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.\" $Id: pty.4,v 1.5 1997/03/07 02:49:33 jmg Exp $ 34.\" 35.Dd November 30, 1993 36.Dt PTY 4 37.Os BSD 4.2 38.Sh NAME 39.Nm pty 40.Nd pseudo terminal driver 41.Sh SYNOPSIS 42.Cd "pseudo-device pty" Op Ar count 43.Sh DESCRIPTION 44The 45.Nm pty 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 67In configuring, if an optional 68.Ar count 69is given in 70the specification, that number of pseudo terminal pairs are configured; 71the default count is 32. 72.Pp 73The following 74.Xr ioctl 2 75calls apply only to pseudo terminals: 76.Bl -tag -width TIOCREMOTE 77.It Dv TIOCSTOP 78Stops output to a terminal (e.g. like typing 79.Ql ^S ) . 80Takes 81no parameter. 82.It Dv TIOCSTART 83Restarts output (stopped by 84.Dv TIOCSTOP 85or by typing 86.Ql ^S ) . 87Takes no parameter. 88.It Dv TIOCPKT 89Enable/disable 90.Em packet 91mode. Packet mode is enabled by specifying (by reference) 92a nonzero parameter and disabled by specifying (by reference) 93a zero parameter. When applied to the master side of a pseudo 94terminal, each subsequent 95.Xr read 2 96from the terminal will return data written on the slave part of 97the pseudo terminal preceded by a zero byte (symbolically 98defined as 99.Dv TIOCPKT_DATA ) , 100or a single byte reflecting control 101status information. In the latter case, the byte is an inclusive-or 102of zero or more of the bits: 103.Bl -tag -width TIOCPKT_FLUSHWRITE 104.It Dv TIOCPKT_FLUSHREAD 105whenever the read queue for the terminal is flushed. 106.It Dv TIOCPKT_FLUSHWRITE 107whenever the write queue for the terminal is flushed. 108.It Dv TIOCPKT_STOP 109whenever output to the terminal is stopped a la 110.Ql ^S . 111.It Dv TIOCPKT_START 112whenever output to the terminal is restarted. 113.It Dv TIOCPKT_DOSTOP 114whenever 115.Em t_stopc 116is 117.Ql ^S 118and 119.Em t_startc 120is 121.Ql ^Q . 122.It Dv TIOCPKT_NOSTOP 123whenever the start and stop characters are not 124.Ql ^S/^Q . 125.Pp 126While this mode is in use, the presence of control status information 127to be read from the master side may be detected by a 128.Xr select 2 129for exceptional conditions. 130.Pp 131This mode is used by 132.Xr rlogin 1 133and 134.Xr rlogind 8 135to implement a remote-echoed, locally 136.Ql ^S/^Q 137flow-controlled 138remote login with proper back-flushing of output; it can be 139used by other similar programs. 140.El 141.It Dv TIOCUCNTL 142Enable/disable a mode that allows a small number of simple user 143.Xr ioctl 2 144commands to be passed through the pseudo-terminal, 145using a protocol similar to that of 146.Dv TIOCPKT . 147The 148.Dv TIOCUCNTL 149and 150.Dv TIOCPKT 151modes are mutually exclusive. 152This mode is enabled from the master side of a pseudo terminal 153by specifying (by reference) 154a nonzero parameter and disabled by specifying (by reference) 155a zero parameter. 156Each subsequent 157.Xr read 2 158from the master side will return data written on the slave part of 159the pseudo terminal preceded by a zero byte, 160or a single byte reflecting a user control operation on the slave side. 161A user control command consists of a special 162.Xr ioctl 2 163operation with no data; the command is given as 164.Dv UIOCCMD Ns (n) , 165where 166.Ar n 167is a number in the range 1-255. 168The operation value 169.Ar n 170will be received as a single byte on the next 171.Xr read 2 172from the master side. 173The 174.Xr ioctl 2 175.Dv UIOCCMD Ns (0) 176is a no-op that may be used to probe for 177the existence of this facility. 178As with 179.Dv TIOCPKT 180mode, command operations may be detected with a 181.Xr select 2 182for exceptional conditions. 183.It Dv TIOCREMOTE 184A mode for the master half of a pseudo terminal, independent 185of 186.Dv TIOCPKT . 187This mode causes input to the pseudo terminal 188to be flow controlled and not input edited (regardless of the 189terminal mode). Each write to the control terminal produces 190a record boundary for the process reading the terminal. In 191normal usage, a write of data is like the data typed as a line 192on the terminal; a write of 0 bytes is like typing an end-of-file 193character. 194.Dv TIOCREMOTE 195can be used when doing remote line 196editing in a window manager, or whenever flow controlled input 197is required. 198.El 199.Sh FILES 200.Bl -tag -width /dev/tty[p-sP-S][0-9a-v]x -compact 201.It Pa /dev/pty[p-sP-S][0-9a-v] 202master pseudo terminals 203.It Pa /dev/tty[p-sP-S][0-9a-v] 204slave pseudo terminals 205.El 206.Sh DIAGNOSTICS 207None. 208.Sh SEE ALSO 209.Xr tty 4 210.Sh HISTORY 211The 212.Nm 213driver appeared in 214.Bx 4.2 . 215