此处都以阿里云的镜像为例子；Ubuntu分为ARM版本和x86版本
阿里云镜像网站：https://opsx.alibaba.com/mirror
里面有ubuntu源的设置说明
以ubuntu16.04为例：
x86版本
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
ARM版本
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial universe
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates universe
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-security main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-security main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-security universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-security universe
你也可以同样的方法去改其它的镜像网站的源。
修改源之后执行
apt-get update
apt-get upgrade
搞之前，别忘了把自带的源给备份一下，稳妥一点嘛！
