accept - accept a connection on a socket
accept(int s, struct sockaddr *addr, socklen_t *addrlen);
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
listen(2). The accept() argument extracts the first connection request
on the queue of pending connections, creates a new socket
with the same
properties of s, and allocates a new file descriptor for the
no pending connections are present on the queue, and the
socket is not
marked as non-blocking, accept() blocks the caller until a
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 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 connecting 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
This call is used with connection-based socket
It is possible to select(2) or poll(2) a socket for the purposes of doing
an accept() by selecting it for read.
For certain protocols which require an explicit confirmation, such as ISO
or DATAKIT, accept() can be thought of as merely dequeuing
the next connection
request and not implying confirmation. Confirmation
can be implied
by a normal read or write on the new file descriptor,
can be implied by closing the new socket.
One can obtain user connection request data without confirming the connection
by issuing a recvmsg(2) call with an msg_iovlen of 0
and a nonzero
msg_controllen, or by issuing a getsockopt(2) request.
one can provide user connection rejection information by issuing a
sendmsg(2) call providing only the control information, or
The call returns -1 on error. If it succeeds, it returns a
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
[EINVAL] The referenced socket is not listening for
(that is, listen(2) has not yet been called).
[EFAULT] The addr parameter is not in a writable part
of the user
The socket is marked non-blocking and no connections are
present to be accepted.
[EMFILE] The per-process descriptor table is full.
[ENFILE] The system file table is full.
A connection has been aborted.
bind(2), connect(2), listen(2), poll(2), select(2), socket(2)
The accept() function appeared in 4.2BSD.
OpenBSD 3.6 February 15, 1999
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