I need CUDA Toolkit version 8 for Ubuntu, because Tensorflow does not support CUDA 9. I can not find links to download previous version of CUDA Toolkit on nvidia.com site.
or sudo apt-get install cuda-8-0
provided that you have this repo added in your /etc/apt/sources.list (possibly adjust the Ubuntu version as needed)
deb http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64 /