func writeAppReaper(p *stage1commontypes.Pod, appName string) error {
	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", fmt.Sprintf("%s Reaper", appName)),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "StopWhenUnneeded", "yes"),
		unit.NewUnitOption("Unit", "Wants", "shutdown.service"),
		unit.NewUnitOption("Unit", "After", "shutdown.service"),
		unit.NewUnitOption("Unit", "Conflicts", "exit.target"),
		unit.NewUnitOption("Unit", "Conflicts", "halt.target"),
		unit.NewUnitOption("Unit", "Conflicts", "poweroff.target"),
		unit.NewUnitOption("Service", "RemainAfterExit", "yes"),
		unit.NewUnitOption("Service", "ExecStop", fmt.Sprintf("/reaper.sh %s", appName)),
	}

	unitsPath := filepath.Join(common.Stage1RootfsPath(p.Root), UnitsDir)
	file, err := os.OpenFile(filepath.Join(unitsPath, fmt.Sprintf("reaper-%s.service", appName)), os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		return errwrap.Wrap(errors.New("failed to create service unit file"), err)
	}
	defer file.Close()

	if _, err = io.Copy(file, unit.Serialize(opts)); err != nil {
		return errwrap.Wrap(errors.New("failed to write service unit file"), err)
	}

	return nil
}

// WriteDefaultTarget writes the default.target unit file
// which is responsible for bringing up the applications
func WriteDefaultTarget(p *stage1commontypes.Pod) error {
	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", "rkt apps target"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
	}

	for i := range p.Manifest.Apps {
		ra := &p.Manifest.Apps[i]
		serviceName := ServiceUnitName(ra.Name)
		opts = append(opts, unit.NewUnitOption("Unit", "After", serviceName))
		opts = append(opts, unit.NewUnitOption("Unit", "Wants", serviceName))
	}

	unitsPath := filepath.Join(common.Stage1RootfsPath(p.Root), UnitsDir)
	file, err := os.OpenFile(filepath.Join(unitsPath, "default.target"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		return err
	}
	defer file.Close()

	if _, err = io.Copy(file, unit.Serialize(opts)); err != nil {
		return err
	}

	return nil
}

func GenerateNetworkInterfaceUnits(unitsPath string, netDescriptions []netDescriber) error {

	for i, netDescription := range netDescriptions {
		ifName := fmt.Sprintf(networking.IfNamePattern, i)
		netAddress := net.IPNet{
			IP:   netDescription.GuestIP(),
			Mask: net.IPMask(netDescription.Mask()),
		}

		address := netAddress.String()

		mac, err := generateMacAddress()
		if err != nil {
			return err
		}

		opts := []*unit.UnitOption{
			unit.NewUnitOption("Unit", "Description", fmt.Sprintf("Network configuration for device: %v", ifName)),
			unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
			unit.NewUnitOption("Service", "Type", "oneshot"),
			unit.NewUnitOption("Service", "RemainAfterExit", "true"),
			unit.NewUnitOption("Service", "ExecStartPre", downInterfaceCommand(ifName)),
			unit.NewUnitOption("Service", "ExecStartPre", setMacCommand(ifName, mac.String())),
			unit.NewUnitOption("Service", "ExecStartPre", upInterfaceCommand(ifName)),
			unit.NewUnitOption("Service", "ExecStart", addAddressCommand(address, ifName)),
			unit.NewUnitOption("Install", "RequiredBy", "default.target"),
		}

		for _, route := range netDescription.Routes() {
			gw := route.GW
			if gw == nil {
				gw = netDescription.Gateway()
			}

			opts = append(
				opts,
				unit.NewUnitOption(
					"Service",
					"ExecStartPost",
					addRouteCommand(route.Dst.String(), gw.String()),
				),
			)
		}

		unitName := fmt.Sprintf("interface-%s", ifName) + ".service"
		unitBytes, err := ioutil.ReadAll(unit.Serialize(opts))
		if err != nil {
			return errwrap.Wrap(fmt.Errorf("failed to serialize network unit file to bytes %q", unitName), err)
		}

		err = ioutil.WriteFile(filepath.Join(unitsPath, unitName), unitBytes, 0644)
		if err != nil {
			return errwrap.Wrap(fmt.Errorf("failed to create network unit file %q", unitName), err)
		}

		log.Printf("network unit created: %q in %q (iface=%q, addr=%q)", unitName, unitsPath, ifName, address)
	}
	return nil
}

// AppReaperUnit writes an app reaper service unit for the given app in the given path using the given unit options.
func (uw *UnitWriter) AppReaperUnit(appName types.ACName, binPath string, opts ...*unit.UnitOption) {
	if uw.err != nil {
		return
	}

	opts = append(opts, []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", fmt.Sprintf("%s Reaper", appName)),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "StopWhenUnneeded", "yes"),
		unit.NewUnitOption("Unit", "Before", "halt.target"),
		unit.NewUnitOption("Unit", "Conflicts", "exit.target"),
		unit.NewUnitOption("Unit", "Conflicts", "halt.target"),
		unit.NewUnitOption("Unit", "Conflicts", "poweroff.target"),
		unit.NewUnitOption("Service", "RemainAfterExit", "yes"),
		unit.NewUnitOption("Service", "ExecStop", fmt.Sprintf(
			"/reaper.sh \"%s\" \"%s\" \"%s\"",
			appName,
			common.RelAppRootfsPath(appName),
			binPath,
		)),
	}...)

	uw.WriteUnit(
		ServiceUnitPath(uw.p.Root, types.ACName(fmt.Sprintf("reaper-%s", appName))),
		fmt.Sprintf("failed to write app %q reaper service", appName),
		opts...,
	)
}

// protectKernelTunables restricts access to some security-sensitive paths under
// /proc and /sys. Entries are either hidden or just made read-only to app.
// This protection is enabled by default.
func protectKernelTunables(opts []*unit.UnitOption, appName types.ACName, systemdVersion int) []*unit.UnitOption {
	roPaths := []string{
		"/proc/bus/",
		"/proc/sys/kernel/core_pattern",
		"/proc/sys/kernel/modprobe",
		"/proc/sys/vm/panic_on_oom",
		"/proc/sysrq-trigger",
		"/sys/block/",
		"/sys/bus/",
		"/sys/class/",
		"/sys/dev/",
		"/sys/devices/",
		"/sys/kernel/",
	}
	hiddenDirs := []string{
		"/sys/firmware/",
		"/sys/fs/",
		"/sys/hypervisor/",
		"/sys/module/",
		"/sys/power/",
	}
	hiddenPaths := []string{
		"/proc/config.gz",
		"/proc/kallsyms",
		"/proc/sched_debug",
		"/proc/kcore",
		"/proc/kmem",
		"/proc/mem",
	}

	// Paths prefixed with "-" are ignored if they do not exist:
	// https://www.freedesktop.org/software/systemd/man/systemd.exec.html#ReadWriteDirectories=
	for _, p := range roPaths {
		opts = append(opts, unit.NewUnitOption("Service", "ReadOnlyDirectories", fmt.Sprintf("-%s", filepath.Join(common.RelAppRootfsPath(appName), p))))
	}
	for _, p := range hiddenDirs {
		opts = append(opts, unit.NewUnitOption("Service", "InaccessibleDirectories", fmt.Sprintf("-%s", filepath.Join(common.RelAppRootfsPath(appName), p))))
	}
	if systemdVersion >= 231 {
		for _, p := range hiddenPaths {
			opts = append(opts, unit.NewUnitOption("Service", "InaccessiblePaths", fmt.Sprintf("-%s", filepath.Join(common.RelAppRootfsPath(appName), p))))
		}
	}
	if systemdVersion >= 233 {
		opts = append(opts, unit.NewUnitOption("Service", "ProtectKernelTunables", "true"))
	}

	return opts
}

// writeShutdownService writes a shutdown.service unit with the given unit options
// if no previous error occured.
// exec specifies how systemctl should be invoked, i.e. ExecStart, or ExecStop.
func (uw *UnitWriter) writeShutdownService(exec string, opts ...*unit.UnitOption) {
	if uw.err != nil {
		return
	}

	flavor, systemdVersion, err := GetFlavor(uw.p)
	if err != nil {
		uw.err = errwrap.Wrap(errors.New("failed to create shutdown service"), err)
		return
	}

	opts = append(opts, []*unit.UnitOption{
		// The default stdout is /dev/console (the tty created by nspawn).
		// But the tty might be destroyed if rkt is executed via ssh and
		// the user terminates the ssh session. We still want
		// shutdown.service to succeed in that case, so don't use
		// /dev/console.
		unit.NewUnitOption("Service", "StandardInput", "null"),
		unit.NewUnitOption("Service", "StandardOutput", "null"),
		unit.NewUnitOption("Service", "StandardError", "null"),
	}...)

	shutdownVerb := "exit"
	// systemd <v227 doesn't allow the "exit" verb when running as PID 1, so
	// use "halt".
	// If systemdVersion is 0 it means it couldn't be guessed, assume it's new
	// enough for "systemctl exit".
	// This can happen, for example, when building rkt with:
	//
	// ./configure --with-stage1-flavors=src --with-stage1-systemd-version=master
	//
	// The patches for the "exit" verb are backported to the "coreos" flavor, so
	// don't rely on the systemd version on the "coreos" flavor.
	if flavor != "coreos" && systemdVersion != 0 && systemdVersion < 227 {
		shutdownVerb = "halt"
	}

	opts = append(
		opts,
		unit.NewUnitOption("Service", exec, fmt.Sprintf("/usr/bin/systemctl --force %s", shutdownVerb)),
	)

	uw.WriteUnit(
		ServiceUnitPath(uw.p.Root, "shutdown"),
		"failed to create shutdown service",
		opts...,
	)
}

func addCpuLimit(opts []*unit.UnitOption, limit *resource.Quantity) ([]*unit.UnitOption, error) {
	if limit.Value() > resource.MaxMilliValue {
		return nil, fmt.Errorf("cpu limit exceeds the maximum millivalue: %v", limit.String())
	}
	quota := strconv.Itoa(int(limit.MilliValue()/10)) + "%"
	opts = append(opts, unit.NewUnitOption("Service", "CPUQuota", quota))
	return opts, nil
}

// installNewMountUnit creates and installs a new mount unit in the default
// systemd location (/usr/lib/systemd/system) inside the pod stage1 filesystem.
// root is pod's absolute stage1 path (from Pod.Root).
// beforeAndrequiredBy creates a systemd unit dependency (can be space separated
// for multi).
// It returns the name of the generated unit.
func installNewMountUnit(root, what, where, fsType, options, beforeAndrequiredBy, unitsDir string) (string, error) {
	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", fmt.Sprintf("Mount unit for %s", where)),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "Before", beforeAndrequiredBy),
		unit.NewUnitOption("Mount", "What", what),
		unit.NewUnitOption("Mount", "Where", where),
		unit.NewUnitOption("Mount", "Type", fsType),
		unit.NewUnitOption("Mount", "Options", options),
		unit.NewUnitOption("Install", "RequiredBy", beforeAndrequiredBy),
	}

	unitsPath := filepath.Join(root, unitsDir)
	unitName := unit.UnitNamePathEscape(where + ".mount")

	if err := writeUnit(opts, filepath.Join(unitsPath, unitName)); err != nil {
		return "", err
	}
	log.Printf("mount unit created: %q in %q (what=%q, where=%q)", unitName, unitsPath, what, where)

	return unitName, nil
}

func writeShutdownService(p *stage1commontypes.Pod) error {
	flavor, systemdVersion, err := GetFlavor(p)
	if err != nil {
		return err
	}

	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", "Pod shutdown"),
		unit.NewUnitOption("Unit", "AllowIsolate", "true"),
		unit.NewUnitOption("Unit", "StopWhenUnneeded", "yes"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Service", "RemainAfterExit", "yes"),
	}

	shutdownVerb := "exit"
	// systemd <v227 doesn't allow the "exit" verb when running as PID 1, so
	// use "halt".
	// If systemdVersion is 0 it means it couldn't be guessed, assume it's new
	// enough for "systemctl exit".
	// This can happen, for example, when building rkt with:
	//
	// ./configure --with-stage1-flavors=src --with-stage1-systemd-version=master
	//
	// The patches for the "exit" verb are backported to the "coreos" flavor, so
	// don't rely on the systemd version on the "coreos" flavor.
	if flavor != "coreos" && systemdVersion != 0 && systemdVersion < 227 {
		shutdownVerb = "halt"
	}

	opts = append(opts, unit.NewUnitOption("Service", "ExecStop", fmt.Sprintf("/usr/bin/systemctl --force %s", shutdownVerb)))

	unitsPath := filepath.Join(common.Stage1RootfsPath(p.Root), UnitsDir)
	file, err := os.OpenFile(filepath.Join(unitsPath, "shutdown.service"), os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		return errwrap.Wrap(errors.New("failed to create unit file"), err)
	}
	defer file.Close()

	if _, err = io.Copy(file, unit.Serialize(opts)); err != nil {
		return errwrap.Wrap(errors.New("failed to write unit file"), err)
	}

	return nil
}

func promptSystemd() {
	if !systemd.IsRunningSystemd() {
		log.Debugf("not running systemd")
		return
	}

	log.Debug("connecting to systemd")
	conn, err := sddbus.New()
	if err != nil {
		log.Errore(err, "connect to systemd")
		return
	}

	defer conn.Close()
	log.Debug("connected")

	props, err := conn.GetUnitProperties("acmetool-redirector.service")
	if err != nil {
		log.Errore(err, "systemd GetUnitProperties")
		return
	}

	if props["LoadState"].(string) != "not-found" {
		log.Info("acmetool-redirector.service unit already installed, skipping")
		return
	}

	r, err := interaction.Auto.Prompt(&interaction.Challenge{
		Title: "Install Redirector as systemd Service?",
		Body: `Would you like acmetool to automatically install the redirector as a systemd service?

The service name will be acmetool-redirector.`,
		ResponseType: interaction.RTYesNo,
		UniqueID:     "acmetool-quickstart-install-redirector-systemd",
	})
	log.Fatale(err, "interaction")

	if r.Cancelled {
		return
	}

	username, err := determineAppropriateUsername()
	if err != nil {
		log.Errore(err, "determine appropriate username")
		return
	}

	f, err := os.OpenFile("/etc/systemd/system/acmetool-redirector.service", os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		log.Errore(err, "acmetool-redirector.service unit file already exists?")
		return
	}
	defer f.Close()

	rdr := sdunit.Serialize([]*sdunit.UnitOption{
		sdunit.NewUnitOption("Unit", "Description", "acmetool HTTP redirector"),
		sdunit.NewUnitOption("Service", "Type", "notify"),
		sdunit.NewUnitOption("Service", "ExecStart", exepath.Abs+` redirector --service.uid=`+username),
		sdunit.NewUnitOption("Service", "Restart", "always"),
		sdunit.NewUnitOption("Service", "RestartSec", "30"),
		sdunit.NewUnitOption("Install", "WantedBy", "multi-user.target"),
	})

	_, err = io.Copy(f, rdr)
	if err != nil {
		log.Errore(err, "cannot write unit file")
		return
	}

	f.Close()
	err = conn.Reload() // softfail
	log.Warne(err, "systemctl daemon-reload failed")

	_, _, err = conn.EnableUnitFiles([]string{"acmetool-redirector.service"}, false, false)
	log.Errore(err, "failed to enable unit acmetool-redirector.service")

	_, err = conn.StartUnit("acmetool-redirector.service", "replace", nil)
	log.Errore(err, "failed to start acmetool-redirector")
	resultStr := "The acmetool-redirector service was successfully started."
	if err != nil {
		resultStr = "The acmetool-redirector service WAS NOT successfully started. You may have a web server listening on port 80. You will need to troubleshoot this yourself."
	}

	_, err = interaction.Auto.Prompt(&interaction.Challenge{
		Title: "systemd Service Installation Complete",
		Body: fmt.Sprintf(`acmetool-redirector has been installed as a systemd service.
    
    %s`, resultStr),
		UniqueID: "acmetool-quickstart-complete",
	})
	log.Errore(err, "interaction")
}

// AppToSystemdMountUnits prepare bind mount unit for empty or host kind mounting
// between stage1 rootfs and chrooted filesystem for application
func AppToSystemdMountUnits(root string, appName types.ACName, volumes []types.Volume, ra *schema.RuntimeApp, unitsDir string) error {
	app := ra.App

	vols := make(map[types.ACName]types.Volume)
	for _, v := range volumes {
		vols[v.Name] = v
	}

	mounts := GenerateMounts(ra, vols)
	for _, m := range mounts {
		vol := vols[m.Volume]

		// source relative to stage1 rootfs to relative pod root
		whatPath := filepath.Join(stage1MntDir, vol.Name.String())
		whatFullPath := filepath.Join(root, whatPath)

		if vol.Kind == "empty" {
			log.Printf("creating an empty volume folder for sharing: %q", whatFullPath)
			err := os.MkdirAll(whatFullPath, 0700)
			if err != nil {
				return err
			}
		}

		// destination relative to stage1 rootfs and relative to pod root
		wherePath := filepath.Join(common.RelAppRootfsPath(appName), m.Path)
		whereFullPath := filepath.Join(root, wherePath)

		// assertion to make sure that "what" exists (created earlier by PodToSystemdHostMountUnits)
		log.Printf("checking required source path: %q", whatFullPath)
		if _, err := os.Stat(whatFullPath); os.IsNotExist(err) {
			return fmt.Errorf("bug: missing source for volume %v", vol.Name)
		}

		// optionally prepare app directory
		log.Printf("optionally preparing destination path: %q", whereFullPath)
		err := os.MkdirAll(whereFullPath, 0700)
		if err != nil {
			return errwrap.Wrap(fmt.Errorf("failed to prepare dir for mount %v", m.Volume), err)
		}

		// install new mount unit for bind mount /mnt/volumeName -> /opt/stage2/{app-id}/rootfs/{{mountPoint.Path}}
		mu, err := installNewMountUnit(
			root,      // where put a mount unit
			whatPath,  // what - stage1 rootfs /mnt/VolumeName
			wherePath, // where - inside chroot app filesystem
			"bind",    // fstype
			"bind",    // options
			serviceUnitName(appName),
			unitsDir,
		)
		if err != nil {
			return errwrap.Wrap(fmt.Errorf("cannot install new mount unit for app %q", appName.String()), err)
		}

		// TODO(iaguis) when we update util-linux to 2.27, this code can go
		// away and we can bind-mount RO with one unit file.
		// http://ftp.kernel.org/pub/linux/utils/util-linux/v2.27/v2.27-ReleaseNotes
		if IsMountReadOnly(vol, app.MountPoints) {
			opts := []*unit.UnitOption{
				unit.NewUnitOption("Unit", "Description", fmt.Sprintf("Remount read-only unit for %s", wherePath)),
				unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
				unit.NewUnitOption("Unit", "After", mu),
				unit.NewUnitOption("Unit", "Wants", mu),
				unit.NewUnitOption("Service", "ExecStart", fmt.Sprintf("/usr/bin/mount -o remount,ro %s", wherePath)),
				unit.NewUnitOption("Install", "RequiredBy", mu),
			}

			remountUnitPath := filepath.Join(root, unitsDir, unit.UnitNamePathEscape(wherePath+"-remount.service"))
			if err := writeUnit(opts, remountUnitPath); err != nil {
				return err
			}
		}
	}
	return nil
}

// TODO use named flags instead of positional
func main() {
	flag.Parse()

	stage1initcommon.InitDebug(debug)

	log, diag, _ = rktlog.NewLogSet("stage1", debug)
	if !debug {
		diag.SetOutput(ioutil.Discard)
	}

	uuid, err := types.NewUUID(flag.Arg(0))
	if err != nil {
		log.PrintE("UUID is missing or malformed", err)
		os.Exit(254)
	}

	appName, err := types.NewACName(flag.Arg(1))
	if err != nil {
		log.PrintE("invalid app name", err)
		os.Exit(254)
	}

	enterEP := flag.Arg(2)

	root := "."
	p, err := stage1types.LoadPod(root, uuid)
	if err != nil {
		log.PrintE("failed to load pod", err)
		os.Exit(254)
	}

	insecureOptions := stage1initcommon.Stage1InsecureOptions{
		DisablePaths:        disablePaths,
		DisableCapabilities: disableCapabilities,
		DisableSeccomp:      disableSeccomp,
	}

	ra := p.Manifest.Apps.Get(*appName)
	if ra == nil {
		log.Printf("failed to get app")
		os.Exit(254)
	}

	if ra.App.WorkingDirectory == "" {
		ra.App.WorkingDirectory = "/"
	}

	binPath, err := stage1initcommon.FindBinPath(p, ra)
	if err != nil {
		log.PrintE("failed to find bin path", err)
		os.Exit(254)
	}

	w := stage1initcommon.NewUnitWriter(p)

	w.AppUnit(ra, binPath, privateUsers, insecureOptions,
		unit.NewUnitOption("Unit", "Before", "halt.target"),
		unit.NewUnitOption("Unit", "Conflicts", "halt.target"),
		unit.NewUnitOption("Service", "StandardOutput", "journal+console"),
		unit.NewUnitOption("Service", "StandardError", "journal+console"),
	)

	w.AppReaperUnit(ra.Name, binPath)

	if err := w.Error(); err != nil {
		log.PrintE("error generating app units", err)
		os.Exit(254)
	}

	args := []string{enterEP}

	args = append(args, fmt.Sprintf("--pid=%s", flag.Arg(3)))
	args = append(args, "/usr/bin/systemctl")
	args = append(args, "daemon-reload")

	cmd := exec.Cmd{
		Path: args[0],
		Args: args,
	}

	if err := cmd.Run(); err != nil {
		log.PrintE("error executing daemon-reload", err)
		os.Exit(254)
	}

	args = []string{enterEP}

	args = append(args, fmt.Sprintf("--pid=%s", flag.Arg(3)))
	args = append(args, "/usr/bin/systemctl")
	args = append(args, "start")
	args = append(args, appName.String())

	cmd = exec.Cmd{
		Path: args[0],
		Args: args,
	}

	if err := cmd.Run(); err != nil {
		log.PrintE(fmt.Sprintf("error starting app %q", appName.String()), err)
//.........这里部分代码省略.........

func MutableEnv(p *stage1commontypes.Pod) error {
	w := NewUnitWriter(p)

	w.WriteUnit(
		TargetUnitPath(p.Root, "default"),
		"failed to write default.target",
		unit.NewUnitOption("Unit", "Description", "rkt apps target"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "Requires", "systemd-journald.service"),
		unit.NewUnitOption("Unit", "After", "systemd-journald.service"),
		unit.NewUnitOption("Unit", "Before", "halt.target"),
		unit.NewUnitOption("Unit", "Conflicts", "halt.target"),
	)

	w.WriteUnit(
		ServiceUnitPath(p.Root, "[email protected]"),
		"failed to write prepare-app service template",
		unit.NewUnitOption("Unit", "Description", "Prepare minimum environment for chrooted applications"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "OnFailureJobMode", "fail"),
		unit.NewUnitOption("Service", "Type", "oneshot"),
		unit.NewUnitOption("Service", "Restart", "no"),
		unit.NewUnitOption("Service", "ExecStart", "/prepare-app %I"),
		unit.NewUnitOption("Service", "User", "0"),
		unit.NewUnitOption("Service", "Group", "0"),
		unit.NewUnitOption("Service", "CapabilityBoundingSet", "CAP_SYS_ADMIN CAP_DAC_OVERRIDE"),
	)

	w.WriteUnit(
		TargetUnitPath(p.Root, "halt"),
		"failed to write halt target",
		unit.NewUnitOption("Unit", "Description", "Halt"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "AllowIsolate", "true"),
		unit.NewUnitOption("Unit", "Requires", "shutdown.service"),
		unit.NewUnitOption("Unit", "After", "shutdown.service"),
	)

	w.writeShutdownService(
		"ExecStart",
		unit.NewUnitOption("Unit", "Description", "Pod shutdown"),
		unit.NewUnitOption("Unit", "AllowIsolate", "true"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Service", "RemainAfterExit", "yes"),
	)

	return w.Error()
}

// appToSystemd transforms the provided RuntimeApp+ImageManifest into systemd units
func appToSystemd(p *stage1commontypes.Pod, ra *schema.RuntimeApp, interactive bool, flavor string, privateUsers string) error {
	app := ra.App
	appName := ra.Name
	image, ok := p.Images[appName.String()]
	if !ok {
		// This is impossible as we have updated the map in LoadPod().
		panic(fmt.Sprintf("No images for app %q", ra.Name.String()))
	}
	imgName := image.Name

	if len(app.Exec) == 0 {
		return fmt.Errorf(`image %q has an empty "exec" (try --exec=BINARY)`, imgName)
	}

	workDir := "/"
	if app.WorkingDirectory != "" {
		workDir = app.WorkingDirectory
	}

	env := app.Environment

	env.Set("AC_APP_NAME", appName.String())
	if p.MetadataServiceURL != "" {
		env.Set("AC_METADATA_URL", p.MetadataServiceURL)
	}

	if err := writeEnvFile(p, env, appName, privateUsers); err != nil {
		return errwrap.Wrap(errors.New("unable to write environment file"), err)
	}

	// This is a partial implementation for app.User and app.Group:
	// For now, only numeric ids (and the string "root") are supported.
	var uid, gid int
	var err error
	if app.User == "root" {
		uid = 0
	} else {
		uid, err = strconv.Atoi(app.User)
		if err != nil {
			return fmt.Errorf("non-numerical user id not supported yet")
		}
	}
	if app.Group == "root" {
		gid = 0
	} else {
		gid, err = strconv.Atoi(app.Group)
		if err != nil {
			return fmt.Errorf("non-numerical group id not supported yet")
		}
	}

	execWrap := []string{"/appexec", common.RelAppRootfsPath(appName), workDir, RelEnvFilePath(appName), strconv.Itoa(uid), generateGidArg(gid, app.SupplementaryGIDs)}
	execStart := quoteExec(append(execWrap, app.Exec...))
	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", fmt.Sprintf("Application=%v Image=%v", appName, imgName)),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "Wants", fmt.Sprintf("reaper-%s.service", appName)),
		unit.NewUnitOption("Service", "Restart", "no"),
		unit.NewUnitOption("Service", "ExecStart", execStart),
		unit.NewUnitOption("Service", "User", "0"),
		unit.NewUnitOption("Service", "Group", "0"),
	}

	if interactive {
		opts = append(opts, unit.NewUnitOption("Service", "StandardInput", "tty"))
		opts = append(opts, unit.NewUnitOption("Service", "StandardOutput", "tty"))
		opts = append(opts, unit.NewUnitOption("Service", "StandardError", "tty"))
	} else {
		opts = append(opts, unit.NewUnitOption("Service", "StandardOutput", "journal+console"))
		opts = append(opts, unit.NewUnitOption("Service", "StandardError", "journal+console"))
		opts = append(opts, unit.NewUnitOption("Service", "SyslogIdentifier", filepath.Base(app.Exec[0])))
	}

	// When an app fails, we shut down the pod
	opts = append(opts, unit.NewUnitOption("Unit", "OnFailure", "halt.target"))

	for _, eh := range app.EventHandlers {
		var typ string
		switch eh.Name {
		case "pre-start":
			typ = "ExecStartPre"
		case "post-stop":
			typ = "ExecStopPost"
		default:
			return fmt.Errorf("unrecognized eventHandler: %v", eh.Name)
		}
		exec := quoteExec(append(execWrap, eh.Exec...))
		opts = append(opts, unit.NewUnitOption("Service", typ, exec))
	}

	// Some pre-start jobs take a long time, set the timeout to 0
	opts = append(opts, unit.NewUnitOption("Service", "TimeoutStartSec", "0"))

	var saPorts []types.Port
	for _, p := range app.Ports {
		if p.SocketActivated {
			saPorts = append(saPorts, p)
		}
	}
//.........这里部分代码省略.........

// appendOptionsList updates an existing unit options list appending
// an array of new properties, one entry at a time.
// This is the preferred method to avoid hitting line length limits
// in unit files. Target property must support multi-line entries.
func appendOptionsList(opts []*unit.UnitOption, section string, property string, prefix string, vals []string) []*unit.UnitOption {
	for _, v := range vals {
		opts = append(opts, unit.NewUnitOption(section, property, fmt.Sprintf("%s%s", prefix, v)))
	}
	return opts
}

// WritePrepareAppTemplate writes service unit files for preparing the pod's applications
func WritePrepareAppTemplate(p *stage1commontypes.Pod) error {
	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", "Prepare minimum environment for chrooted applications"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "OnFailureJobMode", "fail"),
		unit.NewUnitOption("Unit", "Requires", "systemd-journald.service"),
		unit.NewUnitOption("Unit", "After", "systemd-journald.service"),
		unit.NewUnitOption("Service", "Type", "oneshot"),
		unit.NewUnitOption("Service", "Restart", "no"),
		unit.NewUnitOption("Service", "ExecStart", "/prepare-app %I"),
		unit.NewUnitOption("Service", "User", "0"),
		unit.NewUnitOption("Service", "Group", "0"),
		unit.NewUnitOption("Service", "CapabilityBoundingSet", "CAP_SYS_ADMIN CAP_DAC_OVERRIDE"),
	}

	unitsPath := filepath.Join(common.Stage1RootfsPath(p.Root), UnitsDir)
	file, err := os.OpenFile(filepath.Join(unitsPath, "[email protected]"), os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		return errwrap.Wrap(errors.New("failed to create service unit file"), err)
	}
	defer file.Close()

	if _, err = io.Copy(file, unit.Serialize(opts)); err != nil {
		return errwrap.Wrap(errors.New("failed to write service unit file"), err)
	}

	return nil
}

func addMemoryLimit(opts []*unit.UnitOption, limit *resource.Quantity) ([]*unit.UnitOption, error) {
	opts = append(opts, unit.NewUnitOption("Service", "MemoryLimit", strconv.Itoa(int(limit.Value()))))
	return opts, nil
}

func ImmutableEnv(p *stage1commontypes.Pod, interactive bool, privateUsers string, insecureOptions Stage1InsecureOptions) error {
	w := NewUnitWriter(p)

	opts := []*unit.UnitOption{
		unit.NewUnitOption("Unit", "Description", "rkt apps target"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
	}

	for i := range p.Manifest.Apps {
		ra := &p.Manifest.Apps[i]
		serviceName := ServiceUnitName(ra.Name)
		opts = append(opts, unit.NewUnitOption("Unit", "After", serviceName))
		opts = append(opts, unit.NewUnitOption("Unit", "Wants", serviceName))
	}

	w.WriteUnit(
		TargetUnitPath(p.Root, "default"),
		"failed to write default.target",
		opts...,
	)

	w.WriteUnit(
		ServiceUnitPath(p.Root, "[email protected]"),
		"failed to write prepare-app service template",
		unit.NewUnitOption("Unit", "Description", "Prepare minimum environment for chrooted applications"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "OnFailureJobMode", "fail"),
		unit.NewUnitOption("Unit", "Requires", "systemd-journald.service"),
		unit.NewUnitOption("Unit", "After", "systemd-journald.service"),
		unit.NewUnitOption("Service", "Type", "oneshot"),
		unit.NewUnitOption("Service", "Restart", "no"),
		unit.NewUnitOption("Service", "ExecStart", "/prepare-app %I"),
		unit.NewUnitOption("Service", "User", "0"),
		unit.NewUnitOption("Service", "Group", "0"),
		unit.NewUnitOption("Service", "CapabilityBoundingSet", "CAP_SYS_ADMIN CAP_DAC_OVERRIDE"),
	)

	w.WriteUnit(
		TargetUnitPath(p.Root, "halt"),
		"failed to write halt target",
		unit.NewUnitOption("Unit", "Description", "Halt"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Unit", "AllowIsolate", "true"),
	)

	w.writeShutdownService(
		"ExecStop",
		unit.NewUnitOption("Unit", "Description", "Pod shutdown"),
		unit.NewUnitOption("Unit", "AllowIsolate", "true"),
		unit.NewUnitOption("Unit", "StopWhenUnneeded", "yes"),
		unit.NewUnitOption("Unit", "DefaultDependencies", "false"),
		unit.NewUnitOption("Service", "RemainAfterExit", "yes"),
	)

	if err := w.Error(); err != nil {
		return err
	}

	for i := range p.Manifest.Apps {
		ra := &p.Manifest.Apps[i]

		if ra.App.WorkingDirectory == "" {
			ra.App.WorkingDirectory = "/"
		}

		binPath, err := FindBinPath(p, ra)
		if err != nil {
			return err
		}

		var opts []*unit.UnitOption
		if interactive {
			opts = append(opts, unit.NewUnitOption("Service", "StandardInput", "tty"))
			opts = append(opts, unit.NewUnitOption("Service", "StandardOutput", "tty"))
			opts = append(opts, unit.NewUnitOption("Service", "StandardError", "tty"))
		} else {
			opts = append(opts, unit.NewUnitOption("Service", "StandardOutput", "journal+console"))
			opts = append(opts, unit.NewUnitOption("Service", "StandardError", "journal+console"))
		}
		w.AppUnit(ra, binPath, privateUsers, insecureOptions, opts...)

		w.AppReaperUnit(ra.Name, binPath,
			unit.NewUnitOption("Unit", "Wants", "shutdown.service"),
			unit.NewUnitOption("Unit", "After", "shutdown.service"),
		)
	}

	return w.Error()
}

// appToSystemd transforms the provided RuntimeApp+ImageManifest into systemd units
func appToSystemd(p *stage1commontypes.Pod, ra *schema.RuntimeApp, interactive bool, flavor string, privateUsers string) error {
	app := ra.App
	appName := ra.Name
	imgName := p.AppNameToImageName(appName)

	if len(app.Exec) == 0 {
		return fmt.Errorf(`image %q has an empty "exec" (try --exec=BINARY)`, imgName)
	}

	workDir := "/"
	if app.WorkingDirectory != "" {
		workDir = app.WorkingDirectory
	}

	env := app.Environment

	env.Set("AC_APP_NAME", appName.String())
	if p.MetadataServiceURL != "" {
		env.Set("AC_METADATA_URL", p.MetadataServiceURL)
	}

	envFilePath := EnvFilePath(p.Root, appName)

	uidRange := user.NewBlankUidRange()
	if err := uidRange.Deserialize([]byte(privateUsers)); err != nil {
		return err
	}

	if err := writeEnvFile(p, env, appName, uidRange, '\n', envFilePath); err != nil {
		return errwrap.Wrap(errors.New("unable to write environment file for systemd"), err)
	}

	u, g, err := parseUserGroup(p, ra, uidRange)
	if err != nil {
		return err
	}

	if err := generateSysusers(p, ra, u, g, uidRange); err != nil {
		return errwrap.Wrap(errors.New("unable to generate sysusers"), err)
	}

	binPath, err := findBinPath(p, appName, *app, workDir, app.Exec[0])
	if err != nil {
		return er