This is a brief on how to configure sources.list file on Debian 9, codenamed stretch. Debian is one of the, most popular Linux distributions and much of its strength comes from the core of Debian package management - apt. Everything in Debian, be it an application or any other component - is built into a package, and then that package is installed onto your system (either by the Installer or by you).
Understanding APT and sources.list
The package manager for Debian and its derivatives is apt. APT which stands for Advanced Package Tool is a set of tools for managing Debian packages, and therefore the applications installed on your Debian system. APT makes it possible to:
- Install applications
- Remove applications
- Update applications
- Fix broken packages e.t.c
Read Also : How to Install Debian Packages Offline
APT is capable of resolving dependency problems and retrieving requested packages from designated package repositories. It delegates the actual installation and removal of packages to dpkg. APT is primarily used by command-line tools, but there are GUI tools available which you can use.
The file /etc/apt/sources.list in Debian is used by Apt as part of its operation. This file contains a list of the 'sources' from which packages can be obtained. 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
The entries shown above are fictitious and should not be used. Below are the contents of this file when split into different sections:
The first entry on each line - deb or deb-src represent the type of archive.
- deb means the URL provided contain pre-compiled packages. These are the packages installed by default when using package managers like apt-get or aptitude.
- deb-src indicate sources packages with Debian control file (.dsc) and the diff.gz containing the changes needed for packaging the program.
The next entry on the line is a URL to the repository where the packages will be downloaded from. You can find the main list of Debian repository packages from Debian Worldwide sources.list mirrors.
The 'distribution' can be either the release code name / alias (jessie, stretch, buster, sid) or the release class (old stable, 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.
There are normally three components which can be used on Debian, namely:
- main - This contains packages that are part of Debian distribution. These packages are DFSG compliant.
- contrib -The packages here are DFSG compliant but contains packages which are not in the main repository.
- non-free - This contains software packages which do not comply with the DFSG.
Complete sources.list file on Debian 9 will look something like below:
deb http://deb.debian.org/debian stretch main deb-src http://deb.debian.org/debian stretch main deb http://deb.debian.org/debian stretch-updates main deb-src http://deb.debian.org/debian stretch-updates main deb http://security.debian.org/debian-security/ stretch/updates main deb-src http://security.debian.org/debian-security/ stretch/updates main
Then to have the contrib and non-free components, add contrib non-free after main as shown below:
deb http://deb.debian.org/debian stretch main contrib non-free deb-src http://deb.debian.org/debian stretch main contrib non-free deb http://deb.debian.org/debian stretch-updates main contrib non-free deb-src http://deb.debian.org/debian stretch-updates main contrib non-free deb http://security.debian.org/debian-security/ stretch/updates main contrib non-free deb-src http://security.debian.org/debian-security/ stretch/updates main contrib non-free
Once you have made changes to the sources.list file, you have to run the command:
$ sudo apt-get update
This will ensure your apt index is synchronized. Then you can install new packages from the repository.
Adding custom repositories
It is not always advisable to add custom and third-party repositories on the file /etc/apt/sources.list. Instead you can create a file under the /etc/apt/sources.list.d directory. For example, to install docker on Debian 9 from its upstream repository, you'll do:
$ sudo vim /etc/apt/sources.list
Add the content:
deb https://apt.dockerproject.org/repo debian-stretch main
You can then proceed to update apt-cache and install docker package from it. This is a recommended way to add any other third party repositories.
Importing apt keys
When working with apt and sources.list repositories, at some point you are required to import gpg keys. This is usually done using the command apt-key, whose syntax is.
# apt-key adv --keyserver <server-address>--recv-keys <key-id>
As an example, to download docker repository gpg keys, you'll run:
# apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
# apt-get update && apt-get install docker-engine
In general, working with sources.list file is relatively easy. The only thing you have to be keen on is putting the right Distribution. If on stable installation you add a sid repository with unstable packages, you may end up breaking your system or encountering many unresolved dependencies.