Fixing Unknown Health Status in ESXi

The scenario:

When an ESXi host is originally installed, the health status shows green and all is well.  After a while, health status’ begin reporting unknown.

Here are a few fixes I’ve used to address this in a variety of scenarios.

1. In vSphere client, Configuration > Security Profile > Services > Restart CIM Server service. It’s not uncommon to have to try this 2 times or force stop rather than restart.  Then it will be necessary to click Reset Sensors on the hardware tab.  For me, this works 90% of the time.
2. If 1 doesn’t work, the next thing I try is SSH to the host and run services.sh restart. This don’t interfere with the running on of the VMs. Then it will be necessary to click Reset Sensors on the hardware tab.
3. If neither of the two resolve the issue, it’s usually necessary to schedule a reboot of the host.