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# accept

    ACCEPT(2)                   BSD System Calls Manual                  ACCEPT(2)

    NAME
         accept - accept a connection on a socket

    SYNOPSIS
         #include <sys/types.h>
         #include <sys/socket.h>

         int
         accept(int s, struct sockaddr *addr, socklen_t *addrlen);

    DESCRIPTION
         The argument s is a socket that has been created with socket(2), bound to
         an address with bind(2), and is listening for connections after a
         listen(2).  The accept() argument extracts the first connection request
         on the queue of pending connections, creates a new socket with the same
         properties 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 connections.  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 parameter 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) or poll(2) a socket for the purposes of doing
         an accept() by selecting it for read.

         For certain protocols which require an explicit confirmation, such as ISO
         or DATAKIT, accept() can be thought of as merely dequeuing the next con-
         nection request and not implying confirmation.  Confirmation can be
         implied by a normal read or write on the new file descriptor, and rejec-
         tion can be implied by closing the new socket.

         One can obtain user connection request data without confirming the con-
         nection 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 call-
         ing 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 accept() will fail if:

         [EBADF]            The descriptor is invalid.

         [ENOTSOCK]         The descriptor references a file, not a socket.

         [EOPNOTSUPP]       The referenced socket is not of type SOCK_STREAM.

         [EINVAL]           The referenced socket is not listening for connections
                            (that is, listen(2) has not yet been called).

         [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.

         [EMFILE]           The per-process descriptor table is full.

         [ENFILE]           The system file table is full.

         [ECONNABORTED]     A connection has been aborted.

    SEE ALSO
         bind(2), connect(2), listen(2), poll(2), select(2), poll(2), socket(2)

    HISTORY
         The accept() function appeared in 4.2BSD.

    BSD                            February 15, 1999                           BSD

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