网易源：
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
骨头源：
deb http://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
deb-src http://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
deb http://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
/etc/apt/sources.list
sudo apt-get update