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NetBSD 6.1.5 - man page for tty (netbsd section 4)

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 system.

   Terminal Special Files
     Each hardware terminal port on the system usually has two terminal special 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 asso-
     ciated device and prepared the line for normal interactive use (see getty(8)).

     The /dev/dtyXX special file is a SunOS-compatible dial-out device.  Unlike 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 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 pro-
     grams 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 pre-
     ceding 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 wishing 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 interface
     routines (such as read(2) and write(2)), and is responsible for implementing 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 ter-
     minal file behaves and is operated according 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 conjunction with a line discipline other than termios,
     and some may not be supported 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 (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

	   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 underlying 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 implements 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 imple-
		 ments 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 input, 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 provided a mechanism to disas-
		 sociate 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()
		 system call which will place the process into its own session - which has the
		 effect of disassociating it from the controlling terminal.  This is the new and
		 preferred method for programs 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 keyboard).

     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 permitted 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 permitted.

     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 con-
		 tains 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 ter-
		 minal.  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 normal console.  This is usually used on workstations
		 to redirect 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 represented 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 defined 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 extensible.

     TIOCSETD int *ldisc
		 Change to the new line discipline pointed to by ldisc.  The old list of avail-
		 able 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


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