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I wanted to try out KDE on my Ubuntu. Then I found out I need another system (Kubuntu), but I found a way to install Plasma on regular Ubuntu (apt install kde-standard). I did so, and i succesfully logged in into KDE. At first, there was a problem: no matter which session I choose at the Session dropdown at the login screen, I can't get into GNOME. It worked for a bit, until it logged me out, and I couldn't log in back. I booted into recovery mode, dropped into root prompt, removed kde-standard and booted back. But the KDE login screen is there. And I can log in, but when I do, I get a yellow screen where I can slightly see GNOME. This lasts for a few seconds, then it crashes back to the log in screen. Is there a way to fix that without reinstalling?

neofetch --stdout output (recovery root prompt):

root@Marcel-UBU 
--------------- 
OS: Ubuntu 22.04.2 LTS x86_64 
Host: MS-7D18 2.0 
Kernel: 5.19.0-43-generic 
Uptime: 1 min 
Packages: 2469 (dpkg) 
Shell: bash 5.1.16 
Terminal: root 
CPU: 11th Gen Intel i5-11400 (12) @ 4.400GHz 
GPU: NVIDIA GeForce RTX 3060 Lite Hash Rate 
Memory: 178MiB / 15896MiB
MrArsikk
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  • *I am at Windows right now, this is a dualboot setup. – MrArsikk Jun 08 '23 at 01:48
  • Welcome to the Ask Ubuntu community. In order to better diagnose your issue, please edit your question to include the version of the Ubuntu OS that you're running. Thanks – richbl Jun 08 '23 at 01:49
  • FYI: You can have multiple desktops installed; I'm a lover of it, but complications can occur depending on what you do/install/remove etc.. You can also re-install Ubuntu Desktops (esp flavors) non-destructively. By KDE login you likely mean the DM (Kubuntu uses sddm by default; that isn't part of KDE as its where you login & KDE Plasma or the DE only starts after you've logged in) or maybe the plymouth screen... as these aren't part of the DEsktop you change them if you want something else. I don't understand your situation currently so can't offer any help – guiverc Jun 08 '23 at 03:02
  • Well, probably that's plymouth, I've seen something about it on the boot console. @guiverc – MrArsikk Jun 08 '23 at 03:12
  • The Plymouth screen is just a graphic that shows & hides the boot messages that are default on any POSIX/Unix (inc. Linux) type of OS as many users find them scary... it's installed when you add desktop packages, but won't change until you direct it to change (ie. see https://askubuntu.com/questions/2007/how-do-i-change-the-plymouth-bootscreen etc).. On installing a new plymouth screen (likely if you installed KDE) you're asked which you want to use.. You need to just select another, but it's only a screen/wallpaper & doesn't influence anything (just shown on screen pre-DM/greeter) – guiverc Jun 08 '23 at 03:16
  • When apt installing I selected sddm, 'cause this is the KDE one. How do i revert? @guiverc – MrArsikk Jun 08 '23 at 03:18
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    The KDE Display Manager is actually kdm, but Kubuntu uses sddm as kdm is largely deprecated... You can use sudo dpkg-reconfigure sddm which will return to configuring it & select another (sddm could be any installed DM too, eg. gdm3 is the default for recent Ubuntu Desktops with GNOME) FYI: Lubuntu using LXQt & Ubuntu Studio also use sddm as their DM – guiverc Jun 08 '23 at 03:22
  • Going to try it out, thanks. Btw, i can't get any further than a root prompt in recovery, so sudo is redundant. @guiverc – MrArsikk Jun 08 '23 at 03:26
  • create a new user and login with this user. Usually the GUI problems are somewhere in the users profile. – Marco Jun 08 '23 at 04:27
  • @guiverc Almost fixed it. One problem left: there's the KDE cursor. – MrArsikk Jun 08 '23 at 08:39

1 Answers1

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I've fixed this (not 100%):

  1. First, boot selecting these options in GRUB: "Advanced options for Ubuntu" > "Ubuntu with [any kernel] (recovery mode)"
  2. Select "network", enable, then "root", enter
  3. Uninstall the package you used: kde-full, kde-standard, kde-plasma using apt.
  4. Run dpkg-reconfigure sddm, select qdm3 there.
  5. Restart either with resume in the recovery menu or a reboot
  6. The GNOME login screen should greet you. Log in.
  7. If it's been uninstalled, install ubuntu-desktop, then log out and in.
  8. Go to Settings > Appearance, select a color and a light/dark theme so the appearance returns to normal.

What's left:

  • The cursor from the KDE theme you chose before fixing
MrArsikk
  • 29