seed-ubuntu12.04换源

换源可以让我们在使用Ubuntu 12.04系统时，从国内的镜像源中获取软件包，提高下载速度和安装效率。具体操作步骤如下：

1.备份原有的软件源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup

2.修改源地址
sudo gedit /etc/apt/sources.list

将文件中的内容全部删除，然后复制以下内容，保存：

deb http://mirrors.aliyun.com/ubuntu/ precise main restricted universe multiverse
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

3.更新软件源列表
sudo apt-get update

4.升级系统
sudo apt-get upgrade