emqx4.3/rel/config/examples/sys_topics.conf.example

## System Topic
## Publishing client lifecycle events to "$SYS" topics

sys_topics {
    ## Time interval of publishing `$SYS` messages
    sys_msg_interval = 1m

    ## Time interval for publishing following heartbeat messages:
    ##   - `$SYS/brokers/<node>/uptime`
    ##   - `$SYS/brokers/<node>/datetime`
    sys_heartbeat_interval = 30s

    ## Client events messages toggle
    sys_event_messages = {
        client_connected = true
        client_disconnected = true
        client_subscribed = false
        client_unsubscribed = false
    }
}