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
21 The sendmsg() function shall send a message through a connection-mode
22 or connectionless-mode socket. If the socket is connectionless-mode,
23 the message shall be sent to the address specified by msghdr. If the
24 socket is connection-mode, the destination address in msghdr shall be
25 ignored.
26 The sendmsg() function takes the following arguments:
28 socket Specifies the socket file descriptor.
30 message
32 Points to a msghdr structure, containing both the destination
33 address and the buffers for the outgoing message. The length and
34 format of the address depend on the address family of the
35 socket. The msg_flags member is ignored.
36 flags Specifies the type of message transmission. The application may
38 specify 0 or the following flag:
39 MSG_EOR
41 Terminates a record (if supported by the protocol).
42 MSG_OOB
44 Sends out-of-band data on sockets that support out-of-bound
45 data. The significance and semantics of out-of-band data are
46 protocol-specific.
47 The msg_iov and msg_iovlen fields of message specify zero or more buf‐
51 fers containing the data to be sent. msg_iov points to an array of
52 iovec structures; msg_iovlen shall be set to the dimension of this
53 array. In each iovec structure, the iov_base field specifies a storage
54 area and the iov_len field gives its size in bytes. Some of these sizes
55 can be zero. The data from each storage area indicated by msg_iov is
56 sent in turn.
57 Successful completion of a call to sendmsg() does not guarantee deliv‐
59 ery of the message. A return value of -1 indicates only locally-
60 detected errors.
61 If space is not available at the sending socket to hold the message to
63 be transmitted and the socket file descriptor does not have O_NONBLOCK
64 set, the sendmsg() function shall block until space is available. If
65 space is not available at the sending socket to hold the message to be
66 transmitted and the socket file descriptor does have O_NONBLOCK set,
67 the sendmsg() function shall fail.
68 If the socket protocol supports broadcast and the specified address is
70 a broadcast address for the socket protocol, sendmsg() shall fail if
71 the SO_BROADCAST option is not set for the socket.
72 The socket in use may require the process to have appropriate privi‐
74 leges to use the sendmsg() function.
75
77 Upon successful completion, sendmsg() shall return the number of bytes
78 sent. Otherwise, -1 shall be returned and errno set to indicate the
79 error.
80
82 The sendmsg() function shall fail if:
83 EAGAIN or EWOULDBLOCK
85 The socket's file descriptor is marked O_NONBLOCK and the
86 requested operation would block.
87 EAFNOSUPPORT
89 Addresses in the specified address family cannot be used with
90 this socket.
91 EBADF The socket argument is not a valid file descriptor.
93 ECONNRESET
95 A connection was forcibly closed by a peer.
96 EINTR A signal interrupted sendmsg() before any data was transmitted.
98 EINVAL The sum of the iov_len values overflows an ssize_t.
100 EMSGSIZE
102 The message is too large to be sent all at once (as the socket
103 requires), or the msg_iovlen member of the msghdr structure
104 pointed to by message is less than or equal to 0 or is greater
105 than {IOV_MAX}.
106 ENOTCONN
108 The socket is connection-mode but is not connected.
109 ENOTSOCK
111 The socket argument does not refer to a socket.
112 EOPNOTSUPP
114 The socket argument is associated with a socket that does not
115 support one or more of the values set in flags.
116 EPIPE The socket is shut down for writing, or the socket is connec‐
118 tion-mode and is no longer connected. In the latter case, and if
119 the socket is of type SOCK_STREAM, the SIGPIPE signal is gener‐
120 ated to the calling thread.
121 If the address family of the socket is AF_UNIX, then sendmsg() shall
124 fail if:
125 EIO An I/O error occurred while reading from or writing to the file
127 system.
128 ELOOP A loop exists in symbolic links encountered during resolution of
130 the pathname in the socket address.
131 ENAMETOOLONG
133 A component of a pathname exceeded {NAME_MAX} characters, or an
134 entire pathname exceeded {PATH_MAX} characters.
135 ENOENT A component of the pathname does not name an existing file or
137 the path name is an empty string.
138 ENOTDIR
140 A component of the path prefix of the pathname in the socket
141 address is not a directory.
142 The sendmsg() function may fail if:
145 EACCES Search permission is denied for a component of the path prefix;
147 or write access to the named socket is denied.
148 EDESTADDRREQ
150 The socket is not connection-mode and does not have its peer
151 address set, and no destination address was specified.
152 EHOSTUNREACH
154 The destination host cannot be reached (probably because the
155 host is down or a remote router cannot reach it).
156 EIO An I/O error occurred while reading from or writing to the file
158 system.
159 EISCONN
161 A destination address was specified and the socket is already
162 connected.
163 ENETDOWN
165 The local network interface used to reach the destination is
166 down.
167 ENETUNREACH
169 No route to the network is present.
170 ENOBUFS
172 Insufficient resources were available in the system to perform
173 the operation.
174 ENOMEM Insufficient memory was available to fulfill the request.
176 If the address family of the socket is AF_UNIX, then sendmsg() may fail
179 if:
180 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
182 resolution of the pathname in the socket address.
183 ENAMETOOLONG
185 Pathname resolution of a symbolic link produced an intermediate
186 result whose length exceeds {PATH_MAX}.
187 The following sections are informative.
190
192 Done.
193
195 The select() and poll() functions can be used to determine when it is
196 possible to send more data.
197
199 None.
200
202 None.
203
205 getsockopt(), poll(), recv(), recvfrom(), recvmsg(), select(), send(),
206 sendto(), setsockopt(), shutdown(), socket(), the Base Definitions vol‐
207 ume of IEEE Std 1003.1-2001, <sys/socket.h>
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210 Portions of this text are reprinted and reproduced in electronic form
211 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
212 -- Portable Operating System Interface (POSIX), The Open Group Base
213 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
214 Electrical and Electronics Engineers, Inc and The Open Group. In the
215 event of any discrepancy between this version and the original IEEE and
216 The Open Group Standard, the original IEEE and The Open Group Standard
217 is the referee document. The original Standard can be obtained online
218 at http://www.opengroup.org/unix/online.html .
219IEEE/The Open Group 2003 SENDMSG(3P)