code: func Enter(cdir string, podPID int, appName types.ACName, stage1Path string, cmdline []string) error {
  	if err := os.Chdir(cdir); err != nil {
  		return errwrap.Wrap(errors.New("error changing to dir"), err)
  	}
  
  	ep, err := getStage1Entrypoint(cdir, enterEntrypoint)
  	if err != nil {
  		return errwrap.Wrap(errors.New("error determining 'enter' entrypoint"), err)
  	}
  
  	argv := []string{filepath.Join(stage1Path, ep)}
  	argv = append(argv, fmt.Sprintf("--pid=%d", podPID))
  	argv = append(argv, fmt.Sprintf("--appname=%s", appName.String()))
  	argv = append(argv, "--")
  	argv = append(argv, cmdline...)
  	if err := syscall.Exec(argv[0], argv, os.Environ()); err != nil {
  		return errwrap.Wrap(errors.New("error execing enter"), err)
  	}
  
  	// never reached
  	return nil
  }
docs: // Enter enters the pod/app by exec()ing the stage1's /enter similar to /init
  // /enter can expect to have its CWD set to the app root.
  // appName and command are supplied to /enter on argv followed by any arguments.
  // stage1Path is the path of the stage1 rootfs