ORA-12541

Quick fix

Cause

Nothing is listening on the host and port in the connect descriptor: the listener is not started, it listens on another port or address, or a firewall rejects the connection.

Fix

Start the listener (lsnrctl start, or srvctl start listener on Grid Infrastructure), check the HOST and PORT in tnsnames.ora against lsnrctl status, and open the port in the firewall.

lsnrctl status
lsnrctl start
# Oracle Linux: open the port
firewall-cmd --permanent --add-port=1521/tcp && firewall-cmd --reload

Where it comes up

Related error codes