Ubuntu Manpage: lzma, unlzma, lzcat - LZMA compression and decompression tool

NAME

       lzma, unlzma, lzcat - LZMA compression and decompression tool

SYNOPSIS

       lzma [-123456789cdefhkLqtvV] [-S suffix] [filenames ...]
       unlzma [-cfhkLqtvV] [-S suffix] [filenames ...]
       lzcat [-fhLqV] [filenames ...]

DESCRIPTION

LZMA (Lempel-Ziv-Markov chain-Algorithm) is an improved version of famous LZ77 compression
algorithm. It was improved in way of maximum increasing of compression ratio, keeping high
decompression speed and low memory requirements for decompressing.

lzma command line tool has a similar interface to gzip(1) and bzip2(1) and is intended to
make use of LZMA compression easy for the users who are already familiar with gzip and
bzip2.

In this manual lzma is compared mostly to bzip2 because that is currently one of the most
widely used free software to compress tar files made for distribution. Comparing lzma to
gzip is not practical because neither lzma nor bzip2 can compete with gzip in compression
speed. On the other hand the compression ratio of gzip is worse than of lzma and bzip2.

lzma provides notably better compression ratio than bzip2 especially with files having
other than plain text content. The other advantage of lzma is fast decompression which is
many times quicker than bzip2. The major disadvantage is that achieving the highest
compression ratios requires extensive amount of system resources, both CPU time and RAM.
Also software to handle LZMA compressed files is not installed by default on most
distributions.

When compressing or decompressing with lzma, the new file will have the same ownership
information, permissions and timestamps as the original file. However the this information
is not stored into the compressed file like gzip does.

STREAMED VS. NON-STREAMED

       LZMA  files  can  be  either streamed or non-streamed. Non-streamed files are created only
       when the size of the file being compressed is known.  In  practice  this  means  that  the
       source file must be a regular file. In other words, if compressing from the standard input
       or from a named pipe (fifo) the compressed file will always be streamed.

       Both streamed and non-streamed files are compressed identically; the only differences  are
       found  from  the  beginnings and ends of LZMA compressed files: Non-streamed files contain
       the uncompressed  size  of  the  file  in  the  LZMA  file  header;  streamed  files  have
       uncompressed size marked as unknown. To know where to stop decoding, streamed files have a
       special End Of Stream marker at the end of the LZMA file. The EOS  marker  makes  streamed
       files five or six bytes bigger than non-streamed.

       So in practice creating non-streamed files has two advantages: 1) the compressed file is a
       few bytes smaller and 2) the  uncompressed  size  of  the  file  can  be  checked  without
       decompressing the file.

OPTIONS

Short options can be grouped like -cd.

-c --stdout --to-stdout
The output is written to the standard output. The original files are kept
unchanged. When compressing to the standard output there can be only one input
file. This option is implied when input is read from the standard input or the
script is invoked as lzcat.

-d --decompress --uncompress
Force decompression regardless of the invocation name. This the default when called
as unlzma or lzcat.

-f --force
Force compression or decompression even if source file is a symlink, target exists,
or target is a terminal. In contrast to gzip and bzip2, if input data is not in
LZMA format, --force does not make lzma behave like cat. lzma never prompts if
target file should be overwritten; existing files are skipped or, in case of
--force, overwritten.

-h --help
Show a summary of supported options and quit.

-k --keep
Do not delete the input files after compression or decompression.

-L --license
Show licensing information of lzma.

-q --quiet
Suppress all warnings. You can still check the exit status to detect if a warning
had been shown.

-S --suffix .suf
Use .suf instead of the default .lzma. A null suffix forces unlzma to decompress
all the given files regardless of the filename suffix.

-t --test
Check the integrity of the compressed file(s). Without --verbose no output is
produced if no errors are found.

-v --verbose
Show the filename and percentage reduction of each processes file.

-V --version
Show the version number of lzma.

-z --compress
Force compression regardless of the invocation name.

-1 .. -9
Set the compression ratio. These options have no effect when decompressing.

--fast Alias to -1.

--best Alias to -9.

DIAGNOSTICS

       Exit status:
       0 - Everything OK.
       1 - An error occurred.
       2 - Something worth a warning happened but no errors.

       It can be especially useful with tar(1) patched to support LZMA compression.

AUTHORS

       The LZMA algorithm and the implementation used in LZMA utils was developed by Igor Pavlov.
       The   original   code   is   available   in   LZMA   SDK   which   can   be   found   from
       http://7-zip.org/sdk.html .

       lzma command line tool was written by Ville Koskinen.  http://tukaani.org/lzma/

       This manual page is inspired by manual pages of gzip and bzip2.