[systemd-devel] Using systemd --user to manage graphical sessions?

[Martin Pitt]

Hello all,

I've been experimenting with systemd --user as a possible replacement
for bringing up graphical user sessions. We currently bring up most of
that using upstart jobs (simple auto-restart on crashes, rate
limiting, per-job logging, fine-grained startup condition control).
There is one upstart process per session, so this is reasonably
straightforward.

But I still can't wrap my head around the mental model of how this is
supposed to work with the user D-Bus and systemd instance. This works
fine for some services which are not specific to a session, such as
gvfs or pulseaudio, but it's not at all appropriate for user-facing
applications or desktop components, such as gnome-terminal[1],
gnome-session, the window manager, indicators, etc. They are
necessarily per-session, and sometimes even need to be keyed off the
session type (gnome, LXDE, XFCE, etc.). I. e. they should be started
on the first graphical session (not on VT logins) and should be
stopped when stopping the graphical session.

There are some existing discussions [2][3] and while the latter has a
lot of patches and some good direction, it does not really touch the
subject of the mail at all -- how do I get something from a user unit
into the session-*.scope session of logind?

I. e. if I have some ~/.config/systemd/user/xeyes at .service with

   [Unit]
   Description=Xeyes on session %I
   [Service]
   ExecStart=/usr/bin/xeyes

I can start this with "systemctl --user start xeyes@${XDG_SESSION_ID}",
but this will hang off user at 1000.service instead of session-*.scope
and thus it will not be stopped once the X session gets logged out.

One idea was to add PartOf=session-*.scope, but that's a system-level
unit and thus the session process does not know about that. There also
is no Scope= option for a service to make that run in a different
scope. We can certainly hook something into xinit.d/ to *start* a
"master stub" service which then launches the components, but there is
no way to tell it to stop with the logind session.

Is this all in vain, and we need to make the *entire* world of free
software shift over to the new model of "user-wide services" before we
can use systemd --user for graphical stuff? (Colin's patch list is
already impressively long and it is by far not complete)

Or is someone actually using systemd --user for graphical sessions
already and found a trick that I missed?

Thanks,

Martin


[1] https://bugzilla.gnome.org/show_bug.cgi?id=744736
[2] https://mail.gnome.org/archives/desktop-devel-list/2014-January/msg00079.html
[3] https://lists.freedesktop.org/archives/systemd-devel/2013-August/012517.html

-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)