sudo cp /etc/apt/sources.list /etc/apt/source.list.bk
sudo gedit /etc/apt/sources.list
编辑你的源列表，将原来的内容全部删除，添加下面列表中最适合你的源(163,台湾的速度比较快)
sudo apt-get update
可以在运行“sudo apt-get update ”时查看一下错误信息，把不能连接的源删除再重新运行
“sudo apt-get update ”。
sudo apt-get upgrade 升级
或者用ubuntu自带的更新管理器升级也可
#台湾源
://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
-src http://tw.archive.ubuntu.com/ubuntu/ precise main universe restricted multiverse
://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
-src http://tw.archive.ubuntu.com/ubuntu/ precise-security universe main multiverse restricted
://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
-src http://tw.archive.ubuntu.com/ubuntu/ precise-updates universe main multiverse restricted
#网易 （速度很快）
://mirrors.163.com/ubuntu/ precise main universe restricted multiverse
-src http://mirrors.163.com/ubuntu/ precise main universe restricted multiverse
://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted
-src http://mirrors.163.com/ubuntu/ precise-security universe main multiverse restricted
://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted
://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted
-src http://mirrors.163.com/ubuntu/ precise-proposed universe main multiverse restricted
://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted
-src http://mirrors.163.com/ubuntu/ precise-backports universe main multiverse restricted
-src http://mirrors.163.com/ubuntu/ precise-updates universe main multiverse restricted
,deepin
://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
-src http://ubuntu.srt.cn/ubuntu/ precise main universe restricted multiverse
://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
-src http://ubuntu.srt.cn/ubuntu/ precise-security universe main multiverse restricted
://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
-src http://ubuntu.srt.cn/ubuntu/ precise-proposed universe main multiverse restricted
://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
-src http://ubuntu.srt.cn/ubuntu/ precise-backports universe main multiverse restricted
-src http://ubuntu.srt.cn/ubuntu/ precise-updates universe main multiverse restricted
.lupaworld.com的源，速度很快
://mirror.lupaworld.com/ubuntu/archive/ precise main restricted universe multiverse
://mirror.lupaworld.com/ubuntu/archive/ precise-security main restricted universe multiverse
://mirror.lupaworld.com/ubuntu/archive/ precise-updates main restricted universe multiverse
://mirror.lupaworld.com/ubuntu/archive/ precise-backports main restricted universe multiverse
://mirror.lupaworld.com/ubuntu/ubuntu-cn/ precise main restricted universe multiverse
.cn99.com源（推荐）:
://ubuntu.cn99.com/ubuntu/ precise main restricted universe multiverse
://ubuntu.cn99.com/ubuntu/ precise-updates main restricted universe multiverse
://ubuntu.cn99.com/ubuntu/ precise-security main restricted universe multiverse
://ubuntu.cn99.com/ubuntu/ precise-backports main restricted universe multiverse
://ubuntu.cn99.com/ubuntu-cn/ precise main restricted universe multiverse
//教育网源
/教育网，就是用教育网的资源吧，中科大，兰大、厦门大学都有很多资源，尤其是支持ipv6的，那更新速度就按兆算了。
://mirrors.ustc.edu.cn/
://mirrors.xmu.edu.cn/howto/
#电子科技大学
://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse
://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
-src http://ubuntu.uestc.edu.cn/ubuntu/ precise main restricted universe multiverse
-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
-src http://ubuntu.uestc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
#中国科技大学
://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse
://debian.ustc.edu.cn/ubuntu/ precise-backports restricted universe multiverse
://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
-src http://debian.ustc.edu.cn/ubuntu/ precise main restricted universe multiverse
-src http://debian.ustc.edu.cn/ubuntu/ precise-backports main restricted universe multiverse
-src http://debian.ustc.edu.cn/ubuntu/ precise-proposed main restricted universe multiverse
-src http://debian.ustc.edu.cn/ubuntu/ precise-security main restricted universe multiverse
-src http://debian.ustc.edu.cn/ubuntu/ precise-updates main restricted universe multiverse
#北京理工大学
://mirror.bjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
://mirror.bjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
://mirror.bjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
://mirror.bjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
://mirror.bjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
-src http://mirror.bjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
-src http://mirror.bjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
-src http://mirror.bjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
-src http://mirror.bjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
-src http://mirror.bjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
#兰州大学
://mirror.lzu.edu.cn/ubuntu/ precise main multiverse restricted universe
://mirror.lzu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
://mirror.lzu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
://mirror.lzu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
://mirror.lzu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
://mirror.lzu.edu.cn/ubuntu-cn/ precise main multiverse restricted universe
#上海交通大学
://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
://ftp.sjtu.edu.cn/ubuntu-cn/ precise main multiverse restricted universe
-src http://ftp.sjtu.edu.cn/ubuntu/ precise main multiverse restricted universe
-src http://ftp.sjtu.edu.cn/ubuntu/ precise-backports main multiverse restricted universe
-src http://ftp.sjtu.edu.cn/ubuntu/ precise-proposed main multiverse restricted universe
-src http://ftp.sjtu.edu.cn/ubuntu/ precise-security main multiverse restricted universe
-src http://ftp.sjtu.edu.cn/ubuntu/ precise-updates main multiverse restricted universe
