mv /etc/apt/sources.list /etc/apt/sources.list.bak
cat <<EOF >/etc/apt/sources.list deb http://mirrors.ustc.edu.cn/debian stable main contrib non-free deb http://mirrors.ustc.edu.cn/debian stable-updates main contrib non-free EOF
apt update
mv /etc/apt/sources.list.bak /etc/apt/sources.list