Public bug reported:
Summary by AI:
After upgrading Ubuntu 24.04.4 LTS to Ubuntu 26.04 LTS, GDM did not
display the normal login screen.
Instead, it started a complete Ubuntu GNOME desktop session under the
dynamic gdm-greeter user. The desktop included GNOME Shell, Nautilus,
Settings, Terminal, GNOME Software, Ubuntu Dock, and other normal
desktop components.
The home directory of this session was:
/run/gdm3/home/gdm-greeter
The dynamic gdm-greeter user had UID 60578.
Attempting to log in as my normal user resulted in a message similar to:
Account temporarily unavailable
The local user account itself was valid and fully functional from TTY
and SSH.
System information:
Ubuntu 26.04 LTS (Resolute Raccoon)
Upgraded from Ubuntu 24.04.4 LTS
gdm3: 50.0-0ubuntu1
ubuntu-session: 50.0-0ubuntu3.2
gnome-shell: 50.1-0ubuntu1.1
kernel: 7.0.0-28-generic
The upgrade was performed using:
sudo do-release-upgrade -d
The following components were verified and appeared to be working
correctly:
- The normal user account was not locked or expired.
- pamtester successfully completed authentication, account management,
open_session, and close_session for the gdm-password PAM profile.
- systemd-logind, systemd-user-sessions, and accounts-daemon were active.
- The user's home directory ownership and permissions were correct.
- The filesystem and mount configuration were correct.
- GDM, GNOME Shell, ubuntu-session, and related packages were reinstalled.
- There were no failed systemd units.
The process list showed that GDM started the normal Ubuntu session under
gdm-greeter:
/usr/libexec/gnome-session-init-worker ubuntu
/usr/libexec/gnome-session-service --session=ubuntu
/usr/bin/gnome-shell --mode=ubuntu
The journal also showed:
Starting GNOME session target: [email protected]
Reached target [email protected]
GNOME Shell started
Registering display with GDM
The GDM greeter desktop file contained:
/usr/share/gdm/greeter/wayland-sessions/gnome-greeter.desktop
[Desktop Entry]
Name=GNOME Greeter
Comment=The default GNOME Greeter session
Exec=gnome-session
TryExec=gnome-session
Type=Application
DesktopNames=GNOME-Greeter:GNOME
NoDisplay=true
X-GDM-SessionRegisters=true
X-GDM-CanRunHeadless=true
X-Ubuntu-Gettext-Domain=gdm
It appears that the generic command:
Exec=gnome-session
selected the default Ubuntu desktop session instead of the dedicated GDM
login session.
Changing the Exec line to:
Exec=gnome-session --session=gnome-login
and restarting GDM immediately restored the correct graphical login
screen:
sudo systemctl restart gdm.service
The target session file exists and is valid:
/usr/share/gnome-session/sessions/gnome-login.session
[GNOME Session]
Name=GNOME Display Manager
Kiosk=true
Expected result:
GDM should start the dedicated gnome-login session and display the graphical
login screen.
Actual result:
GDM starts the full default Ubuntu desktop session as the dynamic
gdm-greeter user, leaving the user unable to log in normally.
Workaround:
Modify:
/usr/share/gdm/greeter/wayland-sessions/gnome-greeter.desktop
from:
Exec=gnome-session
to:
Exec=gnome-session --session=gnome-login
and restart GDM.
This appears to be a packaging or integration regression between gdm3,
gnome-session, and ubuntu-session. It is potentially security-relevant because
a full desktop environment, including applications such as Terminal, Files,
Settings, and GNOME Software, becomes available in the pre-login greeter
environment.
Idk if its security relevant, AI thinks so, I dont, so I wont flag it. Cheers.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: gdm3 50.0-0ubuntu1 [modified:
usr/share/gdm/greeter/wayland-sessions/gnome-greeter.desktop]
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
CasperMD5CheckMismatches: ./preseed/ubuntu.seed
./pool/restricted/s/sl-modem/sl-modem-daemon_2.9.11~20110321-19ubuntu0.2_i386.deb
./pool/restricted/n/nvidia-graphics-drivers-580/xserver-xorg-video-nvidia-580_580.126.09-0ubuntu0.24.04.1_amd64.deb
./pool/restricted/n/nvidia-graphics-drivers-580/nvidia-kernel-source-580_580.126.09-0ubuntu0.24.04.1_amd64.deb
./pool/restricted/n/nvidia-graphics-drivers-580/nvidia-utils-580_580.126.09-0ubuntu0.24.04.1_amd64.deb
CasperMD5CheckResult: fail
Date: Tue Jul 21 14:34:47 2026
InstallationDate: Installed on 2026-03-03 (140 days ago)
InstallationMedia: Ubuntu 24.04.4 LTS "Noble Numbat" - Release amd64 (20260210)
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
SourcePackage: gdm3
UpgradeStatus: Upgraded to resolute on 2026-07-21 (0 days ago)
** Affects: gdm3 (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute
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Desktop Bugs, which is subscribed to gdm3 in Ubuntu.
https://bugs.launchpad.net/bugs/2161431
Title:
GDM 50 starts a full Ubuntu desktop as gdm-greeter instead of the
login screen after upgrading from 24.04 to 26.04
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