--check for earlier started script with pid PID1 (PID1 must be a uniqe name)
tpid = storage.get('PID1')  
if tpid == nil then 
  pid = os.getpid()
  storage.set('PID1', pid)
else
  pid = os.getpid()   
  storage.set('PID1', pid)   
  os.kill(tpid, signal.SIGKILL) 
end