/***  Example of fork  ***/
// gcc -o fork fork.c
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>

int main(){
  int x = 0;
  pid_t pid;

  fprintf(stdout,"Start...  x=%d\n",x);
  pid=fork();

  if(pid==0){  // Child (prints to standard error)
    x = 1;
    fprintf(stderr,"Child...  x=%d (PID=%d, parent is %d)\n",x,getpid(),getppid());
    sleep(2);  // Child is working...
    fprintf(stderr,"Child ps:\n");
    system("ps -l | grep fork >&2");
    sleep(2);  // Child is working...
    fprintf(stderr,"End child. (PID=%d)\n",getpid());
    return 0;
    }
  else{  // Parent (prints to standard output)
    x = 2;
    fprintf(stdout,"Parent... x=%d (PID=%d)\n",x,getpid());
    sleep(6);  // Parent is working...
    fprintf(stdout,"Parent ps:\n");
    system("ps -l | grep fork");
    sleep(2);  // Parent is working...
    fprintf(stdout,"End parent. (PID=%d)\n",getpid());
    return 0;
    }
  }