SDDM

Abdurrahman Avcı started SDDM in 2013 as a standalone C++ and Qt project, free of the XDM code that KDM had carried for its entire life. The daemon starts an X server or a Wayland session, authenticates through PAM and hands over; the greeter is a Qt Quick program that loads a theme written in QML. A theme is a directory with a Main.qml, so the login screen can be turned into anything without touching C++ — exactly the kind of customisation KDM's XML themes had promised and never quite delivered.

When KDE left kdelibs 4 behind for Plasma 5 in 2014, KDM stayed behind, and SDDM became the official replacement with the Breeze theme as default. Fedora's KDE spin and most other Plasma distributions made the same choice. Development stalled for a few years while the greeter stayed tied to X; then KDE developers stepped in as maintainers, 0.20 arrived in 2023 and the greeter learned to run under a Wayland compositor. Configuration lives in sddm.conf and an sddm.conf.d directory, so distributions stop overwriting each other's settings.