1.\" Copyright (c) 2001 2.\" The FreeBSD Project 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 10.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 11.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 12.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 13.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 14.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 15.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 16.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 17.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 18.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 19.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 20.\" SUCH DAMAGE. 21.\" 22.\" $FreeBSD: src/share/man/man4/nmdm.4,v 1.2.2.1 2001/08/11 00:54:14 mp Exp $ 23.\" $DragonFly: src/share/man/man4/nmdm.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 24.\" 25.Dd July 7, 2001 26.Dt NMDM 4 27.Os 28.Sh NAME 29.Nm nmdm 30.Nd nullmodem terminal driver 31.Sh SYNOPSIS 32.Cd "device nmdm" 33.Sh DESCRIPTION 34The 35.Nm 36driver provides support for a device-pair termed a 37.Em null modem pair . 38A null modem pair is a pair of character devices. 39Each device provides to a process an interface identical 40to that described in 41.Xr tty 4 . 42However, whereas most other devices which provide the 43interface described in 44.Xr tty 4 45have a hardware device of some sort behind them, the 46.Nm 47device has, instead, another process manipulating 48it through the other half of the pair. 49That is, anything written on the first device is 50given to the second device as input and anything written 51on the second device is presented as input on the first 52device. 53.Sh FILES 54.Bl -tag -width /dev/nmdm[N][AB] -compact 55.It Pa /dev/nmdm Ns Ar N Ns Op Pa AB 56nullmodem device nodes. 57Where the 58.Pa A 59node has a matching 60.Pa B 61node. 62.El 63.Sh DIAGNOSTICS 64None. 65.Sh SEE ALSO 66.Xr tty 4 67.Sh HISTORY 68The 69.Nm 70driver first appeared in 71.Fx 4.4 . 72