What does errno 46 (EPFNOSUPPORT) mean?

EPFNOSUPPORT

The family selection failed locally

EPFNOSUPPORT reports that the requested protocol family is not supported. In BSD-derived networking, protocol-family and address-family terminology overlap in many APIs, but they describe different stages of the socket model; do not assume that equal numeric constants make every use interchangeable.

This result precedes hostname resolution, routing, and connection establishment. It is therefore evidence about the local build, platform capability, or configuration passed into the socket layer—not about the state of a remote host.

What to record

• Capture the family constant, the API that received it, and whether a cross-platform wrapper translated a neutral configuration into a BSD-specific value.
• Record the socket type and protocol too; a later compatibility error may otherwise be mistaken for a family error.
• Check whether code accidentally used a protocol-family constant in an address structure or used a family not enabled for the intended platform.

Nearby error

EAFNOSUPPORT is more often tied to a particular address being unsuitable for a socket or operation. EPFNOSUPPORT says the selected family itself is not available to the local stack.

References

• XNU: Darwin errno definitions
• POSIX: socket()
• POSIX: bind()

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