ACCEPT(3)                  POSIX Programmer's Manual                 ACCEPT(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                            ACCEPT(3)
