#StackBounty: #xubuntu #lightdm #display-manager #lightdm-gtk-greeter #light-locker Prevent lightdm from turning off screen when lockin…

Bounty: 100

I am running Xubuntu 18.04. When I lock the session, the screen gets turned off instantly. I am using stock lightdm as display manager and lightlocker for locking the session.

From my viewpoint the following sequence of events happens.

  1. I initiate locking by running xflock4 via keyboard shortcut or clicking “Lock Screen” in the Whisker (Main) menu.
  2. VT8 becomes active, a new lightdm greeter is spawned on this VT terminal and physical screen turns off at the same time.
  3. My usual VT7 terminal gets seized in background with lightlocker which draws “This session is locked” screen.

If press some button on the keyboard or move the mouse, the screen turns on. If I press Control-Alt-F7, I see lightlocker lock screen in my original session. If I press Control-Alt-F8 I go back to the greeter where I can enter my password. After entering the password, VT7 becomes active and lightlocker white-on-black lock screen is no longer shown. If I later go back to VT8 with Control-Alt-F8, I see a completely black screen with only a blinking cursor (seems to be in text mode).

If the session timeouts and gets locked automatically, I also end up with the screen turned off. That can happen several times a day.

I am using an external monitor which is very slow to turn on again. It takes around 10 seconds and that is quite annoying every single time. I would rather keep it on for an hour or more on password dialog before timing it out and turning off automatically.

Also there is a non-zero chance of getting a system freeze due to buggy Intel (KMS?) drivers when doing VT switch and turning of the screen at almost the same time.

I skimmed through lightdm and lightdm greeter docs and found no hints on how to prevent that.

Update 1

  1. I discovered an “Action” applet for the xfce4-panel that can “switch” user sessions without turning off the screen. This essentially locks the session with light-locker and shows greeter on a new VT. After some digging I discovered a command to show greeter, dm-tool switch-to-greeter. I have reassigned keyboard shortcut to lock the screen from xflock4 to dm-tool switch-to-greeter as workaround. But the problem with automatic locking and turning screen still annoys me. What is interesting that dm-tool lock and light-locker-command --lock (xflock4 calls it) behave the same and produce a turned off monitor.
  2. If I uninstall light-locker (with full reboot) and do dm-tool lock, the screen also turns off. So this should not be related to light-locker…


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