Configuring Apt Sources

Apt downloads packages from one or more software repositories (sources) and installs them onto your computer.

A repository is generally a network server, such as the official DebianStable repository. Local directories or CD/DVD are also accepted.

The specific repositories (package sources) configured on your machine affect:

What software packages are available for download
What versions of packages are available
Who packages the software

Commonly used package sources

DebianStable: official Debian repository for the current release
StableProposedUpdates: official Debian repository for upcoming point releases (security and important bug fixes every ~2 months)
StableUpdates: official Debian repository for changes that cannot wait for the next point release, packages are also added to StableProposedUpdates for inclusion in the next point release
DebianSecurity: official Debian repository for frequent security updates
DebianBackports: more recent versions of some packages, compatible with DebianStable.
DebianTesting: current development state of the next stable Debian distribution
DebianUnstable: rolling development version containing the latest packages
DebianExperimental: development version containing the experimental/alpha/beta/untested packages

Editing software sources

Precautions

Being able to change the repositories used by your package management system is a powerful feature but this power comes with some responsibility. Users are cautioned that it is possible to break your system (in a way that could be difficult or impossible to cleanly fix) by adding third-party repositories, or repositories for a Debian version that does not match your current version - these repository create a risk of conflicting package versions, creating what's sometimes called a "Franken-Debian" system. The whole concept behind a Debian stable release is that the Debian developers have picked a set of software and their versions that function nicely together. While this software is patched to fix security issues, the software is frequently not the latest version. It takes some experience to know how the repos may be changed without risk of breaking your system. Users of all levels are advised to change repos cautiously.

Using a graphical program

Some programs allow configuring Apt sources through a graphical interface. For example:

Applications menu > Settings > Software and updates (software-properties-gtk package)

Using a text editor

The main Apt sources configuration file is at /etc/apt/sources.list. You can edit this file (as root) using your favorite text editor. See the sources.list manual page for more info.

To add custom sources, creating separate files under /etc/apt/sources.list.d/ in DEB822 source format is preferred. See the deb822 manual page for more info.

sources.list format

Debian Reference Manual - 2.1.4. Debian archive basics

The entries in this file normally follow this format:

deb http://site.example.com/debian distribution component1 component2 component3
deb-src http://site.example.com/debian distribution component1 component2 component3

Archive type

The first word on each line, deb or deb-src, indicates the type of archive. Deb indicates that the archive contains binary packages (deb), the pre-compiled packages that we normally use. Deb-src indicates source packages, which are the original program sources plus the Debian control file (.dsc) and the diff.gz containing the changes needed for packaging the program.

Repository URL

The next entry on the line is a URL to the repository that you want to download the packages from. The main list of Debian repository mirrors is located here.

Distribution

The 'distribution' can be either the release code name / alias ( stretch, buster, bullseye, bookworm, sid) or the release class (oldoldstable, oldstable, stable, testing, unstable) respectively. If you mean to be tracking a release class then use the class name, if you want to track a Debian point release, use the code name. Avoid using stable in your sources.list as that results in nasty surprises and broken systems when the next release is made; upgrading to a new release should be a deliberate, careful action and editing a file once every two years is not a burden.

For example, if you always want to help test the testing release, use 'testing'. If you are tracking trixie and want to stay with it from testing to end of life, use 'trixie'.

Component

main consists of DFSG-compliant packages, which do not rely on software outside this area to operate. These are the only packages considered part of the Debian distribution.

contrib packages contain DFSG-compliant software, but have dependencies not in main (possibly packaged for Debian in non-free).

non-free contains software that does not comply with the DFSG.

The Debian project has taken the decision in 2022-10 to create a new repository component non-free-firmware, and include its content on installation media for the Debian bookworm to make things easier for our users.

And if you choose to get more information, feel free to follow the firmware GR result - what happens next?.

The Debian wiki has a page about firmware for older releases, bookworm and later.

Example sources.list

Below is an example of a sources.list for Debian 12/Bookworm (stable) released 10th June 2023.

deb http://deb.debian.org/debian bookworm main non-free-firmware
deb-src http://deb.debian.org/debian bookworm main non-free-firmware

deb http://deb.debian.org/debian-security/ bookworm-security main non-free-firmware
deb-src http://deb.debian.org/debian-security/ bookworm-security main non-free-firmware

deb http://deb.debian.org/debian bookworm-updates main non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main non-free-firmware

The equivalent entry in deb822 style under /etc/apt/sources.list.d/debian.sources looks like this:

Types: deb deb-src
URIs: http://deb.debian.org/debian
Suites: bookworm bookworm-updates
Components: main
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb deb-src
URIs: http://deb.debian.org/debian-security
Suites: bookworm-security
Components: main
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

If you need the contrib, non-free and non-free-firmware components, add contrib non-free non-free-firmware after main. For example, for Debian 12/Bookworm:

deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

deb http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware

deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

The equivalent entry in deb822 style including the non-free and non-free-firmware components:

Types: deb deb-src
URIs: http://deb.debian.org/debian
Suites: bookworm bookworm-updates
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb deb-src
URIs: http://deb.debian.org/debian-security
Suites: bookworm-security
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

If you need the Backports, contrib, and non-free components, add bookworm-backports lines. For example, for Debian 12/Bookworm:

deb http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware

The equivalent entry in deb822 style including the non-free non-free-firmware and bookworm-backports component:

Types: deb deb-src
URIs: http://deb.debian.org/debian
Suites: bookworm bookworm-updates bookworm-backports
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb deb-src
URIs: http://deb.debian.org/debian-security
Suites: bookworm-security
Components: main contrib non-free non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Below is an example of a sources.list for Debian 11/Bullseye (oldstable).

deb http://deb.debian.org/debian bullseye main
deb-src http://deb.debian.org/debian bullseye main

deb http://deb.debian.org/debian-security/ bullseye-security main
deb-src http://deb.debian.org/debian-security/ bullseye-security main

deb http://deb.debian.org/debian bullseye-updates main
deb-src http://deb.debian.org/debian bullseye-updates main

If you need the contrib and non-free components, add contrib non-free after main. For example, for Debian 11/Bullseye:

deb http://deb.debian.org/debian bullseye main contrib non-free
deb-src http://deb.debian.org/debian bullseye main contrib non-free

deb http://deb.debian.org/debian-security/ bullseye-security main contrib non-free
deb-src http://deb.debian.org/debian-security/ bullseye-security main contrib non-free

deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb-src http://deb.debian.org/debian bullseye-updates main contrib non-free

If you need the Backports, contrib, and non-free components, add bullseye-backports lines. For example, for Debian 11/Bullseye:

deb http://deb.debian.org/debian bullseye-backports main contrib non-free
deb-src http://deb.debian.org/debian bullseye-backports main contrib non-free

Questions about the support cycle? Click here

If you need the Debian Unstable, then change the distribution to unstable. Note that Updates and Security is not used since Unstable is a rolling development version consisting of the latest packages. That is, unstable main will be the only entry in sources.list.

deb http://deb.debian.org/debian/ unstable main
deb-src http://deb.debian.org/debian/ unstable main

You can instead use https://... in all of the above lines to use the repositories over encrypted HTTPS connections if the according mirror supports HTTPS. (Users of Debian 9/Stretch or older releases will need to install the apt-transport-https package first.)

You can use a GNOME tool to edit your sources.list file. Access it through Menu → System → Administration → Software Sources.

Using Tor with Apt

Apt can retrieve and download updates through Tor. For this to work you need to install the tor and apt-transport-tor packages. You can then use the official onion services provided by Debian.

Here is an example sources.list using the onion services for Debian 11/Bullseye:

deb tor+http://2s4yqjx5ul6okpp3f2gaunr2syex5jgbfpfvhxxbbjwnrsvbk5v3qbid.onion/debian bullseye main
deb-src tor+http://2s4yqjx5ul6okpp3f2gaunr2syex5jgbfpfvhxxbbjwnrsvbk5v3qbid.onion/debian bullseye main

deb tor+http://5ajw6aqf3ep7sijnscdzw77t7xq4xjpsy335yb2wiwgouo7yfxtjlmid.onion/
debian-security bullseye-security main
deb-src tor+http://5ajw6aqf3ep7sijnscdzw77t7xq4xjpsy335yb2wiwgouo7yfxtjlmid.onion/
debian-security bullseye-security main

deb tor+http://2s4yqjx5ul6okpp3f2gaunr2syex5jgbfpfvhxxbbjwnrsvbk5v3qbid.onion/debian bullseye-updates main
deb-src tor+http://2s4yqjx5ul6okpp3f2gaunr2syex5jgbfpfvhxxbbjwnrsvbk5v3qbid.onion/debian bullseye-updates main

CD-ROM

If you'd rather use your CD-ROM for installing packages or updating your system automatically with APT, you can put it in your /etc/apt/sources.list. To do so, you can use the apt-cdrom program like this:

# apt-cdrom add

with the Debian CD-ROM in the drive.

You can use -d for the directory of the CD-ROM mount point or add a non-CD mount point (i.e. a USB keydrive).

Name Resolution

On occasion name resolution can break.

# apt update
0% [Working]Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Unsupported socketcall: 20
Err:1 http://deb.debian.org/debian testing InRelease
  Temporary failure resolving 'deb.debian.org'
Reading package lists... Done
W: Failed to fetch http://deb.debian.org/debian/dists/testing/InRelease  Temporary failure resolving 'deb.debian.org'
W: Some index files failed to download. They have been ignored, or old ones used instead.

You can temporarily work around it by obtaining the IP address from another machine, and then using the IP address rather than the URI:

echo "deb http://128.30.2.26/debian testing main" > /etc/apt/sources.list

apt update
Get:1 http://128.30.2.26/debian testing InRelease [232 kB]
Get:2 http://128.30.2.26/debian testing/main s390x Packages [7583 kB]
Get:3 http://128.30.2.26/debian testing/main Translation-en [5134 kB]    
Fetched 13.0 MB in 32s (403 kB/s)                                              
Reading package lists... Done

Debug Symbol Packages

To debug a crash you often need the related debug symbol files. For most Debian packages these are in dbgsym packages. These are available from a separate archive.

Here is an example entry for your sources.list for Debian 12/Bookworm dbgsym packages:

deb http://deb.debian.org/debian-debug/ bookworm-debug main

And an example for Debian 11/Bullseye:

deb http://deb.debian.org/debian-debug/ bullseye-debug main

The same if you running testing:

deb http://deb.debian.org/debian-debug/ testing-debug main

And one more example if you are using the unstable distribution:

deb http://deb.debian.org/debian-debug/ unstable-debug main

More information

A list of UnofficialRepositories to get extra software ( Skype, Opera, Google )
About deb.debian.org, a service that aims to solve the problem of choosing a Debian mirror.
Adding source lists, including cds, using apt-setup
APT HOWTO
AptCLI
AptPreferences
Backports
Debian on CDs
DebianRepository/UseThirdParty - Instructions to use to a third-party repository
sources.list(5) manual page

CategoryPackageManagement