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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  structure,  with nonzero bits or fields indicating a locked

       TIOCGLCKTRMIOS struct termios *argp
	      Gets the locking status of the termios structure of  the	termi-

       TIOCSLCKTRMIOS const struct termios *argp
	      Sets  the	 locking status of the termios structure of the termi-
	      nal.  Only a process with the CAP_SYS_ADMIN  capability  can  do

   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  win-
       dow  size when the size of the virtual 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	 fore-
       ground 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  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,

   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,

   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 terminal.  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 calling 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  dif-
	      ferent  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	 call-
	      ing  process, give up this controlling terminal.	If the process
	      was session leader, then send SIGHUP and SIGCONT	to  the	 fore-
	      ground  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

       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) opera-
	      tions on the terminal  are  permitted.   (They  will  fail  with
	      EBUSY, except for a process with the CAP_SYS_ADMIN capability.)

       TIOCGEXCL int *argp
	      If  the terminal is currently in exclusive mode, place a nonzero
	      value in the location pointed to by argp; otherwise, place  zero
	      in *argp (since Linux 3.8).

       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 master 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  pseudotermi-
	      nal.   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 infor-
	      mation  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.

       TIOGCPKT	 const int *argp
	      Return the current packet mode setting in the integer pointed to
	      by argp (since Linux 3.8).

       TIOCSPTLCK     int *argp
	      Set (if *argp is nonzero) or remove (if *argp is zero) the pseu-
	      doterminal slave device.	(See also unlockpt(3).)

       TIOCGPTLCK     int *argp
	      Place  the current lock state of the pseudoterminal slave device
	      in the location pointed to by argp (since Linux 3.8).

       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.

       The following bits are used by the above 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)

       TIOCMIWAIT     int arg
	      Wait  for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
	      The bits of interest are specified as a  bit  mask  in  arg,  by
	      ORing  together  any  of	the  bit values, TIOCM_RNG, TIOCM_DSR,
	      TIOCM_CD, and TIOCM_CTS.	The caller should use  TIOCGICOUNT  to
	      see which bit has changed.

       TIOCGICOUNT    struct serial_icounter_struct *argp
	      Get  counts of input serial line interrupts (DCD, RI, DSR, CTS).
	      The counts are written to the  serial_icounter_struct  structure
	      pointed to by argp.

	      Note: both 1->0 and 0->1 transitions are counted, except for RI,
	      where only 0->1 transitions are counted.

   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  significant,	 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.   This  command was
	      removed in Linux 2.5.67.

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

       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 set");
	       puts("TIOCM_DTR is not set");

       ldattach(1), ioctl(2), termios(3), console_ioctl(4), pty(7)

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Linux				  2016-03-15			  TTY_IOCTL(4)