I recently faced this issue , My standalone host which was hosting some critical application , had an issue with Hardware Status ,
when i checked the status of the server Health , all the parameters were Unknown same as below
I did a refresh and reset sensors , But still the status were Unknown , I checked the CIM status and Port 5988 status
later i logged into the esxi shell , and executed /etc/init.d/sfcbd-watchdog restart , which restarted the Watchog service and refreshed the status of health tab, Now the service were up and running and the status was normal
