@@ -375,7 +375,7 @@ func (daemon *Daemon) CopyOnBuild(cID, destPath, srcRoot, srcPath string, decomp

 	destExists := true

 	destDir := false

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	// Work in daemon-local OS specific file paths

 	destPath = filepath.FromSlash(destPath)

@@ -109,7 +109,7 @@ func (daemon *Daemon) setupIpcDirs(c *container.Container) error {

 		}

 		c.ShmPath = "/dev/shm"

 	} else {

-		rootIDs, _ := daemon.idMappings.RootPair()

+		rootIDs := daemon.idMappings.RootPair()

 		if !c.HasMountFor("/dev/shm") {

 			shmPath, err := c.ShmResourcePath()

 			if err != nil {

@@ -147,7 +147,7 @@ func (daemon *Daemon) setupSecretDir(c *container.Container) (setupErr error) {

 	logrus.Debugf("secrets: setting up secret dir: %s", localMountPath)

 	// retrieve possible remapped range start for root UID, GID

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	// create tmpfs

 	if err := idtools.MkdirAllAndChown(localMountPath, 0700, rootIDs); err != nil {

 		return errors.Wrap(err, "error creating secret local mount path")

@@ -232,7 +232,7 @@ func (daemon *Daemon) setupConfigDir(c *container.Container) (setupErr error) {

 	logrus.Debugf("configs: setting up config dir: %s", localPath)

 	// retrieve possible remapped range start for root UID, GID

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	// create tmpfs

 	if err := idtools.MkdirAllAndChown(localPath, 0700, rootIDs); err != nil {

 		return errors.Wrap(err, "error creating config dir")

@@ -117,10 +117,7 @@ func (daemon *Daemon) create(params types.ContainerCreateConfig, managed bool) (

 		return nil, err

 	}

-	rootIDs, err := daemon.idMappings.RootPair()

-	if err != nil {

-		return nil, err

-	}

+	rootIDs := daemon.idMappings.RootPair()

 	if err := idtools.MkdirAndChown(container.Root, 0700, rootIDs); err != nil {

 		return nil, err

 	}

@@ -22,7 +22,7 @@ func (daemon *Daemon) createContainerPlatformSpecificSettings(container *contain

 	}

 	defer daemon.Unmount(container)

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	if err := container.SetupWorkingDirectory(rootIDs); err != nil {

 		return err

 	}

@@ -527,11 +527,7 @@ func NewDaemon(config *config.Config, registryService registry.Service, containe

 	if err != nil {

 		return nil, err

 	}

-	rootIDs, err := idMappings.RootPair()

-	if err != nil {

-		return nil, err

-	}

-

+	rootIDs := idMappings.RootPair()

 	if err := setupDaemonProcess(config); err != nil {

 		return nil, err

 	}

@@ -994,7 +990,7 @@ func prepareTempDir(rootDir string, rootIDs idtools.IDPair) (string, error) {

 }

 func (daemon *Daemon) setupInitLayer(initPath string) error {

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	return initlayer.Setup(initPath, rootIDs)

 }

@@ -1157,14 +1153,5 @@ func CreateDaemonRoot(config *config.Config) error {

 	if err != nil {

 		return err

 	}

-	rootIDs, err := idMappings.RootPair()

-	if err != nil {

-		return err

-	}

-

-	if err := setupDaemonRoot(config, realRoot, rootIDs); err != nil {

-		return err

-	}

-

-	return nil

+	return setupDaemonRoot(config, realRoot, idMappings.RootPair())

 }

@@ -28,10 +28,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		home:       home,

 		idMappings: idtools.NewIDMappingsFromMaps(uidMaps, gidMaps),

 	}

-	rootIDs, err := d.idMappings.RootPair()

-	if err != nil {

-		return nil, err

-	}

+	rootIDs := d.idMappings.RootPair()

 	if err := idtools.MkdirAllAndChown(home, 0700, rootIDs); err != nil {

 		return nil, err

 	}

@@ -79,10 +76,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {

 	}

 	dir := d.dir(id)

-	rootIDs, err := d.idMappings.RootPair()

-	if err != nil {

-		return err

-	}

+	rootIDs := d.idMappings.RootPair()

 	if err := idtools.MkdirAllAndChown(filepath.Dir(dir), 0700, rootIDs); err != nil {

 		return err

 	}

@@ -72,7 +72,7 @@ func (daemon *Daemon) SystemInfo() (*types.Info, error) {

 	if selinuxEnabled() {

 		securityOptions = append(securityOptions, "name=selinux")

 	}

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	if rootIDs.UID != 0 || rootIDs.GID != 0 {

 		securityOptions = append(securityOptions, "name=userns")

 	}

@@ -611,8 +611,7 @@ func (daemon *Daemon) populateCommonSpec(s *specs.Spec, c *container.Container)

 		Path:     c.BaseFS,

 		Readonly: c.HostConfig.ReadonlyRootfs,

 	}

-	rootIDs, _ := daemon.idMappings.RootPair()

-	if err := c.SetupWorkingDirectory(rootIDs); err != nil {

+	if err := c.SetupWorkingDirectory(daemon.idMappings.RootPair()); err != nil {

 		return err

 	}

 	cwd := c.Config.WorkingDir

@@ -130,8 +130,7 @@ func (daemon *Daemon) populateCommonSpec(s *specs.Spec, c *container.Container)

 		Path:     filepath.Dir(c.BaseFS),

 		Readonly: c.HostConfig.ReadonlyRootfs,

 	}

-	rootIDs, _ := daemon.idMappings.RootPair()

-	if err := c.SetupWorkingDirectory(rootIDs); err != nil {

+	if err := c.SetupWorkingDirectory(daemon.idMappings.RootPair()); err != nil {

 		return err

 	}

 	cwd := c.Config.WorkingDir

@@ -54,8 +54,7 @@ func (daemon *Daemon) setupMounts(c *container.Container) ([]container.Mount, er

 			return nil

 		}

-		rootIDs, _ := daemon.idMappings.RootPair()

-		path, err := m.Setup(c.MountLabel, rootIDs, checkfunc)

+		path, err := m.Setup(c.MountLabel, daemon.idMappings.RootPair(), checkfunc)

 		if err != nil {

 			return nil, err

 		}

@@ -85,7 +84,7 @@ func (daemon *Daemon) setupMounts(c *container.Container) ([]container.Mount, er

 	// if we are going to mount any of the network files from container

 	// metadata, the ownership must be set properly for potential container

 	// remapped root (user namespaces)

-	rootIDs, _ := daemon.idMappings.RootPair()

+	rootIDs := daemon.idMappings.RootPair()

 	for _, mount := range netMounts {

 		if err := os.Chown(mount.Source, rootIDs.UID, rootIDs.GID); err != nil {

 			return nil, err

@@ -16,6 +16,5 @@ func (daemon *Daemon) ContainerCreateWorkdir(cID string) error {

 		return err

 	}

 	defer daemon.Unmount(container)

-	rootIDs, _ := daemon.idMappings.RootPair()

-	return container.SetupWorkingDirectory(rootIDs)

+	return container.SetupWorkingDirectory(daemon.idMappings.RootPair())

 }

@@ -803,10 +803,7 @@ func Unpack(decompressedArchive io.Reader, dest string, options *TarOptions) err

 	var dirs []*tar.Header

 	idMappings := idtools.NewIDMappingsFromMaps(options.UIDMaps, options.GIDMaps)

-	rootIDs, err := idMappings.RootPair()

-	if err != nil {

-		return err

-	}

+	rootIDs := idMappings.RootPair()

 	whiteoutConverter := getWhiteoutConverter(options.WhiteoutFormat)

 	// Iterate through the files in the archive.

@@ -1008,10 +1005,7 @@ func (archiver *Archiver) CopyWithTar(src, dst string) error {

 	// if this archiver is set up with ID mapping we need to create

 	// the new destination directory with the remapped root UID/GID pair

 	// as owner

-	rootIDs, err := archiver.IDMappings.RootPair()

-	if err != nil {

-		return err

-	}

+	rootIDs := archiver.IDMappings.RootPair()

 	// Create dst, copy src's content into it

 	logrus.Debugf("Creating dest directory: %s", dst)

 	if err := idtools.MkdirAllAndChownNew(dst, 0755, rootIDs); err != nil {

@@ -47,10 +47,7 @@ func untarHandler(tarArchive io.Reader, dest string, options *archive.TarOptions

 	}

 	idMappings := idtools.NewIDMappingsFromMaps(options.UIDMaps, options.GIDMaps)

-	rootIDs, err := idMappings.RootPair()

-	if err != nil {

-		return err

-	}

+	rootIDs := idMappings.RootPair()

 	dest = filepath.Clean(dest)

 	if _, err := os.Stat(dest); os.IsNotExist(err) {

@@ -158,19 +158,19 @@ func NewIDMappingsFromMaps(uids []IDMap, gids []IDMap) *IDMappings {

 	return &IDMappings{uids: uids, gids: gids}

 }

-// RootPair returns a uid and gid pair for the root user

-func (i *IDMappings) RootPair() (IDPair, error) {

-	uid, gid, err := GetRootUIDGID(i.uids, i.gids)

-	return IDPair{UID: uid, GID: gid}, err

+// RootPair returns a uid and gid pair for the root user. The error is ignored

+// because a root user always exists, and the defaults are correct when the uid

+// and gid maps are empty.

+func (i *IDMappings) RootPair() IDPair {

+	uid, gid, _ := GetRootUIDGID(i.uids, i.gids)

+	return IDPair{UID: uid, GID: gid}

 }

 // ToHost returns the host UID and GID for the container uid, gid.

 // Remapping is only performed if the ids aren't already the remapped root ids

 func (i *IDMappings) ToHost(pair IDPair) (IDPair, error) {

-	target, err := i.RootPair()

-	if err != nil {

-		return IDPair{}, err

-	}

+	var err error

+	target := i.RootPair()

 	if pair.UID != target.UID {

 		target.UID, err = toHost(pair.UID, i.uids)