Provided by: manpages-dev_5.02-1_all bug

NAME

       termios,   tcgetattr,   tcsetattr,   tcsendbreak,  tcdrain,  tcflush,  tcflow,  cfmakeraw,
       cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed  -  get  and  set  terminal
       attributes, line control, get and set baud rate

SYNOPSIS

       #include <termios.h>
       #include <unistd.h>

       int tcgetattr(int fd, struct termios *termios_p);

       int tcsetattr(int fd, int optional_actions,
                     const struct termios *termios_p);

       int tcsendbreak(int fd, int duration);

       int tcdrain(int fd);

       int tcflush(int fd, int queue_selector);

       int tcflow(int fd, int action);

       void cfmakeraw(struct termios *termios_p);

       speed_t cfgetispeed(const struct termios *termios_p);

       speed_t cfgetospeed(const struct termios *termios_p);

       int cfsetispeed(struct termios *termios_p, speed_t speed);

       int cfsetospeed(struct termios *termios_p, speed_t speed);

       int cfsetspeed(struct termios *termios_p, speed_t speed);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       cfsetspeed(), cfmakeraw():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE

DESCRIPTION

       The  termios  functions  describe a general terminal interface that is provided to control
       asynchronous communications ports.

   The termios structure
       Many of the functions described here have a termios_p argument that  is  a  pointer  to  a
       termios structure.  This structure contains at least the following members:

           tcflag_t c_iflag;      /* input modes */
           tcflag_t c_oflag;      /* output modes */
           tcflag_t c_cflag;      /* control modes */
           tcflag_t c_lflag;      /* local modes */
           cc_t     c_cc[NCCS];   /* special characters */

       The  values  that may be assigned to these fields are described below.  In the case of the
       first four bit-mask fields, the definitions of some of the associated flags  that  may  be
       set  are  exposed  only  if  a specific feature test macro (see feature_test_macros(7)) is
       defined, as noted in brackets ("[]").

       In the descriptions below, "not in POSIX"  means  that  the  value  is  not  specified  in
       POSIX.1-2001,  and  "XSI" means that the value is specified in POSIX.1-2001 as part of the
       XSI extension.

       c_iflag flag constants:

       IGNBRK Ignore BREAK condition on input.

       BRKINT If IGNBRK is set, a BREAK is ignored.  If it is not set but BRKINT is set,  then  a
              BREAK  causes the input and output queues to be flushed, and if the terminal is the
              controlling terminal of a foreground process group, it will cause a  SIGINT  to  be
              sent  to  this foreground process group.  When neither IGNBRK nor BRKINT are set, a
              BREAK reads as a null byte ('\0'), except when PARMRK is  set,  in  which  case  it
              reads as the sequence \377 \0 \0.

       IGNPAR Ignore framing errors and parity errors.

       PARMRK If  this  bit  is  set,  input  bytes with parity or framing errors are marked when
              passed to the program.  This bit is meaningful only when INPCK is set and IGNPAR is
              not  set.  The way erroneous bytes are marked is with two preceding bytes, \377 and
              \0.  Thus, the program actually reads three bytes for one erroneous  byte  received
              from  the  terminal.  If a valid byte has the value \377, and ISTRIP (see below) is
              not set, the program might confuse it with the prefix that marks  a  parity  error.
              Therefore,  a  valid byte \377 is passed to the program as two bytes, \377 \377, in
              this case.

              If neither IGNPAR nor PARMRK is set, read  a  character  with  a  parity  error  or
              framing error as \0.

       INPCK  Enable input parity checking.

       ISTRIP Strip off eighth bit.

       INLCR  Translate NL to CR on input.

       IGNCR  Ignore carriage return on input.

       ICRNL  Translate carriage return to newline on input (unless IGNCR is set).

       IUCLC  (not in POSIX) Map uppercase characters to lowercase on input.

       IXON   Enable XON/XOFF flow control on output.

       IXANY  (XSI)  Typing  any character will restart stopped output.  (The default is to allow
              just the START character to restart output.)

       IXOFF  Enable XON/XOFF flow control on input.

       IMAXBEL
              (not in POSIX) Ring bell when input queue is full.  Linux does not  implement  this
              bit, and acts as if it is always set.

       IUTF8 (since Linux 2.6.4)
              (not in POSIX) Input is UTF8; this allows character-erase to be correctly performed
              in cooked mode.

       c_oflag flag constants:

       OPOST  Enable implementation-defined output processing.

       OLCUC  (not in POSIX) Map lowercase characters to uppercase on output.

       ONLCR  (XSI) Map NL to CR-NL on output.

       OCRNL  Map CR to NL on output.

       ONOCR  Don't output CR at column 0.

       ONLRET Don't output CR.

       OFILL  Send fill characters for a delay, rather than using a timed delay.

       OFDEL  Fill character is ASCII DEL (0177).  If unset, fill character is ASCII NUL  ('\0').
              (Not implemented on Linux.)

       NLDLY  Newline delay mask.  Values are NL0 and NL1.  [requires _BSD_SOURCE or _SVID_SOURCE
              or _XOPEN_SOURCE]

       CRDLY  Carriage return  delay  mask.   Values  are  CR0,  CR1,  CR2,  or  CR3.   [requires
              _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

       TABDLY Horizontal  tab  delay  mask.  Values are TAB0, TAB1, TAB2, TAB3 (or XTABS, but see
              the BUGS section).  A value of TAB3, that is, XTABS, expands tabs to  spaces  (with
              tab   stops  every  eight  columns).   [requires  _BSD_SOURCE  or  _SVID_SOURCE  or
              _XOPEN_SOURCE]

       BSDLY  Backspace delay mask.  Values are  BS0  or  BS1.   (Has  never  been  implemented.)
              [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

       VTDLY  Vertical tab delay mask.  Values are VT0 or VT1.

       FFDLY  Form   feed  delay  mask.   Values  are  FF0  or  FF1.   [requires  _BSD_SOURCE  or
              _SVID_SOURCE or _XOPEN_SOURCE]

       c_cflag flag constants:

       CBAUD  (not in POSIX) Baud speed mask (4+1 bits).  [requires _BSD_SOURCE or _SVID_SOURCE]

       CBAUDEX
              (not in POSIX) Extra baud  speed  mask  (1  bit),  included  in  CBAUD.   [requires
              _BSD_SOURCE or _SVID_SOURCE]

              (POSIX  says  that  the  baud  speed  is  stored  in  the termios structure without
              specifying where  precisely,  and  provides  cfgetispeed()  and  cfsetispeed()  for
              getting  at  it.  Some systems use bits selected by CBAUD in c_cflag, other systems
              use separate fields, for example, sg_ispeed and sg_ospeed.)

       CSIZE  Character size mask.  Values are CS5, CS6, CS7, or CS8.

       CSTOPB Set two stop bits, rather than one.

       CREAD  Enable receiver.

       PARENB Enable parity generation on output and parity checking for input.

       PARODD If set, then parity for input and output is odd; otherwise even parity is used.

       HUPCL  Lower modem control lines after last process closes the device (hang up).

       CLOCAL Ignore modem control lines.

       LOBLK  (not in POSIX) Block output from a noncurrent shell layer.  For use by  shl  (shell
              layers).  (Not implemented on Linux.)

       CIBAUD (not  in POSIX) Mask for input speeds.  The values for the CIBAUD bits are the same
              as the values for the CBAUD bits, shifted left IBSHIFT bits.  [requires _BSD_SOURCE
              or _SVID_SOURCE] (Not implemented on Linux.)

       CMSPAR (not  in  POSIX)  Use  "stick"  (mark/space)  parity  (supported  on certain serial
              devices): if PARODD is set, the parity bit is always 1; if PARODD is not set,  then
              the parity bit is always 0.  [requires _BSD_SOURCE or _SVID_SOURCE]

       CRTSCTS
              (not  in  POSIX)  Enable RTS/CTS (hardware) flow control.  [requires _BSD_SOURCE or
              _SVID_SOURCE]

       c_lflag flag constants:

       ISIG   When any of the characters INTR, QUIT, SUSP, or DSUSP are  received,  generate  the
              corresponding signal.

       ICANON Enable canonical mode (described below).

       XCASE  (not  in  POSIX;  not  supported  under  Linux)  If ICANON is also set, terminal is
              uppercase only.  Input is converted to lowercase, except for characters preceded by
              \.   On output, uppercase characters are preceded by \ and lowercase characters are
              converted to uppercase.  [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

       ECHO   Echo input characters.

       ECHOE  If ICANON is also set, the ERASE character erases the  preceding  input  character,
              and WERASE erases the preceding word.

       ECHOK  If ICANON is also set, the KILL character erases the current line.

       ECHONL If ICANON is also set, echo the NL character even if ECHO is not set.

       ECHOCTL
              (not in POSIX) If ECHO is also set, terminal special characters other than TAB, NL,
              START, and STOP are echoed as ^X, where X is the character  with  ASCII  code  0x40
              greater  than the special character.  For example, character 0x08 (BS) is echoed as
              ^H.  [requires _BSD_SOURCE or _SVID_SOURCE]

       ECHOPRT
              (not in POSIX) If ICANON and ECHO are also set, characters are printed as they  are
              being erased.  [requires _BSD_SOURCE or _SVID_SOURCE]

       ECHOKE (not  in  POSIX) If ICANON is also set, KILL is echoed by erasing each character on
              the  line,  as  specified  by  ECHOE  and  ECHOPRT.    [requires   _BSD_SOURCE   or
              _SVID_SOURCE]

       DEFECHO
              (not in POSIX) Echo only when a process is reading.  (Not implemented on Linux.)

       FLUSHO (not  in  POSIX;  not supported under Linux) Output is being flushed.  This flag is
              toggled by typing the DISCARD character.  [requires _BSD_SOURCE or _SVID_SOURCE]

       NOFLSH Disable flushing the input and output queues when generating signals for  the  INT,
              QUIT, and SUSP characters.

       TOSTOP Send the SIGTTOU signal to the process group of a background process which tries to
              write to its controlling terminal.

       PENDIN (not in POSIX; not supported under Linux) All characters in  the  input  queue  are
              reprinted  when  the next character is read.  (bash(1) handles typeahead this way.)
              [requires _BSD_SOURCE or _SVID_SOURCE]

       IEXTEN Enable implementation-defined input processing.  This flag, as well as ICANON  must
              be  enabled  for  the  special  characters  EOL2,  LNEXT,  REPRINT,  WERASE  to  be
              interpreted, and for the IUCLC flag to be effective.

       The c_cc array defines the terminal special characters.   The  symbolic  indices  (initial
       values) and meaning are:

       VDISCARD
              (not  in  POSIX;  not  supported  under  Linux; 017, SI, Ctrl-O) Toggle: start/stop
              discarding pending output.  Recognized when IEXTEN is set, and then not  passed  as
              input.

       VDSUSP (not  in  POSIX;  not  supported  under  Linux;  031,  EM,  Ctrl-Y) Delayed suspend
              character (DSUSP): send SIGTSTP signal when the  character  is  read  by  the  user
              program.   Recognized  when  IEXTEN  and  ISIG are set, and the system supports job
              control, and then not passed as input.

       VEOF   (004, EOT, Ctrl-D) End-of-file character (EOF).   More  precisely:  this  character
              causes  the  pending  tty  buffer  to  be  sent to the waiting user program without
              waiting for end-of-line.  If it is the first character of the line, the read(2)  in
              the user program returns 0, which signifies end-of-file.  Recognized when ICANON is
              set, and then not passed as input.

       VEOL   (0, NUL) Additional end-of-line character (EOL).  Recognized when ICANON is set.

       VEOL2  (not in POSIX; 0, NUL) Yet another end-of-line character (EOL2).   Recognized  when
              ICANON is set.

       VERASE (0177,  DEL,  rubout, or 010, BS, Ctrl-H, or also #) Erase character (ERASE).  This
              erases the previous not-yet-erased character,  but  does  not  erase  past  EOF  or
              beginning-of-line.  Recognized when ICANON is set, and then not passed as input.

       VINTR  (003,  ETX,  Ctrl-C, or also 0177, DEL, rubout) Interrupt character (INTR).  Send a
              SIGINT signal.  Recognized when ISIG is set, and then not passed as input.

       VKILL  (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character (KILL).   This  erases  the
              input  since the last EOF or beginning-of-line.  Recognized when ICANON is set, and
              then not passed as input.

       VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal  next  (LNEXT).   Quotes  the  next  input
              character,  depriving  it of a possible special meaning.  Recognized when IEXTEN is
              set, and then not passed as input.

       VMIN   Minimum number of characters for noncanonical read (MIN).

       VQUIT  (034, FS, Ctrl-\) Quit character (QUIT).  Send  SIGQUIT  signal.   Recognized  when
              ISIG is set, and then not passed as input.

       VREPRINT
              (not  in  POSIX; 022, DC2, Ctrl-R) Reprint unread characters (REPRINT).  Recognized
              when ICANON and IEXTEN are set, and then not passed as input.

       VSTART (021, DC1, Ctrl-Q) Start character (START).  Restarts output stopped  by  the  Stop
              character.  Recognized when IXON is set, and then not passed as input.

       VSTATUS
              (not  in  POSIX;  not  supported  under  Linux;  status request: 024, DC4, Ctrl-T).
              Status character (STATUS).  Display status information at terminal, including state
              of foreground process and amount of CPU time it has consumed.  Also sends a SIGINFO
              signal (not supported on Linux) to the foreground process group.

       VSTOP  (023, DC3, Ctrl-S) Stop character (STOP).  Stop output until Start character typed.
              Recognized when IXON is set, and then not passed as input.

       VSUSP  (032, SUB, Ctrl-Z) Suspend character (SUSP).  Send SIGTSTP signal.  Recognized when
              ISIG is set, and then not passed as input.

       VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch character  (SWTCH).   Used
              in System V to switch shells in shell layers, a predecessor to shell job control.

       VTIME  Timeout in deciseconds for noncanonical read (TIME).

       VWERASE
              (not  in  POSIX; 027, ETB, Ctrl-W) Word erase (WERASE).  Recognized when ICANON and
              IEXTEN are set, and then not passed as input.

       An individual terminal special character can be disabled  by  setting  the  value  of  the
       corresponding c_cc element to _POSIX_VDISABLE.

       The  above  symbolic  subscript values are all different, except that VTIME, VMIN may have
       the same value as VEOL, VEOF, respectively.  In noncanonical mode  the  special  character
       meaning is replaced by the timeout meaning.  For an explanation of VMIN and VTIME, see the
       description of noncanonical mode below.

   Retrieving and changing terminal settings
       tcgetattr() gets the parameters associated with the object referred by fd and stores  them
       in  the  termios  structure  referenced by termios_p.  This function may be invoked from a
       background process; however, the terminal attributes may  be  subsequently  changed  by  a
       foreground process.

       tcsetattr()  sets  the parameters associated with the terminal (unless support is required
       from the underlying hardware that is not available) from the termios structure referred to
       by termios_p.  optional_actions specifies when the changes take effect:

       TCSANOW
              the change occurs immediately.

       TCSADRAIN
              the change occurs after all output written to fd has been transmitted.  This option
              should be used when changing parameters that affect output.

       TCSAFLUSH
              the change occurs after all output written to the object referred by  fd  has  been
              transmitted,  and  all  input that has been received but not read will be discarded
              before the change is made.

   Canonical and noncanonical mode
       The setting of the ICANON canon  flag  in  c_lflag  determines  whether  the  terminal  is
       operating in canonical mode (ICANON set) or noncanonical mode (ICANON unset).  By default,
       ICANON is set.

       In canonical mode:

       * Input is made available line by line.  An input line is available when one of  the  line
         delimiters is typed (NL, EOL, EOL2; or EOF at the start of line).  Except in the case of
         EOF, the line delimiter is included in the buffer returned by read(2).

       * Line editing is enabled (ERASE, KILL; and if the IEXTEN flag is  set:  WERASE,  REPRINT,
         LNEXT).   A  read(2)  returns  at most one line of input; if the read(2) requested fewer
         bytes than are available in the current line of  input,  then  only  as  many  bytes  as
         requested are read, and the remaining characters will be available for a future read(2).

       * The  maximum  line  length  is 4096 chars (including the terminating newline character);
         lines longer than 4096 chars are truncated.  After  4095  characters,  input  processing
         (e.g., ISIG and ECHO* processing) continues, but any input data after 4095 characters up
         to (but not including) any terminating newline is  discarded.   This  ensures  that  the
         terminal can always receive more input until at least one line can be read.

       In  noncanonical  mode  input  is available immediately (without the user having to type a
       line-delimiter character), no input processing is performed, and line editing is disabled.
       The  read  buffer  will  only  accept  4095 chars; this provides the necessary space for a
       newline char if the input mode is switched to canonical.  The settings of MIN (c_cc[VMIN])
       and TIME (c_cc[VTIME]) determine the circumstances in which a read(2) completes; there are
       four distinct cases:

       MIN == 0, TIME == 0 (polling read)
              If data is available, read(2) returns immediately, with the lesser of the number of
              bytes  available,  or  the  number  of  bytes  requested.  If no data is available,
              read(2) returns 0.

       MIN > 0, TIME == 0 (blocking read)
              read(2) blocks until MIN bytes are available, and returns up to the number of bytes
              requested.

       MIN == 0, TIME > 0 (read with timeout)
              TIME  specifies  the limit for a timer in tenths of a second.  The timer is started
              when read(2) is called.  read(2) returns either when at least one byte of  data  is
              available,  or  when  the  timer  expires.   If the timer expires without any input
              becoming available, read(2) returns 0.  If data is already available at the time of
              the  call  to read(2), the call behaves as though the data was received immediately
              after the call.

       MIN > 0, TIME > 0 (read with interbyte timeout)
              TIME specifies the limit for a timer in tenths of a second.  Once an  initial  byte
              of  input  becomes  available,  the  timer  is restarted after each further byte is
              received.  read(2) returns when any of the following conditions is met:

              *  MIN bytes have been received.

              *  The interbyte timer expires.

              *  The number of bytes requested by read(2) has been  received.   (POSIX  does  not
                 specify  this  termination  condition, and on some other implementations read(2)
                 does not return in this case.)

              Because the timer is started only after the  initial  byte  becomes  available,  at
              least  one byte will be read.  If data is already available at the time of the call
              to read(2), the call behaves as though the data was received immediately after  the
              call.

       POSIX  does  not  specify  whether  the  setting  of the O_NONBLOCK file status flag takes
       precedence over  the  MIN  and  TIME  settings.   If  O_NONBLOCK  is  set,  a  read(2)  in
       noncanonical  mode  may  return  immediately,  regardless  of  the setting of MIN or TIME.
       Furthermore, if no data is available, POSIX permits a  read(2)  in  noncanonical  mode  to
       return either 0, or -1 with errno set to EAGAIN.

   Raw mode
       cfmakeraw()  sets  the  terminal  to  something  like  the "raw" mode of the old Version 7
       terminal driver: input is available character by character, echoing is disabled,  and  all
       special  processing  of  terminal  input  and output characters is disabled.  The terminal
       attributes are set as follows:

           termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
                           | INLCR | IGNCR | ICRNL | IXON);
           termios_p->c_oflag &= ~OPOST;
           termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
           termios_p->c_cflag &= ~(CSIZE | PARENB);
           termios_p->c_cflag |= CS8;

   Line control
       tcsendbreak() transmits a continuous stream of zero-valued bits for a  specific  duration,
       if  the  terminal is using asynchronous serial data transmission.  If duration is zero, it
       transmits zero-valued bits for at least 0.25 seconds, and not more that 0.5  seconds.   If
       duration  is not zero, it sends zero-valued bits for some implementation-defined length of
       time.

       If the terminal is not using asynchronous serial data transmission, tcsendbreak()  returns
       without taking any action.

       tcdrain()  waits  until  all  output  written  to  the  object  referred to by fd has been
       transmitted.

       tcflush() discards data written to the object referred to by fd but  not  transmitted,  or
       data received but not read, depending on the value of queue_selector:

       TCIFLUSH
              flushes data received but not read.

       TCOFLUSH
              flushes data written but not transmitted.

       TCIOFLUSH
              flushes both data received but not read, and data written but not transmitted.

       tcflow()  suspends  transmission  or  reception  of  data on the object referred to by fd,
       depending on the value of action:

       TCOOFF suspends output.

       TCOON  restarts suspended output.

       TCIOFF transmits a STOP character, which stops the terminal device from transmitting  data
              to the system.

       TCION  transmits  a START character, which starts the terminal device transmitting data to
              the system.

       The default on open of a terminal file is  that  neither  its  input  nor  its  output  is
       suspended.

   Line speed
       The  baud  rate functions are provided for getting and setting the values of the input and
       output baud rates in the termios structure.  The new  values  do  not  take  effect  until
       tcsetattr() is successfully called.

       Setting  the  speed  to  B0  instructs  the  modem  to  "hang  up".   The  actual bit rate
       corresponding to B38400 may be altered with setserial(8).

       The input and output baud rates are stored in the termios structure.

       cfgetospeed() returns the output baud rate stored in the termios structure pointed  to  by
       termios_p.

       cfsetospeed()  sets  the  output  baud  rate stored in the termios structure pointed to by
       termios_p to speed, which must be one of these constants:

            B0
            B50
            B75
            B110
            B134
            B150
            B200
            B300
            B600
            B1200
            B1800
            B2400
            B4800
            B9600
            B19200
            B38400
            B57600
            B115200
            B230400

       The zero baud rate, B0, is used to terminate the connection.   If  B0  is  specified,  the
       modem control lines shall no longer be asserted.  Normally, this will disconnect the line.
       CBAUDEX is a mask for the speeds beyond those defined in POSIX.1 (57600 and above).  Thus,
       B57600 & CBAUDEX is nonzero.

       cfgetispeed() returns the input baud rate stored in the termios structure.

       cfsetispeed()  sets  the  input  baud rate stored in the termios structure to speed, which
       must be specified as one of the Bnnn constants listed above  for  cfsetospeed().   If  the
       input baud rate is set to zero, the input baud rate will be equal to the output baud rate.

       cfsetspeed()  is  a  4.4BSD  extension.  It takes the same arguments as cfsetispeed(), and
       sets both input and output speed.

RETURN VALUE

       cfgetispeed() returns the input baud rate stored in the termios structure.

       cfgetospeed() returns the output baud rate stored in the termios structure.

       All other functions return:

       0      on success.

       -1     on failure and set errno to indicate the error.

       Note  that  tcsetattr()  returns  success  if  any  of  the  requested  changes  could  be
       successfully  carried out.  Therefore, when making multiple changes it may be necessary to
       follow this call with a further call to tcgetattr() to check that all  changes  have  been
       performed successfully.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌─────────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │tcgetattr(), tcsetattr(), tcdrain(), │ Thread safety │ MT-Safe │
       │tcflush(), tcflow(), tcsendbreak(),  │               │         │
       │cfmakeraw(), cfgetispeed(),          │               │         │
       │cfgetospeed(), cfsetispeed(),        │               │         │
       │cfsetospeed(), cfsetspeed()          │               │         │
       └─────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       tcgetattr(),  tcsetattr(),  tcsendbreak(),  tcdrain(), tcflush(), tcflow(), cfgetispeed(),
       cfgetospeed(), cfsetispeed(), and cfsetospeed() are specified in POSIX.1-2001.

       cfmakeraw() and cfsetspeed() are nonstandard, but available on the BSDs.

NOTES

       UNIX V7 and several later systems have a list of  baud  rates  where  after  the  fourteen
       values  B0,  ..., B9600 one finds the two constants EXTA, EXTB ("External A" and "External
       B").  Many systems extend the list with much higher baud rates.

       The effect of a nonzero duration with tcsendbreak() varies.  SunOS specifies  a  break  of
       duration * N  seconds,  where  N is at least 0.25, and not more than 0.5.  Linux, AIX, DU,
       Tru64 send a break of duration milliseconds.  FreeBSD  and  NetBSD  and  HP-UX  and  MacOS
       ignore  the  value  of  duration.   Under Solaris and UnixWare, tcsendbreak() with nonzero
       duration behaves like tcdrain().

BUGS

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

SEE ALSO

       reset(1), setterm(1), stty(1), tput(1), tset(1), tty(1),  ioctl_console(2),  ioctl_tty(2),
       setserial(8)

COLOPHON

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       found at https://www.kernel.org/doc/man-pages/.