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.
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13 send — send a message on a socket
14
16 #include <sys/socket.h>
17 ssize_t send(int socket, const void *buffer, size_t length, int flags);
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21 The send() function shall initiate transmission of a message from the
22 specified socket to its peer. The send() function shall send a message
23 only when the socket is connected. If the socket is a connectionless-
24 mode socket, the message shall be sent to the pre-specified peer
25 address.
26 The send() function takes the following arguments:
28 socket Specifies the socket file descriptor.
30 buffer Points to the buffer containing the message to send.
32 length Specifies the length of the message in bytes.
34 flags Specifies the type of message transmission. Values of this
36 argument are formed by logically OR'ing zero or more of the
37 following flags:
38 MSG_EOR Terminates a record (if supported by the pro‐
40 tocol).
41 MSG_OOB Sends out-of-band data on sockets that sup‐
43 port out-of-band communications. The signifi‐
44 cance and semantics of out-of-band data are
45 protocol-specific.
46 MSG_NOSIGNAL Requests not to send the SIGPIPE signal if an
48 attempt to send is made on a stream-oriented
49 socket that is no longer connected. The
50 [EPIPE] error shall still be returned.
51 The length of the message to be sent is specified by the length argu‐
53 ment. If the message is too long to pass through the underlying proto‐
54 col, send() shall fail and no data shall be transmitted.
55 Successful completion of a call to send() does not guarantee delivery
57 of the message. A return value of −1 indicates only locally-detected
58 errors.
59 If space is not available at the sending socket to hold the message to
61 be transmitted, and the socket file descriptor does not have O_NONBLOCK
62 set, send() shall block until space is available. If space is not
63 available at the sending socket to hold the message to be transmitted,
64 and the socket file descriptor does have O_NONBLOCK set, send() shall
65 fail. The select() and poll() functions can be used to determine when
66 it is possible to send more data.
67 The socket in use may require the process to have appropriate privi‐
69 leges to use the send() function.
70
72 Upon successful completion, send() shall return the number of bytes
73 sent. Otherwise, −1 shall be returned and errno set to indicate the
74 error.
75
77 The send() function shall fail if:
78 EAGAIN or EWOULDBLOCK
80 The socket's file descriptor is marked O_NONBLOCK and the
81 requested operation would block.
82 EBADF The socket argument is not a valid file descriptor.
84 ECONNRESET
86 A connection was forcibly closed by a peer.
87 EDESTADDRREQ
89 The socket is not connection-mode and no peer address is set.
90 EINTR A signal interrupted send() before any data was transmitted.
92 EMSGSIZE
94 The message is too large to be sent all at once, as the socket
95 requires.
96 ENOTCONN
98 The socket is not connected.
99 ENOTSOCK
101 The socket argument does not refer to a socket.
102 EOPNOTSUPP
104 The socket argument is associated with a socket that does not
105 support one or more of the values set in flags.
106 EPIPE The socket is shut down for writing, or the socket is connec‐
108 tion-mode and is no longer connected. In the latter case, and if
109 the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the
110 MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to
111 the calling thread.
112 The send() function may fail if:
114 EACCES The calling process does not have appropriate privileges.
116 EIO An I/O error occurred while reading from or writing to the file
118 system.
119 ENETDOWN
121 The local network interface used to reach the destination is
122 down.
123 ENETUNREACH
125 No route to the network is present.
126 ENOBUFS
128 Insufficient resources were available in the system to perform
129 the operation.
130 The following sections are informative.
132
134 None.
135
137 If the socket argument refers to a connection-mode socket, the send()
138 function is equivalent to sendto() (with any value for the dest_addr
139 and dest_len arguments, as they are ignored in this case). If the
140 socket argument refers to a socket and the flags argument is 0, the
141 send() function is equivalent to write().
142
144 None.
145
147 None.
148
150 connect(), getsockopt(), poll(), pselect(), recv(), recvfrom(),
151 recvmsg(), sendmsg(), sendto(), setsockopt(), shutdown(), socket(),
152 write()
153 The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>
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157 Portions of this text are reprinted and reproduced in electronic form
158 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
159 -- Portable Operating System Interface (POSIX), The Open Group Base
160 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
161 cal and Electronics Engineers, Inc and The Open Group. (This is
162 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
163 event of any discrepancy between this version and the original IEEE and
164 The Open Group Standard, the original IEEE and The Open Group Standard
165 is the referee document. The original Standard can be obtained online
166 at http://www.unix.org/online.html .
167 Any typographical or formatting errors that appear in this page are
169 most likely to have been introduced during the conversion of the source
170 files to man page format. To report such errors, see https://www.ker‐
171 nel.org/doc/man-pages/reporting_bugs.html .
172IEEE/The Open Group 2013 SEND(3P)