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.\" Copyright (c) 1983, 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" SPDX-License-Identifier: BSD-4-Clause-UC
.\"
.\"     $Id: recv.2,v 1.3 1999/05/13 11:33:38 freitag Exp $
.\"
.\" Modified Sat Jul 24 00:22:20 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Tue Oct 22 17:45:19 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1998,1999 by Andi Kleen
.\" 2001-06-19 corrected SO_EE_OFFENDER, bug report by James Hawtin
.\"
.TH RECV 2 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
recv, recvfrom, recvmsg \- receive a message from a socket
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.PP
.BI "ssize_t recv(int " sockfd ", void *" buf ", size_t " len ", int " flags );
.BI "ssize_t recvfrom(int " sockfd ", void *restrict " buf ", size_t " len \
", int " flags ,
.BI "                 struct sockaddr *restrict " src_addr ,
.BI "                 socklen_t *restrict " addrlen );
.BI "ssize_t recvmsg(int " sockfd ", struct msghdr *" msg ", int " flags );
.fi
.SH DESCRIPTION
The
.BR recv (),
.BR recvfrom (),
and
.BR recvmsg ()
calls are used to receive messages from a socket.
They may be used
to receive data on both connectionless and connection-oriented sockets.
This page first describes common features of all three system calls,
and then describes the differences between the calls.
.PP
The only difference between
.BR recv ()
and
.BR read (2)
is the presence of
.IR flags .
With a zero
.I flags
argument,
.BR recv ()
is generally equivalent to
.BR read (2)
(but see NOTES).
Also, the following call
.PP
    recv(sockfd, buf, len, flags);
.PP
is equivalent to
.PP
    recvfrom(sockfd, buf, len, flags, NULL, NULL);
.PP
All three calls return the length of the message on successful
completion.
If a message is too long to fit in the supplied buffer, excess
bytes may be discarded depending on the type of socket the message is
received from.
.PP
If no messages are available at the socket, the receive calls wait for a
message to arrive, unless the socket is nonblocking (see
.BR fcntl (2)),
in which case the value \-1 is returned and
.I errno
is set to