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32 .\" @(#)termios.4 8.4 (Berkeley) 4/19/94
40 .Nd general terminal line discipline
42 .Fd #include <termios.h>
44 This describes a general terminal line discipline that is
45 supported on tty asynchronous communication ports.
46 .Ss Opening a Terminal Device File
47 When a terminal file is opened, it normally causes the process to wait
48 until a connection is established. For most hardware, the presence
49 of a connection is indicated by the assertion of the hardware
51 If the termios structure associated with the terminal file has the
53 flag set in the cflag, or if the
58 call, then the open will succeed even without
59 a connection being present.
60 In practice, applications
61 seldom open these files; they are opened by special programs, such
67 an application's standard input, output, and error files.
68 .Ss Job Control in a Nutshell
69 Every process is associated with a particular process group and session.
70 The grouping is hierarchical: every member of a particular process group is a
71 member of the same session. This structuring is used in managing groups
72 of related processes for purposes of
73 .\" .Gw "job control" ;
76 ability from the keyboard (or from program control) to simultaneously
78 a complex command (a command composed of one or more related
79 processes). The grouping into process groups allows delivering
80 of signals that stop or start the group as a whole, along with
81 arbitrating which process group has access to the single controlling
82 terminal. The grouping at a higher layer into sessions is to restrict
83 the job control related signals and system calls to within processes
84 resulting from a particular instance of a "login". Typically, a session
85 is created when a user logs in, and the login terminal is setup
86 to be the controlling terminal; all processes spawned from that
87 login shell are in the same session, and inherit the controlling
91 operating interactively (that is, reading commands from a terminal)
92 normally groups related processes together by placing them into the
93 same process group. A set of processes in the same process group
94 is collectively referred to as a "job". When the foreground process
95 group of the terminal is the same as the process group of a particular
96 job, that job is said to be in the "foreground". When the process
97 group of the terminal is different than the process group of
98 a job (but is still the controlling terminal), that job is said
99 to be in the "background". Normally the
100 shell reads a command and starts the job that implements that
101 command. If the command is to be started in the foreground (typical), it
102 sets the process group of the terminal to the process group
103 of the started job, waits for the job to complete, and then
104 sets the process group of the terminal back to its own process
105 group (it puts itself into the foreground). If the job is to
106 be started in the background (as denoted by the shell operator "&"),
107 it never changes the process group of the terminal and doesn't
108 wait for the job to complete (that is, it immediately attempts to read the next
109 command). If the job is started in the foreground, the user may
112 which generates the terminal stop signal
114 and has the affect of stopping the entire job.
115 The shell will notice that the job stopped, and will resume running after
116 placing itself in the foreground.
117 The shell also has commands for placing stopped jobs in the background,
118 and for placing stopped or background jobs into the foreground.
119 .Ss Orphaned Process Groups
120 An orphaned process group is a process group that has no process
121 whose parent is in a different process group, yet is in the same
122 session. Conceptually it means a process group that doesn't have
123 a parent that could do anything if it were to be stopped. For example,
124 the initial login shell is typically in an orphaned process group.
125 Orphaned process groups are immune to keyboard generated stop
126 signals and job control signals resulting from reads or writes to the
127 controlling terminal.
128 .Ss The Controlling Terminal
129 A terminal may belong to a process as its controlling terminal. Each
130 process of a session that has a controlling terminal has the same
131 controlling terminal. A terminal may be the controlling terminal for at
132 most one session. The controlling terminal for a session is allocated by
133 the session leader by issuing the
135 ioctl. A controlling terminal
136 is never acquired by merely opening a terminal device file.
137 When a controlling terminal becomes
138 associated with a session, its foreground process group is set to
139 the process group of the session leader.
141 The controlling terminal is inherited by a child process during a
143 function call. A process relinquishes its controlling terminal when it
144 creates a new session with the
146 function; other processes
147 remaining in the old session that had this terminal as their controlling
148 terminal continue to have it.
149 A process does not relinquish its
150 controlling terminal simply by closing all of its file descriptors
151 associated with the controlling terminal if other processes continue to
154 When a controlling process terminates, the controlling terminal is
155 disassociated from the current session, allowing it to be acquired by a
156 new session leader. Subsequent access to the terminal by other processes
157 in the earlier session will be denied, with attempts to access the
158 terminal treated as if modem disconnect had been sensed.
159 .Ss Terminal Access Control
160 If a process is in the foreground process group of its controlling
161 terminal, read operations are allowed.
162 Any attempts by a process
163 in a background process group to read from its controlling terminal
169 following special cases apply: If the reading process is ignoring or
171 .Dv SIGTTIN signal, or if the process group of the reading
172 process is orphaned, the
178 signal is sent. The default action of the
180 signal is to stop the
181 process to which it is sent.
183 If a process is in the foreground process group of its controlling
184 terminal, write operations are allowed.
185 Attempts by a process in a background process group to write to its
186 controlling terminal will cause the process group to be sent a
188 signal unless one of the following special cases apply: If
193 is set and the process is ignoring or blocking the
195 signal, the process is allowed to write to the terminal and the
197 signal is not sent. If
199 is set, and the process group of
200 the writing process is orphaned, and the writing process is not ignoring
208 and no signal is sent.
210 Certain calls that set terminal parameters are treated in the same
211 fashion as write, except that
213 is ignored; that is, the effect is
214 identical to that of terminal writes when
217 .Ss Input Processing and Reading Data
218 A terminal device associated with a terminal device file may operate in
219 full-duplex mode, so that data may arrive even while output is occurring.
220 Each terminal device file has associated with it an input queue, into
221 which incoming data is stored by the system before being read by a
222 process. The system imposes a limit,
223 .Pf \&{ Dv MAX_INPUT Ns \&} ,
225 bytes that may be stored in the input queue. The behavior of the system
226 when this limit is exceeded depends on the setting of the
230 If this flag is set, the terminal
234 character each time a character is received
235 while the input queue is full. Otherwise, the input queue is flushed
236 upon receiving the character.
238 Two general kinds of input processing are available, determined by
239 whether the terminal device file is in canonical mode or noncanonical
241 input characters are processed according to the
245 fields. Such processing can include echoing, which
246 in general means transmitting input characters immediately back to the
247 terminal when they are received from the terminal. This is useful for
248 terminals that can operate in full-duplex mode.
250 The manner in which data is provided to a process reading from a terminal
251 device file is dependent on whether the terminal device file is in
252 canonical or noncanonical mode.
254 Another dependency is whether the
262 flag is clear, then the read request is
263 blocked until data is available or a signal has been received. If the
265 flag is set, then the read request is completed, without
266 blocking, in one of three ways:
267 .Bl -enum -offset indent
269 If there is enough data available to satisfy the entire request,
270 and the read completes successfully the number of
271 bytes read is returned.
273 If there is not enough data available to satisfy the entire
274 request, and the read completes successfully, having read as
275 much data as possible, the number of bytes read is returned.
277 If there is no data available, the read returns -1, with
282 When data is available depends on whether the input processing mode is
283 canonical or noncanonical.
284 .Ss Canonical Mode Input Processing
285 In canonical mode input processing, terminal input is processed in units
286 of lines. A line is delimited by a newline
288 character, an end-of-file
290 character, or an end-of-line
293 .Sx "Special Characters"
299 This means that a read request will
300 not return until an entire line has been typed, or a signal has been
301 received. Also, no matter how many bytes are requested in the read call,
302 at most one line is returned. It is not, however, necessary to
303 read a whole line at once; any number of bytes, even one, may be
304 requested in a read without losing information.
306 .Pf \&{ Dv MAX_CANON Ns \&}
308 number of bytes in a line.
309 The behavior of the system when this limit is
310 exceeded is the same as when the input queue limit
311 .Pf \&{ Dv MAX_INPUT Ns \&} ,
314 Erase and kill processing occur when either of two special characters,
320 .Sx "Special Characters section" ) ,
322 This processing affects data in the input queue that has not yet been
323 delimited by a newline
328 character. This un-delimited
329 data makes up the current line. The
331 character deletes the last
332 character in the current line, if there is any. The
335 deletes all data in the current line, if there is any. The
339 characters have no effect if there is no data in the current line.
344 characters themselves are not placed in the input
346 .Ss Noncanonical Mode Input Processing
347 In noncanonical mode input processing, input bytes are not assembled into
348 lines, and erase and kill processing does not occur. The values of the
354 array are used to determine how to
355 process the bytes received.
358 represents the minimum number of bytes that should be received when
361 function successfully returns.
363 is a timer of 0.1 second
364 granularity that is used to time out bursty and short term data
368 .Dv \&{ Dv MAX_INPUT Ns \&} ,
370 request is undefined. The four possible values for
375 their interactions are described below.
376 .Ss "Case A: MIN > 0, TIME > 0"
379 serves as an inter-byte timer and is activated after
380 the first byte is received. Since it is an inter-byte timer, it is reset
381 after a byte is received. The interaction between
386 follows: as soon as one byte is received, the inter-byte timer is
389 bytes are received before the inter-byte timer expires
390 (remember that the timer is reset upon receipt of each byte), the read is
391 satisfied. If the timer expires before
393 bytes are received, the
394 characters received to that point are returned to the user. Note that if
396 expires at least one byte is returned because the timer would
397 not have been enabled unless a byte was received. In this case
401 > 0) the read blocks until the
406 activated by the receipt of the first byte, or a signal is received. If
407 data is in the buffer at the time of the
410 if data had been received immediately after the
412 .Ss "Case B: MIN > 0, TIME = 0"
413 In this case, since the value of
415 is zero, the timer plays no role
418 is significant. A pending read is not satisfied until
420 bytes are received (i.e., the pending read blocks until
423 are received), or a signal is received. A program that uses this case to
424 read record-based terminal
426 may block indefinitely in the read
428 .Ss "Case C: MIN = 0, TIME > 0"
433 no longer represents an inter-byte
434 timer. It now serves as a read timer that is activated as soon as the
435 read function is processed. A read is satisfied as soon as a single
436 byte is received or the read timer expires. Note that in this case if
437 the timer expires, no bytes are returned. If the timer does not
438 expire, the only way the read can be satisfied is if a byte is received.
439 In this case the read will not block indefinitely waiting for a byte; if
440 no byte is received within
442 seconds after the read is initiated,
443 the read returns a value of zero, having read no data. If data is
444 in the buffer at the time of the read, the timer is started as if
445 data had been received immediately after the read.
446 .Ss Case D: MIN = 0, TIME = 0
447 The minimum of either the number of bytes requested or the number of
448 bytes currently available is returned without waiting for more
449 bytes to be input. If no characters are available, read returns a
450 value of zero, having read no data.
451 .Ss Writing Data and Output Processing
452 When a process writes one or more bytes to a terminal device file, they
453 are processed according to the
458 implementation may provide a buffering mechanism; as such, when a call to
460 completes, all of the bytes written have been scheduled for
461 transmission to the device, but the transmission will not necessarily
463 .\" See also .Sx "6.4.2" for the effects of
466 .Ss Special Characters
467 Certain characters have special functions on input or output or both.
468 These functions are summarized as follows:
469 .Bl -tag -width indent
471 Special character on input and is recognized if the
475 section) is enabled. Generates a
477 signal which is sent to all processes in the foreground
478 process group for which the terminal is the controlling
484 discarded when processed.
486 Special character on input and is recognized if the
488 flag is enabled. Generates a
491 sent to all processes in the foreground process group
492 for which the terminal is the controlling terminal. If
496 character is discarded when
499 Special character on input and is recognized if the
501 flag is set. Erases the last character in the
503 .Sx "Canonical Mode Input Processing" .
504 It does not erase beyond
505 the start of a line, as delimited by an
515 discarded when processed.
517 Special character on input and is recognized if the
519 flag is set. Deletes the entire line, as
529 character is discarded when processed.
531 Special character on input and is recognized if the
533 flag is set. When received, all the bytes
534 waiting to be read are immediately passed to the
535 process, without waiting for a newline, and the
537 is discarded. Thus, if there are no bytes waiting (that
540 occurred at the beginning of a line), a byte
541 count of zero is returned from the
543 representing an end-of-file indication. If
548 character is discarded when processed.
550 Special character on input and is recognized if the
552 flag is set. It is the line delimiter
555 Special character on input and is recognized if the
557 flag is set. Is an additional line delimiter,
563 flag is enabled, receipt of the
567 signal to be sent to all processes in the
568 foreground process group for which the terminal is the
569 controlling terminal, and the
572 discarded when processed.
574 Special character on both input and output and is
580 control) flag is set. Can be used to temporarily
581 suspend output. It is useful with fast terminals to
582 prevent output from disappearing before it can be read.
587 character is discarded when
590 Special character on both input and output and is
596 control) flag is set. Can be used to resume output that
597 has been suspended by a
603 character is discarded when processed.
605 Special character on input and is recognized if the
607 flag is set; it is the
617 is not set, this character is translated into a
620 has the same effect as a
625 The following special characters are extensions defined by this
626 system and are not a part of 1003.1 termios.
627 .Bl -tag -width indent
631 character. Same function as
634 Special character on input and is recognized if the
636 flag is set. Erases the last word in the current
637 line according to one of two algorithms. If the
639 flag is not set, first any preceding whitespace is
640 erased, and then the maximal sequence of non-whitespace
643 is set, first any preceding
644 whitespace is erased, and then the maximal sequence
645 of alphabetic/underscores or non alphabetic/underscores.
646 As a special case in this second algorithm, the first previous
647 non-whitespace character is skipped in determining
648 whether the preceding word is a sequence of
649 alphabetic/underscores. This sounds confusing but turns
650 out to be quite practical.
652 Special character on input and is recognized if the
654 flag is set. Causes the current input edit line
657 Has similar actions to the
659 character, except that
662 signal is delivered when one of the processes
663 in the foreground process group issues a
666 controlling terminal.
668 Special character on input and is recognized if the
670 flag is set. Receipt of this character causes the next
671 character to be taken literally.
673 Special character on input and is recognized if the
675 flag is set. Receipt of this character toggles the flushing
678 Special character on input and is recognized if the
680 flag is set. Receipt of this character causes a
682 signal to be sent to the foreground process group of the
683 terminal. Also, if the
686 causes the kernel to write a status message to the terminal
687 that displays the current load average, the name of the
688 command in the foreground, its process ID, the symbolic
689 wait channel, the number of user and system seconds used,
690 the percentage of cpu the process is getting, and the resident
691 set size of the process.
698 characters cannot be changed.
699 The values for all the remaining characters can be set and are
700 described later in the document under
701 Special Control Characters.
704 character functions associated with changeable special control characters
705 can be disabled individually by setting their value to
706 .Dv {_POSIX_VDISABLE};
708 .Sx "Special Control Characters" .
710 If two or more special characters have the same value, the function
711 performed when that character is received is undefined.
713 If a modem disconnect is detected by the terminal interface for a
714 controlling terminal, and if
721 signal is sent to the controlling
722 process associated with the terminal. Unless other arrangements have
723 been made, this causes the controlling process to terminate.
724 Any subsequent call to the
726 function returns the value zero,
727 indicating end of file. Thus, processes that read a terminal
728 file and test for end-of-file can terminate appropriately after a
732 .\" condition specified in 6.1.1.4 that applies
733 .\" when the implementation supports job control also exists, it is
734 .\" unspecified whether the
742 to the terminal device returns -1, with
746 until the device is closed.
747 .Sh General Terminal Interface
749 .Ss Closing a Terminal Device File
750 The last process to close a terminal device file causes any output
751 to be sent to the device and any input to be discarded. Then, if
753 is set in the control modes, and the communications port supports a
754 disconnect function, the terminal device performs a disconnect.
755 .Ss Parameters That Can Be Set
756 Routines that need to control certain terminal
759 do so by using the termios structure as defined in the header
761 This structure contains minimally four scalar elements of bit flags
762 and one array of special characters. The scalar flag elements are
769 The character array is named
771 and its maximum index is
776 field describe the basic
777 terminal input control, and are composed of
780 .Bl -tag -width IMAXBEL -offset indent -compact
782 /* ignore BREAK condition */
784 /* map BREAK to SIGINTR */
786 /* ignore (discard) parity errors */
788 /* mark parity and framing errors */
790 /* enable checking of parity errors */
792 /* strip 8th bit off chars */
798 /* map CR to NL (ala CRMOD) */
800 /* enable output flow control */
802 /* enable input flow control */
804 /* any char will restart after stop */
806 /* ring bell on input queue full */
809 In the context of asynchronous serial data transmission, a break
810 condition is defined as a sequence of zero-valued bits that continues for
811 more than the time to send one byte. The entire sequence of zero-valued
812 bits is interpreted as a single break condition, even if it continues for
813 a time equivalent to more than one byte. In contexts other than
814 asynchronous serial data transmission the definition of a break condition
815 is implementation defined.
819 is set, a break condition detected on input is ignored, that
820 is, not put on the input queue and therefore not read by any process. If
824 is set, the break condition flushes the
825 input and output queues and if the terminal is the controlling terminal
826 of a foreground process group, the break condition generates a
829 signal to that foreground process group. If neither
833 is set, a break condition is read as a single
844 is set, a byte with a framing or parity error (other than
851 is not set, a byte with a framing or parity
852 error (other than break) is given to the application as the
853 three-character sequence
860 flag preceding each sequence and X is the data of the character received
861 in error. To avoid ambiguity in this case, if
866 is given to the application as
874 is set, a framing or parity error (other than
875 break) is given to the application as a single character
880 is set, input parity checking is enabled. If
883 input parity checking is disabled, allowing output parity generation
884 without input parity errors. Note that whether input parity checking is
885 enabled or disabled is independent of whether parity detection is enabled
887 .Sx "Control Modes" ) .
888 If parity detection is enabled but input
889 parity checking is disabled, the hardware to which the terminal is
890 connected recognizes the parity bit, but the terminal special file
891 does not check whether this bit is set correctly or not.
895 is set, valid input bytes are first stripped to seven bits,
896 otherwise all eight bits are processed.
902 character is translated into a
908 character is ignored (not
922 is set, start/stop output control is enabled. A received
924 character suspends output and a received
929 is also set, then any character may
937 read, but merely perform flow control functions. When
948 is set, start/stop input control is enabled. The system shall
951 characters, which are intended to cause the
952 terminal device to stop transmitting data, as needed to prevent the input
953 queue from overflowing and causing the undefined behavior described in
954 .Sx "Input Processing and Reading Data" ,
955 and shall transmit one or more
957 characters, which are
958 intended to cause the terminal device to resume transmitting data, as
959 soon as the device can continue transmitting data without risk of
960 overflowing the input queue. The precise conditions under which
964 characters are transmitted are implementation defined.
968 is set and the input queue is full, subsequent input shall cause an
971 character to be transmitted to
974 The initial input control value after
976 is implementation defined.
980 field describe the basic terminal output control,
981 and are composed of the following masks:
983 .Bl -tag -width OXTABS -offset indent -compact
985 /* enable following output processing */
987 /* map NL to CR-NL (ala
991 /* expand tabs to spaces */
1001 is set, the remaining flag masks are interpreted as follows;
1002 otherwise characters are transmitted without change.
1006 is set, newlines are translated to carriage return, linefeeds.
1010 is set, tabs are expanded to the appropriate number of
1011 spaces (assuming 8 column tab stops).
1018 are discarded on output.
1022 field describe the basic
1023 terminal hardware control, and are composed of the
1026 specified are supported by all hardware.
1028 .Bl -tag -width CRTSXIFLOW -offset indent -compact
1030 /* character size mask */
1032 /* 5 bits (pseudo) */
1040 /* send 2 stop bits */
1042 /* enable receiver */
1046 /* odd parity, else even */
1048 /* hang up on last close */
1050 /* ignore modem status lines */
1054 flow control of output */
1060 /* RTS flow control of input */
1062 /* flow control output via Carrier */
1067 bits specify the byte size in bits for both transmission and
1072 and compared with the
1079 This size does not include the parity bit, if any. If
1081 is set, two stop bits are used, otherwise one stop bit. For example, at
1082 110 baud, two stop bits are normally used.
1086 is set, the receiver is enabled. Otherwise, no character is
1088 Not all hardware supports this bit. In fact, this flag
1089 is pretty silly and if it were not part of the
1092 it would be omitted.
1096 is set, parity generation and detection are enabled and a parity
1097 bit is added to each character. If parity is enabled,
1100 odd parity if set, otherwise even parity is used.
1104 is set, the modem control lines for the port are lowered
1105 when the last process with the port open closes the port or the process
1106 terminates. The modem connection is broken.
1110 is set, a connection does not depend on the state of the modem
1113 is clear, the modem status lines are
1116 Under normal circumstances, a call to the
1119 the modem connection to complete. However, if the
1127 immediately without waiting for the connection.
1132 flag is currently unused.
1136 is set then output flow control is controlled by the state
1139 If the object for which the control modes are set is not an asynchronous
1140 serial connection, some of the modes may be ignored; for example, if an
1141 attempt is made to set the baud rate on a network connection to a
1142 terminal on another host, the baud rate may or may not be set on the
1143 connection between that terminal and the machine it is directly connected
1148 field describe the control of
1149 various functions, and are composed of the following
1152 .Bl -tag -width NOKERNINFO -offset indent -compact
1154 /* visual erase for line kill */
1156 /* visually erase chars */
1158 /* enable echoing */
1166 /* visual erase mode for hardcopy */
1168 /* echo control chars as ^(Char) */
1176 /* canonicalize input lines */
1188 /* external processing */
1190 /* stop background jobs from output */
1192 /* output being flushed (state) */
1194 /* no kernel output from
1198 /* XXX retype pending input (state) */
1200 /* don't flush after interrupt */
1205 is set, input characters are echoed back to the terminal. If
1207 is not set, input characters are not echoed.
1215 character causes the terminal
1216 to erase the last character in the current line from the display, if
1217 possible. If there is no character to erase, an implementation may echo
1218 an indication that this was the case or do nothing.
1227 the current line to be discarded and the system echoes the
1240 the current line to be discarded and the system causes
1242 to erase the line from the display.
1248 are set, the system assumes
1249 that the display is a printing device and prints a
1250 backslash and the erased characters when processing
1252 characters, followed by a forward slash.
1256 is set, the system echoes control characters
1257 in a visible fashion using a caret followed by the control character.
1261 is set, the system uses an alternative algorithm
1262 for determining what constitutes a word when processing
1273 character echoes even if
1279 is set, canonical processing is enabled. This enables the
1280 erase and kill edit functions, and the assembly of input characters into
1287 .Sx "Canonical Mode Input Processing" .
1291 is not set, read requests are satisfied directly from the input
1292 queue. A read is not satisfied until at least
1295 received or the timeout value
1297 expired between bytes. The time value
1298 represents tenths of seconds. See
1299 .Sx "Noncanonical Mode Input Processing"
1304 is set, each input character is checked against the special
1310 (job control only). If an input
1311 character matches one of these control characters, the function
1312 associated with that character is performed. If
1315 checking is done. Thus these special input functions are possible only
1322 is set, implementation-defined functions are recognized
1323 from the input data. How
1332 is implementation defined.
1336 implementation-defined functions are not recognized, and the
1337 corresponding input characters are not processed as described for
1346 is set, the normal flush of the input and output queues
1359 is sent to the process group of a process that tries to write to
1360 its controlling terminal if it is not in the foreground process group for
1361 that terminal. This signal, by default, stops the members of the process
1362 group. Otherwise, the output generated by that process is output to the
1363 current output stream. Processes that are blocking or ignoring
1365 signals are excepted and allowed to produce output and the
1372 is set, the kernel does not produce a status message
1377 .Ss Special Control Characters
1378 The special control characters values are defined by the array
1380 This table lists the array index, the corresponding special character,
1381 and the system default value. For an accurate list of
1382 the system defaults, consult the header file
1383 .Aq Pa ttydefaults.h .
1385 .Bl -column "Index Name" "Special Character" -offset indent -compact
1386 .It Em "Index Name Special Character Default Value"
1387 .It Dv VEOF Ta EOF Ta \&^D
1388 .It Dv VEOL Ta EOL Ta _POSIX_VDISABLE
1389 .It Dv VEOL2 Ta EOL2 Ta _POSIX_VDISABLE
1390 .It Dv VERASE Ta ERASE Ta \&^? Ql \&\e177
1391 .It Dv VWERASE Ta WERASE Ta \&^W
1392 .It Dv VKILL Ta KILL Ta \&^U
1393 .It Dv VREPRINT Ta REPRINT Ta \&^R
1394 .It Dv VINTR Ta INTR Ta \&^C
1395 .It Dv VQUIT Ta QUIT Ta \&^\e\e Ql \&\e34
1396 .It Dv VSUSP Ta SUSP Ta \&^Z
1397 .It Dv VDSUSP Ta DSUSP Ta \&^Y
1398 .It Dv VSTART Ta START Ta \&^Q
1399 .It Dv VSTOP Ta STOP Ta \&^S
1400 .It Dv VLNEXT Ta LNEXT Ta \&^V
1401 .It Dv VDISCARD Ta DISCARD Ta \&^O
1402 .It Dv VMIN Ta --- Ta \&1
1403 .It Dv VTIME Ta --- Ta \&0
1404 .It Dv VSTATUS Ta STATUS Ta \&^T
1408 value of one of the changeable special control characters (see
1409 .Sx "Special Characters" )
1411 .Dv {_POSIX_VDISABLE} ,
1412 that function is disabled; that is, no input
1413 data is recognized as the disabled special character.
1417 not set, the value of
1418 .Dv {_POSIX_VDISABLE}
1419 has no special meaning for the
1427 The initial values of the flags and control characters
1431 the values in the header
1432 .Aq Pa sys/ttydefaults.h .