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28 .\" @(#)tty.4 8.3 (Berkeley) 4/19/94
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
59 Even in these cases the details of how the terminal
60 file was opened and set up is already handled by special software
62 Thus, users do not normally need to worry about the details of
63 how these lines are opened or used.
64 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.
78 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.
81 The remainder of 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.
85 .Ss Terminal File Operations
86 All of the following operations are invoked using the
89 Refer to that man page for a description of the
94 In addition to the ioctl
96 defined here, the specific line discipline
97 in effect will define other
99 specific to it (actually
101 defines them as function calls, not ioctl
103 The following section lists the available ioctl requests.
104 The name of the request, a description of its purpose, and the typed
108 For example, the first entry says
110 .D1 Em "TIOCSPGRP int *tpgrp"
112 and would be called on the terminal associated with
113 file descriptor zero by the following code fragment:
118 ioctl(0, TIOCSPGRP, &pgrp);
120 .Ss Terminal File Request Descriptions
121 .Bl -tag -width TIOCGWINSZ
122 .It Dv TIOCSETD Fa int *ldisc
123 This call is obsolete but left for compatibility.
126 it would change to the new line discipline pointed to by
128 .It Dv TIOCGETD Fa int *ldisc
129 Return the current line discipline in the integer pointed to by
131 .It Dv TIOCSBRK Fa void
132 Set the terminal hardware into BREAK condition.
133 .It Dv TIOCCBRK Fa void
134 Clear the terminal hardware BREAK condition.
135 .It Dv TIOCSDTR Fa void
136 Assert data terminal ready (DTR).
137 .It Dv TIOCCDTR Fa void
138 Clear data terminal ready (DTR).
139 .It Dv TIOCGPGRP Fa int *tpgrp
140 Return the current process group with which the terminal is associated
141 in the integer pointed to by
143 This is the underlying call that implements the
147 .It Dv TIOCSPGRP Fa int *tpgrp
148 Associate the terminal with the process group (as an integer) pointed to by
150 This is the underlying call that implements the
154 .It Dv TIOCGETA Fa struct termios *term
155 Place the current value of the termios state associated with the
156 device in the termios structure pointed to by
158 This is the underlying call that implements the
162 .It Dv TIOCSETA Fa struct termios *term
163 Set the termios state associated with the device immediately.
164 This is the underlying call that implements the
170 .It Dv TIOCSETAW Fa struct termios *term
171 First wait for any output to complete, then set the termios state
172 associated with the device.
173 This is the underlying call that implements the
179 .It Dv TIOCSETAF Fa struct termios *term
180 First wait for any output to complete, clear any pending input,
181 then set the termios state associated with the device.
182 This is the underlying call that implements the
188 .It Dv TIOCOUTQ Fa int *num
189 Place the current number of characters in the output queue in the
190 integer pointed to by
192 .It Dv TIOCSTI Fa char *cp
193 Simulate typed input.
194 Pretend as if the terminal received the character pointed to by
196 .It Dv TIOCNOTTY Fa void
197 In the past, when a process that did not have a controlling terminal (see
198 .Em The Controlling Terminal
201 first opened a terminal device, it acquired that terminal as its
202 controlling terminal.
203 For some programs this was a hazard as they
204 did not want a controlling terminal in the first place, and this
205 provides a mechanism to disassociate the controlling terminal from
209 be called by opening the file
213 on that file descriptor.
215 The current system does not allocate a controlling terminal to
218 call: there is a specific ioctl called
220 to make a terminal the controlling
222 In addition, a program can
226 system call which will place the process into its own session - which
227 has the effect of disassociating it from the controlling terminal.
228 This is the new and preferred method for programs to lose their controlling
231 However, environmental restrictions may prohibit the process from being able to
235 system call to disassociate it from the controlling terminal.
236 In this case, it must use
238 .It Dv TIOCSTOP Fa void
239 Stop output on the terminal (like typing ^S at the keyboard).
240 .It Dv TIOCSTART Fa void
241 Start output on the terminal (like typing ^Q at the keyboard).
242 .It Dv TIOCSCTTY Fa void
243 Make the terminal the controlling terminal for the process (the process
244 must not currently have a controlling terminal).
245 .It Dv TIOCDRAIN Fa void
246 Wait until all output is drained, or until the drain wait timeout expires.
247 .It Dv TIOCGDRAINWAIT Fa int *timeout
248 Return the current drain wait timeout in seconds.
249 .It Dv TIOCSDRAINWAIT Fa int *timeout
250 Set the drain wait timeout in seconds.
251 A value of zero disables timeouts.
252 The default drain wait timeout is controlled by the tunable
255 .Va kern.tty_drainwait .
256 .It Dv TIOCEXCL Fa void
257 Set exclusive use on the terminal.
258 No further opens are permitted except by root.
259 Of course, this means that programs that are run by
260 root (or setuid) will not obey the exclusive setting - which limits
261 the usefulness of this feature.
262 .It Dv TIOCNXCL Fa void
263 Clear exclusive use of the terminal.
264 Further opens are permitted.
265 .It Dv TIOCFLUSH Fa int *what
266 If the value of the int pointed to by
272 then all characters in the input queue are cleared.
275 bit, then all characters in the output queue are cleared.
276 If the value of the integer is zero, then it behaves as if both the
280 bits were set (i.e., clears both queues).
281 .It Dv TIOCGWINSZ Fa struct winsize *ws
282 Put the window size information associated with the terminal in the
284 structure pointed to by
286 The window size structure contains the number of rows and columns (and pixels
287 if appropriate) of the devices attached to the terminal.
288 It is set by user software
289 and is the means by which most full\&-screen oriented programs determine the
293 structure is defined in
295 .It Dv TIOCSWINSZ Fa struct winsize *ws
296 Set the window size associated with the terminal to be the value in
299 structure pointed to by
302 .It Dv TIOCCONS Fa int *on
305 points to a non-zero integer, redirect kernel console output (kernel printf's)
309 points to a zero integer, redirect kernel console output back to the normal
311 This is usually used on workstations to redirect kernel messages
312 to a particular window.
313 .It Dv TIOCMSET Fa int *state
314 The integer pointed to by
316 contains bits that correspond to modem state.
317 Following is a list of defined variables and the modem state they represent:
319 .Bl -tag -width TIOCMXCTS -compact
335 Carrier Detect (synonym).
339 Ring Indication (synonym).
344 This call sets the terminal modem state to that represented by
346 Not all terminals may support this.
347 .It Dv TIOCMGET Fa int *state
348 Return the current state of the terminal modem lines as represented
349 above in the integer pointed to by
351 .It Dv TIOCMBIS Fa int *state
352 The bits in the integer pointed to by
354 represent modem state as described above, however the state is OR-ed
355 in with the current state.
356 .It Dv TIOCMBIC Fa int *state
357 The bits in the integer pointed to by
359 represent modem state as described above, however each bit which is on
362 is cleared in the terminal.
364 .Sh IMPLEMENTATION NOTES
365 The total number of input and output bytes
366 through all terminal devices
367 are available via the