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 .