@@ -480,22 +480,12 @@ func loadDaemonCliConfig(opts *daemonOptions) (*config.Config, error) {

 		logrus.Warnf(`The "-g / --graph" flag is deprecated. Please use "--data-root" instead`)

 	}

-	// Labels of the docker engine used to allow multiple values associated with the same key.

-	// This is deprecated in 1.13, and, be removed after 3 release cycles.

-	// The following will check the conflict of labels, and report a warning for deprecation.

-	//

-	// TODO: After 3 release cycles (17.12) an error will be returned, and labels will be

-	// sanitized to consolidate duplicate key-value pairs (config.Labels = newLabels):

-	//

-	// newLabels, err := daemon.GetConflictFreeLabels(config.Labels)

-	// if err != nil {

-	//	return nil, err

-	// }

-	// config.Labels = newLabels

-	//

-	if _, err := config.GetConflictFreeLabels(conf.Labels); err != nil {

-		logrus.Warnf("Engine labels with duplicate keys and conflicting values have been deprecated: %s", err)

+	// Check if duplicate label-keys with different values are found

+	newLabels, err := config.GetConflictFreeLabels(conf.Labels)

+	if err != nil {

+		return nil, err

 	}

+	conf.Labels = newLabels

 	// Regardless of whether the user sets it to true or false, if they

 	// specify TLSVerify at all then we need to turn on TLS

@@ -61,6 +61,28 @@ func TestLoadDaemonCliConfigWithConflicts(t *testing.T) {

 	testutil.ErrorContains(t, err, "as a flag and in the configuration file: labels")

 }

+func TestLoadDaemonCliWithConflictingLabels(t *testing.T) {

+	opts := defaultOptions("")

+	flags := opts.flags

+

+	assert.NoError(t, flags.Set("label", "foo=bar"))

+	assert.NoError(t, flags.Set("label", "foo=baz"))

+

+	_, err := loadDaemonCliConfig(opts)

+	assert.EqualError(t, err, "conflict labels for foo=baz and foo=bar")

+}

+

+func TestLoadDaemonCliWithDuplicateLabels(t *testing.T) {

+	opts := defaultOptions("")

+	flags := opts.flags

+

+	assert.NoError(t, flags.Set("label", "foo=the-same"))

+	assert.NoError(t, flags.Set("label", "foo=the-same"))

+

+	_, err := loadDaemonCliConfig(opts)

+	assert.NoError(t, err)

+}

+

 func TestLoadDaemonCliConfigWithTLSVerify(t *testing.T) {

 	tempFile := fs.NewFile(t, "config", fs.WithContent(`{"tlsverify": true}`))

 	defer tempFile.Remove()

@@ -258,22 +258,12 @@ func Reload(configFile string, flags *pflag.FlagSet, reload func(*Config)) error

 		return fmt.Errorf("file configuration validation failed (%v)", err)

 	}

-	// Labels of the docker engine used to allow multiple values associated with the same key.

-	// This is deprecated in 1.13, and, be removed after 3 release cycles.

-	// The following will check the conflict of labels, and report a warning for deprecation.

-	//

-	// TODO: After 3 release cycles (17.12) an error will be returned, and labels will be

-	// sanitized to consolidate duplicate key-value pairs (config.Labels = newLabels):

-	//

-	// newLabels, err := GetConflictFreeLabels(newConfig.Labels)

-	// if err != nil {

-	//      return err

-	// }

-	// newConfig.Labels = newLabels

-	//

-	if _, err := GetConflictFreeLabels(newConfig.Labels); err != nil {

-		logrus.Warnf("Engine labels with duplicate keys and conflicting values have been deprecated: %s", err)

+	// Check if duplicate label-keys with different values are found

+	newLabels, err := GetConflictFreeLabels(newConfig.Labels)

+	if err != nil {

+		return err

 	}

+	newConfig.Labels = newLabels

 	reload(newConfig)

 	return nil

@@ -9,6 +9,7 @@ import (

 	"github.com/docker/docker/daemon/discovery"

 	"github.com/docker/docker/internal/testutil"

 	"github.com/docker/docker/opts"

+	"github.com/gotestyourself/gotestyourself/fs"

 	"github.com/spf13/pflag"

 	"github.com/stretchr/testify/assert"

 )

@@ -459,3 +460,29 @@ func TestReloadBadDefaultConfig(t *testing.T) {

 	assert.Error(t, err)

 	testutil.ErrorContains(t, err, "unable to configure the Docker daemon with file")

 }

+

+func TestReloadWithConflictingLabels(t *testing.T) {

+	tempFile := fs.NewFile(t, "config", fs.WithContent(`{"labels":["foo=bar","foo=baz"]}`))

+	defer tempFile.Remove()

+	configFile := tempFile.Path()

+

+	var lbls []string

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

+	flags.String("config-file", configFile, "")

+	flags.StringSlice("labels", lbls, "")

+	err := Reload(configFile, flags, func(c *Config) {})

+	testutil.ErrorContains(t, err, "conflict labels for foo=baz and foo=bar")

+}

+

+func TestReloadWithDuplicateLabels(t *testing.T) {

+	tempFile := fs.NewFile(t, "config", fs.WithContent(`{"labels":["foo=the-same","foo=the-same"]}`))

+	defer tempFile.Remove()

+	configFile := tempFile.Path()

+

+	var lbls []string

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

+	flags.String("config-file", configFile, "")

+	flags.StringSlice("labels", lbls, "")

+	err := Reload(configFile, flags, func(c *Config) {})

+	assert.NoError(t, err)

+}

@@ -233,17 +233,6 @@ func (s *DockerDaemonSuite) TestRegistryMirrors(c *check.C) {

 	c.Assert(out, checker.Contains, fmt.Sprintf(" %s", registryMirror2))

 }

-// Test case for #24392

-func (s *DockerDaemonSuite) TestInfoLabels(c *check.C) {

-	testRequires(c, SameHostDaemon, DaemonIsLinux)

-

-	s.d.Start(c, "--label", `test.empty=`, "--label", `test.empty=`, "--label", `test.label="1"`, "--label", `test.label="2"`)

-

-	out, err := s.d.Cmd("info")

-	c.Assert(err, checker.IsNil)

-	c.Assert(out, checker.Contains, "WARNING: labels with duplicate keys and conflicting values have been deprecated")

-}

-

 func existingContainerStates(c *check.C) map[string]int {

 	out, _ := dockerCmd(c, "info", "--format", "{{json .}}")

 	var m map[string]interface{}