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, 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 .