Provided by: zstd_1.4.3+dfsg-1_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 directories

       --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.

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

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

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

              Examples:

              zstd --train-cover FILEs

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

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

              zstd --train-cover=k=50 FILEs

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

              zstd --train-cover=shrink FILEs

              zstd --train-cover=shrink=2 FILEs

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

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

              Examples:

              zstd --train-fastcover FILEs

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

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

              Examples:

              zstd --train-legacy FILEs

              zstd --train-legacy=selectivity=8 FILEs

BENCHMARK

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

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

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

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

       --priority=rt
              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