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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
61 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.
66 Also, these lines are often used
67 for dialing out of a system (through an out-calling modem), but again
68 the system provides programs that hide the details of accessing
69 these terminal special files (see
72 When an interactive user logs in, the system prepares the line to
73 behave in a certain way (called a
74 .Em "line discipline" ) ,
75 the particular details of which is described in
77 at the command level, and in
79 at the programming level.
80 A user may be concerned with changing
81 settings associated with his particular login terminal and should refer
82 to the preceding man pages for the common cases.
83 The remainder of this man page is concerned
84 with describing details of using and controlling terminal devices
85 at a low level, such as that possibly required by a program wishing
86 to provide features similar to those provided by the system.
87 .Ss Terminal File Operations
88 All of the following operations are invoked using the
91 Refer to that man page for a description of the
96 In addition to the ioctl
98 defined here, the specific line discipline
99 in effect will define other
101 specific to it (actually
103 defines them as function calls, not ioctl
105 The following section lists the available ioctl requests.
106 The name of the request, a description of its purpose, and the typed
110 For example, the first entry says
112 .D1 Em "TIOCSPGRP int *tpgrp"
114 and would be called on the terminal associated with
115 file descriptor zero by the following code fragment:
120 ioctl(0, TIOCSPGRP, &pgrp);
122 .Ss Terminal File Request Descriptions
123 .Bl -tag -width TIOCGWINSZ
124 .It Dv TIOCSETD Fa int *ldisc
125 This call is obsolete but left for compatibility.
128 it would change to the new line discipline pointed to by
130 .It Dv TIOCGETD Fa int *ldisc
131 Return the current line discipline in the integer pointed to by
133 .It Dv TIOCSBRK Fa void
134 Set the terminal hardware into BREAK condition.
135 .It Dv TIOCCBRK Fa void
136 Clear the terminal hardware BREAK condition.
137 .It Dv TIOCSDTR Fa void
138 Assert data terminal ready (DTR).
139 .It Dv TIOCCDTR Fa void
140 Clear data terminal ready (DTR).
141 .It Dv TIOCGPGRP Fa int *tpgrp
142 Return the current process group with which the terminal is associated
143 in the integer pointed to by
145 This is the underlying call that implements the
149 .It Dv TIOCSPGRP Fa int *tpgrp
150 Associate the terminal with the process group (as an integer) pointed to by
152 This is the underlying call that implements the
156 .It Dv TIOCGETA Fa struct termios *term
157 Place the current value of the termios state associated with the
158 device in the termios structure pointed to by
160 This is the underlying call that implements the
164 .It Dv TIOCSETA Fa struct termios *term
165 Set the termios state associated with the device immediately.
166 This is the underlying call that implements the
172 .It Dv TIOCSETAW Fa struct termios *term
173 First wait for any output to complete, then set the termios state
174 associated with the device.
175 This is the underlying call that implements the
181 .It Dv TIOCSETAF Fa struct termios *term
182 First wait for any output to complete, clear any pending input,
183 then set the termios state associated with the device.
184 This is the underlying call that implements the
190 .It Dv TIOCOUTQ Fa int *num
191 Place the current number of characters in the output queue in the
192 integer pointed to by
194 .It Dv TIOCSTI Fa char *cp
195 Simulate typed input.
196 Pretend as if the terminal received the character pointed to by
198 .It Dv TIOCNOTTY Fa void
199 This call is obsolete but left for compatibility.
200 In the past, when a process that did not have a controlling terminal (see
201 .Em The Controlling Terminal
204 first opened a terminal device, it acquired that terminal as its
205 controlling terminal.
206 For some programs this was a hazard as they
207 did not want a controlling terminal in the first place, and this
208 provided a mechanism to disassociate the controlling terminal from
212 be called by opening the file
216 on that file descriptor.
218 The current system does not allocate a controlling terminal to
221 call: there is a specific ioctl called
223 to make a terminal the controlling
225 In addition, a program can
229 system call which will place the process into its own session - which
230 has the effect of disassociating it from the controlling terminal.
231 This is the new and preferred method for programs to lose their controlling
233 .It Dv TIOCSTOP Fa void
234 Stop output on the terminal (like typing ^S at the keyboard).
235 .It Dv TIOCSTART Fa void
236 Start output on the terminal (like typing ^Q at the keyboard).
237 .It Dv TIOCSCTTY Fa void
238 Make the terminal the controlling terminal for the process (the process
239 must not currently have a controlling terminal).
240 .It Dv TIOCDRAIN Fa void
241 Wait until all output is drained.
242 .It Dv TIOCEXCL Fa void
243 Set exclusive use on the terminal.
244 No further opens are permitted except by root.
245 Of course, this means that programs that are run by
246 root (or setuid) will not obey the exclusive setting - which limits
247 the usefulness of this feature.
248 .It Dv TIOCNXCL Fa void
249 Clear exclusive use of the terminal.
250 Further opens are permitted.
251 .It Dv TIOCFLUSH Fa int *what
252 If the value of the int pointed to by
258 then all characters in the input queue are cleared.
261 bit, then all characters in the output queue are cleared.
262 If the value of the integer is zero, then it behaves as if both the
266 bits were set (i.e., clears both queues).
267 .It Dv TIOCGWINSZ Fa struct winsize *ws
268 Put the window size information associated with the terminal in the
270 structure pointed to by
272 The window size structure contains the number of rows and columns (and pixels
273 if appropriate) of the devices attached to the terminal.
274 It is set by user software
275 and is the means by which most full\&-screen oriented programs determine the
279 structure is defined in
281 .It Dv TIOCSWINSZ Fa struct winsize *ws
282 Set the window size associated with the terminal to be the value in
285 structure pointed to by
288 .It Dv TIOCCONS Fa int *on
291 points to a non-zero integer, redirect kernel console output (kernel printf's)
295 points to a zero integer, redirect kernel console output back to the normal
297 This is usually used on workstations to redirect kernel messages
298 to a particular window.
299 .It Dv TIOCMSET Fa int *state
300 The integer pointed to by
302 contains bits that correspond to modem state.
303 Following is a list of defined variables and the modem state they represent:
305 .Bl -tag -width TIOCMXCTS -compact
321 Carrier Detect (synonym).
325 Ring Indication (synonym).
330 This call sets the terminal modem state to that represented by
332 Not all terminals may support this.
333 .It Dv TIOCMGET Fa int *state
334 Return the current state of the terminal modem lines as represented
335 above in the integer pointed to by
337 .It Dv TIOCMBIS Fa int *state
338 The bits in the integer pointed to by
340 represent modem state as described above, however the state is OR-ed
341 in with the current state.
342 .It Dv TIOCMBIC Fa int *state
343 The bits in the integer pointed to by
345 represent modem state as described above, however each bit which is on
348 is cleared in the terminal.
350 .Sh IMPLEMENTATION NOTES
351 The total number of input and output bytes
352 through all terminal devices
353 are available via the