16.3.16 ORA-12541

Indicates that the listener cannot be reached.

Message

ORA-12541: Cannot connect. 
No listener at string.

For example:

When using the TCP, TCPS, Exadirect, or Websocket protocol:

ORA-12541: Cannot connect. 
No Listener at host 10.9.7.5 port 1522

In this case, the last tried IP address of the client appears. In case of re-direct, the re-direct IP address appears.

When using the IPC protocol:

ORA-12541: Cannot connect. 
No Listener at key EXTPROC

Cause

The connection request cannot be completed in the following cases:

• The database listener process is not running on the specified host and port.

• An Interprocess Communication (IPC) protocol connection is attempted, but there is no listener for the specified key running on the local machine.

The PL/SQL applications using UTL packages can also get this error if the external server process is not listening at the specified address.

Action

1. If the error displays the host and port that the connection tried to use, then ensure that a listener process is running on that host and is listening on that port. If the message indicates that there is no listener at the specified key, then ensure that the listener is running on the local machine and is listening for the specified key. The listener process is used to initially handle all connections to Oracle Database.

2. Check for mistakes in the specified connection string.

3. If you are using an alias from a tnsnames.ora file, then verify the correctness of the host and port.

   Alternatively, verify the correctness of the key if you are using an IPC connection.

4. If using an Easy Connect connection string, then ensure that the host and port are correct.

5. Use lsnrctl to check that the listener is running and also verify the port or key that the listener is listening to. To do so, run one of the following:

   • lsnrctl status

   • If a listener is named in the listener.ora file, then run:

     lsnrctl status listener_name

   • If an Oracle Connection Manager (Oracle CMAN) proxy listener is named in the cman.ora file, then run:

     cmctl show status -c cman_name