What does errno 125 (EADDRINUSE) mean?

EADDRINUSE

EADDRINUSE is Solaris errno value 125. Oracle describes the condition as an attempt to use an address that is already in use when the protocol does not permit that reuse. For sockets, the exact local address and the operation that failed are more useful than the short text Address already in use.

Check the local endpoint before the remote network

When bind() fails with this errno, compare the address family, local IP address, port, and wildcard-versus-specific binding with existing endpoints. Also inspect the socket options applied before the bind. SO_REUSEADDR changes some reuse rules, but it is not a universal way to force two incompatible bindings to coexist.

If the error comes from another transport operation, record that call separately rather than assuming a bind collision. Solaris defines the errno at the transport-address level. A route, DNS change, or remote service restart does not free a local address that is already occupied under the protocol's binding rules.

References

• Oracle Solaris intro(2): EADDRINUSE
• POSIX bind()
• illumos errno.h

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