一共两处需要更换
第一处：/etc/apt/sources.list.d/raspi.list
jessie 以及 stretch
清华 deb https://mirrors.tuna.tsinghua.edu.cn/raspberrypi/ jessie main ui
中科大 deb https://mirrors.ustc.edu.cn/archive.raspberrypi.org/ jessie main ui
中科大 deb https://mirrors.ustc.edu.cn/archive.raspberrypi.org/ stretch main ui
清华 deb https://mirrors.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui 默认官方源
第二处：/etc/apt/sources.list
stretch以及jessie
中科大 deb http://mirrors.ustc.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
清华 deb https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
中科大 deb http://mirrors.ustc.edu.cn/raspbian/raspbian/ jessie main contrib non-free rpi
清华 deb https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ jessie main contrib non-free rpi