Source list的位置在：
/etc/apt/sources.list
打开后贴上如下内容便能使用镜像库：
deb http://ftp2.cn.debian.org/debian/ jessie main non-free contrib deb http://ftp2.cn.debian.org/debian/ jessie-updates main non-free contrib deb http://ftp2.cn.debian.org/debian/ jessie-backports main non-free contrib deb-src http://ftp2.cn.debian.org/debian/ jessie main non-free contrib deb-src http://ftp2.cn.debian.org/debian/ jessie-updates main non-free contrib deb-src http://ftp2.cn.debian.org/debian/ jessie-backports main non-free contrib deb http://ftp2.cn.debian.org/debian-security/ jessie/updates main non-free contrib deb-src http://ftp2.cn.debian.org/debian-security/ jessie/updates main non-free contrib deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
更多的镜像地址可以通过如下网址获得：
https://www.debian.org/mirror/list
