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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 (consult 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 connec-
       tionless 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 argu-
              ment are formed by logically OR'ing zero or more of the  follow-
              ing 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 com-
              munications.  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 argu-
       ment. If the message is too long to pass through the underlying  proto-
       col, 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 privi-
       leges 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  connec-
              tion-mode and is no longer connected. In the latter case, and if
              the socket is of type SOCK_STREAM, the SIGPIPE signal is  gener-
              ated 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                             SEND(3P)