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     NAME
          zstd - zstd, zstdmt, unzstd, zstdcat - Compress or decompress .zst
          files

     SYNOPSIS
          zstd [OPTIONS] [-|INPUT-FILE] [-o OUTPUT-FILE]

          zstdmt is equivalent to zstd -T0

          unzstd is equivalent to zstd -d

          zstdcat is equivalent to zstd -dcf

     DESCRIPTION
          zstd is a fast lossless compression algorithm and data compression
          tool, with command line syntax similar to gzip (1) and xz (1). It is
          based on the LZ77 family, with further FSE & huff0 entropy stages.
          zstd offers highly configurable compression speed, with fast modes at
          > 200 MB/s per core, and strong modes nearing lzma compression ratios.
          It also features a very fast decoder, with speeds > 500 MB/s per core.

          zstd command line syntax is generally similar to gzip, but features
          the following differences :

          o   Source files are preserved by default. It's possible to remove
              them automatically by using the --rm command.

          o   When compressing a single file, zstd displays progress
              notifications and result summary by default. Use -q to turn them
              off.

          o   zstd does not accept input from console, but it properly accepts
              stdin when it's not the console.

          o   zstd displays a short help page when command line is an error. Use
              -q to turn it off.

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

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

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          o   When compressing, the suffix .zst is appended to the source
              filename to get the target filename.

          o   When decompressing, the .zst suffix is removed from the source
              filename to get the target filename

        Concatenation with .zst files
          It is possible to concatenate .zst files as is. zstd will decompress
          such files as if they were a single .zst file.

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

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

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

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

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

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

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

          -b#  Benchmark file(s) using compression level #

          --train FILEs
               Use FILEs as a training set to create a dictionary. The training
               set should contain a lot of small files (> 100).

          -l, --list

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               Display information related to a zstd compressed file, such as
               size, ratio, and checksum. Some of these fields may not be
               available. This command can be augmented with the -v modifier.

        Operation modifiers
          o   -#: # compression level [1-19] (default: 3)

          o   --ultra: unlocks high compression levels 20+ (maximum 22), using a
              lot more memory. Note that decompression will also require more
              memory when using these levels.

          o   --fast[=#]: switch to ultra-fast compression levels. If =# is not
              present, it defaults to 1. The higher the value, the faster the
              compression speed, at the cost of some compression ratio. This
              setting overwrites compression level if one was set previously.
              Similarly, if a compression level is set after --fast, it
              overrides it.

          o   -T#, --threads=#: Compress using # working threads (default: 1).
              If # is 0, attempt to detect and use the number of physical CPU
              cores. In all cases, the nb of threads is capped to
              ZSTDMT_NBWORKERS_MAX==200. This modifier does nothing if zstd is
              compiled without multithread support.

          o   --single-thread: Does not spawn a thread for compression, use a
              single thread for both I/O and compression. In this mode,
              compression is serialized with I/O, which is slightly slower.
              (This is different from -T1, which spawns 1 compression thread in
              parallel of I/O). This mode is the only one available when
              multithread support is disabled. Single-thread mode features lower
              memory usage. Final compressed result is slightly different from
              -T1.

          o   --adapt[=min=#,max=#] : zstd will dynamically adapt compression
              level to perceived I/O conditions. Compression level adaptation
              can be observed live by using command -v. Adaptation can be
              constrained between supplied min and max levels. The feature works
              when combined with multi-threading and --long mode. It does not
              work with --single-thread. It sets window size to 8 MB by default
              (can be changed manually, see wlog). Due to the chaotic nature of
              dynamic adaptation, compressed result is not reproducible. note :
              at the time of this writing, --adapt can remain stuck at low speed
              when combined with multiple worker threads (>=2).

          o   --long[=#]: enables long distance matching with # windowLog, if
              not # is not present it defaults to 27. This increases the window
              size (windowLog) and memory usage for both the compressor and
              decompressor. This setting is designed to improve the compression
              ratio for files with long matches at a large distance.

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              Note: If windowLog is set to larger than 27, --long=windowLog or
              --memory=windowSize needs to be passed to the decompressor.

          o   -D DICT: use DICT as Dictionary to compress or decompress FILE(s)

          o   --patch-from FILE: Specify the file to be used as a reference
              point for zstd's diff engine. This is effectively dictionary
              compression with some convenient parameter selection, namely that
              windowSize > srcSize.

              Note: cannot use both this and -D together Note: --long mode will
              be automatically activated if chainLog < fileLog (fileLog being
              the windowLog required to cover the whole file). You can also
              manually force it. Node: for all levels, you can use --patch-from
              in --single-thread mode to improve compression ratio at the cost
              of speed Note: for level 19, you can get increased compression
              ratio at the cost of speed by specifying --zstd=targetLength= to
              be something large (i.e 4096), and by setting a large
              --zstd=chainLog=

          o   --rsyncable : zstd will periodically synchronize the compression
              state to make the compressed file more rsync-friendly. There is a
              negligible impact to compression ratio, and the faster compression
              levels will see a small compression speed hit. This feature does
              not work with --single-thread. You probably don't want to use it
              with long range mode, since it will decrease the effectiveness of
              the synchronization points, but your milage may vary.

          o   -C, --[no-]check: add integrity check computed from uncompressed
              data (default: enabled)

          o   --[no-]content-size: enable / disable whether or not the original
              size of the file is placed in the header of the compressed file.
              The default option is --content-size (meaning that the original
              size will be placed in the header).

          o   --no-dictID: do not store dictionary ID within frame header
              (dictionary compression). The decoder will have to rely on
              implicit knowledge about which dictionary to use, it won't be able
              to check if it's correct.

          o   -M#, --memory=#: Set a memory usage limit. By default, Zstandard
              uses 128 MB for decompression as the maximum amount of memory the
              decompressor is allowed to use, but you can override this manually
              if need be in either direction (ie. you can increase or decrease
              it).

              This is also used during compression when using with
              --patch-from=. In this case, this parameter overrides that maximum

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              size allowed for a dictionary. (128 MB).

          o   --stream-size=# : Sets the pledged source size of input coming
              from a stream. This value must be exact, as it will be included in
              the produced frame header. Incorrect stream sizes will cause an
              error. This information will be used to better optimize
              compression parameters, resulting in better and potentially faster
              compression, especially for smaller source sizes.

          o   --size-hint=#: When handling input from a stream, zstd must guess
              how large the source size will be when optimizing compression
              parameters. If the stream size is relatively small, this guess may
              be a poor one, resulting in a higher compression ratio than
              expected. This feature allows for controlling the guess when
              needed. Exact guesses result in better compression ratios.
              Overestimates result in slightly degraded compression ratios,
              while underestimates may result in significant degradation.

          o   -o FILE: save result into FILE

          o   -f, --force: overwrite output without prompting, and (de)compress
              symbolic links

          o   -c, --stdout: force write to standard output, even if it is the
              console

          o   --[no-]sparse: enable / disable sparse FS support, to make files
              with many zeroes smaller on disk. Creating sparse files may save
              disk space and speed up decompression by reducing the amount of
              disk I/O. default: enabled when output is into a file, and
              disabled when output is stdout. This setting overrides default and
              can force sparse mode over stdout.

          o   --rm: remove source file(s) after successful compression or
              decompression. If used in combination with -o, will trigger a
              confirmation prompt (which can be silenced with -f), as this is a
              destructive operation.

          o   -k, --keep: keep source file(s) after successful compression or
              decompression. This is the default behavior.

          o   -r: operate recursively on directories

          o   --filelist FILE read a list of files to process as content from
              FILE. Format is compatible with ls output, with one file per line.

          o   --output-dir-flat DIR: resulting files are stored into target DIR
              directory, instead of same directory as origin file. Be aware that
              this command can introduce name collision issues, if multiple

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              files, from different directories, end up having the same name.
              Collision resolution ensures first file with a given name will be
              present in DIR, while in combination with -f, the last file will
              be present instead.

          o   --output-dir-mirror DIR: similar to --output-dir-flat, the output
              files are stored underneath target DIR directory, but this option
              will replicate input directory hierarchy into output DIR.

              If input directory contains "..", the files in this directory will
              be ignored. If input directory is an absolute directory (i.e.
              "/var/tmp/abc"), it will be stored into the
              "output-dir/var/tmp/abc". If there are multiple input files or
              directories, name collision resolution will follow the same rules
              as --output-dir-flat.

          o   --format=FORMAT: compress and decompress in other formats. If
              compiled with support, zstd can compress to or decompress from
              other compression algorithm formats. Possibly available options
              are zstd, gzip, xz, lzma, and lz4. If no such format is provided,
              zstd is the default.

          o   -h/-H, --help: display help/long help and exit

          o   -V, --version: display version number and exit. Advanced : -vV
              also displays supported formats. -vvV also displays POSIX support.
              -q will only display the version number, suitable for machine
              reading.

          o   -v, --verbose: verbose mode, display more information

          o   -q, --quiet: suppress warnings, interactivity, and notifications.
              specify twice to suppress errors too.

          o   --no-progress: do not display the progress bar, but keep all other
              messages.

          o   --show-default-cparams: Shows the default compression parameters
              that will be used for a particular src file. If the provided src
              file is not a regular file (eg. named pipe), the cli will just
              output the default parameters. That is, the parameters that are
              used when the src size is unknown.

          o   --: All arguments after -- are treated as files

        Restricted usage of Environment Variables
          Using environment variables to set parameters has security

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          implications. Therefore, this avenue is intentionally restricted. Only
          ZSTD_CLEVEL and ZSTD_NBTHREADS are currently supported. They set the
          compression level and number of threads to use during compression,
          respectively.

          ZSTD_CLEVEL can be used to set the level between 1 and 19 (the
          "normal" range). If the value of ZSTD_CLEVEL is not a valid integer,
          it will be ignored with a warning message. ZSTD_CLEVEL just replaces
          the default compression level (3).

          ZSTD_NBTHREADS can be used to set the number of threads zstd will
          attempt to use during compression. If the value of ZSTD_NBTHREADS is
          not a valid unsigned integer, it will be ignored with a warning
          message. 'ZSTD_NBTHREADShas a default value of (1), and is capped at
          ZSTDMT_NBWORKERS_MAX==200.zstd` must be compiled with multithread
          support for this to have any effect.

          They can both be overridden by corresponding command line arguments:
          -# for compression level and -T# for number of compression threads.

     DICTIONARY BUILDER
          zstd offers dictionary compression, which greatly improves efficiency
          on small files and messages. It's possible to train zstd with a set of
          samples, the result of which is saved into a file called a dictionary.
          Then during compression and decompression, reference the same
          dictionary, using command -D dictionaryFileName. Compression of small
          files similar to the sample set will be greatly improved.

          --train FILEs
               Use FILEs as training set to create a dictionary. The training
               set should contain a lot of small files (> 100), and weight
               typically 100x the target dictionary size (for example, 10 MB for
               a 100 KB dictionary).

               Supports multithreading if zstd is compiled with threading
               support. Additional parameters can be specified with
               --train-fastcover. The legacy dictionary builder can be accessed
               with --train-legacy. The cover dictionary builder can be accessed
               with --train-cover. Equivalent to --train-fastcover=d=8,steps=4.

          -o file
               Dictionary saved into file (default name: dictionary).

          --maxdict=#
               Limit dictionary to specified size (default: 112640).

          -#   Use # compression level during training (optional). Will generate
               statistics more tuned for selected compression level, resulting
               in a small compression ratio improvement for this level.

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          -B#  Split input files in blocks of size # (default: no split)

          --dictID=#
               A dictionary ID is a locally unique ID that a decoder can use to
               verify it is using the right dictionary. By default, zstd will
               create a 4-bytes random number ID. It's possible to give a
               precise number instead. Short numbers have an advantage : an ID <
               256 will only need 1 byte in the compressed frame header, and an
               ID < 65536 will only need 2 bytes. This compares favorably to 4
               bytes default. However, it's up to the dictionary manager to not
               assign twice the same ID to 2 different dictionaries.

          --train-cover[=k#,d=#,steps=#,split=#,shrink[=#]]
               Select parameters for the default dictionary builder algorithm
               named cover. If d is not specified, then it tries d = 6 and d =
               8. If k is not specified, then it tries steps values in the range
               [50, 2000]. If steps is not specified, then the default value of
               40 is used. If split is not specified or split <= 0, then the
               default value of 100 is used. Requires that d <= k. If shrink
               flag is not used, then the default value for shrinkDict of 0 is
               used. If shrink is not specified, then the default value for
               shrinkDictMaxRegression of 1 is used.

               Selects segments of size k with highest score to put in the
               dictionary. The score of a segment is computed by the sum of the
               frequencies of all the subsegments of size d. Generally d should
               be in the range [6, 8], occasionally up to 16, but the algorithm
               will run faster with d <= 8. Good values for k vary widely based
               on the input data, but a safe range is [2 * d, 2000]. If split is
               100, all input samples are used for both training and testing to
               find optimal d and k to build dictionary. Supports multithreading
               if zstd is compiled with threading support. Having shrink enabled
               takes a truncated dictionary of minimum size and doubles in size
               until compression ratio of the truncated dictionary is at most
               shrinkDictMaxRegression% worse than the compression ratio of the
               largest dictionary.

               Examples:

               zstd --train-cover FILEs

               zstd --train-cover=k=50,d=8 FILEs

               zstd --train-cover=d=8,steps=500 FILEs

               zstd --train-cover=k=50 FILEs

               zstd --train-cover=k=50,split=60 FILEs

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               zstd --train-cover=shrink FILEs

               zstd --train-cover=shrink=2 FILEs

          --train-fastcover[=k#,d=#,f=#,steps=#,split=#,accel=#]
               Same as cover but with extra parameters f and accel and different
               default value of split If split is not specified, then it tries
               split = 75. If f is not specified, then it tries f = 20. Requires
               that 0 < f < 32. If accel is not specified, then it tries accel =
               1. Requires that 0 < accel <= 10. Requires that d = 6 or d = 8.

               f is log of size of array that keeps track of frequency of
               subsegments of size d. The subsegment is hashed to an index in
               the range [0,2^f - 1]. It is possible that 2 different
               subsegments are hashed to the same index, and they are considered
               as the same subsegment when computing frequency. Using a higher f
               reduces collision but takes longer.

               Examples:

               zstd --train-fastcover FILEs

               zstd --train-fastcover=d=8,f=15,accel=2 FILEs

          --train-legacy[=selectivity=#]
               Use legacy dictionary builder algorithm with the given dictionary
               selectivity (default: 9). The smaller the selectivity value, the
               denser the dictionary, improving its efficiency but reducing its
               possible maximum size. --train-legacy=s=# is also accepted.

               Examples:

               zstd --train-legacy FILEs

               zstd --train-legacy=selectivity=8 FILEs

     BENCHMARK
          -b#  benchmark file(s) using compression level #

          -e#  benchmark file(s) using multiple compression levels, from -b# to
               -e# (inclusive)

          -i#  minimum evaluation time, in seconds (default: 3s), benchmark mode
               only

          -B#, --block-size=#
               cut file(s) into independent blocks of size # (default: no block)

          --priority=rt

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               set process priority to real-time

          Output Format: CompressionLevel#Filename : IntputSize -> OutputSize
          (CompressionRatio), CompressionSpeed, DecompressionSpeed

          Methodology: For both compression and decompression speed, the entire
          input is compressed/decompressed in-memory to measure speed. A run
          lasts at least 1 sec, so when files are small, they are
          compressed/decompressed several times per run, in order to improve
          measurement accuracy.

     ADVANCED COMPRESSION OPTIONS
        --zstd[=options]:
          zstd provides 22 predefined compression levels. The selected or
          default predefined compression level can be changed with advanced
          compression options. The options are provided as a comma-separated
          list. You may specify only the options you want to change and the rest
          will be taken from the selected or default compression level. The list
          of available options:

          strategy=strat, strat=strat
               Specify a strategy used by a match finder.

               There are 9 strategies numbered from 1 to 9, from faster to
               stronger: 1=ZSTD_fast, 2=ZSTD_dfast, 3=ZSTD_greedy, 4=ZSTD_lazy,
               5=ZSTD_lazy2, 6=ZSTD_btlazy2, 7=ZSTD_btopt, 8=ZSTD_btultra,
               9=ZSTD_btultra2.

          windowLog=wlog, wlog=wlog
               Specify the maximum number of bits for a match distance.

               The higher number of increases the chance to find a match which
               usually improves compression ratio. It also increases memory
               requirements for the compressor and decompressor. The minimum
               wlog is 10 (1 KiB) and the maximum is 30 (1 GiB) on 32-bit
               platforms and 31 (2 GiB) on 64-bit platforms.

               Note: If windowLog is set to larger than 27, --long=windowLog or
               --memory=windowSize needs to be passed to the decompressor.

          hashLog=hlog, hlog=hlog
               Specify the maximum number of bits for a hash table.

               Bigger hash tables cause less collisions which usually makes
               compression faster, but requires more memory during compression.

               The minimum hlog is 6 (64 B) and the maximum is 30 (1 GiB).

          chainLog=clog, clog=clog

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               Specify the maximum number of bits for a hash chain or a binary
               tree.

               Higher numbers of bits increases the chance to find a match which
               usually improves compression ratio. It also slows down
               compression speed and increases memory requirements for
               compression. This option is ignored for the ZSTD_fast strategy.

               The minimum clog is 6 (64 B) and the maximum is 29 (524 Mib) on
               32-bit platforms and 30 (1 Gib) on 64-bit platforms.

          searchLog=slog, slog=slog
               Specify the maximum number of searches in a hash chain or a
               binary tree using logarithmic scale.

               More searches increases the chance to find a match which usually
               increases compression ratio but decreases compression speed.

               The minimum slog is 1 and the maximum is 'windowLog' - 1.

          minMatch=mml, mml=mml
               Specify the minimum searched length of a match in a hash table.

               Larger search lengths usually decrease compression ratio but
               improve decompression speed.

               The minimum mml is 3 and the maximum is 7.

          targetLength=tlen, tlen=tlen
               The impact of this field vary depending on selected strategy.

               For ZSTD_btopt, ZSTD_btultra and ZSTD_btultra2, it specifies the
               minimum match length that causes match finder to stop searching.
               A larger targetLength usually improves compression ratio but
               decreases compression speed. t For ZSTD_fast, it triggers
               ultra-fast mode when > 0. The value represents the amount of data
               skipped between match sampling. Impact is reversed : a larger
               targetLength increases compression speed but decreases
               compression ratio.

               For all other strategies, this field has no impact.

               The minimum tlen is 0 and the maximum is 128 Kib.

          overlapLog=ovlog, ovlog=ovlog
               Determine overlapSize, amount of data reloaded from previous job.
               This parameter is only available when multithreading is enabled.
               Reloading more data improves compression ratio, but decreases
               speed.

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               The minimum ovlog is 0, and the maximum is 9. 1 means "no
               overlap", hence completely independent jobs. 9 means "full
               overlap", meaning up to windowSize is reloaded from previous job.
               Reducing ovlog by 1 reduces the reloaded amount by a factor 2.
               For example, 8 means "windowSize/2", and 6 means "windowSize/8".
               Value 0 is special and means "default" : ovlog is automatically
               determined by zstd. In which case, ovlog will range from 6 to 9,
               depending on selected strat.

          ldmHashLog=lhlog, lhlog=lhlog
               Specify the maximum size for a hash table used for long distance
               matching.

               This option is ignored unless long distance matching is enabled.

               Bigger hash tables usually improve compression ratio at the
               expense of more memory during compression and a decrease in
               compression speed.

               The minimum lhlog is 6 and the maximum is 30 (default: 20).

          ldmMinMatch=lmml, lmml=lmml
               Specify the minimum searched length of a match for long distance
               matching.

               This option is ignored unless long distance matching is enabled.

               Larger/very small values usually decrease compression ratio.

               The minimum lmml is 4 and the maximum is 4096 (default: 64).

          ldmBucketSizeLog=lblog, lblog=lblog
               Specify the size of each bucket for the hash table used for long
               distance matching.

               This option is ignored unless long distance matching is enabled.

               Larger bucket sizes improve collision resolution but decrease
               compression speed.

               The minimum lblog is 1 and the maximum is 8 (default: 3).

          ldmHashRateLog=lhrlog, lhrlog=lhrlog
               Specify the frequency of inserting entries into the long distance
               matching hash table.

               This option is ignored unless long distance matching is enabled.

               Larger values will improve compression speed. Deviating far from

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               the default value will likely result in a decrease in compression
               ratio.

               The default value is wlog - lhlog.

        Example
          The following parameters sets advanced compression options to
          something similar to predefined level 19 for files bigger than 256 KB:

          --zstd=wlog=23,clog=23,hlog=22,slog=6,mml=3,tlen=48,strat=6

        -B#:
          Select the size of each compression job. This parameter is available
          only when multi-threading is enabled. Default value is 4 * windowSize,
          which means it varies depending on compression level. -B# makes it
          possible to select a custom value. Note that job size must respect a
          minimum value which is enforced transparently. This minimum is either
          1 MB, or overlapSize, whichever is largest.

     BUGS
          Report bugs at: https://github.com/facebook/zstd/issues

     AUTHOR
          Yann Collet

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