See also: Agent introspection
The juju_start_unit introspection function was introduced in 2.9.
In 2.9 the machine and unit agents were combined into a single process running on juju deployed machines. This tools allows you to see the start a stopped unit agent running inside of that single process. It takes a unit name as input. Example output:
$ juju_start_unit neutron-openvswitch/0
neutron-openvswitch/0: started