1.在修改source.list前，最好先备份一份
执行备份命令
sudo cp /etc/apt/sources.list /etc/apt/sources.list.old
2.执行命令打开source.list文件：
sudo vim /etc/apt/source.list
3.复制源
把下面的复制到source.list中去，并覆盖原来的文件内容。
deb-src http://mirror.neu.edu.cn/ubuntu/ xenial main restricted #Added by software-properties deb http://mirror.neu.edu.cn/ubuntu/ xenial main restricted deb-src http://mirror.neu.edu.cn/ubuntu/ xenial restricted multiverse universe #Added by software-properties deb http://mirror.neu.edu.cn/ubuntu/ xenial-updates main restricted deb-src http://mirror.neu.edu.cn/ubuntu/ xenial-updates main restricted multiverse universe #Added by software-properties deb http://mirror.neu.edu.cn/ubuntu/ xenial universe deb http://mirror.neu.edu.cn/ubuntu/ xenial-updates universe deb http://mirror.neu.edu.cn/ubuntu/ xenial multiverse deb http://mirror.neu.edu.cn/ubuntu/ xenial-updates multiverse deb http://mirror.neu.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://mirror.neu.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse #Added by software-properties deb http://archive.canonical.com/ubuntu xenial partner deb-src http://archive.canonical.com/ubuntu xenial partner deb http://mirror.neu.edu.cn/ubuntu/ xenial-security main restricted deb-src http://mirror.neu.edu.cn/ubuntu/ xenial-security main restricted multiverse universe #Added by software-properties deb http://mirror.neu.edu.cn/ubuntu/ xenial-security universe deb http://mirror.neu.edu.cn/ubuntu/ xenial-security multiverse
清华大学 # deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security universe deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security multiverse
4update命令
sudo apt-get update