I found a missing dependency on /usr/bin/dbus-launch (dbus-x11) in bullseye, somewhere. Not sure this is an xfce4 issue specifically, feel free to reassign to another proper package. In order to replicate the problem: I just installed from scratch a bullseye current image (debian/testing64) in vagrant, with virtualbox provider, an upgraded it. Then installed xfce4i (the metapackage) and started lightdm. After that, the user cannot login and start a session due to missing dbus-launch, with appropriate message at screen. Installing dbus-x11 solves the problem.
Francesco, Is dbus-user-session installed? xfce4-session recommends dbus-user-session, so it SHOULD already be installed. Francesco P. Lovergine wrote: dbus-launch (from "dbus-x11") package is the Old Way, which is still attempted as a fallback. Most systemd linux systems will instead use libpam-systemd to set up the user dbus session. In this case, dbus-launch is not used. You can see this in the source code -- if there's already a dbus session (usually created by systemd), it just returns immediately. https://sources.debian.org/src/xfce4-session/4.16.0-1/xfce4-session/main.c/#L275-L278 This is encoded in the control file like this: https://sources.debian.org/src/xfce4-session/4.16.0-1/debian/control/#L31 On a Debian GNU/Linux architecture, that will default to the systemd path (dbus-user-session). Where systemd isn't available (e.g. Debian GNU/kFreeBSD), it falls back to dbus-x11 (dbus-launch). See also https://sources.debian.org/src/xfce4-session/4.16.0-1/debian/changelog/#L37-L38 https://bugs.debian.org/836062
As explained this is a bug found casually while using testing64, at the stage of its development in that date, by installing xfce4 (the meta-package) after a base system installation (i.e. without any desktop task installed). I have no idea if currently this isssue is still present, but I think it could be reproduced as detailed, something I could eventually try again in a nearest future.