Here is a quick way how you can place a VMware ESX/ESXi host into maintenance mode through command line. SSH into the host and run the following commands:
Determine if the host is currently in maintenance mode
ESXi: # vim-cmd /hostsvc/hostsummary | grep inMaintenanceMode
ESX: # vimsh -n -e /hostsvc/hostsummary | grep inMaintenanceMode
Enter maintenance mode
ESXi: # vim-cmd /hostsvc/maintenance_mode_enter
ESX: # vimsh -n -e /hostsvc/maintenance_mode_enter
Exit maintenance mode
ESXi: # vim-cmd /hostsvc/maintenance_mode_exit
ESX: # vimsh -n -e /hostsvc/maintenance_mode_exit