Bug#946645: KillUserProcesses=no disregarded for some cgroups

[Ansgar]

On Mon, 2020-02-10 at 14:37 +0100, chrysn wrote:
> On Mon, Feb 10, 2020 at 11:25:29AM +0100, Michael Biebl wrote:
> > I assume your GNOME session is managed by systemd --user, i.e.
> > gnome-session is modelled around systemd --user.
> > 
> > Might be that is gnome-session that triggers the cleanup of the
> > session/processes.
> > 
> > You could try with a more minimal desktop session, like openbox, and
> > start tmux in a xterm there and test if that survices a logout (it should)
> 
> In openbox, I could indeed not reproduce this behavior in the sid system
> (Opening xterm via right-click / system / xterm, logging out via
> right-click / ...) on a first attempt.

If I start an xterm via Alt-F2 in gnome, the xterm process runs in a
cgroup like gnome-launched-xterm-489694.scope.  gnome-terminal or an
xterm started in gnome-terminal run in the gnome-terminal-
server.service cgroup.  I expect openbox doesn't do this and processes
started by openbox run in the same cgroup as openbox itself.

`systemd-cgls` is useful to see how processes are organized into
cgroups.

The gnome-launched-*.scope has KillMode=control-group, so all processes
including background processes like tmux get killed when the unit gets
stopped (systemd --user show -p KillMode gnome-launched-....scope).

gnome-terminal-server.service has KillMode=process which doesn't kill
background processes when the unit gets stopped.

I would guess that the unit openbox runs in also has KillMode=process.

Ansgar