init process
 

I am using Ubuntu LTS, I cannot find the file

you can refer this:-
http://ubuntuforums.org/showthread.php?t=1527488

I believe Ubuntu 10.04 is using systemd for init, which doesn't use the /etc/inittab for configuration. Instead, it has several dozen files usually in /lib/systemd... that is used by default, unless it is in /etc/systemd/...

No, ubuntu and its derivatives use upstart as replacement for sysinit. As far as I know ubuntu never used systemd.
More info about upstart is here.

Cheers

I know it is at least available (https://launchpad.net/ubuntu/+source/systemd has the code).

Personally, I think systemd is the worst thing to ever use - it cannot be made reliable, auditable, or fixable in the presence of errors... and doubt it can be made secure either.

Everything else has a real inittab file - otherwise the system will always be in single user mode.