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1.\" $OpenBSD: socketpair.2,v 1.22 2025/08/04 04:59:31 guenther Exp $
2.\" $NetBSD: socketpair.2,v 1.5 1995/02/27 12:38:00 cgd Exp $
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31.\" @(#)socketpair.2 8.1 (Berkeley) 6/4/93
32.\"
33.Dd $Mdocdate: August 4 2025 $
34.Dt SOCKETPAIR 2
35.Os
36.Sh NAME
37.Nm socketpair
38.Nd create a pair of connected sockets
39.Sh SYNOPSIS
40.In sys/socket.h
41.Ft int
42.Fn socketpair "int domain" "int type" "int protocol" "int sv[2]"
43.Sh DESCRIPTION
44The
45.Fn socketpair
46call creates an unnamed pair of connected sockets.
47The descriptors used in referencing the new sockets
48are returned in
49.Fa sv Ns [0]
50and
51.Fa sv Ns [1] .
52The two sockets are indistinguishable.
53.Pp
54The only supported
55.Fa domain
56is
57.Dv AF_UNIX .
58Possible values for the
59.Fa type
60and
61.Fa protocol
62arguments are explained in the
63.Xr socket 2
64manual page.
65The only useful value for
66.Fa protocol
67is 0, which will let the system select an appropriate protocol
68for the requested socket
69.Fa type .
70.Pp
71Any combination of the following flags may additionally be used in the
72.Fa type
73argument:
74.Pp
75.Bl -tag -width "SOCK_NONBLOCKX" -offset indent -compact
76.It SOCK_CLOEXEC
77Set close-on-exec flag on both the new descriptors.
78.It SOCK_CLOFORK
79Set close-on-fork flag on both the new descriptors.
80.It SOCK_NONBLOCK
81Set non-blocking I/O mode on both the new sockets.
82.El
83.Sh RETURN VALUES
84.Rv -std
85.Sh ERRORS
86The call succeeds unless:
87.Bl -tag -width Er
88.It Bq Er EAFNOSUPPORT
89The specified address family is not supported on this machine.
90.It Bq Er EPROTONOSUPPORT
91The specified protocol is not supported on this machine.
92.It Bq Er EOPNOTSUPP
93The specified protocol does not support creation of socket pairs.
94.It Bq Er EPROTOTYPE
95The combination of the specified protocol and type is not supported.
96.It Bq Er EMFILE
97The per-process descriptor table is full.
98.It Bq Er ENFILE
99The system file table is full.
100.It Bq Er ENOBUFS
101Insufficient resources were available in the system
102to perform the operation.
103.It Bq Er EFAULT
104The address
105.Fa sv
106does not specify a valid part of the
107process address space.
108.El
109.Sh SEE ALSO
110.Xr pipe 2 ,
111.Xr read 2 ,
112.Xr socket 2 ,
113.Xr write 2
114.Sh STANDARDS
115The
116.Fn socketpair
117function conforms to
118.St -p1003.1-2024 .
119.Sh HISTORY
120The
121.Fn socketpair
122function call appeared in
123.Bx 4.2 .
124Support for the
125.Dv SOCK_CLOEXEC
126and
127.Dv SOCK_NONBLOCK
128flags appeared in
129.Ox 5.7 .