 In this way it differs from most other init replacements (beside systemd and OpenRC), which usually assume and require complete transition to run properly, and do not support a mixed environment of traditional and new startup methods.Upstart allows for extensions to its event model through the use of initctl to input custom, single events, or event bridges to integrate many or more-complicated events.By default, Upstart includes bridges for socket, dbus, udev, file, and dconf events; additionally, more bridges are possible.