1.\" Copyright (c) 1983, 1991 Regents of the University of California. 2.\" 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.\" $Id$ 33.\" 34.Dd March 28, 1991 35.Dt PTY 4 36.Os BSD 4.2 37.Sh NAME 38.Nm pty 39.Nd pseudo terminal driver 40.Sh SYNOPSIS 41.Nm pty slave_chr_major control_chr_major 42.Op Ar ptycount . 43.Sh DESCRIPTION 44The 45.Xr 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 processes 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 67If an optional 68.Ar count 69is given in 70the device configuration specification, 71that number of pseudo terminal pairs are configured; 72the default count is 8. 73.Pp 74The following 75.Xr ioctl 2 76calls apply only to pseudo terminals: 77.Bl -tag -width TIOCREMOTE 78.It Dv TIOCSTOP 79Stops output to a terminal (e.g. like typing 80.Ql ^S ) . 81Takes 82no parameter. 83.It Dv TIOCSTART 84Restarts output (stopped by 85.Dv TIOCSTOP 86or by typing 87.Ql ^S ) . 88Takes no parameter. 89.It Dv TIOCPKT 90Enable/disable 91.Em packet 92mode. Packet mode is enabled by specifying (by reference) 93a nonzero parameter and disabled by specifying (by reference) 94a zero parameter. When applied to the master side of a pseudo 95terminal, each subsequent 96.Xr read 97from the terminal will return data written on the slave part of 98the pseudo terminal preceded by a zero byte (symbolically 99defined as 100.Dv TIOCPKT_DATA ) , 101or a single byte reflecting control 102status information. In the latter case, the byte is an inclusive-or 103of zero or more of the bits: 104.Bl -tag -width TIOCPKT_FLUSHWRITE 105.It Dv TIOCPKT_FLUSHREAD 106whenever the read queue for the terminal is flushed. 107.It Dv TIOCPKT_FLUSHWRITE 108whenever the write queue for the terminal is flushed. 109.It Dv TIOCPKT_STOP 110whenever output to the terminal is stopped a la 111.Ql ^S . 112.It Dv TIOCPKT_START 113whenever output to the terminal is restarted. 114.It Dv TIOCPKT_DOSTOP 115whenever 116.Em t_stopc 117is 118.Ql ^S 119and 120.Em t_startc 121is 122.Ql ^Q . 123.It Dv TIOCPKT_NOSTOP 124whenever the start and stop characters are not 125.Ql ^S/^Q . 126.Pp 127While this mode is in use, the presence of control status information 128to be read from the master side may be detected by a 129.Xr select 2 130for exceptional conditions. 131.Pp 132This mode is used by 133.Xr rlogin 1 134and 135.Xr rlogind 8 136to implement a remote-echoed, locally 137.Ql ^S/^Q 138flow-controlled 139remote login with proper back-flushing of output; it can be 140used by other similar programs. 141.El 142.It Dv TIOCUCNTL 143Enable/disable a mode that allows a small number of simple user 144.Xr ioctl 145commands to be passed through the pseudo-terminal, 146using a protocol similar to that of 147.Dv TIOCPKT . 148The 149.Dv TIOCUCNTL 150and 151.Dv TIOCPKT 152modes are mutually exclusive. 153This mode is enabled from the master side of a pseudo terminal 154by specifying (by reference) 155a nonzero parameter and disabled by specifying (by reference) 156a zero parameter. 157Each subsequent 158.Xr read 159from the master side will return data written on the slave part of 160the pseudo terminal preceded by a zero byte, 161or a single byte reflecting a user control operation on the slave side. 162A user control command consists of a special 163.Xr ioctl 164operation with no data; the command is given as 165.Dv UIOCCMD Ns (n) , 166where 167.Ar n 168is a number in the range 1-255. 169The operation value 170.Ar n 171will be received as a single byte on the next 172.Xr read 173from the master side. 174The 175.Xr ioctl 176.Dv UIOCCMD Ns (0) 177is a no-op that may be used to probe for 178the existence of this facility. 179As with 180.Dv TIOCPKT 181mode, command operations may be detected with a 182.Xr select 183for exceptional conditions. 184.It Dv TIOCREMOTE 185A mode for the master half of a pseudo terminal, independent 186of 187.Dv TIOCPKT . 188This mode causes input to the pseudo terminal 189to be flow controlled and not input edited (regardless of the 190terminal mode). Each write to the control terminal produces 191a record boundary for the process reading the terminal. In 192normal usage, a write of data is like the data typed as a line 193on the terminal; a write of 0 bytes is like typing an end-of-file 194character. 195.Dv TIOCREMOTE 196can be used when doing remote line 197editing in a window manager, or whenever flow controlled input 198is required. 199.El 200.Sh FILES 201.Bl -tag -width /dev/tty[p-r][0-9a-f]x -compact 202.It Pa /dev/pty[p-r][0-9a-f] 203master pseudo terminals 204.It Pa /dev/tty[p-r][0-9a-f] 205slave pseudo terminals 206.El 207.Sh DIAGNOSTICS 208None. 209.Sh HISTORY 210The 211.Nm 212driver appeared in 213.Bx 4.2 . 214