1. 备份镜像源

   cd /etc/apt
   cp sources.list sources.list.bak

2. 修改镜像源

   vim sources.list
   
   # 复制粘贴下面镜像源，保存退出
   deb http://mirrors.aliyun.com/ubuntu/ xenial main
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial main
   
   deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main
   
   deb http://mirrors.aliyun.com/ubuntu/ xenial universe
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial universe
   deb http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates universe
   
   deb http://mirrors.aliyun.com/ubuntu/ xenial-security main
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main
   deb http://mirrors.aliyun.com/ubuntu/ xenial-security universe
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security universe

3. 执行更新镜像源

sudo apt-get update