.\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)pty.4 8.2 (Berkeley) 11/30/93 .\" .Dd November 30, 1993 .Dt PTY 4 .Os BSD 4.2 .Sh NAME .Nm pty .Nd pseudo terminal driver .Sh SYNOPSIS .Cd "pseudo-device pty" Op Ar count .Sh DESCRIPTION The .Nm pty driver provides support for a device-pair termed a .Em pseudo terminal . A pseudo terminal is a pair of character devices, a .Em master device and a .Em slave device. The slave device provides to a process an interface identical to that described in .Xr tty 4 . However, whereas all other devices which provide the interface described in .Xr tty 4 have a hardware device of some sort behind them, the slave device has, instead, another process manipulating it through the master half of the pseudo terminal. That is, anything written on the master device is given to the slave device as input and anything written on the slave device is presented as input on the master device. .Pp In configuring, if an optional .Ar count is given in the specification, that number of pseudo terminal pairs are configured; the default count is 32. .Pp The following .Xr ioctl 2 calls apply only to pseudo terminals: .Bl -tag -width TIOCREMOTE .It Dv TIOCSTOP Stops output to a terminal (e.g. like typing .Ql ^S ) . Takes no parameter. .It Dv TIOCSTART Restarts output (stopped by .Dv TIOCSTOP or by typing .Ql ^S ) . Takes no parameter. .It Dv TIOCPKT Enable/disable .Em packet mode. Packet mode is enabled by specifying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. When applied to the master side of a pseudo terminal, each subsequent .Xr read 2 from the terminal will return data written on the slave part of the pseudo terminal preceded by a zero byte (symbolically defined as .Dv TIOCPKT_DATA ) , or a single byte reflecting control status information. In the latter case, the byte is an inclusive-or of zero or more of the bits: .Bl -tag -width TIOCPKT_FLUSHWRITE .It Dv TIOCPKT_FLUSHREAD whenever the read queue for the terminal is flushed. .It Dv TIOCPKT_FLUSHWRITE whenever the write queue for the terminal is flushed. .It Dv TIOCPKT_STOP whenever output to the terminal is stopped a la .Ql ^S . .It Dv TIOCPKT_START whenever output to the terminal is restarted. .It Dv TIOCPKT_DOSTOP whenever .Em t_stopc is .Ql ^S and .Em t_startc is .Ql ^Q . .It Dv TIOCPKT_NOSTOP whenever the start and stop characters are not .Ql ^S/^Q . .Pp While this mode is in use, the presence of control status information to be read from the master side may be detected by a .Xr select 2 for exceptional conditions. .Pp This mode is used by .Xr rlogin 1 and .Xr rlogind 8 to implement a remote-echoed, locally .Ql ^S/^Q flow-controlled remote login with proper back-flushing of output; it can be used by other similar programs. .El .It Dv TIOCUCNTL Enable/disable a mode that allows a small number of simple user .Xr ioctl 2 commands to be passed through the pseudo-terminal, using a protocol similar to that of .Dv TIOCPKT . The .Dv TIOCUCNTL and .Dv TIOCPKT modes are mutually exclusive. This mode is enabled from the master side of a pseudo terminal by specifying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. Each subsequent .Xr read 2 from the master side will return data written on the slave part of the pseudo terminal preceded by a zero byte, or a single byte reflecting a user control operation on the slave side. A user control command consists of a special .Xr ioctl 2 operation with no data; the command is given as .Dv UIOCCMD Ns (n) , where .Ar n is a number in the range 1-255. The operation value .Ar n will be received as a single byte on the next .Xr read 2 from the master side. The .Xr ioctl 2 .Dv UIOCCMD Ns (0) is a no-op that may be used to probe for the existence of this facility. As with .Dv TIOCPKT mode, command operations may be detected with a .Xr select 2 for exceptional conditions. .It Dv TIOCREMOTE A mode for the master half of a pseudo terminal, independent of .Dv TIOCPKT . This mode causes input to the pseudo terminal to be flow controlled and not input edited (regardless of the terminal mode). Each write to the control terminal produces a record boundary for the process reading the terminal. In normal usage, a write of data is like the data typed as a line on the terminal; a write of 0 bytes is like typing an end-of-file character. .Dv TIOCREMOTE can be used when doing remote line editing in a window manager, or whenever flow controlled input is required. .El .Sh FILES .Bl -tag -width /dev/tty[p-sP-S][a-z0-9]x -compact .It Pa /dev/pty[p-sP-S][a-z0-9] master pseudo terminals .It Pa /dev/tty[p-sP-S][a-z0-9] slave pseudo terminals .El .Sh DIAGNOSTICS None. .Sh HISTORY The .Nm driver appeared in .Bx 4.2 .