[unix-history] / share / man / man4 / pty.4

.\" Copyright (c) 1983, 1991 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	6.3 (Berkeley) 3/28/91
.\"
.Dd March 28, 1991
.Dt PTY 4
.Os BSD 4.2
.Sh NAME
.Nm pty
.Nd pseudo terminal driver
.Sh SYNOPSIS
.Nm pseudo-device pty
.Op Ar count
.Sh DESCRIPTION
The
.Xr 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 processes
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
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
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
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
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
from the master side.
The
.Xr ioctl
.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
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-r][0-9a-f]x -compact
.It Pa /dev/pty[p-r][0-9a-f]
master pseudo terminals
.It Pa /dev/tty[p-r][0-9a-f]
slave pseudo terminals
.El
.Sh DIAGNOSTICS
None.
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.2 .
Commit	Line	Data
15637ed4 RG	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	.\" @(#)pty.4 6.3 (Berkeley) 3/28/91
	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 pseudo-device pty
	42	.Op Ar count
	43	.Sh DESCRIPTION
	44	The
	45	.Xr pty
	46	driver provides support for a device-pair termed a
	47	.Em pseudo terminal .
	48	A pseudo terminal is a pair of character devices, a
	49	.Em master
	50	device and a
	51	.Em slave
	52	device. The slave device provides processes
	53	an interface identical
	54	to that described in
	55	.Xr tty 4 .
	56	However, whereas all other devices which provide the
	57	interface described in
	58	.Xr tty 4
	59	have a hardware device of some sort behind them, the slave
	60	device has, instead, another process manipulating
	61	it through the master half of the pseudo terminal.
	62	That is, anything written on the master device is
	63	given to the slave device as input and anything written
	64	on the slave device is presented as input on the master
65	device.
66	.Pp
67	In configuring, if an optional
68	.Ar count
69	is given in
70	the specification, that number of pseudo terminal pairs are configured;
71	the default count is 32.
72	.Pp
73	The following
74	.Xr ioctl 2
75	calls apply only to pseudo terminals:
76	.Bl -tag -width TIOCREMOTE
77	.It Dv TIOCSTOP
78	Stops output to a terminal (e.g. like typing
79	.Ql ^S ) .
80	Takes
81	no parameter.
82	.It Dv TIOCSTART
83	Restarts output (stopped by
84	.Dv TIOCSTOP
85	or by typing
86	.Ql ^S ) .
87	Takes no parameter.
88	.It Dv TIOCPKT
89	Enable/disable
90	.Em packet
91	mode. Packet mode is enabled by specifying (by reference)
92	a nonzero parameter and disabled by specifying (by reference)
93	a zero parameter. When applied to the master side of a pseudo
94	terminal, each subsequent
95	.Xr read
96	from the terminal will return data written on the slave part of
97	the pseudo terminal preceded by a zero byte (symbolically
98	defined as
99	.Dv TIOCPKT_DATA ) ,
100	or a single byte reflecting control
101	status information. In the latter case, the byte is an inclusive-or
102	of zero or more of the bits:
103	.Bl -tag -width TIOCPKT_FLUSHWRITE
104	.It Dv TIOCPKT_FLUSHREAD
105	whenever the read queue for the terminal is flushed.
106	.It Dv TIOCPKT_FLUSHWRITE
107	whenever the write queue for the terminal is flushed.
108	.It Dv TIOCPKT_STOP
109	whenever output to the terminal is stopped a la
110	.Ql ^S .
111	.It Dv TIOCPKT_START
112	whenever output to the terminal is restarted.
113	.It Dv TIOCPKT_DOSTOP
114	whenever
115	.Em t_stopc
116	is
117	.Ql ^S
118	and
119	.Em t_startc
120	is
121	.Ql ^Q .
122	.It Dv TIOCPKT_NOSTOP
123	whenever the start and stop characters are not
124	.Ql ^S/^Q .
125	.Pp
126	While this mode is in use, the presence of control status information
127	to be read from the master side may be detected by a
128	.Xr select 2
129	for exceptional conditions.
130	.Pp
131	This mode is used by
132	.Xr rlogin 1
133	and
134	.Xr rlogind 8
135	to implement a remote-echoed, locally
136	.Ql ^S/^Q
137	flow-controlled
138	remote login with proper back-flushing of output; it can be
139	used by other similar programs.
140	.El
141	.It Dv TIOCUCNTL
142	Enable/disable a mode that allows a small number of simple user
143	.Xr ioctl
144	commands to be passed through the pseudo-terminal,
145	using a protocol similar to that of
146	.Dv TIOCPKT .
147	The
148	.Dv TIOCUCNTL
149	and
150	.Dv TIOCPKT
151	modes are mutually exclusive.
152	This mode is enabled from the master side of a pseudo terminal
153	by specifying (by reference)
154	a nonzero parameter and disabled by specifying (by reference)
155	a zero parameter.
156	Each subsequent
157	.Xr read
158	from the master side will return data written on the slave part of
159	the pseudo terminal preceded by a zero byte,
160	or a single byte reflecting a user control operation on the slave side.
161	A user control command consists of a special
162	.Xr ioctl
163	operation with no data; the command is given as
164	.Dv UIOCCMD Ns (n) ,
165	where
166	.Ar n
167	is a number in the range 1-255.
168	The operation value
169	.Ar n
170	will be received as a single byte on the next
171	.Xr read
172	from the master side.
173	The
174	.Xr ioctl
175	.Dv UIOCCMD Ns (0)
176	is a no-op that may be used to probe for
177	the existence of this facility.
178	As with
179	.Dv TIOCPKT
180	mode, command operations may be detected with a
181	.Xr select
182	for exceptional conditions.
183	.It Dv TIOCREMOTE
184	A mode for the master half of a pseudo terminal, independent
185	of
186	.Dv TIOCPKT .
187	This mode causes input to the pseudo terminal
188	to be flow controlled and not input edited (regardless of the
189	terminal mode). Each write to the control terminal produces
190	a record boundary for the process reading the terminal. In
191	normal usage, a write of data is like the data typed as a line
192	on the terminal; a write of 0 bytes is like typing an end-of-file
193	character.
194	.Dv TIOCREMOTE
195	can be used when doing remote line
196	editing in a window manager, or whenever flow controlled input
197	is required.
198	.El
199	.Sh FILES
200	.Bl -tag -width /dev/tty[p-r][0-9a-f]x -compact
201	.It Pa /dev/pty[p-r][0-9a-f]
202	master pseudo terminals
203	.It Pa /dev/tty[p-r][0-9a-f]
204	slave pseudo terminals
205	.El
206	.Sh DIAGNOSTICS
207	None.
208	.Sh HISTORY
209	The
210	.Nm
211	driver appeared in
212	.Bx 4.2 .