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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);

       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];	  /* 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.

       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	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, 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 char‐
	      acters  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 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
	      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 terminal special characters.  The symbolic
       indices (initial values) and meaning are:

       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.

       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 charac‐
	      ter (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  charac‐
	      ter (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  (RE‐
	      PRINT).  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 infor‐
	      mation 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  sig‐
	      nal.  Recognized when ISIG is set, and then not passed as input.

       VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch charac‐
	      ter (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).	Recog‐
	      nized 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.

       The above 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 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.

   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), no input processing is per‐
       formed, 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 immedi‐
	 ately, with the lesser of the number of bytes available, or the  num‐
	 ber 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 started only 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  charac‐
       ter,  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 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 nonzero.

       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.

CONFORMING TO
       tcgetattr(),   tcsetattr(),   tcsendbreak(),   tcdrain(),    tcflush(),
       tcflow(),   cfgetispeed(),   cfgetospeed(),  cfsetispeed(),  and	 cfse‐
       tospeed() 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 3.54 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				  2013-03-15			    TERMIOS(3)
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