Add time exporter

This simple exporter exposes the systems unix time. It's useful to
compare it to the prometheus server time and other targets to detect
clock skew.

collector/time.go

@@ -0,0 +1,47 @@
+// +build !notime
+
+package collector
+
+import (
+	"time"
+
+	"github.com/golang/glog"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	systemTime = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: Namespace,
+		Name:      "time",
+		Help:      "System time in seconds since epoch (1970).",
+	})
+)
+
+type timeCollector struct {
+	config Config
+}
+
+func init() {
+	Factories["time"] = NewTimeCollector
+}
+
+// Takes a config struct and prometheus registry and returns a new Collector exposing
+// the current system time in seconds since epoch.
+func NewTimeCollector(config Config) (Collector, error) {
+	c := timeCollector{
+		config: config,
+	}
+
+	if _, err := prometheus.RegisterOrGet(systemTime); err != nil {
+		return nil, err
+	}
+	return &c, nil
+}
+
+func (c *timeCollector) Update() (updates int, err error) {
+	updates++
+	now := time.Now()
+	glog.V(1).Infof("Set time: %f", now.Unix())
+	systemTime.Set(float64(now.Unix()))
+	return updates, err
+}

node_exporter.go

@@ -26,7 +26,7 @@ var (
 	configFile        = flag.String("config", "node_exporter.conf", "config file.")
 	memProfile        = flag.String("memprofile", "", "write memory profile to this file")
 	listeningAddress  = flag.String("listen", ":8080", "address to listen on")
-	enabledCollectors = flag.String("enabledCollectors", "attributes,diskstats,filesystem,loadavg,meminfo,stat,netdev", "comma-seperated list of collectors to use")
+	enabledCollectors = flag.String("enabledCollectors", "attributes,diskstats,filesystem,loadavg,meminfo,stat,time,netdev", "comma-seperated list of collectors to use")
 	printCollectors   = flag.Bool("printCollectors", false, "If true, print available collectors and exit")
 	interval          = flag.Duration("interval", 60*time.Second, "refresh interval")