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