Gnome introducing stronger dependencies on systemd

Summary

Doesn’t GNOME already depend on systemd? Kinda… GNOME doesn’t have a formal and well defined policy in place about systemd. The rule of thumb is that GNOME doesn’t strictly depend on systemd for critical desktop functionality, but individual features may break without it. GNOME does strongly depend on logind, systemd’s session and seat management service. GNOME first introduced support for logind in 2011, then in 2015 ConsoleKit support was removed and logind became a requirement. However, logind can exist in isolation from systemd: the modern elogind service does just that, and even back in 2015 there were alternatives available. Some distributors chose to patch ConsoleKit support back into GNOME. This way, GNOME can run in environments without systemd, including the BSDs. While GNOME can run with other init systems, most upstream GNOME developers are not testing GNOME in these situations. Our automated testing infrastructure (i.e. GNOME OS) doesn’t test any non-systemd codepaths. And many modules that have non-systemd codepaths do so with the expectation that someone else will maintain them and fix them when they break. What’s changing? GNOME is about to gain a few strong dependencies on systemd, and this will make running GNOME harder in environments that don’t have systemd available. Let’s start with the easier of the changes. GDM is gaining a dependency on systemd’s userdb infrastructure. GNOME and systemd do not support running more than one graphical session under the same user account, but GDM supports multi-seat configurations and Remote Login with RDP. This means that GDM may try to display multiple login screens at once, and thus multiple graphical sessions at once. At the moment, GDM relies on legacy behaviors and straight-up hacks to get this working, but this solution is incompatible with the modern dbus-broker and so we’re looking to clean this up. To that end, GDM now leverages systemd-userdb to dynamically allocate user accounts, and then runs each ...