This bug was fixed in the package gnome-session - 3.26.1-0ubuntu6
---------------
gnome-session (3.26.1-0ubuntu6) artful; urgency=medium
* Add symlinks in /usr/share/xsessions/:
- gnome.desktop -> gnome-xorg.desktop
- ubuntu.desktop -> ubuntu-xorg.desktop
In combination with a gdm3 patch, this ensures a proper fallback session
is selected by gdm when wayland is not enabled (LP: #1718446).
-- Olivier Tilloy <[email protected]> Fri, 13 Oct 2017
13:33:27 +0200
** Changed in: gnome-session (Ubuntu)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1718446
Title:
Ensure wayland -> xorg fallback to the corresponding session
Status in gdm:
Fix Released
Status in gdm3 package in Ubuntu:
Fix Released
Status in gnome-session package in Ubuntu:
Fix Released
Status in gdm3 source package in Artful:
Fix Released
Bug description:
[Impact]
Users upgrading to artful on a system that cannot run wayland may be
logged into an unexpected session at the next boot.
[Steps to reproduce]
1. On a system with wayland capability, log into the "Ubuntu" session.
2. Install gnome-session if it wasn't already installed (this adds two
sessions, "GNOME" and "GNOME on Xorg").
3. Disable wayland (uncomment WaylandEnable=false in /etc/gdm3/custom.conf)
and reboot.
Expected result: at the greeter, the "Ubuntu on Xorg" session is
selected by default (falling back from "Ubuntu" to "Ubuntu on Xorg").
Actual result: at the greeter, the "GNOME on Xorg" session is selected
by default.
[Fix]
The fix consists in using the default fallback mechanism in gdm3, i.e.
/usr/share/wayland-sessions/ubuntu.desktop falls back to
/usr/share/xsessions/ubuntu.desktop, adding corresponding "-xorg.desktop"
session files, and having gdm3 ignore them under wayland. This was discussed
and approved upstream (https://bugzilla.gnome.org/show_bug.cgi?id=788552).
The fix involves a distro-patch in gdm3 (already merged upstream, will go
away with the next release) and changes to the packaging of gnome-session
(added symlinks).
[Test Case]
see [Steps to reproduce]
[Regression Potential]
The gdm3 patch has been thoroughly tested and merged upstream. Since
this is C glib code, reviewers should carefully look for possible
memory leaks, as strings are being allocated.
If a package installs /usr/share/xsessions/foo-xorg.desktop without a
corresponding /usr/share/xsessions/foo.desktop, the session will be
ignored if wayland is disabled. It is however considered a standard
practice that foo-xorg is a fallback for foo, so it wouldn't make much
sense to have the former without the latter.
In case of a partial upgrade:
- only gdm3 upgraded: nothing user-visible should happen, as gdm will ignore
the foo-xorg session only if the corresponding foo session file exists
- only gnome-session upgraded: with wayland disabled, at the greeter the
user might see two sessions that are in fact the same thing: "Ubuntu" and
"Ubuntu on Xorg" (but logging into any of the two will work)
One minor gotcha with this patch: if, with wayland enabled, one intentionally
selects ubuntu-xorg, then disables wayland, then reboots, in the login screen
no session is selected in the dropdown (because gdm ignored ubuntu-xorg).
However this will still launch the ubuntu-xorg session by default (which
effectively is the same as the ubuntu session), so all is good (except for the
fact that no session appears selected in the dropdown). This has the advantage
of retaining the "ubuntu-xorg" session selected by the user if wayland is
re-enabled later, though.
This is a regression in the sense that no session is visually selected in the
dropdown, but it doesn't affect the default session selection.
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