也不知道是什么原因，输入nvidia-smi会有这个bug。看到一个帖子中遇到和我类似的问题：
I have several issues actually, but I am not sure whether they are related.
nvidia-smi out puts no device were found.
The system cannot detect the second display.
The fractional scaling is not working (can only set to 200% even if I set 150%).
The update rate is incorrect in system setting.有一个评论解决了我的问题：
Wrong driver, please either switch to the non “-open” driver version in Software&Updates or set the appropriate module option.我安装的显卡驱动是nvidia-driver-525-open，带有open，换一个不带open的驱动就好了，鬼bug。