1SENDMSG(3P) POSIX Programmer's Manual SENDMSG(3P)
2
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.
10
12 sendmsg — send a message on a socket using a message structure
13
15 #include <sys/socket.h>
16 ssize_t sendmsg(int socket, const struct msghdr *message, int flags);
18
20 The sendmsg() function shall send a message through a connection-mode
21 or connectionless-mode socket. If the socket is a connectionless-mode
22 socket, the message shall be sent to the address specified by msghdr if
23 no pre-specified peer address has been set. If a peer address has been
24 pre-specified, either the message shall be sent to the address speci‐
25 fied in msghdr (overriding the pre-specified peer address), or the
26 function shall return -1 and set errno to [EISCONN]. If the socket is
27 connection-mode, the destination address in msghdr shall be ignored.
28 The sendmsg() function takes the following arguments:
30 socket Specifies the socket file descriptor.
32 message Points to a msghdr structure, containing both the destina‐
34 tion address and the buffers for the outgoing message. The
35 length and format of the address depend on the address fam‐
36 ily of the socket. The msg_flags member is ignored.
37 flags Specifies the type of message transmission. The application
39 may specify 0 or the following flag:
40 MSG_EOR Terminates a record (if supported by the pro‐
42 tocol).
43 MSG_OOB Sends out-of-band data on sockets that sup‐
45 port out-of-bound data. The significance and
46 semantics of out-of-band data are protocol-
47 specific.
48 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
50 attempt to send is made on a stream-oriented
51 socket that is no longer connected. The
52 [EPIPE] error shall still be returned.
53 The msg_iov and msg_iovlen fields of message specify zero or more buf‐
55 fers containing the data to be sent. msg_iov points to an array of
56 iovec structures; msg_iovlen shall be set to the dimension of this
57 array. In each iovec structure, the iov_base field specifies a storage
58 area and the iov_len field gives its size in bytes. Some of these sizes
59 can be zero. The data from each storage area indicated by msg_iov is
60 sent in turn.
61 Successful completion of a call to sendmsg() does not guarantee deliv‐
63 ery of the message. A return value of -1 indicates only locally-
64 detected errors.
65 If space is not available at the sending socket to hold the message to
67 be transmitted and the socket file descriptor does not have O_NONBLOCK
68 set, the sendmsg() function shall block until space is available. If
69 space is not available at the sending socket to hold the message to be
70 transmitted and the socket file descriptor does have O_NONBLOCK set,
71 the sendmsg() function shall fail.
72 If the socket protocol supports broadcast and the specified address is
74 a broadcast address for the socket protocol, sendmsg() shall fail if
75 the SO_BROADCAST option is not set for the socket.
76 The socket in use may require the process to have appropriate privi‐
78 leges to use the sendmsg() function.
79
81 Upon successful completion, sendmsg() shall return the number of bytes
82 sent. Otherwise, -1 shall be returned and errno set to indicate the
83 error.
84
86 The sendmsg() function shall fail if:
87 EAGAIN or EWOULDBLOCK
89 The socket's file descriptor is marked O_NONBLOCK and the
90 requested operation would block.
91 EAFNOSUPPORT
93 Addresses in the specified address family cannot be used with
94 this socket.
95 EBADF The socket argument is not a valid file descriptor.
97 ECONNRESET
99 A connection was forcibly closed by a peer.
100 EINTR A signal interrupted sendmsg() before any data was transmitted.
102 EINVAL The sum of the iov_len values overflows an ssize_t.
104 EMSGSIZE
106 The message is too large to be sent all at once (as the socket
107 requires), or the msg_iovlen member of the msghdr structure
108 pointed to by message is less than or equal to 0 or is greater
109 than {IOV_MAX}.
110 ENOTCONN
112 The socket is connection-mode but is not connected.
113 ENOTSOCK
115 The socket argument does not refer to a socket.
116 EOPNOTSUPP
118 The socket argument is associated with a socket that does not
119 support one or more of the values set in flags.
120 EPIPE The socket is shut down for writing, or the socket is connec‐
122 tion-mode and is no longer connected. In the latter case, and if
123 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
124 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
125 the calling thread.
126 If the address family of the socket is AF_UNIX, then sendmsg() shall
128 fail if:
129 EIO An I/O error occurred while reading from or writing to the file
131 system.
132 ELOOP A loop exists in symbolic links encountered during resolution of
134 the pathname in the socket address.
135 ENAMETOOLONG
137 The length of a component of a pathname is longer than
138 {NAME_MAX}.
139 ENOENT A component of the pathname does not name an existing file or
141 the path name is an empty string.
142 ENOTDIR
144 A component of the path prefix of the pathname in the socket
145 address names an existing file that is neither a directory nor a
146 symbolic link to a directory, or the pathname in the socket
147 address contains at least one non-<slash> character and ends
148 with one or more trailing <slash> characters and the last path‐
149 name component names an existing file that is neither a direc‐
150 tory nor a symbolic link to a directory.
151 The sendmsg() function may fail if:
153 EACCES Search permission is denied for a component of the path prefix;
155 or write access to the named socket is denied.
156 EDESTADDRREQ
158 The socket is not connection-mode and does not have its peer
159 address set, and no destination address was specified.
160 EHOSTUNREACH
162 The destination host cannot be reached (probably because the
163 host is down or a remote router cannot reach it).
164 EIO An I/O error occurred while reading from or writing to the file
166 system.
167 EISCONN
169 A destination address was specified and the socket is already
170 connected.
171 ENETDOWN
173 The local network interface used to reach the destination is
174 down.
175 ENETUNREACH
177 No route to the network is present.
178 ENOBUFS
180 Insufficient resources were available in the system to perform
181 the operation.
182 ENOMEM Insufficient memory was available to fulfill the request.
184 If the address family of the socket is AF_UNIX, then sendmsg() may fail
186 if:
187 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
189 resolution of the pathname in the socket address.
190 ENAMETOOLONG
192 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
193 tion of a symbolic link produced an intermediate result with a
194 length that exceeds {PATH_MAX}.
195 The following sections are informative.
197
199 Done.
200
202 The select() and poll() functions can be used to determine when it is
203 possible to send more data.
204
206 None.
207
209 None.
210
212 getsockopt(), poll(), pselect(), recv(), recvfrom(), recvmsg(), send(),
213 sendto(), setsockopt(), shutdown(), socket()
214 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
216
218 Portions of this text are reprinted and reproduced in electronic form
219 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
220 table Operating System Interface (POSIX), The Open Group Base Specifi‐
221 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
222 Electrical and Electronics Engineers, Inc and The Open Group. In the
223 event of any discrepancy between this version and the original IEEE and
224 The Open Group Standard, the original IEEE and The Open Group Standard
225 is the referee document. The original Standard can be obtained online
226 at http://www.opengroup.org/unix/online.html .
227 Any typographical or formatting errors that appear in this page are
229 most likely to have been introduced during the conversion of the source
230 files to man page format. To report such errors, see https://www.ker‐
231 nel.org/doc/man-pages/reporting_bugs.html .
232IEEE/The Open Group 2017 SENDMSG(3P)