TERMIOS(3) Linux Programmer's Manual TERMIOS(3)
NAME
termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmak-
eraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed - get and
set terminal attributes, line control, get and set baud rate
SYNOPSIS
#include
#include
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(): _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]; /* control chars */
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 only exposed 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 IGNPAR is not set, prefix a character with a parity error or framing
error with /377 /0. 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 defined in POSIX.1:
OPOST Enable implementation-defined output processing.
The remaining c_oflag flag constants are defined in POSIX.1-2001, unless
marked otherwise.
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 (not in POSIX) 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). 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, ASCII control signals other than
TAB, NL, START, and STOP are echoed as ^X, where X is the character
with ASCII code 0x40 greater than the control signal. For example,
character 0x08 (BS) is echoed as ^H. [requires _BSD_SOURCE or
_SVID_SOURCE]
ECHOPRT
(not in POSIX) If ICANON and IECHO 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 special control characters. The symbolic indices
(initial values) and meaning are:
VINTR (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt character.
Send a SIGINT signal. Recognized when ISIG is set, and then not passed
as input.
VQUIT (034, FS, Ctrl-/) Quit character. Send SIGQUIT signal. Recognized
when ISIG is set, and then not passed as input.
VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase character.
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.
VKILL (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character. This erases
the input since the last EOF or beginning-of-line. Recognized when
ICANON is set, and then not passed as input.
VEOF (004, EOT, Ctrl-D) End-of-file character. 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.
VMIN Minimum number of characters for noncanonical read.
VEOL (0, NUL) Additional end-of-line character. Recognized when ICANON is
set.
VTIME Timeout in deciseconds for noncanonical read.
VEOL2 (not in POSIX; 0, NUL) Yet another end-of-line character. Recognized
when ICANON is set.
VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch character.
(Used by shl only.)
VSTART (021, DC1, Ctrl-Q) Start character. Restarts output stopped by the
Stop character. Recognized when IXON is set, and then not passed as
input.
VSTOP (023, DC3, Ctrl-S) Stop character. Stop output until Start character
typed. Recognized when IXON is set, and then not passed as input.
VSUSP (032, SUB, Ctrl-Z) Suspend character. Send SIGTSTP signal. Recognized
when ISIG is set, and then not passed as input.
VDSUSP (not in POSIX; not supported under Linux; 031, EM, Ctrl-Y) Delayed
suspend character: 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.
VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal next. Quotes the next input
character, depriving it of a possible special meaning. Recognized when
IEXTEN is set, and then not passed as input.
VWERASE
(not in POSIX; 027, ETB, Ctrl-W) Word erase. Recognized when ICANON
and IEXTEN are set, and then not passed as input.
VREPRINT
(not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters. Recognized
when ICANON and IEXTEN are set, and then not passed as input.
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.
VSTATUS
(not in POSIX; not supported under Linux; status request: 024, DC4,
Ctrl-T).
These 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 function 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 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).
In noncanonical mode input is available immediately (without the user having
to type a line-delimiter character), and line editing is disabled. 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: 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: read(2) blocks until the lesser of MIN bytes or the
number of bytes requested are available, and returns the lesser of these two
values.
* MIN == 0; TIME > 0: 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.
* MIN > 0; TIME > 0: 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 either when
the lesser of the number of bytes requested or MIN byte have been read, or
when the inter-byte timeout expires. Because the timer is only started
after the initial byte becomes available, at least one byte will be read.
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.
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().
SEE ALSO
stty(1), console_ioctl(4), tty_ioctl(4), setserial(8)
COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-06-20 TERMIOS(3)
