zhang@zhang:~$ rqt
Traceback (most recent call last):
  File "/opt/ros/melodic/bin/rqt", line 13, in <module>
    sys.exit(main.main())
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_gui/main.py", line 65, in main
    hash(os.environ['ROS_PACKAGE_PATH'])))
  File "/opt/ros/melodic/lib/python2.7/dist-packages/qt_gui/main.py", line 600, in main
    plugin_manager.discover()
  File "/opt/ros/melodic/lib/python2.7/dist-packages/qt_gui/plugin_manager.py", line 125, in discover
    self._plugin_menu.add_plugin(plugin_descriptor)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/qt_gui/plugin_menu.py", line 82, in add_plugin
    self._enrich_action(action, action_attributes, base_path)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/qt_gui/plugin_menu.py", line 133, in _enrich_action
    action_attributes['icon'], action_attributes.get('icontype', None), base_path)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/qt_gui/icon_loader.py", line 46, in get_icon
    raise UserWarning('icon "%s" not found' % str(path))
UserWarning: icon "/opt/ros/melodic/share/rqt_virtual_joy/resource/input-gaming.png" not found