How to terminate a child process which is running another program by doing exec

Question

I\'m doing fork in my main program,and doing exec in the child process which will run another program. Now i want to terminate the child(i.e., the program invoked by exec) and r

Answer 1

Either in or outside your program, it is possible to use kill. By including <signal.h>, you can kill a process with a given PID (use the fork return value to do this).

#include <signal.h>

int pid;

switch (pid = fork())
{
case -1:
  /* some stuff */
  break;
case 0: 
  /* some stuff */
  break;
default:
  /* some stuff */
  kill(pid, SIGTERM);
}

It is also possible to use kill command in the shell. To find the PID of your child process, you can run ps command.

man kill
The kill() function shall send a signal to a process or a group of processes specified by pid. The signal to be sent is specified by sig and is either one from the list given in <signal.h> or 0. If sig is 0 (the null signal), error checking is performed but no signal is actually sent. The null signal can be used to check the validity of pid.

Answer 2

POSIX defines the kill(2) system call for this:

kill(pid, SIGKILL);

Answer 3

You need to do the following:

1. Do a kill(pid, SIGTERM) first - this gives the child process an opportunity to terminate gracefully
2. Wait a period of time (use sleep). The period of time depends on the time the child process takes to close down gracefully.
3. Use waitpid(pid, &status, WNOHANG) checking the return value. If the process has not aborted do step 4
4. Do a kill(pid, SIGKILL) then harvest the zombie by doing waitpid(pid, &status, 0).

These steps ensure that you give the child process to have a signal handler to close down and also ensures that you have no zombie processes.