mosquitto/service/systemd

Select appropriate systemd service based on your compile settings. If you
enabled WITH_SYSTEMD, use mosquitto.service.notify, otherwise use
mosquitto.service.simple. The service must be renamed to mosquitto.service
before usage.

With WITH_SYSTEMD mosquitto will notify a complete startup after
initialization. This means that follow-up units can be started after full
initialization of mosquitto (i.e. sockets are opened).