1'\" te 2.\" Copyright (c) 1994, Sun Microsystems, Inc. 3.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License"). You may not use this file except in compliance with the License. 4.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing. See the License for the specific language governing permissions and limitations under the License. 5.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE. If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] 6.\" Copyright 2022 Oxide Computer Company 7.Dd February 5, 2022 8.Dt PTY 4D 9.Os 10.Sh NAME 11.Nm pty 12.Nd legacy pseudo-terminal driver 13.Sh SYNOPSIS 14.Pa /dev/pty[p-r]* 15.Pp 16.Pa /dev/tty[p-r]* 17.Sh DESCRIPTION 18This driver provides support for legacy static pseudo-terminal devices. 19Modern software does not use this driver, preferring instead the STREAMS-based 20.Xr ptm 4D 21and 22.Xr pts 4D 23pseudo-terminal drivers, consumed through the portable 24.Xr posix_openpt 3C 25interface. 26.Pp 27The 28.Nm pty 29driver provides support for a pair of devices collectively known 30as a 31.Em pseudo-terminal . 32The two devices comprising a pseudo-terminal are known as a 33.Em manager 34and a 35.Em subsidiary . 36The subsidiary device distinguishes between the 37.Dv B0 baud rate and other baud rates specified in 38the 39.Fa c_cflag 40field of the 41.Vt termios 42structure, and the 43.Dv CLOCAL 44flag in that member. 45It does not support any of the other 46.Xr termio 4I 47device control functions specified by flags in the 48.Fa c_cflag 49field of the 50.Vt termios 51structure and by the 52.Dv IGNBRK , 53.Dv IGNPAR , 54.Dv PARMRK , 55or 56.Dv INPCK 57flags in the 58.Fa c_iflag 59field of the 60.Vt termios 61structure, as these functions apply only to asynchronous serial ports. 62All other 63.Xr termio 4I 64functions must be performed by STREAMS modules pushed atop the driver; when a 65subsidiary device is opened, the 66.Xr ldterm 4M 67and 68.Xr ttcompat 4M 69STREAMS modules are automatically pushed on top of the stream, providing the 70standard 71.Xr termio 4I 72interface. 73.Pp 74Instead of having a hardware interface and associated hardware that supports 75the terminal functions, the functions are implemented by another process 76manipulating the manager device of the pseudo-terminal. 77.Pp 78The manager and the subsidiary devices of the pseudo-terminal are tightly 79connected. 80Any data written on the manager device is given to the subsidiary device as 81input, as though it had been received from a hardware interface. 82Any data written on the subsidiary terminal can be read from the manager device 83.Pq "rather than being transmitted from a UAR" . 84.Pp 85The driver is statically configured to provide 48 pseudo-terminal pairs. 86Software that requires dynamic pseudo-terminal devices, or a greater number 87of devices, must be converted to use 88.Xr ptm 4D . 89.Sh IOCTLS 90The standard set of 91.Xr termio 4I 92ioctls are supported by the subsidiary device. 93None of the bits in the 94.Fa c_cflag 95field have any effect on the pseudo-terminal, except that if the baud rate is 96set to 97.Dv B0 , 98it will appear to the process on the manager device as if the last process on 99the subsidiary device had closed the line; thus, setting the baud rate to 100.Dv B0 101has the effect of 102.Dq hanging up 103the pseudo-terminal, just as it has the effect of 104.Dq hanging up 105a real terminal. 106.Pp 107There is no notion of 108.Dq parity 109on a pseudo-terminal, so none of the flags in the 110.Fa c_iflag 111field that control the processing of parity errors have any 112effect. 113Similarly, there is no notion of a 114.Fa break , 115so none of the flags that control the processing of breaks, and none of the 116ioctls that generate breaks, have any effect. 117.Pp 118Input flow control is automatically performed; a process that attempts to write 119to the manager device will be blocked if too much unconsumed data is buffered 120on the subsidiary device. 121The input flow control provided by the 122.Dv IXOFF 123flag in the 124.Fa c_iflag 125field is not supported. 126.Pp 127The delays specified in the 128.Fa c_oflag 129field are not supported. 130.Pp 131As there are no modems involved in a pseudo-terminal, the ioctls that return or 132alter the state of modem control lines are silently ignored. 133.Pp 134A few special ioctls are provided on the manager devices of pseudo-terminals to 135provide the functionality needed by applications programs to emulate real 136hardware interfaces: 137.Bl -tag -width Ds 138.It Dv TIOCSTOP 139The argument is ignored. 140Output to the pseudo-terminal is suspended, as if a 141.Sy STOP 142character had been typed. 143.It Dv TIOCSTART 144The argument is ignored. 145Output to the pseudo-terminal is restarted, as if a 146.Sy START 147character had been typed. 148.It Dv TIOCPKT 149The argument is a pointer to an 150.Vt int . 151If the value of the 152.Vt int 153is non-zero, 154.Em packet 155mode is enabled; if the value of the 156.Vt int 157is zero, packet mode is disabled. 158When a pseudo-terminal is in packet mode, each subsequent 159.Xr read 2 160from the manager device will return data written on the subsidiary device 161preceded by a zero byte 162.Po 163symbolically defined as 164.Dv TIOCPKT_DATA 165.Pc , 166or a single byte reflecting control status information. 167In the latter case, the byte is an inclusive-or of zero or more of the bits: 168.Bl -tag -width Ds 169.It Dv TIOCPKT_FLUSHREAD 170Whenever the read queue for the terminal is flushed. 171.It Dv TIOCPKT_FLUSHWRITE 172Whenever the write queue for the terminal is flushed. 173.It Dv TIOCPKT_STOP 174Whenever output to the terminal is stopped using 175.Sy ^S . 176.It Dv TIOCPKT_START 177Whenever output to the terminal is restarted. 178.It Dv TIOCPKT_DOSTOP 179Whenever 180.Em XON/XOFF 181flow control is enabled after being disabled; it is 182considered 183.Dq enabled 184when the 185.Dv IXON 186flag in the 187.Fa c_iflag 188field is set, the 189.Dv VSTOP 190member of the 191.Fa c_cc 192array is 193.Sy ^S 194and the 195.Dv VSTART 196member of the 197.Fa c_cc 198array is 199.Sy ^Q. 200.It Dv TIOCPKT_NOSTOP 201Whenever 202.Em XON/XOFF 203flow control is disabled after being enabled. 204.El 205.It Dv TIOCREMOTE 206The argument is a pointer to an 207.Vt int . 208If the value of the 209.Vt int 210is non-zero, 211.Em remote 212mode is enabled; if the value of the 213.Vt int 214is zero, remote mode is disabled. 215This mode can be enabled or disabled independently of packet mode. 216When a pseudo-terminal is in remote mode, input to the subsidiary device of the 217pseudo-terminal is flow controlled and not input edited (regardless of the mode 218the subsidiary side of the pseudo-terminal). 219.Pp 220Each write to the manager device produces a record boundary for the process 221reading the subsidiary device. 222In normal usage, a write of data is like the data typed as a line on the 223terminal; a write of 0 bytes is like typing an 224.Sy EOF 225character. 226Note: this means that a process writing to a pseudo-terminal manager in remote 227mode must keep track of line boundaries, and write only one line at a time to 228the manager. 229.Pp 230If, for example, it were to buffer up several newline characters and write them 231to the manager with one 232.Xr write 2 , 233it would appear to a process reading from the subsidiary as if a single line 234containing several newline characters had been typed 235.Po 236as if, for example, a user had typed the literal next 237.Pq Sy LNEXT 238character before typing all but the last of those newline characters 239.Pc . 240Remote mode can be used when doing remote line editing in a window manager, or 241whenever flow controlled input is required. 242.El 243.Sh FILES 244.Bl -tag -width Pa 245.It Pa /dev/pty[p-r][0-9a-f] 246Pseudo-terminal manager devices. 247.It Pa /dev/tty[p-r][0-9a-f] 248Pseudo-terminal subsidiary devices. 249.El 250.Sh SEE ALSO 251.Xr rlogin 1 , 252.Xr posix_openpty 3C , 253.Xr ptm 4D , 254.Xr termio 4I , 255.Xr ldterm 4M , 256.Xr ttcompat 4M , 257.Xr rlogind 8 258.Sh NOTES 259This is a legacy device and should not be used by new software. 260.Pp 261It is apparently not possible to send an 262.Sy EOT 263by writing zero bytes in 264.Dv TIOCREMOTE 265mode. 266