@@ -229,6 +229,10 @@ func checkMounted(t *testing.T, p string, expect bool) {

 }

 func TestRootMountCleanup(t *testing.T) {

+	if os.Getuid() != 0 {

+		t.Skip("root required")

+	}

+

 	t.Parallel()

 	testRoot, err := ioutil.TempDir("", t.Name())

@@ -153,6 +153,10 @@ func TestValidContainerNames(t *testing.T) {

 }

 func TestContainerInitDNS(t *testing.T) {

+	if os.Getuid() != 0 {

+		t.Skip("root required") // for chown

+	}

+

 	tmp, err := ioutil.TempDir("", "docker-container-test-")

 	if err != nil {

 		t.Fatal(err)

@@ -1,6 +1,7 @@

 package daemon // import "github.com/docker/docker/daemon"

 import (

+	"os"

 	"reflect"

 	"sort"

 	"testing"

@@ -499,6 +500,9 @@ func TestDaemonDiscoveryReloadOnlyClusterAdvertise(t *testing.T) {

 }

 func TestDaemonReloadNetworkDiagnosticPort(t *testing.T) {

+	if os.Getuid() != 0 {

+		t.Skip("root required")

+	}

 	daemon := &Daemon{

 		imageService: images.NewImageService(images.ImageServiceConfig{}),

 	}

@@ -3,6 +3,7 @@

 package daemon // import "github.com/docker/docker/daemon"

 import (

+	"bytes"

 	"context"

 	"fmt"

 	"os/exec"

@@ -11,6 +12,8 @@ import (

 	"strings"

 	"github.com/docker/docker/api/types/container"

+	"github.com/docker/docker/errdefs"

+	"github.com/pkg/errors"

 )

 func validatePSArgs(psArgs string) error {

@@ -70,6 +73,7 @@ func parsePSOutput(output []byte, procs []uint32) (*container.ContainerTopOKBody

 	for i, name := range procList.Titles {

 		if name == "PID" {

 			pidIndex = i

+			break

 		}

 	}

 	if pidIndex == -1 {

@@ -112,6 +116,20 @@ func parsePSOutput(output []byte, procs []uint32) (*container.ContainerTopOKBody

 	return procList, nil

 }

+// psPidsArg converts a slice of PIDs to a string consisting

+// of comma-separated list of PIDs prepended by "-q".

+// For example, psPidsArg([]uint32{1,2,3}) returns "-q1,2,3".

+func psPidsArg(pids []uint32) string {

+	b := []byte{'-', 'q'}

+	for i, p := range pids {

+		b = strconv.AppendUint(b, uint64(p), 10)

+		if i < len(pids)-1 {

+			b = append(b, ',')

+		}

+	}

+	return string(b)

+}

+

 // ContainerTop lists the processes running inside of the given

 // container by calling ps with the given args, or with the flags

 // "-ef" if no args are given.  An error is returned if the container

@@ -144,9 +162,23 @@ func (daemon *Daemon) ContainerTop(name string, psArgs string) (*container.Conta

 		return nil, err

 	}

-	output, err := exec.Command("ps", strings.Split(psArgs, " ")...).Output()

+	args := strings.Split(psArgs, " ")

+	pids := psPidsArg(procs)

+	output, err := exec.Command("ps", append(args, pids)...).Output()

 	if err != nil {

-		return nil, fmt.Errorf("Error running ps: %v", err)

+		// some ps options (such as f) can't be used together with q,

+		// so retry without it

+		output, err = exec.Command("ps", args...).Output()

+		if err != nil {

+			if ee, ok := err.(*exec.ExitError); ok {

+				// first line of stderr shows why ps failed

+				line := bytes.SplitN(ee.Stderr, []byte{'\n'}, 2)

+				if len(line) > 0 && len(line[0]) > 0 {

+					err = errors.New(string(line[0]))

+				}

+			}

+			return nil, errdefs.System(errors.Wrap(err, "ps"))

+		}

 	}

 	procList, err := parsePSOutput(output, procs)

 	if err != nil {