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EL2NSYNC
EL2NSYNC: Linux legacy errno
EL2NSYNC (errno 2) reports that the legacy level-2 communications state is not synchronized. 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 identity, protocol state, synchronization counters, and last successful event. Save errno immediately after the failing call, together with its return value, because later library or logging calls can overwrite thread-local error state.
Focused test
compare synchronization state before and after a controlled reinitialization of the same stream. Keep the process, device/endpoint and deployed driver version fixed so the comparison changes only the suspected boundary.
Correction
restore protocol synchronization rather than changing unrelated application data. If the interface is provided by a compatibility driver, verify its documented ABI and object lifetime instead of assuming that a numerically similar errno from another UNIX has the same contract.
Verification
Repeat the original system call and confirm it passes the former EL2NSYNC boundary with the same object identity. If another errno appears, preserve it as a separate result from the next failing operation.
Technical references
- Linux man-pages: errno(3)
- Linux kernel: asm-generic errno definitions
- GNU C Library: error codes
- illumos: STREAMS programming documentation
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