1.Ubuntu18.04在安装lightdm之后重启后出现黑屏，光标左上角闪烁
2.nvidia-smi显示NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running.
3.重装显卡驱动然后重新进入桌面就行了
sudo sh NVIDIA-Linux-x86_64-440.100.run
完成重装后成功解决
最后重新进入图形界面即可
sudo init 3
sudo init 5