ZSTD(1) User Commands ZSTD(1)
NAME
zstd - zstd, zstdmt, unzstd, zstdcat - Compress or decompress .zst files
SYNOPSIS
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, from fast modes at > 200 MB/s per
core, to strong modes with excellent compression ratios. It also fea-
tures a very fast decoder, with speeds > 500 MB/s per core, which re-
mains roughly stable at all compression settings.
zstd command line syntax is generally similar to gzip, but features the
following few 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 displays a short help page when command line is an error. Use
-q to turn it off.
• zstd does not accept input from console, though it does accept stdin
when it's not the console.
• zstd does not store the input's filename or attributes, only its
contents.
zstd processes 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 com-
pressed 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 file-
name to get the target filename
Concatenation with .zst Files
It is possible to concatenate multiple .zst files. zstd will decompress
such agglomerated file as if it was 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 ac-
cepted 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 > /dev/null, decompressed data is dis-
carded and checksummed for errors. No files are created or re-
moved.
-b# Benchmark file(s) using compression level #. See BENCHMARK below
for a description of this operation.
--train FILES
Use FILES as a training set to create a dictionary. The training
set should contain a lot of small files (> 100). See DICTIONARY
BUILDER below for a description of this operation.
-l, --list
Display information related to a zstd compressed file, such as
size, ratio, and checksum. Some of these fields may not be avail-
able. This command's output can be augmented with the -v modi-
fier.
Operation Modifiers
• -#: selects # compression level [1-19] (default: 3). Higher compres-
sion levels generally produce higher compression ratio at the ex-
pense of speed and memory. A rough rule of thumb is that compression
speed is expected to be divided by 2 every 2 levels. Technically,
each level is mapped to a set of advanced parameters (that can also
be modified individually, see below). Because the compressor's be-
havior highly depends on the content to compress, there's no guaran-
tee of a smooth progression from one level to another.
• --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.
• --fast[=#]: switch to ultra-fast compression levels. If =# is not
present, it defaults to 1. The higher the value, the faster the com-
pression 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,
which is either 64 in 32-bit mode, or 256 for 64-bit environments.
This modifier does nothing if zstd is compiled without multithread
support.
• --single-thread: Use a single thread for both I/O and compression.
As compression is serialized with I/O, this can be slightly slower.
Single-thread mode features significantly lower memory usage, which
can be useful for systems with limited amount of memory, such as
32-bit systems.
Note 1: this mode is the only available one when multithread support
is disabled.
Note 2: this mode is different from -T1, which spawns 1 compression
thread in parallel with I/O. Final compressed result is also
slightly different from -T1.
• --auto-threads={physical,logical} (default: physical): When using a
default amount of threads via -T0, choose the default based on the
number of detected physical or logical cores.
• --adapt[=min=#,max=#]: zstd will dynamically adapt compression level
to perceived I/O conditions. Compression level adaptation can be ob-
served live by using command -v. Adaptation can be constrained be-
tween 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 MiB by default (can be changed
manually, see wlog). Due to the chaotic nature of dynamic adapta-
tion, 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 # is
not present it defaults to 27. This increases the window size (win-
dowLog) 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.
Note: up to level 15, you can use --patch-from in --single-thread
mode to improve compression ratio marginally at the cost of speed.
Using '--single-thread' above level 15 will lead to lower compres-
sion ratios.
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 a potential impact to
compression speed, perceptible at higher speeds, for example when
combining --rsyncable with many parallel worker threads. This fea-
ture does not work with --single-thread. You probably don't want to
use it with long range mode, since it will decrease the effective-
ness of the synchronization points, but your mileage may vary.
• -C, --[no-]check: add integrity check computed from uncompressed
data (default: enabled)
• --[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 (dictio-
nary compression). The decoder will have to rely on implicit knowl-
edge 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, zstd uses 128
MiB for decompression as the maximum amount of memory the decompres-
sor is allowed to use, but you can override this manually if need be
in either direction (i.e. 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 MiB).
Additionally, this can be used to limit memory for dictionary train-
ing. This parameter overrides the default limit of 2 GiB. zstd will
load training samples up to the memory limit and ignore the rest.
• --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 pro-
duced 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 para-
meters. 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 re-
sult in significant degradation.
• --target-compressed-block-size=#: Attempt to produce compressed
blocks of approximately this size. This will split larger blocks in
order to approach this target. This feature is notably useful for
improved latency, when the receiver can leverage receiving early in-
complete data. This parameter defines a loose target: compressed
blocks will target this size "on average", but individual blocks can
still be larger or smaller. Enabling this feature can decrease com-
pression speed by up to ~10% at level 1. Higher levels will see
smaller relative speed regression, becoming invisible at higher set-
tings.
• -f, --force: disable input and output checks. Allows overwriting ex-
isting files, input from console, output to stdout, operating on
links, block devices, etc. During decompression and when the output
destination is stdout, pass-through unrecognized formats as-is.
• -c, --stdout: write to standard output (even if it is the console);
keep original files (disable --rm).
• -o FILE: save result into FILE. Note that this operation is in con-
flict with -c. If both operations are present on the command line,
the last expressed one wins.
• --[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.
• --[no-]pass-through enable / disable passing through uncompressed
files as-is. During decompression when pass-through is enabled, un-
recognized formats will be copied as-is from the input to the out-
put. By default, pass-through will occur when the output destination
is stdout and the force (-f) option is set.
• --rm: remove source file(s) after successful compression or decom-
pression. This command is silently ignored if output is stdout. If
used in combination with -o, triggers 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 de-
compression. This is the default behavior.
• -r: operate recursively on directories. It selects all files in the
named directory and all its subdirectories. This can be useful both
to reduce command line typing, and to circumvent shell expansion
limitations, when there are a lot of files and naming breaks the
maximum size of a command line.
• --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 in-
stead.
• --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 "out-
put-dir/var/tmp/abc". If there are multiple input files or directo-
ries, name collision resolution will follow the same rules as --out-
put-dir-flat.
• --format=FORMAT: compress and decompress in other formats. If com-
piled 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 immediately exit. note
that, since it exits, flags specified after -V are effectively ig-
nored. Advanced: -vV also displays supported formats. -vvV also dis-
plays POSIX support. -qV will only display the version number, suit-
able 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 input file, based on the provided
compression level and the input size. If the provided file is not a
regular file (e.g. a pipe), this flag will output the parameters
used for inputs of unknown size.
• --exclude-compressed: only compress files that are not already com-
pressed.
• --: All arguments after -- are treated as files
gzip Operation Modifiers
When invoked via a gzip symlink, zstd will support further options that
intend to mimic the gzip behavior:
-n, --no-name
do not store the original filename and timestamps when compress-
ing a file. This is the default behavior and hence a no-op.
--best alias to the option -9.
Environment Variables
Employing environment variables to set parameters has security implica-
tions. Therefore, this avenue is intentionally limited. Only ZSTD_CLEVEL
and ZSTD_NBTHREADS are currently supported. They set the default com-
pression level and number of threads to use during compression, respec-
tively.
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 at-
tempt 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_NBTHREADS has a default value of (1), and is capped at ZSTDMT_NB-
WORKERS_MAX==200. zstd must be compiled with multithread support for
this variable to have any effect.
They can both be overridden by corresponding command line arguments: -#
for compression level and -T# for number of compression threads.
ADVANCED COMPRESSION OPTIONS
zstd provides 22 predefined regular compression levels plus the fast
levels. A compression level is translated internally into multiple ad-
vanced parameters that control the behavior of the compressor (one can
observe the result of this translation with --show-default-cparams).
These advanced parameters can be overridden using advanced compression
options.
--zstd[=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 se-
lected 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 fastest to
strongest: 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 re-
quirements 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 fewer collisions which usually makes
compression faster, but requires more memory during compression.
The minimum hlog is 6 (64 entries / 256 B) and the maximum is 30
(1B entries / 4 GiB).
chainLog=clog, clog=clog
Specify the maximum number of bits for the secondary search
structure, whose form depends on the selected strategy.
Higher numbers of bits increases the chance to find a match which
usually improves compression ratio. It also slows down compres-
sion speed and increases memory requirements for compression.
This option is ignored for the ZSTD_fast strategy, which only has
the primary hash table.
The minimum clog is 6 (64 entries / 256 B) and the maximum is 29
(512M entries / 2 GiB) on 32-bit platforms and 30 (1B entries / 4
GiB) on 64-bit platforms.
searchLog=slog, slog=slog
Specify the maximum number of searches in a hash chain or a bi-
nary 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 im-
prove decompression speed.
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 de-
creases compression speed.
For ZSTD_fast, it triggers ultra-fast mode when > 0. The value
represents the amount of data skipped between match sampling. Im-
pact 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 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 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 ex-
pense of more memory during compression and a decrease in com-
pression 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 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#:
Specify the size of each compression job. This parameter is only avail-
able when multi-threading is enabled. Each compression job is run in
parallel, so this value indirectly impacts the nb of active threads. De-
fault job size varies depending on compression level (generally 4 * win-
dowSize). -B# makes it possible to manually select a custom size. Note
that job size must respect a minimum value which is enforced transpar-
ently. This minimum is either 512 KB, or overlapSize, whichever is
largest. Different job sizes will lead to non-identical compressed
frames.
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 sam-
ples, 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 ideally contain a lot of samples (> 100), and weight
typically 100x the target dictionary size (for example, ~10 MB
for a 100 KB dictionary). --train can be combined with -r to in-
dicate a directory rather than listing all the files, which can
be useful to circumvent shell expansion limits.
Since dictionary compression is mostly effective for small files,
the expectation is that the training set will only contain small
files. In the case where some samples happen to be large, only
the first 128 KiB of these samples will be used for training.
--train supports multithreading if zstd is compiled with thread-
ing support (default). Additional advanced parameters can be
specified with --train-fastcover. The legacy dictionary builder
can be accessed with --train-legacy. The slower cover dictionary
builder can be accessed with --train-cover. Default --train is
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 bytes). As
usual, quantities are expressed in bytes by default, and it's
possible to employ suffixes (like KB or MB) to specify larger
values.
-# 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 into blocks of size # (default: no split)
-M#, --memory=#
Limit the amount of sample data loaded for training (default: 2
GB). Note that the default (2 GB) is also the maximum. This para-
meter can be useful in situations where the training set size is
not well controlled and could be potentially very large. Since
speed of the training process is directly correlated to the size
of the training sample set, a smaller sample set leads to faster
training.
In situations where the training set is larger than maximum mem-
ory, the CLI will randomly select samples among the available
ones, up to the maximum allowed memory budget. This is meant to
improve dictionary relevance by mitigating the potential impact
of clustering, such as selecting only files from the beginning of
a list sorted by modification date, or sorted by alphabetical or-
der. The randomization process is deterministic, so training of
the same list of files with the same parameters will lead to the
creation of the same dictionary.
--dictID=#
A dictionary ID is a locally unique ID. The decoder will use this
value to verify it is using the right dictionary. By default,
zstd will create a 4-bytes random number ID. It's possible to
provide an explicit number ID instead. It's up to the dictionary
manager to not assign twice the same ID to 2 different dictionar-
ies. Note that 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.
Note that RFC8878 reserves IDs less than 32768 and greater than
or equal to 2\^31, so they should not be used in public.
--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 de-
fault 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 shrink-
DictMaxRegression 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 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 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 dictionary
selectivity (default: 9). The smaller the selectivity value, the
denser the dictionary, improving its efficiency but reducing its
achievable maximum size. --train-legacy=s=# is also accepted.
Examples:
zstd --train-legacy FILEs
zstd --train-legacy=selectivity=8 FILEs
BENCHMARK
The zstd CLI provides a benchmarking mode that can be used to easily
find suitable compression parameters, or alternatively to benchmark a
computer's performance. zstd -b [FILE(s)] will benchmark zstd for both
compression and decompression using default compression level. Note that
results are very dependent on the content being compressed. It's possi-
ble to pass multiple files to the benchmark, and even a directory with
-r DIRECTORY. When no FILE is provided, the benchmark will use a proce-
durally generated lorem ipsum text.
• -b#: benchmark file(s) using compression level #
• -e#: benchmark file(s) using multiple compression levels, from -b#
to -e# (inclusive)
• -d: benchmark decompression speed only (requires providing a
zstd-compressed content)
• -i#: minimum evaluation time, in seconds (default: 3s), benchmark
mode only
• -B#, --block-size=#: cut file(s) into independent chunks of size #
(default: no chunking)
• -S: output one benchmark result per input file (default: consoli-
dated result)
• -D dictionary benchmark using dictionary
• --priority=rt: set process priority to real-time (Windows)
Beyond compression levels, benchmarking is also compatible with other
parameters, such as number of threads (-T#), advanced compression para-
meters (--zstd=###), dictionary compression (-D dictionary), or even
disabling checksum verification for example.
Output Format: CompressionLevel#Filename: InputSize -> OutputSize (Com-
pressionRatio), CompressionSpeed, DecompressionSpeed
Methodology: For speed measurement, the entire input is compressed/de-
compressed 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.
SEE ALSO
zstdgrep(1), zstdless(1), gzip(1), xz(1)
The zstandard format is specified in Y. Collet, "Zstandard Compression
and the 'application/zstd' Media Type",
https://www.ietf.org/rfc/rfc8878.txt, Internet RFC 8878 (February 2021).
BUGS
Report bugs at: https://github.com/facebook/zstd/issues
AUTHOR
Yann Collet
zstd 1.5.6 October 2024 ZSTD(1)
Generated by dwww version 1.16 on Tue Dec 16 06:18:09 CET 2025.