when trying to execute dbca from linux terminal got this error message. now execute the command xhost, you probably receiving No protocol specified xhost: unable to open display ":0" issue is your user is not allowed to access the x server. You can use xhost to limit access for X server for security reasons. probably you are logged in as oracle user. switch back to default user and execute xhost again. you should see something like SI:localuser:nuwan solution is adding the oracle to access control list xhost +SI:localuser:oracle now go back to oracle user and try dbca it should be working