I recently upgraded my old Acer netbook (32 bits ) from 16.04 to 18.04 and I found some differences in the boot process compared to a fresh 18.04 installation:
- the grub2 theme: Ubuntu Mate 18.04 no longer uses a theme
- an old lightdm greeter that can’t be configured from the Control Center
The grub theme issue can be solved deleting the folder /boot/grub/themes running:
sudo rm -r /boot/grub/themes
The lightdm greeter issue can be solved uninstalling lightdm-gtk-greeter packages:
sudo apt purge lightdm-gtk-greeter lightdm-gtk-greeter-settings ubuntu-mate-lightdm-theme
I also run
sudo dpkg-reconfigure lightdm (just in case, but I think it’s not necessary).
Note that 18.04 uses slick-greeter.
To check that all the required packages are installed, run:
export LC_ALL=C; apt search lightdm | grep installed
you must get:
liblightdm-gobject-1-0/bionic,now 1.26.0-0ubuntu1 amd64 [installed] lightdm/bionic,now 1.26.0-0ubuntu1 amd64 [installed] lightdm-settings/bionic,bionic,now 1.1.4-0ubuntu1 all [installed] slick-greeter/bionic,now 1.1.4-1 amd64 [installed]