ACCEPT(2) BSD System Calls Manual ACCEPT(2)NAMEaccept — accept a connection on a socket
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int
accept(int s, struct sockaddr *addr, socklen_t *addrlen);
DESCRIPTION
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() call extracts the first connection request on
the queue of pending connections, creates a new socket with the same
properties as 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 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. To ensure that the returned
address fits, *addr should have a size of at least sizeof(struct
sockaddr_storage). 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 con‐
nection request and not implying confirmation. Confirmation can be
implied by a normal read or write on the new file descriptor, and rejec‐
tion can be implied by closing the new socket.
For some applications, performance may be enhanced by using an
accept_filter(9) to pre-process incoming connections.
RETURN VALUES
The call returns -1 on error. If it succeeds, it returns a non-negative
integer that is a descriptor for the accepted socket.
ERRORS
The accept() will fail if:
[EBADF] The descriptor is invalid.
[EINTR] The accept() operation was interrupted.
[EMFILE] The per-process descriptor table is full.
[ENFILE] The system file table is full.
[ENOTSOCK] The descriptor references a file, not a socket.
[EINVAL] listen(2) has not been called on the socket descrip‐
tor.
[EFAULT] The addr parameter is not in a writable part of the
user address space.
[EWOULDBLOCK] The socket is marked non-blocking and no connections
are present to be accepted.
[ECONNABORTED] A connection arrived, but it was closed while waiting
on the listen queue.
SEE ALSObind(2), connect(2), getpeername(2), listen(2), select(2), socket(2),
accept_filter(9)HISTORY
The accept() function appeared in 4.2BSD.
BSD December 11, 1993 BSD
