man2/socketpair.2

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  33 .\"
  34 .\"     @(#)socketpair.2        6.4 (Berkeley) 3/10/91
  35 .\"
  36 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
  37 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
  38 .\" Modified 2002-07-22 by Michael Kerrisk <mtk.manpages@gmail.com>
  39 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
  40 .\" 2008-10-11, mtk: Add description of SOCK_NONBLOCK and SOCK_CLOEXEC
  41 .\"
  42 .TH SOCKETPAIR 2 2019-03-06 "Linux" "Linux Programmer's Manual"
  43 .SH NAME
  44 socketpair \- create a pair of connected sockets
  45 .SH SYNOPSIS
  46 .BR "#include <sys/types.h>" "          /* See NOTES */"
  47 .br
  48 .B #include <sys/socket.h>
  49 .PP
  50 .BI "int socketpair(int " domain ", int " type ", int " protocol \
  51 ", int " sv [2]);
  52 .SH DESCRIPTION
  53 The
  54 .BR socketpair ()
  55 call creates an unnamed pair of connected sockets in the specified
  56 .IR domain ,
  57 of the specified
  58 .IR type ,
  59 and using the optionally specified
  60 .IR protocol .
  61 For further details of these arguments, see
  62 .BR socket (2).
  63 .PP
  64 The file descriptors used in referencing the new sockets are returned in
  65 .IR sv [0]
  66 and
  67 .IR sv [1].
  68 The two sockets are indistinguishable.
  69 .SH RETURN VALUE
  70 On success, zero is returned.
  71 On error, \-1 is returned,
  72 .I errno
  73 is set appropriately, and
  74 .I sv
  75 is left unchanged
  76 .PP
  77 On Linux (and other systems),
  78 .BR socketpair ()
  79 does not modify
  80 .I sv
  81 on failure.
  82 A requirement standardizing this behavior was added in POSIX.1-2016.
  83 .\" http://austingroupbugs.net/view.php?id=483
  84 .SH ERRORS
  85 .TP
  86 .B EAFNOSUPPORT
  87 The specified address family is not supported on this machine.
  88 .TP
  89 .B EFAULT
  90 The address
  91 .I sv
  92 does not specify a valid part of the process address space.
  93 .TP
  94 .B EMFILE
  95 The per-process limit on the number of open file descriptors has been reached.
  96 .TP
  97 .B ENFILE
  98 The system-wide limit on the total number of open files has been reached.
  99 .TP
 100 .B EOPNOTSUPP
 101 The specified protocol does not support creation of socket pairs.
 102 .TP
 103 .B EPROTONOSUPPORT
 104 The specified protocol is not supported on this machine.
 105 .SH CONFORMING TO
 106 POSIX.1-2001, POSIX.1-2008, 4.4BSD.
 107 .BR socketpair ()
 108 first appeared in 4.2BSD.
 109 It is generally portable to/from
 110 non-BSD systems supporting clones of the BSD socket layer (including
 111 System\ V variants).
 112 .SH NOTES
 113 On Linux, the only supported domains for this call are
 114 .B AF_UNIX
 115 (or synonymously,
 116 .BR AF_LOCAL )
 117 and
 118 .B AF_TIPC
 119 .\" commit: 70b03759e9ecfae400605fa34f3d7154cccbbba3
 120 (since Linux 4.12).
 121 .PP
 122 Since Linux 2.6.27,
 123 .BR socketpair ()
 124 supports the
 125 .BR SOCK_NONBLOCK
 126 and
 127 .BR SOCK_CLOEXEC
 128 flags in the
 129 .I type
 130 argument, as described in
 131 .BR socket (2).
 132 .PP
 133 POSIX.1 does not require the inclusion of
 134 .IR <sys/types.h> ,
 135 and this header file is not required on Linux.
 136 However, some historical (BSD) implementations required this header
 137 file, and portable applications are probably wise to include it.
 138 .SH SEE ALSO
 139 .BR pipe (2),
 140 .BR read (2),
 141 .BR socket (2),
 142 .BR write (2),
 143 .BR socket (7),
 144 .BR unix (7)