1TERMIOS(3) Linux Programmer's Manual TERMIOS(3)
2
6 termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow,
7 cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfset‐
8 speed - get and set terminal attributes, line control, get and set baud
9 rate
10
12 #include <termios.h>
13 #include <unistd.h>
14 int tcgetattr(int fd, struct termios *termios_p);
16 int tcsetattr(int fd, int optional_actions,
17 const struct termios *termios_p);
18 int tcsendbreak(int fd, int duration);
20 int tcdrain(int fd);
21 int tcflush(int fd, int queue_selector);
22 int tcflow(int fd, int action);
23 void cfmakeraw(struct termios *termios_p);
25 speed_t cfgetispeed(const struct termios *termios_p);
27 speed_t cfgetospeed(const struct termios *termios_p);
28 int cfsetispeed(struct termios *termios_p, speed_t speed);
30 int cfsetospeed(struct termios *termios_p, speed_t speed);
31 int cfsetspeed(struct termios *termios_p, speed_t speed);
32 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
34 cfsetspeed(), cfmakeraw():
36 Since glibc 2.19:
37 _DEFAULT_SOURCE
38 Glibc 2.19 and earlier:
39 _BSD_SOURCE
40
42 The termios functions describe a general terminal interface that is
43 provided to control asynchronous communications ports.
44 The termios structure
46 Many of the functions described here have a termios_p argument that is
47 a pointer to a termios structure. This structure contains at least the
48 following members:
49 tcflag_t c_iflag; /* input modes */
51 tcflag_t c_oflag; /* output modes */
52 tcflag_t c_cflag; /* control modes */
53 tcflag_t c_lflag; /* local modes */
54 cc_t c_cc[NCCS]; /* special characters */
55 The values that may be assigned to these fields are described below.
57 In the case of the first four bit-mask fields, the definitions of some
58 of the associated flags that may be set are exposed only if a specific
59 feature test macro (see feature_test_macros(7)) is defined, as noted in
60 brackets ("[]").
61 In the descriptions below, "not in POSIX" means that the value is not
63 specified in POSIX.1-2001, and "XSI" means that the value is specified
64 in POSIX.1-2001 as part of the XSI extension.
65 c_iflag flag constants:
67 IGNBRK Ignore BREAK condition on input.
69 BRKINT If IGNBRK is set, a BREAK is ignored. If it is not set but
71 BRKINT is set, then a BREAK causes the input and output queues
72 to be flushed, and if the terminal is the controlling terminal
73 of a foreground process group, it will cause a SIGINT to be sent
74 to this foreground process group. When neither IGNBRK nor
75 BRKINT are set, a BREAK reads as a null byte ('\0'), except when
76 PARMRK is set, in which case it reads as the sequence \377 \0
77 \0.
78 IGNPAR Ignore framing errors and parity errors.
80 PARMRK If this bit is set, input bytes with parity or framing errors
82 are marked when passed to the program. This bit is meaningful
83 only when INPCK is set and IGNPAR is not set. The way erroneous
84 bytes are marked is with two preceding bytes, \377 and \0.
85 Thus, the program actually reads three bytes for one erroneous
86 byte received from the terminal. If a valid byte has the value
87 \377, and ISTRIP (see below) is not set, the program might con‐
88 fuse it with the prefix that marks a parity error. Therefore, a
89 valid byte \377 is passed to the program as two bytes, \377
90 \377, in this case.
91 If neither IGNPAR nor PARMRK is set, read a character with a
93 parity error or framing error as \0.
94 INPCK Enable input parity checking.
96 ISTRIP Strip off eighth bit.
98 INLCR Translate NL to CR on input.
100 IGNCR Ignore carriage return on input.
102 ICRNL Translate carriage return to newline on input (unless IGNCR is
104 set).
105 IUCLC (not in POSIX) Map uppercase characters to lowercase on input.
107 IXON Enable XON/XOFF flow control on output.
109 IXANY (XSI) Typing any character will restart stopped output. (The
111 default is to allow just the START character to restart output.)
112 IXOFF Enable XON/XOFF flow control on input.
114 IMAXBEL
116 (not in POSIX) Ring bell when input queue is full. Linux does
117 not implement this bit, and acts as if it is always set.
118 IUTF8 (since Linux 2.6.4)
120 (not in POSIX) Input is UTF8; this allows character-erase to be
121 correctly performed in cooked mode.
122 c_oflag flag constants:
124 OPOST Enable implementation-defined output processing.
126 OLCUC (not in POSIX) Map lowercase characters to uppercase on output.
128 ONLCR (XSI) Map NL to CR-NL on output.
130 OCRNL Map CR to NL on output.
132 ONOCR Don't output CR at column 0.
134 ONLRET Don't output CR.
136 OFILL Send fill characters for a delay, rather than using a timed de‐
138 lay.
139 OFDEL Fill character is ASCII DEL (0177). If unset, fill character is
141 ASCII NUL ('\0'). (Not implemented on Linux.)
142 NLDLY Newline delay mask. Values are NL0 and NL1. [requires
144 _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
145 CRDLY Carriage return delay mask. Values are CR0, CR1, CR2, or CR3.
147 [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
148 TABDLY Horizontal tab delay mask. Values are TAB0, TAB1, TAB2, TAB3
150 (or XTABS, but see the BUGS section). A value of TAB3, that is,
151 XTABS, expands tabs to spaces (with tab stops every eight col‐
152 umns). [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
153 BSDLY Backspace delay mask. Values are BS0 or BS1. (Has never been
155 implemented.) [requires _BSD_SOURCE or _SVID_SOURCE or
156 _XOPEN_SOURCE]
157 VTDLY Vertical tab delay mask. Values are VT0 or VT1.
159 FFDLY Form feed delay mask. Values are FF0 or FF1. [requires
161 _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
162 c_cflag flag constants:
164 CBAUD (not in POSIX) Baud speed mask (4+1 bits). [requires
166 _BSD_SOURCE or _SVID_SOURCE]
167 CBAUDEX
169 (not in POSIX) Extra baud speed mask (1 bit), included in CBAUD.
170 [requires _BSD_SOURCE or _SVID_SOURCE]
171 (POSIX says that the baud speed is stored in the termios struc‐
173 ture without specifying where precisely, and provides
174 cfgetispeed() and cfsetispeed() for getting at it. Some systems
175 use bits selected by CBAUD in c_cflag, other systems use sepa‐
176 rate fields, for example, sg_ispeed and sg_ospeed.)
177 CSIZE Character size mask. Values are CS5, CS6, CS7, or CS8.
179 CSTOPB Set two stop bits, rather than one.
181 CREAD Enable receiver.
183 PARENB Enable parity generation on output and parity checking for in‐
185 put.
186 PARODD If set, then parity for input and output is odd; otherwise even
188 parity is used.
189 HUPCL Lower modem control lines after last process closes the device
191 (hang up).
192 CLOCAL Ignore modem control lines.
194 LOBLK (not in POSIX) Block output from a noncurrent shell layer. For
196 use by shl (shell layers). (Not implemented on Linux.)
197 CIBAUD (not in POSIX) Mask for input speeds. The values for the CIBAUD
199 bits are the same as the values for the CBAUD bits, shifted left
200 IBSHIFT bits. [requires _BSD_SOURCE or _SVID_SOURCE] (Not im‐
201 plemented on Linux.)
202 CMSPAR (not in POSIX) Use "stick" (mark/space) parity (supported on
204 certain serial devices): if PARODD is set, the parity bit is al‐
205 ways 1; if PARODD is not set, then the parity bit is always 0.
206 [requires _BSD_SOURCE or _SVID_SOURCE]
207 CRTSCTS
209 (not in POSIX) Enable RTS/CTS (hardware) flow control. [re‐
210 quires _BSD_SOURCE or _SVID_SOURCE]
211 c_lflag flag constants:
213 ISIG When any of the characters INTR, QUIT, SUSP, or DSUSP are re‐
215 ceived, generate the corresponding signal.
216 ICANON Enable canonical mode (described below).
218 XCASE (not in POSIX; not supported under Linux) If ICANON is also set,
220 terminal is uppercase only. Input is converted to lowercase,
221 except for characters preceded by \. On output, uppercase char‐
222 acters are preceded by \ and lowercase characters are converted
223 to uppercase. [requires _BSD_SOURCE or _SVID_SOURCE or
224 _XOPEN_SOURCE]
225 ECHO Echo input characters.
227 ECHOE If ICANON is also set, the ERASE character erases the preceding
229 input character, and WERASE erases the preceding word.
230 ECHOK If ICANON is also set, the KILL character erases the current
232 line.
233 ECHONL If ICANON is also set, echo the NL character even if ECHO is not
235 set.
236 ECHOCTL
238 (not in POSIX) If ECHO is also set, terminal special characters
239 other than TAB, NL, START, and STOP are echoed as ^X, where X is
240 the character with ASCII code 0x40 greater than the special
241 character. For example, character 0x08 (BS) is echoed as ^H.
242 [requires _BSD_SOURCE or _SVID_SOURCE]
243 ECHOPRT
245 (not in POSIX) If ICANON and ECHO are also set, characters are
246 printed as they are being erased. [requires _BSD_SOURCE or
247 _SVID_SOURCE]
248 ECHOKE (not in POSIX) If ICANON is also set, KILL is echoed by erasing
250 each character on the line, as specified by ECHOE and ECHOPRT.
251 [requires _BSD_SOURCE or _SVID_SOURCE]
252 DEFECHO
254 (not in POSIX) Echo only when a process is reading. (Not imple‐
255 mented on Linux.)
256 FLUSHO (not in POSIX; not supported under Linux) Output is being
258 flushed. This flag is toggled by typing the DISCARD character.
259 [requires _BSD_SOURCE or _SVID_SOURCE]
260 NOFLSH Disable flushing the input and output queues when generating
262 signals for the INT, QUIT, and SUSP characters.
263 TOSTOP Send the SIGTTOU signal to the process group of a background
265 process which tries to write to its controlling terminal.
266 PENDIN (not in POSIX; not supported under Linux) All characters in the
268 input queue are reprinted when the next character is read.
269 (bash(1) handles typeahead this way.) [requires _BSD_SOURCE or
270 _SVID_SOURCE]
271 IEXTEN Enable implementation-defined input processing. This flag, as
273 well as ICANON must be enabled for the special characters EOL2,
274 LNEXT, REPRINT, WERASE to be interpreted, and for the IUCLC flag
275 to be effective.
276 The c_cc array defines the terminal special characters. The symbolic
278 indices (initial values) and meaning are:
279 VDISCARD
281 (not in POSIX; not supported under Linux; 017, SI, Ctrl-O) Tog‐
282 gle: start/stop discarding pending output. Recognized when IEX‐
283 TEN is set, and then not passed as input.
284 VDSUSP (not in POSIX; not supported under Linux; 031, EM, Ctrl-Y) De‐
286 layed suspend character (DSUSP): send SIGTSTP signal when the
287 character is read by the user program. Recognized when IEXTEN
288 and ISIG are set, and the system supports job control, and then
289 not passed as input.
290 VEOF (004, EOT, Ctrl-D) End-of-file character (EOF). More precisely:
292 this character causes the pending tty buffer to be sent to the
293 waiting user program without waiting for end-of-line. If it is
294 the first character of the line, the read(2) in the user program
295 returns 0, which signifies end-of-file. Recognized when ICANON
296 is set, and then not passed as input.
297 VEOL (0, NUL) Additional end-of-line character (EOL). Recognized
299 when ICANON is set.
300 VEOL2 (not in POSIX; 0, NUL) Yet another end-of-line character (EOL2).
302 Recognized when ICANON is set.
303 VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase charac‐
305 ter (ERASE). This erases the previous not-yet-erased character,
306 but does not erase past EOF or beginning-of-line. Recognized
307 when ICANON is set, and then not passed as input.
308 VINTR (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt charac‐
310 ter (INTR). Send a SIGINT signal. Recognized when ISIG is set,
311 and then not passed as input.
312 VKILL (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character (KILL).
314 This erases the input since the last EOF or beginning-of-line.
315 Recognized when ICANON is set, and then not passed as input.
316 VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal next (LNEXT). Quotes
318 the next input character, depriving it of a possible special
319 meaning. Recognized when IEXTEN is set, and then not passed as
320 input.
321 VMIN Minimum number of characters for noncanonical read (MIN).
323 VQUIT (034, FS, Ctrl-\) Quit character (QUIT). Send SIGQUIT signal.
325 Recognized when ISIG is set, and then not passed as input.
326 VREPRINT
328 (not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters (RE‐
329 PRINT). Recognized when ICANON and IEXTEN are set, and then not
330 passed as input.
331 VSTART (021, DC1, Ctrl-Q) Start character (START). Restarts output
333 stopped by the Stop character. Recognized when IXON is set, and
334 then not passed as input.
335 VSTATUS
337 (not in POSIX; not supported under Linux; status request: 024,
338 DC4, Ctrl-T). Status character (STATUS). Display status infor‐
339 mation at terminal, including state of foreground process and
340 amount of CPU time it has consumed. Also sends a SIGINFO signal
341 (not supported on Linux) to the foreground process group.
342 VSTOP (023, DC3, Ctrl-S) Stop character (STOP). Stop output until
344 Start character typed. Recognized when IXON is set, and then
345 not passed as input.
346 VSUSP (032, SUB, Ctrl-Z) Suspend character (SUSP). Send SIGTSTP sig‐
348 nal. Recognized when ISIG is set, and then not passed as input.
349 VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch charac‐
351 ter (SWTCH). Used in System V to switch shells in shell layers,
352 a predecessor to shell job control.
353 VTIME Timeout in deciseconds for noncanonical read (TIME).
355 VWERASE
357 (not in POSIX; 027, ETB, Ctrl-W) Word erase (WERASE). Recog‐
358 nized when ICANON and IEXTEN are set, and then not passed as in‐
359 put.
360 An individual terminal special character can be disabled by setting the
362 value of the corresponding c_cc element to _POSIX_VDISABLE.
363 The above symbolic subscript values are all different, except that
365 VTIME, VMIN may have the same value as VEOL, VEOF, respectively. In
366 noncanonical mode the special character meaning is replaced by the
367 timeout meaning. For an explanation of VMIN and VTIME, see the de‐
368 scription of noncanonical mode below.
369 Retrieving and changing terminal settings
371 tcgetattr() gets the parameters associated with the object referred by
372 fd and stores them in the termios structure referenced by termios_p.
373 This function may be invoked from a background process; however, the
374 terminal attributes may be subsequently changed by a foreground
375 process.
376 tcsetattr() sets the parameters associated with the terminal (unless
378 support is required from the underlying hardware that is not available)
379 from the termios structure referred to by termios_p. optional_actions
380 specifies when the changes take effect:
381 TCSANOW
383 the change occurs immediately.
384 TCSADRAIN
386 the change occurs after all output written to fd has been trans‐
387 mitted. This option should be used when changing parameters
388 that affect output.
389 TCSAFLUSH
391 the change occurs after all output written to the object re‐
392 ferred by fd has been transmitted, and all input that has been
393 received but not read will be discarded before the change is
394 made.
395 Canonical and noncanonical mode
397 The setting of the ICANON canon flag in c_lflag determines whether the
398 terminal is operating in canonical mode (ICANON set) or noncanonical
399 mode (ICANON unset). By default, ICANON is set.
400 In canonical mode:
402 * Input is made available line by line. An input line is available
404 when one of the line delimiters is typed (NL, EOL, EOL2; or EOF at
405 the start of line). Except in the case of EOF, the line delimiter is
406 included in the buffer returned by read(2).
407 * Line editing is enabled (ERASE, KILL; and if the IEXTEN flag is set:
409 WERASE, REPRINT, LNEXT). A read(2) returns at most one line of in‐
410 put; if the read(2) requested fewer bytes than are available in the
411 current line of input, then only as many bytes as requested are read,
412 and the remaining characters will be available for a future read(2).
413 * The maximum line length is 4096 chars (including the terminating new‐
415 line character); lines longer than 4096 chars are truncated. After
416 4095 characters, input processing (e.g., ISIG and ECHO* processing)
417 continues, but any input data after 4095 characters up to (but not
418 including) any terminating newline is discarded. This ensures that
419 the terminal can always receive more input until at least one line
420 can be read.
421 In noncanonical mode input is available immediately (without the user
423 having to type a line-delimiter character), no input processing is per‐
424 formed, and line editing is disabled. The read buffer will only accept
425 4095 chars; this provides the necessary space for a newline char if the
426 input mode is switched to canonical. The settings of MIN (c_cc[VMIN])
427 and TIME (c_cc[VTIME]) determine the circumstances in which a read(2)
428 completes; there are four distinct cases:
429 MIN == 0, TIME == 0 (polling read)
431 If data is available, read(2) returns immediately, with the
432 lesser of the number of bytes available, or the number of bytes
433 requested. If no data is available, read(2) returns 0.
434 MIN > 0, TIME == 0 (blocking read)
436 read(2) blocks until MIN bytes are available, and returns up to
437 the number of bytes requested.
438 MIN == 0, TIME > 0 (read with timeout)
440 TIME specifies the limit for a timer in tenths of a second. The
441 timer is started when read(2) is called. read(2) returns either
442 when at least one byte of data is available, or when the timer
443 expires. If the timer expires without any input becoming avail‐
444 able, read(2) returns 0. If data is already available at the
445 time of the call to read(2), the call behaves as though the data
446 was received immediately after the call.
447 MIN > 0, TIME > 0 (read with interbyte timeout)
449 TIME specifies the limit for a timer in tenths of a second.
450 Once an initial byte of input becomes available, the timer is
451 restarted after each further byte is received. read(2) returns
452 when any of the following conditions is met:
453 * MIN bytes have been received.
455 * The interbyte timer expires.
457 * The number of bytes requested by read(2) has been received.
459 (POSIX does not specify this termination condition, and on
460 some other implementations read(2) does not return in this
461 case.)
462 Because the timer is started only after the initial byte becomes
464 available, at least one byte will be read. If data is already
465 available at the time of the call to read(2), the call behaves
466 as though the data was received immediately after the call.
467 POSIX does not specify whether the setting of the O_NONBLOCK file sta‐
469 tus flag takes precedence over the MIN and TIME settings. If O_NON‐
470 BLOCK is set, a read(2) in noncanonical mode may return immediately,
471 regardless of the setting of MIN or TIME. Furthermore, if no data is
472 available, POSIX permits a read(2) in noncanonical mode to return ei‐
473 ther 0, or -1 with errno set to EAGAIN.
474 Raw mode
476 cfmakeraw() sets the terminal to something like the "raw" mode of the
477 old Version 7 terminal driver: input is available character by charac‐
478 ter, echoing is disabled, and all special processing of terminal input
479 and output characters is disabled. The terminal attributes are set as
480 follows:
481 termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
483 | INLCR | IGNCR | ICRNL | IXON);
484 termios_p->c_oflag &= ~OPOST;
485 termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
486 termios_p->c_cflag &= ~(CSIZE | PARENB);
487 termios_p->c_cflag |= CS8;
488 Line control
490 tcsendbreak() transmits a continuous stream of zero-valued bits for a
491 specific duration, if the terminal is using asynchronous serial data
492 transmission. If duration is zero, it transmits zero-valued bits for
493 at least 0.25 seconds, and not more than 0.5 seconds. If duration is
494 not zero, it sends zero-valued bits for some implementation-defined
495 length of time.
496 If the terminal is not using asynchronous serial data transmission, tc‐
498 sendbreak() returns without taking any action.
499 tcdrain() waits until all output written to the object referred to by
501 fd has been transmitted.
502 tcflush() discards data written to the object referred to by fd but not
504 transmitted, or data received but not read, depending on the value of
505 queue_selector:
506 TCIFLUSH
508 flushes data received but not read.
509 TCOFLUSH
511 flushes data written but not transmitted.
512 TCIOFLUSH
514 flushes both data received but not read, and data written but
515 not transmitted.
516 tcflow() suspends transmission or reception of data on the object re‐
518 ferred to by fd, depending on the value of action:
519 TCOOFF suspends output.
521 TCOON restarts suspended output.
523 TCIOFF transmits a STOP character, which stops the terminal device from
525 transmitting data to the system.
526 TCION transmits a START character, which starts the terminal device
528 transmitting data to the system.
529 The default on open of a terminal file is that neither its input nor
531 its output is suspended.
532 Line speed
534 The baud rate functions are provided for getting and setting the values
535 of the input and output baud rates in the termios structure. The new
536 values do not take effect until tcsetattr() is successfully called.
537 Setting the speed to B0 instructs the modem to "hang up". The actual
539 bit rate corresponding to B38400 may be altered with setserial(8).
540 The input and output baud rates are stored in the termios structure.
542 cfgetospeed() returns the output baud rate stored in the termios struc‐
544 ture pointed to by termios_p.
545 cfsetospeed() sets the output baud rate stored in the termios structure
547 pointed to by termios_p to speed, which must be one of these constants:
548 B0
550 B50
551 B75
552 B110
553 B134
554 B150
555 B200
556 B300
557 B600
558 B1200
559 B1800
560 B2400
561 B4800
562 B9600
563 B19200
564 B38400
565 B57600
566 B115200
567 B230400
568 The zero baud rate, B0, is used to terminate the connection. If B0 is
570 specified, the modem control lines shall no longer be asserted. Nor‐
571 mally, this will disconnect the line. CBAUDEX is a mask for the speeds
572 beyond those defined in POSIX.1 (57600 and above). Thus, B57600 &
573 CBAUDEX is nonzero.
574 cfgetispeed() returns the input baud rate stored in the termios struc‐
576 ture.
577 cfsetispeed() sets the input baud rate stored in the termios structure
579 to speed, which must be specified as one of the Bnnn constants listed
580 above for cfsetospeed(). If the input baud rate is set to zero, the
581 input baud rate will be equal to the output baud rate.
582 cfsetspeed() is a 4.4BSD extension. It takes the same arguments as cf‐
584 setispeed(), and sets both input and output speed.
585
587 cfgetispeed() returns the input baud rate stored in the termios struc‐
588 ture.
589 cfgetospeed() returns the output baud rate stored in the termios struc‐
591 ture.
592 All other functions return:
594 0 on success.
596 -1 on failure and set errno to indicate the error.
598 Note that tcsetattr() returns success if any of the requested changes
600 could be successfully carried out. Therefore, when making multiple
601 changes it may be necessary to follow this call with a further call to
602 tcgetattr() to check that all changes have been performed successfully.
603
605 For an explanation of the terms used in this section, see at‐
606 tributes(7).
607 ┌────────────────────────────────────────────┬───────────────┬─────────┐
609 │Interface │ Attribute │ Value │
610 ├────────────────────────────────────────────┼───────────────┼─────────┤
611 │tcgetattr(), tcsetattr(), tcdrain(), │ Thread safety │ MT-Safe │
612 │tcflush(), tcflow(), tcsendbreak(), │ │ │
613 │cfmakeraw(), cfgetispeed(), cfgetospeed(), │ │ │
614 │cfsetispeed(), cfsetospeed(), cfsetspeed() │ │ │
615 └────────────────────────────────────────────┴───────────────┴─────────┘
616
618 tcgetattr(), tcsetattr(), tcsendbreak(), tcdrain(), tcflush(),
619 tcflow(), cfgetispeed(), cfgetospeed(), cfsetispeed(), and cfse‐
620 tospeed() are specified in POSIX.1-2001.
621 cfmakeraw() and cfsetspeed() are nonstandard, but available on the BS‐
623 Ds.
624
626 UNIX V7 and several later systems have a list of baud rates where after
627 the fourteen values B0, ..., B9600 one finds the two constants EXTA,
628 EXTB ("External A" and "External B"). Many systems extend the list
629 with much higher baud rates.
630 The effect of a nonzero duration with tcsendbreak() varies. SunOS
632 specifies a break of duration * N seconds, where N is at least 0.25,
633 and not more than 0.5. Linux, AIX, DU, Tru64 send a break of duration
634 milliseconds. FreeBSD and NetBSD and HP-UX and MacOS ignore the value
635 of duration. Under Solaris and UnixWare, tcsendbreak() with nonzero
636 duration behaves like tcdrain().
637
639 On the Alpha architecture before Linux 4.16 (and glibc before 2.28),
640 the XTABS value was different from TAB3 and it was ignored by the N_TTY
641 line discipline code of the terminal driver as a result (because as it
642 wasn't part of the TABDLY mask).
643
645 reset(1), setterm(1), stty(1), tput(1), tset(1), tty(1), ioctl_con‐
646 sole(2), ioctl_tty(2), setserial(8)
647
649 This page is part of release 5.12 of the Linux man-pages project. A
650 description of the project, information about reporting bugs, and the
651 latest version of this page, can be found at
652 https://www.kernel.org/doc/man-pages/.
653Linux 2021-03-22 TERMIOS(3)