Usually an X window is moved under Linux via a click on the tile bar (and a following drag&drop). However, sometimes there are over-sized configuration dialogs or some strange behaviours of windows which move the title bar out of the screen. At that moment the window cannot be moved anymore via the window bar because it is not reachable.
But there is an easy way in Linux (and I wish Windows would have the same!) to move X windows regardless of the window title bar: by pressing and holding the Alt key any window can be moved with the left mouse button. This works under KDE as well as under Gnome.
Everyone who used Linux for a longer time knows that simple shortcut – but maybe there are some new users who don’t know it, and this post is for them.