Session bus vs system bus for an embedded system

[Alan Martinovic]

Great explanation which triggered multiple epiphanies, thanks :)

> A complete, working D-Bus setup consists of a central server process,
> the *message bus*, and some *clients* that connect to the central server.

Just to see if I got this right.
central server process = the *message bus* = dbus-daemon
And in the server part, on Linux, it's one implementation to rule them all
as opposed to a variety of client implementations you chose based on
the requirements?

On Wed, Apr 18, 2018 at 5:15 PM, Simon McVittie <smcv at collabora.com> wrote:
> On Wed, 18 Apr 2018 at 16:03:47 +0100, Simon McVittie wrote:
>> dbus-daemon reads XML policies from /usr/share/dbus-1/system.d
>> and /etc/dbus-1/system.d. In theory the XML in those files is an
>> implementation detail of dbus-daemon (which is why they're documented
>> in the dbus-daemon man page, not in the D-Bus Specification), but some
>> other message bus implementations read them anyway, for interoperability
>> with existing software.
>
> ... and in case I didn't make it obvious enough:
>
> It's only the message bus implementation, like dbus-daemon or dbus-broker,
> that might read and understand policies like these. The policies control
> whether the message bus allows a D-Bus client to own names, and whether
> the message bus allows a D-Bus client to send messages through it.
>
> Ordinary D-Bus client libraries like libdbus, sd-bus and GDBus do not
> need to read these policies, because they are not involved in their
> enforcement.
>
> (Analogous: when you read web pages with Firefox or wget, they are
> not involved in the policy decision of whether to serve the content
> or not. Only the web server like Apache or lighttpd gets to make that
> decision, based on its own configuration, e.g. httpd.conf or .htaccess
> files. A D-Bus app that provides a busconfig XML file for dbus-daemon is
> like a webapp that provides a .htaccess file for Apache.)
>
>     smcv
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