title: what's the meaning of php-fpm's catch_workers_output configure item?
body: <p>Today when i search how to open php-fpm's error log.I found that a lot of articles say that users should turn on <code>catch_workers_output</code>.But this really confusing me after i read this configure's comment:</p>
  <blockquote>
  <p>catch_workers_output boolean</p>
  <p>Redirect worker stdout and stderr into main error log. If not set, stdout and stderr will be redirected to /dev/null according to FastCGI specs.</p>
  <p>Default value: no.</p>
  </blockquote>
  <p>And i tried it,the result is:no matter 'on' or 'off',this configure does not affect php's error log action.What decide the log action is the two: <code>log_errors</code> and <code>error_log</code>.</p>
  <p>So,what's the function of <code>catch_workers_output</code>?</p>