1、在修改源的时候，最好先备份一下原来的系统更新源。执行命令：sudo cp /etc/apt/source.list /etc/apt/source.list.bak
2、打开/etc/apt/source.list，可以使用vim、gedit等工具打开。
3、选择下面的任意一个源翱务校肢复制进去。清华大学# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricteddeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricteddeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricteddeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial universedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates universedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial multiversedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates multiversedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiversedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricteddeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security universedeb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security multiverse
4、阿里云源# deb cdrom:职邗珩垃[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricteddeb-src http://archive.ubuntu.com/ubuntu xenial main restricted #Added by software-propertiesdeb http://mirrors.aliyun.com/ubuntu/ xenial main restricteddeb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted multiverse universe #Added by software-propertiesdeb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricteddeb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted multiverse universe #Added by software-propertiesdeb http://mirrors.aliyun.com/ubuntu/ xenial universedeb http://mirrors.aliyun.com/ubuntu/ xenial-updates universedeb http://mirrors.aliyun.com/ubuntu/ xenial multiversedeb http://mirrors.aliyun.com/ubuntu/ xenial-updates multiversedeb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiversedeb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse #Added by software-propertiesdeb http://archive.canonical.com/ubuntu xenial partnerdeb-src http://archive.canonical.com/ubuntu xenial partnerdeb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricteddeb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted multiverse universe #Added by software-propertiesdeb http://mirrors.aliyun.com/ubuntu/ xenial-security universedeb http://mirrors.aliyun.com/ubuntu/ xenial-security multiverse
5、需要注意的是，新增源里的xenial需要和我们要修改的系统的codename一致。使用lsb_release -a可以看到codename。
6、修改完成后，保存退出。执行sudo apt-get update更新即可。
