upstart-local-bridge

upstart-local-bridge [OPTIONS]

--user-bus ADDRESS
    Specifies the D-Bus address of the user's session bus. If not provided, it typically defaults to the address found in the DBUS_SESSION_BUS_ADDRESS environment variable.

--system-bus ADDRESS
    Specifies the D-Bus address of the system bus. If not provided, it usually defaults to the standard system bus address.

--daemon
    Forks the process into the background, operating as a daemon.

--pidfile FILE
    Writes the process ID (PID) of the daemon to the specified FILE.

--respawn
    Instructs the daemon to restart automatically if it exits unexpectedly.

--version
    Displays the version information of the upstart-local-bridge utility.

--help
    Shows a brief help message with available command-line options.

The upstart-local-bridge daemon acts as a crucial intermediary, facilitating communication between the Upstart init daemon's event system and a user's D-Bus session bus.

Its primary purpose is to allow Upstart to send system-level events (e.g., 'desktop-ready', 'session-started') to the user's graphical or terminal session, enabling user-level applications and services to react to these system state changes. Conversely, it can propagate events generated within a user's session back to the Upstart init daemon, allowing user-initiated actions to trigger system-wide Upstart jobs.

This bridge is typically started automatically by the upstart-session process when a user logs in, ensuring that user-specific Upstart jobs and applications are correctly integrated into the system's event-driven architecture.

upstart-local-bridge is part of the Upstart init system, which has largely been superseded by systemd in most mainstream Linux distributions (e.g., Ubuntu, Debian, Fedora) since the mid-2010s. Therefore, this command is primarily found and relevant in older or specialized Linux systems that still utilize Upstart as their init system. Its functionality relies heavily on the presence and proper configuration of D-Bus and an active Upstart daemon.

This command is rarely invoked directly by a user. Instead, it is typically started automatically by the upstart-session process or a similar mechanism when a user logs into a graphical desktop environment or a user-specific terminal session where Upstart user jobs are active. Its continuous operation in the background ensures seamless event propagation.

The command's core functionality relies on D-Bus, an inter-process communication (IPC) system. It listens for events on one D-Bus bus (e.g., the system bus) and emits corresponding events on another (e.g., the user's session bus), and vice-versa, effectively bridging the two communication channels for Upstart's event model.

upstart-local-bridge was developed as a component of the Upstart init system, which emerged in the mid-2000s as a successor to the traditional System V init scripts. Upstart aimed to be more robust and event-driven, responding to hardware changes, network events, and other asynchronous occurrences. The local bridge was essential for extending Upstart's event model into the user session, enabling more dynamic and integrated desktop environments. Its usage peaked during the period when Ubuntu and other distributions adopted Upstart. However, with the rise of systemd, which offered a more comprehensive and unified approach to service management, Upstart's development and adoption waned, leading to upstart-local-bridge becoming a legacy component in modern Linux systems.

upstart(8), upstart-session(7), dbus-daemon(1), dbus-send(1), init(8), systemd(1)