ZSTD(1) User Commands ZSTD(1)
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 :
o Source files are preserved by default. It's possible to remove them
automatically by using the --rm command.
o When compressing a single file, zstd displays progress notifica-
tions and result summary by default. Use -q to turn them off.
o zstd does not accept input from console, but it properly accepts
stdin when it's not the console.
o 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 ter-
minal : 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:
o When compressing, the suffix .zst is appended to the source file-
name to get the target filename.
o 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 suf-
fix is supported to easily indicate large integers. There must be no
space between the integer and the suffix.
KiB Multiply the integer by 1,024 (2^10). Ki, K, and KB are 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 --decom-
press).
-d, --decompress, --uncompress
Decompress.
-t, --test
Test the integrity of compressed files. This option is equiva-
lent 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 compres-
sion speed, at the cost of some compression ratio. This setting
overwrites compression level if one was set previously. Simi-
larly, 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 mem-
ory 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 (win-
dowLog) and memory usage for both the compressor and decompres-
sor. This setting is designed to improve the compression ratio
for files with long matches at a large distance.
Note: If windowLog is set to larger than 27, --long=windowLog or
--memory=windowSize needs to be passed to the decompressor.
-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 ZST-
DMT_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 serial-
ized 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 dis-
abled. 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 --sin-
gle-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).
--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 parame-
ters, 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 underesti-
mates may result in significant degradation.
--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 com-
pression). 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 decompres-
sion
-k, --keep
keep source file(s) after successful compression or decompres-
sion. This is the default behavior.
-r operate recursively on directories
--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 differ-
ent directories, end up having the same name. Collision resolu-
tion ensures first file with a given name will be present in
dir, while in combination with -f, the last file will be present
instead.
--format=FORMAT
compress and decompress in other formats. If compiled with sup-
port, 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
Restricted usage of Environment Variables
Using environment variables to set parameters has security implica-
tions. Therefore, this avenue is intentionally restricted. Only
ZSTD_CLEVEL is supported currently, for setting compression level.
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). It can be overridden by corresponding command
line arguments.
Parallel Zstd OPTIONS
Additional options for the pzstd utility
-p, --processes
number of threads to use for (de)compression (default:4)
DICTIONARY BUILDER
zstd offers dictionary compression, which greatly improves efficiency
on small files and messages. It's possible to train zstd with a set of
samples, the result of which is saved into a file called a dictionary.
Then during compression and decompression, reference the same dictio-
nary, using command -D dictionaryFileName. Compression of small files
similar to the sample set will be greatly improved.
--train FILEs
Use FILEs as training set to create a dictionary. The training
set should contain a lot of small files (> 100), and weight typ-
ically 100x the target dictionary size (for example, 10 MB for a
100 KB dictionary).
Supports multithreading if zstd is compiled with threading sup-
port. Additional parameters can be specified with --train-fast-
cover. 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 gener-
ate 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 pre-
cise 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 dic-
tionary. The score of a segment is computed by the sum of the
frequencies of all the subsegments of size d. Generally d should
be in the range [6, 8], occasionally up to 16, but the algorithm
will run faster with d <= 8. Good values for k vary widely based
on the input data, but a safe range is [2 * d, 2000]. If split
is 100, all input samples are used for both training and testing
to find optimal d and k to build dictionary. Supports multi-
threading if zstd is compiled with threading support. Having
shrink enabled takes a truncated dictionary of minimum size and
doubles in size until compression ratio of the truncated dictio-
nary is at most shrinkDictMaxRegression% worse than the compres-
sion ratio of the largest dictionary.
Examples:
zstd --train-cover FILEs
zstd --train-cover=k=50,d=8 FILEs
zstd --train-cover=d=8,steps=500 FILEs
zstd --train-cover=k=50 FILEs
zstd --train-cover=k=50,split=60 FILEs
zstd --train-cover=shrink FILEs
zstd --train-cover=shrink=2 FILEs
--train-fastcover[=k#,d=#,f=#,steps=#,split=#,accel=#]
Same as cover but with extra parameters f and accel and differ-
ent default value of split If split is not specified, then it
tries split = 75. If f is not specified, then it tries f = 20.
Requires that 0 < f < 32. If accel is not specified, then it
tries accel = 1. Requires that 0 < accel <= 10. Requires that d
= 6 or d = 8.
f is log of size of array that keeps track of frequency of sub-
segments of size d. The subsegment is hashed to an index in the
range [0,2^f - 1]. It is possible that 2 different subsegments
are hashed to the same index, and they are considered as the
same subsegment when computing frequency. Using a higher f
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 dictio-
nary 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 com-
pressed/decompressed several times per run, in order to improve mea-
surement 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 plat-
forms 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 compres-
sion. 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 over-
lap", hence completely independent jobs. 9 means "full overlap",
meaning up to windowSize is reloaded from previous job. Reducing
ovlog by 1 reduces the reloaded amount by a factor 2. For exam-
ple, 8 means "windowSize/2", and 6 means "windowSize/8". Value 0
is special and means "default" : ovlog is automatically deter-
mined by zstd. In which case, ovlog will range from 6 to 9,
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 com-
pression 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 dis-
tance matching hash table.
This option is ignored unless long distance matching is enabled.
Larger values will improve compression speed. Deviating far from
the default value will likely result in a decrease in compres-
sion ratio.
The default value is wlog - lhlog.
Example
The following parameters sets advanced compression options to something
similar to predefined level 19 for files bigger than 256 KB:
--zstd=wlog=23,clog=23,hlog=22,slog=6,mml=3,tlen=48,strat=6
-B#:
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 pos-
sible to select a custom value. Note that job size must respect a mini-
mum 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
zstd 1.4.4 October 2019 ZSTD(1)
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