title: How does strace connect to an already running process?
body: <p>I do know that <code>strace</code> uses <code>ptrace</code> to do the job,</p>
  
  <p>but it needs to run the target process with <code>TRACE_ME</code> on,</p>
  
  <p>which don't apply for the case of an already running process.</p>
  
  <p>how does it work on an already running process?</p>