The UNKNOWN service status is displayed in grey throughout the Uptime Infrastructure Monitor user interface. A service will enter an UNKNOWN state under any of the following conditions:
The host that the service resides on has gone offline.
The host on which the service resides has entered a scheduled maintenance or downtime period. The service monitor could not be executed by the monitoring station.
Any time the status of the monitor can not be directly verified, the monitor will enter the UNKNOWN state.