mqueuefs – POSIX message queue file system

The mqueuefs module will permit the FreeBSD kernel to support POSIX message queue.  The module contains system calls to manipulate POSIX message queues.  It also contains a file system to implement a view for all message queues of the system.  This helps users to keep track of their message queues and make it more easily usable without having to invent additional tools.

The most common usage is as follows:

      mount -t mqueuefs null /mnt/mqueue

where /mnt/mqueue is a mount point.

It is possible to define an entry in /etc/fstab that looks similar to:

null    /mnt/mqueue     mqueuefs        rw      0       0

This will mount mqueuefs at the /mnt/mqueue mount point during system boot.  Using /mnt/mqueue as a permanent mount point is not advised as its intention has always been to be a temporary mount point.  See hier(7) for more information on FreeBSD directory layout.

Some common tools can be used on the file system, e.g.: cat(1), chmod(1), chown(8), ls(1), rm(1), etc.  To use only the message queue system calls, it is not necessary for user to mount the file system, just load the module or compile it into the kernel.  Manually creating a file, for example, “touch /mnt/mqueue/myqueue”, will create a message queue named myqueue in the kernel, default message queue attributes will be applied to the queue.  It is not advised to use this method to create a queue; it is better to use the mq_open(2) system call to create a queue as it allows the user to specify different attributes.

To see the queue's attributes, just read the file:

      cat /mnt/mqueue/myqueue