What does errno 56 (EDEADLOCK) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: Solaris reports a file-locking deadlock using this older compatibility name.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_CMDS	Win32 error	Windows
EBADRQC	errno	Linux
EISCONN	errno	Mac
SERIAL_DRIVER_INTERNAL	BugCheck Code	Windows

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EISCONN	EBADSLT

EDEADLOCK

File locking deadlock compatibility code

On Solaris, EDEADLOCK is errno value 56. The base message is file locking deadlock error, but the useful diagnostic context is narrower than the short message: solaris reports a file-locking deadlock using this older compatibility name.

For EDEADLOCK, use the Solaris-specific errno table first, then compare with POSIX only for portable behavior. For EDEADLOCK, some Solaris values share names with other UNIX systems but have different numbers or more specific historical meanings.

What to check for EDEADLOCK

Treat it like a lock-ordering failure, not as a storage or permission problem.
Capture the file, byte range, process ids, and lock acquisition order.
Prefer portable handling that also recognizes EDEADLK.

References for EDEADLOCK

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