Bug#983035: Missing dependency on dbus-x11

["Trent W. Buck" <trentbuck@gmail.com>]

Francesco,

Is dbus-user-session installed?
xfce4-session recommends dbus-user-session, so
it SHOULD already be installed.


Francesco P. Lovergine wrote:
> Package: xfce4
> Version: 4.16
> Severity: normal
> 
> 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.

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