Introduction
Sources for most of the information on this page:
- Debian package management (official page)
- DebianReleases (official page) (scroll down to the bottom for a very useful graph)
- Debian Repository Format
- Debian Glossary
Nomenclature
repository: a searchable collection of packages.
archive: synonym for repository; in this document we use "archive" only when refering to a searchable and downloadable collection of Debian packages that contains a "dists/" directory at the top level.
Suites
A suite is "a repository holding one particular "branch" of Debian's development process". A suite undergoes changes as packages move in and out. The suite gets names assigned to it and these names can change over time.
Here is an example:
BEFORE NEW MAJOR RELEASE
------------------
suite-A testing, buster
suite-B stable, stretch, version-9.9
AFTER NEW MAJOR RELEASE
------------------
suite-A testing, bullseye
suite-A' stable, buster, version-10.0
suite-B oldstable, stretch, version-9.9
Note: suite-A' is a copy of suite-A on new release day
AFTER NEW POINT RELEASE
------------------
suite-A testing, bullseye
suite-A' stable, buster, version-10.1
suite-B oldstable, stretch, version-9
Be aware that most suites undergo changes all the time, so, for example,
suite-A under AFTER NEW MAJOR RELEASE will have different contents
than suite-A under AFTER NEW POINT RELEASE.
Some suites will stop changing, most notably, those suites associated with old releases.
Some suites are sets of a packages that are complete operating systems,
e.g., stable, sid, etc., while some suites are sets of packages not
meant to be a complete operating system, e.g., stable-proposed-updates,
testing-updates.
Distributions
In the context of Debian package repositories, the terms "distribution" and "suite" are used interchangably. From Glossary:
Distribution (distro, dist): [...] Used more generally (e.g. in sources.list(5)) as a synonym for suite; hence source URLs which put https://deb.debian.org/debian/dists/experimental/ alongside all the other dists.
Releases
A Debian release is a distribution that has been or is going to be released.
Release version
Each release has a major version number and a minor version number. For example, Debian "wheezy" has major version 7. Every version (starting with "wheezy") also has a minor version number. When "wheezy" was released its version minor version number was "0". Thus, at the time of its release, the current release of Debian was version "7.0".
New releases come out roughly every two years.
Release codename
Every Debian release has a codename associated with the major version:
VERSION CODENAME
7 wheezy
8 jessie
9 stretch
10 buster
11 bullseye
* sid
We will usually refer to a specific Debian release by codename (thus "Debian stretch").
The "sid" codename points to the development versions of packages that are being prepared for the next release.
See also the graph at the bottom of the Debian Releases page.
Release "suite name"
Several releases also have names that indicate how close they are to the most recently released version.
stable: points to the current supported release.
oldstable: points to the PREVIOUS supported version.
oldoldstable: points to the PREVIOUS to the PREVIOUS supported release.
testing: points to the next current development state of the next stable Debian distribution.
unstable: an alias for "sid"
experimental: points at the "experimental" distribution.
At the time of this writing this translated to:
VERSION CODENAME SUITE NAME
7 wheezy oldoldstable
8 jessie oldstable
9 stretch stable
10 buster testing
11 bullseye
* sid sid
When buster is officially released, the above will change to:
VERSION CODENAME SUITE NAME
7 wheezy
8 jessie oldoldstable
9 stretch oldstable
10 buster stable
11 bullseye testing
* sid sid
Notable distributions in each release
Each release consists of several sets of Debian packages called "distributions":
current release (e.g., "stretch"): current point release
proposed updates (e.g., "stretch-proposed-updates"): packages being prepared for next point release
updates (e.g., "stretch-updates"): updates for users who want to install on their systems before the next point release is made, such as updates to virus scanners and timezone data; all packages from stable-updates will be included in point releases
backports (e.g., "stretch-backports"): packages for a later version of software than that in the current release.
security updates (e.g., "stretch/updates"): security updates that need a timely release. Note that usually these packages are served from a different archive (e.g.,
http://security.debian.org/).experimental: packages in pre-alpha.
sid: all the active development of new Debian software and packaging happens here.
The Archive
Most Debian repositories consist of at least one, but sometimes more than one, archive. The most common archive is "debian" but there is also "debian-local", "ubuntu", etc. To reach these archives a URL like the following is usually used:
URL/<archive>/
Some examples:
http://ftp.debian.org/debian/ (Debian's main archive)
http://security.debian.org/debian-security (Debian's security archive)
http://archive.debian.org/debian/ (Debian's old release archive)
Structure of a Debian archive
Each archive contains a variety of files and directories. The most important are
URL/<archive>/dists/
URL/<archive>/pool/
URL/<archive>/project/
The dists directory
The dists directory contains a set of files and directories for each
Debian distribution. For example, here are some of the distributions in
the main Debian mirror:
http://ftp.us.debian.org/debian/ (archive root)
http://ftp.us.debian.org/debian/dists/ (all the distributions)
http://ftp.us.debian.org/debian/dists/experimental/
http://ftp.us.debian.org/debian/dists/stretch-backports/
http://ftp.us.debian.org/debian/dists/stretch-proposed-updates/
http://ftp.us.debian.org/debian/dists/stretch-updates/
http://ftp.us.debian.org/debian/dists/stretch/
...
Files in a distribution
Each distribution contains several files and directories. The most important of these are
Release
Release.gpg
contrib/
main/
non-free/
The Release file
This file contains information about the packages for this suite. The first few lines are fields:
Suite (e.g., stable, oldstable-updates)
Version (e.g., 8.5) [not always present]
Codename (e.g., jessie, wheezy-updates)
Valid-Until (a date; see below)
The rest of this file is a list of files in the directory along with their checksums.
Each Release (or InRelease) file has a Valid_Until except for the
current point releases as these are considered production releases and
hence do not expire.
Security
When a Debian client wants to get a package from a Debian repository, it
starts with the repository URL. It then appends the archive name. Next, it
indicates a suite. This gets it inside of one of the dists/ directories.
The client should then download the Release and Release.gpg file. It
then runs the equivalent to
gpg --verify Release.gpg Release
The pool directory
The packages themselves are in the pool directory.
Example.
How to browse the Debian package repository
Look at the sources.list file
cat /etc/apt/sources.listYou will see something like this:
# The main Debian archive and source tree. deb http://ftp.us.debian.org/debian stretch main non-free contrib deb-src http://ftp.us.debian.org/debian stretch main non-free contribYou can browse the repo by taking one of the above URL's, appending
dists, and then appending the distribution (in this casestretch), and then appending one of the "components" (i.e.,main,non-free, etc.).http://ftp.us.debian.org/debian/dists/stretch/contrib/