mq_open 错误号 13 权限被拒绝

Question

我在尝试使用 mq_open() 调用创建 posix mq 时遇到权限问题运行。我确实合并了此处提到的更改 mq_open Permission denied I looked on other relevant post like this https://groups.google.com/forum/#!topic/comp.unix.programmer/hnTZf6aPpbE 但这也指向同一件事。

此外，在尝试编译时，我运行遇到了未识别 mq 调用的错误，在线显示通过在 gcc 中添加 -lrt 进行编译，post 能够编译，提到因为我不完全了解它的基本原理，也没有通过阅读 post :)

来理解它

gcc server_mq.c -lrt -o 服务器

错误编号为 13

天哪，mqd 出了点问题！ 权限被拒绝

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

#include "client_server.h"

#define PATH "/tmp/servermq"

int main(void)
{
    mqd_t mqd;
    mode_t omask;
    omask = umask(0);
    int flags = O_RDWR | O_CREAT | O_EXCL;
    struct mq_attr attr, *attrp;

    attr.mq_maxmsg = 5;
    attr.mq_msgsize = 1024;

    attrp = &attr;

    mqd = mq_open(PATH, flags, S_IRUSR | S_IWUSR | S_IWGRP, attrp);


    if (mqd == (mqd_t)-1)
    {
        printf("error number is %d \n ",errno);
        printf(" Oh dear, something went wrong with mqd ! %s\n", strerror(errno));
    }

    umask(omask);
    mq_close(mqd);
    mq_unlink(PATH);
    return 0;
}

Answer 1

您不能使用 /tmp/servermq 作为您的名字...

引用 人 mq_overvie:

   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.

您很快就会发现此部分相关：

Mounting the message queue file system
On Linux, message queues are created in a virtual file system. (Other implementations may also provide such a feature, but the details are likely to differ.) This file system can be mounted (by the superuser) using the following commands:
           # mkdir /dev/mqueue
           # mount -t mqueue none /dev/mqueue

       The sticky bit is automatically enabled on the mount directory.

mq_open 错误号 13 权限被拒绝

mq_open err no 13 Permission denied

c

linux

posix

message-queue