NOTA: Você precisará de privilégios root / sudo para isso.
O método da GUI:
Supondo que você esteja usando o Unity, clique na engrenagem no canto superior direito e clique em "Configurações do sistema".
Você deve então ser apresentado com esta janela:
Emseguida,nalinhainferior,cliqueem"Software e atualizações".
Você então será apresentado com esta janela:
Agora, marque / desmarque as fontes que você deseja ativar / desativar. Você será perguntado pela senha SEU no primeiro clique.
O método CLI (Command Line Interface):
Com o seu editor favorito, abra o arquivo /etc/apt/sources.list .
Será algo parecido com isto:
# deb cdrom:[Ubuntu 14.10 _Utopic Unicorn_ - Release amd64 (20141022.1)]/ utopic main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ utopic main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ utopic-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ utopic universe
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic universe
deb http://us.archive.ubuntu.com/ubuntu/ utopic-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ utopic multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic multiverse
deb http://us.archive.ubuntu.com/ubuntu/ utopic-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ utopic-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ utopic-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu utopic-security main restricted
deb-src http://security.ubuntu.com/ubuntu utopic-security main restricted
deb http://security.ubuntu.com/ubuntu utopic-security universe
deb-src http://security.ubuntu.com/ubuntu utopic-security universe
deb http://security.ubuntu.com/ubuntu utopic-security multiverse
deb-src http://security.ubuntu.com/ubuntu utopic-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu utopic partner
deb-src http://archive.canonical.com/ubuntu utopic partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu utopic main
deb-src http://extras.ubuntu.com/ubuntu utopic main
## Depôt MultiSystem
## Depôt MultiSystem
deb http://liveusb.info/multisystem/depot all main
Este arquivo está bem documentado (comentado). Para ativar uma fonte, remova o # na frente da linha. Para desativá-lo, adicione um # .
É isso! :)