Debugging Long Or Hanging Reboot

[sero5]

I have had to install kubuntu multiple times. Whenever there is an issue that i am not sure that i can debug and fix, I just end up removing and reinstall kubuntu.
One of those issues is that when i try to install some virtualization tools that will result in bugged reboots (bugged as in, either they take so long or just hang). When this happens, I resort to just manually force restarting the system (if sudo reboot -f doesn't work).

How can i debug a long reboot issue?
How can i safely turn off a system that is hanging reboot? And if i can't what should i do to recover if there is any damage done?
Finally, in case this happens again and i need to reinstall kubuntu? Where are the kubuntu (kde) settings saved? Or should i just copy the entire "~/" and "/etc/" directories?
Which files/directories does "System Settings" save everything into?
And finally, Any good resources on how to get started with virtualization in linux?

[jglen490]

Any specific virtualization tools that are causing this condition for you?

[Don B. Cilly]

Debugging boot issues...
dmesg -T >Documents/dmesg.txt
then look at the text file and scan the timestamps.
A bit laborious... but if you use QUITE and SPLASH...

Now. getting rid of quiet and splash would let you actually see what hangs at boot.
Then you can find the issue in dmesg.txt and... maybe post it here.

Rebooting safely, if Ctrl-Alt-Del does not listen :·)... google REISUB.

Reinstalling: all you personal settings, including "System Settings", are in your /home/yourusername directory.
So backing up and restoring that will recover your settings.
Of course any software you have installed after the basic installation... will have to be re-installed. But you'll still get your settings for it back.

[EDIT] Ah.
systemd-analyze blame | head -n 20
would also give you pointers on boot issues.

[sero5]

Any specific virtualization tools that are causing this condition for you?

After installing some virtualization tools (by following this video https://www.youtube.com/watch?v=ozYKkaVK0_A) i get buggy reboots on kubuntu 19.10 (but not the LTS 18.04). Don't know which one exactly is it though.

Debugging boot issues...
dmesg -T >Documents/dmesg.txt
then look at the text file and scan the timestamps.
A bit laborious... but if you use QUITE and SPLASH...

Now. getting rid of quiet and splash would let you actually see what hangs at boot.
Then you can find the issue in dmesg.txt and... maybe post it here.

Rebooting safely, if Ctrl-Alt-Del does not listen :·)... google REISUB.

Reinstalling: all you personal settings, including "System Settings", are in your /home/yourusername directory.
So backing up and restoring that will recover your settings.
Of course any software you have installed after the basic installation... will have to be re-installed. But you'll still get your settings for it back.

[EDIT] Ah.
systemd-analyze blame | head -n 20
would also give you pointers on boot issues.

Thanks, I'll try what you mentioned.