.\" Copyright (c) 1993 Michael Haardt

.\" (michael@moria.de)

.\" Fri Apr  2 11:32:09 MET DST 1993

.\"

.\" %%%LICENSE_START(GPLv2+_DOC_FULL)

.\" This is free documentation; you can redistribute it and/or

.\" modify it under the terms of the GNU General Public License as

.\" published by the Free Software Foundation; either version 2 of

.\" the License, or (at your option) any later version.

.\"

.\" The GNU General Public License's references to "object code"

.\" and "executables" are to be interpreted as the output of any

.\" document formatting or typesetting system, including

.\" intermediate and printed output.

.\"

.\" This manual is distributed in the hope that it will be useful,

.\" but WITHOUT ANY WARRANTY; without even the implied warranty of

.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

.\" GNU General Public License for more details.

.\"

.\" You should have received a copy of the GNU General Public

.\" License along with this manual; if not, see

.\" <http://www.gnu.org/licenses/>.

.\" %%%LICENSE_END

.\"

.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>

.\" Modified 1995-02-25 by Jim Van Zandt <jrv@vanzandt.mv.com>

.\" Modified 1995-09-02 by Jim Van Zandt <jrv@vanzandt.mv.com>

.\" moved to man3, aeb, 950919

.\" Modified 2001-09-22 by Michael Kerrisk <mtk.manpages@gmail.com>

.\" Modified 2001-12-17, aeb

.\" Modified 2004-10-31, aeb

.\" 2006-12-28, mtk:

.\"     Added .SS headers to give some structure to this page; and a

.\"     small amount of reordering.

.\"     Added a section on canonical and noncanonical mode.

.\"     Enhanced the discussion of "raw" mode for cfmakeraw().

.\"     Document CMSPAR.

.\"

.TH TERMIOS 3 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH 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

.SH SYNOPSIS

.nf

.B #include <termios.h>

.B #include <unistd.h>

.PP

.BI "int tcgetattr(int " fd ", struct termios *" termios_p );

.PP

.BI "int tcsetattr(int " fd ", int " optional_actions ,

.BI "              const struct termios *" termios_p );

.PP

.BI "int tcsendbreak(int " fd ", int " duration );

.PP

.BI "int tcdrain(int " fd );

.PP

.BI "int tcflush(int " fd ", int " queue_selector );

.PP

.BI "int tcflow(int " fd ", int " action );

.PP

.BI "void cfmakeraw(struct termios *" termios_p );

.PP

.BI "speed_t cfgetispeed(const struct termios *" termios_p );

.PP

.BI "speed_t cfgetospeed(const struct termios *" termios_p );

.PP

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

.PP

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

.PP

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

.fi

.PP

.in -4n

Feature Test Macro Requirements for glibc (see

.BR feature_test_macros (7)):

.in

.PP

.BR cfsetspeed (),

.BR cfmakeraw ():

    Since glibc 2.19:

        _DEFAULT_SOURCE

    Glibc 2.19 and earlier:

        _BSD_SOURCE

.SH DESCRIPTION

The termios functions describe a general terminal interface that is

provided to control asynchronous communications ports.

.SS The termios structure

.PP

Many of the functions described here have a \fItermios_p\fP argument

that is a pointer to a \fItermios\fP structure.

This structure contains at least the following members:

.PP

.in +4n

.EX

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 */

.EE

.in

.PP

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

.BR feature_test_macros (7))

is defined, as noted in brackets ("[]").

.PP

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.

.PP

\fIc_iflag\fP flag constants:

.TP

.B IGNBRK

Ignore BREAK condition on input.

.TP

.B BRKINT

If \fBIGNBRK\fP is set, a BREAK is ignored.

If it is not set

but \fBBRKINT\fP 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

\fBSIGINT\fP to be sent to this foreground process group.

When neither \fBIGNBRK\fP nor \fBBRKINT\fP are set, a BREAK

reads as a null byte (\(aq\\0\(aq), except when \fBPARMRK\fP is set,

in which case it reads as the sequence \\377 \\0 \\0.

.TP

.B IGNPAR

Ignore framing errors and parity errors.

.TP

.B 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

\fBINPCK\fP is set and \fBIGNPAR\fP 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 \fBISTRIP\fP (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.

.IP

If neither \fBIGNPAR\fP nor \fBPARMRK\fP

is set, read a character with a parity error or framing error

as \\0.

.TP

.B INPCK

Enable input parity checking.

.TP

.B ISTRIP

Strip off eighth bit.

.TP

.B INLCR

Translate NL to CR on input.

.TP

.B IGNCR

Ignore carriage return on input.

.TP

.B ICRNL

Translate carriage return to newline on input (unless \fBIGNCR\fP is set).

.TP

.B IUCLC

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

.TP

.B IXON

Enable XON/XOFF flow control on output.

.TP

.B IXANY

(XSI) Typing any character will restart stopped output.

(The default is to allow just the START character to restart output.)

.TP

.B IXOFF

Enable XON/XOFF flow control on input.

.TP

.B 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.

.TP

.BR IUTF8 " (since Linux 2.6.4)"

(not in POSIX) Input is UTF8;

this allows character-erase to be correctly performed in cooked mode.

.PP

.I c_oflag

flag constants:

.TP

.B OPOST

Enable implementation-defined output processing.

.TP

.B OLCUC

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

.TP

.B ONLCR

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

.TP

.B OCRNL

Map CR to NL on output.

.TP

.B ONOCR

Don't output CR at column 0.

.TP

.B ONLRET

Don't output CR.

.TP

.B OFILL

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

.TP

.B OFDEL

Fill character is ASCII DEL (0177).

If unset, fill character is ASCII NUL (\(aq\\0\(aq).

(Not implemented on Linux.)

.TP

.B NLDLY

Newline delay mask.

Values are \fBNL0\fP and \fBNL1\fP.

[requires

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.TP

.B CRDLY

Carriage return delay mask.

Values are \fBCR0\fP, \fBCR1\fP, \fBCR2\fP, or \fBCR3\fP.

[requires

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.TP

.B TABDLY

Horizontal tab delay mask.

Values are \fBTAB0\fP, \fBTAB1\fP, \fBTAB2\fP, \fBTAB3\fP (or \fBXTABS\fP).

A value of TAB3, that is, XTABS, expands tabs to spaces

(with tab stops every eight columns).

[requires

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.TP

.B BSDLY

Backspace delay mask.

Values are \fBBS0\fP or \fBBS1\fP.

(Has never been implemented.)

[requires

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.TP

.B VTDLY

Vertical tab delay mask.

Values are \fBVT0\fP or \fBVT1\fP.

.TP

.B FFDLY

Form feed delay mask.

Values are \fBFF0\fP or \fBFF1\fP.

[requires

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.PP

\fIc_cflag\fP flag constants:

.TP

.B CBAUD

(not in POSIX) Baud speed mask (4+1 bits).

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B CBAUDEX

(not in POSIX) Extra baud speed mask (1 bit), included in

.BR CBAUD .

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.IP

(POSIX says that the baud speed is stored in the

.I termios

structure without specifying where precisely, and provides

.BR cfgetispeed ()

and

.BR cfsetispeed ()

for getting at it.

Some systems use bits selected by

.B CBAUD

in

.IR c_cflag ,

other systems use separate fields, for example,

.I sg_ispeed

and

.IR sg_ospeed .)

.TP

.B CSIZE

Character size mask.

Values are \fBCS5\fP, \fBCS6\fP, \fBCS7\fP, or \fBCS8\fP.

.TP

.B CSTOPB

Set two stop bits, rather than one.

.TP

.B CREAD

Enable receiver.

.TP

.B PARENB

Enable parity generation on output and parity checking for input.

.TP

.B PARODD

If set, then parity for input and output is odd;

otherwise even parity is used.

.TP

.B HUPCL

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

.TP

.B CLOCAL

Ignore modem control lines.

.TP

.B LOBLK

(not in POSIX) Block output from a noncurrent shell layer.

For use by \fBshl\fP (shell layers).  (Not implemented on Linux.)

.TP

.B CIBAUD

(not in POSIX) Mask for input speeds.

The values for the

.B CIBAUD

bits are

the same as the values for the

.B CBAUD

bits, shifted left

.B IBSHIFT

bits.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

(Not implemented on Linux.)

.TP

.B CMSPAR

(not in POSIX)

Use "stick" (mark/space) parity (supported on certain serial

devices): if

.B PARODD

is set, the parity bit is always 1; if

.B PARODD

is not set, then the parity bit is always 0.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B CRTSCTS

(not in POSIX) Enable RTS/CTS (hardware) flow control.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.PP

\fIc_lflag\fP flag constants:

.TP

.B ISIG

When any of the characters INTR, QUIT, SUSP, or DSUSP are received,

generate the corresponding signal.

.TP

.B ICANON

Enable canonical mode (described below).

.TP

.B XCASE

(not in POSIX; not supported under Linux)

If \fBICANON\fP 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

.B _BSD_SOURCE

or

.B _SVID_SOURCE

or

.BR _XOPEN_SOURCE ]

.\" glibc is probably now wrong to allow

.\" Define

.\" .B _XOPEN_SOURCE

.\" to expose

.\" .BR XCASE .

.TP

.B ECHO

Echo input characters.

.TP

.B ECHOE

If \fBICANON\fP is also set, the ERASE character erases the preceding

input character, and WERASE erases the preceding word.

.TP

.B ECHOK

If \fBICANON\fP is also set, the KILL character erases the current line.

.TP

.B ECHONL

If \fBICANON\fP is also set, echo the NL character even if ECHO is not set.

.TP

.B ECHOCTL

(not in POSIX) If \fBECHO\fP is also set,

terminal special characters other than

TAB, NL, START, and STOP are echoed as \fB^X\fP,

where X is the character with

ASCII code 0x40 greater than the special character.

For example, character

0x08 (BS) is echoed as \fB^H\fP.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B ECHOPRT

(not in POSIX) If \fBICANON\fP and \fBECHO\fP are also set, characters

are printed as they are being erased.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B ECHOKE

(not in POSIX) If \fBICANON\fP is also set, KILL is echoed by erasing

each character on the line, as specified by \fBECHOE\fP and \fBECHOPRT\fP.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B DEFECHO

(not in POSIX) Echo only when a process is reading.

(Not implemented on Linux.)

.TP

.B FLUSHO

(not in POSIX; not supported under Linux)

Output is being flushed.

This flag is toggled by typing

the DISCARD character.

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B NOFLSH

Disable flushing the input and output queues when generating signals for the

INT, QUIT, and SUSP characters.

.\" Stevens lets SUSP only flush the input queue

.TP

.B TOSTOP

Send the

.B SIGTTOU

signal to the process group of a background process

which tries to write to its controlling terminal.

.TP

.B PENDIN

(not in POSIX; not supported under Linux)

All characters in the input queue are reprinted when

the next character is read.

.RB ( bash (1)

handles typeahead this way.)

[requires

.B _BSD_SOURCE

or

.BR _SVID_SOURCE ]

.TP

.B IEXTEN

Enable implementation-defined input processing.

This flag, as well as \fBICANON\fP must be enabled for the

special characters EOL2, LNEXT, REPRINT, WERASE to be interpreted,

and for the \fBIUCLC\fP flag to be effective.

.PP

The \fIc_cc\fP array defines the terminal special characters.

The symbolic indices (initial values) and meaning are:

.TP

.B VDISCARD

(not in POSIX; not supported under Linux; 017, SI, Ctrl-O)

Toggle: start/stop discarding pending output.

Recognized when

.B IEXTEN

is set, and then not passed as input.

.TP

.B VDSUSP

(not in POSIX; not supported under Linux; 031, EM, Ctrl-Y)

Delayed suspend character (DSUSP):

send

.B SIGTSTP

signal when the character is read by the user program.

Recognized when

.B IEXTEN

and

.B ISIG

are set, and the system supports

job control, and then not passed as input.

.TP

.B 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

.BR read (2)

in the user program returns 0, which signifies end-of-file.

Recognized when

.B ICANON

is set, and then not passed as input.

.TP

.B VEOL

(0, NUL)

Additional end-of-line character (EOL).

Recognized when

.B ICANON

is set.

.TP

.B VEOL2

(not in POSIX; 0, NUL)

Yet another end-of-line character (EOL2).

Recognized when

.B ICANON

is set.

.TP

.B 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

.B ICANON

is set, and then not passed as input.

.TP

.B VINTR

(003, ETX, Ctrl-C, or also 0177, DEL, rubout)

Interrupt character (INTR).

Send a

.B SIGINT

signal.

Recognized when

.B ISIG

is set, and then not passed as input.

.TP

.B 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

.B ICANON

is set, and then not passed as input.

.TP

.B 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

.B IEXTEN

is set, and then not passed as input.

.TP

.B VMIN

Minimum number of characters for noncanonical read (MIN).

.TP

.B VQUIT

(034, FS, Ctrl-\e)

Quit character (QUIT).

Send

.B SIGQUIT

signal.

Recognized when

.B ISIG

is set, and then not passed as input.

.TP

.B VREPRINT

(not in POSIX; 022, DC2, Ctrl-R)

Reprint unread characters (REPRINT).

Recognized when

.B ICANON

and

.B IEXTEN

are set, and then not passed as input.

.TP

.B VSTART

(021, DC1, Ctrl-Q)

Start character (START).

Restarts output stopped by the Stop character.

Recognized when

.B IXON

is set, and then not passed as input.

.TP

.B 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

.BR SIGINFO

signal (not supported on Linux) to the foreground process group.

.TP

.B VSTOP

(023, DC3, Ctrl-S)

Stop character (STOP).

Stop output until Start character typed.

Recognized when

.B IXON

is set, and then not passed as input.

.TP

.B VSUSP

(032, SUB, Ctrl-Z)

Suspend character (SUSP).

Send

.B SIGTSTP

signal.

Recognized when

.B ISIG

is set, and then not passed as input.

.TP

.B VSWTCH

(not in POSIX; not supported under Linux; 0, NUL)

Switch character (SWTCH).

Used in System V to switch shells in

.IR "shell layers" ,

a predecessor to shell job control.

.TP

.B VTIME

Timeout in deciseconds for noncanonical read (TIME).

.TP

.B VWERASE

(not in POSIX; 027, ETB, Ctrl-W)

Word erase (WERASE).

Recognized when

.B ICANON

and

.B IEXTEN

are set, and then not passed as input.

.PP

An individual terminal special character can be disabled by setting

the value of the corresponding

.I c_cc

element to

.BR _POSIX_VDISABLE .

.PP

The above symbolic subscript values are all different, except that

.BR VTIME ,

.B VMIN

may have the same value as

.BR VEOL ,

.BR VEOF ,

respectively.

In noncanonical mode the special character meaning is replaced

by the timeout meaning.

For an explanation of

.B VMIN

and

.BR VTIME ,

see the description of

noncanonical mode below.

.SS Retrieving and changing terminal settings

.PP

.BR tcgetattr ()

gets the parameters associated with the object referred by \fIfd\fP and

stores them in the \fItermios\fP structure referenced by

\fItermios_p\fP.

This function may be invoked from a background process;

however, the terminal attributes may be subsequently changed by a

foreground process.

.PP

.BR tcsetattr ()

sets the parameters associated with the terminal (unless support is

required from the underlying hardware that is not available) from the

\fItermios\fP structure referred to by \fItermios_p\fP.

\fIoptional_actions\fP specifies when the changes take effect:

.IP \fBTCSANOW\fP

the change occurs immediately.

.IP \fBTCSADRAIN\fP

the change occurs after all output written to

.I fd

has been transmitted.

This option should be used when changing

parameters that affect output.

.IP \fBTCSAFLUSH\fP

the change occurs after all output written to the object referred by

.I fd

has been transmitted, and all input that has been received but not read

will be discarded before the change is made.

.SS Canonical and noncanonical mode

The setting of the

.B ICANON

canon flag in

.I c_lflag

determines whether the terminal is operating in canonical mode

.RB ( ICANON

set) or

noncanonical mode

.RB ( ICANON

unset).

By default,

.B ICANON

is set.

.PP

In canonical mode:

.IP * 2

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

.BR read (2).

.IP * 2

Line editing is enabled (ERASE, KILL;

and if the

.B IEXTEN

flag is set: WERASE, REPRINT, LNEXT).

A

.BR read (2)

returns at most one line of input; if the

.BR 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

.BR read (2).

.IP * 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.,

.B ISIG

and

.B 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.

.PP

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

.RI ( c_cc[VMIN] )

and TIME

.RI ( c_cc[VTIME] )

determine the circumstances in which a

.BR read (2)

completes; there are four distinct cases:

.TP

MIN == 0, TIME == 0 (polling read)

If data is available,

.BR read (2)

returns immediately, with the lesser of the number of bytes

available, or the number of bytes requested.

If no data is available,

.BR read (2)

returns 0.

.TP

MIN > 0, TIME == 0 (blocking read)

.BR read (2)

blocks until MIN bytes are available,

and returns up to the number of bytes requested.

.TP

MIN == 0, TIME > 0 (read with timeout)

TIME specifies the limit for a timer in tenths of a second.

The timer is started when

.BR read (2)

is called.

.BR 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,

.BR read (2)

returns 0.

If data is already available at the time of the call to

.BR read (2),

the call behaves as though the data was received immediately after the call.

.TP

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.

.BR read (2)

returns when any of the following conditions is met:

.RS

.IP * 3

MIN bytes have been received.

.IP *

The interbyte timer expires.

.IP *

The number of bytes requested by

.BR read (2)

has been received.

(POSIX does not specify this termination condition,

and on some other implementations

.\" e.g., Solaris

.BR read (2)

does not return in this case.)

.RE

.IP

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

.BR read (2),

the call behaves as though the data was received immediately after the call.

.PP

POSIX

.\" POSIX.1-2008 XBD 11.1.7

does not specify whether the setting of the

.B O_NONBLOCK

file status flag takes precedence over the MIN and TIME settings.

If

.B O_NONBLOCK

is set, a

.BR 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

.BR read (2)

in noncanonical mode to return either 0, or \-1 with

.I errno

set to

.BR EAGAIN .

.SS Raw mode

.PP

.BR 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:

.PP

.in +4n

.EX

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;

.EE

.in

.\"

.SS Line control

.PP

.BR tcsendbreak ()

transmits a continuous stream of zero-valued bits for a specific

duration, if the terminal is using asynchronous serial data

transmission.

If \fIduration\fP is zero, it transmits zero-valued bits

for at least 0.25 seconds, and not more that 0.5 seconds.

If \fIduration\fP is not zero, it sends zero-valued bits for some

implementation-defined length of time.

.PP

If the terminal is not using asynchronous serial data transmission,

.BR tcsendbreak ()

returns without taking any action.

.PP

.BR tcdrain ()

waits until all output written to the object referred to by

.I fd

has been transmitted.

.PP

.BR tcflush ()

discards data written to the object referred to by

.I fd

but not transmitted, or data received but not read, depending on the