TNS-12521: TNS listener does not currently know of instance requested in connect descriptor

Mehmet Salih Deveci

5 years ago

Hi,

Sometimes You can get “TNS-12521: TNS:listener does not currently know of instance requested in connect descriptor ” error.

Details of error are as follows.

TNS-12521: TNS:listener does not currently know of instance requested in connect descriptor

Cause: The listener received a request to establish a connection to a database or other service. The connect descriptor received by the listener specified in addition to the service name an instance name for an instance (usually a database instance) that either has not yet dynamically registered with the listener or has not been statically configured for the listener. This may be a temporary condition such as after the listener has started, but before the database instance has registered with the listener.

Action:– Wait a moment and try to connect a second time.

– Check which instances are currently known by the listener by executing: lsnrctl services <listener name>

– Check that the INSTANCE_NAME parameter in the connect descriptor specifies an instance name known by the listener.

– Check for an event in the listener.log file.

his error is related with the listener and registered services of database. Check listener status

$ lsnrctl status listener

Listener should be always started.

Check listener services which services are listening.

lsnrctl services <listener name>

Check the SID parameter known by the listener. If the right SID specified or not in the listener status.

If the related service name and instance don’t exist in the listener status, then set it in the database and register it to database as follows.

SQL> alter system set local_listener='(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.63.34)(PORT=1521)))' scope=both;

SQL> alter system register;

Do you want to learn more details about RMAN, then read the following articles.

https://ittutorial.org/rman-backup-restore-and-recovery-tutorials-for-beginners-in-the-oracle-database/