Multiseat setup: black screen with cursor most of the time

Asked by Andy D.

I have a multiseat setup with 4 seats. Every time I boot, it seems random as to if a given seat will produce a login screen or not. If it doesn't, I get a black screen with a cursor I can move with the mouse. I've looked at the logs while I do a:

sudo systemctl stop lightdm
#Look at logs with cd /etc/; tail -fn0 Xorg.*.log lightdm/*.log
sudo systemctl start lighdm

In this specific case, seat0 didn't get a login screen, but seat1 did. The biggest difference I can see in the logs between the two seats is that /var/log/lightdm/seat1-greeter.log gets a lot of stuff and /var/log/lightdm gets very little. Besides that, I don't see any errors in any of the logs that are on seat0 (the one that didn't work) but not on seat1 (the one that worked).

Here is a screenshot showing these two logs side by side with differences highlighted (using meld).

https://paste.pics/96677091ecf69a7a948af79692282f79

My question: How in the world can I debug this if there aren't errors in the logs? I believe the greeter is having a problem starting sometimes, but how can I get more verbose info about what it's doing to help narrow down the problem space?

Thanks for your help.

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Launchpad Janitor (janitor) said :
#1

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#2

So things get expired if no one replies? that sucks.

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#3

poke.

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Launchpad Janitor (janitor) said :
#4

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#5

Hello? What does it take to get some help here?

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Manfred Hampl (m-hampl) said :
#6

For me there is not enough information in your question document that I could start working on it.
Which Ubuntu release are you running (output of "lsb_release -crid"), which kernel version ("uname -a")?
What do you call "multiseat setup"? Is that four different systems with (nearly) identical setup, or is that one system that is accessed remotely from four different workstations?

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#8

Hey thanks so much for your response! :-D

[andromodon@potens ~]$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 22.04 LTS
Release: 22.04
Codename: jammy
[andromodon@potens ~]$ uname -a
Linux potens 5.15.0-37-generic #39-Ubuntu SMP Wed Jun 1 19:16:45 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

I mean multiseat as in a system with several GPUs, keyboards, and mice where I use loginctl to attach each device to a specific seat so multiple users can use the same machine at the same time.

https://wiki.debian.org/Multi_Seat_Debian_HOWTO

Here's the script I use to set up multiseat at the moment.

[andromodon@potens ~]$ cat ~/bin/multiseatSetup
#!/bin/bash
set -x

#This is sort of a "document with code" thing.
#Sets up my multiseat setup from scratch using loginctl

#Clear any previous setup:
sudo loginctl flush-devices

# GPUS and sound cards:
sudo loginctl attach seat0 /sys/devices/pci0000:00/0000:00:01.3/0000:01:00.{0/drm/,1/sound/}card0
sudo loginctl attach seat1 /sys/devices/pci0000:20/0000:20:03.1/0000:21:00.0/drm/card1
#This is with the usb to the monitor connected in the usb3 slot just to the left of the top ethernet port
sudo loginctl attach seat1 /sys/devices/pci0000:00/0000:00:08.1/0000:03:00.3/usb1

#sudo loginctl attach seat2 /sys/devices/pci0000:40/0000:40:03.1/0000:4b:00.{0/drm/card3,1/sound/card4}
#sudo loginctl attach seat3 /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.{0/drm/card2,1/sound/card3}

sudo loginctl attach seatIgnore /sys/devices/pci0000:40/0000:40:03.1/0000:4b:00.0/drm/card3
sudo loginctl attach seatIgnore /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.0/drm/card2
sudo loginctl attach seatIgnore /sys/devices/pci0000:20/0000:20:03.1/0000:21:00.1/sound/card2
sudo loginctl attach seatIgnore /sys/devices/pci0000:20/0000:20:08.1/0000:23:00.4/sound/card3
sudo loginctl attach seatIgnore /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.1/sound/card4
sudo loginctl attach seatIgnore /sys/devices/pci0000:40/0000:40:03.1/0000:4b:00.1/sound/card5

# #Then reboot.
# sudo reboot

I'm just using two seats and rebooting multiple times until I happen to get lucky and get lightdm to successfully run on seat1. seat0 still ends up black with a cursor (lightdm did not finish loading), but I can work around it by ctrl-alt-F2 to a TTY and running startx from there. It's a sloppy work-around and it also won't work when I have more than 2 seats, since I can't go to other TTYs on seats other than seat0.

I think there's a race condition relating to lightdm that only shows up when there are multiple instances run at the same time (which is what's necessary during multiseat).

Anyway, it seems that lightdm is the go-to display manager for multiseat, and multiseat is super helpful for families, computer labs, etc. So it would be amazing if we can get it working again for everyone.

Feel free to let me know if you need anything else.

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Manfred Hampl (m-hampl) said :
#9

I am sorry, but I do not have any experience with such setup and I cannot help further.

The only remark that I can make is that the linked document is for Debian and not for Ubuntu. There may be differences between Debian and Ubuntu that interfere with your intentions.

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#10

Ok. Thanks anyways.

On Sat, Jun 18, 2022 at 9:46 PM Manfred Hampl -
<email address hidden>
<
<email address hidden>> wrote:

> Your question #701779 on unity-greeter in Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+source/unity-greeter/+question/701779
>
> Status: Open => Answered
>
> Manfred Hampl proposed the following answer:
> I am sorry, but I do not have any experience with such setup and I
> cannot help further.
>
> The only remark that I can make is that the linked document is for
> Debian and not for Ubuntu. There may be differences between Debian and
> Ubuntu that interfere with your intentions.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/ubuntu/+source/unity-greeter/+question/701779/+confirm?answer_id=8
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/ubuntu/+source/unity-greeter/+question/701779
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Launchpad Janitor (janitor) said :
#11

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

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Andy D. (0-launchpad-20-andromodon-spamgourmet-com) said :
#12

This is still very much an issue.

Can you help with this problem?

Provide an answer of your own, or ask Andy D. for more information if necessary.

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