[SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

matiasg · 2026-04-05 15:22:52

Trying to move from lightdm to gdm here.

When doing a systemctl start gdm.service I only get a blank screen.
The output of journalctl -u gdm has messages like this every second until the "maximum number" at the bottom shows up.

Apr 05 11:42:35 yogur gdm-launch-environment][3492]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: GdmDisplay: Session never registered, failing
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:36 yogur gdm[1226]: Gdm: Child process -3516 was already dead.
Apr 05 11:42:36 yogur gdm[1226]: Gdm: GdmDisplay: Session never registered, failing
Apr 05 11:42:36 yogur gdm[1226]: Gdm: Child process -3516 was already dead.
Apr 05 11:42:36 yogur gdm-launch-environment][3749]: Gdm: gdm_settings_get_value: assertion 'settings->backends != NULL' failed
Apr 05 11:42:37 yogur gdm[1226]: Gdm: GdmDisplay: Session never registered, failing
Apr 05 11:42:37 yogur gdm[1226]: Gdm: GdmLocalDisplayFactory: maximum number of X display failures reached: check X server log for errors

AFAIU, this should run wayland (the "check X server log" looks suspicious).
I can use lightdm or sddm, but I want to switch to gdm.

gdm is 49.2-1:

$ pacman -Qi gdm                                                                                                                                                              [12:14:08]
Name            : gdm
Version         : 49.2-1
Description     : Display manager and login screen
Architecture    : x86_64
URL             : https://gitlab.gnome.org/GNOME/gdm
Licenses        : GPL-2.0-or-later
Groups          : gnome
Provides        : None
Depends On      : accountsservice  audit  bash  gcc-libs  gdk-pixbuf2  glib2  glibc  gnome-session  gnome-shell  gtk3  json-glib  keyutils  libcanberra  libgudev  libx11  libxau  libxcb
                  libxdmcp  pam  systemd  systemd-libs  upower  libgdm
Optional Deps   : fprintd: fingerprint authentication
Required By     : gdm-settings
Optional For    : None
Conflicts With  : None
Replaces        : None
Installed Size  : 5.12 MiB
Packager        : Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Build Date      : Mon 24 Nov 2025 10:07:16 PM -03
Install Date    : Sun 05 Apr 2026 11:54:41 AM -03
Install Reason  : Explicitly installed
Install Script  : No
Validated By    : Signature

Last edited by matiasg (Yesterday 02:45:40)

seth · 2026-04-05 17:44:22

Did you try to https://wiki.archlinux.org/title/GDM#Use_Xorg_backend ?
This won't work, gnome no longer supports X11 w/ 49

Otherwise please post your complete system journal for the boot:

sudo journalctl -b | nc termbin.com 9999

matiasg · 2026-04-05 18:18:01

I don't want to use X anymore. I prefer to use wayland. But somehow something starts X. I don't know how to prevent this.

The output of journalctl -b is here: https://termbin.com/t4sn

seth · 2026-04-05 18:36:10

That journal is from a boot using lightdm, that's not relevant.
You can access older boots, eg.

sudo journalctl -b -1 | nc termbin.com 9999

for the previous (-1) one.

matiasg · 2026-04-06 02:01:40

Right, sorry. Here's the journalctl with gdm: https://termbin.com/sl5o

seth · 2026-04-06 08:48:36

Apr 05 22:57:11 yogur systemd-logind[801]: New session '1' of user 'gdm-greeter' with class 'greeter' and type 'wayland'.
Apr 05 22:57:11 yogur systemd[1]: Created slice User Slice of UID 60578.
Apr 05 22:57:11 yogur systemd[1]: Starting User Runtime Directory /run/user/60578...
Apr 05 22:57:11 yogur systemd[1]: sys-devices-virtual-misc-rfkill.device: Failed to enqueue SYSTEMD_WANTS job, ignoring: Unit systemd-rfkill.socket is masked.
Apr 05 22:57:11 yogur systemd[1]: Finished User Runtime Directory /run/user/60578.
Apr 05 22:57:11 yogur systemd[1]: Starting User Manager for UID 60578...
Apr 05 22:57:11 yogur unix_chkpwd[974]: could not obtain user info (gdm-greeter)
Apr 05 22:57:11 yogur (systemd)[968]: PAM PAM failed: Authentication service cannot retrieve authentication info
Apr 05 22:57:11 yogur (systemd)[968]: user@60578.service: Failed to set up PAM session: Operation not permitted
Apr 05 22:57:11 yogur (systemd)[968]: user@60578.service: Failed at step PAM spawning /usr/lib/systemd/systemd: Operation not permitted
Apr 05 22:57:11 yogur systemd[1]: user@60578.service: Main process exited, code=exited, status=224/PAM
Apr 05 22:57:11 yogur systemd[1]: user@60578.service: Failed with result 'exit-code'.
Apr 05 22:57:11 yogur systemd[1]: Failed to start User Manager for UID 60578.

https://bbs.archlinux.org/viewtopic.php … 5#p2263495

Arch Linux

#1 2026-04-05 15:22:52

[SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

#2 2026-04-05 17:44:22

Re: [SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

#3 2026-04-05 18:18:01

Re: [SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

#4 2026-04-05 18:36:10

Re: [SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

#5 2026-04-06 02:01:40

Re: [SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

#6 2026-04-06 08:48:36

Re: [SOLVED] gdm fails with assertion 'settings->backends != NULL' failed

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