send(3p) — Linux manual page


SEND(3P)                POSIX Programmer's Manual               SEND(3P)

PROLOG         top

       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.

NAME         top

       send — send a message on a socket

SYNOPSIS         top

       #include <sys/socket.h>

       ssize_t send(int socket, const void *buffer, size_t length, int flags);

DESCRIPTION         top

       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 protocol).

                   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 returned.

       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

       Successful completion of a call to send() does not guarantee
       delivery of the message. A return value of -1 indicates only
       locally-detected errors.

       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.

RETURN VALUE         top

       Upon successful completion, send() shall return the number of
       bytes sent. Otherwise, -1 shall be returned and errno set to
       indicate the error.

ERRORS         top

       The send() function shall fail if:

              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

       EINTR  A signal interrupted send() before any data was

              The message is too large to be sent all at once, as the
              socket requires.

              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
              file system.

              The local network interface used to reach the destination
              is down.

              No route to the network is present.

              Insufficient resources were available in the system to
              perform the operation.

       The following sections are informative.

EXAMPLES         top



       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().

RATIONALE         top




SEE ALSO         top

       connect(3p), getsockopt(3p), poll(3p), pselect(3p), recv(3p),
       recvfrom(3p), recvmsg(3p), sendmsg(3p), sendto(3p),
       setsockopt(3p), shutdown(3p), socket(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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 .

       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               2017                          SEND(3P)

Pages that refer to this page: sys_socket.h(0p)connect(3p)recv(3p)recvfrom(3p)recvmsg(3p)sendmsg(3p)sendto(3p)shutdown(3p)socket(3p)