LightDM cannot launch KDE Plasma (Wayland) [Solved]

Fitzcarraldo · Last edited by Fitzcarraldo on Wed Jul 12, 2023 11:05 am; edited 1 time in total

My Compal NBLB2 laptop* runs Gentoo Linux (~amd64) with OpenRC and elogind. It uses SDDM as the display manager, and KDE Plasma as the desktop environment. It can launch a desktop session with either KDE Plasma (X11) or with KDE Plasma (Wayland).
* Intel Core i7-720QM Clarksfield 1st Generation i7 CPU and ATI Mobility Radeon HD 5650 GPU.

My Clevo W230SS laptop** runs Gentoo Linux (amd64) with OpenRC and elogind. It uses the LightDM display manager, and KDE Plasma as the desktop environment. It can only launch a desktop session with KDE Plasma (X11). Trying to launch KDE Plasma (Wayland) results in a blank screen with a blinking cursor in the top left corner.
** Intel Core i7-4810MQ Haswell 4th Generation i7 CPU with Intel HD Graphics 4600 GT2 IGP, and NVIDIA Optimus with NVIDIA GeForce GTX 860M GPU.

I have been investigating the problem with the installation on the Clevo W230SS laptop. I have no need to run Plasma (Wayland); I am just curious as to why LightDM cannot launch a Plasma Wayland session on that laptop. The versions of the relevant packages are as follows:

tomtom69 · Posted: Mon Jul 10, 2023 7:44 pm Post subject:

Hi,

I am facing the same problem. Your post encouraged me to look at the login screen options of lightdm and I tried to use wayland - with the same result.
My first assumption was that your problem is related to nvidia, but I am using radeon graphics, so it seems not to be related on graphics card.
I am also able to start a plasma wayland session using
dbus-launch --exit-with-session startplasma-wayland
on my setup, so the issue seems to be related on lightdm.
Sorry for not being able to really help here, but I am also interested in any solution to use lightdm with plasma/wayland

Tom

Fitzcarraldo · Posted: Wed Jul 12, 2023 11:03 am Post subject:

Well, after a lot of searching and experimenting, I found a solution that works in my case. Ironically, I found it in a 2020 SDDM bug report ('Plasma 5.20 has Black desktop screen when using wayland in conjunction with SDDM #1335'):

https://github.com/sddm/sddm/issues/1335#issuecomment-743933731

I tried the same approach as SDDM user torokati44; I edited /usr/share/wayland-sessions/plasmawayland.desktop and replaced the line:

tomtom69 · Posted: Thu Jul 13, 2023 10:35 am Post subject:

With the modified /usr/share/wayland-sessions/plasmawayland.desktop file it works.

I also looked at the /usr/share/wayland-sessions/plasmawayland.desktop file, but instead of changing the Exec line, I changed into a terminal after boot and entered the command

acmondor · Posted: Mon Nov 04, 2024 10:37 pm Post subject:

This problem still seems to exist in Plasma6 and the solution presented here works, even though the file was changed to /usr/share/wayland-sessions/plasma.desktop.

Was there ever anything done to find a permanent solution so one does not have to edit that file every time kde-plasma/plasma-workspace is updated or reinstalled?

Fitzcarraldo · Posted: Thu Nov 14, 2024 2:49 pm Post subject:

acmondor,

Interesting that the solution I found for Plasma 5 still works for you in Plasma 6, as it no longer works in my case after updating to Plasma 6. I have not yet found a solution.
_________________
Clevo W230SS: amd64, VIDEO_CARDS="intel modesetting nvidia".
Compal NBLB2: ~amd64, xf86-video-ati. Dual boot Win 7 Pro 64-bit.
OpenRC systemd-utils[udev] elogind KDE on both.
My blog

asturm · Developer Joined: 05 Apr 2007 Posts: 9280

Did you look at the content of this file yet? It is really simple:

/usr/libexec/plasma-dbus-run-session-if-needed:

Fitzcarraldo · Posted: Sun Nov 17, 2024 12:19 am Post subject:

Neither "Exec=/usr/libexec/plasma-dbus-run-session-if-needed /usr/bin/startplasma-wayland" nor "Exec=/usr/bin/dbus-run-session /usr/bin/startplasma-wayland" in /usr/share/wayland-sessions/plasma.desktop worked in my case after upgrading to Plasma 6, so the exec statement in /usr/libexec/plasma-dbus-run-session-if-needed was not helping, even if DBUS_SESSION_BUS_ADDRESS was empty and the exec statement was therefore being expanded to "exec dbus-run-session /usr/bin/startplasma-wayland". However, I then updated the Portage world (I kicked it off on 14 November p.m. and it finally completed on 16 November a.m.):

GDH-gentoo · Posted: Sun Nov 17, 2024 8:18 pm Post subject:

I don't think that plasma-dbus-run-session-if-needed receives an empty DBUS_SESSION_BUS_ADDRESS, though. Gentoo's session wrapper script sources all files in /etc/X11/xinit/xinitrc.d, and among them, there is 80-dbus, installed by sys-apps/dbus, that makes the final exec ${command} in the script effectively:

Fitzcarraldo · Posted: Mon Nov 18, 2024 6:43 pm Post subject:

GDH-gentoo,

Thank you for your reply, which makes sense. As the cause does seem to be a LightDM issue, I have implemented a crude work-around using OpenRC's local.d directory to make sure any updates to /usr/share/wayland-sessions/plasma.desktop when merging @world are reverted to use "Exec=/usr/bin/dbus-run-session /usr/share/wayland-sessions/plasma.desktop" instead of "Exec=/usr/libexec/plasma-dbus-run-session-if-needed /usr/bin/startplasma-wayland":

Hu · Administrator Joined: 06 Mar 2007 Posts: 22683

If you don't like what is installed, the right solution would be a user local patch to modify what is installed, rather than a hook script that runs at some later time to edit the installed file. I suggest using /etc/portage/patches for this.

GDH-gentoo · Posted: Mon Nov 18, 2024 9:25 pm Post subject:

Perhaps it would be best to try a different wrapper script. Despite being used for both X11 and Wayland sessions, /etc/lightdm/Xsession looks quite X11-specific to me.

Calling xrdb, setxkbmap or xmodmap for a Wayland session doesn't seem to be useful, and scripts in /etc/X11/xinit/xinitrc.d would be used by xinit, so I'm not sure that they should be sourced for Wayland sessions either. Reading /etc/profile and ${HOME}/.profile maybe it's OK, and I don't know if /etc/xprofile, ${HOME}/.xprofile or scripts in /etc/X11/Xsession.d would be generic despite their names (do you have anything in the latter?).

Maybe you could try adding: