On Sat, Nov 14, 2015 at 07:36:08PM +0000, Rainer Weikusat wrote:
> Mitt Green <mitt_green@???> writes:
> > Not sure if that was sarcasm though.
> >
> > Anyway, why do we need dbus if we can live
> > without it?
> >
> > I've seen these [1] cool figures explaining what it is
> > but neither them,
> > nor the article didn't give me the answer why it is
> > necessary.
>
> "Necessary" is a bit of a bad category because anything can be
> implemented in some other way, hence nothing is strictly
> necessary. D-BUS is an OO RPC system intended to enable long-running
> applications to call methods implemented by other long-running
> applications provided these other long-running applications run on the
> same computer.
<snip>

Your explanation is pretty good.
But there are a very few more details that I thought should be mentioned:

- Regarding 'long-running', it seems worthwhile to mention that D-Bus
is the main *stateful* IPC protocol available.
In other words, it is designed around the concept that you're dealing with
programs that will not be restarted.
This, apparently, makes it simpler to use, since rather than dealing with
failures of the 'remote' process, you can simply ignore them because it's
irrecoverable anyhow.
This simplicity in use, obviously, makes it a favored API for combination
with the systemd init/service manager/*.

(Anyone who does not see the humor of this probably should either
re-read that or consult the definition of 'service manager'.)

- Regarding 'on the same computer', it's apparently supposed to be
'possible' to set up some method of forwarding over ssh.
I saw references to this being already implemented in one of the threads
Miroslav posted in; but as far as documentation goes, I see only a
two and a half year old page mentioning it as a possible but untested
solution.
(http://www.freedesktop.org/wiki/Software/DBusRemote/)
There's also a third-party program to implement this
(http://gabriel.sf.net/howto.html).

-A caveat is that it's apparently also notorious for being troublesome
when using SSH with X forwarding.

HTH,
Isaac Dunham