Why I cannot find in /etc/inittab? [duplicate]
Ubuntu uses different runlevels than other Linux distros.
It also uses rc*.d instead of inittab ( * going from 0 to 6). Open /etc/rcS.d/README
& /etc/init.d/README
to know more.
/etc/inittab is no longer used in Ubuntu. The configuration it provided for some services (such as TTYs) can be found in the upstart config. Runlevels as a concept has been made obsolete by this and has not been used for this in Ubuntu for quite a while now.