crystalfontz.dbus.select

Convenience functions for configuring the default bus.

DBus has two buses: the user-level "session bus", and the system-wide "system bus".

The session bus starts for your user when you log in, and doesn't have any particular access or permissions. This is used for user-scoped services. Examples include audio servers such as PulseAudio and Pioewire, desktop notification daemons, and the Emacs daemon.

The system bus is used for services accessible for all users, which persist across login sessions. These services are typically run with elevated permissions, and implement access control through many various mechanisms. Examples include networking daemons such as firewalld and NetworkManager, as well as logging services such as journald and rsyslog.

The sdbus library has the concept of a "default bus". This is the bus that a given object uses when another value isn't supplied, and is similar to asyncio's default event loop. Unless otherwise configured, this default bus is the system bus when started through systemd, and the user bus otherwise.

This default isn't necessarily appropriate. In particular, if a service is expected to be run as a system service (as is typical for the crystalfontz service), then the default bus for the DBus client should be the system bus, unless otherwise specified.

The functions in this module are used by the client and service CLIs to configure which bus is used by those programs.

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def select_default_bus() -> None:
    """
    Log that the standard default bus is being used.
    """

    logger.debug("Selecting the default bus")

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def select_session_bus() -> None:
    """
    Select the user session bus as the default bus.
    """

    logger.debug("Selecting the user session bus")
    set_default_bus(sd_bus_open_user())

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def select_system_bus() -> None:
    """
    Select the global system bus as the default bus.
    """

    logger.debug("Selecting the system bus")
    set_default_bus(sd_bus_open_system())