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



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

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
                                 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.

                   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
       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.

       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 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.1-2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              SEND(3)
