accept(2)                                                         accept(2)




 NAME    [Toc]    [Back]
      accept - accept a connection on a socket

 SYNOPSIS    [Toc]    [Back]
      #include <sys/socket.h>

    AF_CCITT only    [Toc]    [Back]
      #include <x25/x25addrstr.h>

      int accept(int s, void *addr, int *addrlen);

    _XOPEN_SOURCE_EXTENDED only (UNIX 98)
      int accept(int s, struct sockaddr *addr, socklen_t *addrlen);

    Obsolescent _XOPEN_SOURCE_EXTENDED only (UNIX 95)    [Toc]    [Back]
      int accept(int s, struct sockaddr *addr, size_t *addrlen);

 DESCRIPTION    [Toc]    [Back]
      The accept() system call is used with connection-based socket types,
      such as SOCK_STREAM.  The argument, s, is a socket descriptor created
      with socket(), bound to a local address by bind(), and listening for
      connections after a listen().  accept() extracts the first connection
      on the queue of pending connections, creates a new socket with the
      same properties as s, and returns a new file descriptor, ns, for the
      socket.

      If no pending connections are present on the queue and nonblocking
      mode has not been enabled with the fcntl() O_NONBLOCK or O_NDELAY
      flags or the ioctl() FIOSNBIO request, accept() blocks the caller
      until a connection is present.  O_NONBLOCK and O_NDELAY are defined in
      <sys/fcntl.h> (see fcntl(2), fcntl(5), and socket(7)).  FIOSNBIO and
      the equivalent request FIONBIO are defined in <sys/ioctl.h>, although
      use of FIONBIO is not recommended (see ioctl(2), ioctl(5), and
      socket(7)).

      If the socket has nonblocking mode enabled and no pending connections
      are present on the queue, accept() returns an error as described
      below.  The accepted socket, ns, cannot be used to accept more
      connections.  The original socket s remains open for incoming
      connection requests.  To determine whether a listening socket has
      pending connection requests ready for an accept() call, use select()
      for reading.

      The argument addr should point to a socket address structure.  The
      accept() call fills in this structure with the address of the
      connecting entity, as known to the underlying protocol.  In the case
      of AF_UNIX sockets, the peer's address is filled in only if the peer
      had done an explicit bind() before doing a connect().  Therefore, for
      AF_UNIX sockets, in the common case, when the peer had not done an
      explicit bind() before doing a connect(), the structure is filled with
      a string of nulls for the address.  The format of the address depends



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 accept(2)                                                         accept(2)




      upon the protocol and the address-family of the socket s.

      The argument addrlen is a pointer to a variable.  Initially, the
      variable should contain the size of the structure pointed to by addr.
      On return, it contains the actual length (in bytes) of the address
      returned.  If the memory pointed to by addr is not large enough to
      contain the entire address, only the first addrlen bytes of the
      address are returned.  If addr is NULL or addrlen contains 0, the
      connecting entity's address will not be returned.

      The fcntl() O_NONBLOCK and O_NDELAY flags and ioctl() FIOSNBIO request
      are all supported.  These features interact as follows:

         +  If the O_NONBLOCK or O_NDELAY flag has been set, accept()
            requests behave accordingly, regardless of any FIOSNBIO
            requests.

         +  If neither the O_NONBLOCK flag nor the O_NDELAY flag has been
            set, FIOSNBIO requests control the behavior of accept().

    AF_CCITT only    [Toc]    [Back]
      The addr parameter to accept() returns addressing information for the
      connecting entity, except for the x25ifname[] field of addr which
      contains the name of the local X.25 interface through which the
      connection request arrived.  Call-acceptance can be controlled with
      the ioctl() X25_CALL_ACPT_APPROVAL request.

 RETURN VALUE    [Toc]    [Back]
      Upon successful completion, accept() returns a nonnegative integer
      which is a descriptor for the accepted socket.

      If an error occurs, accept() returns -1 and sets errno to indicate the
      cause.

 ERRORS    [Toc]    [Back]
      If accept() fails, errno is set to one of the following values:

      [EAGAIN]            Nonblocking I/O is enabled using O_NONBLOCK and no
                          connections are present to be accepted.

      [EBADF]             The argument, s, is not a valid file descriptor.

      [ECONNABORTED]      The socket is being shutdown due to a request by
                          software.  This is usually caused by a shutdown()
                          system call.

      [EFAULT]            The addr parameter is not a valid pointer.

      [EINTR]             The call was interrupted by a signal before a
                          valid connection arrived.




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 accept(2)                                                         accept(2)




      [EINVAL]            The socket referenced by s is not currently a
                          listen socket or has been shut down with
                          shutdown().  A listen() must be done before an
                          accept() is allowed.

      [EMFILE]            The maximum number of file descriptors for this
                          process are currently open.

      [ENFILE]            The system's table of open files is full and no
                          more accept() calls can be processed at this time.

      [ENOBUFS]           No buffer space is available.  The accept() cannot
                          complete.  The queued socket connect request is
                          aborted.

      [ENOMEM]            No memory is available.  The accept() cannot
                          complete.  The queued socket connect request is
                          aborted.

      [ENOTSOCK]          The argument, s, is a valid file descriptor, but
                          it is not a socket.

      [EOPNOTSUPP]        The socket referenced by s does not support
                          accept().

      [EWOULDBLOCK]       Nonblocking I/O is enabled using O_NDELAY or
                          FIOSNBIO and no connections are present to be
                          accepted.

 OBSOLESCENCE    [Toc]    [Back]
      Currently, the socklen_t and size_t types are the same size.  This is
      compatible with both the UNIX 95 and UNIX 98 profiles.  However, in a
      future release, socklen_t might be a different size.  In that case,
      passing a size_t pointer will evoke compile-time warnings, which must
      be corrected in order for the application to behave correctly.
      Applications that use socklen_t now, where appropriate, will avoid
      such migration problems.  On the other hand, applications that need to
      be portable to the UNIX 95 profile should follow the X/Open
      specification (see xopen_networking(7)).

 FUTURE DIRECTION    [Toc]    [Back]
      Currently, the default behavior is the HP-UX BSD Sockets; however, it
      might be changed to X/Open Sockets in a future release.  At that time,
      any HP-UX BSD Sockets behavior that is incompatible with X/Open
      Sockets might be obsoleted.  Applications that conform to the X/Open
      specification now will avoid migration problems (see
      xopen_networking(7)).

 AUTHOR    [Toc]    [Back]
      accept() was developed by HP and the University of California,
      Berkeley.



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 accept(2)                                                         accept(2)




 SEE ALSO    [Toc]    [Back]
      bind(2), connect(2), listen(2), select(2), socket(2),
      thread_safety(5), xopen_networking(7).

 STANDARDS CONFORMANCE    [Toc]    [Back]
      accept(): XPG4


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