现在默认的apt-get源很慢。中科大的源最快，基本满速。还有搜狐和网易的源速度也不错。
使用方法：
1、修改源地址：
cp /etc/apt/sources.list /etc/apt/sources.list.bak vim /etc/apt/sources.list
加入如下内容（中科大的U源）：
deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates main restricted deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates main restricted deb http://mirrors.ustc.edu.cn/ubuntu/ precise universe deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise universe deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates universe deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates universe deb http://mirrors.ustc.edu.cn/ubuntu/ precise multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ precise-updates multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-updates multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu precise-security main restricted deb-src http://security.ubuntu.com/ubuntu precise-security main restricted deb http://security.ubuntu.com/ubuntu precise-security universe deb-src http://security.ubuntu.com/ubuntu precise-security universe deb http://security.ubuntu.com/ubuntu precise-security multiverse deb-src http://security.ubuntu.com/ubuntu precise-security multiverse
备选比较快的源：
搜狐源：
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
网易源：
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
修改完之后最好刷新一下系统的源：
sudo apt-get update
