This is pgsjc/t_setsid.c (Listing 34-2, page 706), 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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/* t_setsid.c

   Demonstrate the use of setsid(2) to start a new session.
#if ! defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 500
#define _XOPEN_SOURCE 500
#include <unistd.h>
#include <fcntl.h>
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    if (fork() != 0)            /* Exit if parent, or on error */

    if (setsid() == -1)

    printf("PID=%ld, PGID=%ld, SID=%ld\n", (long) getpid(),
            (long) getpgrp(), (long) getsid(0));

    /* Following should fail, since we don't have a controlling terminal */

    if (open("/dev/tty", O_RDWR) == -1)
        errExit("open /dev/tty");


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