xref: /freebsd/share/man/man4/tty.4 (revision ae83180158c4c937f170e31eff311b18c0286a93)
1.\" Copyright (c) 1991, 1992, 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.\"     @(#)tty.4	8.3 (Berkeley) 4/19/94
33.\" $FreeBSD$
34.\"
35.Dd August 14, 1992
36.Dt TTY 4
37.Os
38.Sh NAME
39.Nm tty
40.Nd general terminal interface
41.Sh SYNOPSIS
42.In sys/ioctl.h
43.Sh DESCRIPTION
44This section describes the interface to the terminal drivers
45in the system.
46.Ss Terminal Special Files
47Each hardware terminal port on the system usually has a terminal special device
48file associated with it in the directory ``/dev/'' (for
49example, ``/dev/tty03'').
50When a user logs into
51the system on one of these hardware terminal ports, the system has already
52opened the associated device and prepared the line for normal interactive
53use (see
54.Xr getty 8 . )
55There is also a special case of a terminal file that connects not to
56a hardware terminal port, but to another program on the other side.
57These special terminal devices are called
58.Em ptys
59and provide the mechanism necessary to give users the same interface to the
60system when logging in over a network (using
61.Xr rlogin 1 ,
62or
63.Xr telnet 1
64for example).  Even in these cases the details of how the terminal
65file was opened and set up is already handled by special software
66in the system.
67Thus, users do not normally need to worry about the details of
68how these lines are opened or used.  Also, these lines are often used
69for dialing out of a system (through an out-calling modem), but again
70the system provides programs that hide the details of accessing
71these terminal special files (see
72.Xr tip 1 ) .
73.Pp
74When an interactive user logs in, the system prepares the line to
75behave in a certain way (called a
76.Em "line discipline" ) ,
77the particular details of which is described in
78.Xr stty 1
79at the command level, and in
80.Xr termios 4
81at the programming level.  A user may be concerned with changing
82settings associated with his particular login terminal and should refer
83to the preceding man pages for the common cases.  The remainder of
84this man page is concerned
85with describing details of using and controlling terminal devices
86at a low level, such as that possibly required by a program wishing
87to provide features similar to those provided by the system.
88.Ss Line disciplines
89A terminal file is used like any other file in the system in that
90it can be opened, read, and written to using standard system
91calls.  For each existing terminal file, there is a software processing module
92called a
93.Em "line discipline"
94is associated with it.  The
95.Em "line discipline"
96essentially glues the low level device driver code with the high
97level generic interface routines (such as
98.Xr read 2
99and
100.Xr write 2 ) ,
101and is responsible for implementing the semantics associated
102with the device.  When a terminal file is first opened by a program,
103the default
104.Em "line discipline"
105called the
106.Dv termios
107line discipline is associated with the file.  This is the primary
108line discipline that is used in most cases and provides the semantics
109that users normally associate with a terminal.  When the
110.Dv termios
111line discipline is in effect, the terminal file behaves and is
112operated according to the rules described in
113.Xr termios 4 .
114Please refer to that man page for a full description of the terminal
115semantics.
116The operations described here
117generally represent features common
118across all
119.Em "line disciplines" ,
120however some of these calls may not
121make sense in conjunction with a line discipline other than
122.Dv termios ,
123and some may not be supported by the underlying
124hardware (or lack thereof, as in the case of ptys).
125.Ss Terminal File Operations
126All of the following operations are invoked using the
127.Xr ioctl 2
128system call.  Refer to that man page for a description of
129the
130.Em request
131and
132.Em argp
133parameters.
134In addition to the ioctl
135.Em requests
136defined here, the specific line discipline
137in effect will define other
138.Em requests
139specific to it (actually
140.Xr termios 4
141defines them as function calls, not ioctl
142.Em requests . )
143The following section lists the available ioctl requests.  The
144name of the request, a description of its purpose, and the typed
145.Em argp
146parameter (if any)
147are listed.  For example, the first entry says
148.Pp
149.D1 Em "TIOCSETD int *ldisc"
150.Pp
151and would be called on the terminal associated with
152file descriptor zero by the following code fragment:
153.Bd -literal
154	int ldisc;
155
156	ldisc = TTYDISC;
157	ioctl(0, TIOCSETD, &ldisc);
158.Ed
159.Ss Terminal File Request Descriptions
160.Bl -tag -width TIOCGWINSZ
161.It Dv TIOCSETD Fa int *ldisc
162Change to the new line discipline pointed to by
163.Fa ldisc .
164The available line disciplines are listed in
165.Aq Pa sys/ttycom.h
166and currently are:
167.Pp
168.Bl -tag -width NETGRAPHDISC -compact
169.It TTYDISC
170Termios interactive line discipline.
171.It TABLDISC
172Tablet line discipline.
173.It SLIPDISC
174Serial IP line discipline.
175.It PPPDISC
176PPP line discipline.
177.It NETGRAPHDISC
178Netgraph
179.Xr ng_tty 4
180line discipline.
181.El
182.Pp
183.It Dv TIOCGETD Fa int *ldisc
184Return the current line discipline in the integer pointed to by
185.Fa ldisc .
186.It Dv TIOCSBRK Fa void
187Set the terminal hardware into BREAK condition.
188.It Dv TIOCCBRK Fa void
189Clear the terminal hardware BREAK condition.
190.It Dv TIOCSDTR Fa void
191Assert data terminal ready (DTR).
192.It Dv TIOCCDTR Fa void
193Clear data terminal ready (DTR).
194.It Dv TIOCGPGRP Fa int *tpgrp
195Return the current process group with which the terminal is associated
196in the integer pointed to by
197.Fa tpgrp .
198This is the underlying call that implements the
199.Xr termios 4
200.Fn tcgetattr
201call.
202.It Dv TIOCSPGRP Fa int *tpgrp
203Associate the terminal with the process group (as an integer) pointed to by
204.Fa tpgrp .
205This is the underlying call that implements the
206.Xr termios 4
207.Fn tcsetattr
208call.
209.It Dv TIOCGETA Fa struct termios *term
210Place the current value of the termios state associated with the
211device in the termios structure pointed to by
212.Fa term .
213This is the underlying call that implements the
214.Xr termios 4
215.Fn tcgetattr
216call.
217.It Dv TIOCSETA Fa struct termios *term
218Set the termios state associated with the device immediately.
219This is the underlying call that implements the
220.Xr termios 4
221.Fn tcsetattr
222call with the
223.Dv TCSANOW
224option.
225.It Dv TIOCSETAW Fa struct termios *term
226First wait for any output to complete, then set the termios state
227associated with the device.
228This is the underlying call that implements the
229.Xr termios 4
230.Fn tcsetattr
231call with the
232.Dv TCSADRAIN
233option.
234.It Dv TIOCSETAF Fa struct termios *term
235First wait for any output to complete, clear any pending input,
236then set the termios state associated with the device.
237This is the underlying call that implements the
238.Xr termios 4
239.Fn tcsetattr
240call with the
241.Dv TCSAFLUSH
242option.
243.It Dv TIOCOUTQ Fa int *num
244Place the current number of characters in the output queue in the
245integer pointed to by
246.Fa num .
247.It Dv TIOCSTI Fa char *cp
248Simulate typed input.  Pretend as if the terminal received the
249character pointed to by
250.Fa cp .
251.It Dv TIOCNOTTY Fa void
252This call is obsolete but left for compatibility.  In the past, when
253a process that didn't have a controlling terminal (see
254.Em The Controlling Terminal
255in
256.Xr termios 4 )
257first opened a terminal device, it acquired that terminal as its
258controlling terminal.  For some programs this was a hazard as they
259didn't want a controlling terminal in the first place, and this
260provided a mechanism to disassociate the controlling terminal from
261the calling process.  It
262.Em must
263be called by opening the file
264.Pa /dev/tty
265and calling
266.Dv TIOCNOTTY
267on that file descriptor.
268.Pp
269The current system does not allocate a controlling terminal to
270a process on an
271.Fn open
272call: there is a specific ioctl called
273.Dv TIOSCTTY
274to make a terminal the controlling
275terminal.
276In addition, a program can
277.Fn fork
278and call the
279.Fn setsid
280system call which will place the process into its own session - which
281has the effect of disassociating it from the controlling terminal.  This
282is the new and preferred method for programs to lose their controlling
283terminal.
284.It Dv TIOCSTOP Fa void
285Stop output on the terminal (like typing ^S at the keyboard).
286.It Dv TIOCSTART Fa void
287Start output on the terminal (like typing ^Q at the keyboard).
288.It Dv TIOCSCTTY Fa void
289Make the terminal the controlling terminal for the process (the process
290must not currently have a controlling terminal).
291.It Dv TIOCDRAIN Fa void
292Wait until all output is drained.
293.It Dv TIOCEXCL Fa void
294Set exclusive use on the terminal.  No further opens are permitted
295except by root.  Of course, this means that programs that are run by
296root (or setuid) will not obey the exclusive setting - which limits
297the usefulness of this feature.
298.It Dv TIOCNXCL Fa void
299Clear exclusive use of the terminal.  Further opens are permitted.
300.It Dv TIOCFLUSH Fa int *what
301If the value of the int pointed to by
302.Fa what
303contains the
304.Dv FREAD
305bit as defined in
306.Aq Pa sys/file.h ,
307then all characters in the input queue are cleared.  If it contains
308the
309.Dv FWRITE
310bit, then all characters in the output queue are cleared.  If the
311value of the integer is zero, then it behaves as if both the
312.Dv FREAD
313and
314.Dv FWRITE
315bits were set (i.e. clears both queues).
316.It Dv TIOCGWINSZ Fa struct winsize *ws
317Put the window size information associated with the terminal in the
318.Va winsize
319structure pointed to by
320.Fa ws .
321The window size structure contains the number of rows and columns (and pixels
322if appropriate) of the devices attached to the terminal.  It is set by user software
323and is the means by which most full\&-screen oriented programs determine the
324screen size.  The
325.Va winsize
326structure is defined in
327.Aq Pa sys/ioctl.h .
328.It Dv TIOCSWINSZ Fa struct winsize *ws
329Set the window size associated with the terminal to be the value in
330the
331.Va winsize
332structure pointed to by
333.Fa ws
334(see above).
335.It Dv TIOCCONS Fa int *on
336If
337.Fa on
338points to a non-zero integer, redirect kernel console output (kernel printf's)
339to this terminal.
340If
341.Fa on
342points to a zero integer, redirect kernel console output back to the normal
343console.  This is usually used on workstations to redirect kernel messages
344to a particular window.
345.It Dv TIOCMSET Fa int *state
346The integer pointed to by
347.Fa state
348contains bits that correspond to modem state.  Following is a list
349of defined variables and the modem state they represent:
350.Pp
351.Bl -tag -width TIOCMXCTS -compact
352.It TIOCM_LE
353Line Enable.
354.It TIOCM_DTR
355Data Terminal Ready.
356.It TIOCM_RTS
357Request To Send.
358.It TIOCM_ST
359Secondary Transmit.
360.It TIOCM_SR
361Secondary Receive.
362.It TIOCM_CTS
363Clear To Send.
364.It TIOCM_CAR
365Carrier Detect.
366.It TIOCM_CD
367Carrier Detect (synonym).
368.It TIOCM_RNG
369Ring Indication.
370.It TIOCM_RI
371Ring Indication (synonym).
372.It TIOCM_DSR
373Data Set Ready.
374.El
375.Pp
376This call sets the terminal modem state to that represented by
377.Fa state .
378Not all terminals may support this.
379.It Dv TIOCMGET Fa int *state
380Return the current state of the terminal modem lines as represented
381above in the integer pointed to by
382.Fa state .
383.It Dv TIOCMBIS Fa int *state
384The bits in the integer pointed to by
385.Fa state
386represent modem state as described above, however the state is OR-ed
387in with the current state.
388.It Dv TIOCMBIC Fa int *state
389The bits in the integer pointed to by
390.Fa state
391represent modem state as described above, however each bit which is on
392in
393.Fa state
394is cleared in the terminal.
395.El
396.Sh IMPLEMENTATION NOTES
397The total number of input and output bytes
398through all terminal devices
399are available via the
400.Va kern.tk_nin
401and
402.Va kern.tk_nout
403read-only
404.Xr sysctl 8
405variables.
406.Sh SEE ALSO
407.Xr stty 1 ,
408.Xr ioctl 2 ,
409.Xr ng_tty 4 ,
410.Xr pty 4 ,
411.Xr termios 4 ,
412.Xr getty 8
413