Kubuntu 20.04 plasma desktop does not start after login

Question

I have a fresh install of Kubuntu 20.04, only 2 days old. I just installed some apps that I use and configured KDE to my liking.

The system starts up quickly and I see the login screen, but when I enter my password, it shows the loading screen for a long time (earlier it was 2-3 seconds, now it is 30 seconds), then I just see the background wallpaper, a cursor and nothing else. No panel, no icons, nothing. However, keyboard shortcuts (i.e.: print screen) seems to be working.

There was this issue once in the past 2 days, but then a simple reboot solved it. Sadly this became permanent.

I can login on the console pressing ALT+F2. Tried kquitapp5 plasmashell but it gave an error: "Quitting the application plasmashell failed. org.freedesktop.DBus.Error.NoReply"

killall plasmashell worked, but then

kstart5 plasmashell gave the following error: "qt.qpa.xcb: could not connect to display qt.qpa.plugin: could not load the Qt platform plugin "xcb" in "" even though it was found. This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem."

I tried the reinstall with sudo apt-get reinstall xcb but it did not solve the issue.

Rebooting no longer solves the issue. Also tried to run the system with an earlier kernel to no avail. I suspect this is just some user setup, probably regarding to multimonitor setup, as when I login and get the empty desktop, my secondary monitor setup is incorrect. It is pivoted, but the system uses it like it was in portrait mode. When the issue first arised, after the reboot, I had to reconfigure my display setup.

Earlier, I had Linux Mint 17.2 on this machine, never experienced such an issue.

My system is a B250 motherboard with a G4600 CPU, Nvidia GT 730. The system runs on an NVMe Samsung SSD and boots with EFI. I also have 3 HDDs and an additional older SATA SSD (yes, I have a lot of partitions)

Can I just reset the KDE config so the desktop would work? I really do not want to reinstall the whole system again. Honestly, I just chose Kubuntu because Linux Mint ditched KDE and I don't like Cinnamon or Mate

Edit: I found the cause of the issue: I had the "Automatic mounting of removable media" enabled. When I swirched this off, the error disappeared. Now I have a couple of partitionas I want to use and it's bothersome to manually mount them after each login. Should I just use fstab?

Solution

I had the same problem on my Kubuntu 20.04 (i7-9750H + GTX1650 4GB) and I've found a solution that worked for me. Type ALT+F2 to go on your virtual console and login, then type :

sudo service sddm stop
rm ~/.config/plasma-org.kde.plasma.desktop-appletsrc
sudo service sddm start

Then I went back to my desktop and everything was back to normal. The solution that inspired me is here : https://superuser.com/questions/1131728/kde-taskbar-missing

Comments

[Walf]

And how did you disable the automatic mounting feature without a GUI?

[Moha]

Once in about 10 restarts, I reached the GUI so I could switch this off. Other than that, I think it can be switched off by removing the config file.

[Walf]

I thought you might have known which config file. Deleting it seems excessive, you can edit them in a terminal (Ctrl + Alt + F2-F5).

[Louis Go]

I found it might get login loop if the / mounted disk is full. However login to root user doesn't have this issue.