MarsSeed [1] filed a deletion request for lightdm-ubuntu [2]: Orphaned, last updated in 2016. Not needed by anything specifically. Arch hosts a much newer version of lightdm and liblightdm-qt5. AUR has an up-to-date package providing liblightdm-qt4. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/lightdm-ubuntu/