Indicators are various components that display systematic state and features throughout Ubuntu. On the phone they exist on the StatusBar and on the desktop they appear in the MenuBar. Generally they consist of a small service that provides a model to the desktop shell to generate the User Interface.
The architecture of an indicator is to have a small service that specializes in the specific type of information being displayed. It consists of two sections:
- a component that exports a set of actions that represent various user level things that can be done in that domain. These actions are used by various components, like for example system settings, and:
a menu that is exported to the shell for user interaction. The definition of the various items that can be included in the menu is available at the SystemComponents page.
Each indicator installs a small file in /usr/share/unity/indicators which defines where to find it on DBus and how it should be displayed in the panel. Indicator process are managed by the session init daemon.