SP2-0618: Cannot find the Session Identifier. Check PLUSTRACE role is enabled

We often want to enable AUTOTRACE ON,
for administering explain plan, and encounter below error;

U1@mydb_us> set autotrace on
SP2-0618: Cannot find the Session Identifier.  Check PLUSTRACE role is enabled
SP2-0611: Error enabling STATISTICS report
U1@mydb_us> 

ORA-20446: The owner of the job is not registered

If you have encounter the following error in OEM, while creating job, etc:

ORA-20446: The owner of the job is not registered ORA-06512: at "SYSMAN.MGMT_JOBS", line 168 ORA-06512: at "SYSMAN.MGMT_JOBS", line 86 ORA-06512: at line 1

please execute following command after login into database as sys:

execute MGMT_USER.MAKE_EM_USER('USERNAME');

Failed to get an exclusive lock, Unable to perform blackout operation. Please retry after some time

This issue is specific to the environment where the emctl blackout operation takes more than usual. i.e. More than the default of 60 seconds for the single execution. Hence it fails to get an exclusive lock within the 60 seconds window.

ORA-10997: another startup/shutdown operation of this instance inprogress

SQL> startup
ORA-10997: another startup/shutdown operation of this instance inprogress
ORA-09968: unable to lock file
Linux-x86_64 Error: 11: Resource temporarily unavailable

RMAN-06438: error executing package DBMS_RCVMAN in TARGET database

Recovery Manager requires the DBMS_RCVMAN package in the SYS schema of the indicated database. Normally this package is installed during database creation. To re-create the package, run the files dbmsrman.sql and prvtrmns.plb.

$ sqlplus / as sysdba

SQL> @?/rdbms/admin/dbmsrman.sql
SQL> @?/rdbms/admin/prvtrmns.plb