accept(3p) — Linux manual page


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

PROLOG         top

       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         top

       accept — accept a new connection on a socket

SYNOPSIS         top

       #include <sys/socket.h>

       int accept(int socket, struct sockaddr *restrict address,
           socklen_t *restrict address_len);

DESCRIPTION         top

       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

       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         top

       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         top

       The accept() function shall fail if:

              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 open.

       ENFILE The maximum number of file descriptors in the system are
              already open.

              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
              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         top



       When a connection is available, select() indicates that the file
       descriptor for the socket is ready for reading.

RATIONALE         top




SEE ALSO         top

       Section 2.14, File Descriptor Allocation, bind(3p), connect(3p),
       listen(3p), socket(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       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 .

IEEE/The Open Group               2017                        ACCEPT(3P)

Pages that refer to this page: sys_socket.h(0p)connect(3p)getpeername(3p)getsockname(3p)listen(3p)pselect(3p)socket(3p)