"Because the traditional System V init daemon (SysVinit) does
not deal well with modern hardware, including hotplug devices, USB
hard and flash drives, and network-mounted filesystems, Ubuntu
replaced it with the Upstart init daemon.
"Several other replacements for SysVinit are also available. One
of the most prominent, initng, is available for Debian and runs on
Ubuntu. Solaris uses SMF (Service Management Facility) and Mac OS
uses launchd. Over time, Ubuntu will likely come to incorporate
features of each of these systems into Upstart..."