Re: system dbus and Desktop notifications

[Zbigniew Jędrzejewski-Szmek <zbyszek in waw pl>]

On Mon, Jun 23, 2014 at 11:38:43AM +0100, Simon McVittie wrote:
> On 22/06/14 19:31, Rolf Fokkens wrote:
> > For a udev driven backup script (connect the USB the disk, and the
> > backup starts) I'd like to have desktop notifications that say when the
> > backup starts and when the backup is finished so users can disconnect
> > the USB disk.
>
> Consider, for instance:
>
> * Alice is a sysadmin, Bob is an unprivileged user. Alice is logged-in
>   locally, Bob is logged-in remotely. Who should be notified?
>   (I think "Alice but not Bob".)
>
> * The same users, but now Alice is remote and Bob is local. Who should
>   be notified? (I'm not sure.)
>
> If you think the answer to the second is "Bob, because, most likely,
> he's the one physically plugging in the USB disk" then something at the
> level of gvfs (running inside Bob's session) might be a better solution.
>
> If you think the answer to the second is "Alice, because she's the
> sysadmin" then the Unix syslog, or the systemd Journal that extends and
> partially supersedes syslog on systemd systems, might be a good basis
> for an answer.
Something similar has been requested for SMART messages [1]. The
implementation should be quite similar.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=723108

Zbyszek

> > Google is helpful, but seems to tell me that these notifications work
> > via the session dbus, not the system dbus. Apparently a solution is to
> > identfy any logged on user, find the related DBUS_SESSION_BUS_ADDRESS
> > and use that to notify the user.
>
> System-level components injecting events into an arbitrarily-chosen user
> session, or (slightly better) into each user session, is not how the
> system/session split in D-Bus is intended to work. The intended way to
> do this within D-Bus is to run some process in each user session, which
> does something on the system bus (subscribes to broadcast notifications,
> or explicitly requests unicast notifications if there's private data
> involved) and produces popups or whatever.
>
> There is currently no spec for a generic notification-receiving daemon
> that does that on the system bus.
>
> Consider whether every logged-in user should get these notifications
> regardless of their level of privilege - broadcasts on the system bus
> are not access-controlled, and anyone (or anything - system users too)
> can see them.
>
> Also consider what should happen if nobody is logged in...
>
>     S
>
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