• A virtual machine cannot be powered on and shows as unknown in VirtualCenter.
• A virtual machine shows as unknown when connected directly to an ESX host via VMware Infrastructure (VI) Client.
• The virtual machine World ID is still running.

1. Log in as root to the ESX host with an SSH client.
2. Change the directory to:
   
   cd /var/lib/vmware/hostd/stats
   
   
3. There are four files in this directory. To confirm, perform a directory listing with the command:
   
   ls
   
   
4. Remove these files with the command:
   
   rm *
   
   
5. Restart the Management agents. For more information, see Restarting the Management agents on an ESX Server (1003490).

If the preceding steps do not resolve the issue, see:

• Virtual machines appear as unknown in inventory on host and invalid in vCenter Server (1031605)
• Inaccessible virtual machines are named as Unknown VM (2172)