recv(3p) — Linux manual page


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

       recv — receive a message from a connected socket

SYNOPSIS         top

       #include <sys/socket.h>

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

DESCRIPTION         top

       The recv() function shall receive a message from a connection-
       mode or connectionless-mode socket. It is normally used with
       connected sockets because it does not permit the application to
       retrieve the source address of received data.

       The recv() function takes the following arguments:

       socket    Specifies the socket file descriptor.

       buffer    Points to a buffer where the message should be stored.

       length    Specifies the length in bytes of the buffer pointed to
                 by the buffer argument.

       flags     Specifies the type of message reception. Values of this
                 argument are formed by logically OR'ing zero or more of
                 the following values:

                 MSG_PEEK    Peeks at an incoming message. The data is
                             treated as unread and the next recv() or
                             similar function shall still return this

                 MSG_OOB     Requests out-of-band data. The significance
                             and semantics of out-of-band data are

                 MSG_WAITALL On SOCK_STREAM sockets this requests that
                             the function block until the full amount of
                             data can be returned. The function may
                             return the smaller amount of data if the
                             socket is a message-based socket, if a
                             signal is caught, if the connection is
                             terminated, if MSG_PEEK was specified, or
                             if an error is pending for the socket.

       The recv() function shall return the length of the message
       written to the buffer pointed to by the buffer argument. For
       message-based sockets, such as SOCK_DGRAM and SOCK_SEQPACKET, the
       entire message shall be read in a single operation.  If a message
       is too long to fit in the supplied buffer, and MSG_PEEK is not
       set in the flags argument, the excess bytes shall be discarded.
       For stream-based sockets, such as SOCK_STREAM, message boundaries
       shall be ignored. In this case, data shall be returned to the
       user as soon as it becomes available, and no data shall be

       If the MSG_WAITALL flag is not set, data shall be returned only
       up to the end of the first message.

       If no messages are available at the socket and O_NONBLOCK is not
       set on the socket's file descriptor, recv() shall block until a
       message arrives. If no messages are available at the socket and
       O_NONBLOCK is set on the socket's file descriptor, recv() shall
       fail and set errno to [EAGAIN] or [EWOULDBLOCK].

RETURN VALUE         top

       Upon successful completion, recv() shall return the length of the
       message in bytes. If no messages are available to be received and
       the peer has performed an orderly shutdown, recv() shall return
       0. Otherwise, -1 shall be returned and errno set to indicate the

ERRORS         top

       The recv() function shall fail if:

              The socket's file descriptor is marked O_NONBLOCK and no
              data is waiting to be received; or MSG_OOB is set and no
              out-of-band data is available and either the socket's file
              descriptor is marked O_NONBLOCK or the socket does not
              support blocking to await out-of-band data.

       EBADF  The socket argument is not a valid file descriptor.

              A connection was forcibly closed by a peer.

       EINTR  The recv() function was interrupted by a signal that was
              caught, before any data was available.

       EINVAL The MSG_OOB flag is set and no out-of-band data is

              A receive is attempted on a connection-mode socket that is
              not connected.

              The socket argument does not refer to a socket.

              The specified flags are not supported for this socket type
              or protocol.

              The connection timed out during connection establishment,
              or due to a transmission timeout on active connection.

       The recv() function may fail if:

       EIO    An I/O error occurred while reading from or writing to the
              file system.

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

       ENOMEM Insufficient memory was available to fulfill the request.

       The following sections are informative.

EXAMPLES         top



       The recv() function is equivalent to recvfrom() with null pointer
       address and address_len arguments, and to read() if the socket
       argument refers to a socket and the flags argument is 0.

       The select() and poll() functions can be used to determine when
       data is available to be received.

RATIONALE         top




SEE ALSO         top

       poll(3p), pselect(3p), read(3p), recvmsg(3p), recvfrom(3p),
       send(3p), sendmsg(3p), sendto(3p), shutdown(3p), socket(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                          RECV(3P)

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