ORA-12523: TNS listener could not find instance appropriate for the client connection

Hi,

Sometimes You can get “ORA-12523: TNS:listener could not find instance appropriate for the client connection ” error.

Details of error are as follows.

ORA-12523: TNS:listener could not find instance appropriate for the client connection

Check your listener.ora if it contains An extra bracket or missing bracket. If there is missing or extra bracket in the listener.ora, fix it and start listener again.

Or This 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/