make sure the minikube is not running

cmd/minikube/cmd/start.go

@@ -29,7 +29,10 @@ import (
 	"time"
 
 	"github.com/blang/semver"
+	"github.com/docker/machine/libmachine"
+	"github.com/docker/machine/libmachine/drivers"
 	"github.com/docker/machine/libmachine/host"
+	"github.com/docker/machine/libmachine/state"
 	"github.com/golang/glog"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -111,6 +114,7 @@ func runStart(cmd *cobra.Command, args []string) {
 	}
 
 	api, err := machine.NewAPIClient()
+	ensureNotRunning(api, constants.DefaultMachineName)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error getting client: %v\n", err)
 		os.Exit(1)
@@ -463,3 +467,17 @@ func saveConfigToFile(data []byte, file string) error {
 	}
 	return nil
 }
+
+func ensureNotRunning(client libmachine.API, machineName string) {
+
+	hostVm, err := client.Load(machineName)
+
+	if err != nil {
+		fmt.Fprintln(os.Stderr, fmt.Sprintf(err.Error()))
+		os.Exit(1)
+	}
+	if drivers.MachineInState(hostVm.Driver, state.Running)() && hostVm.DriverName != "generic" {
+		fmt.Fprintln(os.Stdout, fmt.Sprintf("The '%s' VM is already running.", machineName))
+		os.Exit(0)
+	}
+}