File extension
.lzma
LZMA alone (.lzma) compressed data
.lzma files are LZMA-compressed streams in the legacy LZMA-alone format: a lossless compressed file with a small header, the predecessor of the .xz container.
Known meanings
Formats and reference material for .lzma
LZMA alone (.lzma) compressed data
Legacy single-stream container for LZMA-compressed data
Details
Format notes
LZMA
LZMA (Lempel-Ziv-Markov chain algorithm) is a compression algorithm designed
by Igor Pavlov, first used in the 7-Zip archiver. The .lzma file, sometimes
called the “LZMA alone” format, is a minimal container holding one stream of
LZMA-compressed data. It was used by early LZMA command-line tools before the
.xz format was introduced.
Technical Notes
A .lzma file has a 13-byte header followed by the compressed data. The header
holds a properties byte that encodes the lc, lp, and pb parameters, a
four-byte dictionary size, and an eight-byte uncompressed size, which may be
set to all ones when the size is unknown, in which case the stream ends with
an end-of-payload marker. The format has no magic number and no integrity
check, so detection relies on plausible header values, and corrupted data may
go unnoticed. These limitations, along with a lack of extensibility, are among
the reasons the .xz format was created. The format is described in a text
document in the XZ Utils repository.
Adoption
Modern tools usually produce .xz (which uses the improved LZMA2 algorithm)
instead, but .lzma files are still readable by XZ Utils (xz --format=lzma,
unlzma), 7-Zip, and various libraries. The LZMA algorithm itself continues
in use inside 7z and xz containers.
Preservation And Security Notes
Because .lzma files lack checksums, consider converting important data to
.xz with an integrity check, or store separate hashes. Decompressors for
untrusted data should limit memory according to the declared dictionary size
and cap the output size.
Further Reading
- LZMA file format (XZ Utils):
https://github.com/tukaani-project/xz/blob/master/doc/lzma-file-format.txt - XZ Utils:
https://tukaani.org/xz/