What does errno 98 (ENOSR) in Mac mean?

ENOSR

ENOSR: a STREAMS-style resource could not be allocated

On Darwin, ENOSR denotes exhaustion in a legacy STREAMS resource pool or an interface preserving that errno contract. The critical question is which stream/message allocation failed, not whether a policy identifier exists.

Measure the resource pressure

Capture the syscall or ioctl, stream/module identity, number of active stream objects, message or queue pressure if exposed, process lifetime, and relevant kernel/provider logs. Preserve errno immediately after the failing call so later diagnostics do not overwrite it.

Verification

Release a controlled set of stream resources or correct a leak, then repeat the same operation at comparable load. A valid fix returns resource use toward baseline and allows the allocation to complete without requiring a reboot to erase the evidence.

Technical references

• Apple XNU errno.h.
• POSIX errno definitions and portability limits.