zstdmt is equivalent to zstd -T0 .
unzstd is equivalent to zstd -d .
zstdcat is equivalent to zstd -dcf .
zstd command line syntax is generally similar to gzip, but features the following differences : .
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: .
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\. .
-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\. .
-# # 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)\. .
--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, 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 underestimates 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 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 .
--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 instead\. .
--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 .
--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 .-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\. .
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\. .--zstd=wlog=23,clog=23,hlog=22,slog=6,mml=3,tlen=48,strat=6 .