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28 .\" @(#)tty.4 8.3 (Berkeley) 4/19/94
29 .\" $FreeBSD: src/share/man/man4/tty.4,v 1.9.2.6 2001/12/17 11:30:12 ru Exp $
36 .Nd general terminal interface
40 This section describes the interface to the terminal drivers
42 .Ss Terminal Special Files
43 Each hardware terminal port on the system usually has a terminal special device
44 file associated with it in the directory ``/dev/'' (for
45 example, ``/dev/tty03'').
47 the system on one of these hardware terminal ports, the system has already
48 opened the associated device and prepared the line for normal interactive
51 There is also a special case of a terminal file that connects not to
52 a hardware terminal port, but to another program on the other side.
53 These special terminal devices are called
55 and provide the mechanism necessary to give users the same interface to the
56 system when logging in over a network (using
60 for example). Even in these cases the details of how the terminal
61 file was opened and set up is already handled by special software
63 Thus, users do not normally need to worry about the details of
64 how these lines are opened or used. Also, these lines are often used
65 for dialing out of a system (through an out-calling modem), but again
66 the system provides programs that hide the details of accessing
67 these terminal special files (see
70 When an interactive user logs in, the system prepares the line to
71 behave in a certain way (called a
72 .Em "line discipline" ) ,
73 the particular details of which is described in
75 at the command level, and in
77 at the programming level. A user may be concerned with changing
78 settings associated with his particular login terminal and should refer
79 to the preceding man pages for the common cases. The remainder of
80 this man page is concerned
81 with describing details of using and controlling terminal devices
82 at a low level, such as that possibly required by a program wishing
83 to provide features similar to those provided by the system.
85 A terminal file is used like any other file in the system in that
86 it can be opened, read, and written to using standard system
87 calls. For each existing terminal file, there is a software processing module
90 is associated with it. The
92 essentially glues the low level device driver code with the high
93 level generic interface routines (such as
97 and is responsible for implementing the semantics associated
98 with the device. When a terminal file is first opened by a program,
100 .Em "line discipline"
103 line discipline is associated with the file. This is the primary
104 line discipline that is used in most cases and provides the semantics
105 that users normally associate with a terminal. When the
107 line discipline is in effect, the terminal file behaves and is
108 operated according to the rules described in
110 Please refer to that man page for a full description of the terminal
112 The operations described here
113 generally represent features common
115 .Em "line disciplines" ,
116 however some of these calls may not
117 make sense in conjunction with a line discipline other than
119 and some may not be supported by the underlying
120 hardware (or lack thereof, as in the case of ptys).
121 .Ss Terminal File Operations
122 All of the following operations are invoked using the
124 system call. Refer to that man page for a description of
130 In addition to the ioctl
132 defined here, the specific line discipline
133 in effect will define other
135 specific to it (actually
137 defines them as function calls, not ioctl
139 The following section lists the available ioctl requests. The
140 name of the request, a description of its purpose, and the typed
143 are listed. For example, the first entry says
145 .D1 Em "TIOCSETD int *ldisc"
147 and would be called on the terminal associated with
148 file descriptor zero by the following code fragment:
153 ioctl(0, TIOCSETD, &ldisc);
155 .Ss Terminal File Request Descriptions
156 .Bl -tag -width ".Dv TIOCGWINSZ"
157 .It Dv TIOCSETD Fa int *ldisc
158 Change to the new line discipline pointed to by
160 The available line disciplines are listed in
164 .Bl -tag -width NETGRAPHDISC -compact
166 Termios interactive line discipline.
168 Tablet line discipline.
170 Serial IP line discipline.
178 .It Dv TIOCGETD Fa int *ldisc
179 Return the current line discipline in the integer pointed to by
181 .It Dv TIOCSBRK Fa void
182 Set the terminal hardware into BREAK condition.
183 .It Dv TIOCCBRK Fa void
184 Clear the terminal hardware BREAK condition.
185 .It Dv TIOCSDTR Fa void
186 Assert data terminal ready (DTR).
187 .It Dv TIOCCDTR Fa void
188 Clear data terminal ready (DTR).
189 .It Dv TIOCGPGRP Fa int *tpgrp
190 Return the current process group with which the terminal is associated
191 in the integer pointed to by
193 This is the underlying call that implements the
197 .It Dv TIOCSPGRP Fa int *tpgrp
198 Associate the terminal with the process group (as an integer) pointed to by
200 This is the underlying call that implements the
204 .It Dv TIOCGETA Fa struct termios *term
205 Place the current value of the termios state associated with the
206 device in the termios structure pointed to by
208 This is the underlying call that implements the
212 .It Dv TIOCSETA Fa struct termios *term
213 Set the termios state associated with the device immediately.
214 This is the underlying call that implements the
220 .It Dv TIOCSETAW Fa struct termios *term
221 First wait for any output to complete, then set the termios state
222 associated with the device.
223 This is the underlying call that implements the
229 .It Dv TIOCSETAF Fa struct termios *term
230 First wait for any output to complete, clear any pending input,
231 then set the termios state associated with the device.
232 This is the underlying call that implements the
238 .It Dv TIOCOUTQ Fa int *num
239 Place the current number of characters in the output queue in the
240 integer pointed to by
242 .It Dv TIOCSTI Fa char *cp
243 Simulate typed input. Pretend as if the terminal received the
244 character pointed to by
246 .It Dv TIOCNOTTY Fa void
247 This call is obsolete but left for compatibility. In the past, when
248 a process that didn't have a controlling terminal (see
249 .Em The Controlling Terminal
252 first opened a terminal device, it acquired that terminal as its
253 controlling terminal. For some programs this was a hazard as they
254 didn't want a controlling terminal in the first place, and this
255 provided a mechanism to disassociate the controlling terminal from
256 the calling process. It
258 be called by opening the file
262 on that file descriptor.
264 The current system does not allocate a controlling terminal to
267 call: there is a specific ioctl called
269 to make a terminal the controlling
271 In addition, a program can
275 system call which will place the process into its own session - which
276 has the effect of disassociating it from the controlling terminal. This
277 is the new and preferred method for programs to lose their controlling
279 .It Dv TIOCSTOP Fa void
280 Stop output on the terminal (like typing ^S at the keyboard).
281 .It Dv TIOCSTART Fa void
282 Start output on the terminal (like typing ^Q at the keyboard).
283 .It Dv TIOCSCTTY Fa void
284 Make the terminal the controlling terminal for the process (the process
285 must not currently have a controlling terminal).
286 .It Dv TIOCDRAIN Fa void
287 Wait until all output is drained.
288 .It Dv TIOCEXCL Fa void
289 Set exclusive use on the terminal. No further opens are permitted
290 except by root. Of course, this means that programs that are run by
291 root (or setuid) will not obey the exclusive setting - which limits
292 the usefulness of this feature.
293 .It Dv TIOCNXCL Fa void
294 Clear exclusive use of the terminal. Further opens are permitted.
295 .It Dv TIOCFLUSH Fa int *what
296 If the value of the int pointed to by
302 then all characters in the input queue are cleared. If it contains
305 bit, then all characters in the output queue are cleared. If the
306 value of the integer is zero, then it behaves as if both the
310 bits were set (i.e. clears both queues).
311 .It Dv TIOCGWINSZ Fa struct winsize *ws
312 Put the window size information associated with the terminal in the
314 structure pointed to by
316 The window size structure contains the number of rows and columns (and pixels
317 if appropriate) of the devices attached to the terminal. It is set by user software
318 and is the means by which most full\&-screen oriented programs determine the
321 structure is defined in
323 .It Dv TIOCSWINSZ Fa struct winsize *ws
324 Set the window size associated with the terminal to be the value in
327 structure pointed to by
330 .It Dv TIOCCONS Fa int *on
333 points to a non-zero integer, redirect kernel console output (kernel printf's)
337 points to a zero integer, redirect kernel console output back to the normal
338 console. This is usually used on workstations to redirect kernel messages
339 to a particular window.
340 .It Dv TIOCMSET Fa int *state
341 The integer pointed to by
343 contains bits that correspond to modem state. Following is a list
344 of defined variables and the modem state they represent:
346 .Bl -tag -width TIOCMXCTS -compact
362 Carrier Detect (synonym).
366 Ring Indication (synonym).
371 This call sets the terminal modem state to that represented by
373 Not all terminals may support this.
374 .It Dv TIOCMGET Fa int *state
375 Return the current state of the terminal modem lines as represented
376 above in the integer pointed to by
378 .It Dv TIOCMBIS Fa int *state
379 The bits in the integer pointed to by
381 represent modem state as described above, however the state is OR-ed
382 in with the current state.
383 .It Dv TIOCMBIC Fa int *state
384 The bits in the integer pointed to by
386 represent modem state as described above, however each bit which is on
389 is cleared in the terminal.
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