“Loading the Linux kernel takes up just a fraction of the time
spent waiting for the login prompt during booting. The system
spends most of its time sitting waiting for init (which has its
origins in Unix System V) to cycle through the various runlevels,
during which it runs innumerable sequences of init scripts. In
Ubuntu and Fedora, Upstart has long replaced the traditional SysV
init.“The current boot sequence, with services starting consecutively
in a fixed sequence, remains unaltered simply because no-one has
sat down and adapted the init scripts for these various services to
the capabilities of Upstart. Upstart simply emulates the SysV init
runlevels (which actually no longer exist on systems running
Upstart) and continues to call the old init scripts. For Ubuntu
9.10, the development team have finally started to convert some
services to Upstart.”