@@ -53,6 +53,7 @@ func (v VersionMiddleware) WrapHandler(handler func(ctx context.Context, w http.

 		w.Header().Set("Server", header)

 		w.Header().Set("API-Version", v.defaultVersion)

 		w.Header().Set("OSType", runtime.GOOS)

+		// nolint: golint

 		ctx = context.WithValue(ctx, "api-version", apiVersion)

 		return handler(ctx, w, r, vars)

 	}

@@ -19,7 +19,7 @@ import (

 )

 var (

-	errDockerfileNotStringArray = errors.New("When using JSON array syntax, arrays must be comprised of strings only.")

+	errDockerfileNotStringArray = errors.New("when using JSON array syntax, arrays must be comprised of strings only")

 )

 const (

@@ -453,7 +453,7 @@ func loadDaemonCliConfig(opts *daemonOptions) (*config.Config, error) {

 		c, err := config.MergeDaemonConfigurations(conf, flags, opts.configFile)

 		if err != nil {

 			if flags.Changed("config-file") || !os.IsNotExist(err) {

-				return nil, fmt.Errorf("unable to configure the Docker daemon with file %s: %v\n", opts.configFile, err)

+				return nil, fmt.Errorf("unable to configure the Docker daemon with file %s: %v", opts.configFile, err)

 			}

 		}

 		// the merged configuration can be nil if the config file didn't exist.

@@ -31,11 +31,11 @@ func (daemon *Daemon) ContainerAttach(prefixOrName string, c *backend.ContainerA

 		return err

 	}

 	if container.IsPaused() {

-		err := fmt.Errorf("Container %s is paused, unpause the container before attach.", prefixOrName)

+		err := fmt.Errorf("container %s is paused, unpause the container before attach", prefixOrName)

 		return stateConflictError{err}

 	}

 	if container.IsRestarting() {

-		err := fmt.Errorf("Container %s is restarting, wait until the container is running.", prefixOrName)

+		err := fmt.Errorf("container %s is restarting, wait until the container is running", prefixOrName)

 		return stateConflictError{err}

 	}

@@ -66,7 +66,7 @@ var (

 	// containerd if none is specified

 	DefaultRuntimeBinary = "docker-runc"

-	errSystemNotSupported = errors.New("The Docker daemon is not supported on this platform.")

+	errSystemNotSupported = errors.New("the Docker daemon is not supported on this platform")

 )

 type daemonStore struct {

@@ -557,13 +557,13 @@ func verifyPlatformContainerSettings(daemon *Daemon, hostConfig *containertypes.

 	// check for various conflicting options with user namespaces

 	if daemon.configStore.RemappedRoot != "" && hostConfig.UsernsMode.IsPrivate() {

 		if hostConfig.Privileged {

-			return warnings, fmt.Errorf("Privileged mode is incompatible with user namespaces.  You must run the container in the host namespace when running privileged mode.")

+			return warnings, fmt.Errorf("privileged mode is incompatible with user namespaces.  You must run the container in the host namespace when running privileged mode")

 		}

 		if hostConfig.NetworkMode.IsHost() && !hostConfig.UsernsMode.IsHost() {

-			return warnings, fmt.Errorf("Cannot share the host's network namespace when user namespaces are enabled")

+			return warnings, fmt.Errorf("cannot share the host's network namespace when user namespaces are enabled")

 		}

 		if hostConfig.PidMode.IsHost() && !hostConfig.UsernsMode.IsHost() {

-			return warnings, fmt.Errorf("Cannot share the host PID namespace when user namespaces are enabled")

+			return warnings, fmt.Errorf("cannot share the host PID namespace when user namespaces are enabled")

 		}

 	}

 	if hostConfig.CgroupParent != "" && UsingSystemd(daemon.configStore) {

@@ -1125,7 +1125,7 @@ func setupDaemonRoot(config *config.Config, rootDir string, rootIDs idtools.IDPa

 				break

 			}

 			if !idtools.CanAccess(dirPath, rootIDs) {

-				return fmt.Errorf("A subdirectory in your graphroot path (%s) restricts access to the remapped root uid/gid; please fix by allowing 'o+x' permissions on existing directories.", config.Root)

+				return fmt.Errorf("a subdirectory in your graphroot path (%s) restricts access to the remapped root uid/gid; please fix by allowing 'o+x' permissions on existing directories", config.Root)

 			}

 		}

 	}

@@ -2664,7 +2664,7 @@ func NewDeviceSet(root string, doInit bool, options []string, uidMaps, gidMaps [

 			devices.metaDataLoopbackSize = size

 		case "dm.fs":

 			if val != "ext4" && val != "xfs" {

-				return nil, fmt.Errorf("devmapper: Unsupported filesystem %s\n", val)

+				return nil, fmt.Errorf("devmapper: Unsupported filesystem %s", val)

 			}

 			devices.filesystem = val

 		case "dm.mkfsarg":

@@ -2786,7 +2786,7 @@ func NewDeviceSet(root string, doInit bool, options []string, uidMaps, gidMaps [

 				Level: int(level),

 			})

 		default:

-			return nil, fmt.Errorf("devmapper: Unknown option %s\n", key)

+			return nil, fmt.Errorf("devmapper: Unknown option %s", key)

 		}

 	}

@@ -121,7 +121,7 @@ func copyDir(srcDir, dstDir string, flags copyFlags) error {

 			}

 		default:

-			return fmt.Errorf("Unknown file type for %s\n", srcPath)

+			return fmt.Errorf("unknown file type for %s", srcPath)

 		}

 		// Everything below is copying metadata from src to dst. All this metadata

@@ -101,7 +101,7 @@ func (p *cmdProbe) run(ctx context.Context, d *Daemon, cntr *container.Container

 		return nil, err

 	}

 	if info.ExitCode == nil {

-		return nil, fmt.Errorf("Healthcheck for container %s has no exit code!", cntr.ID)

+		return nil, fmt.Errorf("healthcheck for container %s has no exit code", cntr.ID)

 	}

 	// Note: Go's json package will handle invalid UTF-8 for us

 	out := output.String()

@@ -162,7 +162,7 @@ func TestCreateError(t *testing.T) {

 		client: mockClient,

 	}

 	mockClient.createLogStreamResult <- &createLogStreamResult{

-		errorResult: errors.New("Error!"),

+		errorResult: errors.New("Error"),

 	}

 	err := stream.create()

@@ -243,7 +243,7 @@ func TestPublishBatchError(t *testing.T) {

 		sequenceToken: aws.String(sequenceToken),

 	}

 	mockClient.putLogEventsResult <- &putLogEventsResult{

-		errorResult: errors.New("Error!"),

+		errorResult: errors.New("Error"),

 	}

 	events := []wrappedEvent{

@@ -203,7 +203,7 @@ func New(info logger.Info) (logger.Logger, error) {

 		}

 		gzipCompressionLevel = int(gzipCompressionLevel64)

 		if gzipCompressionLevel < gzip.DefaultCompression || gzipCompressionLevel > gzip.BestCompression {

-			err := fmt.Errorf("Not supported level '%s' for %s (supported values between %d and %d).",

+			err := fmt.Errorf("not supported level '%s' for %s (supported values between %d and %d)",

 				gzipCompressionLevelStr, splunkGzipCompressionLevelKey, gzip.DefaultCompression, gzip.BestCompression)

 			return nil, err

 		}

@@ -36,7 +36,7 @@ func (daemon *Daemon) StateChanged(id string, e libcontainerd.StateInfo) error {

 	case libcontainerd.StateOOM:

 		// StateOOM is Linux specific and should never be hit on Windows

 		if runtime.GOOS == "windows" {

-			return errors.New("Received StateOOM from libcontainerd on Windows. This should never happen.")

+			return errors.New("received StateOOM from libcontainerd on Windows. This should never happen")

 		}

 		daemon.updateHealthMonitor(c)

 		if err := c.CheckpointTo(daemon.containersReplica); err != nil {

@@ -348,6 +348,7 @@ func (daemon *Daemon) createNetwork(create types.NetworkCreateRequest, id string

 	n, err := c.NewNetwork(driver, create.Name, id, nwOptions...)

 	if err != nil {

 		if _, ok := err.(libnetwork.ErrDataStoreNotInitialized); ok {

+			// nolint: golint

 			return nil, errors.New("This node is not a swarm manager. Use \"docker swarm init\" or \"docker swarm join\" to connect this node to swarm and try again.")

 		}

 		return nil, err

@@ -438,7 +438,7 @@ func ensureShared(path string) error {

 	}

 	if !sharedMount {

-		return fmt.Errorf("Path %s is mounted on %s but it is not a shared mount.", path, sourceMount)

+		return fmt.Errorf("path %s is mounted on %s but it is not a shared mount", path, sourceMount)

 	}

 	return nil

 }

@@ -465,7 +465,7 @@ func ensureSharedOrSlave(path string) error {

 	}

 	if !sharedMount && !slaveMount {

-		return fmt.Errorf("Path %s is mounted on %s but it is not a shared or slave mount.", path, sourceMount)

+		return fmt.Errorf("path %s is mounted on %s but it is not a shared or slave mount", path, sourceMount)

 	}

 	return nil

 }

@@ -27,7 +27,7 @@ func (daemon *Daemon) ContainerStart(name string, hostConfig *containertypes.Hos

 		defer container.Unlock()

 		if container.Paused {

-			return stateConflictError{errors.New("Cannot start a paused container, try unpause instead.")}

+			return stateConflictError{errors.New("cannot start a paused container, try unpause instead")}

 		}

 		if container.Running {

@@ -35,7 +35,7 @@ func (daemon *Daemon) ContainerStart(name string, hostConfig *containertypes.Hos

 		}

 		if container.RemovalInProgress || container.Dead {

-			return stateConflictError{errors.New("Container is marked for removal and cannot be started.")}

+			return stateConflictError{errors.New("container is marked for removal and cannot be started")}

 		}

 		return nil

 	}

@@ -110,7 +110,7 @@ func (daemon *Daemon) containerStart(container *container.Container, checkpoint

 	}

 	if container.RemovalInProgress || container.Dead {

-		return stateConflictError{errors.New("Container is marked for removal and cannot be started.")}

+		return stateConflictError{errors.New("container is marked for removal and cannot be started")}

 	}

 	// if we encounter an error during start we need to ensure that any other

@@ -50,7 +50,7 @@ func (daemon *Daemon) update(name string, hostConfig *container.HostConfig) erro

 	}()

 	if container.RemovalInProgress || container.Dead {

-		return errCannotUpdate(container.ID, fmt.Errorf("Container is marked for removal and cannot be \"update\"."))

+		return errCannotUpdate(container.ID, fmt.Errorf("container is marked for removal and cannot be \"update\""))

 	}

 	container.Lock()

@@ -908,7 +908,7 @@ func fixManifestLayers(m *schema1.Manifest) error {

 			m.FSLayers = append(m.FSLayers[:i], m.FSLayers[i+1:]...)

 			m.History = append(m.History[:i], m.History[i+1:]...)

 		} else if imgs[i].Parent != imgs[i+1].ID {

-			return fmt.Errorf("Invalid parent ID. Expected %v, got %v.", imgs[i+1].ID, imgs[i].Parent)

+			return fmt.Errorf("invalid parent ID. Expected %v, got %v", imgs[i+1].ID, imgs[i].Parent)

 		}

 	}

@@ -10,6 +10,7 @@ import (

 	"github.com/docker/distribution/manifest/schema1"

 	"github.com/docker/distribution/reference"

+	"github.com/docker/docker/pkg/testutil"

 	"github.com/opencontainers/go-digest"

 )

@@ -102,9 +103,8 @@ func TestFixManifestLayersBadParent(t *testing.T) {

 		},

 	}

-	if err := fixManifestLayers(&duplicateLayerManifest); err == nil || !strings.Contains(err.Error(), "Invalid parent ID.") {

-		t.Fatalf("expected an invalid parent ID error from fixManifestLayers")

-	}

+	err := fixManifestLayers(&duplicateLayerManifest)

+	testutil.ErrorContains(t, err, "invalid parent ID")

 }

 // TestValidateManifest verifies the validateManifest function

@@ -2,7 +2,12 @@

   "Vendor": true,

   "Deadline": "2m",

   "Sort": ["linter", "severity", "path"],

-  "Exclude": [".*\\.pb\\.go"],

+  "Exclude": [

+    ".*\\.pb\\.go",

+    "dockerversion/version_autogen.go",

+    "api/types/container/container_.*",

+    "integration-cli/"

+  ],

   "Enable": [

     "gofmt",

@@ -103,7 +103,7 @@ func (s *DockerSuite) TestStartPausedContainer(c *check.C) {

 	// an error should have been shown that you cannot start paused container

 	c.Assert(err, checker.NotNil, check.Commentf("out: %s", out))

 	// an error should have been shown that you cannot start paused container

-	c.Assert(out, checker.Contains, "Cannot start a paused container, try unpause instead.")

+	c.Assert(out, checker.Contains, "cannot start a paused container, try unpause instead")

 }

 func (s *DockerSuite) TestStartMultipleContainers(c *check.C) {

@@ -595,7 +595,7 @@ func createTarFile(path, extractDir string, hdr *tar.Header, reader io.Reader, L

 		return nil

 	default:

-		return fmt.Errorf("Unhandled tar header type %d\n", hdr.Typeflag)

+		return fmt.Errorf("unhandled tar header type %d", hdr.Typeflag)

 	}

 	// Lchown is not supported on Windows.

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

 	"testing"

 	"time"

+	"github.com/stretchr/testify/assert"

 	"golang.org/x/net/context"

 )

@@ -14,7 +15,7 @@ import (

 type errorReader struct{}

 func (r *errorReader) Read(p []byte) (int, error) {

-	return 0, fmt.Errorf("Error reader always fail.")

+	return 0, fmt.Errorf("error reader always fail")

 }

 func TestReadCloserWrapperClose(t *testing.T) {

@@ -35,9 +36,7 @@ func TestReaderErrWrapperReadOnError(t *testing.T) {

 		called = true

 	})

 	_, err := wrapper.Read([]byte{})

-	if err == nil || !strings.Contains(err.Error(), "Error reader always fail.") {

-		t.Fatalf("readErrWrapper should returned an error")

-	}

+	assert.EqualError(t, err, "error reader always fail")

 	if !called {

 		t.Fatalf("readErrWrapper should have call the anonymous function on failure")

 	}

@@ -8,11 +8,10 @@ import (

 	"strings"

 	"time"

-	"github.com/Nvveen/Gotty"

-

+	gotty "github.com/Nvveen/Gotty"

 	"github.com/docker/docker/pkg/jsonlog"

 	"github.com/docker/docker/pkg/term"

-	"github.com/docker/go-units"

+	units "github.com/docker/go-units"

 )

 // JSONError wraps a concrete Code and Message, `Code` is

@@ -187,7 +186,7 @@ func cursorDown(out io.Writer, ti termInfo, l int) {

 func (jm *JSONMessage) Display(out io.Writer, termInfo termInfo) error {

 	if jm.Error != nil {

 		if jm.Error.Code == 401 {

-			return fmt.Errorf("Authentication is required.")

+			return fmt.Errorf("authentication is required")

 		}

 		return jm.Error

 	}

@@ -10,6 +10,7 @@ import (

 	"github.com/docker/docker/pkg/jsonlog"

 	"github.com/docker/docker/pkg/term"

+	"github.com/stretchr/testify/assert"

 )

 func TestError(t *testing.T) {

@@ -198,9 +199,7 @@ func TestJSONMessageDisplayWithJSONError(t *testing.T) {

 	jsonMessage = JSONMessage{Error: &JSONError{401, "Anything"}}

 	err = jsonMessage.Display(data, &noTermInfo{})

-	if err == nil || err.Error() != "Authentication is required." {

-		t.Fatalf("Expected an error \"Authentication is required.\", got %q", err)

-	}

+	assert.EqualError(t, err, "authentication is required")

 }

 func TestDisplayJSONMessagesStreamInvalidJSON(t *testing.T) {

@@ -61,7 +61,7 @@ func (r *Result) Assert(t testingT, exp Expected) *Result {

 	}

 	_, file, line, ok := runtime.Caller(1)

 	if ok {

-		t.Fatalf("at %s:%d - %s", filepath.Base(file), line, err.Error())

+		t.Fatalf("at %s:%d - %s\n", filepath.Base(file), line, err.Error())

 	} else {

 		t.Fatalf("(no file/line info) - %s", err.Error())

 	}

@@ -108,7 +108,7 @@ func (r *Result) Compare(exp Expected) error {

 	if len(errors) == 0 {

 		return nil

 	}

-	return fmt.Errorf("%s\nFailures:\n%s\n", r, strings.Join(errors, "\n"))

+	return fmt.Errorf("%s\nFailures:\n%s", r, strings.Join(errors, "\n"))

 }

 func matchOutput(expected string, actual string) bool {

@@ -29,7 +29,7 @@ func loginV1(authConfig *types.AuthConfig, apiEndpoint APIEndpoint, userAgent st

 	logrus.Debugf("attempting v1 login to registry endpoint %s", serverAddress)

 	if serverAddress == "" {

-		return "", "", systemError{errors.New("Server Error: Server Address not set.")}

+		return "", "", systemError{errors.New("server Error: Server Address not set")}

 	}

 	req, err := http.NewRequest("GET", serverAddress+"users/", nil)

@@ -354,7 +354,7 @@ func ValidateIndexName(val string) (string, error) {

 		val = "docker.io"

 	}

 	if strings.HasPrefix(val, "-") || strings.HasSuffix(val, "-") {

-		return "", fmt.Errorf("Invalid index name (%s). Cannot begin or end with a hyphen.", val)

+		return "", fmt.Errorf("invalid index name (%s). Cannot begin or end with a hyphen", val)

 	}

 	return val, nil

 }

@@ -81,7 +81,7 @@ func ReadCertsDirectory(tlsConfig *tls.Config, directory string) error {

 			keyName := certName[:len(certName)-5] + ".key"

 			logrus.Debugf("cert: %s", filepath.Join(directory, f.Name()))

 			if !hasFile(fs, keyName) {

-				return fmt.Errorf("Missing key %s for client certificate %s. Note that CA certificates should use the extension .crt.", keyName, certName)

+				return fmt.Errorf("missing key %s for client certificate %s. Note that CA certificates should use the extension .crt", keyName, certName)

 			}

 			cert, err := tls.LoadX509KeyPair(filepath.Join(directory, certName), filepath.Join(directory, keyName))

 			if err != nil {

@@ -434,7 +434,7 @@ func (r *Session) GetRepositoryData(name reference.Named) (*RepositoryData, erro

 		// "Get https://index.docker.io/v1/repositories/library/busybox/images: i/o timeout"

 		// was a top search on the docker user forum

 		if isTimeout(err) {

-			return nil, fmt.Errorf("Network timed out while trying to connect to %s. You may want to check your internet connection or if you are behind a proxy.", repositoryTarget)

+			return nil, fmt.Errorf("network timed out while trying to connect to %s. You may want to check your internet connection or if you are behind a proxy", repositoryTarget)

 		}

 		return nil, fmt.Errorf("Error while pulling image: %v", err)

 	}