I download the runtime debian package from cuDNN 7.1 web page.
And install it by doing:
sudo dpkg -i libcudnn7_18.104.22.168-1+cuda9.1_amd64.deb
Now I want to verify the installation, but it seems like the installation guide still does not update their documents, it seems like the verifying method is only for 7.0, because I do not see there is a /usr/src/cudnn_samples_v7 after installation.
Download runtime debian cuDNN 7.1(the most recently update version)