This is not actually caused by LightDM - when you make the guest session active (via logind) it doesn't appear to detect this and turn the screen on.
To reproduce: 1. Login with your account normally. 2. Switch to guest session from the panel menu "Switch Account... -> Guest Session" 3. Switch back to your user account. 4. Find the guest session ID by running loginctl, i.e. $ loginctl SESSION UID USER SEAT c4 1000 bob seat0 c1 135 guest-4aZrXA seat0 5. Switch to the guest session, i.e. $ loginctl activate c1 Observed result: The screen is black until the mouse moves Expected result: The desktop is shown immediately -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1405349 Title: switching to activated guest session causes screen blank To manage notifications about this bug go to: https://bugs.launchpad.net/lightdm/+bug/1405349/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs