[SOLVED] Black screen with mouse cursor on resume from lock

The Iron Wolf · 2025-09-16 20:24:10

Hi,

I am running Xfce 4.18 with lightdm 1.30.0 and Nvidia 575.64.03 proprietary driver. Sometimes, when I return from the lock screen, all I get is black screen and mouse cursor. The only workaround is to restart desktop from TTY. I am not sure if this is Xfce, lightdm or maybe even greeter used in Mint issue.

All kinds of suspend/sleep/display management is disabled in Power Manger. However, when I lock my screen, after a while it gets turned off, so somewhere some sort of power management is still happening. I am new to Linux, so I would appreciate any inputs on how to diagnose this.

One interesting thing is that I found a way to reliably reproduce the issue:

* reboot
* login to desktop
* lock using /usr/bin/dm-tool switch-to-greeter
* unlock

Result is black screen with mouse cursor.

Observations:

* if I open few programs before locking, it does not happen anymore (only very rarely, so it still a problem). But with nothing opened it is 100% repro.
* I replaced light-locker with /usr/bin/dm-tool switch-to-greeter in attempts to fix it.
* nothing stands out in boot session log and xsession log is too noisy, hard to undertstand if it has hints to problem and I lack experience in Linux atm.
* this does not seem to be related to Power Manager/Display tab settings - happens no matter what you set there.
* not sure if related, but firefox often crashes upon return from lock screen.

Any suggestions appreciated.

Last edited by The Iron Wolf (2025-09-18 02:18:27)

eriefisher · 2025-09-16 21:20:12

Try removing light-locker all together. Replace with xfce4-screensaver.

The Iron Wolf · 2025-09-16 21:22:19

eriefisher wrote:

Try removing light-locker all together. Replace with xfce4-screensaver.

Thanks. Light-locker is removed and purged. Do I have to use screensaver?

eriefisher · 2025-09-16 21:26:04

Not really. You can just have it blank the screen or shut it off entirely.

The Iron Wolf · 2025-09-16 21:37:08

eriefisher wrote:

Not really. You can just have it blank the screen or shut it off entirely.

Please, bear with me. I am curious - how xfce4-screensaver is related to lock screen? Does it run there? Just trying to learn.

My current understanding is that lock screen is handled by lightdm/sleek-greeter. But even though I have Display management disabled in Power Options and light-locker removed from the system, something still shuts off the monitor while machine is locked, and I suspect this is the reason for at least some of my problems.

EDIT: found docs about screensaver, reading.

Last edited by The Iron Wolf (2025-09-16 21:43:20)

eriefisher · 2025-09-16 21:45:38

Xfce4-screen saver can also lock the screen if thats what you want. Or not.

Where did you switch the locking you mentioned earlier?

lock using /usr/bin/dm-tool switch-to-greeter

This could also be

dm-tool lock

The Iron Wolf · 2025-09-16 21:57:05

eriefisher wrote:

Xfce4-screen saver can also lock the screen if thats what you want. Or not.
Where did you switch the locking you mentioned earlier?
lock using /usr/bin/dm-tool switch-to-greeter
This could also be
dm-tool lock

I have keyboard shortcut for screen lock, and originally in Mint it had light-locker command there. I read on this forum suggestions that light-locker causes black screen problem, and I removed it a while ago, but black screen still happens sometimes, and it happens reproducibly if I lock with no windows opened.

I am quite confused between all those components. It sounds that I may not need lightdm at all, and instead use xfce4-screensaver. If so, will I be able to stilll have same login screen UI (sleek-greeter?), which I like?

Last edited by The Iron Wolf (2025-09-16 22:02:37)

eriefisher · 2025-09-16 22:08:07

Lightdm is your login manager Light-locker is the screen locker. xfce4-screensaver can take care of the screen lock for you. light-lock have been problematic for years now. Unfortunately it's still a recommend for xfce4 packages, at least with Debian anyway.

If you want a graphical login manager keep Lightdm. You could also use GDM, KDM, SDDM............ Lightdm works just fine though. You can also login with startx/xinitrc. What greeter are you using?

The Iron Wolf · 2025-09-16 22:17:51

eriefisher wrote:

Lightdm is your login manager Light-locker is the screen locker. xfce4-screensaver can take care of the screen lock for you. light-lock have been problematic for years now. Unfortunately it's still a recommend for xfce4 packages, at least with Debian anyway.
If you want a graphical login manager keep Lightdm. You could also use GDM, KDM, SDDM............ Lightdm works just fine though. You can also login with startx/xinitrc. What greeter are you using?

I removed light-locker from my system a while ago. So, occassional black screen with mouse cursor is not caused by that, it is something else.

I believe, I am using slick-greeter for greeter. This is what I got with Mint 22.1 Xfce. I tried some other login screens (I don't remember the details), but they are just a bit too much 90s vibe even for me smile

Let's zoom on one thing. If I have Display management/Suspend disabled in Xfce Power Manager, which component turns screen off while system is locked? Is it lightdm? I am asking, because even though I doubt that is the reason for black screen (see my first post if curious), I have another problem - on resume from lock Firefox crashes, and I suspect it has to do with some sleep/suspend state, and that stuff is problematic even on Windows.

Last edited by The Iron Wolf (2025-09-16 22:18:39)

eriefisher · 2025-09-16 22:30:12

If you have sleep/suspend shut off then it shouldn't have an effect. Likely just hardware blanking the screen. It's possible that the desktop is crashing. Look into the .xsession-errors and .xsession-errors.old if after a restart.

The Iron Wolf · 2025-09-16 22:42:00

eriefisher wrote:

If you have sleep/suspend shut off then it shouldn't have an effect. Likely just hardware blanking the screen. It's possible that the desktop is crashing. Look into the .xsession-errors and .xsession-errors.old if after a restart.

Thanks for all your help so far. Will update this thread if I figure anything out.

Added later 14 h 57 min 15 s:
So, some update from my side. At least the reproducible black screen problem seems to get fixed by adjusting vblank setting mentioned here: https://forum.xfce.org/viewtopic.php?id=13233 Right under my nose smile

I still had black screen happen once, when my screen got blanked based on time set in Power Manager. After unblanking, black screen and cursor.

Now, I am trying to understand how to configure the time it takes for slick-greeter to turn off the screen after locking (and how to configure what it does, blank, suspend or turn off). But, this is more of a Mint issue, not Xfce I guess smile

Gonna resolve this thread after a while. Just want to make sure vblank xpresent actually is usable.

Last edited by The Iron Wolf (2025-09-17 13:40:56)

The Iron Wolf · 2025-09-18 02:17:55

For the screen locker timeout configuration, this worked perfectly: https://askubuntu.com/a/1104341/2330510 One caveat - mistakes in this can prevent booting, so be warned.

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#1 2025-09-16 20:24:10

[SOLVED] Black screen with mouse cursor on resume from lock

#2 2025-09-16 21:20:12

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#3 2025-09-16 21:22:19

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#4 2025-09-16 21:26:04

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#5 2025-09-16 21:37:08

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#6 2025-09-16 21:45:38

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#7 2025-09-16 21:57:05

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#8 2025-09-16 22:08:07

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#9 2025-09-16 22:17:51

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#10 2025-09-16 22:30:12

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#11 2025-09-16 22:42:00

Re: [SOLVED] Black screen with mouse cursor on resume from lock

#12 2025-09-18 02:17:55

Re: [SOLVED] Black screen with mouse cursor on resume from lock

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