Sometimes you need to restart the Gnome panel, e.g. when you installed a new Gnome panel widget but the widget list was cached before.
You often don't want to do sign out and back in for this.
Instead, just run:
killall gnome-panel
This will terminate all gnome-panel processes. On my machine (Ubuntu 11.04) the panel then restarted itself after a moment.
If the panel does not automatically come back, press Alt+F2 to bring up the Gnome "run" box and start gnome-panel from there.
Posted by Arne Hartherz to makandra dev (2012-02-03 10:27)