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 (Arch)

Source: dbus-broker package

• 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
• NotifyOSD / notify-osd

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