This is appearing frequently in /var/log/messages:
Aug 25 12:46:18 bamboo node_exporter: time="2016-08-25T12:46:18Z" level=error msg="ERROR: systemd collector failed after 0.009243s: couldn't get system state: Unknown property" source="node_exporter.go:91"
Not sure if I should care and/or how to silence it.