DBUS

Sources: Wikipedia, D-Bus Specification, Cardinal Peak

D-BUS is an Inter-Process Communication (IPC) specification. Communication is possible via multiple Transports (e.g., Unix sockets, systemd, TCP sockets).

Default D-Bus message buses:

• System-wide instance / message bus (see /usr/share/dbus-1/system.conf or dbus-monitor --system)
• User-session-specific instance / message bus (see /usr/share/dbus-1/session.conf or dbus-monitor --session)

Monitor DBUS signals: dbus-monitor

• GDBus (Gnome)
• QT/KDE D-Bus
• dbus-broker (default on Arch)

Source: dbus-broker package

• Each dbus-broker instance provides a message bus
• Each dbus-broker instance gets started by a parent process (Controller) (e.g., dbus-broker-launch)
• dbus-broker only implements message mediation (bus setup and external communication needs to be handled by the Controller.
• The Controller hands over a unix socket (as file descriptor FD) to the dbus-broker instance (--controller=FD)
• The unix socket is used by dbus-broker to accept commands from the Controller.
• Example commands issued by the Controller: Create listener sockets, specify bus policy, create activatable names, react to bus events.

dbus-broker-launch:

• dbus-broker-launch spawns and manages one message bus
• Configuration file is specified via --config-file or the default is taken from /usr/share/dbus-1/ (session.conf for --scope=user and system.conf as fallback)
• --scope defines which systemd instance (user or system) is used to start the launcher

Source: Arch Wiki

During systemd installation, dbus-broker-units can be chosen as the dbus-units provider. This package provides the dbus-broker systemd service units.

Alternatively to dbus-broker, Arch also supports using the D-BUS reference implementation by installing the dbus-daemon-units instead of the dbus-broker service units.

• Send desktop notification: notify-send test
• Send desktop notification with icon: notify-send -i face-glasses "test" (icons are located in /usr/share/icons/)
• Monitor DBUS desktop notifications: dbus-monitor "interface='org.freedesktop.Notifications'"

Primary source

Daemons:

• dunst: Lightweight, customizable, scriptable, minimalistic and provides features like rules, pausing, notification history
• NotifyOSD / notify-osd: Configurable, animations, sound, merging, overflow, flood prevention, do-not-disturb mode,

Depending on the Desktop Environment, notification daemons are built-in (Cinnamon, Gnome, KDE). Notification daemons can started standalone for other environments (e.g. i3wm). Standalone is possible via XDG autostart or as DBUS service.

Typically, DBUS service files are shipped with notification daemons, e.g., /usr/share/dbus-1/services/org.freedesktop.Notifications.service

Tools:

• Bustle: Recording D-Bus communication, drawing sequence diagrams, inspecting communication
• D-Spy: Inspect buses/interfaces/properties/signals.methods, execute methods (e.g., send test desktop notifications)