gedit /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu/ lucid main restricteddeb http://archive.ubuntu.com/ubuntu/ lucid-updates main restricteddeb http://archive.ubuntu.com/ubuntu/ lucid universedeb http://archive.ubuntu.com/ubuntu/ lucid-updates universedeb http://archive.ubuntu.com/ubuntu/ lucid multiversedeb http://archive.ubuntu.com/ubuntu/ lucid-updates multiversedeb http://archive.canonical.com/ubuntu lucid partnerdeb http://archive.ubuntu.com/ubuntu/ lucid-security main restricteddeb http://archive.ubuntu.com/ubuntu/ lucid-security universedeb http://archive.ubuntu.com/ubuntu/ lucid-security multiversedeb http://packages.medibuntu.org/ lucid free non-free
gksudo gedit /etc/apt/sources.list