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 {

cmd/utils/flags.go

@@ -10,6 +10,8 @@ import (
 	"path/filepath"
 	"runtime"
 
+	"github.com/ethereum/go-ethereum/metrics"
+
 	"github.com/codegangsta/cli"
 	"github.com/ethereum/ethash"
 	"github.com/ethereum/go-ethereum/accounts"
@@ -187,6 +189,10 @@ var (
 		Usage: "Port on which the profiler should listen",
 		Value: 6060,
 	}
+	MetricsEnabledFlag = cli.BoolFlag{
+		Name:  metrics.MetricsEnabledFlag,
+		Usage: "Enables metrics collection and reporting",
+	}
 
 	// RPC settings
 	RPCEnabledFlag = cli.BoolFlag{