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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 $
30 .\" $DragonFly: src/share/man/man4/tty.4,v 1.5 2007/11/20 11:32:28 hasso Exp $
37 .Nd general terminal interface
41 This section describes the interface to the terminal drivers
43 .Ss Terminal Special Files
44 Each hardware terminal port on the system usually has a terminal special device
45 file associated with it in the directory ``/dev/'' (for
46 example, ``/dev/tty03'').
48 the system on one of these hardware terminal ports, the system has already
49 opened the associated device and prepared the line for normal interactive
52 There is also a special case of a terminal file that connects not to
53 a hardware terminal port, but to another program on the other side.
54 These special terminal devices are called
56 and provide the mechanism necessary to give users the same interface to the
57 system when logging in over a network (using
61 for example). Even in these cases the details of how the terminal
62 file was opened and set up is already handled by special software
64 Thus, users do not normally need to worry about the details of
65 how these lines are opened or used. Also, these lines are often used
66 for dialing out of a system (through an out-calling modem), but again
67 the system provides programs that hide the details of accessing
68 these terminal special files (see
71 When an interactive user logs in, the system prepares the line to
72 behave in a certain way (called a
73 .Em "line discipline" ) ,
74 the particular details of which is described in
76 at the command level, and in
78 at the programming level. A user may be concerned with changing
79 settings associated with his particular login terminal and should refer
80 to the preceding man pages for the common cases. The remainder of
81 this man page is concerned
82 with describing details of using and controlling terminal devices
83 at a low level, such as that possibly required by a program wishing
84 to provide features similar to those provided by the system.
86 A terminal file is used like any other file in the system in that
87 it can be opened, read, and written to using standard system
88 calls. For each existing terminal file, there is a software processing module
91 is associated with it. The
93 essentially glues the low level device driver code with the high
94 level generic interface routines (such as
98 and is responsible for implementing the semantics associated
99 with the device. When a terminal file is first opened by a program,
101 .Em "line discipline"
104 line discipline is associated with the file. This is the primary
105 line discipline that is used in most cases and provides the semantics
106 that users normally associate with a terminal. When the
108 line discipline is in effect, the terminal file behaves and is
109 operated according to the rules described in
111 Please refer to that man page for a full description of the terminal
113 The operations described here
114 generally represent features common
116 .Em "line disciplines" ,
117 however some of these calls may not
118 make sense in conjunction with a line discipline other than
120 and some may not be supported by the underlying
121 hardware (or lack thereof, as in the case of ptys).
122 .Ss Terminal File Operations
123 All of the following operations are invoked using the
125 system call. Refer to that man page for a description of
131 In addition to the ioctl
133 defined here, the specific line discipline
134 in effect will define other
136 specific to it (actually
138 defines them as function calls, not ioctl
140 The following section lists the available ioctl requests. The
141 name of the request, a description of its purpose, and the typed
144 are listed. For example, the first entry says
146 .D1 Em "TIOCSETD int *ldisc"
148 and would be called on the terminal associated with
149 file descriptor zero by the following code fragment:
154 ioctl(0, TIOCSETD, &ldisc);
156 .Ss Terminal File Request Descriptions
157 .Bl -tag -width ".Dv TIOCGWINSZ"
158 .It Dv TIOCSETD Fa int *ldisc
159 Change to the new line discipline pointed to by
161 The available line disciplines are listed in
165 .Bl -tag -width NETGRAPHDISC -compact
167 Termios interactive line discipline.
169 Tablet line discipline.
171 Serial IP line discipline.
180 .It Dv TIOCGETD Fa int *ldisc
181 Return the current line discipline in the integer pointed to by
183 .It Dv TIOCSBRK Fa void
184 Set the terminal hardware into BREAK condition.
185 .It Dv TIOCCBRK Fa void
186 Clear the terminal hardware BREAK condition.
187 .It Dv TIOCSDTR Fa void
188 Assert data terminal ready (DTR).
189 .It Dv TIOCCDTR Fa void
190 Clear data terminal ready (DTR).
191 .It Dv TIOCGPGRP Fa int *tpgrp
192 Return the current process group with which the terminal is associated
193 in the integer pointed to by
195 This is the underlying call that implements the
199 .It Dv TIOCSPGRP Fa int *tpgrp
200 Associate the terminal with the process group (as an integer) pointed to by
202 This is the underlying call that implements the
206 .It Dv TIOCGETA Fa struct termios *term
207 Place the current value of the termios state associated with the
208 device in the termios structure pointed to by
210 This is the underlying call that implements the
214 .It Dv TIOCSETA Fa struct termios *term
215 Set the termios state associated with the device immediately.
216 This is the underlying call that implements the
222 .It Dv TIOCSETAW Fa struct termios *term
223 First wait for any output to complete, then set the termios state
224 associated with the device.
225 This is the underlying call that implements the
231 .It Dv TIOCSETAF Fa struct termios *term
232 First wait for any output to complete, clear any pending input,
233 then set the termios state associated with the device.
234 This is the underlying call that implements the
240 .It Dv TIOCOUTQ Fa int *num
241 Place the current number of characters in the output queue in the
242 integer pointed to by
244 .It Dv TIOCSTI Fa char *cp
245 Simulate typed input. Pretend as if the terminal received the
246 character pointed to by
248 .It Dv TIOCNOTTY Fa void
249 This call is obsolete but left for compatibility. In the past, when
250 a process that didn't have a controlling terminal (see
251 .Em The Controlling Terminal
254 first opened a terminal device, it acquired that terminal as its
255 controlling terminal. For some programs this was a hazard as they
256 didn't want a controlling terminal in the first place, and this
257 provided a mechanism to disassociate the controlling terminal from
258 the calling process. It
260 be called by opening the file
264 on that file descriptor.
266 The current system does not allocate a controlling terminal to
269 call: there is a specific ioctl called
271 to make a terminal the controlling
273 In addition, a program can
277 system call which will place the process into its own session - which
278 has the effect of disassociating it from the controlling terminal. This
279 is the new and preferred method for programs to lose their controlling
281 .It Dv TIOCSTOP Fa void
282 Stop output on the terminal (like typing ^S at the keyboard).
283 .It Dv TIOCSTART Fa void
284 Start output on the terminal (like typing ^Q at the keyboard).
285 .It Dv TIOCSCTTY Fa void
286 Make the terminal the controlling terminal for the process (the process
287 must not currently have a controlling terminal).
288 .It Dv TIOCDRAIN Fa void
289 Wait until all output is drained.
290 .It Dv TIOCEXCL Fa void
291 Set exclusive use on the terminal. No further opens are permitted
292 except by root. Of course, this means that programs that are run by
293 root (or setuid) will not obey the exclusive setting - which limits
294 the usefulness of this feature.
295 .It Dv TIOCNXCL Fa void
296 Clear exclusive use of the terminal. Further opens are permitted.
297 .It Dv TIOCFLUSH Fa int *what
298 If the value of the int pointed to by
304 then all characters in the input queue are cleared. If it contains
307 bit, then all characters in the output queue are cleared. If the
308 value of the integer is zero, then it behaves as if both the
312 bits were set (i.e. clears both queues).
313 .It Dv TIOCGWINSZ Fa struct winsize *ws
314 Put the window size information associated with the terminal in the
316 structure pointed to by
318 The window size structure contains the number of rows and columns (and pixels
319 if appropriate) of the devices attached to the terminal. It is set by user software
320 and is the means by which most full\&-screen oriented programs determine the
323 structure is defined in
325 .It Dv TIOCSWINSZ Fa struct winsize *ws
326 Set the window size associated with the terminal to be the value in
329 structure pointed to by
332 .It Dv TIOCCONS Fa int *on
335 points to a non-zero integer, redirect kernel console output (kernel printf's)
339 points to a zero integer, redirect kernel console output back to the normal
340 console. This is usually used on workstations to redirect kernel messages
341 to a particular window.
342 .It Dv TIOCMSET Fa int *state
343 The integer pointed to by
345 contains bits that correspond to modem state. Following is a list
346 of defined variables and the modem state they represent:
348 .Bl -tag -width TIOCMXCTS -compact
364 Carrier Detect (synonym).
368 Ring Indication (synonym).
373 This call sets the terminal modem state to that represented by
375 Not all terminals may support this.
376 .It Dv TIOCMGET Fa int *state
377 Return the current state of the terminal modem lines as represented
378 above in the integer pointed to by
380 .It Dv TIOCMBIS Fa int *state
381 The bits in the integer pointed to by
383 represent modem state as described above, however the state is OR-ed
384 in with the current state.
385 .It Dv TIOCMBIC Fa int *state
386 The bits in the integer pointed to by
388 represent modem state as described above, however each bit which is on
391 is cleared in the terminal.