ACCEPT
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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.
NAME
accept
--- 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 file descriptor shall be allocated
as described in
Section 2.14,
File Descriptor Allocation.
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 successful 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 connection 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,
errno
shall be set to indicate the error, and any object pointed to by
address_len
shall remain unchanged.
ERRORS
The
accept()
function shall fail if:
- EAGAIN or EWOULDBLOCK
-
O_NONBLOCK is set for the socket file descriptor and no connections 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 operation.
- ENOTSOCK
-
The
socket
argument does not refer to a socket.
- EOPNOTSUPP
-
The socket type of the specified socket does not support accepting
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 ALSO
Section 2.14,
File Descriptor Allocation,
bind(),
connect(),
listen(),
socket()
The Base Definitions volume of POSIX.1-2017,
<sys_socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .