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


int
main()
{
        pid_t parentPID = getpid();
        printf("parent pid: %d\n", parentPID);
        printf("parent pgid: %d\n", getpgrp());

        pid_t childPID = fork();
        if (childPID < 0) {
                fprintf(stderr, "fork() failed: %s\n", strerror(errno));
                exit(1);
        } else if (childPID == 0) {
                // child
                childPID = getpid();
                printf("child  pid: %d, pgid: %d\n", childPID, getpgrp());

                printf("child  setpgid(0, 0)\n");
                if (setpgid(0, 0) < 0) {
                        fprintf(stderr, "child: first setpgid() failed: %s\n", strerror(errno));
                        exit(1);
                }
//              printf("child  setsid()\n");
//              if (setsid() < 0) {
//                      fprintf(stderr, "child: setsid() failed: %s\n", strerror(errno));
//                      exit(1);
//              }

                printf("child  pgid: %d\n", getpgrp());

                pid_t grandChildPID = fork();
                if (grandChildPID < 0) {
                        fprintf(stderr, "fork() 2 failed: %s\n", strerror(errno));
                        exit(1);
                } else if (grandChildPID == 0) {
                        // grand child
                        grandChildPID = getpid();
                        printf("gchild pid: %d, pgid: %d\n", grandChildPID, getpgrp());
                        sleep(2);
                        printf("gchild pid: %d, pgid: %d\n", grandChildPID, getpgrp());
                } else {
                        // child
                        sleep(1);

                        printf("child  setpgid(0, %d)\n", parentPID);
                        if (setpgid(0, parentPID) < 0) {
//                      printf("child  setpgid(0, 0)\n");
//                      if (setpgid(0, 0) < 0) {
                                fprintf(stderr, "child: second setpgid() failed: %s\n", strerror(errno));
                                exit(1);
                        }

                        printf("child  pgid: %d\n", getpgrp());
                }

        } else {
                // parent
                sleep(3);
        }

        return 0;
}