尝试使用POSIX消息队列创建消息队列时，权限被拒绝 [英] Permission denied when trying to create message queue using POSIX Message Queues

问题描述

我通过遵循 Linux编程接口来创建带有以下代码段的消息队列.

I am creating a message queue with the following snippet by following The Linux Programming Interface.

if((mq_open("/my_message_queue", O_CREAT, O_RDWR, NULL)) == -1) {
    perror("mq creation failed");
}

运行此代码段时出现错误:权限被拒绝".我想检查一下以前是否创建了队列并且没有销毁它，所以我使用了ipcs.但是，ipcs不会显示任何活动的消息队列.以前(Ubuntu 18.04)我从未在开发环境中使用过POSIX IPC库.我必须做一些设置以允许我的用户进程创建消息队列吗?我使用API​​的方式不正确吗?

Running this snippet I get an error: "permission denied". I wanted to check and see if I had created the queue previously and not destroyed it, so I used ipcs. However, ipcs does not show any active message queues. I have never used the POSIX IPC libraries in my development environment before (Ubuntu 18.04). Is some set up I must do to allow my user process to create a message queue? Am I using the API incorrectly?

推荐答案

来自

oflag参数指定用于控制调用操作的标志. (可以通过包含<fcntl.h>来获得标志值的定义.)确切地，必须在oflag中指定以下之一:

The oflag argument specifies flags that control the operation of the call. (Definitions of the flags values can be obtained by including <fcntl.h>.) Exactly one of the following must be specified in oflag:

O_RDONLY打开队列仅接收消息.

O_RDONLY Open the queue to receive messages only.

O_WRONLY打开队列以仅发送消息.

O_WRONLY Open the queue to send messages only.

O_RDWR打开队列以发送和接收消息.

O_RDWR Open the queue to both send and receive messages.

您的代码中没有这三个值.确切地说，您可以这样做，但是它是在mode参数中，而不是在oflag参数中，其中相应的数字具有完全不同的含义.第三个参数是创建队列时使用的文件系统权限位(就像创建新文件时open()的第三个参数一样)，而不是打开队列的方式.

You have none of those three values in your code. Or rather you do, but it's in the mode argument, not the oflag one, where the corresponding number has a completely different meaning. That third argument is the filesystem permission bits used when creating the queue (just like the third argument to open() when creating a new file), not the mode the queue is opened in.

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