#include <stdio.h>
#include <stdlib.h>      /* For EXIT_SUCCESS. */
#include <sys/types.h>   /* For pid_t. */

int main(int argc, char *argv[]){
    pid_t       pid;

    fprintf(stderr, "pid: %d.\n", getpid()); 
    fprintf(stderr, "fork(): %d.\n", fork());
    fprintf(stderr, "pid: %d.\n", getpid()); 
    fprintf(stdout, "Hello world.\n"); 

    exit(EXIT_SUCCESS);
}