需要更改/etc/apt/sources.list 和 /etc/apt/sources.list.d/raspi.list文件
国内清华源：
/etc/apt/sources.list 修改为：
deb http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
deb-src http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
/etc/apt/sources.list.d/raspi.list修改为：
deb http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
deb-src http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
更新：
sudo apt update && sudo apt upgrade -y
#需要更新固件为next分支,默认master ,一般不需要
sudo BRANCH=next rpi-update关于rpi-update
https://github.com/Hexxeh/rpi-update
