Programming

#include <stdio.h>
#include <stdlib.h>
#include <mqueue.h>
#include <fcntl.h>   
#include <string.h>
#include <errno.h>
#include <sys/stat.h>

int main()
{
    struct mq_attr attr;
    mqd_t mqd;
    if ((mqd = mq_open("/tmp/queue.123", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR, NULL)) == -1)
    {
        printf("damn it: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    mq_getattr(mqd, &attr);
    printf("max message on queue: %ld\n", attr.mq_maxmsg);
    printf("max message size: %ld\n", attr.mq_msgsize);
    printf("current number of message on the queue: %ld\n", attr.mq_curmsgs);
    mq_close(mqd);
    mq_unlink("/tmp/queue.123");
    return EXIT_SUCCESS;
}

damn it: Permission denied

Message queues are created and opened using mq_open(3);  this  function
       returns  a  message queue descriptor (mqd_t), which is used to refer to
       the open message queue in later calls.  Each message queue  is  identi-
       fied by a name of the form /somename; that is, a null-terminated string
       of up to NAME_MAX (i.e.,  255)  characters  consisting  of  an  initial
       slash,  followed  by one or more characters, none of which are slashes.
       Two processes can operate on the same queue by passing the same name to
       mq_open(3).