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



PPRROOLLOOGG
       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.

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

SSYYNNOOPPSSIISS
       #include <sys/socket.h>

       ssize_t sendmsg(int _s_o_c_k_e_t, const struct msghdr *_m_e_s_s_a_g_e, int _f_l_a_g_s);

DDEESSCCRRIIPPTTIIOONN
       The _s_e_n_d_m_s_g() 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 mmssgghhddrr 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 mmssgghhddrr (overriding the pre-specified peer address), or the
       function shall return -1 and set _e_r_r_n_o to [[EEIISSCCOONNNN]].  If the socket is
       connection-mode, the destination address in mmssgghhddrr shall be ignored.

       The _s_e_n_d_m_s_g() function takes the following arguments:

       _s_o_c_k_e_t      Specifies the socket file descriptor.

       _m_e_s_s_a_g_e     Points to a mmssgghhddrr 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 _m_s_g___f_l_a_g_s member is
                   ignored.

       _f_l_a_g_s       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
                                 [[EEPPIIPPEE]] error shall still be returned.

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

       Successful completion of a call to _s_e_n_d_m_s_g() 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 _s_e_n_d_m_s_g() 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 _s_e_n_d_m_s_g() function shall fail.

       If the socket protocol supports broadcast and the specified address is
       a broadcast address for the socket protocol, _s_e_n_d_m_s_g() 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 _s_e_n_d_m_s_g() function.

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

EERRRROORRSS
       The _s_e_n_d_m_s_g() function shall fail if:

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

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

       EEBBAADDFF  The _s_o_c_k_e_t argument is not a valid file descriptor.

       EECCOONNNNRREESSEETT
              A connection was forcibly closed by a peer.

       EEIINNTTRR  A signal interrupted _s_e_n_d_m_s_g() before any data was transmitted.

       EEIINNVVAALL The sum of the _i_o_v___l_e_n values overflows an ssssiizzee__tt.

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

       EENNOOTTCCOONNNN
              The socket is connection-mode but is not connected.

       EENNOOTTSSOOCCKK
              The _s_o_c_k_e_t argument does not refer to a socket.

       EEOOPPNNOOTTSSUUPPPP
              The _s_o_c_k_e_t argument is associated with a socket that does not
              support one or more of the values set in _f_l_a_g_s.

       EEPPIIPPEE  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 _s_e_n_d_m_s_g() shall
       fail if:

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

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

       EENNAAMMEETTOOOOLLOONNGG
              The length of a component of a pathname is longer than
              {NAME_MAX}.

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

       EENNOOTTDDIIRR
              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 _s_e_n_d_m_s_g() function may fail if:

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

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

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

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

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

       EENNEETTDDOOWWNN
              The local network interface used to reach the destination is
              down.

       EENNEETTUUNNRREEAACCHH
              No route to the network is present.

       EENNOOBBUUFFSS
              Insufficient resources were available in the system to perform
              the operation.

       EENNOOMMEEMM Insufficient memory was available to fulfill the request.

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

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

       EENNAAMMEETTOOOOLLOONNGG
              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}.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       Done.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The _s_e_l_e_c_t() and _p_o_l_l() functions can be used to determine when it is
       possible to send more data.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _g_e_t_s_o_c_k_o_p_t(), _p_o_l_l(), _p_s_e_l_e_c_t(), _r_e_c_v(), _r_e_c_v_f_r_o_m(), _r_e_c_v_m_s_g(), _s_e_n_d(),
       _s_e_n_d_t_o(), _s_e_t_s_o_c_k_o_p_t(), _s_h_u_t_d_o_w_n(), _s_o_c_k_e_t()

       The Base Definitions volume of POSIX.1-2017, <<ssyyss__ssoocckkeett..hh>>

CCOOPPYYRRIIGGHHTT
       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                           SENDMSG(3)
