修改ubuntu系统的更新源

ubuntu里自带的更新源不一定适用于中国内地，建议进行更新。

更新之前，首先备份系统自带的更新源

cp /etc/apt/source.list /etc/apt/sourcelist.bk

然后将source.list文件中写入下面内容：

# taiwan source
deb http://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
deb http://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
deb-src http://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
deb http://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
deb-src http://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
#wangyi 163 source

deb http://mirrors.163.com/ubuntu/ precise main universe restricted multiverse

deb-src http://mirrors.163.com/ubuntu/ precise main universe restricted multiverse

deb http://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted

deb-src http://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted

deb http://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted

deb http://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted

deb-src http://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted

deb http://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted

deb-src http://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted

deb-src http://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted
#mirror.lupaworld.com

deb http://mirror.lupaworld.com/ubuntu/archive/ precise main restricted universe multiverse

deb http://mirror.lupaworld.com/ubuntu/archive/ precise-security main restricted universe multiverse

deb http://mirror.lupaworld.com/ubuntu/archive/ precise-updates main restricted universe multiverse

deb http://mirror.lupaworld.com/ubuntu/archive/ precise-backports main restricted universe multiverse

deb http://mirror.lupaworld.com/ubuntu/ubuntu-cn/ precise main restricted universe multiverse
#ubuntu.cn99.com

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
#dianzi keji daxue

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
#zhongguo keji daxue

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
#beijing keji daxue

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

保存即搞定。