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.
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
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
The accepted socket cannot itself accept more connections. The
original socket remains open and can accept more connections.
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.
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
ENFILE The maximum number of file descriptors in the system are
No buffer space is available.
ENOMEM There was insufficient memory available to complete the
The socket argument does not refer to a socket.
The socket type of the specified socket does not support
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.
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 Electrical 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
IEEE/The Open Group 2013 ACCEPT(3P)