1SENDMSG(3P) POSIX Programmer's Manual SENDMSG(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 sendmsg — send a message on a socket using a message structure
14
16 #include <sys/socket.h>
17 ssize_t sendmsg(int socket, const struct msghdr *message, int flags);
19
21 The sendmsg() function shall send a message through a connection-mode
22 or connectionless-mode socket. If the socket is a connectionless-mode
23 socket, the message shall be sent to the address specified by msghdr if
24 no pre-specified peer address has been set. If a peer address has been
25 pre-specified, either the message shall be sent to the address speci‐
26 fied in msghdr (overriding the pre-specified peer address), or the
27 function shall return −1 and set errno to [EISCONN]. If the socket is
28 connection-mode, the destination address in msghdr shall be ignored.
29 The sendmsg() function takes the following arguments:
31 socket Specifies the socket file descriptor.
33 message Points to a msghdr structure, containing both the destina‐
35 tion address and the buffers for the outgoing message. The
36 length and format of the address depend on the address fam‐
37 ily of the socket. The msg_flags member is ignored.
38 flags Specifies the type of message transmission. The application
40 may specify 0 or the following flag:
41 MSG_EOR Terminates a record (if supported by the pro‐
43 tocol).
44 MSG_OOB Sends out-of-band data on sockets that sup‐
46 port out-of-bound data. The significance and
47 semantics of out-of-band data are protocol-
48 specific.
49 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
51 attempt to send is made on a stream-oriented
52 socket that is no longer connected. The
53 [EPIPE] error shall still be returned.
54 The msg_iov and msg_iovlen fields of message specify zero or more buf‐
56 fers containing the data to be sent. msg_iov points to an array of
57 iovec structures; msg_iovlen shall be set to the dimension of this
58 array. In each iovec structure, the iov_base field specifies a storage
59 area and the iov_len field gives its size in bytes. Some of these sizes
60 can be zero. The data from each storage area indicated by msg_iov is
61 sent in turn.
62 Successful completion of a call to sendmsg() does not guarantee deliv‐
64 ery of the message. A return value of −1 indicates only locally-
65 detected errors.
66 If space is not available at the sending socket to hold the message to
68 be transmitted and the socket file descriptor does not have O_NONBLOCK
69 set, the sendmsg() function shall block until space is available. If
70 space is not available at the sending socket to hold the message to be
71 transmitted and the socket file descriptor does have O_NONBLOCK set,
72 the sendmsg() function shall fail.
73 If the socket protocol supports broadcast and the specified address is
75 a broadcast address for the socket protocol, sendmsg() shall fail if
76 the SO_BROADCAST option is not set for the socket.
77 The socket in use may require the process to have appropriate privi‐
79 leges to use the sendmsg() function.
80
82 Upon successful completion, sendmsg() shall return the number of bytes
83 sent. Otherwise, −1 shall be returned and errno set to indicate the
84 error.
85
87 The sendmsg() function shall fail if:
88 EAGAIN or EWOULDBLOCK
90 The socket's file descriptor is marked O_NONBLOCK and the
91 requested operation would block.
92 EAFNOSUPPORT
94 Addresses in the specified address family cannot be used with
95 this socket.
96 EBADF The socket argument is not a valid file descriptor.
98 ECONNRESET
100 A connection was forcibly closed by a peer.
101 EINTR A signal interrupted sendmsg() before any data was transmitted.
103 EINVAL The sum of the iov_len values overflows an ssize_t.
105 EMSGSIZE
107 The message is too large to be sent all at once (as the socket
108 requires), or the msg_iovlen member of the msghdr structure
109 pointed to by message is less than or equal to 0 or is greater
110 than {IOV_MAX}.
111 ENOTCONN
113 The socket is connection-mode but is not connected.
114 ENOTSOCK
116 The socket argument does not refer to a socket.
117 EOPNOTSUPP
119 The socket argument is associated with a socket that does not
120 support one or more of the values set in flags.
121 EPIPE The socket is shut down for writing, or the socket is connec‐
123 tion-mode and is no longer connected. In the latter case, and if
124 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
125 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
126 the calling thread.
127 If the address family of the socket is AF_UNIX, then sendmsg() shall
129 fail if:
130 EIO An I/O error occurred while reading from or writing to the file
132 system.
133 ELOOP A loop exists in symbolic links encountered during resolution of
135 the pathname in the socket address.
136 ENAMETOOLONG
138 The length of a component of a pathname is longer than
139 {NAME_MAX}.
140 ENOENT A component of the pathname does not name an existing file or
142 the path name is an empty string.
143 ENOTDIR
145 A component of the path prefix of the pathname in the socket
146 address names an existing file that is neither a directory nor a
147 symbolic link to a directory, or the pathname in the socket
148 address contains at least one non-<slash> character and ends
149 with one or more trailing <slash> characters and the last path‐
150 name component names an existing file that is neither a direc‐
151 tory nor a symbolic link to a directory.
152 The sendmsg() function may fail if:
154 EACCES Search permission is denied for a component of the path prefix;
156 or write access to the named socket is denied.
157 EDESTADDRREQ
159 The socket is not connection-mode and does not have its peer
160 address set, and no destination address was specified.
161 EHOSTUNREACH
163 The destination host cannot be reached (probably because the
164 host is down or a remote router cannot reach it).
165 EIO An I/O error occurred while reading from or writing to the file
167 system.
168 EISCONN
170 A destination address was specified and the socket is already
171 connected.
172 ENETDOWN
174 The local network interface used to reach the destination is
175 down.
176 ENETUNREACH
178 No route to the network is present.
179 ENOBUFS
181 Insufficient resources were available in the system to perform
182 the operation.
183 ENOMEM Insufficient memory was available to fulfill the request.
185 If the address family of the socket is AF_UNIX, then sendmsg() may fail
187 if:
188 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
190 resolution of the pathname in the socket address.
191 ENAMETOOLONG
193 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
194 tion of a symbolic link produced an intermediate result with a
195 length that exceeds {PATH_MAX}.
196 The following sections are informative.
198
200 Done.
201
203 The select() and poll() functions can be used to determine when it is
204 possible to send more data.
205
207 None.
208
210 None.
211
213 getsockopt(), poll(), pselect(), recv(), recvfrom(), recvmsg(), send(),
214 sendto(), setsockopt(), shutdown(), socket()
215 The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
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219 Portions of this text are reprinted and reproduced in electronic form
220 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
221 -- Portable Operating System Interface (POSIX), The Open Group Base
222 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
223 cal and Electronics Engineers, Inc and The Open Group. (This is
224 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
225 event of any discrepancy between this version and the original IEEE and
226 The Open Group Standard, the original IEEE and The Open Group Standard
227 is the referee document. The original Standard can be obtained online
228 at http://www.unix.org/online.html .
229 Any typographical or formatting errors that appear in this page are
231 most likely to have been introduced during the conversion of the source
232 files to man page format. To report such errors, see https://www.ker‐
233 nel.org/doc/man-pages/reporting_bugs.html .
234IEEE/The Open Group 2013 SENDMSG(3P)