Using: nvidia-installer ncurses user interface
ERROR: An NVIDIA kernel module 'nvidia' appears to already be loaded in your
       kernel.  This may be because it is in use (for example, by the X
       server), but may also happen if your kernel was configured without
       support for module unloading.  Please be sure you have exited X before
       attempting to upgrade your driver.  If you have exited X, know that your
       kernel supports module unloading, and still receive this message, then
       an error may have occured that has corrupted the NVIDIA kernel module's
       usage count; the simplest remedy is to reboot your computer.
ERROR: Installation has failed.  Please see the file
       '/var/log/nvidia-installer.log' for details.  You may find suggestions
       on fixing installation problems in the README available on the Linux
       driver download page at www.nvidia.com.