macOS kernel return 6 (KERN_RESOURCE

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: Mach could not allocate a required system resource; the condition may be temporary.

Could be also:
Constant	Type	OS
ERROR_INVALID_HANDLE	Win32 error	Windows
ippStsDivByZero	Intel Ipp Status	Any
ENXIO	errno	Any
INVALID_PROCESS_DETACH_ATTEMPT	BugCheck Code	Windows

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KERN_FAILURE	KERN_NOT_RECEIVER

KERN_RESOURCE_SHORTAGE

KERN_RESOURCE_SHORTAGE means Mach could not allocate a system resource needed to satisfy the request. XNU explicitly describes this as potentially non-permanent. It is therefore different from a malformed request and different from KERN_NO_SPACE, which refers to an unsuitable virtual address range.

The code by itself does not identify which resource was scarce. Depending on the operation, the limiting factor can be memory-management metadata, a port or IPC-related resource, a kernel allocation, or another subsystem resource. Treating every occurrence as ordinary application heap exhaustion loses that context.

Practical response

Record the exact Mach call, requested size, target task, and the preceding resource lifecycle events.
Release resources that are no longer needed before retrying.
Use a bounded retry only when the caller can safely tolerate a transient failure; an unbounded immediate retry can amplify pressure.
Compare the failure with VM-map state. If the requested address range itself is the issue, KERN_NO_SPACE is the more specific condition.

Apple's Mach model separates task address spaces, memory objects, ports, and IPC resources. The return code tells you allocation failed at the Mach layer; the failing API provides the context required to find the constrained resource.

References

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