I have a c program executable or shell script which I want to run very often. If I want to stop/pause or to notify something I will send signal to that process. So every time I have to check the pid of that process and I have to use kill to send a signal.Every time I have to check pid and remembering that upto system shutdown, really bad. I want that process has to run on particular pid only like init always run on 1.Is there any C api for that? and Also needed script for bash program. 
Run a process to particular/dedicated pid only
process;kill;job control;pid
I don't think you can reserve or assign PIDs.  However, you could start your process in a script like this:myprocess &echo $! > /tmp/myprocess.pidThis creates a pid file, as some other people have referred to it. You can then fetch that in bash with, e.g., $(</tmp/myprocess.pid) or $(cat /tmp/myprocess.pid). Just beware when you do this that if the process died and the pid was recycled, you'll be signalling the wrong thing.  You can check with:pid=$(cat /tmp/myprocess.pid)if [ $(ps -o comm= -p $pid) = myprocess ]; then    ...send your signal...else echo Myprocess is dead!fiSee comments if $(ps -o comm= -p $pid) looks strange to you.  You may want to do a more vigorous validation if there is a chance of someone doing something devious with the content of /tmp/myprocess.pid (which should not be writeable by other users!).