found out many solutions but lastly I got one solution which worked for me.
But well I will post all the possible ways which you can try (as per my knowledge) to overcome this issue.
Xlib: connection to ":0.0" refused by server Xlib: No protocol specified
$ export DISPLAY=localhost:0.0 $ xhost +
Syntax: $ export DISPLAY=(machine_name):0.0 For example: $ export DISPLAY=10.10.20.42:0.0 $ xhost +
Solution 3 (which worked for me)
Login to the user account where you are getting the above error
$ xauth $DISPLAY xauth: creating new authority file /home/oracle/.Xauthority xauth: (argv):1: unknown command ":0.0"
The best way to check whether your Xlib display protocol is working or not is by using xclock command
In case the above solution does not works
Login as root
# xauth $DISPLAY xauth: creating new authority file /home/root/.Xauthority
# xauth list $DISPLAY test.example.com/unix:0 MIT-MAGIC-COOKIE-1 f601e6a29ea688786765434c5c6325071
# su - oracle $ xauth add test.example.com/unix:0 MIT-MAGIC-COOKIE-1 f601e6a29ea688786765434c5c6325071 xauth: creating new authority file /home/oracle/.Xauthority
Now test if your DISPLAY is working