For as long as I can remember locking screen with screensaver had never been working good. The problem that had always been there is that when I move the mouse or press a key screensaver disappears making the screen visible, then a second passes and only after it the lock screen appears - this looks and feels like a bug and can be very undesirable if you don't want other people to see what you were doing when you have left the desk.
Now, as I have installed the latest Xubuntu with XFCE 4.12 there is another problem (in addition to the first one described above): it either does not lock the screen at all or does it twice (so I have to enter the password 2 times to unlock it)
The first problem has been discussed many times already and nobody seems to have found a solution so far.
But I have found it accidentally yesterday:
xscreensaver-command -lock launches the screensaver, locks the screen and does it the right way - the desktop is not exposed when the screensaver disappears if launched this way.
So I would like to disable the desktop environment / display manager native screensaver/lockscreen management features and let it just run the command I define when I am away, simple as this, pretty "unix way"-ish. How can this be achieved?