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28 .\" @(#)termios.4 8.4 (Berkeley) 4/19/94
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 an application's standard input, output, and error files.
64 .Ss Job Control in a Nutshell
65 Every process is associated with a particular process group and session.
66 The grouping is hierarchical: every member of a particular process group is a
67 member of the same session.
68 This structuring is used in managing groups
69 of related processes for purposes of
70 .\" .Gw "job control" ;
73 ability from the keyboard (or from program control) to simultaneously
75 a complex command (a command composed of one or more related
77 The grouping into process groups allows delivering
78 of signals that stop or start the group as a whole, along with
79 arbitrating which process group has access to the single controlling
81 The grouping at a higher layer into sessions is to restrict
82 the job control related signals and system calls to within processes
83 resulting from a particular instance of a
86 is created when a user logs in, and the login terminal is setup
87 to be the controlling terminal; all processes spawned from that
88 login shell are in the same session, and inherit the controlling
92 operating interactively (that is, reading commands from a terminal)
93 normally groups related processes together by placing them into the
95 A set of processes in the same process group
96 is collectively referred to as a
98 When the foreground process
99 group of the terminal is the same as the process group of a particular
100 job, that job is said to be in the
102 When the process group of the terminal is different from the process group of
103 a job (but is still the controlling terminal), that job is said
107 shell reads a command and starts the job that implements that
109 If the command is to be started in the foreground (typical), it
110 sets the process group of the terminal to the process group
111 of the started job, waits for the job to complete, and then
112 sets the process group of the terminal back to its own process
113 group (it puts itself into the foreground).
115 be started in the background (as denoted by the shell operator "&"),
116 it never changes the process group of the terminal and does not
117 wait for the job to complete (that is, it immediately attempts to read the next
119 If the job is started in the foreground, the user may
122 which generates the terminal stop signal
124 and has the effect of stopping the entire job.
125 The shell will notice that the job stopped, and will resume running after
126 placing itself in the foreground.
127 The shell also has commands for placing stopped jobs in the background,
128 and for placing stopped or background jobs into the foreground.
129 .Ss Orphaned Process Groups
130 An orphaned process group is a process group that has no process
131 whose parent is in a different process group, yet is in the same
133 Conceptually it means a process group that does not have
134 a parent that could do anything if it were to be stopped.
136 the initial login shell is typically in an orphaned process group.
137 Orphaned process groups are immune to keyboard generated stop
138 signals and job control signals resulting from reads or writes to the
139 controlling terminal.
140 .Ss The Controlling Terminal
141 A terminal may belong to a process as its controlling terminal.
143 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
147 The controlling terminal for a session is allocated by
148 the session leader by issuing the
151 A controlling terminal
152 is never acquired by merely opening a terminal device file.
153 When a controlling terminal becomes
154 associated with a session, its foreground process group is set to
155 the process group of the session leader.
157 The controlling terminal is inherited by a child process during a
160 A process relinquishes its controlling terminal when it
161 creates a new session with the
163 function; other processes
164 remaining in the old session that had this terminal as their controlling
165 terminal continue to have it.
166 A process does not relinquish its
167 controlling terminal simply by closing all of its file descriptors
168 associated with the controlling terminal if other processes continue to
171 When a controlling process terminates, the controlling terminal is
172 disassociated from the current session, allowing it to be acquired by a
174 Subsequent access to the terminal by other processes
175 in the earlier session will be denied, with attempts to access the
176 terminal treated as if modem disconnect had been sensed.
177 .Ss Terminal Access Control
178 If a process is in the foreground process group of its controlling
179 terminal, read operations are allowed.
180 Any attempts by a process
181 in a background process group to read from its controlling terminal
187 following special cases apply: if the reading process is ignoring or
190 signal, or if the process group of the reading
191 process is orphaned, the
199 The default action of the
201 signal is to stop the
202 process to which it is sent.
204 If a process is in the foreground process group of its controlling
205 terminal, write operations are allowed.
206 Attempts by a process in a background process group to write to its
207 controlling terminal will cause the process group to be sent a
209 signal unless one of the following special cases apply: if
214 is set and the process is ignoring or blocking the
216 signal, the process is allowed to write to the terminal and the
221 is set, and the process group of
222 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 \&} ,
248 bytes that may be stored in the input queue.
249 The behavior of the system
250 when this limit is exceeded depends on the setting of the
254 If this flag is set, the terminal
258 character each time a character is received
259 while the input queue is full.
260 Otherwise, the input queue is flushed upon receiving the character.
262 Two general kinds of input processing are available, determined by
263 whether the terminal device file is in canonical mode or noncanonical
266 input characters are processed according to the
271 Such processing can include echoing, which
272 in general means transmitting input characters immediately back to the
273 terminal when they are received from the terminal.
274 This is useful for terminals that can operate in full-duplex mode.
276 The manner in which data is provided to a process reading from a terminal
277 device file is dependent on whether the terminal device file is in
278 canonical or noncanonical mode.
280 Another dependency is whether the
288 flag is clear, then the read request is
289 blocked until data is available or a signal has been received.
292 flag is set, then the read request is completed, without
293 blocking, in one of three ways:
294 .Bl -enum -offset indent
296 If there is enough data available to satisfy the entire request,
297 and the read completes successfully the number of
298 bytes read is returned.
300 If there is not enough data available to satisfy the entire
301 request, and the read completes successfully, having read as
302 much data as possible, the number of bytes read is returned.
304 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"
328 This means that a read request will
329 not return until an entire line has been typed, or a signal has been
331 Also, no matter how many bytes are requested in the read call,
332 at most one line is returned.
333 It is not, however, necessary to
334 read a whole line at once; any number of bytes, even one, may be
335 requested in a read without losing information.
337 .Pf \&{ Dv MAX_CANON Ns \&}
339 number of bytes in a line.
340 The behavior of the system when this limit is
341 exceeded is the same as when the input queue limit
342 .Pf \&{ Dv MAX_INPUT Ns \&} ,
345 Erase and kill processing occur when either of two special characters,
351 .Sx "Special Characters"
352 section), is received.
353 This processing affects data in the input queue that has not yet been
354 delimited by a newline
361 data makes up the current line.
364 character deletes the last
365 character in the current line, if there is any.
369 deletes all data in the current line, if there is any.
374 characters have no effect if there is no data in the current line.
379 characters themselves are not placed in the input
381 .Ss Noncanonical Mode Input Processing
382 In noncanonical mode input processing, input bytes are not assembled into
383 lines, and erase and kill processing does not occur.
390 array are used to determine how to
391 process the bytes received.
394 represents the minimum number of bytes that should be received when
397 function successfully returns.
399 is a timer of 0.1 second
400 granularity that is used to time out bursty and short term data
405 .Dv \&{ Dv MAX_INPUT Ns \&} ,
407 request is undefined.
408 The four possible values for
413 their interactions are described below.
414 .Ss "Case A: MIN > 0, TIME > 0"
417 serves as an inter-byte timer and is activated after
418 the first byte is received.
419 Since it is an inter-byte timer, it is reset
420 after a byte is received.
421 The interaction between
426 follows: as soon as one byte is received, the inter-byte timer is
430 bytes are received before the inter-byte timer expires
431 (remember that the timer is reset upon receipt of each byte), the read is
433 If the timer expires before
435 bytes are received, the
436 characters received to that point are returned to the user.
439 expires at least one byte is returned because the timer would
440 not have been enabled unless a byte was received.
445 > 0) the read blocks until the
450 activated by the receipt of the first byte, or a signal is received.
451 If data is in the buffer at the time of the
454 if data had been received immediately after the
456 .Ss "Case B: MIN > 0, TIME = 0"
457 In this case, since the value of
459 is zero, the timer plays no role
463 A pending read is not satisfied until
465 bytes are received (i.e., the pending read blocks until
468 are received), or a signal is received.
469 A program that uses this case to read record-based terminal
471 may block indefinitely in the read
473 .Ss "Case C: MIN = 0, TIME > 0"
478 no longer represents an inter-byte
480 It now serves as a read timer that is activated as soon as the
481 read function is processed.
482 A read is satisfied as soon as a single
483 byte is received or the read timer expires.
484 Note that in this case if the timer expires, no bytes are returned.
485 If the timer does not
486 expire, the only way the read can be satisfied is if a byte is received.
487 In this case the read will not block indefinitely waiting for a byte; if
488 no byte is received within
490 seconds after the read is initiated,
491 the read returns a value of zero, having read no data.
493 in the buffer at the time of the read, the timer is started as if
494 data had been received immediately after the read.
495 .Ss Case D: MIN = 0, TIME = 0
496 The minimum of either the number of bytes requested or the number of
497 bytes currently available is returned without waiting for more
499 If no characters are available, read returns a
500 value of zero, having read no data.
501 .Ss Writing Data and Output Processing
502 When a process writes one or more bytes to a terminal device file, they
503 are processed according to the
509 implementation may provide a buffering mechanism; as such, when a call to
511 completes, all of the bytes written have been scheduled for
512 transmission to the device, but the transmission will not necessarily
514 .\" See also .Sx "6.4.2" for the effects of
517 .Ss Special Characters
518 Certain characters have special functions on input or output or both.
519 These functions are summarized as follows:
520 .Bl -tag -width indent
522 Special character on input and is recognized if the
529 signal which is sent to all processes in the foreground
530 process group for which the terminal is the controlling
537 discarded when processed.
539 Special character on input and is recognized if the
545 sent to all processes in the foreground process group
546 for which the terminal is the controlling terminal.
551 character is discarded when
554 Special character on input and is recognized if the
557 Erases the last character in the
559 .Sx "Canonical Mode Input Processing" .
560 It does not erase beyond
561 the start of a line, as delimited by an
572 discarded when processed.
574 Special character on input and is recognized if the
577 Deletes the entire line, as
588 character is discarded when processed.
590 Special character on input and is recognized if the
593 When received, all the bytes
594 waiting to be read are immediately passed to the
595 process, without waiting for a newline, and the
598 Thus, if there are no bytes waiting (that is, the
600 occurred at the beginning of a line), a byte
601 count of zero is returned from the
603 representing an end-of-file indication.
609 character is discarded when processed.
611 Special character on input and is recognized if the
614 It is the line delimiter
617 Special character on input and is recognized if the
620 Is an additional line delimiter, like
625 flag is enabled, receipt of the
629 signal to be sent to all processes in the
630 foreground process group for which the terminal is the
631 controlling terminal, and the
634 discarded when processed.
636 Special character on both input and output and is
642 control) flag is set.
643 Can be used to temporarily suspend output.
644 It is useful with fast terminals to
645 prevent output from disappearing before it can be read.
650 character is discarded when
653 Special character on both input and output and is
659 control) flag is set.
660 Can be used to resume output that has been suspended by a
667 character is discarded when processed.
669 Special character on input and is recognized if the
671 flag is set; it is the
682 is not set, this character is translated into a
685 has the same effect as a
690 The following special characters are extensions defined by this
691 system and are not a part of
694 .Bl -tag -width indent
702 Special character on input and is recognized if the
705 Erases the last word in the current line according to one of two algorithms.
708 flag is not set, first any preceding whitespace is
709 erased, and then the maximal sequence of non-whitespace
713 is set, first any preceding
714 whitespace is erased, and then the maximal sequence
715 of alphabetic/underscores or non alphabetic/underscores.
716 As a special case in this second algorithm, the first previous
717 non-whitespace character is skipped in determining
718 whether the preceding word is a sequence of
719 alphabetic/underscores.
720 This sounds confusing but turns out to be quite practical.
722 Special character on input and is recognized if the
725 Causes the current input edit line to be retyped.
727 Has similar actions to the
729 character, except that
732 signal is delivered when one of the processes
733 in the foreground process group issues a
736 controlling terminal.
738 Special character on input and is recognized if the
741 Receipt of this character causes the next character to be taken literally.
743 Special character on input and is recognized if the
746 Receipt of this character toggles the flushing of terminal output.
748 Special character on input and is recognized if the
751 Receipt of this character causes a
753 signal to be sent to the foreground process group of the
758 causes the kernel to write a status message to the terminal
759 that displays the current load average, the name of the
760 command in the foreground, its process ID, the symbolic
761 wait channel, the number of user and system seconds used,
762 the percentage of cpu the process is getting, and the resident
763 set size of the process.
768 .Va kern.tty_info_kstacks
769 is set to a non-zero value, the running thread's kernel stack is
770 written to the terminal (e.g., for debugging purposes).
777 characters cannot be changed.
778 The values for all the remaining characters can be set and are
779 described later in the document under
780 Special Control Characters.
783 character functions associated with changeable special control characters
784 can be disabled individually by setting their value to
785 .Dv {_POSIX_VDISABLE} ;
787 .Sx "Special Control Characters" .
789 If two or more special characters have the same value, the function
790 performed when that character is received is undefined.
792 If a modem disconnect is detected by the terminal interface for a
793 controlling terminal, and if
800 signal is sent to the controlling
801 process associated with the terminal.
802 Unless other arrangements have
803 been made, this causes the controlling process to terminate.
804 Any subsequent call to the
806 function returns the value zero,
807 indicating end of file.
808 Thus, processes that read a terminal
809 file and test for end-of-file can terminate appropriately after a
813 .\" condition specified in 6.1.1.4 that applies
814 .\" when the implementation supports job control also exists, it is
815 .\" unspecified whether the
823 to the terminal device returns -1, with
827 until the device is closed.
828 .Sh General Terminal Interface
829 .Ss Closing a Terminal Device File
830 The last process to close a terminal device file causes any output
831 to be sent to the device and any input to be discarded.
834 is set in the control modes, and the communications port supports a
835 disconnect function, the terminal device performs a disconnect.
836 .Ss Parameters That Can Be Set
837 Routines that need to control certain terminal
840 do so by using the termios structure as defined in the header
842 This structure contains minimally four scalar elements of bit flags
843 and one array of special characters.
844 The scalar flag elements are named:
850 The character array is named
852 and its maximum index is
857 field describe the basic
858 terminal input control, and are composed of
861 .Bl -tag -width IMAXBEL -offset indent -compact
863 /* ignore BREAK condition */
865 /* map BREAK to SIGINTR */
867 /* ignore (discard) parity errors */
869 /* mark parity and framing errors */
871 /* enable checking of parity errors */
873 /* strip 8th bit off chars */
879 /* map CR to NL (ala CRMOD) */
881 /* enable output flow control */
883 /* enable input flow control */
885 /* any char will restart after stop */
887 /* ring bell on input queue full */
890 In the context of asynchronous serial data transmission, a break
891 condition is defined as a sequence of zero-valued bits that continues for
892 more than the time to send one byte.
893 The entire sequence of zero-valued
894 bits is interpreted as a single break condition, even if it continues for
895 a time equivalent to more than one byte.
896 In contexts other than
897 asynchronous serial data transmission the definition of a break condition
898 is implementation defined.
902 is set, a break condition detected on input is ignored, that
903 is, not put on the input queue and therefore not read by any process.
908 is set, the break condition flushes the
909 input and output queues and if the terminal is the controlling terminal
910 of a foreground process group, the break condition generates a
913 signal to that foreground process group.
918 is set, a break condition is read as a single
929 is set, a byte with a framing or parity error (other than
936 is not set, a byte with a framing or parity
937 error (other than break) is given to the application as the
938 three-character sequence
945 flag preceding each sequence and X is the data of the character received
947 To avoid ambiguity in this case, if
952 is given to the application as
960 is set, a framing or parity error (other than
961 break) is given to the application as a single character
966 is set, input parity checking is enabled.
970 input parity checking is disabled, allowing output parity generation
971 without input parity errors.
972 Note that whether input parity checking is
973 enabled or disabled is independent of whether parity detection is enabled
975 .Sx "Control Modes" ) .
976 If parity detection is enabled but input
977 parity checking is disabled, the hardware to which the terminal is
978 connected recognizes the parity bit, but the terminal special file
979 does not check whether this bit is set correctly or not.
983 is set, valid input bytes are first stripped to seven bits,
984 otherwise all eight bits are processed.
990 character is translated into a
997 character is ignored (not
1012 is set, start/stop output control is enabled.
1015 character suspends output and a received
1021 is also set, then any character may
1030 read, but merely perform flow control functions.
1038 characters are read.
1042 is set, start/stop input control is enabled.
1043 The system shall transmit one or more
1045 characters, which are intended to cause the
1046 terminal device to stop transmitting data, as needed to prevent the input
1047 queue from overflowing and causing the undefined behavior described in
1048 .Sx "Input Processing and Reading Data" ,
1049 and shall transmit one or more
1051 characters, which are
1052 intended to cause the terminal device to resume transmitting data, as
1053 soon as the device can continue transmitting data without risk of
1054 overflowing the input queue.
1055 The precise conditions under which
1059 characters are transmitted are implementation defined.
1063 is set and the input queue is full, subsequent input shall cause an
1066 character to be transmitted to
1069 The initial input control value after
1071 is implementation defined.
1075 field describe the basic terminal output control,
1076 and are composed of the following masks:
1078 .Bl -tag -width ONOEOT -offset indent -compact
1080 /* enable following output processing */
1082 /* map NL to CR-NL (ala
1088 /* tab delay mask */
1090 /* no tab delay and expansion */
1092 /* expand tabs to spaces */
1099 /* do not transmit CRs on column 0 */
1101 /* on the terminal NL performs the CR function */
1106 is set, the remaining flag masks are interpreted as follows;
1107 otherwise characters are transmitted without change.
1111 is set, newlines are translated to carriage return, linefeeds.
1115 is set, carriage returns are translated to newlines.
1119 bits specify the tab delay.
1124 and compared with the
1131 is set, tabs are expanded to the appropriate number of
1132 spaces (assuming 8 column tab stops).
1139 are discarded on output.
1143 is set, no CR character is transmitted when at column 0 (first position).
1147 is set, the NL character is assumed to do the carriage-return function;
1148 the column pointer will be set to 0.
1152 field describe the basic
1153 terminal hardware control, and are composed of the
1156 specified are supported by all hardware.
1158 .Bl -tag -width CRTSXIFLOW -offset indent -compact
1160 /* character size mask */
1162 /* 5 bits (pseudo) */
1170 /* send 2 stop bits */
1172 /* enable receiver */
1176 /* odd parity, else even */
1178 /* hang up on last close */
1180 /* ignore modem status lines */
1184 flow control of output */
1190 /* RTS flow control of input */
1192 /* flow control output via Carrier */
1194 /* Do not assert RTS or DTR automatically */
1199 bits specify the byte size in bits for both transmission and
1205 and compared with the
1212 This size does not include the parity bit, if any.
1215 is set, two stop bits are used, otherwise one stop bit.
1216 For example, at 110 baud, two stop bits are normally used.
1220 is set, the receiver is enabled.
1221 Otherwise, no character is received.
1222 Not all hardware supports this bit.
1223 In fact, this flag is pretty silly and if it were not part of the
1226 it would be omitted.
1230 is set, parity generation and detection are enabled and a parity
1231 bit is added to each character.
1232 If parity is enabled,
1235 odd parity if set, otherwise even parity is used.
1239 is set, the modem control lines for the port are lowered
1240 when the last process with the port open closes the port or the process
1242 The modem connection is broken.
1246 is set, a connection does not depend on the state of the modem
1250 is clear, the modem status lines are
1253 Under normal circumstances, a call to the
1256 the modem connection to complete.
1265 immediately without waiting for the connection.
1270 flag is currently unused.
1274 is set then output flow control is controlled by the state
1279 is set then the RTS and DTR lines will not be asserted when the device
1281 As a result, this flag is only useful on initial-state devices.
1283 If the object for which the control modes are set is not an asynchronous
1284 serial connection, some of the modes may be ignored; for example, if an
1285 attempt is made to set the baud rate on a network connection to a
1286 terminal on another host, the baud rate may or may not be set on the
1287 connection between that terminal and the machine it is directly connected
1292 field describe the control of
1293 various functions, and are composed of the following
1296 .Bl -tag -width NOKERNINFO -offset indent -compact
1298 /* visual erase for line kill */
1300 /* visually erase chars */
1302 /* enable echoing */
1310 /* visual erase mode for hardcopy */
1312 /* echo control chars as ^(Char) */
1320 /* canonicalize input lines */
1332 /* external processing */
1334 /* stop background jobs from output */
1336 /* output being flushed (state) */
1338 /* no kernel output from
1342 /* XXX retype pending input (state) */
1344 /* don't flush after interrupt */
1349 is set, input characters are echoed back to the terminal.
1352 is not set, input characters are not echoed.
1360 character causes the terminal
1361 to erase the last character in the current line from the display, if
1363 If there is no character to erase, an implementation may echo
1364 an indication that this was the case or do nothing.
1373 the current line to be discarded and the system echoes the
1386 the current line to be discarded and the system causes
1388 to erase the line from the display.
1394 are set, the system assumes
1395 that the display is a printing device and prints a
1396 backslash and the erased characters when processing
1398 characters, followed by a forward slash.
1402 is set, the system echoes control characters
1403 in a visible fashion using a caret followed by the control character.
1407 is set, the system uses an alternative algorithm
1408 for determining what constitutes a word when processing
1419 character echoes even if
1425 is set, canonical processing is enabled.
1427 erase and kill edit functions, and the assembly of input characters into
1434 .Sx "Canonical Mode Input Processing" .
1438 is not set, read requests are satisfied directly from the input
1440 A read is not satisfied until at least
1443 received or the timeout value
1445 expired between bytes.
1447 represents tenths of seconds.
1449 .Sx "Noncanonical Mode Input Processing"
1454 is set, each input character is checked against the special
1462 character matches one of these control characters, the function
1463 associated with that character is performed.
1468 Thus these special input functions are possible only
1475 is set, implementation-defined functions are recognized
1476 from the input data.
1486 is implementation defined.
1490 implementation-defined functions are not recognized, and the
1491 corresponding input characters are not processed as described for
1500 is set, the normal flush of the input and output queues
1513 is sent to the process group of a process that tries to write to
1514 its controlling terminal if it is not in the foreground process group for
1516 This signal, by default, stops the members of the process group.
1517 Otherwise, the output generated by that process is output to the
1518 current output stream.
1519 Processes that are blocking or ignoring
1521 signals are excepted and allowed to produce output and the
1528 is set, the kernel does not produce a status message
1533 .Ss Special Control Characters
1534 The special control characters values are defined by the array
1536 This table lists the array index, the corresponding special character,
1537 and the system default value.
1538 For an accurate list of
1539 the system defaults, consult the header file
1540 .In sys/ttydefaults.h .
1542 .Bl -column "Index Name" "Special Character" -offset indent -compact
1543 .It Em "Index Name Special Character Default Value"
1544 .It Dv VEOF Ta EOF Ta \&^D
1545 .It Dv VEOL Ta EOL Ta _POSIX_VDISABLE
1546 .It Dv VEOL2 Ta EOL2 Ta _POSIX_VDISABLE
1547 .It Dv VERASE Ta ERASE Ta \&^? Ql \&\e177
1548 .It Dv VWERASE Ta WERASE Ta \&^W
1549 .It Dv VKILL Ta KILL Ta \&^U
1550 .It Dv VREPRINT Ta REPRINT Ta \&^R
1551 .It Dv VINTR Ta INTR Ta \&^C
1552 .It Dv VQUIT Ta QUIT Ta \&^\e\e Ql \&\e34
1553 .It Dv VSUSP Ta SUSP Ta \&^Z
1554 .It Dv VDSUSP Ta DSUSP Ta \&^Y
1555 .It Dv VSTART Ta START Ta \&^Q
1556 .It Dv VSTOP Ta STOP Ta \&^S
1557 .It Dv VLNEXT Ta LNEXT Ta \&^V
1558 .It Dv VDISCARD Ta DISCARD Ta \&^O
1559 .It Dv VMIN Ta --- Ta \&1
1560 .It Dv VTIME Ta --- Ta \&0
1561 .It Dv VSTATUS Ta STATUS Ta \&^T
1565 value of one of the changeable special control characters (see
1566 .Sx "Special Characters" )
1568 .Dv {_POSIX_VDISABLE} ,
1569 that function is disabled; that is, no input
1570 data is recognized as the disabled special character.
1574 not set, the value of
1575 .Dv {_POSIX_VDISABLE}
1576 has no special meaning for the
1584 The initial values of the flags and control characters
1588 the values in the header
1589 .In sys/ttydefaults.h .
1593 .Xr tcgetwinsize 3 ,