1.\" $NetBSD: pty.4,v 1.3 1994/11/30 16:22:30 jtc Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)pty.4 8.2 (Berkeley) 11/30/93 35.\" 36.Dd November 30, 1993 37.Dt PTY 4 38.Os BSD 4.2 39.Sh NAME 40.Nm pty 41.Nd pseudo terminal driver 42.Sh SYNOPSIS 43.Nm pseudo-device pty 44.Op Ar count 45.Sh DESCRIPTION 46The 47.Xr pty 48driver provides support for a device-pair termed a 49.Em pseudo terminal . 50A pseudo terminal is a pair of character devices, a 51.Em master 52device and a 53.Em slave 54device. The slave device provides to a process 55an interface identical 56to that described in 57.Xr tty 4 . 58However, whereas all other devices which provide the 59interface described in 60.Xr tty 4 61have a hardware device of some sort behind them, the slave 62device has, instead, another process manipulating 63it through the master half of the pseudo terminal. 64That is, anything written on the master device is 65given to the slave device as input and anything written 66on the slave device is presented as input on the master 67device. 68.Pp 69In configuring, if an optional 70.Ar count 71is given in 72the specification, that number of pseudo terminal pairs are configured; 73the default count is 32. 74.Pp 75The following 76.Xr ioctl 2 77calls apply only to pseudo terminals: 78.Bl -tag -width TIOCREMOTE 79.It Dv TIOCSTOP 80Stops output to a terminal (e.g. like typing 81.Ql ^S ) . 82Takes 83no parameter. 84.It Dv TIOCSTART 85Restarts output (stopped by 86.Dv TIOCSTOP 87or by typing 88.Ql ^S ) . 89Takes no parameter. 90.It Dv TIOCPKT 91Enable/disable 92.Em packet 93mode. Packet mode is enabled by specifying (by reference) 94a nonzero parameter and disabled by specifying (by reference) 95a zero parameter. When applied to the master side of a pseudo 96terminal, each subsequent 97.Xr read 98from the terminal will return data written on the slave part of 99the pseudo terminal preceded by a zero byte (symbolically 100defined as 101.Dv TIOCPKT_DATA ) , 102or a single byte reflecting control 103status information. In the latter case, the byte is an inclusive-or 104of zero or more of the bits: 105.Bl -tag -width TIOCPKT_FLUSHWRITE 106.It Dv TIOCPKT_FLUSHREAD 107whenever the read queue for the terminal is flushed. 108.It Dv TIOCPKT_FLUSHWRITE 109whenever the write queue for the terminal is flushed. 110.It Dv TIOCPKT_STOP 111whenever output to the terminal is stopped a la 112.Ql ^S . 113.It Dv TIOCPKT_START 114whenever output to the terminal is restarted. 115.It Dv TIOCPKT_DOSTOP 116whenever 117.Em t_stopc 118is 119.Ql ^S 120and 121.Em t_startc 122is 123.Ql ^Q . 124.It Dv TIOCPKT_NOSTOP 125whenever the start and stop characters are not 126.Ql ^S/^Q . 127.Pp 128While this mode is in use, the presence of control status information 129to be read from the master side may be detected by a 130.Xr select 2 131for exceptional conditions. 132.Pp 133This mode is used by 134.Xr rlogin 1 135and 136.Xr rlogind 8 137to implement a remote-echoed, locally 138.Ql ^S/^Q 139flow-controlled 140remote login with proper back-flushing of output; it can be 141used by other similar programs. 142.El 143.It Dv TIOCUCNTL 144Enable/disable a mode that allows a small number of simple user 145.Xr ioctl 146commands to be passed through the pseudo-terminal, 147using a protocol similar to that of 148.Dv TIOCPKT . 149The 150.Dv TIOCUCNTL 151and 152.Dv TIOCPKT 153modes are mutually exclusive. 154This mode is enabled from the master side of a pseudo terminal 155by specifying (by reference) 156a nonzero parameter and disabled by specifying (by reference) 157a zero parameter. 158Each subsequent 159.Xr read 160from the master side will return data written on the slave part of 161the pseudo terminal preceded by a zero byte, 162or a single byte reflecting a user control operation on the slave side. 163A user control command consists of a special 164.Xr ioctl 165operation with no data; the command is given as 166.Dv UIOCCMD Ns (n) , 167where 168.Ar n 169is a number in the range 1-255. 170The operation value 171.Ar n 172will be received as a single byte on the next 173.Xr read 174from the master side. 175The 176.Xr ioctl 177.Dv UIOCCMD Ns (0) 178is a no-op that may be used to probe for 179the existence of this facility. 180As with 181.Dv TIOCPKT 182mode, command operations may be detected with a 183.Xr select 184for exceptional conditions. 185.It Dv TIOCREMOTE 186A mode for the master half of a pseudo terminal, independent 187of 188.Dv TIOCPKT . 189This mode causes input to the pseudo terminal 190to be flow controlled and not input edited (regardless of the 191terminal mode). Each write to the control terminal produces 192a record boundary for the process reading the terminal. In 193normal usage, a write of data is like the data typed as a line 194on the terminal; a write of 0 bytes is like typing an end-of-file 195character. 196.Dv TIOCREMOTE 197can be used when doing remote line 198editing in a window manager, or whenever flow controlled input 199is required. 200.El 201.Sh FILES 202.Bl -tag -width /dev/tty[p-r][0-9a-f]x -compact 203.It Pa /dev/pty[p-r][0-9a-f] 204master pseudo terminals 205.It Pa /dev/tty[p-r][0-9a-f] 206slave pseudo terminals 207.El 208.Sh DIAGNOSTICS 209None. 210.Sh HISTORY 211The 212.Nm 213driver appeared in 214.Bx 4.2 . 215