I installed CUDA 6.5 on ubuntu 14.04, and after rebooting got a message saying the installation of nvidia-340 failed. I didn't install a driver along with CUDA (yet) although some installation instructions implied it may well be necessary. Everything display still works as usual after the restart and error message.
Why would this error message show, and would I really need to install a driver along with installing that version of CUDA?
The FAQ says an option will be displayed to replace my display driver along with the CUDA installation, which I don't recall happening (well, admittedly it was late at night...). So I'm a bit puzzled about all this driver integration.
Conversely, how should I determine if CUDA is good to go and everything is already just in place, in the most straightforward way?