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.\"     @(#)socketpair.2	8.1 (Berkeley) 6/4/93
.\"
.Dd November 29, 2022
.Dt SOCKETPAIR 2
.Os
.Sh NAME
.Nm socketpair
.Nd create a pair of connected sockets
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn socketpair "int d" "int type" "int protocol" "int *sv"
.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 Li [0]
and
.Fa sv Ns Li [1] .
The two sockets are indistinguishable.
.Pp
Possible values for the
.Fa type
argument are
.Dv SOCK_STREAM ,
.Dv SOCK_DGRAM ,
and
.Dv SOCK_SEQPACKET ;
the only supported value for the
.Fa protocol
is 0,
which will let the system select an appropriate
protocol for the requested socket
.Fa type .
.Pp
Any combination of the following flags may
additionally be used in the
.Fa type
argument:
.Pp
.Bl -tag -width Dv -offset indent -compact
.It Dv SOCK_CLOEXEC
Set close-on-exec flag on both the new descriptors.
.It Dv 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 EFAULT
The address
.Fa sv
does not specify a valid part of the
process address space.
.It Bq Er EMFILE
Too many descriptors are in use by this process.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EOPNOTSUPP
The specified protocol does not support creation of socket pairs.
.It Bq Er EPROTONOSUPPORT
The specified protocol is not supported on this machine.
.El
.Sh SEE ALSO
.Xr pipe 2 ,
.Xr read 2 ,
.Xr socket 2 ,
.Xr write 2
.Sh HISTORY
The
.Fn socketpair
function call appeared in
.Bx 4.2 .
.Pp
Support for the
.Dv SOCK_CLOEXEC
and
.Dv SOCK_NONBLOCK
flags appeared in
.Nx 6.0 .
.Sh BUGS
This call is currently implemented only for the
.Dv PF_LOCAL
domain.