NAME

     accept - accept a connection on a socket

SYNOPSIS

     #include <sys/types.h>

     #include <sys/socket.h>

     int accept(int s, struct sockaddr *addr, int *addrlen

DESCRIPTION

     The argument s is  a  socket  that  has  been  created  with
     socket(2),  bound to an address with bind(2), and is listen-
     ing for connections after a listen(2).  The accept  function
     extracts  the first connection request on the queue of pend-
     ing connections, creates a new socket with the same  proper-
     ties  of  s  and  allocates  a  new  file descriptor for the
     socket.  If no pending connections are present on the queue,
     and  the socket is not marked as non-blocking, accept blocks
     the caller until a connection is present.  If the socket  is
     marked  non-blocking  and no pending connections are present
     on the queue, accept returns an error  as  described  below.
     The  accepted  socket may not be used to accept more connec-
     tions.  The original socket s remains open.

     The argument addr is a result parameter that  is  filled  in
     with  the  address of the connecting entity, as known to the
     communications layer.  The exact format of the addr  parame-
     ter  is  determined by the domain in which the communication
     is occurring.  The addrlen is a value-result  parameter;  it
     should  initially  contain the amount of space pointed to by
     addr; on return it will contain the actual length (in bytes)
     of   the   address   returned.    This  call  is  used  with
     connection-based socket types, currently with SOCK_STREAM.

     It is possible to select(2) a socket  for  the  purposes  of
     doing an accept by selecting it for read.

     For certain protocols which require  an  explicit  confirma-
     tion,  such  as  ISO or DATAKIT, accept can be thought of as
     merely dequeuing the next connection request and not  imply-
     ing  confirmation.   Confirmation can be implied by a normal
     read or write on the new file descriptor, and rejection  can
     be implied by closing the new socket.

     One can obtain user connection request data without confirm-
     ing  the  connection  by  issuing  a recvmsg(2) call with an
     msg_iovlen of 0 and a non-zero msg_controllen, or by issuing
     a  getsockopt(2)  request.   Similarly, one can provide user
     connection rejection information  by  issuing  a  sendmsg(2)
     call with providing only the control information, or by cal-
     ling setsockopt(2).

RETURN VALUES

     The call returns -1 on error.  If it succeeds, it returns  a
     non-negative  integer  that is a descriptor for the accepted
     socket.

ERRORS

     The BSD man page documents five possible error returns.

     EBADF
          The descriptor is invalid.

     ENOTSOCK
          The descriptor references a file, not a socket.

     EOPNOTSUPP
          The referenced socket is not of type SOCK_STREAM.

     EFAULT
          The addr parameter is not in a  writable  part  of  the
          user address space.

     EWOULDBLOCK
          The socket is marked non-blocking  and  no  connections
          are present to be accepted.

     Various Linux kernels can return various other  errors  such
     as  EMFILE,  EINVAL,  ENOSR, ENOBUFS, EAGAIN, EPERM, ECONNA-
     BORTED, ESOCKTNOSUPPORT, EPROTONOSUPPORT,  ETIMEDOUT,  ERES-
     TARTSYS.

CONFORMING TO

     SVr4, 4.4BSD (the accept  function  first  appeared  in  BSD
     4.2).   IRIX  documents additional errors EMFILE and ENFILE.
     Solaris documents additional errors EINTR,  ENODEV,  ENOMEM,
     ENOSR and EPROTO.

SEE ALSO

     bind(2), connect(2), listen(2),