What does errno 42 (ENOMSG) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A nonblocking System V message-queue receive found no message matching the requested type or position.

Could be also:
Constant	Type	OS
KERN_SEMAPHORE_DESTROYED	Kern return	Mac
ippStsI18nGetMessageFail	Intel Ipp Status	Any
ENOPROTOOPT	errno	Mac
EUNATCH	errno	Solaris
EILSEQ	errno	Windows
INCONSISTENT_IRP	BugCheck Code	Windows

Previous	Next
ENOTEMPTY	ENOPROTOOPT

ENOMSG

A queue state result, not a broken queue

ENOMSG is commonly returned by msgrcv() when the caller asks for a message without waiting and no message matching the requested type is present. The queue can still exist, contain other message types, and be functioning normally. The result is therefore closer to “nothing currently matches this selection” than to an I/O failure.

The selected type matters. System V message queues allow receivers to request the first message, a specific positive type, a message of a different type, or the lowest suitable type for a negative request. A producer and consumer can both be healthy yet disagree on that selection rule. With checkpoint-oriented MSG_COPY, an unavailable ordinal position can also produce the same result.

How to use it correctly

Record the queue identifier, requested type, flags, and queue depth when handling the result.
Use IPC_NOWAIT only when polling or a no-message outcome is an expected part of the protocol.
Do not treat ENOMSG as proof that a producer is dead; check type selection and consumer competition first.
Use a timeout, event-driven wakeup, or explicit application acknowledgement when polling would create unnecessary load.

References

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