ccfd3aab30
This allows users to increase the maximum amount of pseudo-terminals without changing any source code. Users must increase UT_LINESIZE before attempting to increase kern.pts_maxdev.
196 lines
5.9 KiB
Groff
196 lines
5.9 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 August 20, 2008
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.Dt PTS 4
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.Os
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.Sh NAME
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.Nm pts
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.Nd pseudo-terminal driver
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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 TIOCPTMASTER
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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.
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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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.Dv VSTOP
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is
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.Ql ^S
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and
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.Dv VSTART
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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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.El
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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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.It Dv TIOCGPTN
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Obtain device unit number, which can be used to generate the filename of
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the pseudo-terminal slave device. This
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.Xr ioctl 2
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should not be used directly. Instead, the
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.Xr ptsname 3
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function should be used.
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.It Dv TIOCPTMASTER
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Determine whether the file descriptor is pointing to a pseudo-terminal
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master device.
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This
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.Xr ioctl 2
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should not be used directly. It is used to implement routines like
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.Xr grantpt 3 .
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.El
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.Pp
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The maximum number of pseudo-terminals is limited to 1000.
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It is not possible to use more than 1000 pseudo-terminals, as all software
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which use
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.Xr utmp 5
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will not be able to handle pseudo-terminals with number superior to 999.
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.Sh FILES
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The files used by this
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pseudo-terminals implementation are:
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.Pp
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.Bl -tag -width ".Pa /dev/pts/[num]"
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.It Pa /dev/ptmx
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Control device, returns a file descriptor to a new master pseudo-terminal
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when opened. This device should not be opened directly. It's only
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available for binary compatibility. New devices should only be created
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though
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.Xr posix_openpt 2 .
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.It Pa /dev/pts/[num]
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Pseudo-terminal slave devices.
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.El
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.Sh SYSCTL VARIABLES
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The following
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.Xr sysctl 8
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variables can be used to modify or monitor
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.Nm
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behavior.
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.Bl -tag -width indent
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.It Va kern.pts_maxdev
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Highest pseudo-terminal unit number to be allocated.
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Because
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.Xr utmp 5
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is restricted to an 8-byte line name size,
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.Nm
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will not create any pseudo-terminals with a unit number above 999 by
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default.
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After increasing
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.Dv UT_LINESIZE ,
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this variable can be changed to allow more than 1000 pseudo-terminals to
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be allocated simultaneously.
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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 grantpt 3 ,
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.Xr posix_openpt 2 ,
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.Xr ptsname 3 ,
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.Xr pty 4 ,
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.Xr tty 4
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.Sh HISTORY
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A
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pseudo-terminal driver appeared in
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.Bx 4.2 .
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In
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.Fx 8.0 ,
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it was replaced with the
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.Nm
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driver.
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