Cause:

I face this weird error while installing recovery catalog.I have not installed catalog before and this is the first time i install catalog but not sure why this error creep in.

[oracle@orcl ~]$ rman target /

Recovery Manager: Release 12.1.0.2.0 - Production on Sat Mar 6 18:30:10 2021

Copyright (c) 1982, 2014, Oracle and/or its affiliates.  All rights reserved.

connected to target database: ORCL (DBID=1559282684)

RMAN> connect catalog rcat/rcat

connected to recovery catalog database
RMAN> create catalog;

error creating db
ORACLE error from recovery catalog database: ORA-00955: name is already used by an existing object

ORACLE error from recovery catalog database: ORA-00942: table or view does not exist

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-06433: error installing recovery catalog

RMAN> register database;

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of register command at 03/06/2021 18:28:49
RMAN-06428: recovery catalog is not installed

RMAN> exit

Workaround:

Drop the existing catalog and recreate catalog database from RMAN

RMAN> drop catalog;

recovery catalog owner is RCAT
enter DROP CATALOG command again to confirm catalog removal

RMAN> drop catalog;

recovery catalog dropped

RMAN> create catalog;

recovery catalog created

RMAN> register database;

database registered in recovery catalog
starting full resync of recovery catalog
full resync complete

RMAN>