向子进程发出信号

Question

我必须编写一个C程序，它创建一个子程序并等待一个SIGHUP信号。收到后，它会向其孩子发送信号。子进程执行接收信号的默认动作。

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

void sigint();
void sighup();
pid_t pid, pid_parent;

int main(int argc, char const *argv[])
{

    if ((pid = fork()) < 0) {
        perror("fail1!");
        exit(1);
    }

    else if (pid == 0) {
        signal(SIGINT, sigint);
        while(1) pause();
        exit(1);
    }

    signal(SIGHUP, sighup);
    printf("PARENT's pid: %d\n", pid_parent = getpid());
    while(1) pause(); 

    return 0;
}

void sighup()
{
    signal(SIGHUP,sighup);
    kill(pid,SIGINT);
    printf("PARENT(%d): I received a SIGHUP. I'll send something to my child(%d).\n",getpid(),pid);
    printf("OK");
}

void sigint()
{
    signal(SIGINT,sigint);
    printf("CHILD: I received a SIGINT. I'll execute it.");
    signal(SIGINT,SIG_DFL);
}

似乎它在kill(pid, SIGQUIT)之后无效。我真的没有想法为什么。