sendmsg(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

SENDMSG(3P)             POSIX Programmer's Manual            SENDMSG(3P)

PROLOG         top

       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         top

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

SYNOPSIS         top

       #include <sys/socket.h>

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

DESCRIPTION         top

       The sendmsg() function shall send a message through a connection-
       mode or connectionless-mode socket. If the socket is a
       connectionless-mode socket, the message shall be sent to the
       address specified by msghdr if no pre-specified peer address has
       been set. If a peer address has been pre-specified, either the
       message shall be sent to the address specified in msghdr
       (overriding the pre-specified peer address), or the function
       shall return -1 and set errno to [EISCONN].  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.

                   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 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         top

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

ERRORS         top

       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 or
              SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set, 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
              The length of a component of a pathname is longer than
              {NAME_MAX}.

       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 names an existing file that is neither a
              directory nor a symbolic link to a directory, or the
              pathname in the socket address contains at least one
              non-<slash> character and ends with one or more trailing
              <slash> characters and the last pathname component names
              an existing file that is neither a directory nor a
              symbolic link to 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
              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate
              result with a length that exceeds {PATH_MAX}.

       The following sections are informative.

EXAMPLES         top

       Done.

APPLICATION USAGE         top

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

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       getsockopt(3p), poll(3p), pselect(3p), recv(3p), recvfrom(3p),
       recvmsg(3p), send(3p), sendto(3p), setsockopt(3p), shutdown(3p),
       socket(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       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:https://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                       SENDMSG(3P)

Pages that refer to this page: netinet_in.h(0p)sys_socket.h(0p)pselect(3p)recv(3p)recvfrom(3p)recvmsg(3p)send(3p)sendto(3p)socket(3p)