转自：http://www.ibloglife.com/archives/ubuntu-12-04-gengxinyuan.html
ubuntu 12.04更新源的快慢、稳定与否，影响到ubuntu更新速度，选择一个稳定、快速的更新源就显得很重要。那么要如何选择、修改ubuntu 12.04更新源呢？
不同版本找软件源的方法见链接：http://teliute.org/linux/Ubsetup/lesson9/lesson9.html
方法一：从Ubuntu收录的源中选择
1.打开软件中心->编辑->软件源，然后点击源的列表->其他站点（注意，此处打开软件中心，然后才能在最上面的选项编辑中找到软件源选项，如下）
如下图：
2.然后手工选择一个稳定、快速的源，如163源，CN99源，或者点击“选择最佳服务器”，如下图：
方法二：手工修改源文件
1.备份原有的源列表文件sources.list：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2.修改源列表，将sources.list文件中的的源列表用新的源列表替换：
sudo gedit /etc/apt/sources.list
3.保存退出后，刷新一下系统的源：
sudo apt-get update
以下是一些比较稳定，快速的国内源列表：
163源
deb http://mirrors.163.com/ubuntu/ precise main restricted deb http://mirrors.163.com/ubuntu/ precise-updates main restricted deb http://mirrors.163.com/ubuntu/ precise universe deb http://mirrors.163.com/ubuntu/ precise-updates universe deb http://mirrors.163.com/ubuntu/ precise multiverse deb http://mirrors.163.com/ubuntu/ precise-updates multiverse deb http://mirrors.163.com/ubuntu/ precise-backports main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ precise-security main restricted deb http://mirrors.163.com/ubuntu/ precise-security universe deb http://mirrors.163.com/ubuntu/ precise-security multiverse deb http://extras.ubuntu.com/ubuntu precise main
cn99源
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
sohu源
deb http://cn.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse deb http://cn.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse deb http://cn.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse deb http://cn.archive.ubuntu.com/ubuntu/ precise-proposed main restricted universe multiverse deb http://cn.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
lupaworld源
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
【阿里云源】
deb http://mirrors.aliyun.com/ubuntu/ precise-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ precise-backports main restricted universe multiverse