1、先备份
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup （备份下当前的源列表，有备无患嘛）

2、修改更新源
sudo gedit /etc/apt/sources.list （打开Ubuntu 8.04源列表文件）

在最下面加入
deb http://ubuntu.cn99.com/ubuntu/ hardy main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ hardy-security main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ hardy-updates main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ hardy-proposed main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ hardy-backports main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ hardy main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ hardy-security main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ hardy-updates main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ hardy-proposed main restricted universe multiverse
deb-src http://ubuntu.cn99.com/ubuntu/ hardy-backports main restricted universe multiverse

3、通知 ubuntu 8.40 启用新的更新源
sudo apt-get update