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TTY(4)			 BSD Kernel Interfaces Manual			TTY(4)

NAME
     tty — general terminal interface

SYNOPSIS
     #include <sys/ioctl.h>

DESCRIPTION
     This section describes the interface to the terminal drivers in the sys‐
     tem.

   Terminal Special Files
     Each hardware terminal port on the system usually has a terminal special
     device file associated with it in the directory ``/dev/'' (for example,
     ``/dev/tty03'').  When a user logs into the system on one of these hard‐
     ware terminal ports, the system has already opened the associated device
     and prepared the line for normal interactive use (see getty(8).)  There
     is also a special case of a terminal file that connects not to a hardware
     terminal port, but to another program on the other side.  These special
     terminal devices are called ptys and provide the mechanism necessary to
     give users the same interface to the system when logging in over a net‐
     work (using rlogin(1), or telnet(1) for example).	Even in these cases
     the details of how the terminal file was opened and set up is already
     handled by special software in the system.	 Thus, users do not normally
     need to worry about the details of how these lines are opened or used.
     Also, these lines are often used for dialing out of a system (through an
     out-calling modem), but again the system provides programs that hide the
     details of accessing these terminal special files (see tip(1)).

     When an interactive user logs in, the system prepares the line to behave
     in a certain way (called a line discipline), the particular details of
     which is described in stty(1) at the command level, and in termios(4) at
     the programming level.  A user may be concerned with changing settings
     associated with his particular login terminal and should refer to the
     preceding man pages for the common cases.	The remainder of this man page
     is concerned with describing details of using and controlling terminal
     devices at a low level, such as that possibly required by a program wish‐
     ing to provide features similar to those provided by the system.

   Terminal File Operations
     All of the following operations are invoked using the ioctl(2) system
     call.  Refer to that man page for a description of the request and argp
     parameters.  In addition to the ioctl requests defined here, the specific
     line discipline in effect will define other requests specific to it
     (actually termios(4) defines them as function calls, not ioctl requests.)
     The following section lists the available ioctl requests.	The name of
     the request, a description of its purpose, and the typed argp parameter
     (if any) are listed.  For example, the first entry says

	   TIOCSPGRP int *tpgrp

     and would be called on the terminal associated with file descriptor zero
     by the following code fragment:

	     int pgrp;

	     pgrp = getpgrp();
	     ioctl(0, TIOCSPGRP, &pgrp);

   Terminal File Request Descriptions
     TIOCSETD int *ldisc
		 This call is obsolete but left for compatibility.  Before
		 FreeBSD 8.0, it would change to the new line discipline
		 pointed to by ldisc.

     TIOCGETD int *ldisc
		 Return the current line discipline in the integer pointed to
		 by ldisc.

     TIOCSBRK void
		 Set the terminal hardware into BREAK condition.

     TIOCCBRK void
		 Clear the terminal hardware BREAK condition.

     TIOCSDTR void
		 Assert data terminal ready (DTR).

     TIOCCDTR void
		 Clear data terminal ready (DTR).

     TIOCGPGRP int *tpgrp
		 Return the current process group with which the terminal is
		 associated in the integer pointed to by tpgrp.	 This is the
		 underlying call that implements the termios(4) tcgetattr()
		 call.

     TIOCSPGRP int *tpgrp
		 Associate the terminal with the process group (as an integer)
		 pointed to by tpgrp.  This is the underlying call that imple‐
		 ments the termios(4) tcsetattr() call.

     TIOCGETA struct termios *term
		 Place the current value of the termios state associated with
		 the device in the termios structure pointed to by term.  This
		 is the underlying call that implements the termios(4)
		 tcgetattr() call.

     TIOCSETA struct termios *term
		 Set the termios state associated with the device immediately.
		 This is the underlying call that implements the termios(4)
		 tcsetattr() call with the TCSANOW option.

     TIOCSETAW struct termios *term
		 First wait for any output to complete, then set the termios
		 state associated with the device.  This is the underlying
		 call that implements the termios(4) tcsetattr() call with the
		 TCSADRAIN option.

     TIOCSETAF struct termios *term
		 First wait for any output to complete, clear any pending
		 input, then set the termios state associated with the device.
		 This is the underlying call that implements the termios(4)
		 tcsetattr() call with the TCSAFLUSH option.

     TIOCOUTQ int *num
		 Place the current number of characters in the output queue in
		 the integer pointed to by num.

     TIOCSTI char *cp
		 Simulate typed input.	Pretend as if the terminal received
		 the character pointed to by cp.

     TIOCNOTTY void
		 This call is obsolete but left for compatibility.  In the
		 past, when a process that did not have a controlling terminal
		 (see The Controlling Terminal in termios(4)) first opened a
		 terminal device, it acquired that terminal as its controlling
		 terminal.  For some programs this was a hazard as they did
		 not want a controlling terminal in the first place, and this
		 provided a mechanism to disassociate the controlling terminal
		 from the calling process.  It must be called by opening the
		 file /dev/tty and calling TIOCNOTTY on that file descriptor.

		 The current system does not allocate a controlling terminal
		 to a process on an open() call: there is a specific ioctl
		 called TIOCSCTTY to make a terminal the controlling terminal.
		 In addition, a program can fork() and call the setsid() sys‐
		 tem call which will place the process into its own session -
		 which has the effect of disassociating it from the control‐
		 ling terminal.	 This is the new and preferred method for pro‐
		 grams to lose their controlling terminal.

     TIOCSTOP void
		 Stop output on the terminal (like typing ^S at the keyboard).

     TIOCSTART void
		 Start output on the terminal (like typing ^Q at the key‐
		 board).

     TIOCSCTTY void
		 Make the terminal the controlling terminal for the process
		 (the process must not currently have a controlling terminal).

     TIOCDRAIN void
		 Wait until all output is drained.

     TIOCEXCL void
		 Set exclusive use on the terminal.  No further opens are per‐
		 mitted except by root.	 Of course, this means that programs
		 that are run by root (or setuid) will not obey the exclusive
		 setting - which limits the usefulness of this feature.

     TIOCNXCL void
		 Clear exclusive use of the terminal.  Further opens are per‐
		 mitted.

     TIOCFLUSH int *what
		 If the value of the int pointed to by what contains the FREAD
		 bit as defined in <sys/file.h>, then all characters in the
		 input queue are cleared.  If it contains the FWRITE bit, then
		 all characters in the output queue are cleared.  If the value
		 of the integer is zero, then it behaves as if both the FREAD
		 and FWRITE bits were set (i.e., clears both queues).

     TIOCGWINSZ struct winsize *ws
		 Put the window size information associated with the terminal
		 in the winsize structure pointed to by ws.  The window size
		 structure contains the number of rows and columns (and pixels
		 if appropriate) of the devices attached to the terminal.  It
		 is set by user software and is the means by which most full-
		 screen oriented programs determine the screen size.  The
		 winsize structure is defined in <sys/ioctl.h>.

     TIOCSWINSZ struct winsize *ws
		 Set the window size associated with the terminal to be the
		 value in the winsize structure pointed to by ws (see above).

     TIOCCONS int *on
		 If on points to a non-zero integer, redirect kernel console
		 output (kernel printf's) to this terminal.  If on points to a
		 zero integer, redirect kernel console output back to the nor‐
		 mal console.  This is usually used on workstations to redi‐
		 rect kernel messages to a particular window.

     TIOCMSET int *state
		 The integer pointed to by state contains bits that correspond
		 to modem state.  Following is a list of defined variables and
		 the modem state they represent:

		 TIOCM_LE   Line Enable.
		 TIOCM_DTR  Data Terminal Ready.
		 TIOCM_RTS  Request To Send.
		 TIOCM_ST   Secondary Transmit.
		 TIOCM_SR   Secondary Receive.
		 TIOCM_CTS  Clear To Send.
		 TIOCM_CAR  Carrier Detect.
		 TIOCM_CD   Carrier Detect (synonym).
		 TIOCM_RNG  Ring Indication.
		 TIOCM_RI   Ring Indication (synonym).
		 TIOCM_DSR  Data Set Ready.

		 This call sets the terminal modem state to that represented
		 by state.  Not all terminals may support this.

     TIOCMGET int *state
		 Return the current state of the terminal modem lines as rep‐
		 resented above in the integer pointed to by state.

     TIOCMBIS int *state
		 The bits in the integer pointed to by state represent modem
		 state as described above, however the state is OR-ed in with
		 the current state.

     TIOCMBIC int *state
		 The bits in the integer pointed to by state represent modem
		 state as described above, however each bit which is on in
		 state is cleared in the terminal.

IMPLEMENTATION NOTES
     The total number of input and output bytes through all terminal devices
     are available via the kern.tk_nin and kern.tk_nout read-only sysctl(8)
     variables.

SEE ALSO
     stty(1), ioctl(2), ng_tty(4), pty(4), termios(4), getty(8)

BSD			       December 26, 2009			   BSD
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