GLib's `gdbus introspect` can show you the parameter names if they're
included in the introspection XML:
gdbus introspect -y -d org.freedesktop.systemd1 -o
/org/freedesktop/systemd1/unit/cups_2eservice
But introspection is mainly for use by language bindings (e.g. perl-dbus) –
it is not a substitute for documentation.
For anything beyond that, systemd has manual pages for each bus service it
implements, e.g.:
man org.freedesktop.systemd1
https://www.freedesktop.org/software/systemd/man/latest/org.freedesktop.systemd1.html
On Tue, Jun 17, 2025, 06:33 Chris Kottaridis <ch...@quietwind.net> wrote:
> I am beginning to use the sd-bus library. I have been able to get a couple of
> properties, MainPID and SubState.
>
> I would like to use the Stop method. I am using cups as an example. This
> commands shows that in thee Unit interface there is a Start and Stop method:
>
> $ busctl introspect org.freedesktop.systemd1
> /org/freedesktop/systemd1/unit/cups_2eservice
>
> NAME TYPE SIGNATURE RESULT/VALUE FLAGS
>
> org.freedesktop.systemd1.Unit interface - -
> -
>
> .Start method s o
> -
> .Stop method s o
> -
>
> Each has a signature of "s" I assume it takes one parameter of type string.
>
> I have tried the sample on this page. Pasting it into a file and compiling
> and running it works
> great.
>
> https://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html
>
> This sample starts the cups service by acccessing the systemd Manager and
> calling StartUnit.
>
> /* Issue the method call and store the respons message in m */
> r = sd_bus_call_method(bus,
> "org.freedesktop.systemd1", /* service to contact */
> "/org/freedesktop/systemd1", /* object path */
> "org.freedesktop.systemd1.Manager", /* interface
> name */ "StartUnit",
> /* method name */ &error,
> /* object to return error in */ &m,
> /* return message on success */
> "ss", /* input signature */
> "cups.service", /* first
> argument */ "replace");
> /* second argument */
>
> It has a signature of "ss" which I assume means the method takes 2 arguments
> each of a type string.
>
> My question is for any given method how do I get what the arguments for it
> are ?
>
> Like if I use Start what are valid values to pass for the one argument?
>
> In StartUnit the first argument seems obvious with an example to be the unit
> you want to start. I
> am not sure what the "replace" means or what other strings would be valid.
>
> Again I am interested in the Stop method specifically, but in general would
> like to know where I can
> get a list of the arguments and possible values for any method.
>
> Thanks
> Chris
>
>
