my first thought would be whether or not a fresh install wouldn’t be easier (if this is a fairly fresh install itself) than trying to run down what the problem might be.
my second (if a fresh install isn’t your preference) would be to try and reinstall the desktop. of course it might be a lightdm issue as well. your askubuntu link combined with this one (keeping in mind they are both older articles) suggest that you might be able to do so with sudo apt install --reinstall kubuntu-desktop.
if that doesn’t work or you are still just trying to troubleshoot dmesg --level=err (usually a shorter list) or dmesg --level=warn might be able to give you some idea of what is going wrong with the boot.
As far as fresh install is concerned I´d rather opt out of that one.
I´m funding my whole internet experience by using an umts-stick with a data volume of 6 GB per month. A new installation with all the updates would be less than optimal in that respect.
Even if I have to use Kubuntu by typing “startx” in TTY1… That would be a bit of a nuisance at most.
Still I´d like to get things back to normal again and thus I consider the other steps you suggested. As soon as I know more I´ll get back here.
i remember your mention of that umts-stick before. i wasn’t thinking about data caps and iso’s + plus initial updates certainly do weigh heavy in that regard. hopefully we can get you past having to use startx
one more thought i had was to check in synaptic package manager (or install it if you need to) and check if it shows any broken packages. i’ve not used kubuntu so i don’t know if it has a software center or the like. i think the install should be sudo apt install synaptic.
You could try changing GRUB_CMDLINE_LINUX_DEFAULT=“quiet splash” to GRUB_CMDLINE_LINUX_DEFAULT=“elevator=deadline quiet splash” and then doing sudo update-grub. As you know how to get there I don’t think you need this, but just in case you’re not 100% sure- getid admin:///etc/default/grub into terminal to get this up. It is important to do the grub update or it won’t work
Let us know how you get on as it will help others who may have the same problem at some time - Thanks
it seems like reinstalling the desktop display manager (sddm) has solved your issue. if you would like to mark this post as the solution, i believe that might be helpful to someone who has a similar issue in the future. if not, i will probably circle back around in a few days and do so
i found an informative article (link below) about common ubuntu display managers. i’m including it in case someone else does indeed run into a similar issue, but doesn’t happen to be running sddm. an easy way to check a system’s current display manager is by running cat /etc/X11/default-display-manager. a few other display managers listed in the article are gdm, gdm3, lightdm and kdm.