Manual: unzstd
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
features a very fast decoder, with speeds > 500 MB/s per core, which remains roughly stable at all compression setā
tings.
zstd command line syntax is generally similar to gzip, but features the following few differences:
ā¢ Source files are preserved by default. It's possible to remove them automatically by using the --rm command.
ā¢ When compressing a single file, zstd displays progress notifications and result summary by default. Use -q to
turn them off.
ā¢ zstd displays a short help page when command line is an error. Use -q to turn it off.
ā¢ zstd does not accept input from console, though it does accept stdin when it's not the console.
ā¢ 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 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:
ā¢ When compressing, the suffix .zst is appended to the source filename to get the target filename.
ā¢ 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 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 inteā
gers. 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 > /dev/null, decomā
pressed data is discarded and checksummed for errors. No files are created or removed.
-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 available. This command's output can be augmented with the -v modifier.
Operation Modifiers
ā¢ -#: selects # compression level [1-19] (default: 3). Higher compression levels generally produce higher compresā
sion ratio at the expense 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 behavior highly depends on the content to compress,
there's no guarantee of a smooth progression from one level to another.
ā¢ --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.
ā¢ --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 compresā
sion level if one was set previously. Similarly, if a compression level is set after --fast, it overrides it.
ā¢ -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.
ā¢ --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.
ā¢ --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.
ā¢ --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 --sinā
gle-thread. It sets window size to 8 MiB by default (can be changed manually, see wlog). Due to the chaotic naā
ture 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).
ā¢ --long[=#]: enables long distance matching with # windowLog, if # is not present it defaults to 27. This inā
creases 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.
ā¢ -D DICT: use DICT as Dictionary to compress or decompress FILE(s)
ā¢ --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 compression ratios.
Note: for level 19, you can get increased compression ratio at the cost of speed by specifying --zstd=tarā
getLength= to be something large (i.e. 4096), and by setting a large --zstd=chainLog=.
ā¢ --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 feaā
ture 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 mileage may vary.
ā¢ -C, --[no-]check: add integrity check computed from uncompressed data (default: enabled)
ā¢ --[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).
ā¢ --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.
ā¢ -M#, --memory=#: Set a memory usage limit. By default, zstd uses 128 MiB for decompression as the maximum amount
of memory the decompressor 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 training. This parameter overrides the default
limit of 2 GiB. zstd will load training samples up to the memory limit and ignore the rest.
ā¢ --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 parameters, resulting in better and potentially faster compression, espeā
cially for smaller source sizes.
ā¢ --size-hint=#: When handling input from a stream, zstd must guess how large the source size will be when optimizā
ing 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 underesā
timates may result in significant degradation.
ā¢ --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 incomplete 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 compression speed by up to ~10% at level 1. Higher levels will see smaller relative speed
regression, becoming invisible at higher settings.
ā¢ -f, --force: disable input and output checks. Allows overwriting existing 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.
ā¢ -c, --stdout: write to standard output (even if it is the console); keep original files (disable --rm).
ā¢ -o FILE: save result into FILE. Note that this operation is in conflict with -c. If both operations are present
on the command line, the last expressed one wins.
ā¢ --[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.
ā¢ --[no-]pass-through enable / disable passing through uncompressed files as-is. During decompression when
pass-through is enabled, unrecognized formats will be copied as-is from the input to the output. By default,
pass-through will occur when the output destination is stdout and the force (-f) option is set.
ā¢ --rm: remove source file(s) after successful compression or decompression. 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.
ā¢ -k, --keep: keep source file(s) after successful compression or decompression. This is the default behavior.
ā¢ -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.
ā¢ --filelist FILE read a list of files to process as content from FILE. Format is compatible with ls output, with
one file per line.
ā¢ --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 directoā
ries, 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 instead.
ā¢ --output-dir-mirror DIR: similar to --output-dir-flat, the output files are stored underneath target DIR direcā
tory, 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 "output-dir/var/tmp/abc". If there are multiple input
files or directories, name collision resolution will follow the same rules as --output-dir-flat.
ā¢ --format=FORMAT: compress and decompress in other formats. If compiled with support, zstd can compress to or deā
compress 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.
ā¢ -h/-H, --help: display help/long help and exit
ā¢ -V, --version: display version number and immediately exit. note that, since it exits, flags specified after -V
are effectively ignored. Advanced: -vV also displays supported formats. -vvV also displays POSIX support. -qV
will only display the version number, suitable for machine reading.
ā¢ -v, --verbose: verbose mode, display more information
ā¢ -q, --quiet: suppress warnings, interactivity, and notifications. specify twice to suppress errors too.
ā¢ --no-progress: do not display the progress bar, but keep all other messages.
ā¢ --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.
ā¢ --exclude-compressed: only compress files that are not already compressed.
ā¢ --: 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 compressing 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 implications. Therefore, this avenue is intentionally
limited. Only ZSTD_CLEVEL and ZSTD_NBTHREADS are currently supported. They set the default compression level and numā
ber of threads to use during compression, respectively.
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 attempt 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 deā
fault value of (1), and is capped at ZSTDMT_NBWORKERS_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 interā
nally into multiple advanced 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 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 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 requirements for the compressor and decompressor. The minimum wlog is 10 (1 KiB) and the maxā
imum 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 compression 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 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 '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 improve 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 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 targetLength increases compression speed but decreases compresā
sion 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 multiā
threading 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 reā
loaded amount by a factor 2. For example, 8 means "windowSize/2", and 6 means "windowSize/8". Value 0 is speā
cial 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 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 deā
crease 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 bigā
ger 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 available when multi-threading is enabled. Each comā
pression job is run in parallel, so this value indirectly impacts the nb of active threads. Default job size varies
depending on compression level (generally 4 * windowSize). -B# makes it possible to manually select a custom size.
Note that job size must respect a minimum value which is enforced transparently. 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 samples, the result of which is saved into a file called a dictionary. Then, during compresā
sion 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 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 indicate 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 threading support (default). Additional advanced paā
rameters 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 deā
fault, 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 compresā
sion 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 parameter 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 memory, 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 order. 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 dicā
tionary. 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 dictionaries.
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 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], occaā
sionally 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 unā
til compression ratio of the truncated dictionary is at most shrinkDictMaxRegression% worse than the compresā
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 different default value of split If split is not specā
ified, then it tries split = 75. If f is not specified, then it tries f = 20. Requires that 0 < f < 32. If acā
cel 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 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 alterā
natively to benchmark a computer's performance. zstd -b [FILE(s)] will benchmark zstd for both compression and decomā
pression using default compression level. Note that results are very dependent on the content being compressed. It's
possible to pass multiple files to the benchmark, and even a directory with -r DIRECTORY. When no FILE is provided,
the benchmark will use a procedurally generated lorem ipsum text.
ā¢ -b#: benchmark file(s) using compression level #
ā¢ -e#: benchmark file(s) using multiple compression levels, from -b# to -e# (inclusive)
ā¢ -d: benchmark decompression speed only (requires providing a zstd-compressed content)
ā¢ -i#: minimum evaluation time, in seconds (default: 3s), benchmark mode only
ā¢ -B#, --block-size=#: cut file(s) into independent chunks of size # (default: no chunking)
ā¢ -S: output one benchmark result per input file (default: consolidated result)
ā¢ -D dictionary benchmark using dictionary
ā¢ --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 parameters (--zstd=###), dictionary compression (-D dictionary), or even disabling checksum verā
ification for example.
Output Format: CompressionLevel#Filename: InputSize -> OutputSize (CompressionRatio), CompressionSpeed, Decompresā
sionSpeed
Methodology: For speed measurement, 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.
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)