TERMIOS(3)                (2020-08-13)                 TERMIOS(3)

          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

          #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

          cfsetspeed(), cfmakeraw():
              Since glibc 2.19:
              Glibc 2.19 and earlier:

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

        The termios structure

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          Many of the functions described here have a termios_p argu-
          ment that is a pointer to a termios structure.  This struc-
          ture 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 brack-
          ets ("[]").

          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

          c_iflag flag constants:

               Ignore BREAK condition on input.

               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 pro-
               cess group.  When neither IGNBRK nor BRKINT are set, a
               BREAK reads as a null byte (aq\0aq), except when PARMRK
               is set, in which case it reads as the sequence \377 \0

               Ignore framing errors and parity errors.

               If this bit is set, input bytes with parity or framing
               errors are marked when passed to the program.  This bit
               is meaningful only when INPCK is set and IGNPAR is not
               set.  The way erroneous bytes are marked is with two
               preceding bytes, \377 and \0.  Thus, the program actu-
               ally reads three bytes for one erroneous byte received
               from the terminal.  If a valid byte has the value \377,
               and ISTRIP (see below) is not set, the program might
               confuse it with the prefix that marks a parity error.
               Therefore, a valid byte \377 is passed to the program

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               as two bytes, \377 \377, in this case.

               If neither IGNPAR nor PARMRK is set, read a character
               with a parity error or framing error as \0.

               Enable input parity checking.

               Strip off eighth bit.

               Translate NL to CR on input.

               Ignore carriage return on input.

               Translate carriage return to newline on input (unless
               IGNCR is set).

               (not in POSIX) Map uppercase characters to lowercase on

          IXON Enable XON/XOFF flow control on output.

               (XSI) Typing any character will restart stopped output.
               (The default is to allow just the START character to
               restart output.)

               Enable XON/XOFF flow control on input.

               (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:

               Enable implementation-defined output processing.

               (not in POSIX) Map lowercase characters to uppercase on

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               (XSI) Map NL to CR-NL on output.

               Map CR to NL on output.

               Don't output CR at column 0.

               Don't output CR.

               Send fill characters for a delay, rather than using a
               timed delay.

               Fill character is ASCII DEL (0177).  If unset, fill
               character is ASCII NUL (aq\0aq).  (Not implemented on

               Newline delay mask.  Values are NL0 and NL1.  [requires
               _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

               Carriage return delay mask.  Values are CR0, CR1, CR2,
               or CR3.  [requires _BSD_SOURCE or _SVID_SOURCE or

               Horizontal tab delay mask.  Values are TAB0, TAB1,
               TAB2, TAB3 (or XTABS, but see the BUGS section).  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]

               Backspace delay mask.  Values are BS0 or BS1.  (Has
               never been implemented.)  [requires _BSD_SOURCE or
               _SVID_SOURCE or _XOPEN_SOURCE]

               Vertical tab delay mask.  Values are VT0 or VT1.

               Form feed delay mask.  Values are FF0 or FF1.
               [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

          c_cflag flag constants:


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               (not in POSIX) Baud speed mask (4+1 bits).  [requires
               _BSD_SOURCE or _SVID_SOURCE]

               (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 get-
               ting at it.  Some systems use bits selected by CBAUD in
               c_cflag, other systems use separate fields, for exam-
               ple, sg_ispeed and sg_ospeed.)

               Character size mask.  Values are CS5, CS6, CS7, or CS8.

               Set two stop bits, rather than one.

               Enable receiver.

               Enable parity generation on output and parity checking
               for input.

               If set, then parity for input and output is odd; other-
               wise even parity is used.

               Lower modem control lines after last process closes the
               device (hang up).

               Ignore modem control lines.

               (not in POSIX) Block output from a noncurrent shell
               layer.  For use by shl (shell layers).  (Not imple-
               mented on Linux.)

               (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

               (not in POSIX) Use "stick" (mark/space) parity

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               (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]

               (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.

               Enable canonical mode (described below).

               (not in POSIX; not supported under Linux) If ICANON is
               also set, terminal is uppercase only.  Input is con-
               verted to lowercase, except for characters preceded by
               \.  On output, uppercase characters are preceded by \
               and lowercase characters are converted to uppercase.
               [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]

          ECHO Echo input characters.

               If ICANON is also set, the ERASE character erases the
               preceding input character, and WERASE erases the pre-
               ceding word.

               If ICANON is also set, the KILL character erases the
               current line.

               If ICANON is also set, echo the NL character even if
               ECHO is not set.

               (not in POSIX) If ECHO is also set, terminal special
               characters other than TAB, NL, START, and STOP are
               echoed as haX, where X is the character with ASCII code
               0x40 greater than the special character.  For example,
               character 0x08 (BS) is echoed as haH.  [requires
               _BSD_SOURCE or _SVID_SOURCE]

               (not in POSIX) If ICANON and ECHO are also set, charac-
               ters are printed as they are being erased.  [requires
               _BSD_SOURCE or _SVID_SOURCE]

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               (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

               (not in POSIX) Echo only when a process is reading.
               (Not implemented on Linux.)

               (not in POSIX; not supported under Linux) Output is
               being flushed.  This flag is toggled by typing the DIS-
               CARD character.  [requires _BSD_SOURCE or _SVID_SOURCE]

               Disable flushing the input and output queues when gen-
               erating signals for the INT, QUIT, and SUSP characters.

               Send the SIGTTOU signal to the process group of a back-
               ground process which tries to write to its controlling

               (not in POSIX; not supported under Linux) All charac-
               ters in the input queue are reprinted when the next
               character is read.  (bash(1) handles typeahead this
               way.)  [requires _BSD_SOURCE or _SVID_SOURCE]

               Enable implementation-defined input processing.  This
               flag, as well as ICANON must be enabled for the special
               characters EOL2, LNEXT, REPRINT, WERASE to be inter-
               preted, 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:

               (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

               (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.

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          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).  Rec-
               ognized when ICANON is set.

               (not in POSIX; 0, NUL) Yet another end-of-line charac-
               ter (EOL2).  Recognized when ICANON is set.

               (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #)
               Erase character (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.

               (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt
               character (INTR).  Send a SIGINT signal.  Recognized
               when ISIG is set, and then not passed as input.

               (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.

               (not in POSIX; 026, SYN, Ctrl-V) Literal next (LNEXT).
               Quotes the next input character, depriving it of a pos-
               sible special meaning.  Recognized when IEXTEN is set,
               and then not passed as input.

          VMIN Minimum number of characters for noncanonical read

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

               (not in POSIX; 022, DC2, Ctrl-R) Reprint unread charac-
               ters (REPRINT).  Recognized when ICANON and IEXTEN are
               set, and then not passed as input.

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               (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.

               (not in POSIX; not supported under Linux; status
               request: 024, DC4, Ctrl-T).  Status character (STATUS).
               Display status information 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.

               (023, DC3, Ctrl-S) Stop character (STOP).  Stop output
               until Start character typed.  Recognized when IXON is
               set, and then not passed as input.

               (032, SUB, Ctrl-Z) Suspend character (SUSP).  Send
               SIGTSTP signal.  Recognized when ISIG is set, and then
               not passed as input.

               (not in POSIX; not supported under Linux; 0, NUL)
               Switch character (SWTCH).  Used in System V to switch
               shells in shell layers, a predecessor to shell job con-

               Timeout in deciseconds for noncanonical read (TIME).

               (not in POSIX; 027, ETB, Ctrl-W) Word erase (WERASE).
               Recognized 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

          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 char-
          acter 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 ref-
          erenced by termios_p.  This function may be invoked from a

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          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:

               the change occurs immediately.

               the change occurs after all output written to fd has
               been transmitted.  This option should be used when
               changing parameters that affect output.

               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 dis-
               carded 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 is 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

          * The maximum line length is 4096 chars (including the ter-
            minating newline character); lines longer than 4096 chars
            are truncated.  After 4095 characters, input processing
            (e.g., ISIG and ECHO* processing) continues, but any input
            data after 4095 characters up to (but not including) any
            terminating newline is discarded.  This ensures that the
            terminal can always receive more input until at least one

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            line can be read.

          In noncanonical mode input is available immediately (without
          the user having to type a line-delimiter character), no
          input processing is performed, and line editing is disabled.
          The read buffer will only accept 4095 chars; this provides
          the necessary space for a newline char if the input mode is
          switched to canonical.  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 (polling read)
               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 (blocking read)
               read(2) blocks until MIN bytes are available, and
               returns up to the number of bytes requested.

          MIN == 0, TIME > 0 (read with timeout)
               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.  If data is already available at the time of
               the call to read(2), the call behaves as though the
               data was received immediately after the call.

          MIN > 0, TIME > 0 (read with interbyte timeout)
               TIME specifies the limit for a timer in tenths of a
               second.  Once an initial byte of input becomes avail-
               able, the timer is restarted after each further byte is
               received.  read(2) returns when any of the following
               conditions is met:

               *  MIN bytes have been received.

               *  The interbyte timer expires.

               *  The number of bytes requested by read(2) has been
                  received.  (POSIX does not specify this termination
                  condition, and on some other implementations read(2)
                  does not return in this case.)

               Because the timer is started only after the initial
               byte becomes available, at least one byte will be read.
               If data is already available at the time of the call to
               read(2), the call behaves as though the data was
               received immediately after the call.

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          POSIX does not specify whether the setting of the O_NONBLOCK
          file status flag takes precedence over the MIN and TIME set-
          tings.  If O_NONBLOCK is set, a read(2) in noncanonical mode
          may return immediately, regardless of the setting of MIN or
          TIME.  Furthermore, if no data is available, POSIX permits a
          read(2) in noncanonical mode to return either 0, or -1 with
          errno set to EAGAIN.

        Raw mode
          cfmakeraw() sets the terminal to something like the "raw"
          mode of the old Version 7 terminal driver: input is avail-
          able 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 &= ti(IGNBRK | BRKINT | PARMRK | ISTRIP
                              | INLCR | IGNCR | ICRNL | IXON);
              termios_p->c_oflag &= tiOPOST;
              termios_p->c_lflag &= ti(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
              termios_p->c_cflag &= ti(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 asyn-
          chronous serial data transmission.  If duration is zero, it
          transmits zero-valued bits for at least 0.25 seconds, and
          not more than 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 trans-
          mission, 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:

               flushes data received but not read.

               flushes data written but not transmitted.

               flushes both data received but not read, and data writ-
               ten but not transmitted.

          tcflow() suspends transmission or reception of data on the

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          object referred to by fd, depending on the value of action:

               suspends output.

               restarts suspended output.

               transmits a STOP character, which stops the terminal
               device from transmitting data to the system.

               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

          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 ter-
          mios structure pointed to by termios_p to speed, which must
          be one of these constants:


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          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

          cfgetispeed() returns the input baud rate stored in the ter-
          mios 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 argu-
          ments as cfsetispeed(), and sets both input and output

          cfgetispeed() returns the input baud rate stored in the ter-
          mios 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.  There-
          fore, 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.

          For an explanation of the terms used in this section, see
          attributes(7).  allbox; lbw36 lb lb l l l.
          Interface Attribute Value T{ tcgetattr(), tcsetattr(),
          tcdrain(), tcflush(), tcflow(), tcsendbreak(), cfmakeraw(),
          cfgetispeed(), cfgetospeed(), cfsetispeed(), cfsetospeed(),

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          cfsetspeed() T}   Thread safety  MT-Safe

          tcgetattr(),    tcsetattr(),    tcsendbreak(),    tcdrain(),
          tcflush(),     tcflow(),    cfgetispeed(),    cfgetospeed(),
          cfsetispeed(), and cfsetospeed() are specified  in  POSIX.1-

          cfmakeraw() and cfsetspeed() are nonstandard, but  available
          on the BSDs.

          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().

          On the Alpha  architecture  before  Linux  4.16  (and  glibc
          before 2.28), the XTABS value was different from TAB3 and it
          was ignored by the N_TTY line discipline code of the  termi-
          nal  driver  as  a  result (because as it wasn't part of the
          TABDLY mask).

          reset(1), setterm(1),  stty(1),  tput(1),  tset(1),  tty(1),
          ioctl_console(2), ioctl_tty(2), setserial(8)

          This page is part of release 5.10  of  the  Linux  man-pages
          project.   A  description  of the project, information about
          reporting bugs, and the latest version of this page, can  be
          found at https://www.kernel.org/doc/man-pages/.

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