#include <fcntl.h>           /* For O_* constants */
#include <sys/stat.h>        /* For mode constants */
#include <semaphore.h>
#include <stdio.h>
#include <errno.h>

int main (){
  sem_t * testSem = sem_open("/aaa", O_CREAT|O_EXCL, 0600, 1);
  printf("HELLO %d\n", errno); // errno is set to 2 (no such file or dir)
  sem_close(testSem);
}