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Linux 2.6 - man page for tty_ioctl (linux section 4)

TTY_IOCTL(4)			    Linux Programmer's Manual			     TTY_IOCTL(4)

       tty_ioctl - ioctls for terminals and serial lines

       #include <termios.h>

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

       The  ioctl(2) 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  nonportable  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 terminal can be locked.  The lock is itself a termios struc-
       ture, with nonzero 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  a  process
	      with the CAP_SYS_ADMIN capability 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  vir-
       tual console changes, for example, by loading a new font).

       The following constants and structure are defined in <sys/ioctl.h>.

       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 nonzero,  nobody
	      knows what will happen.

	      (SVr4,  UnixWare,  Solaris,  Linux  treat tcsendbreak(fd,arg) with nonzero 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 nonzero) as a
	      time interval measured in milliseconds.  HP-UX ignores arg.)

       TCSBRKP	 int arg
	      So-called "POSIX version" of TCSBRK.  It treats nonzero arg as a timeinterval  mea-
	      sured 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 ter-
	      minal.  If that was a pseudoterminal master, send it to the slave.  In Linux before
	      version  2.6.10,	anybody can do this as long as the output was not redirected yet;
	      since version 2.6.10, only a process with the CAP_SYS_ADMIN capability may do this.
	      If  output was redirected already EBUSY is returned, but redirection can be stopped
	      by using this ioctl with fd pointing at /dev/console or /dev/tty0.

   Controlling terminal
       TIOCSCTTY int arg
	      Make the given terminal the controlling terminal of the calling process.	The call-
	      ing  process  must be a session leader and not have a controlling terminal already.
	      For this case, arg should be specified as zero.

	      If this terminal is already the controlling terminal of a different  session  group
	      then the ioctl fails with EPERM, unless the caller has the CAP_SYS_ADMIN capability
	      and arg equals 1, in which case the terminal is stolen, and all processes that  had
	      it as controlling terminal lose it.

       TIOCNOTTY void
	      If  the given terminal was the controlling terminal of the calling process, give up
	      this controlling terminal.  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 terminal.

   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 terminal.

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

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

   Exclusive mode
       TIOCEXCL  void
	      Put  the terminal into exclusive mode.  No further open(2) operations on the termi-
	      nal are permitted.  (They will fail with EBUSY,  except  for  a  process	with  the
	      CAP_SYS_ADMIN capability.)

       TIOCNXCL  void
	      Disable exclusive mode.

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

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

   Pseudoterminal ioctls
       TIOCPKT	 const int *argp
	      Enable  (when *argp is nonzero) or disable packet mode.  Can be applied to the mas-
	      ter side of a pseudoterminal only (and will return ENOTTY  otherwise).   In  packet
	      mode,  each  subsequent  read(2) will return a packet that either contains a single
	      nonzero control byte, or has a single byte containing zero (' ') followed  by  data
	      written  on  the	slave  side  of  the  pseudoterminal.	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 nonzero, and clear it otherwise.

       If the CLOCAL flag for a line is off, the hardware carrier detect (DCD) signal is signifi-
       cant, and an open(2) of the corresponding terminal  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.

       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.

       The  ioctl(2)  system  call  returns  0 on success.  On error it returns -1 and sets errno

       EINVAL Invalid command parameter.

	      Unknown command.

       ENOTTY Inappropriate fd.

       EPERM  Insufficient permission.

       Check the condition of DTR on the serial port.

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

	   int fd, serial;

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

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

       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at

Linux					    2013-11-12				     TTY_IOCTL(4)

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