polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.consolekit.system.stop" ||
        action.id == "org.freedesktop.login1.power-off" ||
        action.id == "org.freedesktop.login1.power-off-multiple-sessions" ||
        action.id == "org.xfce.session.xfsm-shutdown-helper")
    {

        try{
            polkit.spawn(["/usr/bin/pendrive-reminder/check_pendrive.sh", subject.user]);
            return polkit.Result.YES;

        }catch(error){
            polkit.spawn(["/usr/bin/pendrive-reminder/send_notify.sh", subject.user]);
        return polkit.Result.NO;
     }
   }
  }