Illustrating how orphaned children aren't necessarily adopted 2 by PID 1

orphan.c

/* For illustrating how orphaned children aren't necessarily adopted
   by PID 1.

   See also: http://stackoverflow.com/questions/284325/how-to-make-child-process-die-after-parent-exits/36945270#36945270

   2016, Georg Sauthoff <[email protected]>
*/


#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>


int main()
{
 fprintf(stderr, "grandparent: %ju (ppid %ju)\n",
     (uintmax_t) getpid(), (uintmax_t)getppid());
  int pid = fork();
  if (pid == -1) { perror(0); exit(1); }
  if (pid) { // parent
    sleep(3);
    fprintf(stderr, "granparent %ju exiting\n", (uintmax_t) getpid());
  } else { // child
    fprintf(stderr, "parent: %ju (ppid %ju)\n",
        (uintmax_t) getpid(), (uintmax_t)getppid() );
    int pid2 = fork();
    if (pid2 == -1) { perror(0); exit(1); }
    if (pid2) { //parent
      fprintf(stderr, "parent %ju exiting\n", (uintmax_t) getpid());
    } else { // child
      sleep(1);
      fprintf(stderr, "child: %ju (ppid %ju)\n",
          (uintmax_t) getpid(), (uintmax_t) getppid());
      fprintf(stderr, "child %ju exiting\n", (uintmax_t) getpid());
    }
  }
  return 0;
}

/* Example output on Fedora 25, inside Wayland and a Gnome terminal:

$ pstree -ps $$ 
systemd(1)───systemd(1750)───gnome-terminal-(2250)───zsh(8375)─┬─pstree(9080)
                                                               └─vim(8431)
$ cc -Wall -g    fork.c   -o fork
$ ./fork
grandparent: 9102 (ppid 8375)
parent: 9103 (ppid 9102)
parent 9103 exiting
child: 9104 (ppid 1750)
child 9104 exiting
granparent 9102 exiting


Note that the ppid of the child is 1750 and not (as perhaps traditionally
expected) 1.

*/