1SEND(3P) POSIX Programmer's Manual SEND(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.
10
12 send — send a message on a socket
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15 #include <sys/socket.h>
16 ssize_t send(int socket, const void *buffer, size_t length, int flags);
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20 The send() function shall initiate transmission of a message from the
21 specified socket to its peer. The send() function shall send a message
22 only when the socket is connected. If the socket is a connectionless-
23 mode socket, the message shall be sent to the pre-specified peer
24 address.
25 The send() function takes the following arguments:
27 socket Specifies the socket file descriptor.
29 buffer Points to the buffer containing the message to send.
31 length Specifies the length of the message in bytes.
33 flags Specifies the type of message transmission. Values of this
35 argument are formed by logically OR'ing zero or more of the
36 following flags:
37 MSG_EOR Terminates a record (if supported by the pro‐
39 tocol).
40 MSG_OOB Sends out-of-band data on sockets that sup‐
42 port out-of-band communications. The signifi‐
43 cance and semantics of out-of-band data are
44 protocol-specific.
45 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
47 attempt to send is made on a stream-oriented
48 socket that is no longer connected. The
49 [EPIPE] error shall still be returned.
50 The length of the message to be sent is specified by the length argu‐
52 ment. If the message is too long to pass through the underlying proto‐
53 col, send() shall fail and no data shall be transmitted.
54 Successful completion of a call to send() does not guarantee delivery
56 of the message. A return value of -1 indicates only locally-detected
57 errors.
58 If space is not available at the sending socket to hold the message to
60 be transmitted, and the socket file descriptor does not have O_NONBLOCK
61 set, send() shall block until space is available. If space is not
62 available at the sending socket to hold the message to be transmitted,
63 and the socket file descriptor does have O_NONBLOCK set, send() shall
64 fail. The select() and poll() functions can be used to determine when
65 it is possible to send more data.
66 The socket in use may require the process to have appropriate privi‐
68 leges to use the send() function.
69
71 Upon successful completion, send() shall return the number of bytes
72 sent. Otherwise, -1 shall be returned and errno set to indicate the
73 error.
74
76 The send() function shall fail if:
77 EAGAIN or EWOULDBLOCK
79 The socket's file descriptor is marked O_NONBLOCK and the
80 requested operation would block.
81 EBADF The socket argument is not a valid file descriptor.
83 ECONNRESET
85 A connection was forcibly closed by a peer.
86 EDESTADDRREQ
88 The socket is not connection-mode and no peer address is set.
89 EINTR A signal interrupted send() before any data was transmitted.
91 EMSGSIZE
93 The message is too large to be sent all at once, as the socket
94 requires.
95 ENOTCONN
97 The socket is not connected.
98 ENOTSOCK
100 The socket argument does not refer to a socket.
101 EOPNOTSUPP
103 The socket argument is associated with a socket that does not
104 support one or more of the values set in flags.
105 EPIPE The socket is shut down for writing, or the socket is connec‐
107 tion-mode and is no longer connected. In the latter case, and if
108 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
109 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
110 the calling thread.
111 The send() function may fail if:
113 EACCES The calling process does not have appropriate privileges.
115 EIO An I/O error occurred while reading from or writing to the file
117 system.
118 ENETDOWN
120 The local network interface used to reach the destination is
121 down.
122 ENETUNREACH
124 No route to the network is present.
125 ENOBUFS
127 Insufficient resources were available in the system to perform
128 the operation.
129 The following sections are informative.
131
133 None.
134
136 If the socket argument refers to a connection-mode socket, the send()
137 function is equivalent to sendto() (with any value for the dest_addr
138 and dest_len arguments, as they are ignored in this case). If the
139 socket argument refers to a socket and the flags argument is 0, the
140 send() function is equivalent to write().
141
143 None.
144
146 None.
147
149 connect(), getsockopt(), poll(), pselect(), recv(), recvfrom(),
150 recvmsg(), sendmsg(), sendto(), setsockopt(), shutdown(), socket(),
151 write()
152 The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>
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156 Portions of this text are reprinted and reproduced in electronic form
157 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
158 table Operating System Interface (POSIX), The Open Group Base Specifi‐
159 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
160 Electrical and Electronics Engineers, Inc and The Open Group. In the
161 event of any discrepancy between this version and the original IEEE and
162 The Open Group Standard, the original IEEE and The Open Group Standard
163 is the referee document. The original Standard can be obtained online
164 at http://www.opengroup.org/unix/online.html .
165 Any typographical or formatting errors that appear in this page are
167 most likely to have been introduced during the conversion of the source
168 files to man page format. To report such errors, see https://www.ker‐
169 nel.org/doc/man-pages/reporting_bugs.html .
170IEEE/The Open Group 2017 SEND(3P)