Provided by: zstd_1.4.8+dfsg-3build1_amd64 bug


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


       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


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

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

       •   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 notifications and result
           summary by default. Use -q to turn them off.

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

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

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

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

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

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

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


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

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

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

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

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

       -d, --decompress, --uncompress

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

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

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

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

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

       •   --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  setting  overwrites  compression  level  if  one  was   set
           previously. Similarly, 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==200.  This modifier does nothing if zstd is compiled
           without multithread support.

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

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

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

           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.  Node:  for  all  levels,  you  can  use
           --patch-from in --single-thread mode to improve compression ratio at the cost of speed
           Note: for level 19, you can get increased compression ratio at the cost  of  speed  by
           specifying  --zstd=targetLength=  to  be  something large (i.e 4096), and by setting a
           large --zstd=chainLog=--rsyncable : zstd will periodically synchronize the compression  state  to  make  the
           compressed  file  more  rsync-friendly.  There  is  a negligible impact to compression
           ratio, and the faster compression levels will see a small compression speed hit.  This
           feature  does  not  work  with --single-thread. You probably don´t want to use it with
           long range mode, since it will  decrease  the  effectiveness  of  the  synchronization
           points, but your milage may vary.

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

       •   --[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 (dictionary  compression).
           The  decoder will have to rely on implicit knowledge about which dictionary to use, it
           won´t be able to check if it´s correct.

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

           This is also used during compression when using with --patch-from=. In this case, this
           parameter overrides that maximum size allowed for a dictionary. (128 MB).

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

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

       •   -o FILE: save result into FILE-f, --force: overwrite output without prompting, and (de)compress symbolic links

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

       •   --[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.

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

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

       •   -r: operate recursively on directories

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

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

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

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

       •   -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  src  file.  If  the  provided src file is not a regular file (eg. named
           pipe), the cli will just output the default parameters. That is, the  parameters  that
           are used when the src size is unknown.

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

   Restricted usage of Environment Variables
       Using  environment  variables to set parameters has security implications. Therefore, this
       avenue is intentionally restricted. Only  ZSTD_CLEVEL  and  ZSTD_NBTHREADS  are  currently
       supported. They set the compression level and number of threads to use during compression,

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

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

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


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

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

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

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

              Limit dictionary to specified size (default: 112640).

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

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

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

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

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


              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

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

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


              zstd --train-fastcover FILEs

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

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


              zstd --train-legacy FILEs

              zstd --train-legacy=selectivity=8 FILEs


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

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

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

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

              set process priority to real-time

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

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


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

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

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

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

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

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

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

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

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

       chainLog=clog, clog=clog
              Specify the maximum number of bits for a hash chain or a binary tree.

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

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

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

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

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

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

              Larger search lengths usually decrease compression ratio but improve  decompression

              The minimum mml is 3 and the maximum is 7.

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

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

              For all other strategies, this field has no impact.

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

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

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

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

              This option is ignored unless long distance matching is enabled.

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

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

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

              This option is ignored unless long distance matching is enabled.

              Larger/very small values usually decrease compression ratio.

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

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

              This option is ignored unless long distance matching is enabled.

              Larger bucket sizes improve collision resolution but decrease compression speed.

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

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

              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 compression ratio.

              The default value is wlog - lhlog.

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


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


       Report bugs at:


       Yann Collet