KDE does not start when using lightdm

[Thomas Gebert]

When switching the displaymanager from sddm to lightdm, login fails due to misconfigured lightdm configuration file.

$ cat /usr/share/lightdm/lightdm.conf.d/40-kde-plasma-kf5.conf
[SeatDefaults]
user-session=kde-plasma-kf5

$ls /usr/share/xsessions/*
/usr/share/xsessions/plasma.desktop

#####

Changing /usr/share/lightdm/lightdm.conf.d/40-kde-plasma-kf5.conf to

$ cat /usr/share/lightdm/lightdm.conf.d/40-kde-plasma-kf5.conf
[SeatDefaults]
user-session=plasma

or renaming /usr/share/xsessions/plasma.desktop to /usr/share/xsessions/kde-plasma-kf5.desktop solves the issue.

#####

$ lsb_release -rd
Description: Ubuntu 16.04.1 LTS
Release: 16.04

$ apt-cache policy plasma-workspace
plasma-workspace:
  Installed: 4:5.5.5.2-0ubuntu1
  Candidate: 4:5.5.5.2-0ubuntu1
  Version table:
 *** 4:5.5.5.2-0ubuntu1 500
        500 http://de.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

#####

[Simon Quigley (tsimonq2)]

Hello, thanks for reporting this, but in order to properly triage this, I need more information.

How exactly did you install LightDM? Did you remove SDDM after installing LightDM?

And most importantly, is this still an issue for you?

This looks awfully similar to a bug I've seen before, so for now I'm marking as Incomplete, but if this still affects you, please change it back to New.

Thanks for making Kubuntu better! :)

[Thomas Gebert (thomaswood)]

Hi Simon,

> How exactly did you install LightDM? Did you remove SDDM after installing LightDM?
I did not remove SDDM after the installation of LightDM and just ran the configuration and set LightDM as default.

At the moment it is not really an issue for us, as we apply the above mentioned workaround:

$ cat /usr/share/lightdm/lightdm.conf.d/40-kde-plasma-kf5.conf
[SeatDefaults]
user-session=kde-plasma-kf5

Let me know if you need further information.

Thanks
Thomas

[Launchpad Janitor (janitor)]

[Expired for plasma-workspace (Ubuntu) because there has been no activity for 60 days.]

[Tomasz Makara (csowiec)]

2020 and still not fixed, thanks for solution

[Open Sense Solutions (opensense)]

I ran into the same problem in 20.04 after switching to lightdm and it took me a while to figure out.

Just as Simon pointed out:
/usr/share/lightdm/lightdm.conf.d/40-kde-plasma-kf5.conf
should have:
user-session=plasma
instead of
user-session=kde-plasma-kf5
since there is no kde-plasma-kf5.desktop in /usr/share/xsessions

I understand that most people aren't switching the display manager but this is such an easy fix I'd hope that it's done to save a lot of frustration for the few that do.

[Dieter Toews (dtoews)]

This is still a problem in Ubuntu/Kubuntu & Linux mint with KDE.

Please fix this one liner!

[John Chaney (jdally987)]

Just chiming in to say that opensense's solution above also fixed it for me. I created /etc/lightdm/lightdm.conf and put in it:

[SeatDefaults]
user-session=plasma

and it worked to fix the "Failed to start session" error in the greeter after entering my password.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.