What does errno 56 (EDEADLOCK) in Solaris mean?

EDEADLOCK

File locking deadlock compatibility code

EDEADLOCK is Solaris errno 56 (file locking deadlock error). Solaris reports a file-locking deadlock using this older compatibility name.

Treat this compatibility value as a locking result, not as a scheduler failure. Preserve the file, byte range, lock owner, and competing lock request so the actual cycle or incompatible lock ordering can be reconstructed.

What to check

• 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

• Oracle Solaris intro(2): error numbers
• illumos errno.h definitions
• POSIX errno.h