List of error codes

In the following is a list of networking error codes, the protocol or operation during which the error is likely to occur is given at the beginning of the explanation.

I/O errors

EALREADY	Operation already in progress
EINPROGRESS	Operation now in progress
EWOULDBLOCK	Operation would block

Argument errors

EADDRINUSE	Address already in use	An attempt was made to create a socket with a UNIX pathname which already exists.
EAFNOSUPPORT	Address family not supported by protocol family
EDESTADDRREQ	Destination address required
EMSGSIZE	Message too long
ENOTSOCK	Socket operation on non-socket
EOPNOTSUPP	Operation not supported on socket
EPFNOSUPPORT	Protocol family not supported
EPROTONOSUPPORT	Protocol not supported	Creating a socket. Unknown protocol or protocol not supported.
EPROTOTYPE	Protocol wrong type for socket	Creating a socket. Socket type request has no supporting protocol.
ESOCKTNOSUPPORT	Socket type not supported

Operational errors

ECONNABORTED	Software caused connection abort
ECONNREFUSED	Connection refused	Socket connection. The host refused service for some reason. This error is usually caused by a server process not being present at the requested name.
ECONNRESET	Connection reset by peer	The remote peer forced the session to be closed.
EISCONN	Socket is already connected	An attempt was made to establish a connection on a socket that already has one or an attempt was made to send a datagram with the destination address specified and the socket is already connected.
ENOBUFS	No buffer space available	Any socket operation. The system lacks sufficient memory for an internal data structure.
ENOENT	No such file or directory	Connection could not be established.
ENOTCONN	Socket is not connected	An attempt was made to send a datagram, but no destination address is specified, and the socket has not been connected.
ESHUTDOWN	Cannot send after socket shutdown

Miscellaneous errors

ENOPROTOOPT

Protocol not available