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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 two terminal	spe-
     cial device files associated with it in the directory /dev/ (for example,
     /dev/tty03	and /dev/dty03).

     The /dev/ttyXX special file is used for dial-in modems and	terminals.
     When a user logs into the system on one of	these hardware terminal	ports,
     the system	has already opened the associated device and prepared the line
     for normal	interactive use	(see getty(8)).

     The /dev/dtyXX special file is a SunOS-compatible dial-out	device.	 Un-
     like the dial-in device, opening the dial-out device never	blocks.	 If
     the corresponding dial-in device is already opened	(not blocked in	the
     open waiting for carrier),	then the dial-out open will fail immediately;
     otherwise it will succeed immediately.  While the dial-out	device is
     open, the dial-in device may not be opened.  If the dial-in open is
     blocking, it will wait until the dial-out device is closed	(and carrier
     is	detected); otherwise it	will fail immediately.

     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 (pseudo terminals) and provide
     the mechanism necessary to	give users the same interface to the system
     when logging in over a network (using rlogin(1), or telnet(1) for exam-
     ple.)  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 pro-
     vides 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.

   Line	disciplines
     A terminal	file is	used like any other file in the	system in that it can
     be	opened,	read, and written to using standard system calls.  For each
     existing terminal file, there is a	software processing module called a
     line discipline associated	with it.  The line discipline essentially
     glues the low level device	driver code with the high level	generic	inter-
     face routines (such as read(2) and	write(2)), and is responsible for im-
     plementing	the semantics associated with the device.  When	a terminal
     file is first opened by a program,	the default line discipline called the
     termios line discipline is	associated with	the file.  This	is the primary
     line discipline that is used in most cases	and provides the semantics
     that users	normally associate with	a terminal.  When the termios line
     discipline	is in effect, the terminal file	behaves	and is operated	ac-
     cording to	the rules described in termios(4).  Please refer to that man
     page for a	full description of the	terminal semantics.  The operations
     described here generally represent	features common	across all line
     disciplines, however some of these	calls may not make sense in conjunc-
     tion with a line discipline other than termios, and some may not be sup-
     ported by the underlying hardware (or lack	thereof, as in the case	of
     ptys).

   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 (ac-
     tually 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

	   TIOCSLINED char name[32]

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

	     ioctl(0, TIOCSLINED, "termios");

   Terminal File Request Descriptions
     TIOCSLINED	char name[32]
		 Change	to the new line	discipline called name.

     TIOCGLINED	char name[32]
		 Return	the current line discipline in the string pointed to
		 by name.

     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 the terminal is associated
		 with in the integer pointed to	by tpgrp.  This	is the under-
		 lying call that implements the	tcgetpgrp(3) 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 tcsetpgrp(3)	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 tcgetattr(3) call.

     TIOCSETA struct termios *term
		 Set the termios state associated with the device immediately.
		 This is the underlying	call that implements the tcsetattr(3)
		 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 tcsetattr(3) call with the TCSADRAIN
		 option.

     TIOCSETAF struct termios *term
		 First wait for	any output to complete,	clear any pending in-
		 put, then set the termios state associated with the device.
		 This is the underlying	call that implements the tcsetattr(3)
		 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 didn't 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	didn't
		 want a	controlling terminal in	the first place, and this pro-
		 vided 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/fcntl.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).

     TIOCGQSIZE	int *qsize
		 Get the current size of the tty input and output queues.

     TIOCSQSIZE	int *qsize
		 Set the size of the tty input and output queues.  Valid sizes
		 are between 1024 and 65536 and	input values are converted to
		 a power of two.  All pending input and	output is dropped.

     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.

     TIOCSFLAGS	int *state
		 The bits in the integer pointed to by state contain bits that
		 correspond to serial port state.  Following is	a list of de-
		 fined flag values and the serial port state they represent:

		 TIOCFLAG_SOFTCAR  Ignore hardware carrier.
		 TIOCFLAG_CLOCAL   Set the termios(4) CLOCAL flag on open.
		 TIOCFLAG_CRTSCTS  Set the termios(4) CRTSCTS flag on open.
		 TIOCFLAG_MDMBUF   Set the termios(4) MDMBUF flag on open.

		 This call sets	the serial port	state to that represented by
		 state.	 Not all serial	ports may support this.

     TIOCGFLAGS	int *state
		 Return	the current state of the serial	port as	represented
		 above in the integer pointed to by state.

COMPATIBILITY
     Two ioctls	are maintained for backwards compatibility.  They provide
     methods to	get and	set the	current	line discipline, but are not extensi-
     ble.

     TIOCSETD int *ldisc
		 Change	to the new line	discipline pointed to by ldisc.	 The
		 old list of available line disciplines	are listed in
		 <sys/ttycom.h>	and are:

		 TTYDISC     Termios interactive line discipline.
		 TABLDISC    Tablet line discipline.
		 SLIPDISC    Serial IP line discipline.
		 PPPDISC     Point to Point Protocol line discipline.
		 STRIPDISC   Starmode Radio IP line discipline.

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

SEE ALSO
     stty(1), ioctl(2),	tcgetattr(3), tcsetattr(3), ttyaction(3), pty(4),
     termios(4), ttys(5), getty(8), linedisc(9)

HISTORY
     Separate dial-out device files were implemented in	SunOS 4.  They were
     cloned by Charles M. Hannum for NetBSD 1.4.

BSD			       September 9, 2011			   BSD

NAME | SYNOPSIS | DESCRIPTION | COMPATIBILITY | SEE ALSO | HISTORY

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