更换国内源
/etc/apt/sources.list
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
deb http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
deb-src http://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
OR apt install apt-transport-https
/etc/apt/sources.list
deb https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
deb-src https://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ stretch main contrib non-free rpi
/etc/apt/sources.list.d/raspi.list
deb https://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui
deb-src https://mirror.tuna.tsinghua.edu.cn/raspberrypi/ stretch main ui