This error occurs because RAC is not linked to the RDBMS home.
You can check whether RAC is linked to the RDBMS home using the following steps.
(1) Navigate to $ORACLE_HOME/rdbms/lib
cd $ORACLE_HOME/rdbms/lib
(2) Run the following command:
nm -r libknlopt.a | grep -c kcsm.o
If the return value is 0, it is not linked;
If the return value is greater than 0, it is already linked.
Solution:
1. Shut down the instance.
2. Navigate to $ORACLE_HOME/rdbms/lib
cd $ORACLE_HOME/rdbms/lib
3. Relink as the Oracle user:
make -f ins_rdbms.mk rac_on ioracle
Alternatively, perform it in two steps:
make -f ins_rdbms.mk rac_on
make -f ins_rdbms.mk ioracle
4. Restart the instance