RMAN - keeping a backup valid for long term

rdbms : 10.2.0.4
o/s : RHEL4
Step 1 : From the sql session
SQL > SHUTDOWN IMMEDIATE
SQL > startup mount;

Step 2: From RMAN session
RMAN> BACKUP DATABASE KEEP FOREVER NOLOGS TAG 'ARCHIVE_1'
#make long-term consistent backup
# mark backup as unavailable in the repository
# so that RMAN does not attempt to restore it unless explicitly specified on the restore.
RMAN> CHANGE BACKUP TAG 'ARCHIVE_1' unavailable
RMAN>sql 'alter database open';

Note : Nocatalog mode is not supported for keep forever.
RMAN 06522 : KEEP FOREVER option is not supported without the recovery catalog