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1 | .\" Copyright (c) 1983, 1990, 1991 The Regents of the University of California. |
2 | .\" All rights reserved. | |
3 | .\" | |
a9cd9cb7 | 4 | .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) |
fea681da MK |
5 | .\" Redistribution and use in source and binary forms, with or without |
6 | .\" modification, are permitted provided that the following conditions | |
7 | .\" are met: | |
8 | .\" 1. Redistributions of source code must retain the above copyright | |
9 | .\" notice, this list of conditions and the following disclaimer. | |
10 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
11 | .\" notice, this list of conditions and the following disclaimer in the | |
12 | .\" documentation and/or other materials provided with the distribution. | |
13 | .\" 3. All advertising materials mentioning features or use of this software | |
14 | .\" must display the following acknowledgement: | |
15 | .\" This product includes software developed by the University of | |
16 | .\" California, Berkeley and its contributors. | |
17 | .\" 4. Neither the name of the University nor the names of its contributors | |
18 | .\" may be used to endorse or promote products derived from this software | |
19 | .\" without specific prior written permission. | |
20 | .\" | |
21 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
22 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
23 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
24 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
25 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
26 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
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30 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
31 | .\" SUCH DAMAGE. | |
8c9302dc | 32 | .\" %%%LICENSE_END |
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33 | .\" |
34 | .\" $Id: recv.2,v 1.3 1999/05/13 11:33:38 freitag Exp $ | |
35 | .\" | |
36 | .\" Modified Sat Jul 24 00:22:20 1993 by Rik Faith <faith@cs.unc.edu> | |
37 | .\" Modified Tue Oct 22 17:45:19 1996 by Eric S. Raymond <esr@thyrsus.com> | |
38 | .\" Modified 1998,1999 by Andi Kleen | |
39 | .\" 2001-06-19 corrected SO_EE_OFFENDER, bug report by James Hawtin | |
40 | .\" | |
4b8c67d9 | 41 | .TH RECV 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
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42 | .SH NAME |
43 | recv, recvfrom, recvmsg \- receive a message from a socket | |
44 | .SH SYNOPSIS | |
45 | .\" .B #include <sys/uio.h> | |
46 | .\" .br | |
16c892d3 | 47 | .nf |
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48 | .B #include <sys/types.h> |
49 | .br | |
50 | .B #include <sys/socket.h> | |
68e4db0a | 51 | .PP |
c4e7b714 | 52 | .BI "ssize_t recv(int " sockfd ", void *" buf ", size_t " len ", int " flags ); |
68e4db0a | 53 | .PP |
c4e7b714 | 54 | .BI "ssize_t recvfrom(int " sockfd ", void *" buf ", size_t " len ", int " flags , |
6926dbf5 | 55 | .BI " struct sockaddr *" src_addr ", socklen_t *" addrlen ); |
68e4db0a | 56 | .PP |
c4e7b714 | 57 | .BI "ssize_t recvmsg(int " sockfd ", struct msghdr *" msg ", int " flags ); |
16c892d3 | 58 | .fi |
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59 | .SH DESCRIPTION |
60 | The | |
e39a21b5 MK |
61 | .BR recv (), |
62 | .BR recvfrom (), | |
fea681da | 63 | and |
e511ffb6 | 64 | .BR recvmsg () |
ea629944 | 65 | calls are used to receive messages from a socket. |
e39a21b5 MK |
66 | They may be used |
67 | to receive data on both connectionless and connection-oriented sockets. | |
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68 | This page first describes common features of all three system calls, |
69 | and then describes the differences between the calls. | |
fea681da | 70 | .PP |
90425b93 HS |
71 | The only difference between |
72 | .BR recv () | |
73 | and | |
74 | .BR read (2) | |
75 | is the presence of | |
76 | .IR flags . | |
77 | With a zero | |
78 | .I flags | |
79 | argument, | |
80 | .BR recv () | |
36c8e721 MK |
81 | is generally equivalent to |
82 | .BR read (2) | |
83 | (but see NOTES). | |
90425b93 | 84 | Also, the following call |
efeece04 | 85 | .PP |
90425b93 | 86 | recv(sockfd, buf, len, flags); |
efeece04 | 87 | .PP |
90425b93 | 88 | is equivalent to |
efeece04 | 89 | .PP |
90425b93 HS |
90 | recvfrom(sockfd, buf, len, flags, NULL, NULL); |
91 | .PP | |
ea629944 | 92 | All three calls return the length of the message on successful |
c13182ef MK |
93 | completion. |
94 | If a message is too long to fit in the supplied buffer, excess | |
fea681da | 95 | bytes may be discarded depending on the type of socket the message is |
7080c286 | 96 | received from. |
fea681da MK |
97 | .PP |
98 | If no messages are available at the socket, the receive calls wait for a | |
ff40dbb3 | 99 | message to arrive, unless the socket is nonblocking (see |
62d4f1bd | 100 | .BR fcntl (2)), |
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101 | in which case the value \-1 is returned and the external variable |
102 | .I errno | |
86426e0b | 103 | is set to |