accept - accept a connection on a socket
ns = accept(s, addr, addrlen)
int ns, s;
struct sockaddr *addr;
The argument s is a socket that has been created with socket(2), bound to an address with
bind(2), and is listening for connections after a listen(2). Accept extracts the first
connection on the queue of pending connections, creates a new socket with the same proper-
ties of s and allocates a new file descriptor, ns, for the socket. If no pending connec-
tions are present on the queue, and the socket is not marked as non-blocking, accept
blocks the caller until a connection is present. If the socket is marked non-blocking and
no pending connections are present on the queue, accept returns an error as described
below. The accepted socket, ns, may not be used to accept more connections. The original
socket s remains open.
The argument addr is a result parameter that is filled in with the address of the connect-
ing entity, as known to the communications layer. The exact format of the addr parameter
is determined by the domain in which the communication is occurring. The addrlen is a
value-result parameter; it should initially contain the amount of space pointed to by
addr; on return it will contain the actual length (in bytes) of the address returned.
This call is used with connection-based socket types, currently with SOCK_STREAM.
It is possible to select(2) a socket for the purposes of doing an accept by selecting it
The call returns -1 on error. If it succeeds, it returns a non-negative integer that is a
descriptor for the accepted socket.
The accept will fail if:
[EBADF] The descriptor is invalid.
[ENOTSOCK] The descriptor references a file, not a socket.
[EOPNOTSUPP] The referenced socket is not of type SOCK_STREAM.
[EFAULT] The addr parameter is not in a writable part of the user address
[EWOULDBLOCK] The socket is marked non-blocking and no connections are present to be
bind(2), connect(2), listen(2), select(2), socket(2)
4.2 Berkeley Distribution May 22, 1986 ACCEPT(2)