[systemd-devel] question regarding DBUS_SESSION_BUS_ADDRESS in multiseat environment

[Simon McVittie]

On Fri, 02 Dec 2016 at 13:58:01 +0530, Mohan R wrote:
> Let say if a user already have a session(session0) in a seat (customseat0) and
> he want to start another session in another seat (customseat1).

Does this mean your user is trying to be physically present in two places
at the same time? How is this a useful thing to do? :-)

> Is there any way to make pam_systemd provides uniq DBUS_SESSION_BUS_ADDRESS for
> every session (may be unix:path=$XDG_RUNTIME_DIR/$XDG_SESSION_ID/bus)? or is
> there any way to ask 'systemd --user' to provide different
> DBUS_SESSION_BUS_ADDRESS to the childs?

More background on user-sessions in general:
https://lists.freedesktop.org/archives/systemd-devel/2015-January/027711.html

pam_systemd does not do this unless you have configured dbus-daemon
to provide one bus per logind user-session
(./configure --enable-user-session), which is not the default.
Either you or your OS vendor have explicitly chosen this model: if that
doesn't match your requirements, you need to revert this choice.

If you require multiple D-Bus sessions per logind user-session, you must
either configure dbus without --enable-user-session (the default is
equivalent to --disable-user-session), or mask or remove the
dbus.service and dbus.socket systemd user units that are installed
by enabling that option (/usr/lib/systemd/dbus.*).

The user-session support in dbus is designed to be easy to enable or
disable by adding/removing packages, if your OS vendor packages it
suitably. For example, in Debian (including derivatives like Ubuntu),
/usr/lib/systemd/dbus.* are packaged separately in the dbus-user-session
package, so you can remove that package to go back to the older model.

If your OS vendor has not packaged dbus like that, perhaps ask them to
look at how it's done in Debian? Or if they have deliberately chosen
not to support multiple D-Bus sessions per logind user-session, then
that OS distribution is not suitable for your requirements, and you
need to change either your requirements or your OS distribution.

Regards,
    S