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.\"     @(#)socketpair.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: May 29 2016 $
.Dt SOCKETPAIR 2
.Os
.Sh NAME
.Nm socketpair
.Nd create a pair of connected sockets
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn socketpair "int d" "int type" "int protocol" "int sv[2]"
.Sh DESCRIPTION
The
.Fn socketpair
call creates an unnamed pair of connected sockets in
the specified domain
.Fa d ,
of the specified
.Fa type ,
and using the optionally specified
.Fa protocol .
The descriptors used in referencing the new sockets
are returned in
.Fa sv Ns [0]
and
.Fa sv Ns [1] .
The two sockets are indistinguishable.
.Pp
Any combination of the following flags may additionally be used in the
.Fa type
argument:
.Pp
.Bl -tag -width "SOCK_NONBLOCKX" -offset indent -compact
.It SOCK_CLOEXEC
Set close-on-exec flag on both the new descriptors.
.It SOCK_NONBLOCK
Set non-blocking I/O mode on both the new sockets.
.El
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The call succeeds unless:
.Bl -tag -width Er
.It Bq Er EAFNOSUPPORT
The specified address family is not supported on this machine.
.It Bq Er EPROTONOSUPPORT
The specified protocol is not supported on this machine.
.It Bq Er EOPNOTSUPP
The specified protocol does not support creation of socket pairs.
.It Bq Er EPROTOTYPE
The combination of the specified protocol and type is not supported.
.It Bq Er EMFILE
The per-process descriptor table is full.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er ENOBUFS
Insufficient resources were available in the system
to perform the operation.
.It Bq Er EFAULT
The address
.Fa sv
does not specify a valid part of the
process address space.
.El
.Sh SEE ALSO
.Xr pipe 2 ,
.Xr read 2 ,
.Xr socket 2 ,
.Xr write 2
.Sh STANDARDS
The
.Fn socketpair
function conforms to
.St -p1003.1-2008 .
The
.Dv SOCK_CLOEXEC
and
.Dv SOCK_NONBLOCK
flags are expected to conform to a future revision of that standard.
.Sh HISTORY
The
.Fn socketpair
function call appeared in
.Bx 4.2 .
Support for the
.Dv SOCK_CLOEXEC
and
.Dv SOCK_NONBLOCK
flags appeared in
.Ox 5.7 .
.Sh BUGS
This call is currently implemented only for the LOCAL domain.
Many operating systems only accept a
.Fa protocol
of
.Dv AF_UNSPEC ,
so that should be used instead of
.Dv AF_LOCAL
for maximal portability.