This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The send() function shall initiate transmission of a message from the
specified socket to its peer. The send() function shall send a
message only when the socket is connected. If the socket is a
connectionless-mode socket, the message shall be sent to the pre-
specified peer address.
The send() function takes the following arguments:
socket Specifies the socket file descriptor.
buffer Points to the buffer containing the message to send.
length Specifies the length of the message in bytes.
flags Specifies the type of message transmission. Values of
this argument are formed by logically OR'ing zero or more
of the following flags:
MSG_EOR Terminates a record (if supported by the
MSG_OOB Sends out-of-band data on sockets that
support out-of-band communications. The
significance and semantics of out-of-band
data are protocol-specific.
MSG_NOSIGNAL Requests not to send the SIGPIPE signal if
an attempt to send is made on a stream-
oriented socket that is no longer
connected. The [EPIPE] error shall still be
The length of the message to be sent is specified by the length
argument. If the message is too long to pass through the underlying
protocol, send() shall fail and no data shall be transmitted.
Successful completion of a call to send() does not guarantee delivery
of the message. A return value of −1 indicates only locally-detected
If space is not available at the sending socket to hold the message
to be transmitted, and the socket file descriptor does not have
O_NONBLOCK set, send() shall block until space is available. If space
is not available at the sending socket to hold the message to be
transmitted, and the socket file descriptor does have O_NONBLOCK set,
send() shall fail. The select() and poll() functions can be used to
determine when it is possible to send more data.
The socket in use may require the process to have appropriate
privileges to use the send() function.
The send() function shall fail if:
EAGAIN or EWOULDBLOCK
The socket's file descriptor is marked O_NONBLOCK and the
requested operation would block.
EBADF The socket argument is not a valid file descriptor.
A connection was forcibly closed by a peer.
The socket is not connection-mode and no peer address is set.
EINTR A signal interrupted send() before any data was transmitted.
The message is too large to be sent all at once, as the socket
The socket is not connected.
The socket argument does not refer to a socket.
The socket argument is associated with a socket that does not
support one or more of the values set in flags.
EPIPE The socket is shut down for writing, or the socket is
connection-mode and is no longer connected. In the latter
case, and if the socket is of type SOCK_STREAM or
SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set, the
SIGPIPE signal is generated to the calling thread.
The send() function may fail if:
EACCES The calling process does not have appropriate privileges.
EIO An I/O error occurred while reading from or writing to the
The local network interface used to reach the destination is
No route to the network is present.
Insufficient resources were available in the system to perform
The following sections are informative.
If the socket argument refers to a connection-mode socket, the send()
function is equivalent to sendto() (with any value for the dest_addr
and dest_len arguments, as they are ignored in this case). If the
socket argument refers to a socket and the flags argument is 0, the
send() function is equivalent to write().
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 SEND(3P)