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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. If the socket is  a  connectionless-
       mode  socket,  the  message  shall  be  sent  to the pre-specified peer
       address.
       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 pro-
                                 tocol).
                   MSG_OOB       Sends  out-of-band  data on sockets that sup-
                                 port out-of-band communications. The signifi-
                                 cance  and  semantics of out-of-band data are
                                 protocol-specific.
                   MSG_NOSIGNAL  Requests not to send the SIGPIPE signal if an
                                 attempt  to send is made on a stream-oriented
                                 socket  that  is  no  longer  connected.  The
                                 [EPIPE] error shall still be returned.
       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.
       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 or SOCK_SEQPACKET and the
              MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
              the calling thread.
       The send() function may fail if:
       EACCES The calling process does not have 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
       If the socket argument refers to a connection-mode socket,  the  send()
       function  is  equivalent  to sendto() (with any value for the dest_addr
       and dest_len arguments, as they are  ignored  in  this  case).  If  the
       socket  argument  refers  to  a socket and the flags argument is 0, the
       send() function is equivalent to write().
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       connect(),  getsockopt(),  poll(),   pselect(),   recv(),   recvfrom(),
       recvmsg(),  sendmsg(),  sendto(),  setsockopt(),  shutdown(), socket(),
       write()
       The Base Definitions volume of POSIX.1-2008, <sys_socket.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                             SEND(3P)