man2/socketpair.2

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  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, and
  72 .I errno
  73 is set appropriately.
  74 .PP
  75 On Linux (and other systems),
  76 .BR socketpair ()
  77 does not modify
  78 .I sv
  79 on failure.
  80 A requirement standardizing this behavior was added in POSIX.1-2016.
  81 .\" http://austingroupbugs.net/view.php?id=483
  82 .SH ERRORS
  83 .TP
  84 .B EAFNOSUPPORT
  85 The specified address family is not supported on this machine.
  86 .TP
  87 .B EFAULT
  88 The address
  89 .I sv
  90 does not specify a valid part of the process address space.
  91 .TP
  92 .B EMFILE
  93 The per-process limit on the number of open file descriptors has been reached.
  94 .TP
  95 .B ENFILE
  96 The system-wide limit on the total number of open files has been reached.
  97 .TP
  98 .B EOPNOTSUPP
  99 The specified protocol does not support creation of socket pairs.
 100 .TP
 101 .B EPROTONOSUPPORT
 102 The specified protocol is not supported on this machine.
 103 .SH CONFORMING TO
 104 POSIX.1-2001, POSIX.1-2008, 4.4BSD.
 105 .BR socketpair ()
 106 first appeared in 4.2BSD.
 107 It is generally portable to/from
 108 non-BSD systems supporting clones of the BSD socket layer (including
 109 System\ V variants).
 110 .SH NOTES
 111 On Linux, the only supported domains for this call are
 112 .B AF_UNIX
 113 (or synonymously,
 114 .BR AF_LOCAL )
 115 and
 116 .B AF_TIPC
 117 .\" commit: 70b03759e9ecfae400605fa34f3d7154cccbbba3
 118 (since Linux 4.12).
 119 .PP
 120 Since Linux 2.6.27,
 121 .BR socketpair ()
 122 supports the
 123 .BR SOCK_NONBLOCK
 124 and
 125 .BR SOCK_CLOEXEC
 126 flags in the
 127 .I type
 128 argument, as described in
 129 .BR socket (2).
 130 .PP
 131 POSIX.1 does not require the inclusion of
 132 .IR <sys/types.h> ,
 133 and this header file is not required on Linux.
 134 However, some historical (BSD) implementations required this header
 135 file, and portable applications are probably wise to include it.
 136 .SH SEE ALSO
 137 .BR pipe (2),
 138 .BR read (2),
 139 .BR socket (2),
 140 .BR write (2),
 141 .BR socket (7),
 142 .BR unix (7)