1D-Bus supplies both a system daemon (for events such as "new hardware device 2added" or "printer queue changed") and a per-user-login-session daemon (for 3general IPC needs among user applications). Also, the message bus is built on 4top of a general one-to-one message passing framework, which can be used by 5any two apps to communicate directly (without going through the message bus 6daemon). 7