ACCEPT(2) System Calls ACCEPT(2)
accept - accept a connection on a socket
int accept (int s, struct sockaddr *addr, int *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 after a
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 socket. If
no pending connections 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 connec-
tions 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
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 for read.
For certain protocols which require an explicit confirmation, such as
ISO or DATAKIT, accept can be thought of as merely dequeueing the next
connection request and not implying confirmation. Confirmation can be
implied by a normal read or write on the new file descriptor, and
rejection can be implied by closing the new socket.
One can obtain user connection request data without confirming the con-
nection by issuing a recvmsg(2) call with an msg_iovlen of 0 and a non-
zero msg_controllen, or by issuing a getsockopt(2) request. Similarly,
one can provide user connection rejection information by issuing a
sendmsg(2) call with providing only the control information, or by
The call returns -1 on error. If it succeeds, it returns a non-nega-
tive integer that is a descriptor for the accepted socket.
The accept will fail if:
EBADF The descriptor is invalid.
The descriptor references a file, not a socket.
The referenced socket is not of type SOCK_STREAM.
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.
bind(2), connect(2), listen(2), select(2), socket(2)
The accept function appeared in 4.2BSD. The first appearance in GNO
was in v2.0.5.
GNO 16 January 1997 ACCEPT(2)
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