Kill all child processes of a parent but leave the parent alive

Question

What would be the best way to kill all the processes of a parent but not the parent? Let's say I have an undetermined number of child processes that I've forked and on a given alarm, in my signal handler, I'd like to kill all my child processes but keep myself running for various reasons.

As of now, I am using kill(-1*parentPid, SIGKILL) but this kills my parent along with its children.

Answer 1

One way to accomplish this is to deliver some signal that can be caught (not SIGKILL). Then, install a signal handler that detects if the current process is the parent process or not, and calls _exit() if it is not the parent process.

You could use SIGUSR1 or SIGUSR2, or perhaps SIGQUIT.

I've illustrated this technique here.

Optionally (as suggested by Lidong), the parent process can use SIG_IGN on the signal before issuing the kill() command.

signal(SIGQUIT, SIG_IGN);
kill(0, SIGQUIT);

Answer 2

you can set the child process a new process group at the fork time, and while you want to kill the child process and its descendants, you can use killpg, example code as:

#include <unistd.h>
#include <signal.h>
#include <stdio.h>

void parent(pid_t pid) {
    killpg(pid, SIGKILL);
}

void child(void) {
    if (-1 == setsid())
        return;

    while(1) {
        sleep(1);
        printf("child\n");
    } 
}


int main() {
    pid_t pid;
    switch ((pid=fork())) {
    case 0: // child
        child();
        break;

    default: // parent
        getchar();
        getchar();
        parent(pid);
    }

    return 0;
}