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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 also the legacy .lzma format and raw compressed streams
       with no container format headers are 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 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:

       o  File is not a regular file. Symbolic links are not followed, 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, or

       After successfully compressing or decompressing the file, xz copies the
       owner, group, permissions, access time, and modification time from the
       source file to the target file. If copying the group fails, the
       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 affect also the memory usage of the decompressor.
       Typically the decompressor needs only 5 % to 20 % of the amount of RAM
       that the compressor needed when creating the file. Still, the worst-
       case memory usage of the decompressor is several gigabytes.

       To prevent uncomfortable surprises caused by huge memory usage, xz has
       a built-in memory usage limiter. While some operating systems provide
       ways to limit the memory usage of processes, relying on it wasn't
       deemed to be flexible enough. The default limit depends on the total
       amount of physical RAM:

       o  If 40 % of RAM is at least 80 MiB, 40 % of RAM is used as the limit.

       o  If 80 % of RAM is over 80 MiB, 80 MiB is used as the limit.

       o  Otherwise 80 % of RAM is used as the limit.

       When compressing, if the selected compression settings exceed the
       memory usage limit, the settings are automatically adjusted downwards
       and a notice about this is displayed. As an exception, if the memory
       usage limit is exceeded when compressing with --format=raw, an error is
       displayed and xz will exit with exit status 1.

       If source file cannot be decompressed without exceeding the memory
       usage limit, an error message is displayed and the file is skipped.
       Note that compressed files may contain many blocks, which may have been
       compressed with different settings. Typically all blocks will have
       roughly the same memory requirements, but it is possible that a block
       later in the file will exceed the memory usage limit, and an error
       about too low memory usage limit gets displayed after some data has
       already been decompressed.

       The absolute value of the active memory usage limit can be seen with
       --info-memory or near the bottom of the output of --long-help.  The
       default limit can be overridden with --memory=limit.

   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    The integer is multiplied by 1,024 (2^10). Also Ki, k, kB, K,
              and KB are accepted as synonyms for KiB.

       MiB    The integer is multiplied by 1,048,576 (2^20). Also Mi, m, M,
              and MB are accepted as synonyms for MiB.

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

       A 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.  No files are created or
              removed. This option is equivalent to --decompress --stdout
              except that the decompressed data is discarded instead of being
              written to standard output.

       -l, --list
              View information about the 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.

              This feature has not been implemented yet.

   Operation modifiers
       -k, --keep
              Keep (don't delete) the input files.

       -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
                 setuid, setgid, or sticky bit set.  The setuid, setgid, and
                 sticky bits are not copied to the target file.

              o  If combined with --decompress --stdout and xz doesn't
                 recognize the type of the source file, xz will copy the
                 source file as is to standard output. This allows using xzcat
                 --force 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.

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

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

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

              o  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.

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

              o  lzma or 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

              o  raw: Compress or uncompress a raw stream (no headers). This
                 is meant for advanced users only. To decode raw streams, you
                 need to set not only --format=raw but also specify the filter
                 chain, which would normally be stored in the container format

       -C check, --check=check
              Specify the type of the integrity check, which is calculated
              from the uncompressed data. 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:

              o  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.

              o  crc32: Calculate CRC32 using the polynomial from IEEE-802.3

              o  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

              o  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.

       -0 ... -9
              Select compression preset. If a preset level is specified
              multiple times, the last one takes effect.

              The compression preset levels can be categorised roughly into
              three categories:

              -0 ... -2
                     Fast presets with relatively low memory usage.  -1 and -2
                     should give compression speed and ratios comparable to
                     bzip2 -1 and bzip2 -9, respectively.  Currently -0 is not
                     very good (not much faster than -1 but much worse
                     compression). In future, -0 may be indicate some fast
                     algorithm instead of LZMA2.

              -3 ... -5
                     Good compression ratio with low to medium memory usage.
                     These are significantly slower than levels 0-2.

              -6 ... -9
                     Excellent compression with medium to high memory usage.
                     These are also slower than the lower preset levels. The
                     default is -6.  Unless you want to maximize the
                     compression ratio, you probably don't want a higher
                     preset level than -7 due to speed and memory usage.

              The exact compression settings (filter chain) used by each
              preset may vary between xz versions. The settings may also vary
              between files being compressed, if xz determines that modified
              settings will probably give better compression ratio without
              significantly affecting compression time or memory usage.

              Because the settings may vary, the memory usage may vary too.
              The following table lists the maximum memory usage of each
              preset level, which won't be exceeded even in future versions of

              FIXME: The table below is just a rough idea.

                      Preset         Compression          Decompression
                     -0            6 MiB                1 MiB
                     -1            6 MiB                1 MiB
                     -2           10 MiB                1 MiB
                     -3           20 MiB                2 MiB
                     -4           30 MiB                3 MiB
                     -5           60 MiB                6 MiB
                     -6          100 MiB               10 MiB
                     -7          200 MiB               20 MiB
                     -8          400 MiB               40 MiB
                     -9          800 MiB               80 MiB

              When compressing, xz automatically adjusts the compression
              settings downwards if the memory usage limit would be exceeded,
              so it is safe to specify a high preset level even on systems
              that don't have lots of RAM.

       --fast and --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.

              Especially the name of --best is misleading, because the
              definition of best depends on the input data, and that usually
              people don't want the very best compression ratio anyway,
              because it would be very slow.

       -e, --extreme
              Modify the compression preset (-0 ... -9) so that a little bit
              better compression ratio can be achieved without increasing
              memory usage of the compressor or decompressor (exception:
              compressor memory usage may increase a little with presets -0
              ... -2). The downside is that the compression time will increase
              dramatically (it can easily double).

       -M limit, --memory=limit
              Set the memory usage limit. If this option is specified multiple
              times, the last one takes effect. 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: --memory=80MiB

              o  The limit can be specified as a percentage of physical RAM.
                 Example: --memory=70%

              o  The limit can be reset back to its default value by setting
                 it to 0.  See the section Memory usage for how the default
                 limit is defined.

              o  The memory usage limiting can be effectively disabled by
                 setting limit to max.  This isn't recommended. It's usually
                 better to use, for example, --memory=90%.

              The current limit can be seen near the bottom of the output of
              the --long-help option.

       -T threads, --threads=threads
              Specify the maximum number of worker threads to use. The default
              is the number of available CPU cores. You can see the current
              value of threads near the end of the output of the --long-help

              The actual number of worker threads can be less than threads if
              using more threads would exceed the memory usage limit.  In
              addition to CPU-intensive worker threads, xz may use a few
              auxiliary threads, which don't use a lot of CPU time.

              Multithreaded compression and decompression are not implemented
              yet, so this option has no effect for now.

   Custom compressor filter chains
       A custom filter chain allows specifying the compression settings in
       detail instead of relying on the settings associated to the preset
       levels.  When a custom filter chain is specified, the compression
       preset level options (-0 ... -9 and --extreme) are silently ignored.

       A filter chain is comparable to piping on the UN*X 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 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.

       --lzma1[=options], --lzma2[=options]
              Add LZMA1 or LZMA2 filter to the filter chain. These filter 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

                     The default preset is 6, from which the default values
                     for the rest of the LZMA1 or LZMA2 options are taken.

                     Dictionary (history buffer) size indicates how many bytes
                     of the recently processed uncompressed data is kept in
                     memory. One method to reduce size of the uncompressed
                     data is to store distance-length pairs, which indicate
                     what data to repeat from the dictionary buffer. The
                     bigger the dictionary, the better the compression ratio
                     usually is, but dictionaries bigger than the uncompressed
                     data are waste of RAM.

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

                     Dictionary size has the biggest effect on compression
                     ratio.  Dictionary size and match finder together
                     determine the memory usage of the LZMA1 or LZMA2 encoder.
                     The same 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.

              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.

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

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

                     Compression mode specifies the function used to analyze
                     the data produced by the match finder.  Supported modes
                     are fast and normal.  The default is fast for presets 0-2
                     and normal for presets 3-9.

              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. Hash
                     Chains are usually used together with mode=fast and
                     Binary Trees with mode=normal.  The memory usage formulas
                     are only rough estimates, which are closest to 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

                     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

                     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 expense of speed. The default
                     depends on the preset level.

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

                     Using very high values for depth can make the encoder
                     extremely slow with carefully crafted files.  Avoid
                     setting the depth over 1000 unless you are prepared to
                     interrupt the compression in case it is taking too long.

              When decoding raw streams (--format=raw), LZMA2 needs only the
              value of dict.  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 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 allows e.g. LZMA2 to
              get better compression ratio.

              The BCJ filters are always reversible, so using a BCJ filter for
              wrong type of data doesn't cause any data loss. However,
              applying a BCJ filter for wrong type of data is a bad idea,
              because it tends to make the compression ratio worse.

              Different instruction sets have have different alignment:

                     Filter      Alignment    Notes
                     x86                 1    32-bit and 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:

                     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.

                     Specifying a non-zero start offset is probably useful
                     only if the executable has multiple sections, and there
                     are many cross-section jumps or calls. Applying a BCJ
                     filter separately for each section with proper start
                     offset and then compressing the result as a single chunk
                     may give some improvement in compression ratio compared
                     to applying the BCJ filter with the default offset for
                     the whole executable.

              Add Delta filter to the filter chain. The Delta filter can be
              used only as 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.

              Supported options:

                     Specify the distance of the delta calculation as 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 (useful mostly for

              The progress indicator shows the following information:

              o  Completion percentage is shown if the size of the input file
                 is known.  That is, 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 once a few
                 seconds have passed since xz started processing the file.

              o  Elapsed time or estimated time remaining.  Elapsed time is
                 displayed in the format M:SS or H:MM:SS.  The estimated
                 remaining time is displayed in a less precise format which
                 never has colons, for example, 2 min 30 s. The estimate can
                 be 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.

              When standard error is not a terminal, --verbose will make xz
              print the filename, compressed size, uncompressed size,
              compression ratio, speed, and elapsed time on a single line to
              standard error after compressing or decompressing the file. If
              operating took at least a few seconds, also the speed and
              elapsed time are printed. 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.
              Currently --robot is implemented only for --info-memory and
              --version, but the idea is to make it usable for actual
              compression and decompression too.

              Display the current memory usage limit in human-readable format
              on a single line, and exit successfully. To see how much RAM xz
              thinks your system has, use --memory=100% --info-memory.  To get
              machine-parsable output (memory usage limit as bytes without
              thousand separators), specify --robot before --info-memory.

       -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

       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_OPT A space-separated list of options is parsed from XZ_OPT before
              parsing the options given on the command line. Note that only
              options are parsed from XZ_OPT; all non-options are silently
              ignored. Parsing is done with getopt_long(3) which is used also
              for the command line arguments.

       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
               -1      64 KiB       64 KiB
               -2     512 KiB        1 MiB
               -3       1 MiB      512 KiB
               -4       2 MiB        1 MiB
               -5       4 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
               -1       2 MiB        2 MiB
               -2       5 MiB       12 MiB
               -3      13 MiB       12 MiB
               -4      25 MiB       16 MiB
               -5      48 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 8 MiB dictionary by default.

   Streamed vs. non-streamed .lzma files
       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 dictionary size of 2^n
       (a power of 2), but accepts files with any dictionary size.  liblzma
       accepts only .lzma files which have 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 files.

       If there is data left after the first .lzma stream, xz considers the
       file to be corrupt. 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 implementing --rsyncable to create rsyncable .xz
       files is not going to happen without freezing a part of the encoder
       implementation, which can then be used with --rsyncable.

   Embedded .xz decompressors
       Embedded .xz decompressor implementations like XZ Embedded don't
       necessarily support files created with 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

       xzdec(1), gzip(1), bzip2(1)

       XZ Utils: <>
       XZ Embedded: <>
       LZMA SDK: <>

Tukaani                           2010-03-07                             XZ(1)


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