写在前面：本文摘录自网上，经过验证，大胆使用。
一、ubuntu16.04更换国内源
1.备份原始源文件source.list
桌面打开终端，执行命令：sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2.修改源文件source.list
（1）终端执行命令：sudo chmod 777 /etc/apt/sources.list 更改文件权限使其可编辑；
（2）执行命令：sudo gedit /etc/apt/sources.list 打开文件进行编辑；
（3）删除原来的文件内容，复制下面的任意一个到其中并保存（常用的是阿里源和清华源，推荐阿里源）；
阿里源：
deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
3.更新
sudo apt-get update