Provided by: zstd_1.3.3+dfsg-2ubuntu1.2_amd64 bug

NAME

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

SYNOPSIS

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

       zstdmt is equivalent to zstd -T0

       unzstd is equivalent to zstd -d

       zstdcat is equivalent to zstd -dcf

DESCRIPTION

       zstd is a fast lossless compression algorithm and data compression tool, with command line
       syntax similar to gzip (1) and xz (1). It is based on the LZ77 family, with further FSE  &
       huff0  entropy  stages. zstd offers highly configurable compression speed, with fast modes
       at > 200 MB/s per code, 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
           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 .zst files as is. zstd will decompress such files as if they
       were a single .zst file.

OPTIONS

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

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

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

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

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

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

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

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

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

       -l, --list
              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.

       --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.

       -T#, --threads=#
              Compress using # 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_NBTHREADS_MAX==256. This modifier does nothing if zstd is  compiled  without
              multithread support.

       -D file
              use file as Dictionary to compress or decompress FILE(s)

       --nodictID
              do  not  store  dictionary  ID  within  frame  header (dictionary compression). The
              decoder will have to rely on implicit knowledge about which dictionary to  use,  it
              won´t be able to check if it´s correct.

       -o file
              save result into file (only possible with a single INPUT-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

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

       -r     operate recursively on dictionaries

       --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 gzip, xz, lzma, and lz4.

       -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.

       -v     verbose mode

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

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

       --     All arguments after -- are treated as files

DICTIONARY BUILDER

       zstd offers dictionary compression,  useful  for  very  small  files  and  messages.  It´s
       possible  to train zstd with some samples, the result of which is saved into a file called
       a dictionary. Then during compression and decompression, reference the same dictionary. It
       will  improve  compression ratio of small files. Typical gains range from 10% (at 64KB) to
       x5 better (at <1KB).

       --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-cover. The legacy dictionary builder can
              be accessed with --train-legacy. Equivalent to --train-cover=d=8,steps=4.

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

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

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

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

       --train-cover[=k#,d=#,steps=#]
              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. Requires that d <= k.

              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]. Supports multithreading if  zstd  is
              compiled with threading support.

              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

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

              Examples:

              zstd --train-legacy FILEs

              zstd --train-legacy=selectivity=8 FILEs

BENCHMARK

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

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

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

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

       --priority=rt
              set process priority to real-time

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

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

ADVANCED COMPRESSION OPTIONS

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

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

              There are 8 strategies numbered from 1 to 8, 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.

       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 26 (128 MiB).

       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 28 (256 MiB).

       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 26.

       searchLength=slen, slen=slen
              Specify the minimum searched length of a match in a hash table.

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

              The minimum slen is 3 and the maximum is 7.

       targetLen=tlen, tlen=tlen
              Specify the minimum match length that causes a match finder to stop  searching  for
              better matches.

              A  larger  minimum  match  length  usually improves compression ratio but decreases
              compression speed.  This  option  is  only  used  with  strategies  ZSTD_btopt  and
              ZSTD_btultra.

              The minimum tlen is 4 and the maximum is 999.

       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.  0 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 amount of reload by a
              factor 2. Default ovlog is 6, which means "reload windowSize / 8". Exception :  the
              maximum compression level (22) has a default ovlog of 9.

       ldmHashLog=ldmhlog, ldmhlog=ldmhlog
              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 ldmhlog is 6 and the maximum is 26 (default: 20).

       ldmSearchLength=ldmslen, ldmslen=ldmslen
              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 ldmslen is 4 and the maximum is 4096 (default: 64).

       ldmBucketSizeLog=ldmblog, ldmblog=ldmblog
              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 ldmblog is 0 and the maximum is 8 (default: 3).

       ldmHashEveryLog=ldmhevery, ldmhevery=ldmhevery
              Specify the frequency of inserting entries into the  long  distance  matching  hash
              table.

              This option is ignored unless long distance matching is enabled.

              Larger  values will improve compression speed. Deviating far from the default value
              will likely result in a decrease in compression ratio.

              The default value is wlog - ldmhlog.

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

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

       --zstd=windowLog=23,chainLog=23,hashLog=22,searchLog=6,searchLength=3,targetLength=48,strategy=6

BUGS

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

AUTHOR

       Yann Collet