mq_open giving "too many open files"

Question

I created a message queue with following code. First few times it works properly.

int main()
{
    mqd_t mqdes;
    char mq_name[10] = "/mq";
    int oflag = O_CREAT | O_RDWR, ret;
    struct mq_attr attr;

    attr.mq_maxmsg = 1024;
    attr.mq_msgsize = 2048; 

    mqdes = mq_open(mq_name, oflag, 0766, &attr);
    if(mqdes == -1) {
            perror("mq_open");
            if(errno == EMFILE)
                    perror("EMFILE");
            exit(1);
    }

    printf("mqueue created, mq_descriptor: %d\n", mqdes);

    ret = mq_close(mqdes);
    if(ret == -1) {
            perror("mq_close");
            exit(2);
    }
    printf(" mq closed successful\n");


    return 0;
}

After that, it's giving following error

mq_open: Too many open files
EMFILE: Too many open files

But why i'm getting this error? How can I see possix message queues like ipcs is for system V?

Are you getting the `mq closed successful\n` message at the end of the session? [HERE](http://stackoverflow.com/a/3056992/645128) is another example of using mq_open, maybe you can see something there that you are not doing. — ryyker, Oct 08 '13 at 15:00
@ryyker: how can it goes to end of the program? mq_open fails and giving error. — gangadhars, Oct 08 '13 at 15:02
Regarding your question _How can I see possix message queues like ipcs is for system V?_ [THIS](http://www.linuxforums.org/forum/red-hat-fedora-linux/93230-what-posix-equivalent-ipcs-m.html) link talks a little about it. I do not see anything else in what you posted that would suggest that you should have too many files open. — ryyker, Oct 08 '13 at 17:40

Fabio · Answer 1 · 2016-06-22T20:24:44.183

3

Try to set the resource limits:

#include <sys/resource.h>

struct rlimit rlim;
memset(&rlim, 0, sizeof(rlim));
rlim.rlim_cur = RLIM_INFINITY;
rlim.rlim_max = RLIM_INFINITY;

setrlimit(RLIMIT_MSGQUEUE, &rlim);

edited Jun 22 '16 at 20:24

answered Jun 22 '16 at 18:55

Fabio

31
2

Worked for me thanks, but not sure why increasing limit from ulimit command did not helped me. – mSatyam Dec 17 '21 at 15:05

alimg · Answer 2 · 2014-03-06T23:10:23.260

2

I had the same issue while trying something. If you have by accident too many open message queues left on your system, you can try deleting your mqueue's in directory /dev/mqueue. This worked for me.

Also you might want to use mq_unlink(const char *name) after the mq_close() to ensure that the queue is removed from the system as described here.

edited Mar 06 '14 at 23:10

answered Feb 27 '14 at 13:19

alimg

141
9

score 1 · Answer 3 · answered Aug 25 '14 at 16:17

I had the same problem and I solved it by increasing RLIMIT_MSGQUEUE via setrlimit.

If the hard limit (rlim_max) is too low as well (which was the case for me), you will have to give your process the CAP_SYS_RESOURCE privilege so that you can set the hard limit before you set the process limit (rlim_cur). Either run $ setcap 'CAP_SYS_RESOURCE=+ep' /path/to/executable over an executable or edit /etc/security/capability.conf to give CAP_SYS_RESOURCE to a user/group.

mq_open giving "too many open files"

3 Answers3