By default qdbus will list all service names of services that are running and you can manipulate at the moment.
You can also manipulate and run several types of methods for each dbus-enabled application.
the service to connect to (e.g., org.freedesktop.DBus)
the path to the object (e.g., /)
the method to call, with or without the interface
arguments to pass to the call
connect to the system bus
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Here is an example of using qdbus to list all status information about a service:
% qdbus org.ktorrent.ktorrent