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30 .\" @(#)tty.4 8.3 (Berkeley) 4/19/94
31 .\"
32 .Dd October 7, 2006
33 .Dt TTY 4
34 .Os
35 .Sh NAME
36 .Nm tty
37 .Nd general terminal interface
38 .Sh SYNOPSIS
39 .In sys/ioctl.h
40 .Sh DESCRIPTION
41 This section describes the interface to the terminal drivers
42 in the system.
43 .Ss Terminal Special Files
44 Each hardware terminal port on the system usually has two terminal special
45 device files associated with it in the directory
46 .Pa /dev/
47 (for example,
48 .Pa /dev/tty03
49 and
50 .Pa /dev/dty03 ) .
51 .Pp
52 The
53 .Pa /dev/ttyXX
54 special file is used for dial-in modems and terminals.
55 When a user logs into
56 the system on one of these hardware terminal ports, the system has already
57 opened the associated device and prepared the line for normal interactive
58 use (see
59 .Xr getty 8 ) .
60 .Pp
61 The
62 .Pa /dev/dtyXX
63 special file is a SunOS-compatible dial-out device. Unlike
64 the dial-in device, opening the dial-out device never blocks. If the
65 corresponding dial-in device is already opened (not blocked in the open waiting
66 for carrier), then the dial-out open will fail immediately; otherwise it will
67 succeed immediately. While the dial-out device is open, the dial-in device may
68 not be opened. If the dial-in open is blocking, it will wait until the dial-out
69 device is closed (and carrier is detected); otherwise it will fail immediately.
70 .Pp
71 There is also a special case of a terminal file that connects not to
72 a hardware terminal port, but to another program on the other side.
73 These special terminal devices are called
74 .Em ptys
75 (pseudo terminals)
76 and provide the mechanism necessary to give users the same interface to the
77 system when logging in over a network (using
78 .Xr rlogin 1 ,
79 or
80 .Xr telnet 1
81 for example.) Even in these cases the details of how the terminal
82 file was opened and set up is already handled by special software
83 in the system.
84 Thus, users do not normally need to worry about the details of
85 how these lines are opened or used. Also, these lines are often used
86 for dialing out of a system (through an out-calling modem), but again
87 the system provides programs that hide the details of accessing
88 these terminal special files (see
89 .Xr tip 1 ) .
90 .Pp
91 When an interactive user logs in, the system prepares the line to
92 behave in a certain way (called a
93 .Em line discipline ) ,
94 the particular details of which is described in
95 .Xr stty 1
96 at the command level, and in
97 .Xr termios 4
98 at the programming level. A user may be concerned with changing
99 settings associated with his particular login terminal and should refer
100 to the preceding man pages for the common cases. The remainder of
101 this man page is concerned
102 with describing details of using and controlling terminal devices
103 at a low level, such as that possibly required by a program wishing
104 to provide features similar to those provided by the system.
105 .Ss Line disciplines
106 A terminal file is used like any other file in the system in that
107 it can be opened, read, and written to using standard system
108 calls. For each existing terminal file, there is a software processing module
109 called a
110 .Em line discipline
111 associated with it. The
112 .Em line discipline
113 essentially glues the low level device driver code with the high
114 level generic interface routines (such as
115 .Xr read 2
116 and
117 .Xr write 2 ) ,
118 and is responsible for implementing the semantics associated
119 with the device. When a terminal file is first opened by a program,
120 the default
121 .Em line discipline
122 called the
123 .Dv termios
124 line discipline is associated with the file. This is the primary
125 line discipline that is used in most cases and provides the semantics
126 that users normally associate with a terminal. When the
127 .Dv termios
128 line discipline is in effect, the terminal file behaves and is
129 operated according to the rules described in
130 .Xr termios 4 .
131 Please refer to that man page for a full description of the terminal
132 semantics.
133 The operations described here
134 generally represent features common
135 across all
136 .Em line disciplines ,
137 however some of these calls may not
138 make sense in conjunction with a line discipline other than
139 .Dv termios ,
140 and some may not be supported by the underlying
141 hardware (or lack thereof, as in the case of ptys).
142 .Ss Terminal File Operations
143 All of the following operations are invoked using the
144 .Xr ioctl 2
145 system call. Refer to that man page for a description of
146 the
147 .Em request
148 and
149 .Em argp
150 parameters.
151 In addition to the ioctl
152 .Em requests
153 defined here, the specific line discipline
154 in effect will define other
155 .Em requests
156 specific to it (actually
157 .Xr termios 4
158 defines them as function calls, not ioctl
159 .Em requests . )
160 The following section lists the available ioctl requests. The
161 name of the request, a description of its purpose, and the typed
162 .Em argp
163 parameter (if any)
164 are listed. For example, the first entry says
165 .Pp
166 .D1 Em TIOCSLINED char name[32]
167 .Pp
168 and would be called on the terminal associated with
169 file descriptor zero by the following code fragment:
170 .Bd -literal
171 ioctl(0, TIOCSLINED, "termios");
172 .Ed
173 .Ss Terminal File Request Descriptions
174 .Bl -tag -width TIOCGWINSZ
175 .It Dv TIOCSLINED Fa char name[32]
176 Change to the new line discipline called
177 .Fa name .
178 .Pp
179 .It Dv TIOCGLINED Fa char name[32]
180 Return the current line discipline in the string pointed to by
181 .Fa name .
182 .It Dv TIOCSBRK Fa void
183 Set the terminal hardware into BREAK condition.
184 .It Dv TIOCCBRK Fa void
185 Clear the terminal hardware BREAK condition.
186 .It Dv TIOCSDTR Fa void
187 Assert data terminal ready (DTR).
188 .It Dv TIOCCDTR Fa void
189 Clear data terminal ready (DTR).
190 .It Dv TIOCGPGRP Fa int *tpgrp
191 Return the current process group the terminal is associated
192 with in the integer pointed to by
193 .Fa tpgrp .
194 This is the underlying call that implements the
195 .Xr tcgetpgrp 3
196 call.
197 .It Dv TIOCSPGRP Fa int *tpgrp
198 Associate the terminal with the process group (as an integer) pointed to by
199 .Fa tpgrp .
200 This is the underlying call that implements the
201 .Xr tcsetpgrp 3
202 call.
203 .It Dv TIOCGETA Fa struct termios *term
204 Place the current value of the termios state associated with the
205 device in the termios structure pointed to by
206 .Fa term .
207 This is the underlying call that implements the
208 .Xr tcgetattr 3
209 call.
210 .It Dv TIOCSETA Fa struct termios *term
211 Set the termios state associated with the device immediately.
212 This is the underlying call that implements the
213 .Xr tcsetattr 3
214 call with the
215 .Dv TCSANOW
216 option.
217 .It Dv TIOCSETAW Fa struct termios *term
218 First wait for any output to complete, then set the termios state
219 associated with the device.
220 This is the underlying call that implements the
221 .Xr tcsetattr 3
222 call with the
223 .Dv TCSADRAIN
224 option.
225 .It Dv TIOCSETAF Fa struct termios *term
226 First wait for any output to complete, clear any pending input,
227 then set the termios state associated with the device.
228 This is the underlying call that implements the
229 .Xr tcsetattr 3
230 call with the
231 .Dv TCSAFLUSH
232 option.
233 .It Dv TIOCOUTQ Fa int *num
234 Place the current number of characters in the output queue in the
235 integer pointed to by
236 .Fa num .
237 .It Dv TIOCSTI Fa char *cp
238 Simulate typed input. Pretend as if the terminal received the
239 character pointed to by
240 .Fa cp .
241 .It Dv TIOCNOTTY Fa void
242 This call is obsolete but left for compatibility. In the past, when
243 a process that didn't have a controlling terminal (see
244 .Em The Controlling Terminal
245 in
246 .Xr termios 4 )
247 first opened a terminal device, it acquired that terminal as its
248 controlling terminal. For some programs this was a hazard as they
249 didn't want a controlling terminal in the first place, and this
250 provided a mechanism to disassociate the controlling terminal from
251 the calling process. It
252 .Em must
253 be called by opening the file
254 .Pa /dev/tty
255 and calling
256 .Dv TIOCNOTTY
257 on that file descriptor.
258 .Pp
259 The current system does not allocate a controlling terminal to
260 a process on an
261 .Fn open
262 call: there is a specific ioctl called
263 .Dv TIOCSCTTY
264 to make a terminal the controlling
265 terminal.
266 In addition, a program can
267 .Fn fork
268 and call the
269 .Fn setsid
270 system call which will place the process into its own session - which
271 has the effect of disassociating it from the controlling terminal. This
272 is the new and preferred method for programs to lose their controlling
273 terminal.
274 .It Dv TIOCSTOP Fa void
275 Stop output on the terminal (like typing ^S at the keyboard).
276 .It Dv TIOCSTART Fa void
277 Start output on the terminal (like typing ^Q at the keyboard).
278 .It Dv TIOCSCTTY Fa void
279 Make the terminal the controlling terminal for the process (the process
280 must not currently have a controlling terminal).
281 .It Dv TIOCDRAIN Fa void
282 Wait until all output is drained.
283 .It Dv TIOCEXCL Fa void
284 Set exclusive use on the terminal. No further opens are permitted
285 except by root. Of course, this means that programs that are run by
286 root (or setuid) will not obey the exclusive setting - which limits
287 the usefulness of this feature.
288 .It Dv TIOCNXCL Fa void
289 Clear exclusive use of the terminal. Further opens are permitted.
290 .It Dv TIOCFLUSH Fa int *what
291 If the value of the int pointed to by
292 .Fa what
293 contains the
294 .Dv FREAD
295 bit as defined in
296 .Aq Pa sys/fcntl.h ,
297 then all characters in the input queue are cleared. If it contains
298 the
299 .Dv FWRITE
300 bit, then all characters in the output queue are cleared. If the
301 value of the integer is zero, then it behaves as if both the
302 .Dv FREAD
303 and
304 .Dv FWRITE
305 bits were set (i.e. clears both queues).
306 .It Dv TIOCGWINSZ Fa struct winsize *ws
307 Put the window size information associated with the terminal in the
308 .Va winsize
309 structure pointed to by
310 .Fa ws .
311 The window size structure contains the number of rows and columns (and pixels
312 if appropriate) of the devices attached to the terminal. It is set by user software
313 and is the means by which most full\&-screen oriented programs determine the
314 screen size. The
315 .Va winsize
316 structure is defined in
317 .Aq Pa sys/ioctl.h .
318 .It Dv TIOCSWINSZ Fa struct winsize *ws
319 Set the window size associated with the terminal to be the value in
320 the
321 .Va winsize
322 structure pointed to by
323 .Fa ws
324 (see above).
325 .It Dv TIOCCONS Fa int *on
326 If
327 .Fa on
328 points to a non-zero integer, redirect kernel console output (kernel printf's)
329 to this terminal.
330 If
331 .Fa on
332 points to a zero integer, redirect kernel console output back to the normal
333 console. This is usually used on workstations to redirect kernel messages
334 to a particular window.
335 .It Dv TIOCMSET Fa int *state
336 The integer pointed to by
337 .Fa state
338 contains bits that correspond to modem state.
339 Following is a list of defined variables and the modem state they represent:
340 .Pp
341 .Bl -tag -width TIOCMXCTS -compact
342 .It TIOCM_LE
343 Line Enable.
344 .It TIOCM_DTR
345 Data Terminal Ready.
346 .It TIOCM_RTS
347 Request To Send.
348 .It TIOCM_ST
349 Secondary Transmit.
350 .It TIOCM_SR
351 Secondary Receive.
352 .It TIOCM_CTS
353 Clear To Send.
354 .It TIOCM_CAR
355 Carrier Detect.
356 .It TIOCM_CD
357 Carrier Detect (synonym).
358 .It TIOCM_RNG
359 Ring Indication.
360 .It TIOCM_RI
361 Ring Indication (synonym).
362 .It TIOCM_DSR
363 Data Set Ready.
364 .El
365 .Pp
366 This call sets the terminal modem state to that represented by
367 .Fa state .
368 Not all terminals may support this.
369 .It Dv TIOCMGET Fa int *state
370 Return the current state of the terminal modem lines as represented
371 above in the integer pointed to by
372 .Fa state .
373 .It Dv TIOCMBIS Fa int *state
374 The bits in the integer pointed to by
375 .Fa state
376 represent modem state as described above, however the state is OR-ed
377 in with the current state.
378 .It Dv TIOCMBIC Fa int *state
379 The bits in the integer pointed to by
380 .Fa state
381 represent modem state as described above, however each bit which is on
382 in
383 .Fa state
384 is cleared in the terminal.
385 .It Dv TIOCSFLAGS Fa int *state
386 The bits in the integer pointed to by
387 .Fa state
388 contain bits that correspond to serial port state.
389 Following is a list of defined flag values and the serial port state they
390 represent:
391 .Pp
392 .Bl -tag -width TIOCFLAG_SOFTCAR -compact
393 .It TIOCFLAG_SOFTCAR
394 Ignore hardware carrier.
395 .It TIOCFLAG_CLOCAL
396 Set the
397 .Xr termios 4
398 .Dv CLOCAL
399 flag on open.
400 .It TIOCFLAG_CRTSCTS
401 Set the
402 .Xr termios 4
403 .Dv CRTSCTS
404 flag on open.
405 .It TIOCFLAG_MDMBUF
406 Set the
407 .Xr termios 4
408 .Dv MDMBUF
409 flag on open.
410 .El
411 .Pp
412 This call sets the serial port state to that represented by
413 .Fa state .
414 Not all serial ports may support this.
415 .It Dv TIOCGFLAGS Fa int *state
416 Return the current state of the serial port as represented
417 above in the integer pointed to by
418 .Fa state .
419 .El
420 .Sh COMPATIBILITY
421 Two ioctls are maintained for backwards compatibility. They provide
422 methods to get and set the current line discipline, but are not
423 extensible.
424 .Bl -tag -width TIOCGWINSZ
425 .It Dv TIOCSETD Fa int *ldisc
426 Change to the new line discipline pointed to by
427 .Fa ldisc .
428 The old list of available line disciplines are listed in
429 .Aq Pa sys/ttycom.h
430 and are:
431 .Pp
432 .Bl -tag -width TIOCGWINSZ -compact
433 .It TTYDISC
434 Termios interactive line discipline.
435 .It TABLDISC
436 Tablet line discipline.
437 .It SLIPDISC
438 Serial IP line discipline.
439 .It PPPDISC
440 Point to Point Protocol line discipline.
441 .It STRIPDISC
442 Starmode Radio IP line discipline.
443 .El
444 .Pp
445 .It Dv TIOCGETD Fa int *ldisc
446 Return the current line discipline in the integer pointed to by
447 .Fa ldisc .
448 .El
449 .Sh SEE ALSO
450 .Xr stty 1 ,
451 .Xr ioctl 2 ,
452 .Xr tcgetattr 3 ,
453 .Xr tcsetattr 3 ,
454 .Xr ttyaction 3 ,
455 .Xr pty 4 ,
456 .Xr termios 4 ,
457 .Xr ttys 5 ,
458 .Xr getty 8 ,
459 .Xr linedisc 9
460 .Sh HISTORY
461 Separate dial-out device files were implemented in SunOS 4. They were cloned
462 by Charles M. Hannum for
463 .Nx 1.4 .