1、修改更新源
sudo vi /etc/apt/sources.list （打开Ubuntu 12.04源列表文件）
2、清空sources.list, 将下面的代码粘贴进去

#台湾源 
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 

#网易 Ubuntu 11.10 源（速度很快） 
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，骨头源是bones7456架设的一个Ubuntu源 ，提供ubuntu,deepin 
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 

#mirror.lupaworld.com的源，速度很快 
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 

#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 

#兰州大学 
deb ftp://mirror.lzu.edu.cn/ubuntu/ precise main multiverse restricted universe 
deb ftp://mirror.lzu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe 
deb ftp://mirror.lzu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe 
deb ftp://mirror.lzu.edu.cn/ubuntu/ precise-security main multiverse restricted universe 
deb ftp://mirror.lzu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe 
deb ftp://mirror.lzu.edu.cn/ubuntu-cn/ precise main multiverse restricted universe 

#上海交通大学 
deb http://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe 
deb http://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe 
deb http://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe 
deb http://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe 
deb http://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe 
deb http://ftp.sjtu.edu.cn/ubuntu-cn/ precise main multiverse restricted universe 
deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe 
deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe 
deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe 
deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe 
deb-src http://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe 

3、通知ubuntu启用新的更新源

sudo apt-get update