Stopping X Server 
Caution
If you stop X Server on the database computer, the database cannot be accessed by database tools and applications which are located on remote computers any longer.
The JDBC interface also requires the X Server for local communication.
End of the caution.
Prerequisites
On Unix and Linux: You must be logged on as an operating system user belonging to <sdba_group>.
More information: Database Administration, Special Operating System Users and Groups (Unix and Linux)
Procedure
x_server stop