[systemd-devel] RFC: user session lifetimes vs. $DISPLAY

Lennart Poettering mztabzr at 0pointer.de
Tue Mar 5 12:10:17 PST 2013

On Tue, 05.03.13 11:59, Kok, Auke-jan H (auke-jan.h.kok at intel.com) wrote:

> On Tue, Mar 5, 2013 at 11:48 AM, Lennart Poettering <mztabzr at 0pointer.de> wrote:
> > On Mon, 18.02.13 11:08, Kok, Auke-jan H (auke-jan.h.kok at intel.com) wrote:
> >
> >> I believe that the DBus bits are properly in place to have one single
> >> user bus per user session.
> >
> > Nope, we never finished that. However, you currently can invoke
> > "dbus-daemon --session" in a per-user rather than per-session context
> > and things should just work, and that's what most folks do, but in the
> > long run, we really should fix this.
> What's actually missing here?

Well, D-Bus would need to learn about this new bus, and determine the
socket in $XDG_RUNTIME_DIR automatically, and also fallback from the
session to the user bus if the session bus is not reachable otherwise...

> >> For each login, you'd have an instance service (e.g.
> >> gnome-session@:0.service) to serve that display.
> >
> > Well, I am not convinced it is necessary to instantiate
> > everything. People can do that if they really really want to make things
> > work to allow one local user to run multiple sessions, but I am pretty
> > sure that should be out of scope for GNOME. GNOME components should just
> > be normal services that are started on the user bus and which find their
> > display from XDG_RUNTIME_DIR.
> >
> >> GUI processes running under a gnome-session@:0.service should be able
> >> to getenv(DISPLAY) if it's set by gnome-session at .service
> >> (Environment=DISPLAY=%I).
> >
> > Yes and no. For the instantiation case you are right, but as mentioned I
> > don't think GNOME and suchlike really should bother with that. I'd hence
> > expect that GNOME apps would run without $DISPLAY set, but libX11 would
> > be capable of using $XDG_RUNTIME_DIR/display in that case.
> ok, thanks for replying - I'm trying to figure out the direction here
> and seeing if I can get some of the X11 folks here engaged in removing
> some of the blockers.

The patch should be trivial actually, and they sounded quite positive
about this already.


Lennart Poettering - Red Hat, Inc.

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