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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 <&lt;termios.h>&gt;
       #include <&lt;unistd.h>&gt;

       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  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 non-current 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, 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(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  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(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 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
              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  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.  For an explanation of VMIN and VTIME, see the description  of
       non-canonical 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 non-canonical mode
       The  setting of the ICANON canon flag in c_lflag determines whether the
       terminal is operating in canonical mode (ICANON set)  or  non-canonical
       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 non-canonical 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])  deter-
       mine  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  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 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 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.

CONFORMING TO
       tcgetattr(),    tcsetattr(),   tcsendbreak(),   tcdrain(),   tcflush(),
       tcflow(),  cfgetispeed(),  cfgetospeed(),  cfsetispeed(),   and   cfse-
       tospeed() are specified in POSIX.1-2001.

       cfmakeraw()  and  cfsetspeed()  are  non-standard, 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  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
       milliseconds.  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), console_ioctl(4), tty_ioctl(4), setserial(8)

COLOPHON
       This page is part of release 3.05 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                             2007-11-26                        TERMIOS(3)