Hi Simon, Thanks for responding quickly. I can see your viewpoint here. I think given what you've said, the better choice would be to put someone in this situation on KDE Wayland. They would at least get the desktop they expect, rather than try to figure out why they're back in Gnome. To me, that would be the least surprising thing to happen.
In my case, the machine was originally a Gnome Ubuntu installation back around 18.04. I've upgraded it several times, and eventually switched to KDE because Gnome had broken focus-follows-mouse with no sign of planning to fix it. Sigh. The fact that X11 support is going away means I'm stuck between Gnome with broken focus-follows-mouse, KDE with zombie X11, or KDE with Wayland and non-working session support. Thanks Jerry On Fri, Oct 16, 2026 at 4:25 AM Simon Johnsson <[email protected]> wrote: > Hey there! Thanks for the very detailed bug report Jerry, it really > helped me get a picture of the bug quickly. > > I think this situation is a bit complex, and I'm hesitant to make a > quirk for it. Let me share my thoughts: > > For this to happen IIUC, the system needs to have both GNOME and KDE > Plasma installed. If this was a Kubuntu only system without GNOME, then > the system would correctly migrate Plasma from X11 to Wayland (which is > the new default), and SDDM would pick Plasma correctly. > > Secondly, this system also has `ubuntu-desktop` installed, and thus the > upgrader is currently treating it as a normal Ubuntu Desktop system > where GNOME is the default. Thus landing in GNOME post-upgrade is not > *that* unexpected. In this case, I would refer users that prefer KDE to > Kubuntu instead. > > Finally, as of KDE Plasma 6.8, support for X11 has been dropped > (Resolute provides 6.6). Essentially this means that any compositor bug- > fixes made upstream will only apply to Wayland. For users of an LTS, I > would prefer for them to get the best supported alternative by default. > > In short: I don't think there are any bugs here. > * KDE migrated (correctly) to Wayland > * The system had GNOME installed as well > * SDDM picked the default session (GNOME) on Ubuntu Desktop > > Based on this, please let me know what you think. > > All the best, > Simon > > ** Changed in: ubuntu-release-upgrader (Ubuntu) > Status: New => Opinion > > -- > You received this bug notification because you are subscribed to the bug > report. > https://bugs.launchpad.net/bugs/2171038 > > Title: > Upgrade 24.04 -> 26.04 silently drops Plasma X11 session; SDDM falls > back to GNOME > > Status in meta-kde package in Ubuntu: > New > Status in ubuntu-release-upgrader package in Ubuntu: > Opinion > > Bug description: > 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). > > To manage notifications about this bug go to: > > https://bugs.launchpad.net/ubuntu/+source/meta-kde/+bug/2171038/+subscriptions > > -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2171038 Title: Upgrade 24.04 -> 26.04 silently drops Plasma X11 session; SDDM falls back to GNOME To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/meta-kde/+bug/2171038/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
