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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, cfsetspeed - 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 communica-
       tions 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 charac-
              ter 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 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 non-current shell layer.  For use by shl (shell layers).  (Not imple-
              mented 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  pre-
              ceded  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 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 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  con-
              trolling 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 effec-
              tive.

       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 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.  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 sig-
              nal 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 pos-
              sible 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) 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 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 struc-
       ture 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  speci-
       fies 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 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 charac-
       ter), and line editing is disabled.  The settings of MIN (c_cc[VMIN]) and TIME (c_cc[VTIME]) determine the cir-
       cumstances 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  avail-
         able, 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 character, 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 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.  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 non-zero.

       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 out-
       put 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  tcge-
       tattr() to check that all changes have been performed successfully.

CONFORMING TO
       tcgetattr(),   tcsetattr(),   tcsendbreak(),  tcdrain(),  tcflush(),  tcflow(),  cfgetispeed(),  cfgetospeed(),
       cfsetispeed(), and cfsetospeed() 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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2007-11-26                        TERMIOS(3)