Basic Questions
 

Question1:

I need to understand description of this commands.

ls -l /etc/init.d

Question2:

Is below statements correct ?

init = system level , at boot time
rc.d = application level , After on system , all scripts are here


Application Level control services manage by rc.d , after starting it reads rc.d

To manage rc.d a utility is chkconfig

Question3

Question : What does rc1.d & rc0.d and so on contains ...........................

Asks for a long directory listing of the directory /etc/init.d which exists on some unixes.
init = A brief name for sysvinit, the older standard boot process. Others worth noting are systemd and initng
rc.d = Nothing. Usually, in /etc/rc.d there is rc0.d/ ... rc6.d/ for the various runlevels, and init.d for the scripts. The directories in rc0.d-rc6.d have only symlinks to these scripts.
chkconfig is a red hat utility program. Various systems differ wildly, and it is better to learn the one you have to(your own).
Symlinks to the scripts for runlevel 0 & 1

@OP I see you've been given answers. And they are correct. A question I have is whether or not there is any coherence for all this. The impression I get is that you've been guided to run that 'ls' command and then observe the various things you see under that directory structure. Are you just asking these questions to fill in blanks for an assignment, or are you exploring your system and trying to learn about it more. I suggest that you go to your /etc directory, issue:Observe what you see there and then explore the /etc/init.d directory to understand what many of the links are pointing too. If you have more detailed questions, please show that you have issued these commands and attempted to find some answers on your own versus just asking. Because while you may get direct, and correct answers, if you don't understand either the answers or the questions, then what's the point?

Perhaps you should look into the Site FAQ to aid you in understanding how to better formulate your questions.

...and I'll follow your questions up with:

• Question 4: Is this homework? Because it sure sounds like it.
• Question 5: Did you read the "Question Guidelines" link in my posting signature, where it mentions you doing some basic research on your own before post?