950cce9b30
It was added 22 years ago for emacs to use, but emacs gave up on it it 17 years ago.
195 lines
5.7 KiB
Groff
195 lines
5.7 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)pty.4 8.2 (Berkeley) 11/30/93
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.\" $FreeBSD$
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.\"
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.Dd November 30, 1993
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.Dt PTY 4
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.Os
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.Sh NAME
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.Nm pty
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.Nd pseudo terminal driver
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.Sh SYNOPSIS
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.Cd "device pty"
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.Sh DESCRIPTION
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The
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.Nm
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driver provides support for a device-pair termed a
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.Em pseudo terminal .
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A pseudo terminal is a pair of character devices, a
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.Em master
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device and a
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.Em slave
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device.
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The slave device provides to a process an interface identical
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to that described in
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.Xr tty 4 .
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However, whereas all other devices which provide the
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interface described in
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.Xr tty 4
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have a hardware device of some sort behind them, the slave
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device has, instead, another process manipulating
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it through the master half of the pseudo terminal.
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That is, anything written on the master device is
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given to the slave device as input and anything written
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on the slave device is presented as input on the master
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device.
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.Pp
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The following
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.Xr ioctl 2
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calls apply only to pseudo terminals:
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.Bl -tag -width TIOCREMOTE
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.It Dv TIOCSTOP
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Stops output to a terminal (e.g. like typing
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.Ql ^S ) .
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Takes
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no parameter.
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.It Dv TIOCSTART
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Restarts output (stopped by
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.Dv TIOCSTOP
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or by typing
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.Ql ^S ) .
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Takes no parameter.
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.It Dv TIOCPKT
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Enable/disable
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.Em packet
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mode.
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Packet mode is enabled by specifying (by reference)
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a nonzero parameter and disabled by specifying (by reference)
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a zero parameter.
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When applied to the master side of a pseudo terminal, each subsequent
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.Xr read 2
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from the terminal will return data written on the slave part of
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the pseudo terminal preceded by a zero byte (symbolically
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defined as
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.Dv TIOCPKT_DATA ) ,
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or a single byte reflecting control
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status information. In the latter case, the byte is an inclusive-or
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of zero or more of the bits:
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.Bl -tag -width TIOCPKT_FLUSHWRITE
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.It Dv TIOCPKT_FLUSHREAD
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whenever the read queue for the terminal is flushed.
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.It Dv TIOCPKT_FLUSHWRITE
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whenever the write queue for the terminal is flushed.
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.It Dv TIOCPKT_STOP
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whenever output to the terminal is stopped a la
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.Ql ^S .
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.It Dv TIOCPKT_START
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whenever output to the terminal is restarted.
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.It Dv TIOCPKT_DOSTOP
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whenever
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.Em t_stopc
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is
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.Ql ^S
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and
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.Em t_startc
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is
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.Ql ^Q .
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.It Dv TIOCPKT_NOSTOP
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whenever the start and stop characters are not
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.Ql ^S/^Q .
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.Pp
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While this mode is in use, the presence of control status information
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to be read from the master side may be detected by a
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.Xr select 2
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for exceptional conditions.
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.Pp
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This mode is used by
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.Xr rlogin 1
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and
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.Xr rlogind 8
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to implement a remote-echoed, locally
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.Ql ^S/^Q
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flow-controlled
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remote login with proper back-flushing of output; it can be
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used by other similar programs.
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.El
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.It Dv TIOCUCNTL
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Enable/disable a mode that allows a small number of simple user
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.Xr ioctl 2
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commands to be passed through the pseudo-terminal,
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using a protocol similar to that of
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.Dv TIOCPKT .
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The
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.Dv TIOCUCNTL
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and
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.Dv TIOCPKT
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modes are mutually exclusive.
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This mode is enabled from the master side of a pseudo terminal
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by specifying (by reference)
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a nonzero parameter and disabled by specifying (by reference)
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a zero parameter.
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Each subsequent
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.Xr read 2
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from the master side will return data written on the slave part of
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the pseudo terminal preceded by a zero byte,
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or a single byte reflecting a user control operation on the slave side.
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A user control command consists of a special
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.Xr ioctl 2
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operation with no data; the command is given as
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.Dv UIOCCMD Ns (n) ,
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where
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.Ar n
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is a number in the range 1-255.
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The operation value
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.Ar n
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will be received as a single byte on the next
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.Xr read 2
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from the master side.
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The
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.Xr ioctl 2
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.Dv UIOCCMD Ns (0)
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is a no-op that may be used to probe for
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the existence of this facility.
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As with
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.Dv TIOCPKT
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mode, command operations may be detected with a
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.Xr select 2
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for exceptional conditions.
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.El
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.Sh FILES
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.Bl -tag -width /dev/tty[p-sP-S][0-9a-v]x -compact
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.It Pa /dev/pty[p-sP-S][0-9a-v]
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master pseudo terminals
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.It Pa /dev/tty[p-sP-S][0-9a-v]
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slave pseudo terminals
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.El
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.Sh DIAGNOSTICS
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None.
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.Sh SEE ALSO
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.Xr tty 4
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.Sh HISTORY
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The
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.Nm
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driver appeared in
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.Bx 4.2 .
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