<P> Easy transition and perfect backward compatibility with sysvinit were the explicit design goals; accordingly, Upstart can run unmodified sysvinit scripts . 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 . </P> <P> 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 (for example, a Mach ports bridge, or a devd (found on FreeBSD systems) bridge) are possible . </P> <P> Runit is an init scheme for Unix - like operating systems that initializes, supervises, and ends processes throughout the operating system . It is a reimplementation of the daemontools process supervision toolkit that runs on the Linux, Mac OS X, * BSD, and Solaris operating systems . Runit features parallelization of the start up of system services, which can speed up the boot time of the operating system . </P> <P> Runit is an init daemon, so it is the direct or indirect ancestor of all other processes . It is the first process started during booting, and continues running until the system is shut down . </P>

Describe the boot order of a linux machine