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NAME

       tty ioctl - ioctls for terminals and serial lines

SYNOPSIS

       #include <termios.h>

       int ioctl(int fd, int cmd, ...);

DESCRIPTION

       The  ioctl()  call for terminals and serial ports accepts many possible
       command arguments.  Most require a third  argument,  of  varying  type,
       here called argp or arg.

       Use  of ioctl makes for non-portable programs.  Use the POSIX interface
       described in termios(3) whenever possible.

   Get and Set Terminal Attributes
       TCGETS    struct termios *argp
              Equivalent to tcgetattr(fd, argp).
              Get the current serial port settings.

       TCSETS    const struct termios *argp
              Equivalent to tcsetattr(fd, TCSANOW, argp).
              Set the current serial port settings.

       TCSETSW   const struct termios *argp
              Equivalent to tcsetattr(fd, TCSADRAIN, argp).
              Allow the output buffer to drain, and  set  the  current  serial
              port settings.

       TCSETSF   const struct termios *argp
              Equivalent to tcsetattr(fd, TCSAFLUSH, argp).
              Allow the output buffer to drain, discard pending input, and set
              the current serial port settings.

       The following four  ioctls  are  just  like  TCGETS,  TCSETS,  TCSETSW,
       TCSETSF,  except  that  they take a struct termio * instead of a struct
       termios *.

       TCGETA    struct termio *argp

       TCSETA    const struct termio *argp

       TCSETAW   const struct termio *argp

       TCSETAF   const struct termio *argp

   Locking the termios structure
       The termios structure of a tty can be locked.  The  lock  is  itself  a
       termios  structure,  with  non-zero  bits or fields indicating a locked
       value.

       TIOCGLCKTRMIOS struct termios *argp
              Gets  the  locking  status  of  the  termios  structure  of  the
              terminal.

       TIOCSLCKTRMIOS const struct termios *argp
              Sets  the  locking  status  of  the  termios  structure  of  the
              terminal.  Only root can do this.

   Get and Set Window Size
       Window sizes are kept in the kernel, but not used by the kernel (except
       in  the  case  of  virtual  consoles,  where the kernel will update the
       window size when the size of the virtual console changes, for  example,
       by loading a new font).

       TIOCGWINSZ     struct winsize *argp
              Get window size.

       TIOCSWINSZ     const struct winsize *argp
              Set window size.

       The struct used by these ioctls is defined as

           struct winsize {
               unsigned short ws_row;
               unsigned short ws_col;
               unsigned short ws_xpixel;   /* unused */
               unsigned short ws_ypixel;   /* unused */
           };

       When  the  window  size  changes,  a  SIGWINCH  signal  is  sent to the
       foreground process group.

   Sending a Break
       TCSBRK    int arg
              Equivalent to tcsendbreak(fd, arg).
              If the terminal is using asynchronous serial data  transmission,
              and  arg  is zero, then send a break (a stream of zero bits) for
              between 0.25 and 0.5 seconds.  If  the  terminal  is  not  using
              asynchronous  serial  data  transmission, then either a break is
              sent, or the function returns without doing anything.  When  arg
              is non-zero, nobody knows what will happen.

              (SVr4,  UnixWare,  Solaris, Linux treat tcsendbreak(fd,arg) with
              non-zero  arg  like  tcdrain(fd).   SunOS  treats   arg   as   a
              multiplier, and sends a stream of bits arg times as long as done
              for zero arg.  DG/UX and AIX treat  arg  (when  non-zero)  as  a
              timeinterval measured in milliseconds.  HP-UX ignores arg.)

       TCSBRKP   int arg
              So-called  "POSIX version" of TCSBRK.  It treats non-zero arg as
              a timeinterval measured in deciseconds, and  does  nothing  when
              the driver does not support breaks.

       TIOCSBRK  void
              Turn break on, that is, start sending zero bits.

       TIOCCBRK  void
              Turn break off, that is, stop sending zero bits.

   Software flow control
       TCXONC    int arg
              Equivalent to tcflow(fd, arg).
              See  tcflow(3)  for  the  argument values TCOOFF, TCOON, TCIOFF,
              TCION.

   Buffer count and flushing
       FIONREAD  int *argp
              Get the number of bytes in the input buffer.

       TIOCINQ   int *argp
              Same as FIONREAD.

       TIOCOUTQ  int *argp
              Get the number of bytes in the output buffer.

       TCFLSH    int arg
              Equivalent to tcflush(fd, arg).
              See tcflush(3)  for  the  argument  values  TCIFLUSH,  TCOFLUSH,
              TCIOFLUSH.

   Faking input
       TIOCSTI   const char *argp
              Insert the given byte in the input queue.

   Redirecting console output
       TIOCCONS  void
              Redirect   output  that  would  have  gone  to  /dev/console  or
              /dev/tty0 to the given tty.  If that was a pty master,  send  it
              to the slave.  Anybody can do this as long as the output was not
              redirected yet.  If it was redirected already EBUSY is returned,
              but  root  may  stop  redirection  by  using  this ioctl with fd
              pointing at /dev/console or /dev/tty0.

   Controlling tty
       TIOCSCTTY int arg
              Make the given tty the controlling tty of the  calling  process.
              The  calling  process  must  be  a session leader and not have a
              controlling tty already.  If this tty is already the controlling
              tty  of  a  different  session  group  then the ioctl fails with
              EPERM, unless the caller is root and arg equals 1, in which case
              the  tty is stolen, and all processes that had it as controlling
              tty lose it.

       TIOCNOTTY void
              If the given tty was the controlling tty of the calling process,
              give  up  this  controlling  tty.   If  the  process was session
              leader, then send SIGHUP and SIGCONT to the  foreground  process
              group  and  all  processes  in  the  current  session lose their
              controlling tty.

   Process group and session ID
       TIOCGPGRP pid_t *argp
              When successful, equivalent to *argp = tcgetpgrp(fd).
              Get the process group ID of the foreground process group on this
              tty.

       TIOCSPGRP const pid_t *argp
              Equivalent to tcsetpgrp(fd, *argp).
              Set the foreground process group ID of this tty.

       TIOCGSID  pid_t *argp
              Get the session ID of the given tty.  This will fail with ENOTTY
              in case the tty is not a master pty and not our controlling tty.
              Strange.

   Exclusive mode
       TIOCEXCL  void
              Put  the tty into exclusive mode.  No further open(2) operations
              on the terminal are permitted.   (They  will  fail  with  EBUSY,
              except for root.)

       TIOCNXCL  void
              Disable exclusive mode.

   Line discipline
       TIOCGETD  int *argp
              Get the line discipline of the tty.

       TIOCSETD  const int *argp
              Set the line discipline of the tty.

   Pseudo-tty ioctls
       TIOCPKT   const int *argp
              Enable  (when *argp is non-zero) or disable packet mode.  Can be
              applied to the master side of a pseudo-terminal only  (and  will
              return  ENOTTY  otherwise).   In  packet  mode,  each subsequent
              read(2) will return a packet that either contains a single  non-
              zero  control  byte,  or has a single byte containing zero (' ')
              followed by data written on the slave side of the pty.   If  the
              first  byte  is not TIOCPKT_DATA (0), it is an OR of one or more
              of the following bits:

              TIOCPKT_FLUSHREAD   The read queue for the terminal is flushed.
              TIOCPKT_FLUSHWRITE  The write queue for the terminal is flushed.
              TIOCPKT_STOP        Output to the terminal is stopped.
              TIOCPKT_START       Output to the terminal is restarted.
              TIOCPKT_DOSTOP      The start and stop characters are ^S/^Q.
              TIOCPKT_NOSTOP      The start and stop characters are not ^S/^Q.

              While this mode is  in  use,  the  presence  of  control  status
              information to be read from the master side may be detected by a
              select(2) for exceptional conditions.

              This mode is used by rlogin(1) and  rlogind(8)  to  implement  a
              remote-echoed, locally ^S/^Q flow-controlled remote login.

              The  BSD  ioctls TIOCSTOP, TIOCSTART, TIOCUCNTL, TIOCREMOTE have
              not been implemented under Linux.

   Modem control
       TIOCMGET  int *argp
              get the status of modem bits.

       TIOCMSET  const int *argp
              set the status of modem bits.

       TIOCMBIC  const int *argp
              clear the indicated modem bits.

       TIOCMBIS  const int *argp
              set the indicated modem bits.

       Bits used by these four ioctls:

       TIOCM_LE        DSR (data set ready/line enable)
       TIOCM_DTR       DTR (data terminal ready)
       TIOCM_RTS       RTS (request to send)
       TIOCM_ST        Secondary TXD (transmit)
       TIOCM_SR        Secondary RXD (receive)
       TIOCM_CTS       CTS (clear to send)
       TIOCM_CAR       DCD (data carrier detect)
       TIOCM_CD         see TIOCM_CAR
       TIOCM_RNG       RNG (ring)
       TIOCM_RI         see TIOCM_RNG
       TIOCM_DSR       DSR (data set ready)

   Marking a line as local
       TIOCGSOFTCAR   int *argp
              ("Get software carrier flag") Get the status of the CLOCAL  flag
              in the c_cflag field of the termios structure.

       TIOCSSOFTCAR   const int *argp
              ("Set software carrier flag") Set the CLOCAL flag in the termios
              structure when *argp is non-zero, and clear it otherwise.

       If the CLOCAL flag for a line is off, the hardware carrier detect (DCD)
       signal  is  significant,  and  an open(2) of the corresponding tty will
       block until DCD is asserted, unless the O_NONBLOCK flag is  given.   If
       CLOCAL  is  set,  the  line  behaves as if DCD is always asserted.  The
       software carrier flag is usually turned on for local  devices,  and  is
       off for lines with modems.

   Linux-specific
       For the TIOCLINUX ioctl, see console_ioctl(4).

   Kernel debugging
       #include <linux/tty.h>

       TIOCTTYGSTRUCT struct tty_struct *argp
              Get the tty_struct corresponding to fd.

RETURN VALUE

       The  ioctl()  system call returns 0 on success.  On error it returns -1
       and sets errno appropriately.

ERRORS

       EINVAL Invalid command parameter.

       ENOIOCTLCMD
              Unknown command.

       ENOTTY Inappropriate fd.

       EPERM  Insufficient permission.

EXAMPLE

       Check the condition of DTR on the serial port.

       #include <termios.h>
       #include <fcntl.h>
       #include <sys/ioctl.h>

       int
       main(void)
       {
           int fd, serial;

           fd = open("/dev/ttyS0", O_RDONLY);
           ioctl(fd, TIOCMGET, &serial);
           if (serial & TIOCM_DTR)
               puts("TIOCM_DTR is not set");
           else
               puts("TIOCM_DTR is set");
           close(fd);
       }

SEE ALSO

       ioctl(2), termios(3), console_ioctl(4), pty(7)

COLOPHON

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