There is no "Lock" option showing up in the user menu, and the standard shortcuts (Ctrl+L or Ctrl+Alt+L) don't do anything.
I'm running Fedora 19 with Gnome Shell 3.8.3, and XDM 1.1.11.
I'm using XDM because of broken XDMCP support in GDM – but before I upgraded to Fedora 19, I did have the lock option, even when using XDM.
I've posted an answer reflecting the results of my own research. It basically says that it's not possible to have screen-lock integrated into Gnome 3.8 without running GDM.
I really hope there's a better answer available though – so please add your own answer if there's any way to do this that I overlooked.
Best Answer
In Gnome Shell 3.6 and earlier, the old
gnome-screensaver
program was present, and if GDM was not running,gnome-screensaver
would be invoked - allowing you to lock the screen.Starting in Gnome Shell 3.8 (included in Fedora 19),
gnome-screensaver
support has been dropped completely. This was done for three reasons: reduced code complexity coupled with the fact that the screensaver is seen as an unneeded feature, and the fact that the eventual move to Wayland will require screensaver, locking, etc. support to be in the compositor.So the only Gnome-integrated way of locking the screen is to have GDM running, which will respond to a dbus message telling it to lock the screen. Other display managers (such as XDM) have not been designed to respond to this dbus message, and so the screen cannot be locked.
From this link: