Red Hat

I was trying to generate core dump of a process.But it is not generated.
While digging up the issue I found that Core File Size is set to 0.
I set it with #ulimit -c unlimited.After that I found the core file size is set to 0 (ulimit -a).I exit that session and again logged in.But found the core file size became 0 again.

How to set it permanently?
I am using RED HAT 5.9.

Like any other runtime setting, it doesn't get set unless something sets it. Put it in your ~/.profile, ~/.bashrc, or whatever equivalent file your shell uses for interactive logins.

One of my process is crashing erratically and I need crash dump of the same.
While typing #ps -p $$, it tells me
PID TTY TIME CMD
11794 pts/3 00:00:00 bash

So I am using bash shell.From which location I can find the ~/.profile, ~/.bashrc file.
Do I need to put ulimit -c unlimited in that file?

In my system under /etc/profile.d directory there are 17 files.
I need to modify in which file?

Those files are searched in a certain order, which right now escapes me (man bash lists them in detail). The first one found is executed, and is the right one to receive your setting. The remaining ones are ignored.

Changes you make in your own shell don't apply to anything which isn't run from that particular running shell. So, I should have asked this first: What runs this process? You, in the shell, or something else, somewhere else?

My application uses .csh. Then how to change in it?

That's not really what I asked. Are you running it? Are you typing ./myscript.csh or similar in your shell to run it? Or is some system script running it?