1TERMIOS(3)                 Linux Programmer's Manual                TERMIOS(3)
2
3
4

NAME

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

SYNOPSIS

12       #include <termios.h>
13       #include <unistd.h>
14
15       int tcgetattr(int fd, struct termios *termios_p);
16
17       int tcsetattr(int fd, int optional_actions,
18                     const struct termios *termios_p);
19
20       int tcsendbreak(int fd, int duration);
21
22       int tcdrain(int fd);
23
24       int tcflush(int fd, int queue_selector);
25
26       int tcflow(int fd, int action);
27
28       void cfmakeraw(struct termios *termios_p);
29
30       speed_t cfgetispeed(const struct termios *termios_p);
31
32       speed_t cfgetospeed(const struct termios *termios_p);
33
34       int cfsetispeed(struct termios *termios_p, speed_t speed);
35
36       int cfsetospeed(struct termios *termios_p, speed_t speed);
37
38       int cfsetspeed(struct termios *termios_p, speed_t speed);
39
40   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
41
42       cfsetspeed(), cfmakeraw():
43           Since glibc 2.19:
44               _DEFAULT_SOURCE
45           Glibc 2.19 and earlier:
46               _BSD_SOURCE
47

DESCRIPTION

49       The termios functions describe a general  terminal  interface  that  is
50       provided to control asynchronous communications ports.
51
52   The termios structure
53       Many  of the functions described here have a termios_p argument that is
54       a pointer to a termios structure.  This structure contains at least the
55       following members:
56
57           tcflag_t c_iflag;      /* input modes */
58           tcflag_t c_oflag;      /* output modes */
59           tcflag_t c_cflag;      /* control modes */
60           tcflag_t c_lflag;      /* local modes */
61           cc_t     c_cc[NCCS];   /* special characters */
62
63       The  values  that  may be assigned to these fields are described below.
64       In the case of the first four bit-mask fields, the definitions of  some
65       of  the associated flags that may be set are exposed only if a specific
66       feature test macro (see feature_test_macros(7)) is defined, as noted in
67       brackets ("[]").
68
69       In  the  descriptions below, "not in POSIX" means that the value is not
70       specified in POSIX.1-2001, and "XSI" means that the value is  specified
71       in POSIX.1-2001 as part of the XSI extension.
72
73       c_iflag flag constants:
74
75       IGNBRK Ignore BREAK condition on input.
76
77       BRKINT If  IGNBRK  is  set,  a  BREAK is ignored.  If it is not set but
78              BRKINT is set, then a BREAK causes the input and  output  queues
79              to  be  flushed, and if the terminal is the controlling terminal
80              of a foreground process group, it will cause a SIGINT to be sent
81              to  this  foreground  process  group.   When  neither IGNBRK nor
82              BRKINT are set, a BREAK reads as a null byte ('\0'), except when
83              PARMRK  is  set,  in which case it reads as the sequence \377 \0
84              \0.
85
86       IGNPAR Ignore framing errors and parity errors.
87
88       PARMRK If this bit is set, input bytes with parity  or  framing  errors
89              are  marked  when passed to the program.  This bit is meaningful
90              only when INPCK is set and IGNPAR is not set.  The way erroneous
91              bytes  are  marked  is  with  two  preceding bytes, \377 and \0.
92              Thus, the program actually reads three bytes for  one  erroneous
93              byte  received from the terminal.  If a valid byte has the value
94              \377, and ISTRIP (see below) is not set, the program might  con‐
95              fuse it with the prefix that marks a parity error.  Therefore, a
96              valid byte \377 is passed to the  program  as  two  bytes,  \377
97              \377, in this case.
98
99              If  neither  IGNPAR  nor  PARMRK is set, read a character with a
100              parity error or framing error as \0.
101
102       INPCK  Enable input parity checking.
103
104       ISTRIP Strip off eighth bit.
105
106       INLCR  Translate NL to CR on input.
107
108       IGNCR  Ignore carriage return on input.
109
110       ICRNL  Translate carriage return to newline on input (unless  IGNCR  is
111              set).
112
113       IUCLC  (not in POSIX) Map uppercase characters to lowercase on input.
114
115       IXON   Enable XON/XOFF flow control on output.
116
117       IXANY  (XSI)  Typing  any  character will restart stopped output.  (The
118              default is to allow just the START character to restart output.)
119
120       IXOFF  Enable XON/XOFF flow control on input.
121
122       IMAXBEL
123              (not in POSIX) Ring bell when input queue is full.   Linux  does
124              not implement this bit, and acts as if it is always set.
125
126       IUTF8 (since Linux 2.6.4)
127              (not  in POSIX) Input is UTF8; this allows character-erase to be
128              correctly performed in cooked mode.
129
130       c_oflag flag constants:
131
132       OPOST  Enable implementation-defined output processing.
133
134       OLCUC  (not in POSIX) Map lowercase characters to uppercase on output.
135
136       ONLCR  (XSI) Map NL to CR-NL on output.
137
138       OCRNL  Map CR to NL on output.
139
140       ONOCR  Don't output CR at column 0.
141
142       ONLRET Don't output CR.
143
144       OFILL  Send fill characters for a delay,  rather  than  using  a  timed
145              delay.
146
147       OFDEL  Fill character is ASCII DEL (0177).  If unset, fill character is
148              ASCII NUL ('\0').  (Not implemented on Linux.)
149
150       NLDLY  Newline  delay  mask.   Values  are  NL0  and  NL1.    [requires
151              _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
152
153       CRDLY  Carriage  return  delay mask.  Values are CR0, CR1, CR2, or CR3.
154              [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
155
156       TABDLY Horizontal tab delay mask.  Values are TAB0,  TAB1,  TAB2,  TAB3
157              (or XTABS, but see the BUGS section).  A value of TAB3, that is,
158              XTABS, expands tabs to spaces (with tab stops every  eight  col‐
159              umns).  [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
160
161       BSDLY  Backspace  delay  mask.  Values are BS0 or BS1.  (Has never been
162              implemented.)   [requires   _BSD_SOURCE   or   _SVID_SOURCE   or
163              _XOPEN_SOURCE]
164
165       VTDLY  Vertical tab delay mask.  Values are VT0 or VT1.
166
167       FFDLY  Form  feed  delay  mask.   Values  are  FF0  or  FF1.  [requires
168              _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
169
170       c_cflag flag constants:
171
172       CBAUD  (not  in  POSIX)  Baud  speed  mask   (4+1   bits).    [requires
173              _BSD_SOURCE or _SVID_SOURCE]
174
175       CBAUDEX
176              (not in POSIX) Extra baud speed mask (1 bit), included in CBAUD.
177              [requires _BSD_SOURCE or _SVID_SOURCE]
178
179              (POSIX says that the baud speed is stored in the termios  struc‐
180              ture   without   specifying   where   precisely,   and  provides
181              cfgetispeed() and cfsetispeed() for getting at it.  Some systems
182              use  bits  selected by CBAUD in c_cflag, other systems use sepa‐
183              rate fields, for example, sg_ispeed and sg_ospeed.)
184
185       CSIZE  Character size mask.  Values are CS5, CS6, CS7, or CS8.
186
187       CSTOPB Set two stop bits, rather than one.
188
189       CREAD  Enable receiver.
190
191       PARENB Enable parity generation  on  output  and  parity  checking  for
192              input.
193
194       PARODD If  set, then parity for input and output is odd; otherwise even
195              parity is used.
196
197       HUPCL  Lower modem control lines after last process closes  the  device
198              (hang up).
199
200       CLOCAL Ignore modem control lines.
201
202       LOBLK  (not  in POSIX) Block output from a noncurrent shell layer.  For
203              use by shl (shell layers).  (Not implemented on Linux.)
204
205       CIBAUD (not in POSIX) Mask for input speeds.  The values for the CIBAUD
206              bits are the same as the values for the CBAUD bits, shifted left
207              IBSHIFT  bits.   [requires  _BSD_SOURCE  or  _SVID_SOURCE]  (Not
208              implemented on Linux.)
209
210       CMSPAR (not  in  POSIX)  Use  "stick" (mark/space) parity (supported on
211              certain serial devices): if PARODD is set,  the  parity  bit  is
212              always 1; if PARODD is not set, then the parity bit is always 0.
213              [requires _BSD_SOURCE or _SVID_SOURCE]
214
215       CRTSCTS
216              (not  in  POSIX)  Enable  RTS/CTS   (hardware)   flow   control.
217              [requires _BSD_SOURCE or _SVID_SOURCE]
218
219       c_lflag flag constants:
220
221       ISIG   When  any  of  the  characters  INTR,  QUIT,  SUSP, or DSUSP are
222              received, generate the corresponding signal.
223
224       ICANON Enable canonical mode (described below).
225
226       XCASE  (not in POSIX; not supported under Linux) If ICANON is also set,
227              terminal  is  uppercase  only.  Input is converted to lowercase,
228              except for characters preceded by \.  On output, uppercase char‐
229              acters  are preceded by \ and lowercase characters are converted
230              to  uppercase.   [requires  _BSD_SOURCE   or   _SVID_SOURCE   or
231              _XOPEN_SOURCE]
232
233       ECHO   Echo input characters.
234
235       ECHOE  If  ICANON is also set, the ERASE character erases the preceding
236              input character, and WERASE erases the preceding word.
237
238       ECHOK  If ICANON is also set, the KILL  character  erases  the  current
239              line.
240
241       ECHONL If ICANON is also set, echo the NL character even if ECHO is not
242              set.
243
244       ECHOCTL
245              (not in POSIX) If ECHO is also set, terminal special  characters
246              other than TAB, NL, START, and STOP are echoed as ^X, where X is
247              the character with ASCII code  0x40  greater  than  the  special
248              character.   For  example,  character 0x08 (BS) is echoed as ^H.
249              [requires _BSD_SOURCE or _SVID_SOURCE]
250
251       ECHOPRT
252              (not in POSIX) If ICANON and ECHO are also set,  characters  are
253              printed  as  they  are  being  erased.  [requires _BSD_SOURCE or
254              _SVID_SOURCE]
255
256       ECHOKE (not in POSIX) If ICANON is also set, KILL is echoed by  erasing
257              each  character  on the line, as specified by ECHOE and ECHOPRT.
258              [requires _BSD_SOURCE or _SVID_SOURCE]
259
260       DEFECHO
261              (not in POSIX) Echo only when a process is reading.  (Not imple‐
262              mented on Linux.)
263
264       FLUSHO (not  in  POSIX;  not  supported  under  Linux)  Output is being
265              flushed.  This flag is toggled by typing the DISCARD  character.
266              [requires _BSD_SOURCE or _SVID_SOURCE]
267
268       NOFLSH Disable  flushing  the  input  and output queues when generating
269              signals for the INT, QUIT, and SUSP characters.
270
271       TOSTOP Send the SIGTTOU signal to the process  group  of  a  background
272              process which tries to write to its controlling terminal.
273
274       PENDIN (not  in POSIX; not supported under Linux) All characters in the
275              input queue are reprinted  when  the  next  character  is  read.
276              (bash(1)  handles typeahead this way.)  [requires _BSD_SOURCE or
277              _SVID_SOURCE]
278
279       IEXTEN Enable implementation-defined input processing.  This  flag,  as
280              well  as ICANON must be enabled for the special characters EOL2,
281              LNEXT, REPRINT, WERASE to be interpreted, and for the IUCLC flag
282              to be effective.
283
284       The  c_cc  array defines the terminal special characters.  The symbolic
285       indices (initial values) and meaning are:
286
287       VDISCARD
288              (not in POSIX; not supported under Linux; 017, SI, Ctrl-O)  Tog‐
289              gle: start/stop discarding pending output.  Recognized when IEX‐
290              TEN is set, and then not passed as input.
291
292       VDSUSP (not in POSIX; not  supported  under  Linux;  031,  EM,  Ctrl-Y)
293              Delayed  suspend character (DSUSP): send SIGTSTP signal when the
294              character is read by the user program.  Recognized  when  IEXTEN
295              and  ISIG are set, and the system supports job control, and then
296              not passed as input.
297
298       VEOF   (004, EOT, Ctrl-D) End-of-file character (EOF).  More precisely:
299              this  character  causes the pending tty buffer to be sent to the
300              waiting user program without waiting for end-of-line.  If it  is
301              the first character of the line, the read(2) in the user program
302              returns 0, which signifies end-of-file.  Recognized when  ICANON
303              is set, and then not passed as input.
304
305       VEOL   (0,  NUL)  Additional  end-of-line  character (EOL).  Recognized
306              when ICANON is set.
307
308       VEOL2  (not in POSIX; 0, NUL) Yet another end-of-line character (EOL2).
309              Recognized when ICANON is set.
310
311       VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase charac‐
312              ter (ERASE).  This erases the previous not-yet-erased character,
313              but  does  not  erase past EOF or beginning-of-line.  Recognized
314              when ICANON is set, and then not passed as input.
315
316       VINTR  (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt  charac‐
317              ter (INTR).  Send a SIGINT signal.  Recognized when ISIG is set,
318              and then not passed as input.
319
320       VKILL  (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character  (KILL).
321              This  erases  the input since the last EOF or beginning-of-line.
322              Recognized when ICANON is set, and then not passed as input.
323
324       VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal next  (LNEXT).   Quotes
325              the  next  input  character,  depriving it of a possible special
326              meaning.  Recognized when IEXTEN is set, and then not passed  as
327              input.
328
329       VMIN   Minimum number of characters for noncanonical read (MIN).
330
331       VQUIT  (034,  FS,  Ctrl-\) Quit character (QUIT).  Send SIGQUIT signal.
332              Recognized when ISIG is set, and then not passed as input.
333
334       VREPRINT
335              (not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters  (RE‐
336              PRINT).  Recognized when ICANON and IEXTEN are set, and then not
337              passed as input.
338
339       VSTART (021, DC1, Ctrl-Q) Start  character  (START).   Restarts  output
340              stopped by the Stop character.  Recognized when IXON is set, and
341              then not passed as input.
342
343       VSTATUS
344              (not in POSIX; not supported under Linux; status  request:  024,
345              DC4, Ctrl-T).  Status character (STATUS).  Display status infor‐
346              mation at terminal, including state of  foreground  process  and
347              amount of CPU time it has consumed.  Also sends a SIGINFO signal
348              (not supported on Linux) to the foreground process group.
349
350       VSTOP  (023, DC3, Ctrl-S) Stop character  (STOP).   Stop  output  until
351              Start  character  typed.   Recognized when IXON is set, and then
352              not passed as input.
353
354       VSUSP  (032, SUB, Ctrl-Z) Suspend character (SUSP).  Send SIGTSTP  sig‐
355              nal.  Recognized when ISIG is set, and then not passed as input.
356
357       VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch charac‐
358              ter (SWTCH).  Used in System V to switch shells in shell layers,
359              a predecessor to shell job control.
360
361       VTIME  Timeout in deciseconds for noncanonical read (TIME).
362
363       VWERASE
364              (not  in  POSIX;  027, ETB, Ctrl-W) Word erase (WERASE).  Recog‐
365              nized when ICANON and IEXTEN are set, and  then  not  passed  as
366              input.
367
368       An individual terminal special character can be disabled by setting the
369       value of the corresponding c_cc element to _POSIX_VDISABLE.
370
371       The above symbolic subscript values  are  all  different,  except  that
372       VTIME,  VMIN  may  have the same value as VEOL, VEOF, respectively.  In
373       noncanonical mode the special character  meaning  is  replaced  by  the
374       timeout  meaning.   For  an  explanation  of  VMIN  and  VTIME, see the
375       description of noncanonical mode below.
376
377   Retrieving and changing terminal settings
378       tcgetattr() gets the parameters associated with the object referred  by
379       fd  and  stores  them in the termios structure referenced by termios_p.
380       This function may be invoked from a background  process;  however,  the
381       terminal  attributes  may  be  subsequently  changed  by  a  foreground
382       process.
383
384       tcsetattr() sets the parameters associated with  the  terminal  (unless
385       support is required from the underlying hardware that is not available)
386       from the termios structure referred to by termios_p.   optional_actions
387       specifies when the changes take effect:
388
389       TCSANOW
390              the change occurs immediately.
391
392       TCSADRAIN
393              the change occurs after all output written to fd has been trans‐
394              mitted.  This option should be  used  when  changing  parameters
395              that affect output.
396
397       TCSAFLUSH
398              the  change  occurs  after  all  output  written  to  the object
399              referred by fd has been transmitted, and all input that has been
400              received  but  not  read  will be discarded before the change is
401              made.
402
403   Canonical and noncanonical mode
404       The setting of the ICANON canon flag in c_lflag determines whether  the
405       terminal  is  operating  in canonical mode (ICANON set) or noncanonical
406       mode (ICANON unset).  By default, ICANON is set.
407
408       In canonical mode:
409
410       * Input is made available line by line.  An  input  line  is  available
411         when  one  of  the line delimiters is typed (NL, EOL, EOL2; or EOF at
412         the start of line).  Except in the case of EOF, the line delimiter is
413         included in the buffer returned by read(2).
414
415       * Line  editing is enabled (ERASE, KILL; and if the IEXTEN flag is set:
416         WERASE, REPRINT, LNEXT).  A read(2)  returns  at  most  one  line  of
417         input; if the read(2) requested fewer bytes than are available in the
418         current line of input, then only as many bytes as requested are read,
419         and the remaining characters will be available for a future read(2).
420
421       * The maximum line length is 4096 chars (including the terminating new‐
422         line character); lines longer than 4096 chars are  truncated.   After
423         4095  characters,  input processing (e.g., ISIG and ECHO* processing)
424         continues, but any input data after 4095 characters up  to  (but  not
425         including)  any  terminating newline is discarded.  This ensures that
426         the terminal can always receive more input until at  least  one  line
427         can be read.
428
429       In  noncanonical  mode input is available immediately (without the user
430       having to type a line-delimiter character), no input processing is per‐
431       formed, and line editing is disabled.  The read buffer will only accept
432       4095 chars; this provides the necessary space for a newline char if the
433       input  mode is switched to canonical.  The settings of MIN (c_cc[VMIN])
434       and TIME (c_cc[VTIME]) determine the circumstances in which  a  read(2)
435       completes; there are four distinct cases:
436
437       MIN == 0, TIME == 0 (polling read)
438              If  data  is  available,  read(2)  returns immediately, with the
439              lesser of the number of bytes available, or the number of  bytes
440              requested.  If no data is available, read(2) returns 0.
441
442       MIN > 0, TIME == 0 (blocking read)
443              read(2)  blocks until MIN bytes are available, and returns up to
444              the number of bytes requested.
445
446       MIN == 0, TIME > 0 (read with timeout)
447              TIME specifies the limit for a timer in tenths of a second.  The
448              timer is started when read(2) is called.  read(2) returns either
449              when at least one byte of data is available, or when  the  timer
450              expires.  If the timer expires without any input becoming avail‐
451              able, read(2) returns 0.  If data is already  available  at  the
452              time of the call to read(2), the call behaves as though the data
453              was received immediately after the call.
454
455       MIN > 0, TIME > 0 (read with interbyte timeout)
456              TIME specifies the limit for a timer  in  tenths  of  a  second.
457              Once  an  initial  byte of input becomes available, the timer is
458              restarted after each further byte is received.  read(2)  returns
459              when any of the following conditions is met:
460
461              *  MIN bytes have been received.
462
463              *  The interbyte timer expires.
464
465              *  The  number  of bytes requested by read(2) has been received.
466                 (POSIX does not specify this termination  condition,  and  on
467                 some  other  implementations  read(2) does not return in this
468                 case.)
469
470              Because the timer is started only after the initial byte becomes
471              available,  at  least one byte will be read.  If data is already
472              available at the time of the call to read(2), the  call  behaves
473              as though the data was received immediately after the call.
474
475       POSIX  does not specify whether the setting of the O_NONBLOCK file sta‐
476       tus flag takes precedence over the MIN and TIME  settings.   If  O_NON‐
477       BLOCK  is  set,  a read(2) in noncanonical mode may return immediately,
478       regardless of the setting of MIN or TIME.  Furthermore, if no  data  is
479       available,  POSIX  permits  a  read(2)  in  noncanonical mode to return
480       either 0, or -1 with errno set to EAGAIN.
481
482   Raw mode
483       cfmakeraw() sets the terminal to something like the "raw" mode  of  the
484       old  Version 7 terminal driver: input is available character by charac‐
485       ter, echoing is disabled, and all special processing of terminal  input
486       and  output characters is disabled.  The terminal attributes are set as
487       follows:
488
489           termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
490                           | INLCR | IGNCR | ICRNL | IXON);
491           termios_p->c_oflag &= ~OPOST;
492           termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
493           termios_p->c_cflag &= ~(CSIZE | PARENB);
494           termios_p->c_cflag |= CS8;
495
496   Line control
497       tcsendbreak() transmits a continuous stream of zero-valued bits  for  a
498       specific  duration,  if  the terminal is using asynchronous serial data
499       transmission.  If duration is zero, it transmits zero-valued  bits  for
500       at  least  0.25 seconds, and not more that 0.5 seconds.  If duration is
501       not zero, it sends zero-valued  bits  for  some  implementation-defined
502       length of time.
503
504       If  the  terminal  is  not using asynchronous serial data transmission,
505       tcsendbreak() returns without taking any action.
506
507       tcdrain() waits until all output written to the object referred  to  by
508       fd has been transmitted.
509
510       tcflush() discards data written to the object referred to by fd but not
511       transmitted, or data received but not read, depending on the  value  of
512       queue_selector:
513
514       TCIFLUSH
515              flushes data received but not read.
516
517       TCOFLUSH
518              flushes data written but not transmitted.
519
520       TCIOFLUSH
521              flushes  both  data  received but not read, and data written but
522              not transmitted.
523
524       tcflow() suspends transmission or  reception  of  data  on  the  object
525       referred to by fd, depending on the value of action:
526
527       TCOOFF suspends output.
528
529       TCOON  restarts suspended output.
530
531       TCIOFF transmits a STOP character, which stops the terminal device from
532              transmitting data to the system.
533
534       TCION  transmits a START character, which starts  the  terminal  device
535              transmitting data to the system.
536
537       The  default  on  open of a terminal file is that neither its input nor
538       its output is suspended.
539
540   Line speed
541       The baud rate functions are provided for getting and setting the values
542       of  the  input and output baud rates in the termios structure.  The new
543       values do not take effect until tcsetattr() is successfully called.
544
545       Setting the speed to B0 instructs the modem to "hang up".   The  actual
546       bit rate corresponding to B38400 may be altered with setserial(8).
547
548       The input and output baud rates are stored in the termios structure.
549
550       cfgetospeed() returns the output baud rate stored in the termios struc‐
551       ture pointed to by termios_p.
552
553       cfsetospeed() sets the output baud rate stored in the termios structure
554       pointed to by termios_p to speed, which must be one of these constants:
555
556            B0
557            B50
558            B75
559            B110
560            B134
561            B150
562            B200
563            B300
564            B600
565            B1200
566            B1800
567            B2400
568            B4800
569            B9600
570            B19200
571            B38400
572            B57600
573            B115200
574            B230400
575
576       The  zero baud rate, B0, is used to terminate the connection.  If B0 is
577       specified, the modem control lines shall no longer be  asserted.   Nor‐
578       mally, this will disconnect the line.  CBAUDEX is a mask for the speeds
579       beyond those defined in POSIX.1 (57600  and  above).   Thus,  B57600  &
580       CBAUDEX is nonzero.
581
582       cfgetispeed()  returns the input baud rate stored in the termios struc‐
583       ture.
584
585       cfsetispeed() sets the input baud rate stored in the termios  structure
586       to  speed,  which must be specified as one of the Bnnn constants listed
587       above for cfsetospeed().  If the input baud rate is set  to  zero,  the
588       input baud rate will be equal to the output baud rate.
589
590       cfsetspeed()  is  a  4.4BSD  extension.  It takes the same arguments as
591       cfsetispeed(), and sets both input and output speed.
592

RETURN VALUE

594       cfgetispeed() returns the input baud rate stored in the termios  struc‐
595       ture.
596
597       cfgetospeed() returns the output baud rate stored in the termios struc‐
598       ture.
599
600       All other functions return:
601
602       0      on success.
603
604       -1     on failure and set errno to indicate the error.
605
606       Note that tcsetattr() returns success if any of the  requested  changes
607       could  be  successfully  carried  out.  Therefore, when making multiple
608       changes it may be necessary to follow this call with a further call  to
609       tcgetattr() to check that all changes have been performed successfully.
610

ATTRIBUTES

612       For   an   explanation   of   the  terms  used  in  this  section,  see
613       attributes(7).
614
615       ┌─────────────────────────────────────┬───────────────┬─────────┐
616Interface                            Attribute     Value   
617       ├─────────────────────────────────────┼───────────────┼─────────┤
618tcgetattr(), tcsetattr(), tcdrain(), │ Thread safety │ MT-Safe │
619tcflush(), tcflow(), tcsendbreak(),  │               │         │
620cfmakeraw(), cfgetispeed(),          │               │         │
621cfgetospeed(), cfsetispeed(),        │               │         │
622cfsetospeed(), cfsetspeed()          │               │         │
623       └─────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

625       tcgetattr(),   tcsetattr(),   tcsendbreak(),   tcdrain(),    tcflush(),
626       tcflow(),   cfgetispeed(),   cfgetospeed(),  cfsetispeed(),  and  cfse‐
627       tospeed() are specified in POSIX.1-2001.
628
629       cfmakeraw() and cfsetspeed() are nonstandard, but available on the  BS‐
630       Ds.
631

NOTES

633       UNIX V7 and several later systems have a list of baud rates where after
634       the fourteen values B0, ..., B9600 one finds the  two  constants  EXTA,
635       EXTB  ("External  A"  and  "External B").  Many systems extend the list
636       with much higher baud rates.
637
638       The effect of a nonzero  duration  with  tcsendbreak()  varies.   SunOS
639       specifies  a  break  of duration * N seconds, where N is at least 0.25,
640       and not more than 0.5.  Linux, AIX, DU, Tru64 send a break of  duration
641       milliseconds.   FreeBSD and NetBSD and HP-UX and MacOS ignore the value
642       of duration.  Under Solaris and UnixWare,  tcsendbreak()  with  nonzero
643       duration behaves like tcdrain().
644

BUGS

646       On  the  Alpha  architecture before Linux 4.16 (and glibc before 2.28),
647       the XTABS value was different from TAB3 and it was ignored by the N_TTY
648       line  discipline code of the terminal driver as a result (because as it
649       wasn't part of the TABDLY mask).
650

SEE ALSO

652       reset(1), setterm(1), stty(1),  tput(1),  tset(1),  tty(1),  ioctl_con‐
653       sole(2), ioctl_tty(2), setserial(8)
654

COLOPHON

656       This  page  is  part of release 5.02 of the Linux man-pages project.  A
657       description of the project, information about reporting bugs,  and  the
658       latest     version     of     this    page,    can    be    found    at
659       https://www.kernel.org/doc/man-pages/.
660
661
662
663Linux                             2019-03-06                        TERMIOS(3)
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