> $ lsmod | grep nvidia
> if there's no output, you aren't using the nvidia driver.
> Run
> $ grep nvidia /var/log/dmesg
No output
> $ grep EE /var/log/Xorg.0.log
Only output here is
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 19.290] (II) Loading extension MIT-SCREEN-SAVER