Login screen flashes

When I go to login when turning on the computer, the login screen flashes. It only blinks in the username, place for password, and language gaps and desktops, It blinks between black and its original color, any solution?

To help, we’d firstly need to know your release of Lubuntu, and secondly we’ll likely need some details of your video card.

To get details of your video card, I’d suggest using the command

sudo lshw -C video

which will list-hardware of class video.

I have the same issue…not sure if I need to open a new thread or if its ok to add to this one? I am running Lubuntu 20.04. When I get to the login screen, 2 or 3 boxes are flashing, including my userid and the Language box at the top of screen. Is there a way to keep these from flashing?
Output from lshw -C video
description: VGA compatible controller
product: G72 [GeForce 7300 LE]
vendor: NVIDIA Corporation
physical id: 0
bus info: pci@0000:01:00.0
version: a1
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
configuration: driver=nouveau latency=0
resources: irq:29 memory:dd000000-ddffffff memory:c0000000-cfffffff memory:de000000-deffffff memory:c0000-dffff

Since the description sounds like the same thing (and since the OP never responded anyways), we might as well use this thread.

Any chance you can provide a video of this?

I’ve never had a problem with the standard open source driver (nouveau), but you may want to consider using the closed source ones.

@vbdanl Your description sounds like the issue I try to describe in bug report

I also had the issue on a i386 box long ago (prior cycle, but i386 was being dropped and I couldn’t reproduce in amd64 not having a like card)

I didn’t try the closed source drivers (I only used the box for QA-test installs)


i’m not too good at getting videos from my phone to the pc, but here is a link that should work… https://photos.app.goo.gl/NiLdyTDbdCpo3t2L9


wxl did you see the video?

The video looks like what my bug report is about;; with the minor exception of when it flashes black on the d960 there are no characters visible in the background. Same areas of the screen just I saw pure black (I provided photo only during the black flash stage).

I didn’t try, but autologin will skip this login window (if you’re in a position to be able to autologin). Because I was using that box primarily for install QA-tests, as I knew the box was impacted by that bug I’d often opt for doing autologin tests on it to skip re-reporting that issue.

If you can’t autologin, switching sddm to another DM/greeter maybe another option. If you’re not familiar with what I mean or would prefer me to try this first, please just ask.

The test box that experienced this issue
dell [optiplex] 990 (i7-2600, 16gb, nvidia geforce gt 6600 gt)


Same problem with NVIDIA GeForce Go 7400

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Because of another r.pi question, I booted a groovy system (amd64) and added xdm and made it default (instead of sddm). No issues. Yes the greeter looks like old Ubuntu, but it works.

It was done on a different box (different nvidia that doesn’t suffer from this issue), but I suspect it’ll work too for boxes where sddm flashes.


Sorry for no answer in a while but Thanks for posting the bug report @guiverc

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Kubuntu uses SDDM, too. I wonder if any of their greeters are problematic.

@wxl I never installed Kubuntu on the d960 (not that I recall anyway; this nvidia issue), however

on dell [optiplex] 755 (c2d-e6850, 5gb, amd/ati radeon rv516/x1300/x1550) does impact Kubuntu & other greeters selected from Kubuntu. It contains Lubuntu with kubuntu-desktop added, where I tried various sddm greeters (easily added within Plasma) and a number are impacted (somewhat differently). There is no mention of it in that bug report, and I don’t know if the Kubuntu default greeter has an issue; if I tried it I don’t recall.

ps: If you want me to do some testing on the d960, it’s currently still in my possession.

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@guiverc yeah I think it’s worth investigating further.

I just installed hirsute on the d960 with intention of starting to explore this… The effect is different to any groovy install, which maybe is a clue as to package anyway.

I’ll run out of time today, but my current purpose is to find a solution useful for users to mitigate this issue…

I tried each of

sddm-theme-debian-elarun - 'Debian Elarun' Theme for SDDM X11 display manager
sddm-theme-debian-maui - 'Debian Maui' theme for SDDM X11 display manager
sddm-theme-elarun - 'Elarun' Theme for SDDM X11 display manager
sddm-theme-lubuntu - Lubuntu theme for SDDM X11 display manager
sddm-theme-maldives - 'Maldives' theme for SDDM X11 display manager
sddm-theme-maui - 'Maui' theme for SDDM X11 display manager
sddm-theme-maya - 'Maya' theme for SDDM X11 display manager

and it was the same (flashing effect) for each theme (I skipped trying sddm-theme-breeze as it was going to pull in a lot of KF5 etc, I can’t see why it would be different, let me know if it’s worth trying)

I added & made default xdm and the login flashing disappeared.

This however had the effect of changing the theme used by the panel (I noticed it too on hp dc7700). I don’t consider this an issue though; they are easily changed back in Appearances. Changes are

– sddm

  • qt style - breeze
  • lxqt-theme - Lubuntu Arc

– xdm

  • qt style - fusion
  • lxqt-theme - frost
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Kubuntu I think does use sddm-theme-breeze. It unfortunately depends on Plasma stuff, which is why it’s got all the depends. I’m not sure why. It might be good to try it out, honestly.

I added sddm-theme-breeze and rebooted, yuk! (I had forgotten to perform the sudo update-alternatives --config sddm-ubuntu-theme step but sddm had been changed by the additional of a virtual keyboard) making it harder to use.

I’ve seen this before (semi-recently with dual screens) and recalled the on-screen keyboard appearing on secondary display, but it booted with keyboard drawn on black background, on mouse movement etc it would flash between black, on-screen keyboard (using 2/3rds of single display) & background… yuk

If a user watched the display, they’d have trouble being able to login.

sddm is still working, if I close my eyes & login as I’d expect it to operate, I’m logged in, but visually it’s a mess & unusable on that box.

The behavior is very familiar though, I added kubuntu-desktop to my Lubuntu focal installs on d755-5 (mentioned 4 messages up, AMD and flashing sddm; lp 1865837) and that box has only single display and it had the same behavior if I recall correctly. (it was also added to hp8200 install which has the two displays)

Finally I performed the sudo update-alternatives --config sddm-ubuntu-theme to make the ‘new’ breeze default, and on reboot it hung before eventual shutdown…errors?

sddm didn’t appear again. The GUI session now has a large pointer, which I can move around with the mouse, but nothing more.

I can fix this currently by changing the theme to something else, but with the virtual keyboard appearing on all themes now, they’re all rather annoying…

I’ve taken some photos of messages I see on screen (sddm-greeter & nouveau) but my phone is being annoying (no messages in dmesg or journalctl which I could easily paste; & /var/log/sddm.log is empty). Most messages appear during shutdown which was ultra slow with breeze the default.

Switching to another theme and shutdown returns to normal, messages gone (just virtual terminal remains which isn’t helpful).

The one message I get on text terminal (with breeze active) is
[ 120.676863] nouveau 0000:01:00.0: DRM: GPU lockup - switching to software fbcon
written after the “Optiplex990 login:”

Either a requirement is missing (package error) or we’re missing something in config??

– links to photos

FYI: I booted Kubuntu hirsute daily (yesterday) for a live test, and logged out (so as to get to sddm).

sddm appears static with no flashing at the login screen. However if left to timeout (when it removes the username/password box), flashing is evident as that is removed from the screen, and on the user (me) causing the username/password box to be re-displayed, again flashing… The flashing there felt different as it wasn’t cyclic (like time based as it appears in Lubuntu) but related to graphic glitches.

To me that session matched this bug which was originally filed on a different 18.04.5/i386 nvidia box (esp. given issues once logged in) so it’s noted in that bug report.

I’m hearing (please correct me if I’m wrong) but it sounds like this affects NVIDIA GeForce 6 and 7 series cards only with the open source driver.

Do the proprietary drivers help?

@wzl I had a play with this today, but failed.

The graphics drivers the d990 (geforce gt 6600) seems to need are nvidia-graphics-drivers-304 that are no longer supported (outside of xenial)

Note: I’m not good with video drivers.

The hp dx6120 [winfast clone of nvidia 7600gt] where I also experienced it, only had it appear on 5.3 kernel (eoan), but as that box was only ever used with QA installs up to alpha of disco/19.04 (then newer 18.04 ISOs) I ignored it [i386].