.lz File Extension

What kind of file is a .lz?

A .lz file is a byte stream compressed with Lzip. It uses a constrained form of LZMA compression and is lossless, so successful decompression reproduces the original bytes. The usual MIME label is application/x-lzip, a deployed but unregistered media type. IANA does not currently list application/x-lzip or the proposed application/lzip replacement.¹²

Lzip compresses data rather than organizing files and directories. A name such as source.tar.lz normally means that TAR first bundled the files, then Lzip compressed the resulting stream.

Every Lzip member starts with ASCII LZIP, or 4C 5A 49 50 in hexadecimal. The next byte is the format version, currently 01. Check those bytes and validate the complete stream instead of trusting the suffix.¹

How do I open a .lz on my computer?

• On Windows, use a Windows build of lzip or another archive utility that explicitly supports Lzip.
• On macOS and Linux, install lzip with your package manager, then use it from Terminal.
• For a .tar.lz archive, GNU tar can select the Lzip filter from the filename when the external lzip program is available.³

To keep the compressed source while writing the decompressed file, run:

lzip -dk report.csv.lz

Test the full stream without saving its output with lzip -tv download.lz. For a tarball, inspect the member list before extraction with tar -tf source.tar.lz.

Lzip does not store the original filename, timestamp, ownership, or similar metadata. Choose the output name yourself when a generic filename does not reveal what the decompressed bytes contain.¹

Poly support for .lz

Poly recognizes .lz as Lzip data. It stores, syncs, shares, versions, and downloads the file, and you can find it by filename and ordinary file properties.

Poly does not decompress the stream, inspect TAR members, generate a thumbnail, provide an archive preview, or index the compressed contents. The Poly agent cannot read the payload. Decompress the file with a trusted utility and add the resulting supported files separately when you need content search, preview, or agent access.

History of .lz

Antonio Diaz Diaz designed Lzip in 2008 as a Unix-style alternative to Gzip and Bzip2.⁴ Its command-line interface follows familiar compressor conventions, while its format uses a fixed six-byte header and a 20-byte trailer for each member.

The trailer records a CRC32, the uncompressed data size, and the complete member size. These three checks help detect damage and let recovery tools locate intact members in a multi-member file.¹ The Lzip project provides reference, parallel, library, TAR, and recovery-oriented implementations.⁵

Working with .lz and alternatives

Choose the format for the workflow:

Lzip members can use dictionaries from 4 KiB through 512 MiB, so memory needs depend on how the stream was created.¹ A small compressed input can also expand dramatically. Set resource limits for untrusted data, and inspect TAR paths, links, and executables before extraction. CRC and size checks detect accidental damage; they do not authenticate the sender or make the output safe.