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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:

Commonly used package sources

Editing software sources


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:

Using a text editor

The main Apt sources configuration file is at /etc/apt/sources.list. You can edit this files (as root) using your favorite text editor.

To add custom sources, creating separate files under /etc/apt/sources.list.d/ is preferred.

See man 5 sources.list

sources.list format

The entries in this file normally follow this format:

deb distribution component1 component2 component3
deb-src 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.


The 'distribution' can be either the release code name / alias (jessie, stretch, buster, sid) or the release class (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 bookworm and want to stay with it from testing to end of life, use 'bookworm'.


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.

Example sources.list

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

deb bullseye main
deb-src bullseye main

deb bullseye-security main
deb-src bullseye-security main

deb bullseye-updates main
deb-src bullseye-updates main

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

deb bullseye main contrib non-free
deb-src bullseye main contrib non-free

deb bullseye-security main contrib non-free
deb-src bullseye-security main contrib non-free

deb bullseye-updates main contrib non-free
deb-src bullseye-updates main contrib non-free

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

deb bullseye-backports main contrib non-free
deb-src bullseye-backports main contrib non-free

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. The hosts currently do not have publicly verifiable SSL certificates on HTTPS and hence cannot be used with HTTPS at the moment.)

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

gksu --desktop /usr/share/applications/software-properties.desktop /usr/bin/software-properties-gtk

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://vwakviie2ienjx6t.onion/debian bullseye main
deb-src tor+http://vwakviie2ienjx6t.onion/debian bullseye main

deb tor+http://sgvtcaew4bxjd7ln.onion/debian-security bullseye-security main
deb-src tor+http://sgvtcaew4bxjd7ln.onion/debian-security bullseye-security main

deb tor+http://vwakviie2ienjx6t.onion/debian bullseye-updates main
deb-src tor+http://vwakviie2ienjx6t.onion/debian bullseye-updates main


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. For example, below is from a S/390x Port running in a QEMU Chroot:

# 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 testing InRelease
  Temporary failure resolving ''
Reading package lists... Done
W: Failed to fetch  Temporary failure resolving ''
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 testing main" > /etc/apt/sources.list

apt update
Get:1 testing InRelease [232 kB]
Get:2 testing/main s390x Packages [7583 kB]
Get:3 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 11/Bullseye dbgsym packages:

deb bullseye-debug main

The same if you running testing.

deb testing-debug main

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

deb unstable-debug main

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