DGMGRL Error: ORA-16647: could not start more than one observer

Problem Description:

DGMGRL start observer failed with Error: ORA-16647: could not start more than one observer
Failed.
DGMGRL> start observer;
Error: ORA-16647: could not start more than one observer
Failed.
DGMGRL> exit
Solution Description

The problem is the observer is already started. Check whether observer is up or not with the following commands. The Observer: value should be (none) to start the observer again. If you have some server/host name already present there (Observer:         (none)) then you cannot start the observer again.

DGMGRL> show configuration verbose;

….
….

Fast-Start Failover: ENABLED
  Threshold:        30 seconds
  Target:           TRPRO_STANDBY
  Observer:         (none)
  Lag Limit:        30 seconds (not in use)
  Shutdown Primary: TRUE
  Auto-reinstate:   TRUE

Configuration Status:

WARNING
Even the observer is showing a valid server name and you are getting Error: ORA-16820: fast-start failover observer is no longer observing this database, and then you stop the observer and start again using following commands.
dgmgrl -logfile $HOME/observer.log sys/abc123 "stop observer" &

dgmgrl -logfile $HOME/observer.log sys/abc123 "start observer" &