Hi,
I am looking at linux startup services, like Cron which runs at level 5 located in init.d, in the startup script I can only see the script file and location of binary file which is executed on startup. Where can I see the actual source code of this services
It depends on your distribution, but Debian has source packages for each package, e.g. http://packages.debian.org/source/lenny/cron
On Debian (or Debian based) systems, you can also apt-get source <packagename>, assuming you have the appropriate deb-src URLs in /etc/apt/sources.list.
This works for underprivileged users, it will fetch the source and uncompress it in the current working directory.
To reproduce the builds, its a good idea to have debhelper installed, or let apt satisfy the dependencies automagically by using apt-get build-dep <packagename>
Its a lot more convenient than googling / searching for the source archive that will reproduce the version of the program you want to study or modify.