|
HTML rendering created 2026-09-09 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
|
|
|
termios(3type) termios(3type)
termios - terminal input/output settings
Standard C library (libc)
#include <termios.h>
struct termios {
// At least these members, in no particular order
tcflag_t c_iflag;
tcflag_t c_oflag;
tcflag_t c_cflag;
tcflag_t c_lflag;
cc_t c_cc[NCCS];
};
.c_iflag
Input modes.
.c_oflag
Output modes.
.c_cflag
Control modes.
.c_lflag
Local modes.
.c_cc 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.
The below 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.
[1m.c_iflag[24m 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.
[1m.c_oflag[24m 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 The NL character is assumed to do the carriage-return
function; the kernel's idea of the current column is set to
0 after both NL and 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]
[1m.c_cflag[24m 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 in glibc, supported on Linux
via TCGET* and TCSET* ioctls; see ioctl_tty(2))
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]
[1m.c_lflag[24m 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.
[1m.c_cc[24m array indices
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.
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.
POSIX.1-2024.
POSIX.1-2001.
On the Alpha architecture before Linux 4.16 (and glibc before
glibc 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).
cc_t(3type), tcflag_t(3type), termios(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.19.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2026-09-09. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.19 2026-07-02 termios(3type)
Pages that refer to this page: setpgid(2), cc_t(3type), cfmakeraw(3), cfsetspeed(3), getpass(3), tcsetattr(3), credentials(7), termios(7)
|
HTML rendering created 2026-09-09 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|