Apt > sources.list
As part of its operation, Apt uses a file that lists the 'sources' from which packages can be obtained. This file is /etc/apt/sources.list.
The entries in this file normally follow this format (the entries below are fictitious and should not be used):
deb http://site.example.com/debian distribution component1 component2 component3 deb-src http://site.example.com/debian distribution component1 component2 component3
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.
The 'distribution' can be either the release code name / alias (wheezy, jessie, stretch, 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.
For example, if you have a system running Debian 8.4 "jessie" and don't want to upgrade when Debian stretch releases, use 'jessie' instead of 'stable' for the distribution. If you always want to help test the testing release, use 'testing'. If you are tracking stretch and want to stay with it from testing to end of life, use 'stretch'.
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 for Debian 8 "Jessie"
deb http://httpredir.debian.org/debian jessie main deb-src http://httpredir.debian.org/debian jessie main deb http://httpredir.debian.org/debian jessie-updates main deb-src http://httpredir.debian.org/debian jessie-updates main deb http://security.debian.org/ jessie/updates main deb-src http://security.debian.org/ jessie/updates main
If you also want the contrib and non-free components, add contrib non-free after main.
You can use a GNOME tool to edit your sources.list file. (Menu System>Administration>Software Sources).
gksu --desktop /usr/share/applications/software-properties.desktop /usr/bin/software-properties-gtk
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).
sources.list(5) man page
A list of UnofficialRepositories to get extra software ( Skype, Opera, Google )