xubuntu / bionic / nvidia-driver-390 can only be used by one user at a time

I can confirm the bug on Xubuntu 18.04.
My graphics card is an nVidia GeForce GTX 570 (GF110).

I tried with a fresh Ubuntu 18.04 (and not Xubuntu) and there's no bug.

So I think the issue is related to lightdm, which is used on Xubuntu and not Ubuntu.

The bug is not related to lightdm because it also occurs with gdm3.

I have several Linux boxes with graphic cards nVidia GTX 570, GTX 670 and Quadro K2000, and the problem appears on each one, with different resolutions for the second user and sometimes with a very slow rendering.

I analyzed the Xorg logs and found that for the second user, the ModulePath is incorrectly set to "/usr/lib/xorg/modules" instead of "/usr/lib/x86_64-linux-gnu/nvidia/xorg". Thus the nvidia modules are not found when the X server starts. Note that this problem does not occur for the first user...

So, here is a workaround for this problem:

1. Create an xorg.conf file for your nVidia device. All you have to do for this is to launch the command:

sudo nvidia-xconfig

This will create a file /etc/X11/xorg.conf.

2. Edit the created file /etc/X11/xorg.conf and add at the end the lines:

Section "Files"
 ModulePath "/usr/lib/x86_64-linux-gnu/nvidia/xorg"
 ModulePath "/usr/lib/xorg/modules"
EndSection

3. Save and restart the X server. Now, for the first and second user you should have the nvidia driver in use, with the correct resolution and fast rendering. You can check it using the command:

glxgears -info |grep NVIDIA

which should return the nvidia opengl version.

Note, there is also a problem of slow scrolling in the virtual console (Ctrl-Alt-F1). To solve this, edit /etc/default/grub and set the GRUB_CMDLINE_LINUX variable as:

GRUB_CMDLINE_LINUX="video=vesafb:mtrr:3,ywrap"

then do:

sudo update-grub

and reboot. Now, the scrolling speed in the virtual console should be very fast.

Status changed to 'Confirmed' because the bug affects multiple users.

Same issue with Xubuntu 18.10 Cosmic and nvidia-driver-415.

Fixed with:

Section "Files"
    ModulePath "/usr/lib/x86_64-linux-gnu/xorg"
    ModulePath "/usr/lib/xorg/modules"
EndSection

What should be done if everything in post #2 is set as directed, but on the following step...:
glxgears -info |grep NVIDIA

...the following is returned?:
X Error of failed request: BadValue (integer parameter out of range for operation)
  Major opcode of failed request: 154 (GLX)
  Minor opcode of failed request: 3 (X_GLXCreateContext)
  Value in failed request: 0x0
  Serial number of failed request: 31
  Current serial number in output stream: 32

NOTE: The workaround provided in post #2 above did in fact solve this issue for a few months on my setup until this morning when this problem started happening again.

My computers Specs:
CPU: Two Intel(R) Xeon(R) CPU E5-2687W v3 @ 3.10GHz
Mem: 64GB
OS: Xubuntu 18.04.2 LTS
Graphics: NVIDIA Quadro P6000
Software & Updates panel:
  [Ubuntu Software Tab]: (The following are checked)
  * Canonical-supported free and open-source software (main)
  * Community-maintained free and open-source software (universe)
  * Proprietary drivers for devices (restricted)
  * Software restricted by copyright or legal issues (multiverse)
  [Additional Drivers Tab]: (The following graphics driver is in use)
  * Using NVIDIA driver metapackage from nvidia-driver-390 (proprietary, tested)

If I'm remembering correctly this setup is currently utalizing some of the functionality provided by the proprietary drivers that can not be provided by the more generic Noveau driver. I can't quite remember what this is at the moment but I would prefer to stick with the proprietary driver if at all possible while solving this problem.

Please let me know if there are any other logs or information that I might be able to report in order to help verify or narrow down what is causing this issue to re-occur after the fix provided in step #2 has been applied.

Thanks.

Same issue with Xubuntu 18.04.3
Used workaround with "Files" section, but I had to use /usr/lib/x86_64-linux-gnu/nvidia-430 path.
/usr/lib/x86_64-linux-gnu/nvidia/xorg and /usr/lib/x86_64-linux-gnu/xorg do not exist in my system.

I just had this problem on a Mint-19.3 XFCE upgraded from 18.3. For me, the fix was:

* `sudo nvidia-xconfig`
* `sudo vi /etc/X11/xorg.conf`
The 'Section "Files"..EndSection' block already existed but was empty. I added this:
 Section "Files"
     ModulePath "/usr/lib/nvidia-340/xorg"
     ModulePath "/usr/lib/xorg/modules"
 EndSection
* Then `sudo systemctl restart lightdm.service` which logged me out of my sessions!

Drat, I meant to add this too:
Search keywords: linux mint switch user wrong resolution

Just to mention, I am having this bothersome issue also. My Ubuntu 18.04 is completely up to date. Does anyone know of a DM that works better? Cheers...