title: Where is located the qDebug qWarning qCritical and qFatal log by default on Qt?
body: <p>When running my Qt5 application on linux, I don't see any output from qDebug, qWarning, qCritical or qFatal. I know that I can use <code>qInstallMsgHandler</code> to install a message handler and see them, but this is rather heavyweight.</p>
  
  <p>I just want to check the qWarning log to see if there is any signal that mis-connected. Is there a way to look at this log? A special command-line option, an environment variable?</p>
  
  <p>I think I remember that in the past, everything was printed to stderr, perhaps that's a Qt5 change?</p>