why nvidia installer fails with "Unable to load: nvidia-installer ncurses v6 user interface" ?

Issue

• Nvidia installer fails with following error

nvidia-installer command line:
    ./nvidia-installer

Unable to load: nvidia-installer ncurses v6 user interface

Using: nvidia-installer ncurses user interface
-> Detected 48 CPUs online; setting concurrency level to 32.
-> Tagging shared libraries with chcon -t textrel_shlib_t.
-> The file '/tmp/.X2-lock' exists and appears to contain the process ID '2027' of a runnning X server.
ERROR: You appear to be running an X server; please exit X before installing.  For further details, please see the section INSTALLING THE NVIDIA DRIVER in the README available on the Linux driver download page at www.nvidia.com.
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.