Description of problem:
Attempting to lock the screen using "dm-tool lock"/"dm-tool switch-to-greeter" or the GUI equivalents appears to break LightDM entirely, making it impossible to log back in graphically, use a tty, or restart X with keyboard shortcuts or the terminal.
Version-Release number of selected component (if applicable):
This appears to have started after updating from lightdm-1.10.6-2.fc23.x86_64 to lightdm-1.10.6-4.fc23.x86_64. However, I updated lightdm along with a bunch of other packages, so I'm not certain if there's something else involved.
Steps to Reproduce:
1. Log in to a graphical session using LightDM (in my case, I'm running XFCE).
2. Run "dm-tool lock".
I get dumped to what appears to be tty2, and can't get back into my graphical session. Additionally, half of my keyboard inputs get eaten seemingly at random, rendering it effectively impossible to log in to the tty, switch ttys, or kill the X server.
Hitting the power button on the machine still works, and triggers a normal shutdown, as do SysRq inputs. Lately, I've taken to SSHing into the machine and restarting the lightdm service that way, after which things seem to work again.
The graphical session is locked, allowing the user to unlock their session or log in with a new one via the LightDM greeter.
Given the weirdness of the situation, and the fact that no one else has reported it, I'd hazard a guess that there's something specific to my setup involved here. As to what that could be, I haven't a clue. I am running the NVIDIA binary drivers via kmod-nvidia from RPM Fusion, in case that's relevant.
Yeah, dm-tool isn't useful as far as I can tell, I would recommend not relying on it.
That said, ALT-F1, ALT-F2, should still be able to switch VT's
While other issues with display switching have arisen (on boot and on lock LightDM's greeter VTs are blank until I switch away and switch back - much more manageable at least), this particular issue is no longer reproducible with my latest batch of updates. At a glance I'd guess kernel-4.6.4-201.fc23.x86_64 or xorg-x11-drv-nvidia-1:367.35-1.fc23.x86_64 from RPM Fusion to be the relevant package. Given the new VT issues, probably more likely the NVIDIA binary driver.