Пакет: zstd

ZSTD(1)				 User Commands			       ZSTD(1)



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

SYNOPSIS
       allbox; 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, from fast modes at > 200
       MB/s per core, to strong modes with excellent  compression  ratios.  It
       also  features  a  very	fast decoder, with speeds > 500 MB/s per core,
       which remains roughly stable at all compression settings.

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

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

       •   When compressing a single file, zstd	 displays  progress  notifica‐
	   tions and result summary by default. Use -q to turn them off.

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

       •   zstd does not accept input from  console,  though  it  does	accept
	   stdin when it's not the console.

       •   zstd	 does  not  store the input's filename or attributes, only its
	   contents.



       zstd processes 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:

       •   When compressing, the suffix .zst is appended to the	 source	 file‐
	   name to get the target filename.

       •   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 multiple .zst files. zstd will decompress
       such agglomerated file as if it was a single .zst file.

OPTIONS
   Integer Suffixes and Special Values
       In  most places where an integer argument is expected, an optional suf‐
       fix 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 ac‐
	      cepted as synonyms for KiB.

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

   Operation Mode
       If  multiple  operation	mode options are given, the last one takes ef‐
       fect.

       -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  --decom‐
	      press).

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

       -t, --test
	      Test  the	 integrity of compressed files. This option is equiva‐
	      lent to --decompress --stdout > /dev/null, decompressed data  is
	      discarded	 and  checksummed  for errors. No files are created or
	      removed.

       -b#    Benchmark file(s) using compression level #. See BENCHMARK below
	      for a description of this operation.

       --train FILES
	      Use FILES as a training set to create a dictionary. The training
	      set should contain a lot of small files (> 100). See  DICTIONARY
	      BUILDER below for a description of this operation.

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

   Operation Modifiers
       •   -#: selects # compression level [1-19] (default:  3).  Higher  com‐
	   pression  levels  generally produce higher compression ratio at the
	   expense of speed and memory. A rough rule of thumb is that compres‐
	   sion	 speed	is expected to be divided by 2 every 2 levels. Techni‐
	   cally, each level is mapped to a set of advanced  parameters	 (that
	   can also be modified individually, see below). Because the compres‐
	   sor's behavior highly depends on the content to  compress,  there's
	   no guarantee of a smooth progression from one level to another.

       •   --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.

       •   --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 set‐
	   ting overwrites compression level if one was set previously.	 Simi‐
	   larly, if a compression level is set after --fast, it overrides it.

       •   -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,
	   which is either 64 in 32-bit mode, or 256 for 64-bit	 environments.
	   This	 modifier does nothing if zstd is compiled without multithread
	   support.

       •   --single-thread: Use a single thread for both I/O and  compression.
	   As compression is serialized with I/O, this can be slightly slower.
	   Single-thread mode features significantly lower memory usage, which
	   can	be  useful  for systems with limited amount of memory, such as
	   32-bit systems.

	   Note 1: this mode is the only available one when  multithread  sup‐
	   port is disabled.

	   Note 2: this mode is different from -T1, which spawns 1 compression
	   thread in parallel  with  I/O.  Final  compressed  result  is  also
	   slightly different from -T1.

       •   --auto-threads={physical,logical} (default: physical): When using a
	   default amount of threads via -T0, choose the default based on  the
	   number of detected physical or logical cores.

       •   --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  com‐
	   bined  with	multi-threading and --long mode. It does not work with
	   --single-thread. It sets window size to 8 MiB 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).

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

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

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

       •   --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.

	   Note:  up  to level 15, you can use --patch-from in --single-thread
	   mode to improve compression ratio marginally at the cost of	speed.
	   Using  '--single-thread' above level 15 will lead to lower compres‐
	   sion ratios.

	   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=.

       •   --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 a potential  impact  to
	   compression	speed,	perceptible at higher speeds, for example when
	   combining --rsyncable with many parallel worker threads. This  fea‐
	   ture does not work with --single-thread. You probably don't want to
	   use it with long range mode, since it will decrease the  effective‐
	   ness of the synchronization points, but your mileage may vary.

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

       •   --[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).

       •   --no-dictID:	 do  not store dictionary ID within frame header (dic‐
	   tionary 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.

       •   -M#, --memory=#: Set a memory usage limit. By  default,  zstd  uses
	   128	MiB  for decompression as the maximum amount of memory the de‐
	   compressor is allowed to use, but you can override this manually if
	   need be in either direction (i.e. 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	 size  allowed
	   for a dictionary. (128 MiB).

	   Additionally,  this	can  be	 used  to  limit memory for dictionary
	   training. This parameter overrides the default limit of 2 GiB. zstd
	   will	 load  training	 samples up to the memory limit and ignore the
	   rest.

       •   --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 param‐
	   eters, resulting in better and potentially faster compression,  es‐
	   pecially for smaller source sizes.

       •   --size-hint=#:  When	 handling input from a stream, zstd must guess
	   how large the source size will be when optimizing  compression  pa‐
	   rameters. 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.

       •   --target-compressed-block-size=#:  Attempt  to  produce  compressed
	   blocks of approximately this size. This will split larger blocks in
	   order to approach this target. This feature is notably  useful  for
	   improved  latency,  when  the receiver can leverage receiving early
	   incomplete data. This parameter defines a loose target:  compressed
	   blocks  will	 target	 this size "on average", but individual blocks
	   can still be larger or smaller. Enabling this feature can  decrease
	   compression	speed by up to ~10% at level 1. Higher levels will see
	   smaller relative speed regression,  becoming	 invisible  at	higher
	   settings.

       •   -f,	--force:  disable  input and output checks. Allows overwriting
	   existing files, input from console, output to stdout, operating  on
	   links, block devices, etc. During decompression and when the output
	   destination is stdout, pass-through unrecognized formats as-is.

       •   -c, --stdout: write to standard output (even if it is the console);
	   keep original files (disable --rm).

       •   -o FILE: save result into FILE. Note that this operation is in con‐
	   flict with -c. If both operations are present on the command	 line,
	   the last expressed one wins.

       •   --[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.

       •   --[no-]pass-through enable / disable passing	 through  uncompressed
	   files as-is. During decompression when pass-through is enabled, un‐
	   recognized formats will be copied as-is from the input to the  out‐
	   put.	 By  default, pass-through will occur when the output destina‐
	   tion is stdout and the force (-f) option is set.

       •   --rm: remove source file(s) after successful compression or	decom‐
	   pression.  This command is silently ignored if output is stdout. If
	   used in combination with -o, triggers a confirmation prompt	(which
	   can be silenced with -f), as this is a destructive operation.

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

       •   -r: operate recursively on directories. It selects all files in the
	   named directory and all its subdirectories. This can be useful both
	   to reduce command line typing, and to  circumvent  shell  expansion
	   limitations,	 when  there  are a lot of files and naming breaks the
	   maximum size of a command line.

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

       •   --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
	   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.

       •   --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	 "out‐
	   put-dir/var/tmp/abc". If there are multiple input files or directo‐
	   ries,  name	collision  resolution  will  follow  the same rules as
	   --output-dir-flat.

       •   --format=FORMAT: compress and decompress in other formats. If  com‐
	   piled  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.

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

       •   -V, --version: display version number and  immediately  exit.  note
	   that,  since it exits, flags specified after -V are effectively ig‐
	   nored. Advanced: -vV also displays  supported  formats.  -vvV  also
	   displays  POSIX  support. -qV will only display the version number,
	   suitable for machine reading.

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

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

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

       •   --show-default-cparams: shows the  default  compression  parameters
	   that	 will  be  used for a particular input file, based on the pro‐
	   vided compression level and the input size. If the provided file is
	   not a regular file (e.g. a pipe), this flag will output the parame‐
	   ters used for inputs of unknown size.

       •   --exclude-compressed: only compress files that are not already com‐
	   pressed.

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



   gzip Operation Modifiers
       When invoked via a gzip symlink, zstd will support further options that
       intend to mimic the gzip behavior:

       -n, --no-name
	      do not store the original filename and timestamps when compress‐
	      ing a file. This is the default behavior and hence a no-op.

       --best alias to the option -9.

   Environment Variables
       Employing environment variables to set parameters has security implica‐
       tions.  Therefore,  this	 avenue	  is   intentionally   limited.	  Only
       ZSTD_CLEVEL  and	 ZSTD_NBTHREADS	 are currently supported. They set the
       default compression level and number of threads to use during  compres‐
       sion, 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  at‐
       tempt  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_NBTHREADS  has a default value of (1), and is capped at ZSTDMT_NB‐
       WORKERS_MAX==200. zstd must be compiled with  multithread  support  for
       this variable to have any effect.

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

ADVANCED COMPRESSION OPTIONS
       zstd provides 22 predefined regular compression levels  plus  the  fast
       levels.	A compression level is translated internally into multiple ad‐
       vanced parameters that control the behavior of the compressor (one  can
       observe	the  result  of this translation with --show-default-cparams).
       These advanced parameters can be overridden using advanced  compression
       options.

   --zstd[=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 fastest to
	      strongest:     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 re‐
	      quirements 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 fewer collisions which usually makes
	      compression faster, but requires more memory during compression.

	      The minimum hlog is 6 (64 entries / 256 B) and the maximum is 30
	      (1B entries / 4 GiB).

       chainLog=clog, clog=clog
	      Specify  the  maximum  number  of	 bits for the secondary search
	      structure, whose form depends on the selected strategy.

	      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 compres‐
	      sion.  This  option is ignored for the ZSTD_fast strategy, which
	      only has the primary hash table.

	      The minimum clog is 6 (64 entries / 256 B) and the maximum is 29
	      (512M  entries / 2 GiB) on 32-bit platforms and 30 (1B entries /
	      4 GiB) on 64-bit platforms.

       searchLog=slog, slog=slog
	      Specify the maximum number of searches in a hash chain or a  bi‐
	      nary 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 im‐
	      prove 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 de‐
	      creases compression speed.

	      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 en‐
	      abled.  Reloading	 more data improves compression ratio, but de‐
	      creases speed.

	      The minimum ovlog is 0, and the maximum is 9. 1 means "no	 over‐
	      lap", 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 exam‐
	      ple, 8 means "windowSize/2", and 6 means "windowSize/8". Value 0
	      is  special  and	means "default": ovlog is automatically deter‐
	      mined by zstd. In which case, ovlog will range from 6 to 9,  de‐
	      pending 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  ex‐
	      pense  of	 more memory during compression and a decrease in com‐
	      pression 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 dis‐
	      tance matching hash table.

	      This option is ignored unless long distance matching is enabled.

	      Larger values will improve compression speed. Deviating far from
	      the  default  value will likely result in a decrease in compres‐
	      sion 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#:
       Specify the size of each compression job. This parameter is only avail‐
       able when multi-threading is enabled. Each compression job  is  run  in
       parallel,  so  this  value indirectly impacts the nb of active threads.
       Default job size varies depending on compression level (generally  4  *
       windowSize).  -B#  makes	 it possible to manually select a custom size.
       Note that job size must respect	a  minimum  value  which  is  enforced
       transparently. This minimum is either 512 KB, or overlapSize, whichever
       is largest. Different job sizes will lead to  non-identical  compressed
       frames.

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  dictio‐
       nary,  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 ideally contain a lot of samples (> 100), and weight
	      typically 100x the target dictionary size (for example,  ~10  MB
	      for a 100 KB dictionary). --train can be combined with -r to in‐
	      dicate a directory rather than listing all the files, which  can
	      be useful to circumvent shell expansion limits.

	      Since  dictionary	 compression  is  mostly  effective  for small
	      files, the expectation is that the training set will  only  con‐
	      tain  small  files.  In the case where some samples happen to be
	      large, only the first 128 KiB of these samples will be used  for
	      training.

	      --train supports multithreading if zstd is compiled with thread‐
	      ing support (default). Additional	 advanced  parameters  can  be
	      specified	 with --train-fastcover. The legacy dictionary builder
	      can be accessed with --train-legacy. The slower cover dictionary
	      builder  can  be accessed with --train-cover. Default --train is
	      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  bytes).  As
	      usual,  quantities  are  expressed in bytes by default, and it's
	      possible to employ suffixes (like KB or MB)  to  specify	larger
	      values.

       -#     Use  # compression level during training (optional). Will gener‐
	      ate statistics more tuned for selected  compression  level,  re‐
	      sulting in a small compression ratio improvement for this level.

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

       -M#, --memory=#
	      Limit  the amount of sample data loaded for training (default: 2
	      GB). Note that the default (2 GB) is also the maximum. This  pa‐
	      rameter  can be useful in situations where the training set size
	      is not well controlled and  could	 be  potentially  very	large.
	      Since  speed  of	the training process is directly correlated to
	      the size of the training sample set, a smaller sample set	 leads
	      to faster training.

	      In situations where the training set is larger than maximum mem‐
	      ory, the CLI will randomly select samples	 among	the  available
	      ones,  up to the maximum allowed memory budget. This is meant to
	      improve dictionary relevance by mitigating the potential	impact
	      of  clustering,  such as selecting only files from the beginning
	      of a list sorted by modification date, or sorted by alphabetical
	      order.  The  randomization process is deterministic, so training
	      of the same list of files with the same parameters will lead  to
	      the creation of the same dictionary.

       --dictID=#
	      A	 dictionary  ID	 is  a locally unique ID. The decoder will use
	      this value to verify it is using the right  dictionary.  By  de‐
	      fault,  zstd will create a 4-bytes random number ID. It's possi‐
	      ble to provide an explicit number ID instead.  It's  up  to  the
	      dictionary  manager to not assign twice the same ID to 2 differ‐
	      ent dictionaries. Note that 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	favor‐
	      ably to 4 bytes default.

	      Note  that RFC8878 reserves IDs less than 32768 and greater than
	      or equal to 2\^31, so they should not be used in public.

       --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 dic‐
	      tionary.	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 multi‐
	      threading 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 dictio‐
	      nary is at most shrinkDictMaxRegression% worse than the compres‐
	      sion 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

	      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  differ‐
	      ent  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 sub‐
	      segments 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 re‐
	      duces 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  dictio‐
	      nary  selectivity	 (default:  9).	 The  smaller  the selectivity
	      value, the denser the dictionary, improving its  efficiency  but
	      reducing its achievable maximum size. --train-legacy=s=# is also
	      accepted.

	      Examples:

	      zstd --train-legacy FILEs

	      zstd --train-legacy=selectivity=8 FILEs

BENCHMARK
       The zstd CLI provides a benchmarking mode that can be  used  to	easily
       find  suitable  compression parameters, or alternatively to benchmark a
       computer's performance. zstd -b [FILE(s)] will benchmark zstd for  both
       compression  and	 decompression	using  default compression level. Note
       that results are very dependent on the content being  compressed.  It's
       possible	 to pass multiple files to the benchmark, and even a directory
       with -r DIRECTORY. When no FILE is provided, the benchmark will	use  a
       procedurally generated lorem ipsum text.

       •   -b#: benchmark file(s) using compression level #

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

       •   -d:	benchmark  decompression  speed	 only  (requires  providing  a
	   zstd-compressed content)

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

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

       •   -S:	output	one benchmark result per input file (default: consoli‐
	   dated result)

       •   -D dictionary benchmark using dictionary

       •   --priority=rt: set process priority to real-time (Windows)



       Beyond compression levels, benchmarking is also compatible  with	 other
       parameters,  such  as number of threads (-T#), advanced compression pa‐
       rameters (--zstd=###), dictionary compression (-D dictionary), or  even
       disabling checksum verification for example.

       Output Format: CompressionLevel#Filename: InputSize -> OutputSize (Com‐
       pressionRatio), CompressionSpeed, DecompressionSpeed

       Methodology: For speed measurement, the entire input is	compressed/de‐
       compressed  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.

SEE ALSO
       zstdgrep(1), zstdless(1), gzip(1), xz(1)

       The  zstandard format is specified in Y. Collet, "Zstandard Compression
       and	   the	       'application/zstd'	  Media		Type",
       https://www.ietf.org/rfc/rfc8878.txt,   Internet	  RFC  8878  (February
       2021).

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

AUTHOR
       Yann Collet



zstd 1.5.6			 October 2024			       ZSTD(1)

ZSTD(1)				 User Commands			       ZSTD(1)



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

SYNOPSIS
       allbox; 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, from fast modes at > 200
       MB/s per core, to strong modes with excellent  compression  ratios.  It
       also  features  a  very	fast decoder, with speeds > 500 MB/s per core,
       which remains roughly stable at all compression settings.

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

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

       •   When compressing a single file, zstd	 displays  progress  notifica‐
	   tions and result summary by default. Use -q to turn them off.

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

       •   zstd does not accept input from  console,  though  it  does	accept
	   stdin when it's not the console.

       •   zstd	 does  not  store the input's filename or attributes, only its
	   contents.



       zstd processes 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:

       •   When compressing, the suffix .zst is appended to the	 source	 file‐
	   name to get the target filename.

       •   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 multiple .zst files. zstd will decompress
       such agglomerated file as if it was a single .zst file.

OPTIONS
   Integer Suffixes and Special Values
       In  most places where an integer argument is expected, an optional suf‐
       fix 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 ac‐
	      cepted as synonyms for KiB.

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

   Operation Mode
       If  multiple  operation	mode options are given, the last one takes ef‐
       fect.

       -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  --decom‐
	      press).

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

       -t, --test
	      Test  the	 integrity of compressed files. This option is equiva‐
	      lent to --decompress --stdout > /dev/null, decompressed data  is
	      discarded	 and  checksummed  for errors. No files are created or
	      removed.

       -b#    Benchmark file(s) using compression level #. See BENCHMARK below
	      for a description of this operation.

       --train FILES
	      Use FILES as a training set to create a dictionary. The training
	      set should contain a lot of small files (> 100). See  DICTIONARY
	      BUILDER below for a description of this operation.

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

   Operation Modifiers
       •   -#: selects # compression level [1-19] (default:  3).  Higher  com‐
	   pression  levels  generally produce higher compression ratio at the
	   expense of speed and memory. A rough rule of thumb is that compres‐
	   sion	 speed	is expected to be divided by 2 every 2 levels. Techni‐
	   cally, each level is mapped to a set of advanced  parameters	 (that
	   can also be modified individually, see below). Because the compres‐
	   sor's behavior highly depends on the content to  compress,  there's
	   no guarantee of a smooth progression from one level to another.

       •   --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.

       •   --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 set‐
	   ting overwrites compression level if one was set previously.	 Simi‐
	   larly, if a compression level is set after --fast, it overrides it.

       •   -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,
	   which is either 64 in 32-bit mode, or 256 for 64-bit	 environments.
	   This	 modifier does nothing if zstd is compiled without multithread
	   support.

       •   --single-thread: Use a single thread for both I/O and  compression.
	   As compression is serialized with I/O, this can be slightly slower.
	   Single-thread mode features significantly lower memory usage, which
	   can	be  useful  for systems with limited amount of memory, such as
	   32-bit systems.

	   Note 1: this mode is the only available one when  multithread  sup‐
	   port is disabled.

	   Note 2: this mode is different from -T1, which spawns 1 compression
	   thread in parallel  with  I/O.  Final  compressed  result  is  also
	   slightly different from -T1.

       •   --auto-threads={physical,logical} (default: physical): When using a
	   default amount of threads via -T0, choose the default based on  the
	   number of detected physical or logical cores.

       •   --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  com‐
	   bined  with	multi-threading and --long mode. It does not work with
	   --single-thread. It sets window size to 8 MiB 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).

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

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

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

       •   --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.

	   Note:  up  to level 15, you can use --patch-from in --single-thread
	   mode to improve compression ratio marginally at the cost of	speed.
	   Using  '--single-thread' above level 15 will lead to lower compres‐
	   sion ratios.

	   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=.

       •   --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 a potential  impact  to
	   compression	speed,	perceptible at higher speeds, for example when
	   combining --rsyncable with many parallel worker threads. This  fea‐
	   ture does not work with --single-thread. You probably don't want to
	   use it with long range mode, since it will decrease the  effective‐
	   ness of the synchronization points, but your mileage may vary.

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

       •   --[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).

       •   --no-dictID:	 do  not store dictionary ID within frame header (dic‐
	   tionary 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.

       •   -M#, --memory=#: Set a memory usage limit. By  default,  zstd  uses
	   128	MiB  for decompression as the maximum amount of memory the de‐
	   compressor is allowed to use, but you can override this manually if
	   need be in either direction (i.e. 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	 size  allowed
	   for a dictionary. (128 MiB).

	   Additionally,  this	can  be	 used  to  limit memory for dictionary
	   training. This parameter overrides the default limit of 2 GiB. zstd
	   will	 load  training	 samples up to the memory limit and ignore the
	   rest.

       •   --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 param‐
	   eters, resulting in better and potentially faster compression,  es‐
	   pecially for smaller source sizes.

       •   --size-hint=#:  When	 handling input from a stream, zstd must guess
	   how large the source size will be when optimizing  compression  pa‐
	   rameters. 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.

       •   --target-compressed-block-size=#:  Attempt  to  produce  compressed
	   blocks of approximately this size. This will split larger blocks in
	   order to approach this target. This feature is notably  useful  for
	   improved  latency,  when  the receiver can leverage receiving early
	   incomplete data. This parameter defines a loose target:  compressed
	   blocks  will	 target	 this size "on average", but individual blocks
	   can still be larger or smaller. Enabling this feature can  decrease
	   compression	speed by up to ~10% at level 1. Higher levels will see
	   smaller relative speed regression,  becoming	 invisible  at	higher
	   settings.

       •   -f,	--force:  disable  input and output checks. Allows overwriting
	   existing files, input from console, output to stdout, operating  on
	   links, block devices, etc. During decompression and when the output
	   destination is stdout, pass-through unrecognized formats as-is.

       •   -c, --stdout: write to standard output (even if it is the console);
	   keep original files (disable --rm).

       •   -o FILE: save result into FILE. Note that this operation is in con‐
	   flict with -c. If both operations are present on the command	 line,
	   the last expressed one wins.

       •   --[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.

       •   --[no-]pass-through enable / disable passing	 through  uncompressed
	   files as-is. During decompression when pass-through is enabled, un‐
	   recognized formats will be copied as-is from the input to the  out‐
	   put.	 By  default, pass-through will occur when the output destina‐
	   tion is stdout and the force (-f) option is set.

       •   --rm: remove source file(s) after successful compression or	decom‐
	   pression.  This command is silently ignored if output is stdout. If
	   used in combination with -o, triggers a confirmation prompt	(which
	   can be silenced with -f), as this is a destructive operation.

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

       •   -r: operate recursively on directories. It selects all files in the
	   named directory and all its subdirectories. This can be useful both
	   to reduce command line typing, and to  circumvent  shell  expansion
	   limitations,	 when  there  are a lot of files and naming breaks the
	   maximum size of a command line.

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

       •   --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
	   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.

       •   --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	 "out‐
	   put-dir/var/tmp/abc". If there are multiple input files or directo‐
	   ries,  name	collision  resolution  will  follow  the same rules as
	   --output-dir-flat.

       •   --format=FORMAT: compress and decompress in other formats. If  com‐
	   piled  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.

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

       •   -V, --version: display version number and  immediately  exit.  note
	   that,  since it exits, flags specified after -V are effectively ig‐
	   nored. Advanced: -vV also displays  supported  formats.  -vvV  also
	   displays  POSIX  support. -qV will only display the version number,
	   suitable for machine reading.

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

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

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

       •   --show-default-cparams: shows the  default  compression  parameters
	   that	 will  be  used for a particular input file, based on the pro‐
	   vided compression level and the input size. If the provided file is
	   not a regular file (e.g. a pipe), this flag will output the parame‐
	   ters used for inputs of unknown size.

       •   --exclude-compressed: only compress files that are not already com‐
	   pressed.

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



   gzip Operation Modifiers
       When invoked via a gzip symlink, zstd will support further options that
       intend to mimic the gzip behavior:

       -n, --no-name
	      do not store the original filename and timestamps when compress‐
	      ing a file. This is the default behavior and hence a no-op.

       --best alias to the option -9.

   Environment Variables
       Employing environment variables to set parameters has security implica‐
       tions.  Therefore,  this	 avenue	  is   intentionally   limited.	  Only
       ZSTD_CLEVEL  and	 ZSTD_NBTHREADS	 are currently supported. They set the
       default compression level and number of threads to use during  compres‐
       sion, 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  at‐
       tempt  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_NBTHREADS  has a default value of (1), and is capped at ZSTDMT_NB‐
       WORKERS_MAX==200. zstd must be compiled with  multithread  support  for
       this variable to have any effect.

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

ADVANCED COMPRESSION OPTIONS
       zstd provides 22 predefined regular compression levels  plus  the  fast
       levels.	A compression level is translated internally into multiple ad‐
       vanced parameters that control the behavior of the compressor (one  can
       observe	the  result  of this translation with --show-default-cparams).
       These advanced parameters can be overridden using advanced  compression
       options.

   --zstd[=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 fastest to
	      strongest:     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 re‐
	      quirements 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 fewer collisions which usually makes
	      compression faster, but requires more memory during compression.

	      The minimum hlog is 6 (64 entries / 256 B) and the maximum is 30
	      (1B entries / 4 GiB).

       chainLog=clog, clog=clog
	      Specify  the  maximum  number  of	 bits for the secondary search
	      structure, whose form depends on the selected strategy.

	      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 compres‐
	      sion.  This  option is ignored for the ZSTD_fast strategy, which
	      only has the primary hash table.

	      The minimum clog is 6 (64 entries / 256 B) and the maximum is 29
	      (512M  entries / 2 GiB) on 32-bit platforms and 30 (1B entries /
	      4 GiB) on 64-bit platforms.

       searchLog=slog, slog=slog
	      Specify the maximum number of searches in a hash chain or a  bi‐
	      nary 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 im‐
	      prove 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 de‐
	      creases compression speed.

	      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 en‐
	      abled.  Reloading	 more data improves compression ratio, but de‐
	      creases speed.

	      The minimum ovlog is 0, and the maximum is 9. 1 means "no	 over‐
	      lap", 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 exam‐
	      ple, 8 means "windowSize/2", and 6 means "windowSize/8". Value 0
	      is  special  and	means "default": ovlog is automatically deter‐
	      mined by zstd. In which case, ovlog will range from 6 to 9,  de‐
	      pending 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  ex‐
	      pense  of	 more memory during compression and a decrease in com‐
	      pression 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 dis‐
	      tance matching hash table.

	      This option is ignored unless long distance matching is enabled.

	      Larger values will improve compression speed. Deviating far from
	      the  default  value will likely result in a decrease in compres‐
	      sion 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#:
       Specify the size of each compression job. This parameter is only avail‐
       able when multi-threading is enabled. Each compression job  is  run  in
       parallel,  so  this  value indirectly impacts the nb of active threads.
       Default job size varies depending on compression level (generally  4  *
       windowSize).  -B#  makes	 it possible to manually select a custom size.
       Note that job size must respect	a  minimum  value  which  is  enforced
       transparently. This minimum is either 512 KB, or overlapSize, whichever
       is largest. Different job sizes will lead to  non-identical  compressed
       frames.

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  dictio‐
       nary,  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 ideally contain a lot of samples (> 100), and weight
	      typically 100x the target dictionary size (for example,  ~10  MB
	      for a 100 KB dictionary). --train can be combined with -r to in‐
	      dicate a directory rather than listing all the files, which  can
	      be useful to circumvent shell expansion limits.

	      Since  dictionary	 compression  is  mostly  effective  for small
	      files, the expectation is that the training set will  only  con‐
	      tain  small  files.  In the case where some samples happen to be
	      large, only the first 128 KiB of these samples will be used  for
	      training.

	      --train supports multithreading if zstd is compiled with thread‐
	      ing support (default). Additional	 advanced  parameters  can  be
	      specified	 with --train-fastcover. The legacy dictionary builder
	      can be accessed with --train-legacy. The slower cover dictionary
	      builder  can  be accessed with --train-cover. Default --train is
	      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  bytes).  As
	      usual,  quantities  are  expressed in bytes by default, and it's
	      possible to employ suffixes (like KB or MB)  to  specify	larger
	      values.

       -#     Use  # compression level during training (optional). Will gener‐
	      ate statistics more tuned for selected  compression  level,  re‐
	      sulting in a small compression ratio improvement for this level.

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

       -M#, --memory=#
	      Limit  the amount of sample data loaded for training (default: 2
	      GB). Note that the default (2 GB) is also the maximum. This  pa‐
	      rameter  can be useful in situations where the training set size
	      is not well controlled and  could	 be  potentially  very	large.
	      Since  speed  of	the training process is directly correlated to
	      the size of the training sample set, a smaller sample set	 leads
	      to faster training.

	      In situations where the training set is larger than maximum mem‐
	      ory, the CLI will randomly select samples	 among	the  available
	      ones,  up to the maximum allowed memory budget. This is meant to
	      improve dictionary relevance by mitigating the potential	impact
	      of  clustering,  such as selecting only files from the beginning
	      of a list sorted by modification date, or sorted by alphabetical
	      order.  The  randomization process is deterministic, so training
	      of the same list of files with the same parameters will lead  to
	      the creation of the same dictionary.

       --dictID=#
	      A	 dictionary  ID	 is  a locally unique ID. The decoder will use
	      this value to verify it is using the right  dictionary.  By  de‐
	      fault,  zstd will create a 4-bytes random number ID. It's possi‐
	      ble to provide an explicit number ID instead.  It's  up  to  the
	      dictionary  manager to not assign twice the same ID to 2 differ‐
	      ent dictionaries. Note that 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	favor‐
	      ably to 4 bytes default.

	      Note  that RFC8878 reserves IDs less than 32768 and greater than
	      or equal to 2\^31, so they should not be used in public.

       --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 dic‐
	      tionary.	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 multi‐
	      threading 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 dictio‐
	      nary is at most shrinkDictMaxRegression% worse than the compres‐
	      sion 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

	      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  differ‐
	      ent  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 sub‐
	      segments 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 re‐
	      duces 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  dictio‐
	      nary  selectivity	 (default:  9).	 The  smaller  the selectivity
	      value, the denser the dictionary, improving its  efficiency  but
	      reducing its achievable maximum size. --train-legacy=s=# is also
	      accepted.

	      Examples:

	      zstd --train-legacy FILEs

	      zstd --train-legacy=selectivity=8 FILEs

BENCHMARK
       The zstd CLI provides a benchmarking mode that can be  used  to	easily
       find  suitable  compression parameters, or alternatively to benchmark a
       computer's performance. zstd -b [FILE(s)] will benchmark zstd for  both
       compression  and	 decompression	using  default compression level. Note
       that results are very dependent on the content being  compressed.  It's
       possible	 to pass multiple files to the benchmark, and even a directory
       with -r DIRECTORY. When no FILE is provided, the benchmark will	use  a
       procedurally generated lorem ipsum text.

       •   -b#: benchmark file(s) using compression level #

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

       •   -d:	benchmark  decompression  speed	 only  (requires  providing  a
	   zstd-compressed content)

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

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

       •   -S:	output	one benchmark result per input file (default: consoli‐
	   dated result)

       •   -D dictionary benchmark using dictionary

       •   --priority=rt: set process priority to real-time (Windows)



       Beyond compression levels, benchmarking is also compatible  with	 other
       parameters,  such  as number of threads (-T#), advanced compression pa‐
       rameters (--zstd=###), dictionary compression (-D dictionary), or  even
       disabling checksum verification for example.

       Output Format: CompressionLevel#Filename: InputSize -> OutputSize (Com‐
       pressionRatio), CompressionSpeed, DecompressionSpeed

       Methodology: For speed measurement, the entire input is	compressed/de‐
       compressed  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.

SEE ALSO
       zstdgrep(1), zstdless(1), gzip(1), xz(1)

       The  zstandard format is specified in Y. Collet, "Zstandard Compression
       and	   the	       'application/zstd'	  Media		Type",
       https://www.ietf.org/rfc/rfc8878.txt,   Internet	  RFC  8878  (February
       2021).

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

AUTHOR
       Yann Collet



zstd 1.5.6			 October 2024			       ZSTD(1)

ZSTD(1)				 User Commands			       ZSTD(1)



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

SYNOPSIS
       allbox; 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, from fast modes at > 200
       MB/s per core, to strong modes with excellent  compression  ratios.  It
       also  features  a  very	fast decoder, with speeds > 500 MB/s per core,
       which remains roughly stable at all compression settings.

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

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

       •   When compressing a single file, zstd	 displays  progress  notifica‐
	   tions and result summary by default. Use -q to turn them off.

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

       •   zstd does not accept input from  console,  though  it  does	accept
	   stdin when it's not the console.

       •   zstd	 does  not  store the input's filename or attributes, only its
	   contents.



       zstd processes 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:

       •   When compressing, the suffix .zst is appended to the	 source	 file‐
	   name to get the target filename.

       •   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 multiple .zst files. zstd will decompress
       such agglomerated file as if it was a single .zst file.

OPTIONS
   Integer Suffixes and Special Values
       In  most places where an integer argument is expected, an optional suf‐
       fix 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 ac‐
	      cepted as synonyms for KiB.

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

   Operation Mode
       If  multiple  operation	mode options are given, the last one takes ef‐
       fect.

       -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  --decom‐
	      press).

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

       -t, --test
	      Test  the	 integrity of compressed files. This option is equiva‐
	      lent to --decompress --stdout > /dev/null, decompressed data  is
	      discarded	 and  checksummed  for errors. No files are created or
	      removed.

       -b#    Benchmark file(s) using compression level #. See BENCHMARK below
	      for a description of this operation.

       --train FILES
	      Use FILES as a training set to create a dictionary. The training
	      set should contain a lot of small files (> 100). See  DICTIONARY
	      BUILDER below for a description of this operation.

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

   Operation Modifiers
       •   -#: selects # compression level [1-19] (default:  3).  Higher  com‐
	   pression  levels  generally produce higher compression ratio at the
	   expense of speed and memory. A rough rule of thumb is that compres‐
	   sion	 speed	is expected to be divided by 2 every 2 levels. Techni‐
	   cally, each level is mapped to a set of advanced  parameters	 (that
	   can also be modified individually, see below). Because the compres‐
	   sor's behavior highly depends on the content to  compress,  there's
	   no guarantee of a smooth progression from one level to another.

       •   --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.

       •   --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 set‐
	   ting overwrites compression level if one was set previously.	 Simi‐
	   larly, if a compression level is set after --fast, it overrides it.

       •   -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,
	   which is either 64 in 32-bit mode, or 256 for 64-bit	 environments.
	   This	 modifier does nothing if zstd is compiled without multithread
	   support.

       •   --single-thread: Use a single thread for both I/O and  compression.
	   As compression is serialized with I/O, this can be slightly slower.
	   Single-thread mode features significantly lower memory usage, which
	   can	be  useful  for systems with limited amount of memory, such as
	   32-bit systems.

	   Note 1: this mode is the only available one when  multithread  sup‐
	   port is disabled.

	   Note 2: this mode is different from -T1, which spawns 1 compression
	   thread in parallel  with  I/O.  Final  compressed  result  is  also
	   slightly different from -T1.

       •   --auto-threads={physical,logical} (default: physical): When using a
	   default amount of threads via -T0, choose the default based on  the
	   number of detected physical or logical cores.

       •   --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  com‐
	   bined  with	multi-threading and --long mode. It does not work with
	   --single-thread. It sets window size to 8 MiB 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).

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

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

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

       •   --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.

	   Note:  up  to level 15, you can use --patch-from in --single-thread
	   mode to improve compression ratio marginally at the cost of	speed.
	   Using  '--single-thread' above level 15 will lead to lower compres‐
	   sion ratios.

	   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=.

       •   --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 a potential  impact  to
	   compression	speed,	perceptible at higher speeds, for example when
	   combining --rsyncable with many parallel worker threads. This  fea‐
	   ture does not work with --single-thread. You probably don't want to
	   use it with long range mode, since it will decrease the  effective‐
	   ness of the synchronization points, but your mileage may vary.

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

       •   --[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).

       •   --no-dictID:	 do  not store dictionary ID within frame header (dic‐
	   tionary 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.

       •   -M#, --memory=#: Set a memory usage limit. By  default,  zstd  uses
	   128	MiB  for decompression as the maximum amount of memory the de‐
	   compressor is allowed to use, but you can override this manually if
	   need be in either direction (i.e. 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	 size  allowed
	   for a dictionary. (128 MiB).

	   Additionally,  this	can  be	 used  to  limit memory for dictionary
	   training. This parameter overrides the default limit of 2 GiB. zstd
	   will	 load  training	 samples up to the memory limit and ignore the
	   rest.

       •   --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 param‐
	   eters, resulting in better and potentially faster compression,  es‐
	   pecially for smaller source sizes.

       •   --size-hint=#:  When	 handling input from a stream, zstd must guess
	   how large the source size will be when optimizing  compression  pa‐
	   rameters. 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.

       •   --target-compressed-block-size=#:  Attempt  to  produce  compressed
	   blocks of approximately this size. This will split larger blocks in
	   order to approach this target. This feature is notably  useful  for
	   improved  latency,  when  the receiver can leverage receiving early
	   incomplete data. This parameter defines a loose target:  compressed
	   blocks  will	 target	 this size "on average", but individual blocks
	   can still be larger or smaller. Enabling this feature can  decrease
	   compression	speed by up to ~10% at level 1. Higher levels will see
	   smaller relative speed regression,  becoming	 invisible  at	higher
	   settings.

       •   -f,	--force:  disable  input and output checks. Allows overwriting
	   existing files, input from console, output to stdout, operating  on
	   links, block devices, etc. During decompression and when the output
	   destination is stdout, pass-through unrecognized formats as-is.

       •   -c, --stdout: write to standard output (even if it is the console);
	   keep original files (disable --rm).

       •   -o FILE: save result into FILE. Note that this operation is in con‐
	   flict with -c. If both operations are present on the command	 line,
	   the last expressed one wins.

       •   --[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.

       •   --[no-]pass-through enable / disable passing	 through  uncompressed
	   files as-is. During decompression when pass-through is enabled, un‐
	   recognized formats will be copied as-is from the input to the  out‐
	   put.	 By  default, pass-through will occur when the output destina‐
	   tion is stdout and the force (-f) option is set.

       •   --rm: remove source file(s) after successful compression or	decom‐
	   pression.  This command is silently ignored if output is stdout. If
	   used in combination with -o, triggers a confirmation prompt	(which
	   can be silenced with -f), as this is a destructive operation.

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

       •   -r: operate recursively on directories. It selects all files in the
	   named directory and all its subdirectories. This can be useful both
	   to reduce command line typing, and to  circumvent  shell  expansion
	   limitations,	 when  there  are a lot of files and naming breaks the
	   maximum size of a command line.

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

       •   --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
	   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.

       •   --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	 "out‐
	   put-dir/var/tmp/abc". If there are multiple input files or directo‐
	   ries,  name	collision  resolution  will  follow  the same rules as
	   --output-dir-flat.

       •   --format=FORMAT: compress and decompress in other formats. If  com‐
	   piled  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.

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

       •   -V, --version: display version number and  immediately  exit.  note
	   that,  since it exits, flags specified after -V are effectively ig‐
	   nored. Advanced: -vV also displays  supported  formats.  -vvV  also
	   displays  POSIX  support. -qV will only display the version number,
	   suitable for machine reading.

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

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

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

       •   --show-default-cparams: shows the  default  compression  parameters
	   that	 will  be  used for a particular input file, based on the pro‐
	   vided compression level and the input size. If the provided file is
	   not a regular file (e.g. a pipe), this flag will output the parame‐
	   ters used for inputs of unknown size.

       •   --exclude-compressed: only compress files that are not already com‐
	   pressed.

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



   gzip Operation Modifiers
       When invoked via a gzip symlink, zstd will support further options that
       intend to mimic the gzip behavior:

       -n, --no-name
	      do not store the original filename and timestamps when compress‐
	      ing a file. This is the default behavior and hence a no-op.

       --best alias to the option -9.

   Environment Variables
       Employing environment variables to set parameters has security implica‐
       tions.  Therefore,  this	 avenue	  is   intentionally   limited.	  Only
       ZSTD_CLEVEL  and	 ZSTD_NBTHREADS	 are currently supported. They set the
       default compression level and number of threads to use during  compres‐
       sion, 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  at‐
       tempt  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_NBTHREADS  has a default value of (1), and is capped at ZSTDMT_NB‐
       WORKERS_MAX==200. zstd must be compiled with  multithread  support  for
       this variable to have any effect.

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

ADVANCED COMPRESSION OPTIONS
       zstd provides 22 predefined regular compression levels  plus  the  fast
       levels.	A compression level is translated internally into multiple ad‐
       vanced parameters that control the behavior of the compressor (one  can
       observe	the  result  of this translation with --show-default-cparams).
       These advanced parameters can be overridden using advanced  compression
       options.

   --zstd[=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 fastest to
	      strongest:     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 re‐
	      quirements 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 fewer collisions which usually makes
	      compression faster, but requires more memory during compression.

	      The minimum hlog is 6 (64 entries / 256 B) and the maximum is 30
	      (1B entries / 4 GiB).

       chainLog=clog, clog=clog
	      Specify  the  maximum  number  of	 bits for the secondary search
	      structure, whose form depends on the selected strategy.

	      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 compres‐
	      sion.  This  option is ignored for the ZSTD_fast strategy, which
	      only has the primary hash table.

	      The minimum clog is 6 (64 entries / 256 B) and the maximum is 29
	      (512M  entries / 2 GiB) on 32-bit platforms and 30 (1B entries /
	      4 GiB) on 64-bit platforms.

       searchLog=slog, slog=slog
	      Specify the maximum number of searches in a hash chain or a  bi‐
	      nary 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 im‐
	      prove 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 de‐
	      creases compression speed.

	      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 en‐
	      abled.  Reloading	 more data improves compression ratio, but de‐
	      creases speed.

	      The minimum ovlog is 0, and the maximum is 9. 1 means "no	 over‐
	      lap", 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 exam‐
	      ple, 8 means "windowSize/2", and 6 means "windowSize/8". Value 0
	      is  special  and	means "default": ovlog is automatically deter‐
	      mined by zstd. In which case, ovlog will range from 6 to 9,  de‐
	      pending 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  ex‐
	      pense  of	 more memory during compression and a decrease in com‐
	      pression 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 dis‐
	      tance matching hash table.

	      This option is ignored unless long distance matching is enabled.

	      Larger values will improve compression speed. Deviating far from
	      the  default  value will likely result in a decrease in compres‐
	      sion 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#:
       Specify the size of each compression job. This parameter is only avail‐
       able when multi-threading is enabled. Each compression job  is  run  in
       parallel,  so  this  value indirectly impacts the nb of active threads.
       Default job size varies depending on compression level (generally  4  *
       windowSize).  -B#  makes	 it possible to manually select a custom size.
       Note that job size must respect	a  minimum  value  which  is  enforced
       transparently. This minimum is either 512 KB, or overlapSize, whichever
       is largest. Different job sizes will lead to  non-identical  compressed
       frames.

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  dictio‐
       nary,  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 ideally contain a lot of samples (> 100), and weight
	      typically 100x the target dictionary size (for example,  ~10  MB
	      for a 100 KB dictionary). --train can be combined with -r to in‐
	      dicate a directory rather than listing all the files, which  can
	      be useful to circumvent shell expansion limits.

	      Since  dictionary	 compression  is  mostly  effective  for small
	      files, the expectation is that the training set will  only  con‐
	      tain  small  files.  In the case where some samples happen to be
	      large, only the first 128 KiB of these samples will be used  for
	      training.

	      --train supports multithreading if zstd is compiled with thread‐
	      ing support (default). Additional	 advanced  parameters  can  be
	      specified	 with --train-fastcover. The legacy dictionary builder
	      can be accessed with --train-legacy. The slower cover dictionary
	      builder  can  be accessed with --train-cover. Default --train is
	      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  bytes).  As
	      usual,  quantities  are  expressed in bytes by default, and it's
	      possible to employ suffixes (like KB or MB)  to  specify	larger
	      values.

       -#     Use  # compression level during training (optional). Will gener‐
	      ate statistics more tuned for selected  compression  level,  re‐
	      sulting in a small compression ratio improvement for this level.

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

       -M#, --memory=#
	      Limit  the amount of sample data loaded for training (default: 2
	      GB). Note that the default (2 GB) is also the maximum. This  pa‐
	      rameter  can be useful in situations where the training set size
	      is not well controlled and  could	 be  potentially  very	large.
	      Since  speed  of	the training process is directly correlated to
	      the size of the training sample set, a smaller sample set	 leads
	      to faster training.

	      In situations where the training set is larger than maximum mem‐
	      ory, the CLI will randomly select samples	 among	the  available
	      ones,  up to the maximum allowed memory budget. This is meant to
	      improve dictionary relevance by mitigating the potential	impact
	      of  clustering,  such as selecting only files from the beginning
	      of a list sorted by modification date, or sorted by alphabetical
	      order.  The  randomization process is deterministic, so training
	      of the same list of files with the same parameters will lead  to
	      the creation of the same dictionary.

       --dictID=#
	      A	 dictionary  ID	 is  a locally unique ID. The decoder will use
	      this value to verify it is using the right  dictionary.  By  de‐
	      fault,  zstd will create a 4-bytes random number ID. It's possi‐
	      ble to provide an explicit number ID instead.  It's  up  to  the
	      dictionary  manager to not assign twice the same ID to 2 differ‐
	      ent dictionaries. Note that 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	favor‐
	      ably to 4 bytes default.

	      Note  that RFC8878 reserves IDs less than 32768 and greater than
	      or equal to 2\^31, so they should not be used in public.

       --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 dic‐
	      tionary.	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 multi‐
	      threading 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 dictio‐
	      nary is at most shrinkDictMaxRegression% worse than the compres‐
	      sion 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

	      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  differ‐
	      ent  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 sub‐
	      segments 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 re‐
	      duces 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  dictio‐
	      nary  selectivity	 (default:  9).	 The  smaller  the selectivity
	      value, the denser the dictionary, improving its  efficiency  but
	      reducing its achievable maximum size. --train-legacy=s=# is also
	      accepted.

	      Examples:

	      zstd --train-legacy FILEs

	      zstd --train-legacy=selectivity=8 FILEs

BENCHMARK
       The zstd CLI provides a benchmarking mode that can be  used  to	easily
       find  suitable  compression parameters, or alternatively to benchmark a
       computer's performance. zstd -b [FILE(s)] will benchmark zstd for  both
       compression  and	 decompression	using  default compression level. Note
       that results are very dependent on the content being  compressed.  It's
       possible	 to pass multiple files to the benchmark, and even a directory
       with -r DIRECTORY. When no FILE is provided, the benchmark will	use  a
       procedurally generated lorem ipsum text.

       •   -b#: benchmark file(s) using compression level #

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

       •   -d:	benchmark  decompression  speed	 only  (requires  providing  a
	   zstd-compressed content)

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

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

       •   -S:	output	one benchmark result per input file (default: consoli‐
	   dated result)

       •   -D dictionary benchmark using dictionary

       •   --priority=rt: set process priority to real-time (Windows)



       Beyond compression levels, benchmarking is also compatible  with	 other
       parameters,  such  as number of threads (-T#), advanced compression pa‐
       rameters (--zstd=###), dictionary compression (-D dictionary), or  even
       disabling checksum verification for example.

       Output Format: CompressionLevel#Filename: InputSize -> OutputSize (Com‐
       pressionRatio), CompressionSpeed, DecompressionSpeed

       Methodology: For speed measurement, the entire input is	compressed/de‐
       compressed  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.

SEE ALSO
       zstdgrep(1), zstdless(1), gzip(1), xz(1)

       The  zstandard format is specified in Y. Collet, "Zstandard Compression
       and	   the	       'application/zstd'	  Media		Type",
       https://www.ietf.org/rfc/rfc8878.txt,   Internet	  RFC  8878  (February
       2021).

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

AUTHOR
       Yann Collet



zstd 1.5.6			 October 2024			       ZSTD(1)

ZSTDLESS(1)			 User Commands			   ZSTDLESS(1)



NAME
       zstdless - view zstandard-compressed files

SYNOPSIS
       zstdless [flags] [file ...]

DESCRIPTION
       zstdless	 runs less(1) on files or stdin, if no file argument is given,
       after decompressing them with zstdcat(1).

SEE ALSO
       zstd(1)



zstd 1.5.6			  March 2024			   ZSTDLESS(1)

ZSTDGREP(1)			 User Commands			   ZSTDGREP(1)



NAME
       zstdgrep - print lines matching a pattern in zstandard-compressed files

SYNOPSIS
       zstdgrep [grep-flags] [--] pattern [files ...]

DESCRIPTION
       zstdgrep runs grep(1) on files, or stdin if no files argument is given,
       after decompressing them with zstdcat(1).

       The grep-flags and pattern arguments are passed on to grep(1). If an -e
       flag  is	 found in the grep-flags, zstdgrep will not look for a pattern
       argument.

       Note that modern grep alternatives  such	 as  ripgrep  (rg(1))  support
       zstd-compressed files out of the box, and can prove better alternatives
       than zstdgrep notably for unsupported complex  pattern  searches.  Note
       though  that such alternatives may also feature some minor command line
       differences.

EXIT STATUS
       In case of missing arguments or missing pattern, 1  will	 be  returned,
       otherwise 0.

SEE ALSO
       zstd(1)

AUTHORS
       Thomas Klausner wiz@NetBSD.org



zstd 1.5.6			  March 2024			   ZSTDGREP(1)