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. 97In the latter case, the byte is an inclusive-or 98of zero or more of the bits: 99.Bl -tag -width TIOCPKT_FLUSHWRITE 100.It Dv TIOCPKT_FLUSHREAD 101whenever the read queue for the terminal is flushed. 102.It Dv TIOCPKT_FLUSHWRITE 103whenever the write queue for the terminal is flushed. 104.It Dv TIOCPKT_STOP 105whenever output to the terminal is stopped a la 106.Ql ^S . 107.It Dv TIOCPKT_START 108whenever output to the terminal is restarted. 109.It Dv TIOCPKT_DOSTOP 110whenever 111.Em t_stopc 112is 113.Ql ^S 114and 115.Em t_startc 116is 117.Ql ^Q . 118.It Dv TIOCPKT_NOSTOP 119whenever the start and stop characters are not 120.Ql ^S/^Q . 121.El 122.Pp 123While this mode is in use, the presence of control status information 124to be read from the master side may be detected by a 125.Xr select 2 126for exceptional conditions. 127.Pp 128This mode is used by 129.Xr rlogin 1 130and 131.Xr rlogind 8 132to implement a remote-echoed, locally 133.Ql ^S/^Q 134flow-controlled 135remote login with proper back-flushing of output; it can be 136used by other similar programs. 137.It Dv TIOCUCNTL 138Enable/disable a mode that allows a small number of simple user 139.Xr ioctl 2 140commands to be passed through the pseudo-terminal, 141using a protocol similar to that of 142.Dv TIOCPKT . 143The 144.Dv TIOCUCNTL 145and 146.Dv TIOCPKT 147modes are mutually exclusive. 148This mode is enabled from the master side of a pseudo terminal 149by specifying (by reference) 150a nonzero parameter and disabled by specifying (by reference) 151a zero parameter. 152Each subsequent 153.Xr read 2 154from the master side will return data written on the slave part of 155the pseudo terminal preceded by a zero byte, 156or a single byte reflecting a user control operation on the slave side. 157A user control command consists of a special 158.Xr ioctl 2 159operation with no data; the command is given as 160.Dv UIOCCMD Ns (n) , 161where 162.Ar n 163is a number in the range 1-255. 164The operation value 165.Ar n 166will be received as a single byte on the next 167.Xr read 2 168from the master side. 169The 170.Xr ioctl 2 171.Dv UIOCCMD Ns (0) 172is a no-op that may be used to probe for 173the existence of this facility. 174As with 175.Dv TIOCPKT 176mode, command operations may be detected with a 177.Xr select 2 178for exceptional conditions. 179.El 180.Pp 181There is currently two 182.Nm 183systems available: the original 184.Bx Nm , 185and a 186SysVR4 pts-like implementation. 187It is possible to switch between the two implementations by setting the 188.Va kern.pts.enable 189sysctl. 190Setting it to 0 will use the 191.Bx Nm , 192to non-zero the pts implementation. 193It defaults to 0. 194It is possible to set the maximum number of ptys 195which can be allocated at the same time with the 196.Va kern.pts.max 197sysctl. 198It defaults to 1000. 199It is not recommended to use more than 1000 pseudo-terminals, as all software 200which use 201.Xr utmp 5 202will not be able to handle pseudo-terminals with number superior to 999. 203.Pp 204The pts implementation also supports the 205.Dv TIOCGPTN 206.Xr ioctl 2 207call, which takes a pointer to an 208.Vt "unsigned int" 209as a parameter and provides the 210number of the pty. 211.Sh FILES 212The files used by the 213.Bx 214pseudo terminals implementation are: 215.Pp 216.Bl -tag -width ".Pa /dev/tty[p-sP-S][0-9a-v]" -compact 217.It Pa /dev/pty[p-sP-S][0-9a-v] 218master pseudo terminals 219.It Pa /dev/tty[p-sP-S][0-9a-v] 220slave pseudo terminals 221.El 222.Pp 223The files used by the pts implementation are: 224.Pp 225.Bl -tag -width ".Pa /dev/pts/[num]" -compact 226.It Pa /dev/ptmx 227control device, returns a file descriptor to a new master pseudo terminal 228when opened. 229.It Pa /dev/pty[num] 230master pseudo terminals 231.It Pa /dev/pts/[num] 232slave pseudo terminals 233.El 234.Sh DIAGNOSTICS 235None. 236.Sh SEE ALSO 237.Xr tty 4 238.Sh HISTORY 239The 240.Nm 241driver appeared in 242.Bx 4.2 . 243