52.8. Message Queue Limits

SUSv3 defines two limits for POSIX message queues:

MQ_PRIO_MAX

We described this limit, which defines the maximum priority for a message, in Section 52.5.1.

MQ_OPEN_MAX

An implementation can define this limit to indicate the maximum number of message queues that a process can hold open. SUSv3 requires this limit to be at least _POSIX_MQ_OPEN_MAX (8). Linux doesn’t define this limit. Instead, because Linux implements message queue descriptors as file descriptors (Section 52.7), the applicable limits are those that apply to file descriptors. (In other words, on Linux, the per-process and system-wide limits on the number of file descriptors actually apply to the sum of file descriptors and message queue descriptors.) For further details on the applicable limits, see the discussion of the RLIMIT_NOFILE resource limit in Section 36.3.