Some users get the following error when they do
nvidia-smi in the shell.
NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running.
This issue is easily fixed by re-installing the drivers and rebooting:
sudo apt-get update
sudo apt-get install --no-install-recommends nvidia-384 libcuda1-384 nvidia-opencl-icd-384