Debian

Last reviewed on 2026-05-13 Reference
In short
  • Debian is a Linux distribution developed entirely by a volunteer community, organised under the Debian Social Contract.
  • The project maintains three rolling branches — stable, testing and unstable — plus an experimental staging area.
  • A new stable release is published roughly every two years, with codenames drawn from Toy Story characters.
  • Many widely-used Linux distributions — Ubuntu, Linux Mint, Pop!_OS, Raspberry Pi OS — are direct Debian derivatives.

About the project

Debian is one of the oldest Linux distributions still actively developed, founded by Ian Murdock in 1993. It is run entirely by an unincorporated community of volunteers — there is no company behind it — and its governance, infrastructure, technical policies and release decisions are all made by the project itself.

Two formal documents shape much of the project's identity:

  • The Debian Social Contract, which commits the project to remaining 100% free software, to giving back to the wider free software community, and to not hiding problems from users.
  • The Debian Free Software Guidelines (DFSG), which define what counts as "free" for the purposes of inclusion in the main archive. The DFSG were a significant influence on the later Open Source Definition.

Together they explain why software with restrictive licences ends up in separate contrib or non-free archives rather than in main: it is not a judgement of usefulness, it is a question of meeting the project's freedom criteria.

Release branches

Debian doesn't have a single "version" the way some distributions do. At any time, three branches exist:

stable

The current stable release is the one most users run. Packages are not updated to newer upstream versions during a stable release's lifetime; only security and important bug fixes are backported. This conservatism is the reason Debian stable is a common choice for servers and for users who want a system that won't surprise them.

testing

The branch that will become the next stable release. Packages flow in from unstable after they have had time to settle and no release-critical bugs are open against them. Running testing is a popular choice for users who want more recent packages than stable provides but don't want the bleeding edge.

unstable (sid)

Where new package versions land first. Always carries the codename "sid". Useful as a development environment and as a way to follow upstream more closely, with the trade-off that occasional breakage is expected.

There is also an experimental staging area for packages too disruptive for unstable.

Codenames and the Toy Story tradition

Every Debian release has a codename drawn from a Toy Story character — Buzz, Rex, Bo, Hamm, Slink, Potato, Woody, Sarge, Etch, Lenny, Squeeze, Wheezy, Jessie, Stretch, Buster, Bullseye, Bookworm, Trixie, and so on. The unstable branch keeps the same name, sid, indefinitely (in the film, Sid is the boy who destroys toys).

Codenames are not just decoration. They appear in /etc/apt/sources.list; using the codename rather than the symbolic name stable pins your system to a specific release and prevents a surprise upgrade when the next stable comes out.

How releases happen

Debian releases when it is ready, rather than on a fixed calendar. In practice the project has settled into a roughly two-year cycle. The process moves through stages with increasingly strict freeze rules — transitions freeze, soft freeze, hard freeze, full freeze — during which fewer and fewer kinds of changes are accepted into testing. Eventually testing is declared stable and renamed; the old stable becomes oldstable; the cycle starts again.

Long-term support is handled separately. The Debian LTS team continues to provide security updates for releases after the official support window ends, extending the useful life of a stable release.

Software model

Debian uses the apt package manager and .deb format that it originated. The archive is organised into three sections:

  • main — software that meets the DFSG. Forms the official Debian system.
  • contrib — free software that depends on something in non-free to be useful (a free game with non-free assets, for instance).
  • non-free and non-free-firmware — software that doesn't meet the DFSG. The firmware archive is a relatively recent split made to simplify hardware support during installation.

By policy, Debian packages are signed and built reproducibly where possible. That means a third party can independently rebuild a package from source and verify that the binary in the archive is the one the source produces.

Derivatives

A number of well-known Linux distributions are direct Debian derivatives:

  • Ubuntu, by Canonical, takes a snapshot of Debian unstable or testing and builds its own release on top.
  • Linux Mint exists in two variants: an Ubuntu-based main edition and a directly Debian-based "LMDE" edition.
  • Pop!_OS, by System76, is Ubuntu-based and therefore indirectly Debian-based.
  • Raspberry Pi OS, the official operating system for the Raspberry Pi, is a Debian derivative.
  • Tails, the privacy-focused live distribution, is also Debian-based.

A complete list is maintained by the project itself on the Debian Derivatives Census.

Following the project

Related reading on this site