Getting back Ubuntu's default boot splash

Solution 1:

If you want to quickly change it back, sudo update-alternatives --config default.plymouth will give you a list of screens you can choose from.

Solution 2:

Or simply

sudo apt-get remove plymouth-theme-kubuntu-logo

If you don't want drop KDE

Solution 3:

If you do this, you should be back to normal:

sudo apt-get purge kubuntu-desktop
sudo apt-get autoremove --purge
sudo apt-get install ubuntu-deskop

The splash screen is selected via update-alternatives, but the above should restore the links too.

Solution 4:

Trying out codeMonk's answer gave me an error after I selected the ubuntu-logo option:

update-alternatives: warning: forcing reinstallation of alternative /lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth because link group default.plymouth is broken.

Running this command fixed that for me:

sudo apt-get install --reinstall plymouth-theme-ubuntu-logo