cmd, core, eth, metrics, p2p: require enabling metrics

cmd/geth/main.go

@@ -272,6 +272,7 @@ JavaScript API. See https://github.com/ethereum/go-ethereum/wiki/Javascipt-Conso
 		utils.LogJSONFlag,
 		utils.PProfEanbledFlag,
 		utils.PProfPortFlag,
+		utils.MetricsEnabledFlag,
 		utils.SolcPathFlag,
 		utils.GpoMinGasPriceFlag,
 		utils.GpoMaxGasPriceFlag,

cmd/geth/monitorcmd.go

@@ -75,7 +75,12 @@ func monitor(ctx *cli.Context) {
 	if len(monitored) == 0 {
 		list := expandMetrics(metrics, "")
 		sort.Strings(list)
-		utils.Fatalf("No metrics specified.\n\nAvailable:\n - %s", strings.Join(list, "\n - "))
+
+		if len(list) > 0 {
+			utils.Fatalf("No metrics specified.\n\nAvailable:\n - %s", strings.Join(list, "\n - "))
+		} else {
+			utils.Fatalf("No metrics specified.\n\nNo metrics collected (--metrics)\n")
+		}
 	}
 	sort.Strings(monitored)
 	if cols := len(monitored) / ctx.Int(monitorCommandRowsFlag.Name); cols > 6 {