1 #include <errno.h>
2 #include <stdio.h>
3 #include <stdlib.h>
4 #include <string.h>
5 #include <unistd.h>
6
7
8 int
main()9 main()
10 {
11 pid_t parentPID = getpid();
12 printf("parent pid: %d\n", parentPID);
13 printf("parent pgid: %d\n", getpgrp());
14
15 pid_t childPID = fork();
16 if (childPID < 0) {
17 fprintf(stderr, "fork() failed: %s\n", strerror(errno));
18 exit(1);
19 } else if (childPID == 0) {
20 // child
21 childPID = getpid();
22 printf("child pid: %d, pgid: %d\n", childPID, getpgrp());
23
24 printf("child setpgid(0, 0)\n");
25 if (setpgid(0, 0) < 0) {
26 fprintf(stderr, "child: first setpgid() failed: %s\n", strerror(errno));
27 exit(1);
28 }
29 // printf("child setsid()\n");
30 // if (setsid() < 0) {
31 // fprintf(stderr, "child: setsid() failed: %s\n", strerror(errno));
32 // exit(1);
33 // }
34
35 printf("child pgid: %d\n", getpgrp());
36
37 pid_t grandChildPID = fork();
38 if (grandChildPID < 0) {
39 fprintf(stderr, "fork() 2 failed: %s\n", strerror(errno));
40 exit(1);
41 } else if (grandChildPID == 0) {
42 // grand child
43 grandChildPID = getpid();
44 printf("gchild pid: %d, pgid: %d\n", grandChildPID, getpgrp());
45 sleep(2);
46 printf("gchild pid: %d, pgid: %d\n", grandChildPID, getpgrp());
47 } else {
48 // child
49 sleep(1);
50
51 printf("child setpgid(0, %d)\n", parentPID);
52 if (setpgid(0, parentPID) < 0) {
53 // printf("child setpgid(0, 0)\n");
54 // if (setpgid(0, 0) < 0) {
55 fprintf(stderr, "child: second setpgid() failed: %s\n", strerror(errno));
56 exit(1);
57 }
58
59 printf("child pgid: %d\n", getpgrp());
60 }
61
62 } else {
63 // parent
64 sleep(3);
65 }
66
67 return 0;
68 }
69