ESX host Maintenance mode from ESX CLI

1) login to ESX host to execute below.

To enter Maintenance Mode, at the ESX console:

vimsh -n -e /hostsvc/maintenance_mode_enter

To exit Maintenance Mode :

vimsh -n -e /hostsvc/maintenance_mode_exit

To display whether the ESX Server is currently in maintenance mode or not type:

vimsh -n -e"hostsvc/hostsummary" | grep inMaintenanceMode

Using system libcrypto, version 90810F

inMaintenanceMode = false, 

(False - means "not in maintenance mode" / True - Means "in maintenance mode")