GNOME will not start after upgrade: recovering the Wayland session

troubleshooting · linux published 05/2026

After the Debian 12 → 13 upgrade the login ends on a black screen and the session drops back to GDM. Diagnosis, the actual cause and a permanent fix.

Problem

After a standard apt full-upgrade from Debian 12 to 13 the screen goes black for a few seconds once the password is entered in GDM and the session returns to the login. The X11 fallback works, the Wayland session does not.

Symptoms

login loop only in the Wayland session, X11 starts fine
no error message in GDM
gnome-shell exits within 2 s of start with exit code 1

Environment

OS Debian 13 (trixie)

desktop GNOME 48, GDM, Wayland

GPU Intel Iris Xe, mesa 25.x

Diagnosis

The first step is the session log from the last failed start:

COMMAND

journalctl --user -b -u org.gnome.Shell@wayland.service

OUTPUT

gnome-shell[2114]: JS ERROR: Extension launcher@example
TypeError: Main.panel._leftBox is undefined
gnome-shell[2114]: Execution of main.js threw exception

NOTE The session log runs under the user — journalctl --user, not the system journal. That is the most common dead end.

Root cause

An incompatible GNOME extension installed per-user survived the upgrade and crashes the whole shell when the Wayland session starts. X11 is unaffected because the extension loads later there.

Fix

Disable extensions outside the session (from a TTY or the X11 fallback):

COMMAND

gsettings set org.gnome.shell disable-user-extensions true

The Wayland session then starts. Afterwards update and re-enable extensions one at a time; the incompatible one lives in ~/.local/share/gnome-shell/extensions.

WARNING Do not reinstall GDM or switch to X11 permanently — the problem is not in the display manager, and the X11 fallback is being phased out in Debian 13.

Notes and limits

The same pattern (extension → shell crash → login loop) applies to other distributions with GNOME 46+. The diagnostic procedure carries over.

Sources

GNOME Shell issue tracker — extension compatibility after a major upgrade ↗
Debian release notes: trixie, Desktop chapter ↗
Own verification, 18/05/2026, environment as above