1、首先备份Ubuntu12.04源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup （备份下当前的源列表）
2、修改更新源
sudo gedit /etc/apt/sources.list （打开Ubuntu 12.04源列表文件）
3、把里面的列表替换成下面的列表
163源
deb http://mirrors.163.com/ubuntu/ precise main restricted deb-src http://mirrors.163.com/ubuntu/ precise main restricted deb http://mirrors.163.com/ubuntu/ precise-updates main restricted deb-src http://mirrors.163.com/ubuntu/ precise-updates main restricted deb http://mirrors.163.com/ubuntu/ precise universe deb-src http://mirrors.163.com/ubuntu/ precise universe deb http://mirrors.163.com/ubuntu/ precise-updates universe deb-src http://mirrors.163.com/ubuntu/ precise-updates universe deb http://mirrors.163.com/ubuntu/ precise multiverse deb-src http://mirrors.163.com/ubuntu/ precise multiverse deb http://mirrors.163.com/ubuntu/ precise-updates multiverse deb-src http://mirrors.163.com/ubuntu/ precise-updates multiverse deb http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ precise-security main restricted deb-src http://mirrors.163.com/ubuntu/ precise-security main restricted deb http://mirrors.163.com/ubuntu/ precise-security universe deb-src http://mirrors.163.com/ubuntu/ precise-security universe deb http://mirrors.163.com/ubuntu/ precise-security multiverse deb-src http://mirrors.163.com/ubuntu/ precise-security multiverse deb http://extras.ubuntu.com/ubuntu precise main deb-src http://extras.ubuntu.com/ubuntu precise main
sohu源
deb http://mirrors.sohu.com/ubuntu/ precise main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise main restricted deb http://mirrors.sohu.com/ubuntu/ precise-updates main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise-updates main restricted deb http://mirrors.sohu.com/ubuntu/ precise universe deb-src http://mirrors.sohu.com/ubuntu/ precise universe deb http://mirrors.sohu.com/ubuntu/ precise-updates universe deb-src http://mirrors.sohu.com/ubuntu/ precise-updates universe deb http://mirrors.sohu.com/ubuntu/ precise multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise multiverse deb http://mirrors.sohu.com/ubuntu/ precise-updates multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-updates multiverse deb http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ precise-security main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise-security main restricted deb http://mirrors.sohu.com/ubuntu/ precise-security universe deb-src http://mirrors.sohu.com/ubuntu/ precise-security universe deb http://mirrors.sohu.com/ubuntu/ precise-security multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-security multiverse deb http://extras.ubuntu.com/ubuntu precise main deb-src http://extras.ubuntu.com/ubuntu precise main
ubuntu.cn99.com源（推荐）:
deb http://ubuntu.cn99.com/ubuntu/ precise main restricted universe multiverse deb http://ubuntu.cn99.com/ubuntu/ precise-updates main restricted universe multiverse deb http://ubuntu.cn99.com/ubuntu/ precise-security main restricted universe multiverse deb http://ubuntu.cn99.com/ubuntu/ precise-backports main restricted universe multiverse deb http://ubuntu.cn99.com/ubuntu-cn/ precise main restricted universe multiverse
教育网源
如果你是在校大学生，可以使用校园网/教育网，就是用教育网的资源吧，尤其是支持ipv6的，那更新速度就按兆算了。
#电子科技大学
deb http://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse deb http://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse deb-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
#中国科技大学
deb http://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse deb http://debian.ustc.edu.cn/ubuntu/ precise-backports restricted universe multiverse deb http://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse deb http://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse deb http://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse deb-src http://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse deb-src http://debian.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse deb-src http://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse deb-src http://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse deb-src http://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
#北京理工大学
deb http://mirror.bjtu.edu.cn/ubuntu/ precise main multiverse restricted universe deb http://mirror.bjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe deb http://mirror.bjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe deb http://mirror.bjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe deb http://mirror.bjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe deb-src http://mirror.bjtu.edu.cn/ubuntu/ precise main multiverse restricted universe deb-src http://mirror.bjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe deb-src http://mirror.bjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe deb-src http://mirror.bjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe deb-src http://mirror.bjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
4、更新源
sudo apt-get update