You place a host in maintenance mode to service it, for example, to install more memory. A host enters or leaves maintenance mode only as the result of a user request.
vicfg-hostops suspends virtual machines by default, or powers off the virtual machine if you run vicfg-hostops --action poweroff.
The host is in a state of Entering Maintenance Mode until all running virtual machines are suspended or migrated. When a host is entering maintenance mode, you cannot power on virtual machines on it or migrate virtual machines to it.
When you run the vicfg-hostops vCLI command, you can specify one of the options listed in Connection Options for vCLI Host Management Commands in place of <conn_options>.
After all virtual machines on the host have been suspended or migrated, the host enters maintenance mode. You cannot deploy or power on a virtual machine on hosts in maintenance mode.
You can put all hosts in a cluster or data center in maintenance mode by using the --cluster or --datacenter option. You must not use those options unless suspending all virtual machines in that cluster or data center is no problem.
You can later run vicfg-hostops <conn_options> --operation exit to exit maintenance mode.