Xorg aborts with ../../../../dix/privates.c:384: dixRegisterPrivateKey: Assertion `!global_keys[type].created' failed.

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

Also tracking in:

https://gitlab.freedesktop.org/xorg/xserver/issues/939

and

https://errors.ubuntu.com/problem/e1038a75ca80364c2c74351221e2ad5ec5d00916

See also bug 1792932

1792932 was fixed upstream in 1.20.2, so this is something different

Could this be a regression of Bug #1792932 ?

I am using nvidia-driver-460 version 460.39-0ubuntu0.20.04.1.

    xserver-common version 2:1.20.9-2ubuntu1.2~20.04.1
    xserver-xephyr version 2:1.20.9-2ubuntu1.2~20.04.1
    xserver-xorg version 1:7.7+19ubuntu14
    xserver-xorg-core version 2:1.20.9-2ubuntu1.2~20.04.1

The GDM screen would only appear after typing Ctrl+Alt+F2 followed by Ctrl+Alt+F1.

The following seems to have fixed the issue for me, and the GDM screen now appears without having to resort to the above "trick".

 1. Edit the file /lib/udev/rules.d/61-gdm.rules.

    sudo nano /lib/udev/rules.d/61-gdm.rules

    The original file looks like this:

    # disable Wayland on Hi1710 chipsets
    ATTR{vendor}=="0x19e5", ATTR{device}=="0x1711", RUN+="/usr/lib/gdm3/gdm-disable-wayland"
    # disable Wayland when using the proprietary nvidia driver
    DRIVER=="nvidia", RUN+="/usr/lib/gdm3/gdm-disable-wayland"

    Comment all of the lines as shown:

    # disable Wayland on Hi1710 chipsets
    # ATTR{vendor}=="0x19e5", ATTR{device}=="0x1711", RUN+="/usr/lib/gdm3/gdm-disable-wayland"
    # disable Wayland when using the proprietary nvidia driver
    # DRIVER=="nvidia", RUN+="/usr/lib/gdm3/gdm-disable-wayland"

    Type Ctrl+X to exit, then Y, and then Enter to save the file.

 2. Ensure that the Wayland is not disabled in GDM.

    sudo nano /etc/gdm3/custom.conf

    Comment the "WaylandEnable" line, if it is not already commented, as shown:

    # WaylandEnable=false

    Type Ctrl+X to exit. If you made changes, type Y, and then Enter to save the file.

 3. Finally, reboot.

Explanation

The /lib/udev/rules.d/61-gdm.rules file is supposed to prevent GDM from displaying the Wayland session option when the NVIDIA proprietary drivers are installed, since NVIDIA does not support Wayland.

However, in Ubuntu 20.04, there seems to be another redundant mechanism or rule that also prevents GDM from displaying the Wayland session option. I suspect this, because even after making the above change, the Wayland session option is still not displayed in GDM. (Setting WaylandEnable=true in /etc/gdm3/custom.conf has no effect).

Therefore, I have a hunch that there are two conflicting rules, and disabling one of the rules (i.e. /lib/udev/rules.d/61-gdm.rules) seems to remove the conflict.

Here is the journalctl boot log before making the above changes. You can see there is an error loading the "fb" module.

/usr/lib/gdm3/gdm-x-session[964]: (II) Loading sub module "fb"
/usr/lib/gdm3/gdm-x-session[964]: (II) LoadModule: "fb"
/usr/lib/gdm3/gdm-x-session[964]: (II) Loading /usr/lib/xorg/modules/libfb.so
/usr/lib/gdm3/gdm-x-session[964]: (II) Module fb: vendor="X.Org Foundation"
/usr/lib/gdm3/gdm-x-session[964]: compiled for 1.20.9, module version = 1.0.0
/usr/lib/gdm3/gdm-x-session[964]: ABI class: X.Org ANSI C Emulation, version 0.4
/usr/lib/gdm3/gdm-x-session[964]: Xorg: ../../../../dix/privates.c:384: dixRegisterPrivateKey: Assertion `!global_keys[type].created' failed.
/usr/lib/gdm3/gdm-x-session[964]: (EE)
/usr/lib/gdm3/gdm-x-session[964]: (EE) Backtrace:
/usr/lib/gdm3/gdm-x-session[964]: (EE) 0: /usr/lib/xorg/Xorg (OsLookupColor+0x13c) [0x55936e23a59c]
/usr/lib/gdm3/gdm-x-...

It appears this is the top crasher of Xorg in 20.04 right now:

https://errors.ubuntu.com/?release=Ubuntu%2020.04&package=xorg-server&period=month

Unfortunately bug 1863689 prevents us from using the link of the top crasher:

https://errors.ubuntu.com/bucket/?id=/usr/lib/xorg/Xorg%3AXorg%3A%20../../../../dix/privates.c%3A384%3A%20dixRegisterPrivateKey%3A%20Assertion%20%60%21global_keys%5Btype%5D.created%27%27%20failed.

I have the same issue but I found a different workaround without having to resort to the Ctrl-Alt-F2 then back to Ctrl-Alt-F1 trick for the login screen to appear :

https://askubuntu.com/questions/1389869/multiple-monitors-black-screen-with-blinking-cursor-and-gnome-desktop-login-on

I have to ensure that the "Primary Display" is set to the laptop monitor instead of the external monitor connected via HDMI.

No crashes reported since Ubuntu 21.04 so consider it fixed.