xz

Updated

September 4, 2026

Overview

xz compresses and decompresses files in the XZ format (LZMA2), typically yielding better ratios than gzip/bzip2 at the cost of more CPU and memory — especially at high presets. Common for source tarballs (*.tar.xz), package payloads, and cold archives.

Companion commands: unxz, xzcat, xzgrep.

Syntax

xz [options] [file...]
unxz [options] [file...]
xzcat [file...]

Common Options

Option	Description
`-z` / `-d`	Compress (default) / decompress
`-c`	Write to stdout
`-k`, `--keep`	Keep input files
`-f`	Force
`-t`	Test integrity
`-l`	List information about `.xz` files
`-0` … `-9`	Compression preset (default 6); higher = smaller/slower/more RAM
`-e`, `--extreme`	Try harder within preset (more CPU)
`-T N`, `--threads=N`	Multithreaded compression (when built with support)
`-v`	Verbose
`-q`	Quiet
`--memlimit=SIZE`	Cap memory usage

Examples with Explanations

Basic

xz file.tar
xz -k file.tar
unxz file.tar.xz
xz -d file.tar.xz

Pipelines with tar

tar -cJf archive.tar.xz dir/          # tar invokes xz
tar -caf archive.tar.xz dir/          # auto by extension (GNU tar)
xz -dc archive.tar.xz | tar xf -
tar -xJf archive.tar.xz

Presets and threads

xz -0 -T0 fast.dat          # fast, multi-thread (T0 = all cores when supported)
xz -9e cold-archive.img     # max effort; watch RAM
xz -T4 -6 backup.sql

Test and list

xz -t archive.tar.xz
xz -l *.xz
xz -lv package.tar.xz

Keep and stdout

xz -kc file > file.xz
xzcat file.xz | less

Memory safety on small hosts

xz --memlimit=50% -T2 big.img

High -9 on a 1 GB VPS can invoke the OOM killer — lower preset or set a memlimit.

Convert from gzip (recompress)

gzip -dc old.tar.gz | xz -T0 -c > new.tar.xz

Notes / Pitfalls

Decompression is faster than compression but still heavier than gzip for weak CPUs.
Multi-threaded mode increases memory roughly with threads × preset needs.
Not as ubiquitous as .gz on ancient appliances — confirm consumer support.
Default may delete inputs without -k (like gzip).
Don’t use extreme presets for live log shipping; use zstd/gzip.

2026-relevant notes

Many distros ship packages and kernel sources as .tar.xz.
For new internal pipelines, zstd often wins on speed with comparable ratio at mid levels; xz remains fine for cold distribution archives.
pixz / threaded xz variants exist for parallelize-friendly workflows.

Additional Resources

man xz