ORACLE INSTALLATION: Error: Can’t open display: :0.0

I was recently trying to install oracle. I added a new user and could not start any x-windows as this new user. “xhost +” was the solution.

The following error was displayed:

====
oracle@manoj:/home/oracle/database$ xclock
No protocol specified
Error: Can't open display: :0.0
=====

The solution is below:

Run "xhost +" via root:

=====
root@manoj:/home/oracle/database# xhost +
access control disabled, clients can connect from any host


OR

You can also run the below command:
=====
root@manoj:/home/oracle/database#  xhost local:oracle
access control disabled, clients can connect from any host
=====

Now, login as oracle user and try to run "xclock".
=====
root@manoj:/home/oracle/database# su oracle

Now it should work:

oracle@manoj:/home/oracle/database$ xclock
======

ONLY FOR FURTHER REFERENCE:
-----------------------------------------------
Note: If xclock command is not found in the server.  Install it using yum as below:
=====
yum install xorg-x11-apps

Also, to set the display variable use the below command.

DISPLAY=:0.0
export=DISPLAY
======