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32 .\" @(#)tty.4 8.3 (Berkeley) 4/19/94
40 .Nd general terminal interface
42 .Fd #include <sys/ioctl.h>
44 This section describes the interface to the terminal drivers
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'').
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
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
59 and provide the mechanism necessary to give users the same interface to the
60 system when logging in over a network (using
64 for example). Even in these cases the details of how the terminal
65 file was opened and set up is already handled by special software
67 Thus, users do not normally need to worry about the details of
68 how these lines are opened or used. Also, these lines are often used
69 for dialing out of a system (through an out-calling modem), but again
70 the system provides programs that hide the details of accessing
71 these terminal special files (see
74 When an interactive user logs in, the system prepares the line to
75 behave in a certain way (called a
76 .Em "line discipline" ) ,
77 the particular details of which is described in
79 at the command level, and in
81 at the programming level. A user may be concerned with changing
82 settings associated with his particular login terminal and should refer
83 to the preceding man pages for the common cases. The remainder of
84 this man page is concerned
85 with describing details of using and controlling terminal devices
86 at a low level, such as that possibly required by a program wishing
87 to provide features similar to those provided by the system.
89 A terminal file is used like any other file in the system in that
90 it can be opened, read, and written to using standard system
91 calls. For each existing terminal file, there is a software processing module
94 is associated with it. The
96 essentially glues the low level device driver code with the high
97 level generic interface routines (such as
101 and is responsible for implementing the semantics associated
102 with the device. When a terminal file is first opened by a program,
104 .Em "line discipline"
107 line discipline is associated with the file. This is the primary
108 line discipline that is used in most cases and provides the semantics
109 that users normally associate with a terminal. When the
111 line discipline is in effect, the terminal file behaves and is
112 operated according to the rules described in
114 Please refer to that man page for a full description of the terminal
116 The operations described here
117 generally represent features common
119 .Em "line disciplines" ,
120 however some of these calls may not
121 make sense in conjunction with a line discipline other than
123 and some may not be supported by the underlying
124 hardware (or lack thereof, as in the case of ptys).
125 .Ss Terminal File Operations
126 All of the following operations are invoked using the
128 system call. Refer to that man page for a description of
134 In addition to the ioctl
136 defined here, the specific line discipline
137 in effect will define other
139 specific to it (actually
141 defines them as function calls, not ioctl
143 The following section lists the available ioctl requests. The
144 name of the request, a description of its purpose, and the typed
147 are listed. For example, the first entry says
149 .D1 Em "TIOCSETD int *ldisc"
151 and would be called on the terminal associated with
152 file descriptor zero by the following code fragment:
157 ioctl(0, TIOCSETD, &ldisc);
159 .Ss Terminal File Request Descriptions
160 .Bl -tag -width TIOCGWINSZ
161 .It Dv TIOCSETD Fa int *ldisc
162 Change to the new line discipline pointed to by
164 The available line disciplines are listed in
168 .Bl -tag -width TIOCGWINSZ -compact
170 Termios interactive line discipline.
172 Tablet line discipline.
174 Serial IP line discipline.
179 .It Dv TIOCGETD Fa int *ldisc
180 Return the current line discipline in the integer pointed to by
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
194 This is the underlying call that implements the
198 .It Dv TIOCSPGRP Fa int *tpgrp
199 Associate the terminal with the process group (as an integer) pointed to by
201 This is the underlying call that implements the
205 .It Dv TIOCGETA Fa struct termios *term
206 Place the current value of the termios state associated with the
207 device in the termios structure pointed to by
209 This is the underlying call that implements the
213 .It Dv TIOCSETA Fa struct termios *term
214 Set the termios state associated with the device immediately.
215 This is the underlying call that implements the
221 .It Dv TIOCSETAW Fa struct termios *term
222 First wait for any output to complete, then set the termios state
223 associated with the device.
224 This is the underlying call that implements the
230 .It Dv TIOCSETAF Fa struct termios *term
231 First wait for any output to complete, clear any pending input,
232 then set the termios state associated with the device.
233 This is the underlying call that implements the
239 .It Dv TIOCOUTQ Fa int *num
240 Place the current number of characters in the output queue in the
241 integer pointed to by
243 .It Dv TIOCSTI Fa char *cp
244 Simulate typed input. Pretend as if the terminal received the
245 character pointed to by
247 .It Dv TIOCNOTTY Fa void
248 This call is obsolete but left for compatibility. In the past, when
249 a process that didn't have a controlling terminal (see
250 .Em The Controlling Terminal
253 first opened a terminal device, it acquired that terminal as its
254 controlling terminal. For some programs this was a hazard as they
255 didn't want a controlling terminal in the first place, and this
256 provided a mechanism to disassociate the controlling terminal from
257 the calling process. It
259 be called by opening the file
263 on that file descriptor.
265 The current system does not allocate a controlling terminal to
268 call: there is a specific ioctl called
270 to make a terminal the controlling
272 In addition, a program can
276 system call which will place the process into its own session - which
277 has the effect of disassociating it from the controlling terminal. This
278 is the new and preferred method for programs to lose their controlling
280 .It Dv TIOCSTOP Fa void
281 Stop output on the terminal (like typing ^S at the keyboard).
282 .It Dv TIOCSTART Fa void
283 Start output on the terminal (like typing ^Q at the keyboard).
284 .It Dv TIOCSCTTY Fa void
285 Make the terminal the controlling terminal for the process (the process
286 must not currently have a controlling terminal).
287 .It Dv TIOCDRAIN Fa void
288 Wait until all output is drained.
289 .It Dv TIOCEXCL Fa void
290 Set exclusive use on the terminal. No further opens are permitted
291 except by root. Of course, this means that programs that are run by
292 root (or setuid) will not obey the exclusive setting - which limits
293 the usefulness of this feature.
294 .It Dv TIOCNXCL Fa void
295 Clear exclusive use of the terminal. Further opens are permitted.
296 .It Dv TIOCFLUSH Fa int *what
297 If the value of the int pointed to by
303 then all characters in the input queue are cleared. If it contains
306 bit, then all characters in the output queue are cleared. If the
307 value of the integer is zero, then it behaves as if both the
311 bits were set (i.e. clears both queues).
312 .It Dv TIOCGWINSZ Fa struct winsize *ws
313 Put the window size information associated with the terminal in the
315 structure pointed to by
317 The window size structure contains the number of rows and columns (and pixels
318 if appropriate) of the devices attached to the terminal. It is set by user software
319 and is the means by which most full\&-screen oriented programs determine the
322 structure is defined in
324 .It Dv TIOCSWINSZ Fa struct winsize *ws
325 Set the window size associated with the terminal to be the value in
328 structure pointed to by
331 .It Dv TIOCCONS Fa int *on
334 points to a non-zero integer, redirect kernel console output (kernel printf's)
338 points to a zero integer, redirect kernel console output back to the normal
339 console. This is usually used on workstations to redirect kernel messages
340 to a particular window.
341 .It Dv TIOCMSET Fa int *state
342 The integer pointed to by
344 contains bits that correspond to modem state. Following is a list
345 of defined variables and the modem state they represent:
347 .Bl -tag -width TIOCMXCTS -compact
363 Carrier Detect (synonym).
367 Ring Indication (synonym).
372 This call sets the terminal modem state to that represented by
374 Not all terminals may support this.
375 .It Dv TIOCMGET Fa int *state
376 Return the current state of the terminal modem lines as represented
377 above in the integer pointed to by
379 .It Dv TIOCMBIS Fa int *state
380 The bits in the integer pointed to by
382 represent modem state as described above, however the state is OR-ed
383 in with the current state.
384 .It Dv TIOCMBIC Fa int *state
385 The bits in the integer pointed to by
387 represent modem state as described above, however each bit which is on
390 is cleared in the terminal.
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