@@ -154,14 +154,20 @@ func parseClusterAdvertiseSettings(clusterStore, clusterAdvertise string) (strin

 }

 // ReloadConfiguration reads the configuration in the host and reloads the daemon and server.

-func ReloadConfiguration(configFile string, flags *flag.FlagSet, reload func(*Config)) {

+func ReloadConfiguration(configFile string, flags *flag.FlagSet, reload func(*Config)) error {

 	logrus.Infof("Got signal to reload configuration, reloading from: %s", configFile)

 	newConfig, err := getConflictFreeConfiguration(configFile, flags)

 	if err != nil {

-		logrus.Error(err)

-	} else {

-		reload(newConfig)

+		return err

 	}

+	reload(newConfig)

+	return nil

+}

+

+// boolValue is an interface that boolean value flags implement

+// to tell the command line how to make -name equivalent to -name=true.

+type boolValue interface {

+	IsBoolFlag() bool

 }

 // MergeDaemonConfigurations reads a configuration file,

@@ -206,6 +212,36 @@ func getConflictFreeConfiguration(configFile string, flags *flag.FlagSet) (*Conf

 			return nil, err

 		}

+		// Override flag values to make sure the values set in the config file with nullable values, like `false`,

+		// are not overriden by default truthy values from the flags that were not explicitly set.

+		// See https://github.com/docker/docker/issues/20289 for an example.

+		//

+		// TODO: Rewrite configuration logic to avoid same issue with other nullable values, like numbers.

+		namedOptions := make(map[string]interface{})

+		for key, value := range configSet {

+			f := flags.Lookup("-" + key)

+			if f == nil { // ignore named flags that don't match

+				namedOptions[key] = value

+				continue

+			}

+

+			if _, ok := f.Value.(boolValue); ok {

+				f.Value.Set(fmt.Sprintf("%v", value))

+			}

+		}

+		if len(namedOptions) > 0 {

+			// set also default for mergeVal flags that are boolValue at the same time.

+			flags.VisitAll(func(f *flag.Flag) {

+				if opt, named := f.Value.(opts.NamedOption); named {

+					v, set := namedOptions[opt.Name()]

+					_, boolean := f.Value.(boolValue)

+					if set && boolean {

+						f.Value.Set(fmt.Sprintf("%v", v))

+					}

+				}

+			})

+		}

+

 		config.valuesSet = configSet

 	}

@@ -245,14 +281,16 @@ func findConfigurationConflicts(config map[string]interface{}, flags *flag.FlagS

 	// 2. Discard values that implement NamedOption.

 	// Their configuration name differs from their flag name, like `labels` and `label`.

-	unknownNamedConflicts := func(f *flag.Flag) {

-		if namedOption, ok := f.Value.(opts.NamedOption); ok {

-			if _, valid := unknownKeys[namedOption.Name()]; valid {

-				delete(unknownKeys, namedOption.Name())

+	if len(unknownKeys) > 0 {

+		unknownNamedConflicts := func(f *flag.Flag) {

+			if namedOption, ok := f.Value.(opts.NamedOption); ok {

+				if _, valid := unknownKeys[namedOption.Name()]; valid {

+					delete(unknownKeys, namedOption.Name())

+				}

 			}

 		}

+		flags.VisitAll(unknownNamedConflicts)

 	}

-	flags.VisitAll(unknownNamedConflicts)

 	if len(unknownKeys) > 0 {

 		var unknown []string

@@ -291,3 +291,80 @@ func TestLoadDaemonConfigWithMapOptions(t *testing.T) {

 		t.Fatalf("expected log tag `test`, got %s", tag)

 	}

 }

+

+func TestLoadDaemonConfigWithTrueDefaultValues(t *testing.T) {

+	c := &daemon.Config{}

+	common := &cli.CommonFlags{}

+	flags := mflag.NewFlagSet("test", mflag.ContinueOnError)

+	flags.BoolVar(&c.EnableUserlandProxy, []string{"-userland-proxy"}, true, "")

+

+	f, err := ioutil.TempFile("", "docker-config-")

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if err := flags.ParseFlags([]string{}, false); err != nil {

+		t.Fatal(err)

+	}

+

+	configFile := f.Name()

+	f.Write([]byte(`{

+		"userland-proxy": false

+}`))

+	f.Close()

+

+	loadedConfig, err := loadDaemonCliConfig(c, flags, common, configFile)

+	if err != nil {

+		t.Fatal(err)

+	}

+	if loadedConfig == nil {

+		t.Fatal("expected configuration, got nil")

+	}

+

+	if loadedConfig.EnableUserlandProxy {

+		t.Fatal("expected userland proxy to be disabled, got enabled")

+	}

+

+	// make sure reloading doesn't generate configuration

+	// conflicts after normalizing boolean values.

+	err = daemon.ReloadConfiguration(configFile, flags, func(reloadedConfig *daemon.Config) {

+		if reloadedConfig.EnableUserlandProxy {

+			t.Fatal("expected userland proxy to be disabled, got enabled")

+		}

+	})

+	if err != nil {

+		t.Fatal(err)

+	}

+}

+

+func TestLoadDaemonConfigWithTrueDefaultValuesLeaveDefaults(t *testing.T) {

+	c := &daemon.Config{}

+	common := &cli.CommonFlags{}

+	flags := mflag.NewFlagSet("test", mflag.ContinueOnError)

+	flags.BoolVar(&c.EnableUserlandProxy, []string{"-userland-proxy"}, true, "")

+

+	f, err := ioutil.TempFile("", "docker-config-")

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if err := flags.ParseFlags([]string{}, false); err != nil {

+		t.Fatal(err)

+	}

+

+	configFile := f.Name()

+	f.Write([]byte(`{}`))

+	f.Close()

+

+	loadedConfig, err := loadDaemonCliConfig(c, flags, common, configFile)

+	if err != nil {

+		t.Fatal(err)

+	}

+	if loadedConfig == nil {

+		t.Fatal("expected configuration, got nil")

+	}

+

+	if !loadedConfig.EnableUserlandProxy {

+		t.Fatal("expected userland proxy to be enabled, got disabled")

+	}

+}

@@ -8,6 +8,7 @@ import (

 	"os/signal"

 	"syscall"

+	"github.com/Sirupsen/logrus"

 	apiserver "github.com/docker/docker/api/server"

 	"github.com/docker/docker/daemon"

 	"github.com/docker/docker/pkg/mflag"

@@ -58,7 +59,9 @@ func setupConfigReloadTrap(configFile string, flags *mflag.FlagSet, reload func(

 	signal.Notify(c, syscall.SIGHUP)

 	go func() {

 		for range c {

-			daemon.ReloadConfiguration(configFile, flags, reload)

+			if err := daemon.ReloadConfiguration(configFile, flags, reload); err != nil {

+				logrus.Error(err)

+			}

 		}

 	}()

 }

@@ -50,7 +50,9 @@ func setupConfigReloadTrap(configFile string, flags *mflag.FlagSet, reload func(

 			logrus.Debugf("Config reload - waiting signal at %s", ev)

 			for {

 				syscall.WaitForSingleObject(h, syscall.INFINITE)

-				daemon.ReloadConfiguration(configFile, flags, reload)

+				if err := daemon.ReloadConfiguration(configFile, flags, reload); err != nil {

+					logrus.Error(err)

+				}

 			}

 		}

 	}()