TERMIOS(3)						     Linux Programmer's Manual							TERMIOS(3)

NAME

       termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfset-
       speed - 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(): _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 speci-
       fied 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 (''), except when PARMRK  is  set,
	      in which case it reads as the sequence 377  .

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

       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 ('').  (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 char-
	      acter  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.  Recog-
	      nized 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  non-
       canonical 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  avail-
       able) 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 dis-
       abled.  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  char-
       acter,  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  con-
       stants:

	    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 success-
       fully.

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)