Session bus vs system bus for an embedded system

[Simon McVittie]

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