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ORA-12528:  TNS : listener tips

Oracle Error Tips by Burleson Consulting


The Oracle docs note this on the ORA-12528 error:

      SQL> oerr ora 12528
ORA-12528: TNS: listener: all appropriate instances are blocking new connections

Cause: All instances supporting the service requested by the client reported that they were blocking the new connections. This condition may be temporary, such as at instance startup.

Attempt the connection again. If error persists, then contact the administrator to check the status of the instances.

The ORA-12528 is a new error which has begun with Oracle 10g.  Restarting the Oracle instance can solve transient ORA-12528 errors.

Typically (in Oracle 9i and above), when you "shutdown" an Oracle database, that process "unregisters" the database with the LISTENER. Then when you "startup" the database, it "registers" with the LISTENER.

If the "unregister" did not complete properly, then when you go to "startup" the next time, since the LISTENER did not unregister the instance, you receive the error, "ORA-12528: TNS:listener: all appropriate instances are blocking new connections" since an "appropriate" instance is already running.

Check the status of the listener by

LSNRCTL> status

One method that should resolve this problem is to restart (bounce) the LISTENER:

LSNRCTL> start

Then restart your instance: sqlplus with sysdba privileges

SQL> startup

Make sure all parameters are set.


Adding some information to the listener.ora file will let the listener know where to find the database even when it's down. Here's basically what can be added under the SID_LIST_LISTENER:

(ORACLE_HOME = %Oracle_Home%)


Furthermore, on Oracle Forums, a user describes ORA-12528 as suggesting "that your instance is either not open or opened in exclusive mode."



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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