https://www.debian.org/mirror/list
nano /etc/apt/sources.list
deb http://ftp.cn.debian.org/debian stretch main
deb http://ftp.cn.debian.org/debian stretch-updates main
deb http://ftp.cn.debian.org/debian-security/ stretch/updates main
https://www.debian.org/mirror/list
nano /etc/apt/sources.list
deb http://ftp.cn.debian.org/debian stretch main
deb http://ftp.cn.debian.org/debian stretch-updates main
deb http://ftp.cn.debian.org/debian-security/ stretch/updates main