Previously, the sysvinit package provided the init daemon for the default configuration. When the system started, this init daemon ran the
/etc/inittab script to start system processes defined for each runlevel. The default configuration now uses an event-driven init daemon provided by the upstart package. Whenever particular events occur, the init daemon processes jobs stored in the
/etc/event.d directory. The init daemon recognizes the start of the system as such an event.
Each job typically specifies a program, and the events that trigger init to run or to stop the program. Some jobs are constructed as tasks, which perform actions and then terminate until another event triggers the job again. Other jobs are constructed as services, which init keeps running until another event (or the user) stops it.
For example, the
/etc/events.d/tty2 job is a service to maintain a virtual terminal on tty2 from the time that the system starts until the system shuts down, or another event (such as a change in runlevel) stops the job. The job is constructed so that init will restart the virtual terminal if it stops unexpectedly during that time:
# tty2 - getty
# This service maintains a getty on tty2 from the point the system is
# started until it is shut down again.
start on stopped rc2
start on stopped rc3
start on stopped rc4
start on started prefdm
stop on runlevel 0
stop on runlevel 1
stop on runlevel 6
exec /sbin/mingetty tty2