sudo vim /etc/apt/sources.list
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial main restricted
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-updates main restricted
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial universe
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-updates universe
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial multiverse
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-updates multiverse
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-backports main restricted universe multiverse
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-security main restricted
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-security universe
deb http://ftp.cuhk.edu.hk/pub/Linux/ubuntu/ xenial-security multiverse