在debian图形化安装过程中就可以选择网络镜像的位置
据说电信用清华的源快，移动的用网易源快
备份源配置文件：
cp /etc/apt/sources.list /etc/apt/sources.listbak
sudo nano /etc/apt/sources.list
deb http://mirrors.163.com/debian/ stretch main non-free contrib deb http://mirrors.163.com/debian/ stretch-updates main non-free contrib deb http://mirrors.163.com/debian/ stretch-backports main non-free contrib deb-src http://mirrors.163.com/debian/ stretch main non-free contrib deb-src http://mirrors.163.com/debian/ stretch-updates main non-free contrib deb-src http://mirrors.163.com/debian/ stretch-backports main non-free contrib deb http://mirrors.163.com/debian-security/ stretch/updates main non-free contrib deb-src http://mirrors.163.com/debian-security/ stretch/updates main non-free contrib
更新源：
apt-get update