l n l.  Filter;Alignment;Notes x86;1;32-bit or
                64-bit x86 PowerPC;4;Big endian only ARM;4;Little endian
                only ARM-Thumb;2;Little endian only IA-64;16;Big or little
                endian SPARC;4;Big or little endian

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

           All BCJ filters support the same options:

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

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

           Currently only simple byte-wise delta calculation is supported.
           It can be useful when compressing e.g. uncompressed bitmap images
           or uncompressed PCM audio.  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:

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



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                                 2015-05-11



                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.  Specifying --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 cannot 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 since xz started processing the file.

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

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

           When standard error is not a terminal, --verbose will make xz
           print the filename, compressed size, uncompressed size,
           compression ratio, and possibly also the speed and elapsed time
           on a single line to standard error after compressing or
           decompressing the file.  The speed and elapsed time are included
           only when the operation took at least a few seconds.  If the



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                                 2015-05-11



           operation didn't finish, e.g. due to user interruption, also the
           completion percentage is printed if the size of the input file is
           known.

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

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

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

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

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

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

      XZ_VERSION=XYYYZZZS
      LIBLZMA_VERSION=XYYYZZZS

      X    Major version.



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 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

      ZZZ  Patch level for stable releases or just a counter for development
           releases.

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

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

      Examples: 4.999.9beta is 49990091 and 5.0.0 is 50000002.

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

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

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

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

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

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

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

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

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

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



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                                 2015-05-11



           block lines are shown after all the stream lines; different line
           types are not interleaved.

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



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                                 2015-05-11



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

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




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                                 2015-05-11



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

 EXIT STATUS
      0    All is good.

      1    An error occurred.

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

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

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

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

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

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

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

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

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



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                                 2015-05-11



      sometimes cause problems.

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

           tab(;); c c c c n n.  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:

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

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

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

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

    Unsupported .lzma files
      The .lzma format allows lc values up to 8, and lp values up to 4.
      LZMA Utils can 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



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      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 files.

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

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

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

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



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 XZ Utils                                                           XZ Utils

                                 2015-05-11



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

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

           xz foo

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

           xz -dk bar.xz

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

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

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

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

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

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

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




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      A script may want to know that it is using new enough xz.  The
      following sh(1) script checks that the version number of the xz tool
      is at least 5.0.0.  This method is 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."
           fi
           unset XZ_VERSION LIBLZMA_VERSION

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

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

    Custom compressor filter chains
      The simplest use for custom filter chains is customizing a LZMA2
      preset.  This can be 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:

           tab(;); c c n n.  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.




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                                 2015-05-11



      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 uncompressed 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 libfoo.so

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

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

      The image has to be saved in uncompressed format, e.g. as uncompressed
      TIFF.  The distance parameter of the Delta filter is set to match the



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                                 2015-05-11



      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.

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

      XZ Utils: <http://tukaani.org/xz/>
      XZ Embedded: <http://tukaani.org/xz/embedded.html>
      LZMA SDK: <http://7-zip.org/sdk.html>



































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