sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

sudo gedit /etc/apt/sources.list

# 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

sudo apt-get update

sudo apt-get upgrade

sudo apt-get install vim