在重启服务器的时候，发现nvidia驱动自动升级，使用 nvidia-smi 命令会报错如下，故重装nvidia驱动，参考
Ubuntu18.04的驱动nvidia驱动升级为450版本后，ssh速度很慢的解决方案
NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running.
卸载旧驱动
sudo apt-get --purge remove nvidia*
sudo apt autoremove
重启，使得所有nvidia残余进程被杀掉，否则无法安装
sudo shutdown -r now
下载安装驱动
实验证明440.100版本驱动对18.04十分适合，版本请自行查询。
wget https://cn.download.nvidia.com/XFree86/Linux-x86_64/440.100/NVIDIA-Linux-x86_64-440.100.run
sudo chmod a+x NVIDIA-Linux-x86_64-440.100.run
sudo ./NVIDIA-Linux-x86_64-440.100.run -no-x-check -no-nouveau-check -no-opengl-files
安装过程
The distribution-provided pre-install script failed! Are you sure you want to continue? 选择 yes 继续。
Would you like to register the kernel module souces with DKMS? This will allow DKMS to automatically build a new module, if you install a different kernel later? 选择 No 继续。
Would you like to run the nvidia-xconfigutility to automatically update your x configuration so that the NVIDIA x driver will be used when you restart x? Any pre-existing x confile will be backed up. 选择No
重启
sudo shutdown -r now
提升nvidia-smi运行速度
方法1：
sudo /usr/bin/nvidia-persistenced --verbose
也可直接把该命令放到开机自动运行
echo "/usr/bin/nvidia-persistenced --verbose" | sudo tee -a /etc/init.d/rc.local
方法2：
设置持久模式：0/DISABLED,1/ENABLED
sudo nvidia-smi -pm 1