title: how to run a external daemon-process then kill it in anytime
body: <p>I want to achieve this.</p>
  
  <p>I can run the process by os.system('PROCESS_NAME &amp;')</p>
  
  <p>But I don't know how to kill it. </p>
  
  <p>And I don't wanna the external process blocking in my process</p>
  
  <pre><code>run external daemon process
  
  do my jobs, do anything
  
  kill the `running external daemon process`
  </code></pre>
  
  <p>On Linux OS, I wonder kill the task when meets some requirement</p>