How to solve the issue of no listener in Oracle (ORA-12…

ORA-12541 error refers to the inability of the client to connect to the Oracle database server, possibly due to the database server not being started or the listener program not being started. To resolve this issue, you can follow the steps below:

1. Make sure that the Oracle database server is already running. You can check the status of the listener by running the command “lsnrctl status” on the server. If the listener is not running, you can start it by using the command “lsnrctl start”.
2. Make sure that the client is using the correct connection string, which includes the hostname, port number, and service name. The correct connection string configuration can be found in the tnsnames.ora file.
3. Check the firewall settings on the client computer. If the firewall is blocking communication with the database server, you can try disabling the firewall or changing the firewall settings.
4. Check the network connection of the client computer to ensure it can communicate with the database server. You can try using the ping command to test the connection to the database server.
5. If the above steps do not solve the issue, you can try restarting the Oracle database server and listener program. Use the “lsnrctl stop” command to stop the listener program, and the “lsnrctl start” command to start it.

If the above methods still cannot resolve the issue, you can refer to the official Oracle documentation or contact Oracle technical support for further assistance.