Recently I was busy with the mod_oc4j clustering of two standalone OHS machines. As Oracle has integrated ONS into OC4J in 10.1.3.x you have to provide your own ons.conf file (just copy one from a 10.1.2.0.2 environment).
But what happend to me was strange. I added a new node (machine_C.mydomain.local) while I removed another one (machine_A.mydomain.local).
However getting the
opmnctl status @farm
still showed the machine_A in the list.
Some investigation delivered the following:
In the directory $ORACLE_HOME\opmn\logs\states two entries do exist:
When you shutdown the OPMN the p* file will disappear. However the .opmndat file will remain there.
Remove it, it will be rebuild with the next opmnctl startall.
Now my machine_A.mydomain.local was gone and the machine_C showed up.