NAME

       sendmsg - send a message on a socket using a message structure

SYNOPSIS

       #include <sys/socket.h>

       ssize_t sendmsg(int socket, const struct msghdr *message, int flags);

DESCRIPTION

       The  sendmsg()  function shall send a message through a connection-mode or connectionless-
       mode socket. If the socket is connectionless-mode,  the  message  shall  be  sent  to  the
       address  specified by msghdr. If the socket is connection-mode, the destination address in
       msghdr shall be ignored.

       The sendmsg() function takes the following arguments:

       socket Specifies the socket file descriptor.

       message
              Points to a msghdr structure, containing  both  the  destination  address  and  the
              buffers  for  the  outgoing message. The length and format of the address depend on
              the address family of the socket. The msg_flags member is ignored.

       flags  Specifies the type of message transmission. The application may specify  0  or  the
              following flag:

       MSG_EOR
              Terminates a record (if supported by the protocol).

       MSG_OOB
              Sends out-of-band data on sockets that support out-of-bound data.  The significance
              and semantics of out-of-band data are protocol-specific.

       The msg_iov and msg_iovlen fields of message specify zero or more buffers  containing  the
       data  to be sent.  msg_iov points to an array of iovec structures; msg_iovlen shall be set
       to the dimension of this array. In each iovec structure, the iov_base  field  specifies  a
       storage  area  and  the  iov_len field gives its size in bytes. Some of these sizes can be
       zero. The data from each storage area indicated by msg_iov is sent in turn.

       Successful completion of a call to sendmsg() 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,  the  sendmsg()  function  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, the
       sendmsg() function shall fail.

       If the socket protocol supports broadcast and the specified address is a broadcast address
       for the socket protocol, sendmsg() shall fail if the SO_BROADCAST option is  not  set  for
       the socket.

       The  socket  in  use  may  require  the  process to have appropriate privileges to use the
       sendmsg() function.

RETURN VALUE

       Upon successful completion, sendmsg() shall return the number of bytes sent. Otherwise, -1
       shall be returned and errno set to indicate the error.

ERRORS

       The sendmsg() function shall fail if:

       EAGAIN or EWOULDBLOCK
              The socket's file descriptor is marked O_NONBLOCK and the requested operation would
              block.

       EAFNOSUPPORT
              Addresses in the specified address family cannot be used with this socket.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNRESET
              A connection was forcibly closed by a peer.

       EINTR  A signal interrupted sendmsg() before any data was transmitted.

       EINVAL The sum of the iov_len values overflows an ssize_t.

       EMSGSIZE
              The message is too large to be sent all at once (as the socket  requires),  or  the
              msg_iovlen  member  of  the  msghdr structure pointed to by message is less than or
              equal to 0 or is greater than {IOV_MAX}.

       ENOTCONN
              The socket is connection-mode but 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, the
              SIGPIPE signal is generated to the calling thread.

       If the address family of the socket is AF_UNIX, then sendmsg() shall fail if:

       EIO    An I/O error occurred while reading from or writing to the file system.

       ELOOP  A  loop  exists  in symbolic links encountered during resolution of the pathname in
              the socket address.

       ENAMETOOLONG
              A component of a pathname exceeded {NAME_MAX} characters,  or  an  entire  pathname
              exceeded {PATH_MAX} characters.

       ENOENT A  component  of the pathname does not name an existing file or the path name is an
              empty string.

       ENOTDIR
              A component of the path prefix of the pathname in  the  socket  address  is  not  a
              directory.

       The sendmsg() function may fail if:

       EACCES Search  permission is denied for a component of the path prefix; or write access to
              the named socket is denied.

       EDESTADDRREQ
              The socket is not connection-mode and does not have its peer address  set,  and  no
              destination address was specified.

       EHOSTUNREACH
              The  destination  host  cannot  be  reached (probably because the host is down or a
              remote router cannot reach it).

       EIO    An I/O error occurred while reading from or writing to the file system.

       EISCONN
              A destination address was specified and the socket is already connected.

       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.

       ENOMEM Insufficient memory was available to fulfill the request.

       If the address family of the socket is AF_UNIX, then sendmsg() may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during  resolution  of  the
              pathname in the socket address.

       ENAMETOOLONG
              Pathname resolution of a symbolic link produced an intermediate result whose length
              exceeds {PATH_MAX}.

       The following sections are informative.

EXAMPLES

       Done.

APPLICATION USAGE

       The select() and poll() functions can be used to determine when it  is  possible  to  send
       more data.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       getsockopt()  ,  poll() , recv() , recvfrom() , recvmsg() , select() , send() , 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 .