ACCEPT(3P) POSIX Programmer's Manual ACCEPT(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEaccept — accept a new connection on a socket
SYNOPSIS
#include <sys/socket.h>
int accept(int socket, struct sockaddr *restrict address,
socklen_t *restrict address_len);
DESCRIPTION
The accept() function shall extract the first connection on the queue
of pending connections, create a new socket with the same socket type
protocol and address family as the specified socket, and allocate a new
file descriptor for that socket.
The accept() function takes the following arguments:
socket Specifies a socket that was created with socket(), has been
bound to an address with bind(), and has issued a success‐
ful call to listen().
address Either a null pointer, or a pointer to a sockaddr structure
where the address of the connecting socket shall be
returned.
address_len Either a null pointer, if address is a null pointer, or a
pointer to a socklen_t object which on input specifies the
length of the supplied sockaddr structure, and on output
specifies the length of the stored address.
If address is not a null pointer, the address of the peer for the
accepted connection shall be stored in the sockaddr structure pointed
to by address, and the length of this address shall be stored in the
object pointed to by address_len.
If the actual length of the address is greater than the length of the
supplied sockaddr structure, the stored address shall be truncated.
If the protocol permits connections by unbound clients, and the peer is
not bound, then the value stored in the object pointed to by address is
unspecified.
If the listen queue is empty of connection requests and O_NONBLOCK is
not set on the file descriptor for the socket, accept() shall block
until a connection is present. If the listen() queue is empty of con‐
nection requests and O_NONBLOCK is set on the file descriptor for the
socket, accept() shall fail and set errno to [EAGAIN] or [EWOULDBLOCK].
The accepted socket cannot itself accept more connections. The original
socket remains open and can accept more connections.
RETURN VALUE
Upon successful completion, accept() shall return the non-negative file
descriptor of the accepted socket. Otherwise, −1 shall be returned and
errno set to indicate the error.
ERRORS
The accept() function shall fail if:
EAGAIN or EWOULDBLOCK
O_NONBLOCK is set for the socket file descriptor and no connec‐
tions are present to be accepted.
EBADF The socket argument is not a valid file descriptor.
ECONNABORTED
A connection has been aborted.
EINTR The accept() function was interrupted by a signal that was
caught before a valid connection arrived.
EINVAL The socket is not accepting connections.
EMFILE All file descriptors available to the process are currently
open.
ENFILE The maximum number of file descriptors in the system are already
open.
ENOBUFS
No buffer space is available.
ENOMEM There was insufficient memory available to complete the opera‐
tion.
ENOTSOCK
The socket argument does not refer to a socket.
EOPNOTSUPP
The socket type of the specified socket does not support accept‐
ing connections.
The accept() function may fail if:
EPROTO A protocol error has occurred; for example, the STREAMS protocol
stack has not been initialized.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
When a connection is available, select() indicates that the file
descriptor for the socket is ready for reading.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSObind(), connect(), listen(), socket()
The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ACCEPT(3P)
