packages icon

 LZ4(1)                           lz4 1.9.2                           LZ4(1)
 User Commands                                                 User Commands

                                  July 2019

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


      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 compresses a single file by default (see -m for multiple

      +   lz4 file1 file2 means : compress file1 into file2

      +   lz4 file.lz4 will default to decompression (use -z to force

      +   lz4 preserves original files

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

      +   When no destination is specified, result is sent on implicit
          output, which depends on stdout status. When stdout is Not the
          console, it becomes the implicit output. Otherwise, if stdout is
          the console, the implicit output is filename.lz4.

      +   It is considered bad practice to rely on implicit output in
          scripts. because the script's environment may change. Always use
          explicit output in scripts. -c ensures that output will be stdout.
          Conversely, providing a destination name, or using -m ensures that
          the output will be either the specified name, or filename.lz4

                                    - 1 -      Formatted:  February 22, 2024

 LZ4(1)                           lz4 1.9.2                           LZ4(1)
 User Commands                                                 User Commands

                                  July 2019


      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 become disabled by default (use -v to enable them).
          This mode has a behavior which more closely mimics gzip command
          line, with the main remaining difference being that source files
          are preserved by default.

      +   Similarly, lz4 -m -d can decompress multiple *.lz4 files.

      +   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

                                    - 2 -      Formatted:  February 22, 2024

 LZ4(1)                           lz4 1.9.2                           LZ4(1)
 User Commands                                                 User Commands

                                  July 2019

           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.

      -b#  Benchmark mode, using # compression level.

           List information about .lz4 files. note : current implementation
           is limited to single-frame .lz4 files.

    Operation modifiers
      -#   Compression level, with # being any value from 1 to 12. Higher
           values trade compression speed for compression ratio. Values
           above 12 are considered the same as 12. 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.

           Switch to ultra-fast compression levels. The higher the value,
           the faster the compression speed, at the cost of some compression
           ratio. If =# is not present, it defaults to 1. This setting
           overrides compression level if one was set previously. Similarly,
           if a compression level is set after --fast, it overrides it.

           Set highest compression level. Same as -12.

           Generate compressed data optimized for decompression speed.
           Compressed data will be larger as a consequence (typically by
           ~0.5%), while decompression speed will be improved by 5-20%,
           depending on use cases. This option only works in combination
           with very high compression levels (>=10).

      -D dictionaryName
           Compress, decompress or benchmark using dictionary
           dictionaryName. Compression and decompression must use the same
           dictionary to be compatible. Using a different dictionary during

                                    - 3 -      Formatted:  February 22, 2024

 LZ4(1)                           lz4 1.9.2                           LZ4(1)
 User Commands                                                 User Commands

                                  July 2019

           decompression will either abort due to decompression error, or
           generate a checksum error.

      -f --[no-]force
           This option has several effects:

           If the target file already exists, overwrite it without

           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. Can also
           be used to list multiple files. lz4 -m has a behavior equivalent
           to gzip -k (it preserves source files by default).

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

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

      -BI  Produce independent blocks (default)

      -BD  Blocks depend on predecessors (improves compression ratio, more
           noticeable 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)

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

                                    - 4 -      Formatted:  February 22, 2024

 LZ4(1)                           lz4 1.9.2                           LZ4(1)
 User Commands                                                 User Commands

                                  July 2019

    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)

      --rm Delete source files on successful compression or decompression

      --   Treat all subsequent arguments as files

    Benchmark mode
      -b#  Benchmark file(s), using # compression level

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

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

      Report bugs at:

      Yann Collet

                                    - 5 -      Formatted:  February 22, 2024