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32 .\" @(#)tty.4 8.3 (Berkeley) 4/19/94
33 .\" $FreeBSD$
34 .\"
35 .Dd Jun 27, 2007
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
44 This section describes the interface to the terminal drivers
45 in the system.
46 .Ss Terminal Special Files
47 Each hardware terminal port on the system usually has a terminal special device
48 file associated with it in the directory ``/dev/'' (for
49 example, ``/dev/tty03'').
50 When a user logs into
51 the system on one of these hardware terminal ports, the system has already
52 opened the associated device and prepared the line for normal interactive
53 use (see
54 .Xr getty 8 . )
55 There is also a special case of a terminal file that connects not to
56 a hardware terminal port, but to another program on the other side.
57 These special terminal devices are called
58 .Em ptys
59 and provide the mechanism necessary to give users the same interface to the
60 system when logging in over a network (using
61 .Xr rlogin 1 ,
62 or
63 .Xr telnet 1
64 for example).
65 Even in these cases the details of how the terminal
66 file was opened and set up is already handled by special software
67 in the system.
68 Thus, users do not normally need to worry about the details of
69 how these lines are opened or used.
70 Also, these lines are often used
71 for dialing out of a system (through an out-calling modem), but again
72 the system provides programs that hide the details of accessing
73 these terminal special files (see
74 .Xr tip 1 ) .
75 .Pp
76 When an interactive user logs in, the system prepares the line to
77 behave in a certain way (called a
78 .Em "line discipline" ) ,
79 the particular details of which is described in
80 .Xr stty 1
81 at the command level, and in
82 .Xr termios 4
83 at the programming level.
84 A user may be concerned with changing
85 settings associated with his particular login terminal and should refer
86 to the preceding man pages for the common cases.
87 The remainder of this man page is concerned
88 with describing details of using and controlling terminal devices
89 at a low level, such as that possibly required by a program wishing
90 to provide features similar to those provided by the system.
91 .Ss Line disciplines
92 A terminal file is used like any other file in the system in that
93 it can be opened, read, and written to using standard system
94 calls.
95 For each existing terminal file, there is a software processing module
96 called a
97 .Em "line discipline"
98 is associated with it.
99 The
100 .Em "line discipline"
101 essentially glues the low level device driver code with the high
102 level generic interface routines (such as
103 .Xr read 2
104 and
105 .Xr write 2 ) ,
106 and is responsible for implementing the semantics associated
107 with the device.
108 When a terminal file is first opened by a program, the default
109 .Em "line discipline"
110 called the
111 .Dv termios
112 line discipline is associated with the file.
113 This is the primary
114 line discipline that is used in most cases and provides the semantics
115 that users normally associate with a terminal.
116 When the
117 .Dv termios
118 line discipline is in effect, the terminal file behaves and is
119 operated according to the rules described in
120 .Xr termios 4 .
121 Please refer to that man page for a full description of the terminal
122 semantics.
123 The operations described here
124 generally represent features common
125 across all
126 .Em "line disciplines" ,
127 however some of these calls may not
128 make sense in conjunction with a line discipline other than
129 .Dv termios ,
130 and some may not be supported by the underlying
131 hardware (or lack thereof, as in the case of ptys).
132 .Ss Terminal File Operations
133 All of the following operations are invoked using the
134 .Xr ioctl 2
135 system call.
136 Refer to that man page for a description of the
137 .Em request
138 and
139 .Em argp
140 parameters.
141 In addition to the ioctl
142 .Em requests
143 defined here, the specific line discipline
144 in effect will define other
145 .Em requests
146 specific to it (actually
147 .Xr termios 4
148 defines them as function calls, not ioctl
149 .Em requests . )
150 The following section lists the available ioctl requests.
151 The name of the request, a description of its purpose, and the typed
152 .Em argp
153 parameter (if any)
154 are listed.
155 For example, the first entry says
156 .Pp
157 .D1 Em "TIOCSETD int *ldisc"
158 .Pp
159 and would be called on the terminal associated with
160 file descriptor zero by the following code fragment:
161 .Bd -literal
162 int ldisc;
164 ldisc = TTYDISC;
165 ioctl(0, TIOCSETD, &ldisc);
166 .Ed
167 .Ss Terminal File Request Descriptions
168 .Bl -tag -width TIOCGWINSZ
169 .It Dv TIOCSETD Fa int *ldisc
170 Change to the new line discipline pointed to by
171 .Fa ldisc .
172 The available line disciplines are listed in
173 .In sys/ttycom.h
174 and currently are:
175 .Pp
176 .Bl -tag -width NETGRAPHDISC -compact
177 .It TTYDISC
178 Termios interactive line discipline.
179 .It TABLDISC
180 Tablet line discipline.
181 .It SLIPDISC
182 Serial IP line discipline.
183 .It PPPDISC
184 PPP line discipline.
185 .It NETGRAPHDISC
186 Netgraph
187 .Xr ng_tty 4
188 line discipline.
189 .El
190 .Pp
191 .It Dv TIOCGETD Fa int *ldisc
192 Return the current line discipline in the integer pointed to by
193 .Fa ldisc .
194 .It Dv TIOCSBRK Fa void
195 Set the terminal hardware into BREAK condition.
196 .It Dv TIOCCBRK Fa void
197 Clear the terminal hardware BREAK condition.
198 .It Dv TIOCSDTR Fa void
199 Assert data terminal ready (DTR).
200 .It Dv TIOCCDTR Fa void
201 Clear data terminal ready (DTR).
202 .It Dv TIOCGPGRP Fa int *tpgrp
203 Return the current process group with which the terminal is associated
204 in the integer pointed to by
205 .Fa tpgrp .
206 This is the underlying call that implements the
207 .Xr termios 4
208 .Fn tcgetattr
209 call.
210 .It Dv TIOCSPGRP Fa int *tpgrp
211 Associate the terminal with the process group (as an integer) pointed to by
212 .Fa tpgrp .
213 This is the underlying call that implements the
214 .Xr termios 4
215 .Fn tcsetattr
216 call.
217 .It Dv TIOCGETA Fa struct termios *term
218 Place the current value of the termios state associated with the
219 device in the termios structure pointed to by
220 .Fa term .
221 This is the underlying call that implements the
222 .Xr termios 4
223 .Fn tcgetattr
224 call.
225 .It Dv TIOCSETA Fa struct termios *term
226 Set the termios state associated with the device immediately.
227 This is the underlying call that implements the
228 .Xr termios 4
229 .Fn tcsetattr
230 call with the
231 .Dv TCSANOW
232 option.
233 .It Dv TIOCSETAW Fa struct termios *term
234 First wait for any output to complete, then set the termios state
235 associated with the device.
236 This is the underlying call that implements the
237 .Xr termios 4
238 .Fn tcsetattr
239 call with the
240 .Dv TCSADRAIN
241 option.
242 .It Dv TIOCSETAF Fa struct termios *term
243 First wait for any output to complete, clear any pending input,
244 then set the termios state associated with the device.
245 This is the underlying call that implements the
246 .Xr termios 4
247 .Fn tcsetattr
248 call with the
249 .Dv TCSAFLUSH
250 option.
251 .It Dv TIOCOUTQ Fa int *num
252 Place the current number of characters in the output queue in the
253 integer pointed to by
254 .Fa num .
255 .It Dv TIOCSTI Fa char *cp
256 Simulate typed input.
257 Pretend as if the terminal received the character pointed to by
258 .Fa cp .
259 .It Dv TIOCNOTTY Fa void
260 This call is obsolete but left for compatibility.
261 In the past, when a process that did not have a controlling terminal (see
262 .Em The Controlling Terminal
263 in
264 .Xr termios 4 )
265 first opened a terminal device, it acquired that terminal as its
266 controlling terminal.
267 For some programs this was a hazard as they
268 did not want a controlling terminal in the first place, and this
269 provided a mechanism to disassociate the controlling terminal from
270 the calling process.
271 It
272 .Em must
273 be called by opening the file
274 .Pa /dev/tty
275 and calling
276 .Dv TIOCNOTTY
277 on that file descriptor.
278 .Pp
279 The current system does not allocate a controlling terminal to
280 a process on an
281 .Fn open
282 call: there is a specific ioctl called
283 .Dv TIOCSCTTY
284 to make a terminal the controlling
285 terminal.
286 In addition, a program can
287 .Fn fork
288 and call the
289 .Fn setsid
290 system call which will place the process into its own session - which
291 has the effect of disassociating it from the controlling terminal.
292 This is the new and preferred method for programs to lose their controlling
293 terminal.
294 .It Dv TIOCSTOP Fa void
295 Stop output on the terminal (like typing ^S at the keyboard).
296 .It Dv TIOCSTART Fa void
297 Start output on the terminal (like typing ^Q at the keyboard).
298 .It Dv TIOCSCTTY Fa void
299 Make the terminal the controlling terminal for the process (the process
300 must not currently have a controlling terminal).
301 .It Dv TIOCDRAIN Fa void
302 Wait until all output is drained.
303 .It Dv TIOCEXCL Fa void
304 Set exclusive use on the terminal.
305 No further opens are permitted except by root.
306 Of course, this means that programs that are run by
307 root (or setuid) will not obey the exclusive setting - which limits
308 the usefulness of this feature.
309 .It Dv TIOCNXCL Fa void
310 Clear exclusive use of the terminal.
311 Further opens are permitted.
312 .It Dv TIOCFLUSH Fa int *what
313 If the value of the int pointed to by
314 .Fa what
315 contains the
316 .Dv FREAD
317 bit as defined in
318 .In sys/file.h ,
319 then all characters in the input queue are cleared.
320 If it contains the
321 .Dv FWRITE
322 bit, then all characters in the output queue are cleared.
323 If the value of the integer is zero, then it behaves as if both the
324 .Dv FREAD
325 and
326 .Dv FWRITE
327 bits were set (i.e., clears both queues).
328 .It Dv TIOCGWINSZ Fa struct winsize *ws
329 Put the window size information associated with the terminal in the
330 .Va winsize
331 structure pointed to by
332 .Fa ws .
333 The window size structure contains the number of rows and columns (and pixels
334 if appropriate) of the devices attached to the terminal.
335 It is set by user software
336 and is the means by which most full\&-screen oriented programs determine the
337 screen size.
338 The
339 .Va winsize
340 structure is defined in
341 .In sys/ioctl.h .
342 .It Dv TIOCSWINSZ Fa struct winsize *ws
343 Set the window size associated with the terminal to be the value in
344 the
345 .Va winsize
346 structure pointed to by
347 .Fa ws
348 (see above).
349 .It Dv TIOCCONS Fa int *on
350 If
351 .Fa on
352 points to a non-zero integer, redirect kernel console output (kernel printf's)
353 to this terminal.
354 If
355 .Fa on
356 points to a zero integer, redirect kernel console output back to the normal
357 console.
358 This is usually used on workstations to redirect kernel messages
359 to a particular window.
360 .It Dv TIOCMSET Fa int *state
361 The integer pointed to by
362 .Fa state
363 contains bits that correspond to modem state.
364 Following is a list of defined variables and the modem state they represent:
365 .Pp
366 .Bl -tag -width TIOCMXCTS -compact
367 .It TIOCM_LE
368 Line Enable.
369 .It TIOCM_DTR
370 Data Terminal Ready.
371 .It TIOCM_RTS
372 Request To Send.
373 .It TIOCM_ST
374 Secondary Transmit.
375 .It TIOCM_SR
376 Secondary Receive.
377 .It TIOCM_CTS
378 Clear To Send.
379 .It TIOCM_CAR
380 Carrier Detect.
381 .It TIOCM_CD
382 Carrier Detect (synonym).
383 .It TIOCM_RNG
384 Ring Indication.
385 .It TIOCM_RI
386 Ring Indication (synonym).
387 .It TIOCM_DSR
388 Data Set Ready.
389 .El
390 .Pp
391 This call sets the terminal modem state to that represented by
392 .Fa state .
393 Not all terminals may support this.
394 .It Dv TIOCMGET Fa int *state
395 Return the current state of the terminal modem lines as represented
396 above in the integer pointed to by
397 .Fa state .
398 .It Dv TIOCMBIS Fa int *state
399 The bits in the integer pointed to by
400 .Fa state
401 represent modem state as described above, however the state is OR-ed
402 in with the current state.
403 .It Dv TIOCMBIC Fa int *state
404 The bits in the integer pointed to by
405 .Fa state
406 represent modem state as described above, however each bit which is on
407 in
408 .Fa state
409 is cleared in the terminal.
410 .El
411 .Sh IMPLEMENTATION NOTES
412 The total number of input and output bytes
413 through all terminal devices
414 are available via the
415 .Va kern.tk_nin
416 and
417 .Va kern.tk_nout
418 read-only
419 .Xr sysctl 8
420 variables.
421 .Sh SEE ALSO
422 .Xr stty 1 ,
423 .Xr ioctl 2 ,
424 .Xr ng_tty 4 ,
425 .Xr pty 4 ,
426 .Xr termios 4 ,
427 .Xr getty 8