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

NAME

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

SYNOPSIS

       #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);

DESCRIPTION

       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  possible	to
       send more data.

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

       MSG_OOB
	      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.

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

       MSG_DONTWAIT
	      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)).

       MSG_NOSIGNAL
	      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).

RETURN VALUE

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

ERRORS

       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 pages.

       EBADF  An invalid descriptor was specified.

       ENOTSOCK
	      The argument s is not a socket.

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

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

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

       ENOBUFS
	      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 overflows.)

       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.

CONFORMING TO

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

       MSG_CONFIRM is a Linux extension.

NOTE

       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 argument 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).

SEE ALSO

       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)