How to kill a child process by the parent process?

Send a SIGTERM or a SIGKILL to it:

http://en.wikipedia.org/wiki/SIGKILL

http://en.wikipedia.org/wiki/SIGTERM

SIGTERM is polite and lets the process clean up before it goes, whereas, SIGKILL is for when it won’t listen >:)

Example from the shell (man page: http://unixhelp.ed.ac.uk/CGI/man-cgi?kill )

kill -9 pid

In C, you can do the same thing using the kill syscall:

kill(pid, SIGKILL);

See the following man page: http://linux.die.net/man/2/kill