unlz4(1) Compress or decompress .lz4 files

Other Alias

lz4, lz4cat



unlz4 is equivalent to lz4 -d
lz4cat is equivalent to lz4 -dc

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. lz4 supports a command line syntax similar to gzip(1). The native file format is the .lz4 format.

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
  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 extensionq
-t, --test
Test the integrity of compressed .lz4 files. The decompressed data is discarded. No files are created nor removed.

Operation modifiers


 fast compression (default)

 high compression

-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 file names.
 By default, the second filename is used as the output filename for the compressed file.
 With -m , you can specify any number of input filenames. Each of them will be compressed independently, and the resulting name of the compressed file will be filename.lz4


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

 block dependency (improve compression ratio)

 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 (useful for Linux Kernel compression)

Other options

-v, --verbose

 verbose mode
-q, --quiet

 suppress warnings; specify twice to suppress errors too

 display help/long help and exit
-V, --version

 display Version number and exit
-k, --keep

 Don't delete source file. This is default behavior anyway, so this option is just for compatibility with gzip/xz.

 benchmark file(s)

 iteration loops [1-9](default : 3), benchmark mode only


Report bugs at: https://github.com/Cyan4973/lz4


Yann Collet