Ubuntu 12.04, 3.5.0-36-generic kernel through LTS Hardware Enablement stack. HD4600 GPU on top of an Intel Core i7-4770.
When I use the "Lock Screen" feature of the desktop, sometimes I will go back to the machine hours later and will see one of the following two glitches:
- the screen is mostly black with a bunch of glitchy graphics on it. I can still move the mouse, can't click on anything though, and nothing happens.
- the system looks unlocked (and if I remember correctly, the monitor is on). Whatever was on the screen before the lock is now fully visible, although you can't click on anything. This has showed my email inbox contents to the rest of the office more than once.
The OS hasn't actually frozen at this point. I usually open a TTY with (CTRL+ALT+F1) and run:
sudo stop lightdm sudo start lightdm
and am able to resume work, even though all of the processes open before (like Firefox, skype etc) seem to be gone.
First of all, is this an known issue and can I fix it? Secondly, is there a log somewhere I could look at to see what the specific issue is? /var/log/lightdm didn't reveal much, but I might have been looking in the wrong place.
Any suggestions would be super welcome.
Workaround I stumbled upon: If someone else is running into this issue, there's no reason to reboot the machine when it happens. I think switching to a virtual tty with ALT+CTRL+F1 and then back to ALT+CTRL+F7 seems to fix the problem. Even better, you can avoid it altogether by locking the screen in X and then switching to tty1 when you want to leave the machine alone for some time. Switch back to X when you're back. Hasn't glitched out on me yet, probably because it forces some kind of "full refresh" every time you do it.