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SEND(2) 			    Linux Programmer's Manual				  SEND(2)

       send, sendto, sendmsg - send a message from a socket

       #include <sys/types.h>
       #include <sys/socket.h>

       int send(int s, const void *msg, size_t len, int flags);
       int  sendto(int	s,  const  void  *msg,	size_t len, int flags, const struct sockaddr *to,
       socklen_t tolen);
       int sendmsg(int s, const struct msghdr *msg, int flags);

       Send, sendto, and sendmsg are used to transmit a message to another socket.  Send  may  be
       used only when the socket is in a connected state, while sendto and sendmsg may be used at
       any time.

       The address of the target is given by to with tolen specifying its size.   The  length  of
       the  message  is  given by len.	If the message is too long to pass atomically through the
       underlying protocol, the error EMSGSIZE is returned, and the message is not transmitted.

       No indication of failure to deliver is implicit in a send.  Locally  detected  errors  are
       indicated by a return value of -1.

       When  the  message  does not fit into the send buffer of the socket, send normally blocks,
       unless the socket has been placed in non-blocking I/O mode.  In non-blocking mode it would
       return EAGAIN in this case.  The select(2) call may be used to determine when it is possi-
       ble to send more data.

       The flags parameter is a flagword and can contain the following flags:

	      Sends out-of-band data on sockets that support this notion (e.g.	SOCK_STREAM); the
	      underlying protocol must also support out-of-band data.

	      Dont't  use  a  gateway to send out the packet, only send to hosts on directly con-
	      nected networks. This is usually used only by diagnostic or routing programs.  This
	      is only defined for protocol families that route; packet sockets don't.

	      Enables  non-blocking  operation;  if the operation would block, EAGAIN is returned
	      (this can also be enabled using the O_NONBLOCK with the F_SETFL fcntl(2)).

	      Requests not to send SIGPIPE on errors on stream oriented sockets  when  the  other
	      end breaks the connection. The EPIPE error is still returned.

       MSG_CONFIRM (Linux 2.3+ only)
	      Tell  the link layer that forward process happened: you got a successful reply from
	      the other side. If the link layer doesn't get  this  it'll  regularly  reprobe  the
	      neighbour  (e.g. via a unicast ARP).  Only valid on SOCK_DGRAM and SOCK_RAW sockets
	      and currently only implemented for IPv4 and IPv6. See arp(7) for details.

       The definition of the msghdr structure  follows.  See  recv(2)  and  below  for	an  exact
       description of its fields.

	      struct msghdr {
		  void	       * msg_name;     /* optional address */
		  socklen_t    msg_namelen;    /* size of address */
		  struct iovec * msg_iov;      /* scatter/gather array */
		  size_t       msg_iovlen;     /* # elements in msg_iov */
		  void	       * msg_control;  /* ancillary data, see below */
		  socklen_t    msg_controllen; /* ancillary data buffer len */
		  int	       msg_flags;      /* flags on received message */

       You  may  send  control	information using the msg_control and msg_controllen members. The
       maximum control buffer length the  kernel  can  process	is  limited  per  socket  by  the
       net.core.optmem_max sysctl; see socket(7).

       The calls return the number of characters sent, or -1 if an error occurred.

       These  are  some  standard  errors generated by the socket layer. Additional errors may be
       generated and returned from the underlying protocol modules; see their  respective  manual

       EBADF  An invalid descriptor was specified.

	      The argument s is not a socket.

       EFAULT An invalid user space address was specified for a parameter.

	      The socket requires that message be sent atomically, and the size of the message to
	      be sent made this impossible.

	      The socket is marked non-blocking and the requested operation would block.

	      The output queue for a network interface was full.  This generally  indicates  that
	      the  interface  has  stopped  sending,  but  may be caused by transient congestion.
	      (This cannot occur in Linux, packets are just silently dropped when a device  queue

       EINTR  A signal occurred.

       ENOMEM No memory available.

       EINVAL Invalid argument passed.

       EPIPE  The local end has been shut down on a connection oriented socket.  In this case the
	      process will also receive a SIGPIPE unless MSG_NOSIGNAL is set.

       4.4BSD, SVr4, POSIX 1003.1g draft (these function calls appeared in 4.2BSD).

       MSG_CONFIRM is a Linux extension.

       The prototypes given above follow the Single Unix Specification, as glibc2 also does;  the
       flags  argument was `int' in BSD 4.*, but `unsigned int' in libc4 and libc5; the len argu-
       ment was `int' in BSD 4.* and libc4, but `size_t' in libc5; the tolen argument  was  `int'
       in BSD 4.* and libc4 and libc5.	See also accept(2).

       fcntl(2),  recv(2), select(2), getsockopt(2), sendfile(2), socket(2), write(2), socket(7),
       ip(7), tcp(7), udp(7)

Linux Man Page				     1999-07					  SEND(2)
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