Public bug reported:
Description:
After upgrading from Ubuntu 24.04 to 26.04 with do-release-upgrade, a user
whose last session was Plasma (X11) cannot log back into it. The upgrade does
not install plasma-session-x11, so /usr/share/xsessions/plasma.desktop is gone
(the whole /usr/share/xsessions/ directory is gone). SDDM's remembered session
no longer exists, and it silently falls back to the first session
alphabetically. On this machine that was GNOME Classic (Wayland). The user is
not warned that their desktop session was removed.
Cause:
In 26.04 the Plasma X11 session was split into a separate package,
plasma-session-x11. kde-plasma-desktop 5:166ubuntu2 has
Depends: plasma-session-wayland (>= 4:6.5.4) | plasma-session-x11 (>=
4:6.5.4)
apt satisfies the alternative with the first option (Wayland), so
plasma-session-x11 is never installed on upgrade, even though the user was
actively using the X11 session before the upgrade. kwin-x11 *is* kept/upgraded
(4:6.6.4-0ubuntu1), so the X11 stack is present; only the session package is
missing.
Steps to reproduce:
1. Ubuntu 24.04 with Kubuntu/Plasma installed (also GNOME, from ubuntu-desktop),
using SDDM and logging into "Plasma (X11)".
2. do-release-upgrade to 26.04.
3. Reboot and log in at SDDM.
Expected:
The Plasma X11 session is still available and preselected (e.g. the upgrader
installs plasma-session-x11 when the X11 session was in use, or at minimum
warns that the X11 session will no longer be available).
Actual:
No X11 sessions exist. SDDM preselects GNOME Classic. The user has to diagnose
the problem and run "apt install plasma-session-x11" manually (or switch to
Plasma Wayland).
Evidence:
- Before upgrade (journal, 2026-10-15 19:03):
sddm: Session "/usr/share/xsessions/plasma.desktop" selected, command:
"/usr/bin/startplasma-x11"
- After upgrade (2026-10-15 23:26):
sddm: Session "/usr/share/wayland-sessions/gnome-classic.desktop" selected
- apt-cache policy plasma-session-x11: Installed: (none), Candidate:
4:6.6.6-0ubuntu0.1
Versions:
ubuntu-release-upgrader-core 1:26.04.27
kde-plasma-desktop 5:166ubuntu2
plasma-workspace 4:6.6.6-0ubuntu0.1
plasma-session-wayland 4:6.6.6-0ubuntu0.1
kwin-x11 4:6.6.4-0ubuntu1
sddm 0.21.0+git20250502.4fe234b-2ubuntu3
Suggested fix:
Add a release-upgrader quirk that installs plasma-session-x11 when
plasma-workspace was installed on the source release (the noble
plasma-workspace shipped the X11 session), or reorder/strengthen the
dependency so existing X11 users keep their session. Related:
LP #2127248 (upgrade removes X.org packages with MATE).
** Affects: meta-kde (Ubuntu)
Importance: Undecided
Status: New
** Affects: ubuntu-release-upgrader (Ubuntu)
Importance: Undecided
Status: New
** Tags: dist-upgrade resolute
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https://bugs.launchpad.net/bugs/2171038
Title:
Upgrade 24.04 -> 26.04 silently drops Plasma X11 session; SDDM falls
back to GNOME
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