Maximum number of messages that can be created. If a msgsnd call attempts to exceed this limit, the request is deferred until a message header is available. Or, if the request has set the IPC_NOWAIT flag, the request fails with the error EGAIN.
0 to MAXINT
No. Loaded into msgtql field of msginfo structure.
When msgsnd() calls block or return with error of EGAIN, or at the recommendation of a software vendor.