1.查看ubuntu版本的方法：
使用命令 sudo lsb_release -a
输出如下：
root@localhost:/etc/apt# sudo lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.4 LTS
Release: 14.04
Codename: trusty
2.保存原源
root@localhost:/etc/apt# cp sources.list sources.list.bak
root@localhost:/etc/apt# vi sources.list
修改为下面的内容：
中国科学技术大学源：
Trusty(14.04)
deb http://mirrors.ustc.edu.cn/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ trusty-backports main restricted universe multiverse
3.修改完成后
root@localhost:/etc/apt# apt-get update
鸣谢：
http://blog.csdn.net/debug_cpp/article/details/2687067
http://linux.it.net.cn/Ubuntu/2015/0111/11849.html