List of error codes (Internet domain)

In the following 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

Error Name	Description	Explanation
EALREADY	Operation already in progress
EINPROGRESS	Operation now in progress
EWOULDBLOCK	Operation would block

Argument errors

Error Name	Description	Explanation
EADDRINUSE	Address already in use	TCP and UDP. An attempt was made to create a socket with a port which has already been allocated.
EADDRNOTAVAIL	Can't assign requested address	TCP and UDP. An attempt was made to create a socket with a network address for which no network interface 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

Error Name	Description	Explanation
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	TCP. The remote peer forced the session to be closed.
EISCONN	Socket is already connected	IP and UDP. 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. TCP. An attempt was made to establish a connection on a socket that already has one.
ENETDOWN	Network is down	Socket connection. Status information received by the client host from the underlying communication services indicates the net or the remote host is down.
ENETRESET	Network dropped connection on reset
ENETUNREACH	Network is unreachable
ENOBUFS	No buffer space available	TCP, IP, and UDP. Any Socket Operation. The system lacks sufficient memory for an internal data structure.
ENOTCONN	Socket is not connected	UDP. 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
ETIMEDOUT	Connection timed out	Socket connection. After failing to establish a connection during a period of time (excessive retransmissions), the system decided there was no point in retrying any more. The cause for this error is usually that the remote host is down or that problems in the network resulted in transmissions being lost.

Miscellaneous errors

Error Name	Description	Explanation
EHOSTDOWN	Host is down	Socket connection. Status information received by the client host from the underlying communication services indicates the net or the remote host is down.
EHOSTUNREACH	No route to host	Socket connection. These operational errors can occur either because the network or host is unknown (no route to the host or network is present) or because status information to that effect has been delivered to the client host by the underlying communication services.
ENOPROTOOPT	Protocol not available