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xz(1)                              XZ Utils                              xz(1)


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


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


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

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


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

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

       o  When decompressing, the .xz, .lzma, or .lz 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:

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

       o  File has more than one hard link.

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

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

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

       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 or if an error occurs.

       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 (for
       example, using ulimit(1) to limit virtual memory tends to cripple

       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, for example,
       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, for example, 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

   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, for example, if the .xz file is stored on a medium that
       measures file sizes in 512-byte blocks.

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


   Integer suffixes and special values
       In most places where an integer argument is expected, an optional
       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

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

       -d, --decompress, --uncompress

       -t, --test
              Test the integrity of compressed files.  This option is
              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, for
              example, less -S may be convenient if the terminal isn't wide

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

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

              Since xz 5.2.6, this option also makes xz 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.  In earlier versions this was only done with

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

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

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

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

       -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 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, .tlz, or .lz
              suffix.  If the source file has the suffix .suf, the suffix is
              removed to get the target filename.

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

              Read the filenames to process from file; if file is omitted,
              filenames are read from standard input.  Filenames must be
              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.

              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-

              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

              lzip   Accept only .lz files when decompressing.  Compression is
                     not supported.

                     The .lz format version 0 and the unextended version 1 are
                     supported.  Version 0 files were produced by lzip 1.3 and
                     older.  Such files aren't common but may be found from
                     file archives as a few source packages were released in
                     this format.  People might have old personal files in
                     this format too.  Decompression support for the format
                     version 0 was removed in lzip 1.18.

                     lzip 1.4 and later create files in the format version 1.
                     The sync flush marker extension to the format version 1
                     was added in lzip 1.6.  This extension is rarely used and
                     isn't supported by xz (diagnosed as corrupt input).

              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

              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

              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

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

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

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

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

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

              o  Speeding up decompression.  This matters mostly with SHA-256
                 or with files that have compressed extremely well.  It's
                 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).

              -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

              -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 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:

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

              Column descriptions:

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

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

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

              o  DecMem contains the decompressor memory requirements.  That
                 is, the compression settings determine the memory
                 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.

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

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

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

              When compressing to the .xz format, split the input data into
              blocks of size bytes.  The blocks are compressed independently
              from each other, which helps with multi-threading and makes
              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 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.

              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

              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

              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 attempt to
              adjust the settings downwards so that the limit is no longer
              exceeded and display a notice that automatic adjustment was
              done.  The adjustments are done in this order: reducing the
              number of threads, switching to single-threaded mode if even one
              thread in multi-threaded mode exceeds the limit, and finally
              reducing the LZMA2 dictionary size.

              When compressing with --format=raw or if --no-adjust has been
              specified, only the number of threads may be reduced since it
              can be done without affecting the compressed output.

              If the limit cannot be met even with the adjustments described
              above, an error is displayed and xz will exit with exit status

              The limit can be specified in multiple ways:

              o  The limit can be an absolute value in bytes.  Using an
                 integer suffix like MiB can be useful.  Example:

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

              o  The limit can be reset back to its default value by setting
                 it to 0.  This is currently equivalent to setting the limit
                 to max (no memory usage limit).

              For 32-bit xz there is a special case: if the limit would be
              over 4020 MiB, the limit is set to 4020 MiB.  On MIPS32 2000 MiB
              is used instead.  (The values 0 and max aren't affected by this.
              A similar feature doesn't exist for decompression.)  This can be
              helpful when a 32-bit executable has access to 4 GiB address
              space (2 GiB on MIPS32) while hopefully doing no harm in other

              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.

              Set a memory usage limit for multi-threaded decompression.  This
              can only affect the number of threads; this will never make xz
              refuse to decompress a file.  If limit is too low to allow any
              multi-threading, the limit is ignored and xz will continue in
              single-threaded mode.  Note that if also --memlimit-decompress
              is used, it will always apply to both single-threaded and multi-
              threaded modes, and so the effective limit for multi-threading
              will never be higher than the limit set with

              In contrast to the other memory usage limit options,
              --memlimit-mt-decompress=limit has a system-specific default
              limit.  xz --info-memory can be used to see the current value.

              This option and its default value exist because without any
              limit the threaded decompressor could end up allocating an
              insane amount of memory with some input files.  If the default
              limit is too low on your system, feel free to increase the limit
              but never set it to a value larger than the amount of usable RAM
              as with appropriate input files xz will attempt to use that
              amount of memory even with a low number of threads.  Running out
              of memory or swapping will not improve decompression

              See --memlimit-compress=limit for possible ways to specify the
              limit.  Setting limit to 0 resets the limit to the default
              system-specific value.

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

              Display an error and exit if the memory usage limit cannot be
              met without adjusting settings that affect the compressed
              output.  That is, this prevents xz from switching the encoder
              from multi-threaded mode to single-threaded mode and from
              reducing the LZMA2 dictionary size.  Even when this option is
              used the number of threads may be reduced to meet the memory
              usage limit as that won't affect the compressed output.

              Automatic adjusting is always disabled when creating raw streams

       -T threads, --threads=threads
              Specify the number of worker threads to use.  Setting threads to
              a special value 0 makes xz use up to as many threads as the
              processor(s) on the system support.  The actual number of
              threads can be fewer 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.

              The single-threaded and multi-threaded compressors produce
              different output.  Single-threaded compressor will give the
              smallest file size but only the output from the multi-threaded
              compressor can be decompressed using multiple threads.  Setting
              threads to 1 will use the single-threaded mode.  Setting threads
              to any other value, including 0, will use the multi-threaded
              compressor even if the system supports only one hardware thread.
              (xz 5.2.x used single-threaded mode in this situation.)

              To use multi-threaded mode with only one thread, set threads to
              +1.  The + prefix has no effect with values other than 1.  A
              memory usage limit can still make xz switch to single-threaded
              mode unless --no-adjust is used.  Support for the + prefix was
              added in xz 5.4.0.

              If an automatic number of threads has been requested and no
              memory usage limit has been specified, then a system-specific
              default soft limit will be used to possibly limit the number of
              threads.  It is a soft limit in sense that it is ignored if the
              number of threads becomes one, thus a soft limit will never stop
              xz from compressing or decompressing.  This default soft limit
              will not make xz switch from multi-threaded mode to single-
              threaded mode.  The active limits can be seen with xz

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

              Threaded decompression only works on files that contain multiple
              blocks with size information in block headers.  All large enough
              files compressed in multi-threaded mode meet this condition, but
              files compressed in single-threaded mode don't even if
              --block-size=size has been 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
       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

       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.

              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 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

                     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.  For example, 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, test 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 alignment is known, setting pb accordingly may
                     reduce the file size a little.  For example, 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

                     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)

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

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

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

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

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

                     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

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

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

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

              These BCJ filters have known problems related to the compression

              o  Some types of files containing executable code (for example,
                 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

              o  If a BCJ filter is applied on an archive, it is possible that
                 it makes the compression ratio worse than not using a BCJ
                 filter.  For example, if there are similar or even identical
                 executables then filtering will likely make the files less
                 similar and thus compression is worse.  The contents of non-
                 executable files in the same archive can matter too.  In
                 practice one has to try with and without a BCJ filter to see
                 which is better in each situation.

              Different instruction sets have different alignment: the
              executable file must be aligned to a multiple of this value in
              the input data to make the filter work.

                     Filter      Alignment   Notes
                     x86             1       32-bit or 64-bit x86
                     ARM             4
                     ARM-Thumb       2
                     ARM64           4       4096-byte alignment is best
                     PowerPC         4       Big endian only
                     IA-64          16       Itanium
                     SPARC           4

              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 or even pb=4,lp=4,lc=0 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, for example, 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, for example, with flac(1).

              Supported options:

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

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

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

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

              o  Amount of compressed data produced (compressing) or consumed

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

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

              o  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.

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

              o  Estimated remaining time is shown only when the size of the
                 input file is known and a couple of seconds have already
                 passed since xz started processing the file.  The time is
                 shown in a less precise format which never has any colons,
                 for example, 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
              operation didn't finish, for example, 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.

              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) and how many processor threads xz thinks the system has
              and the memory usage limits for compression and decompression,
              and exit successfully.

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

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

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


       The robot mode is activated with the --robot option.  It makes the
       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.

       xz --robot --version prints 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 multiple tab-
       separated columns:

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

       2.  Memory usage limit for compression in bytes (--memlimit-compress).
           A special value of 0 indicates the default setting which for
           single-threaded mode is the same as no limit.

       3.  Memory usage limit for decompression in bytes
           (--memlimit-decompress).  A special value of 0 indicates the
           default setting which for single-threaded mode is the same as no

       4.  Since xz 5.3.4alpha: Memory usage for multi-threaded decompression
           in bytes (--memlimit-mt-decompress).  This is never zero because a
           system-specific default value shown in the column 5 is used if no
           limit has been specified explicitly.  This is also never greater
           than the value in the column 3 even if a larger value has been
           specified with --memlimit-mt-decompress.

       5.  Since xz 5.3.4alpha: A system-specific default memory usage limit
           that is used to limit the number of threads when compressing with
           an automatic number of threads (--threads=0) and no memory usage
           limit has been specified (--memlimit-compress).  This is also used
           as the default value for --memlimit-mt-decompress.

       6.  Since xz 5.3.4alpha: Number of available processor threads.

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

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

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

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

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

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

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

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

       The columns of the file lines:
              2.  Number of streams in the file
              3.  Total number of blocks in the stream(s)
              4.  Compressed size of the file
              5.  Uncompressed size of the file
              6.  Compression ratio, for example, 0.123.  If ratio is over
                  9.999, three dashes (---) are displayed instead of the
              7.  Comma-separated list of integrity check names.  The
                  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
              6.  Uncompressed start offset relative to the beginning of the
              7.  Total compressed size of the block (includes headers)
              8.  Uncompressed size
              9.  Compression ratio
              10. Name of the integrity check

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

       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

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


       0      All is good.

       1      An error occurred.

       2      Something worth a warning occurred, but no actual errors

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


       xz parses space-separated lists of options from the environment
       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.

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

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

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

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

                     export XZ_OPT


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

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

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

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

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

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

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

       xz supports decompressing .lzma files with or without end-of-payload
       marker, but all .lzma files created by xz will use end-of-payload
       marker and have uncompressed size marked as unknown in the .lzma
       header.  This may be a problem in some uncommon situations.  For
       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.

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

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

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

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


   Compressed output may vary
       The exact compressed output produced from the same uncompressed input
       file may vary between XZ Utils versions even if compression options are
       identical.  This is because the encoder can be improved (faster or
       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.

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


       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 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}'

       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."
              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

   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:

              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 (for example,
       32 MiB) to compress well, but you want to compress it quicker than xz
       -8 would do, a preset with a low CompCPU value (for example, 1) can be
       modified to use a bigger dictionary:

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

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

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

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

       Using -vv (--verbose --verbose) like in the above example can be useful
       to see the memory requirements of the compressor and decompressor.
       Remember that using a dictionary bigger than the size of the
       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, for example, 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.  For example,
       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.  For example, 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, for example, as
       uncompressed TIFF.  The distance parameter of the Delta filter is set
       to match the number of bytes per pixel in the image.  For example,
       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 (for example,
       .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                           2024-01-19                             xz(1)

xz 5.4.6 - Generated Wed Feb 14 06:21:42 CST 2024
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