Linux Administration Cookbook

How it works...

Both Upstart and traditional init systems rely on the /etc/init.d/ directory and then the various rc directories to instruct them what to start at which runlevel:

rc0.d/ rc1.d/ rc2.d/ rc3.d/ rc4.d/ rc5.d/ rc6.d/ rcS.d/ 

Looking at Debian's inittab we can see the default runlevel as configured:

# The default runlevel.id:2:initdefault:

So, we know we'll likely end up at runlevel 2, meaning we can check the services that start at that runlevel.

The same can be said for Upstart, and on our CentOS system, we can see the default is set to 3:

id:3:initdefault:

Though it must be said, this is literally the only function that inittab serves on Upstart systems.