Section: POSIX Programmer's Manual (3P)
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.
--- accept a new connection on a socket
int accept(int socket, struct sockaddr *restrict address,
socklen_t *restrict address_len);
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
, File Descriptor Allocation.
function takes the following arguments:
Specifies a socket that was created with
has been bound to an address with
and has issued a successful call to
Either a null pointer, or a pointer to a
structure where the address of the connecting socket shall be returned.
Either a null pointer, if
is a null pointer, or a pointer to a
object which on input specifies the length of the supplied
structure, and on output specifies the length of the stored address.
is not a null pointer, the address of the peer for the accepted
connection shall be stored in the
structure pointed to by
and the length of this address shall be stored in the object pointed to
If the actual length of the address is greater than the length of the
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
If the listen queue is empty of connection requests and O_NONBLOCK is
not set on the file descriptor for the socket,
shall block until a connection is present. If the
queue is empty of connection requests and O_NONBLOCK is set on the file
descriptor for the socket,
shall fail and set
The accepted socket cannot itself accept more connections. The original
socket remains open and can accept more connections.
Upon successful completion,
shall return the non-negative file descriptor of the accepted socket.
Otherwise, -1 shall be returned,
shall be set to indicate the error, and any object pointed to by
shall remain unchanged.
function shall fail if:
- EAGAIN or EWOULDBLOCK
O_NONBLOCK is set for the socket file descriptor and no connections are
present to be accepted.
argument is not a valid file descriptor.
A connection has been aborted.
function was interrupted by a signal that was caught before a valid
is not accepting connections.
All file descriptors available to the process are currently open.
The maximum number of file descriptors in the system are already open.
No buffer space is available.
There was insufficient memory available to complete the operation.
argument does not refer to a socket.
The socket type of the specified socket does not support accepting
function may fail if:
A protocol error has occurred;
for example, the STREAMS protocol stack has not been initialized.
The following sections are informative.
When a connection is available,
indicates that the file descriptor for the socket is ready for reading.
, File Descriptor Allocation,
The Base Definitions volume of POSIX.1-2017,
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
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