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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);

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

       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.

       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 struc-
	      ture  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	 sepa-
	      rate fields, e.g.	 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 Parity for input and output is odd.

       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.)

       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.  This enables the special characters EOF,
	      EOL, EOL2, ERASE, KILL, LNEXT, REPRINT, STATUS, and WERASE,  and
	      buffers by lines.

       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 char-
	      acters are preceded by \ and lowercase characters are  converted
	      to uppercase.

       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 imple-
	      mented 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 the
	      SIGINT, SIGQUIT and SIGSUSP signals.

       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  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  charac-
	      ter.  Send  a  SIGINT  signal.  Recognized when ISIG is set, and
	      then not passed as input.

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

       VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase charac-
	      ter. 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.  Rec-
	      ognized 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 wait-
	      ing user program without waiting for end-of-line.	 If it is  the
	      first  character	of  the	 line,	the read() 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 non-canonical read.

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

       VTIME  Timeout in deciseconds for non-canonical read.

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

       VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch charac-
	      ter. (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 char-
	      acter  typed.   Recognized when IXON is set, and then not passed
	      as input.

       VSUSP  (032, SUB, Ctrl-Z) Suspend character. Send SIGTSTP signal.  Rec-
	      ognized 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  charac-
	      ter  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)  Tog-
	      gle: start/stop discarding pending output.  Recognized when IEX-
	      TEN 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.	 MIN (indexed using VMIN) represents  the  minimum  number  of
       characters  that should be received to satisfy the read.	 TIME (indexed
       using VTIME) is a decisecond-valued timer. When both are	 set,  a  read
       will  wait  until  at  least  one character has been received, and then
       return as soon as either MIN characters have been received or time TIME
       has  passed  since the last character was received. If only MIN is set,
       the read will not return before MIN characters have been	 received.  If
       only  TIME  is set, the read will return as soon as either at least one
       character has been received, or the timer times out. If neither is set,
       the  read  will	return	immediately, only giving the currently already
       available characters.

       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 pro-
       cess.

       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 trans-
	      mitted.  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.

       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.

       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.

       cfmakeraw() sets the terminal attributes 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;

       cfgetospeed() returns the output baud rate stored in the termios struc-
       ture 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.  Nor-
       mally, 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 non-zero.

       cfgetispeed() returns the input baud rate stored in the termios	struc-
       ture.

       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 struc-
       ture.

       cfgetospeed() returns the output baud rate stored in the termios struc-
       ture.

       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.


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 non-zero 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 mil-
       liseconds.   FreeBSD and NetBSD and HP-UX and MacOS ignore the value of
       duration.  Under Solaris	 and  Unixware,	 tcsendbreak()	with  non-zero
       duration behaves like tcdrain().

SEE ALSO
       stty(1), feature_test_macros(7), setserial(8)



Linux				  2004-10-31			    TERMIOS(3)
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