pgsjc/disc_SIGHUP.c

#define _GNU_SOURCE     /* Get strsignal() declaration from <string.h> */
#include <string.h>
#include <signal.h>
#include "tlpi_hdr.h"

static void             /* Handler for SIGHUP */
handler(int sig)
{
    printf("PID %ld: caught signal %2d (%s)\n", (long) getpid(),
            sig, strsignal(sig));
                        /* UNSAFE (see Section 21.1.2) */
}

int
main(int argc, char *argv[])
{
    pid_t parentPid, childPid;
    int j;
    struct sigaction sa;

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s {d|s}... [ > sig.log 2>&1 ]\n", argv[0]);

    setbuf(stdout, NULL);               /* Make stdout unbuffered */

    parentPid = getpid();
    printf("PID of parent process is:       %ld\n", (long) parentPid);
    printf("Foreground process group ID is: %ld\n",
            (long) tcgetpgrp(STDIN_FILENO));

    for (j = 1; j < argc; j++) {        /* Create child processes */
        childPid = fork();
        if (childPid == -1)
            errExit("fork");

        if (childPid == 0) {            /* If child... */
            if (argv[j][0] == 'd')      /* 'd' --> to different pgrp */
                if (setpgid(0, 0) == -1)
                    errExit("setpgid");

            sigemptyset(&sa.sa_mask);
            sa.sa_flags = 0;
            sa.sa_handler = handler;
            if (sigaction(SIGHUP, &sa, NULL) == -1)
                errExit("sigaction");
            break;                      /* Child exits loop */
        }
    }

    /* All processes fall through to here */

    alarm(60);      /* Ensure each process eventually terminates */

    printf("PID=%ld PGID=%ld\n", (long) getpid(), (long) getpgrp());
    for (;;)
        pause();        /* Wait for signals */
}