ERROR: Unable to verify the graphical display setup. This application requires X display. Make sure that xdpyinfo exist under PATH variable.

Error: During running the runInstaller to Setup Oracle Database, we are getting the following error

ERROR: Unable to verify the graphical display setup. This application requires X display. Make sure that xdpyinfo exist under PATH variable.
Authorization required, but no authorization protocol specified
Can't connect to X11 window server using ':0' as the value of the DISPLAY variable.

Solution:

Install the x11 package in Ubuntu operating system.

Sudo apt-get install x11-utils

Add the user Oracle to access control list for X11 with command: xhost +SI:localuser:<user>

oracle@Oracle1:/u01/app/oracle$ su root

Password: 

root@Oracle1:/u01/app/oracle# xhost +SI:localuser:oracle

localuser:oracle being added to access control list

root@Oracle1:/u01/app/oracle#

Try again to start the runInstaller

oracle@Oracle1:/u01/app/oracle$ ./runInstaller 

Launching Oracle Database Setup Wizard...