ORA-00439: feature not enabled: Real Application Clusters

Just a quick heads up based on my recent experience.

If you are upgrading your RAC database to Oracle 11g Release 2 on Unix system (hp-ux 11.31 in my case), you might want to check if feature Real Application Clusters is enabled. Easiest way to do so is to run following select from any single database which is running from same ORACLE_HOME:

select value from v$option where parameter='Real Application Clusters';

If value is FALSE, your RAC database will not come up. Follow RAC Survival Kit: Rac On / Rac Off - Relinking the RAC Option (Doc ID 211177.1):

Login as the Oracle software owner and shutdown all database instances on all nodes in the cluster.

cd $ORACLE_HOME/rdbms/lib
make -f ins_rdbms.mk rac_on

If this step did not fail with fatal errors then proceed to next step

make -f ins_rdbms.mk ioracle