This is pgsjc/disc_SIGHUP.c (Listing 34-4, page 712), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* disc_SIGHUP.c

   This program demonstrates that when a "terminal disconnect" occurs, SIGHUP
   is sent to all the members of the foreground process group for this terminal.

   Try using the following command to run this program in an X-window, and then
   closing the window:

        exec disc_SIGHUP > sig.log 2>&1

   (Since the above will replace the shell with this program, it will be the
   controlling process for the terminal.)
#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) */
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)

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

            sa.sa_flags = 0;
            sa.sa_handler = handler;
            if (sigaction(SIGHUP, &sa, NULL) == -1)
            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 */


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