lz4 man page

lz4 — lz4, unlz4, lz4cat — Compress or decompress .lz4 files


lz4 [Options] [-|INPUT-FILE] OUTPUT-FILE

unlz4 is equivalent to lz4 -d

lz4cat is equivalent to lz4 -dcfm

When writing scripts that need to decompress files, it is recommended to always use the name lz4 with appropriate arguments (lz4 -d or lz4 -dc) instead of the names unlz4 and lz4cat.


lz4 is an extremely fast lossless compression algorithm, based on byte-aligned LZ77 family of compression scheme. lz4 offers compression speeds of 400 MB/s per core, linearly scalable with multi-core CPUs. It features an extremely fast decoder, with speed in multiple GB/s per core, typically reaching RAM speed limit on multi-core systems. The native file format is the .lz4 format.

Difference between lz4 and gzip

lz4 supports a command line syntax similar but not identical to gzip(1). Differences are :

  • lz4 preserves original files

  • lz4 compresses a single file by default (see -m for multiple files)

  • lz4 file1 file2 means : compress file1 into file2

  • lz4 shows real-time notification statistics during compression or decompression of a single file (use -q to silent them)

  • If no destination name is provided, result is sent to stdout except if stdout is the console.

  • If no destination name is provided, and if stdout is the console, file is compressed into file.lz4.

  • As a consequence of previous rules, note the following example : lz4 file | consumer sends compressed data to consumer through stdout, hence it does not create any file.lz4.

Default behaviors can be modified by opt-in commands, detailed below.

  • lz4 -m makes it possible to provide multiple input filenames, which will be compressed into files using suffix .lz4. Progress notifications are also disabled by default. This mode has a behavior which more closely mimics gzip command line, with the main difference being that source files are preserved by default.

  • It´s possible to opt-in to erase source files on successful compression or decompression, using --rm command.

  • Consequently, lz4 -m --rm behaves the same as gzip.

Concatenation of .lz4 files

It is possible to concatenate .lz4 files as is. lz4 will decompress such files as if they were a single .lz4 file. For example: lz4 file1 > foo.lz4 lz4 file2 >> foo.lz4

then lz4cat foo.lz4

is equivalent to : cat file1 file2


Short commands concatenation

In some cases, some options can be expressed using short command -x or long command --long-word. Short commands can be concatenated together. For example, -d -c is equivalent to -dc. Long commands cannot be concatenated. They must be clearly separated by a space.

Multiple commands

When multiple contradictory commands are issued on a same command line, only the latest one will be applied.

Operation mode

-z --compress

Compress. This is the default operation mode when no operation mode option is specified, no other operation mode is implied from the command name (for example, unlz4 implies --decompress), nor from the input file name (for example, a file extension .lz4 implies --decompress by default). -z can also be used to force compression of an already compressed .lz4 file.

-d --decompress --uncompress

Decompress. --decompress is also the default operation when the input filename has an .lz4 extension.

-t --test

Test the integrity of compressed .lz4 files. The decompressed data is discarded. No files are created nor removed.


Benchmark mode, using # compression level.

Operation modifiers


Compression level, with # being any value from 1 to 16. Higher values trade compression speed for compression ratio. Values above 16 are considered the same as 16. Recommended values are 1 for fast compression (default), and 9 for high compression. Speed/compression trade-off will vary depending on data to compress. Decompression speed remains fast at all settings.

-f --[no-]force

This option has several effects:

If the target file already exists, overwrite it without prompting.

When used with --decompress and lz4 cannot recognize the type of the source file, copy the source file as is to standard output. This allows lz4cat --force to be used like cat (1) for files that have not been compressed with lz4.

-c --stdout --to-stdout

Force write to standard output, even if it is the console.

-m --multiple

Multiple input files. Compressed file names will be appended a .lz4 suffix. This mode also reduces notification level. lz4 -m has a behavior equivalent to gzip -k (it preserves source files by default).


operate recursively on directories. This mode also sets -m (multiple input files).


Block size [4-7](default : 7)
-B4= 64KB ; -B5= 256KB ; -B6= 1MB ; -B7= 4MB


Block Dependency (improves compression ratio on small blocks)


Select frame checksum (default:enabled)


Header includes original size (default:not present)
Note : this option can only be activated when the original size can be determined, hence for a file. It won´t work with unknown source size, such as stdin or pipe.


Sparse mode support (default:enabled on file, disabled on stdout)


Use Legacy format (typically for Linux Kernel compression)
Note : -l is not compatible with -m (--multiple) nor -r

Other options

-v --verbose

Verbose mode

-q --quiet

Suppress warnings and real-time statistics; specify twice to suppress errors too

-h -H --help

Display help/long help and exit

-V --version

Display Version number and exit

-k --keep

Preserve source files (default behavior)


Delete source files on successful compression or decompression

Benchmark mode


Benchmark file(s), using # compression level


Benchmark multiple compression levels, from b# to e# (included)


Minimum evaluation in seconds [1-9] (default : 3)


Operate recursively on directories


Report bugs at: https://github.com/lz4/lz4/issues


Yann Collet


November 2016 lz4 1.7.4 User Commands