After plasma 6.7 update, impossible to get graphic display -- sddm or plasmaahell?

[joneall]

I updated this morning and plasma 6.7 was installed. But when I boot, I just get a tty login invite. I can login, but can't do anything afterwards. I can't launch plasmashell and it knows no command kwin.

During the update, it asked if I wanted plasmashell or sddm. Not having any idea what that means, I selected the default, which was sddm. What is sddm? Could that be my pb

Thanks in advance for any help.

[claydoh]

it asked if I wanted plasmashell or sddm

That was to select the desired login manager, SDDM or Plasmalogin, as Plasmalogin is now installed by default.

SDDM is the login manager favored by KDE for some years now

Plasmalogin is its replacement. It is actully based on SDDM, so it will have the same sort of look at the moment.

It is fine to use SDDM, but if you do any package cleanup, it will be removed, so you will end op on Plasmalogin anyway.

As to the upgrade to Plasma 6.7 , I do not know what might be causing your problem. Mine was fine, other than a notification for 2 phantom, non-existant updates that showed in Discover, that went away after a while. (Nope, they are still there)

The command to start Plasma from a tty login will be startplasma-wayland, or startplasma-x11 if you use that.

You might check for updates if you can, maybe you did not get all of them?

[Carmikatze]

I had the same issue with my machine. I was able to get it running again. After a login I could start plasma with:

exec /usr/bin/dbus-launch --exit-with-session startplasma-wayland

After I had that running I reeinstalled plasmalogin:

sudo apt install --reinstall plasmalogin

and reloaded the service:

sudo systemctl daemon-reload

[joneall]

The command to start Plasma from a tty login will be startplasma-wayland, or startplasma-x11 if you use that.

I tried startplasma-wayland and got

/usr/bin/xrdbCa't open display
xcb_connect() failed

[joneall]

I tried Carmikatze's method, but after
exec /usr/bin/dbus-launch --exit-with-session startplasma-wayland
my system was completely hung. no possibility of entering any command. even ctl-C, D or X failed to get any response.

Now I'm afraid to update my other system.

[joneall]

I tried installing a new system with plasma 7. For some reason, there are several choices of iso files now. I first tried the one called desktop, then the one called bigscreen, without having any idea what the difference might be. Result: I cannot launch the "live" version of either. The bigscreen version popped up a message saying

error: invalid magic number.
error: you need to load the kernel first.

Press any key yo continue...

and died. no more response, impossible to enter anything. I tried to USB key on two different computers, with the same result. The sha256 sum was good tho.

[claydoh]

https://plasma-bigscreen.org/

https://plasma-mobile.org/

Both have been around in neon for ages, just never linked to on the website.

Can't say why these don't like your computer, though.

[joneall]

With a newly installed Neon with plasma7 on a new computer, I have to do a tty login and enter the command Claydoh suggested: startplasma-wayland. That works fine, but i should not have to do that every time. I have done a dist-upgrade also, but that has not helped.

Any more suggestions?

Btw. Mint works just fine. And Mint is usable, but it lacks a lot of plasma features I have grown used to, in particular, different backgrounds on activities/workspaces and recognizable, standard icons for firefox et al.

[claydoh]

Just for clarity, we are talking about Plasma 6.7 Plasma 7 is way way off in the unplanned future.


EDIT: This may not be relevant now
Which ISO was used? What new PC?


-------------
Ok, what we are missing is the correct instruction to enable the plasmalogin service, which is the bug you are seeing.


so to fix it:

sudo systemctl disable sddm
sudo systemctl enable plasmalogin​

If you are using the most current ISO and have 6.7 out of the box, the first command won't do anything, and you will see a message, as it isn't installed to begin with.

The bug here is neon specific, and not related to Plasma 6.7 at all.

What is happening is that the updates and upgrades are replacing the old SDDM login manager with the new plasmalogin.
What is supposed to happen is that there should be a popup from apt asking to choose which login manager to use, which would then enable plasmalogin if selected.
This does not appear to be happening for all, and there is no login manager set to load, even though both are installed. (one can have multiple login managers installed, but only one set to load.)

Another way is to run:

sudo dpkg-reconfigure plasmalogin

Which will show the selection box.



EDIT:
The above may not be relevant, depending on the ISO you use.

Are you using the current ISO image with Plasma 6.7.0, or are you installing to a previous ISO with Plasma 6.6.5 and updating ( both of which gets you to 6.7.2)? The most current image dated from July 9 (with Plasma 6.7.0) should not have this issue as far as I can see.

But even testing updating from 6.6.5 to 6.7 on a couple of VMs, I don't see this problem happening for me so far.

[joneall]

Thanks, claydoh, but...

$sudo systemctl disable sddm
sddm.service is not a native service, redirecting to systemd-sysv-install.
Executing: /usr/lib/systemd/systemd-sysv-install disable sddm​

$ sudo systemctl enable plasmalogin​
Invalid unit name "plasmalogin​" escaped as "plasmalogin\xe2\x80\x8b" (maybe you should use systemd-escape?).
Failed to enable unit: Unit file plasmalogin\xe2\x80\x8b.service does not exist.​

WHAT is systemd-escape?

sudo dpkg-recongfigure plasmalogin ==> E: Unable to locate package dpkg-recongfigure

'man dpkg' says

To reconfigure a package which has already been configured, try the dpkg-reconfigure(8) command instead (which is part of the debconf project).
But debconf is installed

For info:
$ kinfo
Operating System: KDE neon User Edition
KDE Plasma Version: 6.7.2
KDE Frameworks Version: 6.28.0
Qt Version: 6.11.1
Kernel Version: 6.17.0-35-generic (64-bit)
Graphics Platform: Wayland

It's an updated version of a plasma 6 system.

[claydoh]

I did say it may not be relevant

Especially with a typo:

sudo dpkg-reconfigure plasmalogin

I had a stray letter in there, now fixed.

None of that makes a difference since you don't have sddm installed since you are on the most current ISO, so there is no choice needed for selecting sddm or plasmalogin.

I have zero idea why your fresh install does not show the login screen and you end up at a TTY prompt.



Are you ending up at a tty prompt directly, or are you switching to one using ctrl-alt-F{number} ?

What new PC specs?

[joneall]

The login prompt comes up directly, without my typing anything. Then I enter username, pw and startplasma-wayland.
I have not tried Carmilkatze's sudo apt install --reinstall plasmalogin and sudo systemctl daemon-reload. Any point in that?

$ kinfo
Operating System: KDE neon User Edition
KDE Plasma Version: 6.7.2
KDE Frameworks Version: 6.28.0
Qt Version: 6.11.1
Kernel Version: 6.17.0-35-generic (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 8700G w/ Radeon 780M Graphics
Memory: 16 GiB of RAM (14.7 GiB usable)
Graphics Processor: AMD Radeon 780M Graphics

I kinduv went whole hog on the new machine. Figure it will last the rest of my life.

[claydoh]

I have not tried Carmilkatze's sudo apt install --reinstall plasmalogin and sudo systemctl daemon-reload. Any point in that?

It won't hurt anything, for sure. The second one is not needed, but also won't be harmful or anything.

If my typo in the dpkg-reconfigure command had not been present, this might have actually fixed your login manager.

But lets look at a couple of things:

apt policy sddm

and

apt policy plasmalogin

You may see that both plasmalogin and sddm are installed at the same time. This should be fine. Only one can actually be enabled at a time. I suspect that neither is enabled.


Next, let's see if plasmalogin's service is actually enabled:

systemctl status plasmalogin

It is supposed to look similar to this:

claydoh@blinken:~$ systemctl status plasmalogin
● plasmalogin.service - Plasma Login Manager
Loaded: loaded (/usr/lib/systemd/system/plasmalogin.service; enabled; preset: enabled)
Active: active (running) since Sun 2026-07-12 09:00:28 AEST; 7h ago
Docs: man: plasmalogin(1)sudo apt reinstall plasmalogin
man: plasmalogin.conf(5)
Main PID: 1396 (plasmalogin)
Tasks: 2 (limit: 34734)
Memory: 37.0M (peak: 66.8M)
CPU: 124ms
CGroup: /system.slice/plasmalogin.service
└─1396 /usr/bin/plasmalogin

See what you have
There will be more text underneath this, but this can be ignored unless you see something in red, or a warning/error.

If it shows "disabled" in place of the blue text above, then it is not turned on. Reinstalling plasmalogin in theory should do this, but since it isn't enable now, we might still need to manually do that.

You do the same with sddm if you want, but won't be necessary.


So try reinstalling plasmalogin, and see what happens.

sudo apt reinstall plasmalogin

Then run

systemctl status plasmalogin

again to see if it is properly enabled.


If plasmalogin is still not enabled, you can try the two commands I gave in my messy post before:

sudo systemctl disable sddm

This will turn off SDDM if it is enabled, it may give an error if it wasn't. No biggie.

sudo systemctl enable plasmalogin​​

This enables plasmlogin.

Now, once you are up and runing with plasmalogin, you can uninstall sddm if you want. Or leave it for now, just in case.

Another option on the table if plasmalogin itself is actually broken is to switch to sddm.
I doubt this is the case, as I'd find bug reports and posts on this everywhere, which I am not seeing so far.

[joneall]

It appears sddm is not installed.

$ apt policy sddm
sddm:
Installed: (none)
Candidate: 0.21.0-6+24.04+noble+release+build32
Version table:
...

$ apt policy plasmalogin
plasmalogin:
Installed: 6.7.2-0zneon+24.04+noble+release+build22
Candidate: 6.7.2-0zneon+24.04+noble+release+build22
Version table:
*** 6.7.2-0zneon+24.04+noble+release+build22 500 ...

However, this is botheresome.

$ systemctl status plasmalogin
○ plasmalogin.service - Plasma Login Manager
Loaded: error (Reason: Unit plasmalogin.service failed to load properly, please adjust/correct and reload service manager: File exists)
Active: inactive (dead)
Docs: manlasmalogin(1)
manlasmalogin.conf(5)

I reinstalled plasmalogin, but that changed nothing.

$ systemctl status plasmalogin
○ plasmalogin.service - Plasma Login Manager
Loaded: error (Reason: Unit plasmalogin.service failed to load properly, please adjust/correct and reload service manager: File exists)
Active: inactive (dead)
Docs: manlasmalogin(1)
manlasmalogin.conf(5)

Thanks for all the assistance

[claydoh]

Ok, try enabling it:

sudo systemctl enable plasmalogin

and try checking status again

If you stay at the tty instead of starting Plasma manually, you can try to run plasmalogin manually as well"

sudo systemctl start plasmalogin

But really, at least for now, I tihnk it may be better to switch to sddm,

sudo apt install sddm

This should get you the selection thing you saw originally, where you do want to select sddm. This should enable and set SDDM as the login.

You can verify this with

sudo systemctl status sddm

Then log out. You will be back at the TTY iirc, so either reboot or (from the tty):

systemctl restart sddm

I have no idea what is happening here, and I am not seeing this exact problem anywhere so far.

Especially as you are doing a clean installation. I have not done a clean install on my PC with this ISO, just a lot of VMs,. maybe 6 or so. No issues at all.


Maybe others with better systemd experience can chime in?