errno 49 (EUNATCH) in Linux: meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: EUNATCH is a legacy Linux errno meaning protocol driver not attached to the legacy stream.

Could be also:
Constant	Type	OS
KERN_OPERATION_TIMED_OUT	Kern return	Mac
ippStsFeatureNotSupported	Intel Ipp Status	Any
EADDRNOTAVAIL	errno	Mac
EDQUOT	errno	Solaris
PHASE0_INITIALIZATION_FAILED	BugCheck Code	Windows

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ENOTSUP	EADDRNOTAVAIL

EUNATCH

EUNATCH: Linux legacy errno

EUNATCH (errno 3) reports that the required protocol driver/module is not attached to the legacy stream. These names come from historical System V/XENIX compatibility interfaces; on modern Linux they usually point to a driver, STREAMS-compatibility layer, or legacy IPC contract rather than a general filesystem error.

Evidence to capture

Record stream/device, expected protocol module, current module stack, and failing request.

Focused test

enumerate the stream modules and reproduce after attaching only the required protocol module.

Correction

attach/configure the required protocol module through the supported stream lifecycle.

Verification

Repeat the original system call and confirm it passes the former EUNATCH boundary with the same object identity.

Technical references

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