#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main(void){
    pid_t pid;

    if ((pid = fork()) < 0){
        perror("fork error");
    }
    else if (pid == 0){
        if ((pid = fork()) < 0){
            perror("fork error");
        }
        else if (pid > 0){
            exit(0);
        }

        // while (getppid() != 1) sleep(1);
        sleep(2);
        printf("second child, parent pid = %ld\n", (long)getppid());
        exit(0);
    }

    if (waitpid(pid, NULL, 0) != pid){
        perror("waitpid error");
    }

    exit(0);
}