$ vi kill.c
$ gcc kill.c -o kill
$ ./kill
pid = 4204
I am parent, pid = 4204, child = 4205
I am child, child = 4205
I am parent, pid = 4204, child = 4205
I am child, child = 4205
I am parent, pid = 4204, child = 4205
I am child, child = 4205
I am parent, pid = 4204, child = 4205
I am child, child = 4205
I am parent, pid = 4204, child = 4205
I am child, child = 4205
kill child = 4205 success!
I am parent, pid = 4204, child = 4205
I am parent, pid = 4204, child = 4205
I am parent, pid = 4204, child = 4205
I am parent, pid = 4204, child = 4205
I am parent, pid = 4204, child = 4205
$