[systemd-devel] Specification for org.freedesktop.DisplayManager DBus API?

Mathieu Parent math.parent at gmail.com
Tue Mar 10 06:45:34 PDT 2015

(Note 1: please CC me)
(Note 2: I have CC-ed two contacts from gnome-shell, one from gdm, one
from lightdm, and the system-logind ML)


There are currently several ways to ask the DM to switch to the login screen:
- gdm3 uses org.gnome.DisplayManager.LocalDisplayFactory CreateTransientDisplay
- lightdm uses org.freedesktop.DisplayManager SwitchToGreeter
- old gdm, and kdm seems to use a socket without DBus
- ...

I am not involved in those projects, but I recently needed to switch
to LightDM to have guest sessions, while keeping gnome-shell
([debian-guest-sessions]). gnome-shell send a CreateTransientDisplay
when "Switch user", without any effect.

I proposed a patch to gnome-shell [gnome-shell-SwitchToGreeter], which
currently waiting for an implementation in gdm [gdm-SwitchToGreeter]
and a written specification.

This mail is to start a discussion about this DisplayManager specification.

The current DBus interfaces used by lightDM seems to be a good
starting point [lightDM-API], but some of its API may overlap with

Also, how can this work in the Wayland world?

What is the way forward to have the same API in all DM?

[gnome-shell-SwitchToGreeter]: https://bugzilla.gnome.org/show_bug.cgi?id=745940
[gdm-SwitchToGreeter]: https://bugzilla.gnome.org/show_bug.cgi?id=745938
[lightDM-API]: http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/vivid/lightdm/vivid/view/head:/src/lightdm.c#L784


Mathieu Parent

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