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. The slave device provides to a process 53an 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. Packet mode is enabled by specifying (by reference) 86a nonzero parameter and disabled by specifying (by reference) 87a zero parameter. When applied to the master side of a pseudo 88terminal, each subsequent 89.Xr read 2 90from the terminal will return data written on the slave part of 91the pseudo terminal preceded by a zero byte (symbolically 92defined as 93.Dv TIOCPKT_DATA ) , 94or a single byte reflecting control 95status information. In the latter case, the byte is an inclusive-or 96of zero or more of the bits: 97.Bl -tag -width TIOCPKT_FLUSHWRITE 98.It Dv TIOCPKT_FLUSHREAD 99whenever the read queue for the terminal is flushed. 100.It Dv TIOCPKT_FLUSHWRITE 101whenever the write queue for the terminal is flushed. 102.It Dv TIOCPKT_STOP 103whenever output to the terminal is stopped a la 104.Ql ^S . 105.It Dv TIOCPKT_START 106whenever output to the terminal is restarted. 107.It Dv TIOCPKT_DOSTOP 108whenever 109.Em t_stopc 110is 111.Ql ^S 112and 113.Em t_startc 114is 115.Ql ^Q . 116.It Dv TIOCPKT_NOSTOP 117whenever the start and stop characters are not 118.Ql ^S/^Q . 119.Pp 120While this mode is in use, the presence of control status information 121to be read from the master side may be detected by a 122.Xr select 2 123for exceptional conditions. 124.Pp 125This mode is used by 126.Xr rlogin 1 127and 128.Xr rlogind 8 129to implement a remote-echoed, locally 130.Ql ^S/^Q 131flow-controlled 132remote login with proper back-flushing of output; it can be 133used by other similar programs. 134.El 135.It Dv TIOCUCNTL 136Enable/disable a mode that allows a small number of simple user 137.Xr ioctl 2 138commands to be passed through the pseudo-terminal, 139using a protocol similar to that of 140.Dv TIOCPKT . 141The 142.Dv TIOCUCNTL 143and 144.Dv TIOCPKT 145modes are mutually exclusive. 146This mode is enabled from the master side of a pseudo terminal 147by specifying (by reference) 148a nonzero parameter and disabled by specifying (by reference) 149a zero parameter. 150Each subsequent 151.Xr read 2 152from the master side will return data written on the slave part of 153the pseudo terminal preceded by a zero byte, 154or a single byte reflecting a user control operation on the slave side. 155A user control command consists of a special 156.Xr ioctl 2 157operation with no data; the command is given as 158.Dv UIOCCMD Ns (n) , 159where 160.Ar n 161is a number in the range 1-255. 162The operation value 163.Ar n 164will be received as a single byte on the next 165.Xr read 2 166from the master side. 167The 168.Xr ioctl 2 169.Dv UIOCCMD Ns (0) 170is a no-op that may be used to probe for 171the existence of this facility. 172As with 173.Dv TIOCPKT 174mode, command operations may be detected with a 175.Xr select 2 176for exceptional conditions. 177.It Dv TIOCREMOTE 178A mode for the master half of a pseudo terminal, independent 179of 180.Dv TIOCPKT . 181This mode causes input to the pseudo terminal 182to be flow controlled and not input edited (regardless of the 183terminal mode). Each write to the control terminal produces 184a record boundary for the process reading the terminal. In 185normal usage, a write of data is like the data typed as a line 186on the terminal; a write of 0 bytes is like typing an end-of-file 187character. 188.Dv TIOCREMOTE 189can be used when doing remote line 190editing in a window manager, or whenever flow controlled input 191is required. 192.El 193.Sh FILES 194.Bl -tag -width /dev/tty[p-sP-S][0-9a-v]x -compact 195.It Pa /dev/pty[p-sP-S][0-9a-v] 196master pseudo terminals 197.It Pa /dev/tty[p-sP-S][0-9a-v] 198slave pseudo terminals 199.El 200.Sh DIAGNOSTICS 201None. 202.Sh SEE ALSO 203.Xr tty 4 204.Sh HISTORY 205The 206.Nm 207driver appeared in 208.Bx 4.2 . 209