Automatically shut down the machine after a period of inactivity.
The last-modified time of a file (default: /run/last_heartbeat) is
used to indicate when the machine was last active. The file is checked
at a fixed interval (default: one minute). There is a grace period
(default: five minutes) before the machine is powered off, by which
time a new heartbeat may have arrived.
The check-interval and grace-duration arguments accept numbers
with a unit: h, m, or s. For example, 5m indicates five
minutes.
The default shutdown command is poweroff.