para ler o conteudo do /etc/apt/sources.list basta vc ir no terminial e escreve:
sudo gedit /etc/apt/sources.list
Esse é o resultado:
# Sources.list para a família Ubuntu Feisty Fawn
# See
http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb
http://br.archive.ubuntu.com/ubuntu/ feisty main restricted
deb-src
http://br.archive.ubuntu.com/ubuntu/ feisty main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb
http://br.archive.ubuntu.com/ubuntu/ feisty-updates main restricted
deb-src
http://br.archive.ubuntu.com/ubuntu/ feisty-updates main restricted
## 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
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb
http://br.archive.ubuntu.com/ubuntu/ feisty universe
deb-src
http://br.archive.ubuntu.com/ubuntu/ feisty 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://br.archive.ubuntu.com/ubuntu/ feisty multiverse
deb-src
http://br.archive.ubuntu.com/ubuntu/ feisty multiverse
## Uncomment the following two lines to add software from the 'backports'
## repository.
## 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://br.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
deb-src
http://br.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
deb
http://security.ubuntu.com/ubuntu feisty-security main restricted
deb-src
http://security.ubuntu.com/ubuntu feisty-security main restricted
deb
http://security.ubuntu.com/ubuntu feisty-security universe
deb-src
http://security.ubuntu.com/ubuntu feisty-security universe
deb
http://security.ubuntu.com/ubuntu feisty-security multiverse
deb-src
http://security.ubuntu.com/ubuntu feisty-security multiverse
########### Outros ##################
#############################################################
# Todas linhas com "#" no início não serão interpretadas pelo Linux
# Ativar ou descomentar = retirar o # do início da linha
# Desativar ou comentar = colocar # no início da linha
# Após modificações, salvar o sources.list e depois no terminal
# sudo apt-get update
# Os repositórios abaixo não são oficiais, use-os com moderação.
# Descomente um grupo por vez. Não deve ser feito upgrade com estes repositórios ativos
# Após uso destes, comente-os matendo o sources.list exatamente como apresentado.
#############################################################
#Cristhian Marillat (multimidia) - Descomente apenas para instalar os codecs necessários.
# Opção alternativa do Seveas (libdvdcss2, w32codecs, realplayer).
# deb
http://www.debian-multimedia.org sarge main
# deb
http://www.debian-multimedia.org etch main
# deb
http://www.debian-multimedia.org sid main
## Skype
# deb
http://download.skype.com/linux/repos/debian/ stable non-free
deb
http://packages.medibuntu.org/ feisty free non-free
#AUTOMATIX REPOS START
deb
http://www.getautomatix.com/apt feisty main
deb
http://archive.canonical.com/ubuntu feisty-commercial main
deb
http://archive.ubuntu.com/ubuntu feisty-updates universe multiverse
deb
http://archive.ubuntu.com/ubuntu feisty-security main restricted universe multiverse
#AUTOMATIX REPOS END