Bug#935194: xfce4-session: Xfce session fails to start when previously logged into GNOME
> I have no idea why SESSION_MANAGER is already set when you start Xfce
> the second time, but it looks like a bug in either gdm or gnome.
As I said, the variable SESSION_MANAGER will be set when you log into
GNOME (or GNOMEish desktop environments like Cinnamon or MATE). The
variable is added to the systemd manager environment block. You can
verify this by calling
systemctl --user show-environment | grep SESSION_MANAGER
The systemd manager environment block is persistent across subsequent
logins (not reboots), even when using different desktop environments.
This is implemented in /etc/X11/Xsession.d/95dbus_update-activation-env
As I said, I am not very familiar with all the details around the
SESSION_MANAGER variable, but it seems like it is only set by GNOMEish
desktop environments. Even Xfce itself doesn't set the variable. It only
checks the variable and fails to start if it is set, which is happening
> Just ignoring the fact that a manager might be running doesn't look sound.
> Can you get in touch with gnome and gdm people about this?
OK, adding firstname.lastname@example.org to CC.