If users can not connect to the database, how can you see if the listener is actually running?
The best way is to issue the command lsnrctl status.
Another way is to look for the process to see if it is running (either in Windows Task Manager or by issuing the unix command ps-ef). We would see the Oracle listener running. If issuing the Unix command ps-ef, you would see a process something like this:
In the above line, LISTENER refers to the listener name (which can vary).
Using a utility such as tnsping is not the best way to check on the listener if the users can’t connect to the database. In that case, running tnsping doesn’t add any useful information.