Add system shutdown timestamp

Add a metric for the scheduled shutdown time from systemd.

Signed-off-by: Ben Kochie <superq@gmail.com>

collector/systemd_linux.go

@@ -68,6 +68,7 @@ type systemdCollector struct {
 	unitTasksCurrentDesc          *prometheus.Desc
 	unitTasksMaxDesc              *prometheus.Desc
 	systemRunningDesc             *prometheus.Desc
+	systemShutdownDesc            *prometheus.Desc
 	summaryDesc                   *prometheus.Desc
 	nRestartsDesc                 *prometheus.Desc
 	timerLastTriggerDesc          *prometheus.Desc
@@ -112,6 +113,11 @@ func NewSystemdCollector(logger log.Logger) (Collector, error) {
 		"Whether the system is operational (see 'systemctl is-system-running')",
 		nil, nil,
 	)
+	systemShutdownDesc := prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, subsystem, "system_shutdown_timestamp"),
+		"Time for a scheduled shutdown (see 'systemctl status systemd-shutdownd.service')",
+		nil, nil,
+	)
 	summaryDesc := prometheus.NewDesc(
 		prometheus.BuildFQName(namespace, subsystem, "units"),
 		"Summary of systemd unit states", []string{"state"}, nil)
@@ -161,6 +167,7 @@ func NewSystemdCollector(logger log.Logger) (Collector, error) {
 		unitTasksCurrentDesc:          unitTasksCurrentDesc,
 		unitTasksMaxDesc:              unitTasksMaxDesc,
 		systemRunningDesc:             systemRunningDesc,
+		systemShutdownDesc:            systemShutdownDesc,
 		summaryDesc:                   summaryDesc,
 		nRestartsDesc:                 nRestartsDesc,
 		timerLastTriggerDesc:          timerLastTriggerDesc,
@@ -265,6 +272,10 @@ func (c *systemdCollector) Update(ch chan<- prometheus.Metric) error {
 		level.Debug(c.logger).Log("msg", "collectSystemState took", "duration_seconds", time.Since(begin).Seconds())
 	}
 
+	begin = time.Now()
+	err = c.collectScheduledShutdownMetrics(conn, ch)
+	level.Debug(c.logger).Log("msg", "collectScheduledShutdownMetrics took", "duration_seconds", time.Since(begin).Seconds())
+
 	return err
 }
 
@@ -343,6 +354,23 @@ func (c *systemdCollector) collectSockets(conn *dbus.Conn, ch chan<- prometheus.
 	}
 }
 
+func (c *systemdCollector) collectScheduledShutdownMetrics(conn *dbus.Conn, ch chan<- prometheus.Metric) error {
+	var shutdownTimeUsec uint64
+
+	timestampValue, err := conn.GetServicePropertyContext(context.TODO(), "org.freedesktop.login1", "ScheduledShutdown")
+	if err != nil {
+		level.Debug(c.logger).Log("msg", "couldn't get ScheduledShutdown", "err", err)
+		return errors.New("Couldn't get ScheduledShutdown property")
+	}
+	shutdownTimeUsec = timestampValue.Value.Value().(uint64)
+
+	ch <- prometheus.MustNewConstMetric(
+		c.systemShutdownDesc, prometheus.GaugeValue,
+		float64(shutdownTimeUsec)/1e6,
+	)
+	return nil
+}
+
 func (c *systemdCollector) collectUnitStartTimeMetrics(conn *dbus.Conn, ch chan<- prometheus.Metric, units []unit) {
 	var startTimeUsec uint64