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28 .\" @(#)termios.4 8.4 (Berkeley) 4/19/94
29 .\" $FreeBSD: head/share/man/man4/termios.4 263142 2014-03-14 03:07:51Z eadler $
36 .Nd general terminal line discipline
40 This describes a general terminal line discipline that is
41 supported on tty asynchronous communication ports.
42 .Ss Opening a Terminal Device File
43 When a terminal file is opened, it normally causes the process to wait
44 until a connection is established.
45 For most hardware, the presence
46 of a connection is indicated by the assertion of the hardware
49 If the termios structure associated with the terminal file has the
51 flag set in the cflag, or if the
56 call, then the open will succeed even without
57 a connection being present.
58 In practice, applications
59 seldom open these files; they are opened by special programs, such
63 .Xr rlogind 8 Pq Pa net/bsdrcmds ,
65 an application's standard input, output, and error files.
66 .Ss Job Control in a Nutshell
67 Every process is associated with a particular process group and session.
68 The grouping is hierarchical: every member of a particular process group is a
69 member of the same session.
70 This structuring is used in managing groups
71 of related processes for purposes of
72 .\" .Gw "job control" ;
75 ability from the keyboard (or from program control) to simultaneously
77 a complex command (a command composed of one or more related
79 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
83 The grouping at a higher layer into sessions is to restrict
84 the job control related signals and system calls to within processes
85 resulting from a particular instance of a
88 is created when a user logs in, and the login terminal is setup
89 to be the controlling terminal; all processes spawned from that
90 login shell are in the same session, and inherit the controlling
94 operating interactively (that is, reading commands from a terminal)
95 normally groups related processes together by placing them into the
97 A set of processes in the same process group is collectively referred to as a
99 When the foreground process
100 group of the terminal is the same as the process group of a particular
101 job, that job is said to be in the
103 When the process group of the terminal is different from the process group of
104 a job (but is still the controlling terminal), that job is said
108 shell reads a command and starts the job that implements that
110 If the command is to be started in the foreground (typical), it
111 sets the process group of the terminal to the process group
112 of the started job, waits for the job to complete, and then
113 sets the process group of the terminal back to its own process
114 group (it puts itself into the foreground).
116 be started in the background (as denoted by the shell operator "&"),
117 it never changes the process group of the terminal and does not
118 wait for the job to complete (that is, it immediately attempts to read the next
120 If the job is started in the foreground, the user may
123 which generates the terminal stop signal
125 and has the effect of stopping the entire job.
126 The shell will notice that the job stopped, and will resume running after
127 placing itself in the foreground.
128 The shell also has commands for placing stopped jobs in the background,
129 and for placing stopped or background jobs into the foreground.
130 .Ss Orphaned Process Groups
131 An orphaned process group is a process group that has no process
132 whose parent is in a different process group, yet is in the same
134 Conceptually it means a process group that does not have
135 a parent that could do anything if it were to be stopped.
137 the initial login shell is typically in an orphaned process group.
138 Orphaned process groups are immune to keyboard generated stop
139 signals and job control signals resulting from reads or writes to the
140 controlling terminal.
141 .Ss The Controlling Terminal
142 A terminal may belong to a process as its controlling terminal.
143 Each process of a session that has a controlling terminal has the same
144 controlling terminal.
145 A terminal may be the controlling terminal for at most one session.
146 The controlling terminal for a session is allocated by
147 the session leader by issuing the
150 A controlling terminal
151 is never acquired by merely opening a terminal device file.
152 When a controlling terminal becomes
153 associated with a session, its foreground process group is set to
154 the process group of the session leader.
156 The controlling terminal is inherited by a child process during a
159 A process relinquishes its controlling terminal when it
160 creates a new session with the
162 function; other processes
163 remaining in the old session that had this terminal as their controlling
164 terminal continue to have it.
165 A process does not relinquish its
166 controlling terminal simply by closing all of its file descriptors
167 associated with the controlling terminal if other processes continue to
170 When a controlling process terminates, the controlling terminal is
171 disassociated from the current session, allowing it to be acquired by a
173 Subsequent access to the terminal by other processes
174 in the earlier session will be denied, with attempts to access the
175 terminal treated as if modem disconnect had been sensed.
176 .Ss Terminal Access Control
177 If a process is in the foreground process group of its controlling
178 terminal, read operations are allowed.
179 Any attempts by a process
180 in a background process group to read from its controlling terminal
186 following special cases apply: if the reading process is ignoring or
189 signal, or if the process group of the reading
190 process is orphaned, the
198 The default action of the
200 signal is to stop the
201 process to which it is sent.
203 If a process is in the foreground process group of its controlling
204 terminal, write operations are allowed.
205 Attempts by a process in a background process group to write to its
206 controlling terminal will cause the process group to be sent a
208 signal unless one of the following special cases apply: if
213 is set and the process is ignoring or blocking the
215 signal, the process is allowed to write to the terminal and the
220 is set, and the process group of
221 the writing process is orphaned, and the writing process is not ignoring
230 and no signal is sent.
232 Certain calls that set terminal parameters are treated in the same
233 fashion as write, except that
235 is ignored; that is, the effect is
236 identical to that of terminal writes when
239 .Ss Input Processing and Reading Data
240 A terminal device associated with a terminal device file may operate in
241 full-duplex mode, so that data may arrive even while output is occurring.
242 Each terminal device file has associated with it an input queue, into
243 which incoming data is stored by the system before being read by a
245 The system imposes a limit,
246 .Pf \&{ Dv MAX_INPUT Ns \&} ,
247 on the number of bytes that may be stored in the input queue.
248 The behavior of the system
249 when this limit is exceeded depends on the setting of the
253 If this flag is set, the terminal
257 character each time a character is received
258 while the input queue is full.
259 Otherwise, the input queue is flushed upon receiving the character.
261 Two general kinds of input processing are available, determined by
262 whether the terminal device file is in canonical mode or noncanonical
265 input characters are processed according to the
270 Such processing can include echoing, which
271 in general means transmitting input characters immediately back to the
272 terminal when they are received from the terminal.
273 This is useful for terminals that can operate in full-duplex mode.
275 The manner in which data is provided to a process reading from a terminal
276 device file is dependent on whether the terminal device file is in
277 canonical or noncanonical mode.
279 Another dependency is whether the
287 flag is clear, then the read request is
288 blocked until data is available or a signal has been received.
291 flag is set, then the read request is completed, without
292 blocking, in one of three ways:
293 .Bl -enum -offset indent
295 If there is enough data available to satisfy the entire request,
296 and the read completes successfully the number of
297 bytes read is returned.
299 If there is not enough data available to satisfy the entire
300 request, and the read completes successfully, having read as
301 much data as possible, the number of bytes read is returned.
303 If there is no data available, the read returns -1, with
309 When data is available depends on whether the input processing mode is
310 canonical or noncanonical.
311 .Ss Canonical Mode Input Processing
312 In canonical mode input processing, terminal input is processed in units
314 A line is delimited by a newline
316 character, an end-of-file
318 character, or an end-of-line
322 .Sx "Special Characters"
323 section for more information on
327 This means that a read request will
328 not return until an entire line has been typed, or a signal has been
330 Also, no matter how many bytes are requested in the read call,
331 at most one line is returned.
332 It is not, however, necessary to
333 read a whole line at once; any number of bytes, even one, may be
334 requested in a read without losing information.
336 .Pf \&{ Dv MAX_CANON Ns \&}
338 number of bytes in a line.
339 The behavior of the system when this limit is
340 exceeded is the same as when the input queue limit
341 .Pf \&{ Dv MAX_INPUT Ns \&} ,
344 Erase and kill processing occur when either of two special characters,
350 .Sx "Special Characters"
351 section), is received.
352 This processing affects data in the input queue that has not yet been
353 delimited by a newline
359 This un-delimited data makes up the current line.
362 character deletes the last character in the current line, if there is any.
366 deletes all data in the current line, if there is any.
371 characters have no effect if there is no data in the current line.
376 characters themselves are not placed in the input
378 .Ss Noncanonical Mode Input Processing
379 In noncanonical mode input processing, input bytes are not assembled into
380 lines, and erase and kill processing does not occur.
387 array are used to determine how to
388 process the bytes received.
391 represents the minimum number of bytes that should be received when
394 function successfully returns.
396 is a timer of 0.1 second
397 granularity that is used to time out bursty and short term data
402 .Dv \&{ Dv MAX_INPUT Ns \&} ,
404 request is undefined.
405 The four possible values for
410 their interactions are described below.
411 .Ss "Case A: MIN > 0, TIME > 0"
414 serves as an inter-byte timer and is activated after
415 the first byte is received.
416 Since it is an inter-byte timer, it is reset after a byte is received.
417 The interaction between
422 follows: as soon as one byte is received, the inter-byte timer is
426 bytes are received before the inter-byte timer expires
427 (remember that the timer is reset upon receipt of each byte), the read is
429 If the timer expires before
431 bytes are received, the
432 characters received to that point are returned to the user.
435 expires at least one byte is returned because the timer would
436 not have been enabled unless a byte was received.
441 > 0) the read blocks until the
446 activated by the receipt of the first byte, or a signal is received.
447 If data is in the buffer at the time of the
450 if data had been received immediately after the
452 .Ss "Case B: MIN > 0, TIME = 0"
453 In this case, since the value of
455 is zero, the timer plays no role
459 A pending read is not satisfied until
461 bytes are received (i.e., the pending read blocks until
464 are received), or a signal is received.
465 A program that uses this case to read record-based terminal
467 may block indefinitely in the read
469 .Ss "Case C: MIN = 0, TIME > 0"
474 no longer represents an inter-byte
476 It now serves as a read timer that is activated as soon as the
477 read function is processed.
478 A read is satisfied as soon as a single
479 byte is received or the read timer expires.
480 Note that in this case if the timer expires, no bytes are returned.
481 If the timer does not
482 expire, the only way the read can be satisfied is if a byte is received.
483 In this case the read will not block indefinitely waiting for a byte; if
484 no byte is received within
486 seconds after the read is initiated,
487 the read returns a value of zero, having read no data.
488 If data is in the buffer at the time of the read, the timer is started as if
489 data had been received immediately after the read.
490 .Ss Case D: MIN = 0, TIME = 0
491 The minimum of either the number of bytes requested or the number of
492 bytes currently available is returned without waiting for more
494 If no characters are available, read returns a
495 value of zero, having read no data.
496 .Ss Writing Data and Output Processing
497 When a process writes one or more bytes to a terminal device file, they
498 are processed according to the
503 The implementation may provide a buffering mechanism; as such, when a call to
505 completes, all of the bytes written have been scheduled for
506 transmission to the device, but the transmission will not necessarily
508 .\" See also .Sx "6.4.2" for the effects of
511 .Ss Special Characters
512 Certain characters have special functions on input or output or both.
513 These functions are summarized as follows:
514 .Bl -tag -width indent
516 Special character on input and is recognized if the
523 signal which is sent to all processes in the foreground
524 process group for which the terminal is the controlling terminal.
530 discarded when processed.
532 Special character on input and is recognized if the
537 signal which is sent to all processes in the foreground process group
538 for which the terminal is the controlling terminal.
543 character is discarded when
546 Special character on input and is recognized if the
549 Erases the last character in the current line; see
550 .Sx "Canonical Mode Input Processing" .
551 It does not erase beyond
552 the start of a line, as delimited by an
563 discarded when processed.
565 Special character on input and is recognized if the
568 Deletes the entire line, as delimited by a
578 character is discarded when processed.
580 Special character on input and is recognized if the
583 When received, all the bytes waiting to be read are immediately passed to the
584 process, without waiting for a newline, and the
587 Thus, if there are no bytes waiting (that is, the
589 occurred at the beginning of a line), a byte
590 count of zero is returned from the
592 representing an end-of-file indication.
598 character is discarded when processed.
600 Special character on input and is recognized if the
603 It is the line delimiter
606 Special character on input and is recognized if the
609 Is an additional line delimiter, like
614 flag is enabled, receipt of the
618 signal to be sent to all processes in the
619 foreground process group for which the terminal is the
620 controlling terminal, and the
623 discarded when processed.
625 Special character on both input and output and is
631 control) flag is set.
632 Can be used to temporarily suspend output.
633 It is useful with fast terminals to
634 prevent output from disappearing before it can be read.
639 character is discarded when
642 Special character on both input and output and is
648 control) flag is set.
649 Can be used to resume output that has been suspended by a
656 character is discarded when processed.
658 Special character on input and is recognized if the
660 flag is set; it is the
671 is not set, this character is translated into a
674 has the same effect as a
679 The following special characters are extensions defined by this
680 system and are not a part of
683 .Bl -tag -width indent
691 Special character on input and is recognized if the
694 Erases the last word in the current line according to one of two algorithms.
697 flag is not set, first any preceding whitespace is
698 erased, and then the maximal sequence of non-whitespace
702 is set, first any preceding
703 whitespace is erased, and then the maximal sequence
704 of alphabetic/underscores or non alphabetic/underscores.
705 As a special case in this second algorithm, the first previous
706 non-whitespace character is skipped in determining
707 whether the preceding word is a sequence of
708 alphabetic/underscores.
709 This sounds confusing but turns out to be quite practical.
711 Special character on input and is recognized if the
714 Causes the current input edit line to be retyped.
716 Has similar actions to the
718 character, except that
721 signal is delivered when one of the processes
722 in the foreground process group issues a
725 controlling terminal.
727 Special character on input and is recognized if the
730 Receipt of this character causes the next character to be taken literally.
732 Special character on input and is recognized if the
735 Receipt of this character toggles the flushing of terminal output.
737 Special character on input and is recognized if the
740 Receipt of this character causes a
742 signal to be sent to the foreground process group of the terminal.
746 causes the kernel to write a status message to the terminal
747 that displays the current load average, the name of the
748 command in the foreground, its process ID, the symbolic
749 wait channel, the number of user and system seconds used,
750 the percentage of cpu the process is getting, and the resident
751 set size of the process.
758 characters cannot be changed.
759 The values for all the remaining characters can be set and are
760 described later in the document under
761 Special Control Characters.
764 character functions associated with changeable special control characters
765 can be disabled individually by setting their value to
766 .Dv {_POSIX_VDISABLE} ;
768 .Sx "Special Control Characters" .
770 If two or more special characters have the same value, the function
771 performed when that character is received is undefined.
773 If a modem disconnect is detected by the terminal interface for a
774 controlling terminal, and if
781 signal is sent to the controlling
782 process associated with the terminal.
783 Unless other arrangements have
784 been made, this causes the controlling process to terminate.
785 Any subsequent call to the
787 function returns the value zero,
788 indicating end of file.
789 Thus, processes that read a terminal
790 file and test for end-of-file can terminate appropriately after a
794 .\" condition specified in 6.1.1.4 that applies
795 .\" when the implementation supports job control also exists, it is
796 .\" unspecified whether the
804 to the terminal device returns -1, with
808 until the device is closed.
809 .Sh General Terminal Interface
810 .Ss Closing a Terminal Device File
811 The last process to close a terminal device file causes any output
812 to be sent to the device and any input to be discarded.
815 is set in the control modes, and the communications port supports a
816 disconnect function, the terminal device performs a disconnect.
817 .Ss Parameters That Can Be Set
818 Routines that need to control certain terminal
821 do so by using the termios structure as defined in the header
823 This structure contains minimally four scalar elements of bit flags
824 and one array of special characters.
825 The scalar flag elements are named:
831 The character array is named
833 and its maximum index is
838 field describe the basic
839 terminal input control, and are composed of
842 .Bl -tag -width IMAXBEL -offset indent -compact
844 /* ignore BREAK condition */
846 /* map BREAK to SIGINTR */
848 /* ignore (discard) parity errors */
850 /* mark parity and framing errors */
852 /* enable checking of parity errors */
854 /* strip 8th bit off chars */
860 /* map CR to NL (ala CRMOD) */
862 /* enable output flow control */
864 /* enable input flow control */
866 /* any char will restart after stop */
868 /* ring bell on input queue full */
871 In the context of asynchronous serial data transmission, a break
872 condition is defined as a sequence of zero-valued bits that continues for
873 more than the time to send one byte.
874 The entire sequence of zero-valued
875 bits is interpreted as a single break condition, even if it continues for
876 a time equivalent to more than one byte.
877 In contexts other than
878 asynchronous serial data transmission the definition of a break condition
879 is implementation defined.
883 is set, a break condition detected on input is ignored, that
884 is, not put on the input queue and therefore not read by any process.
889 is set, the break condition flushes the
890 input and output queues and if the terminal is the controlling terminal
891 of a foreground process group, the break condition generates a
894 signal to that foreground process group.
899 is set, a break condition is read as a single
910 is set, a byte with a framing or parity error (other than
917 is not set, a byte with a framing or parity
918 error (other than break) is given to the application as the
919 three-character sequence
926 flag preceding each sequence and X is the data of the character received
928 To avoid ambiguity in this case, if
933 is given to the application as
941 is set, a framing or parity error (other than
942 break) is given to the application as a single character
947 is set, input parity checking is enabled.
951 input parity checking is disabled, allowing output parity generation
952 without input parity errors.
953 Note that whether input parity checking is
954 enabled or disabled is independent of whether parity detection is enabled
956 .Sx "Control Modes" ) .
957 If parity detection is enabled but input
958 parity checking is disabled, the hardware to which the terminal is
959 connected recognizes the parity bit, but the terminal special file
960 does not check whether this bit is set correctly or not.
964 is set, valid input bytes are first stripped to seven bits,
965 otherwise all eight bits are processed.
971 character is translated into a
978 character is ignored (not
993 is set, start/stop output control is enabled.
996 character suspends output and a received
1002 is also set, then any character may
1010 characters are not read, but merely perform flow control functions.
1018 characters are read.
1022 is set, start/stop input control is enabled.
1023 The system shall transmit one or more
1025 characters, which are intended to cause the
1026 terminal device to stop transmitting data, as needed to prevent the input
1027 queue from overflowing and causing the undefined behavior described in
1028 .Sx "Input Processing and Reading Data" ,
1029 and shall transmit one or more
1031 characters, which are
1032 intended to cause the terminal device to resume transmitting data, as
1033 soon as the device can continue transmitting data without risk of
1034 overflowing the input queue.
1035 The precise conditions under which
1039 characters are transmitted are implementation defined.
1043 is set and the input queue is full, subsequent input shall cause an
1046 character to be transmitted to
1049 The initial input control value after
1051 is implementation defined.
1055 field describe the basic terminal output control,
1056 and are composed of the following masks:
1058 .Bl -tag -width OXTABS -offset indent -compact
1060 /* enable following output processing */
1062 /* map NL to CR-NL (ala
1068 /* tab delay mask */
1070 /* no tab delay and expansion */
1072 /* expand tabs to spaces */
1074 /* alias for TAB3 */
1081 /* do not transmit CRs on column 0 */
1083 /* on the terminal NL performs the CR function */
1088 is set, the remaining flag masks are interpreted as follows;
1089 otherwise characters are transmitted without change.
1093 is set, newlines are translated to carriage return, linefeeds.
1097 is set, carriage returns are translated to newlines.
1101 bits specify the tab delay.
1106 and compared with the
1115 is set, tabs are expanded to the appropriate number of
1116 spaces (assuming 8 column tab stops).
1123 are discarded on output.
1127 is set, no CR character is transmitted when at column 0 (first position).
1131 is set, the NL character is assumed to do the carriage-return function;
1132 the column pointer will be set to 0.
1136 field describe the basic
1137 terminal hardware control, and are composed of the
1140 specified are supported by all hardware.
1142 .Bl -tag -width CRTSXIFLOW -offset indent -compact
1144 /* character size mask */
1146 /* 5 bits (pseudo) */
1154 /* send 2 stop bits */
1156 /* enable receiver */
1160 /* odd parity, else even */
1162 /* hang up on last close */
1164 /* ignore modem status lines */
1168 flow control of output */
1174 /* RTS flow control of input */
1176 /* flow control output via Carrier */
1181 bits specify the byte size in bits for both transmission and reception.
1186 and compared with the
1193 This size does not include the parity bit, if any.
1196 is set, two stop bits are used, otherwise one stop bit.
1197 For example, at 110 baud, two stop bits are normally used.
1201 is set, the receiver is enabled.
1202 Otherwise, no character is received.
1203 Not all hardware supports this bit.
1204 In fact, this flag is pretty silly and if it were not part of the
1207 it would be omitted.
1211 is set, parity generation and detection are enabled and a parity
1212 bit is added to each character.
1213 If parity is enabled,
1215 specifies odd parity if set, otherwise even parity is used.
1219 is set, the modem control lines for the port are lowered
1220 when the last process with the port open closes the port or the process
1222 The modem connection is broken.
1226 is set, a connection does not depend on the state of the modem
1230 is clear, the modem status lines are monitored.
1232 Under normal circumstances, a call to the
1234 function waits for the modem connection to complete.
1242 immediately without waiting for the connection.
1247 flag is currently unused.
1251 is set then output flow control is controlled by the state
1254 If the object for which the control modes are set is not an asynchronous
1255 serial connection, some of the modes may be ignored; for example, if an
1256 attempt is made to set the baud rate on a network connection to a
1257 terminal on another host, the baud rate may or may not be set on the
1258 connection between that terminal and the machine it is directly connected
1263 field describe the control of
1264 various functions, and are composed of the following
1267 .Bl -tag -width NOKERNINFO -offset indent -compact
1269 /* visual erase for line kill */
1271 /* visually erase chars */
1273 /* enable echoing */
1281 /* visual erase mode for hardcopy */
1283 /* echo control chars as ^(Char) */
1291 /* canonicalize input lines */
1303 /* external processing */
1305 /* stop background jobs from output */
1307 /* output being flushed (state) */
1309 /* no kernel output from
1313 /* XXX retype pending input (state) */
1315 /* don't flush after interrupt */
1320 is set, input characters are echoed back to the terminal.
1323 is not set, input characters are not echoed.
1331 character causes the terminal
1332 to erase the last character in the current line from the display, if
1334 If there is no character to erase, an implementation may echo
1335 an indication that this was the case or do nothing.
1344 the current line to be discarded and the system echoes the
1357 the current line to be discarded and the system causes
1359 to erase the line from the display.
1365 are set, the system assumes
1366 that the display is a printing device and prints a
1367 backslash and the erased characters when processing
1369 characters, followed by a forward slash.
1373 is set, the system echoes control characters
1374 in a visible fashion using a caret followed by the control character.
1378 is set, the system uses an alternative algorithm
1379 for determining what constitutes a word when processing
1390 character echoes even if
1396 is set, canonical processing is enabled.
1398 erase and kill edit functions, and the assembly of input characters into
1405 .Sx "Canonical Mode Input Processing" .
1409 is not set, read requests are satisfied directly from the input queue.
1410 A read is not satisfied until at least
1413 received or the timeout value
1415 expired between bytes.
1416 The time value represents tenths of seconds.
1418 .Sx "Noncanonical Mode Input Processing"
1423 is set, each input character is checked against the special
1430 If an input character matches one of these control characters, the function
1431 associated with that character is performed.
1434 is not set, no checking is done.
1435 Thus these special input functions are possible only if
1441 is set, implementation-defined functions are recognized from the input data.
1451 is implementation defined.
1455 implementation-defined functions are not recognized, and the
1456 corresponding input characters are not processed as described for
1465 is set, the normal flush of the input and output queues
1478 is sent to the process group of a process that tries to write to
1479 its controlling terminal if it is not in the foreground process group for
1481 This signal, by default, stops the members of the process group.
1482 Otherwise, the output generated by that process is output to the
1483 current output stream.
1484 Processes that are blocking or ignoring
1486 signals are excepted and allowed to produce output and the
1493 is set, the kernel does not produce a status message
1498 .Ss Special Control Characters
1499 The special control characters values are defined by the array
1501 This table lists the array index, the corresponding special character,
1502 and the system default value.
1503 For an accurate list of the system defaults, consult the header file
1504 .In sys/ttydefaults.h .
1506 .Bl -column "Index Name" "Special Character" -offset indent -compact
1507 .It Em "Index Name Special Character Default Value"
1508 .It Dv VEOF Ta EOF Ta \&^D
1509 .It Dv VEOL Ta EOL Ta _POSIX_VDISABLE
1510 .It Dv VEOL2 Ta EOL2 Ta _POSIX_VDISABLE
1511 .It Dv VERASE Ta ERASE Ta \&^? Ql \&\e177
1512 .It Dv VWERASE Ta WERASE Ta \&^W
1513 .It Dv VKILL Ta KILL Ta \&^U
1514 .It Dv VREPRINT Ta REPRINT Ta \&^R
1515 .It Dv VINTR Ta INTR Ta \&^C
1516 .It Dv VQUIT Ta QUIT Ta \&^\e\e Ql \&\e34
1517 .It Dv VSUSP Ta SUSP Ta \&^Z
1518 .It Dv VDSUSP Ta DSUSP Ta \&^Y
1519 .It Dv VSTART Ta START Ta \&^Q
1520 .It Dv VSTOP Ta STOP Ta \&^S
1521 .It Dv VLNEXT Ta LNEXT Ta \&^V
1522 .It Dv VDISCARD Ta DISCARD Ta \&^O
1523 .It Dv VMIN Ta --- Ta \&1
1524 .It Dv VTIME Ta --- Ta \&0
1525 .It Dv VSTATUS Ta STATUS Ta \&^T
1529 value of one of the changeable special control characters (see
1530 .Sx "Special Characters" )
1532 .Dv {_POSIX_VDISABLE} ,
1533 that function is disabled; that is, no input
1534 data is recognized as the disabled special character.
1538 not set, the value of
1539 .Dv {_POSIX_VDISABLE}
1540 has no special meaning for the
1548 The initial values of the flags and control characters
1552 the values in the header
1553 .In sys/ttydefaults.h .