Provided by: zstd_1.3.8+dfsg-3_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 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
           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)

       --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.

       --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 # 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_NBTHREADS_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).

       --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.

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

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

       -o 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 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.

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

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

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

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

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

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

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

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

       --train-cover[=k#,d=#,steps=#,split=#]
              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.

              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.

              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

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

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

              Examples:

              zstd --train-fastcover FILEs

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

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

              Examples:

              zstd --train-legacy FILEs

              zstd --train-legacy=selectivity=8 FILEs

BENCHMARK

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

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

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

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

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

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

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

ADVANCED COMPRESSION OPTIONS

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

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

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

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

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

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

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

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

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

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

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

              The minimum mml is 3 and the maximum is 7.

       targetLen=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  targetLen  usually
              improves compression ratio but decreases 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
              targetLen 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 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.  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 26 (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 0 and the maximum is 8 (default: 3).

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

              This option is ignored unless long distance matching is enabled.

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

              The default value is wlog - lhlog.

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

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

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

BUGS

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

AUTHOR

       Yann Collet