void sigtstp_handler(int sig){
  char msg[] = "Caught sigstp\n";
  write(1, msg, sizeof(msg));
  return;
}
void sigint_handler(int sig){
  char msg[] = "Caught sigint\n";
  write(1, msg, sizeof(msg));
  return;
}
void hello(int sig){
  char msg[] = "Caught sigusr1\n";
  write(1, msg, sizeof(msg));
  return;
}