errno 133 (EISCONN): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: Socket is already connected

Could be also:
Constant	Type	OS
ERROR_IS_JOIN_TARGET	Win32 error	Windows
EOWNERDEAD	errno	Windows
SETUP_FAILURE	BugCheck Code	Windows

Previous	Next
ENOBUFS	ENOTCONN

EISCONN

The endpoint already has connection state

EISCONN is about socket state, not reachability. Solaris documents two important cases: another connect request is made on an already connected endpoint, or sendto()/sendmsg() supplies a destination for an endpoint whose connection already determines the peer.

This differs from EALREADY, where a nonblocking operation is still in progress, and from ENOTCONN, where a connection-required operation has no established peer. Checking the state transition and the exact API call is therefore more useful than testing routers or firewall policy.

What to inspect in socket code

Trace socket creation, every successful or pending connect(), and any descriptor reuse after connection pooling.
For datagram or message sends, verify whether the application intentionally connected the socket; a connected socket can use send-style operations without specifying a destination each time.
In multithreaded code, establish which thread changed the socket state before the failing call.

References

Looking for a different code? Search another status or error code.