title: do not send hangup signal to background process when bash exit
body: <p>I know when shell exits or itself receives SIGHUP, it will send SIGHUP to all background process.</p>
  <p>'nohup cmd' or 'disown' will tell bash not to send SIGHUP. Is there a shell setting so that bash will always not send SIGHUP?</p>
  <p>I want my backgroup process to run when bash got killed accidentally for various reasons.</p>
  <p>Thanks.</p>