POSIX message queue - Does it still exists after reboot?

Question

On linux, wrote a simple program to create a POSIX message queue, and send a msg to it, after the process terminated, it seems the msg is still there.

The questions are:

• Does the msg still there after reboot?
• If it exists, then it's on disk, how did it guarantee the performance if it stores msg on disk instead of memory.

Answer 1

On Linux, message queues are mounted on a virtual file system, and the presence of a file does not imply that anything is written to physical media. This implementation is specific to Linux and not required POSIX behaviour.

The mq_overview man page describes the implementation.