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



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       send - send a message on a socket

SYNOPSIS
       #include <sys/socket.h>

       ssize_t send(int socket, const void *buffer, size_t length, int flags);


DESCRIPTION
       The  send()  function shall initiate transmission of a message from the specified socket to its peer. The send() function
       shall send a message only when the socket is connected (including when the peer of a connectionless socket has  been  set
       via connect()).

       The send() function takes the following arguments:

       socket Specifies the socket file descriptor.

       buffer Points to the buffer containing the message to send.

       length Specifies the length of the message in bytes.

       flags  Specifies the type of message transmission. Values of this argument are formed by logically OR'ing zero or more of
              the following flags:

       MSG_EOR
              Terminates a record (if supported by the protocol).

       MSG_OOB
              Sends out-of-band data on sockets that support out-of-band communications.  The significance and semantics of out-
              of-band data are protocol-specific.



       The  length of the message to be sent is specified by the length argument. If the message is too long to pass through the
       underlying protocol, send() shall fail and no data shall be transmitted.

       Successful completion of a call to send() does not guarantee delivery of the message. A return value of -1 indicates only
       locally-detected errors.

       If  space  is  not  available at the sending socket to hold the message to be transmitted, and the socket file descriptor
       does not have O_NONBLOCK set, send() shall block until space is available.  If space is  not  available  at  the  sending
       socket to hold the message to be transmitted, and the socket file descriptor does have O_NONBLOCK set, send() shall fail.
       The select() and poll() functions can be used to determine when it is possible to send more data.

       The socket in use may require the process to have appropriate privileges to use the send() function.

RETURN VALUE
       Upon successful completion, send() shall return the number of bytes sent. Otherwise, -1 shall be returned and  errno  set
       to indicate the error.

ERRORS
       The send() function shall fail if:

       EAGAIN or EWOULDBLOCK

              The socket's file descriptor is marked O_NONBLOCK and the requested operation would block.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNRESET
              A connection was forcibly closed by a peer.

       EDESTADDRREQ

              The socket is not connection-mode and no peer address is set.

       EINTR  A signal interrupted send() before any data was transmitted.

       EMSGSIZE
              The message is too large to be sent all at once, as the socket requires.

       ENOTCONN
              The socket is not connected or otherwise has not had the peer pre-specified.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EOPNOTSUPP
              The socket argument is associated with a socket that does not support one or more of the values set in flags.

       EPIPE  The  socket  is  shut down for writing, or the socket is connection-mode and is no longer connected. In the latter
              case, and if the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling thread.


       The send() function may fail if:

       EACCES The calling process does not have the appropriate privileges.

       EIO    An I/O error occurred while reading from or writing to the file system.

       ENETDOWN
              The local network interface used to reach the destination is down.

       ENETUNREACH

              No route to the network is present.

       ENOBUFS
              Insufficient resources were available in the system to perform the operation.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The send() function is equivalent to sendto() with a null pointer dest_len argument, and to write() if no flags are used.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       connect(), getsockopt(), poll(), recv(), recvfrom(), recvmsg(), select(), sendmsg(), sendto(), setsockopt(),  shutdown(),
       socket(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      SEND(3P)