I already had a "user" db2admin. By mistake I modified the value of SYSADM_GROUP to this "db2admin". This change was made successfully - I wish it hadn't!
Now since there is no "group" by the name of "db2admin" I cannot set this back to empty - the original value even when logged in as administrator. Iget the error that "administrator" does not have the right to make this change.
The system does not allow me to create a "group" by the name of "db2admin" (so I can reconfigure as a member of SYSADM_GROUP), apparently, because there is already a db2admin "user".
I'd appreciate very much if somebody could suggest a way out of this quagmire, so I don't have to reinstall the database.