[mag@vertex:~]% cat a.c     
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    printf("pid: %d\n", getpid());
    if(fork())
    {
        sleep(1);
        exit(0);
    }
    printf("in child: parent pid: %d\n", getppid());
    printf("setpgid returns %d\n", setpgid(0, 0));
    printf("in child after setpgid: parent pid: %d\n", getppid());
}
[mag@vertex:~]% gcc -o a a.c
[mag@vertex:~]% ./a         
pid: 8066
in child: parent pid: 8066
setpgid returns 0
in child after setpgid: parent pid: 8066
[mag@vertex:~]%