tty

NAME

SYNOPSIS

#include <sys/ioctl.h>

DESCRIPTION

This section describes the interface to the terminal drivers in the system.

Terminal special files

Each terminal on the system usually has a terminal special device file associated with it in the directory /dev/ (for example, /dev/ttyn02). When a user logs into the system on one of these terminals, the system has already opened the associated device and prepared the line for normal interactive use. 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 network (using 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.

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(1) 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 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 is 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 terminal file behaves and is operated according to the rules described in termios(1). 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

The majority of terminal settings can be handled through the tc family of interfaces. Termios(1) defines them as function calls, not ioctl(2) requests. The following section lists the available ioctl(2) 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

TIOCGWINSZ

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

struct winsize ws;
ioctl(0, TIOCGWINSZ, &ws);

Terminal file request descriptions

TIOCSETD int ldisc

Change to a new line discipline, indicated by ldisc. Line disciplines are define in <sys/termios.h>; currently only TTYDISC (termios interactive line discipline) is supported.

TIOCGETD int ldisc

Get current line disciple in ldisc.

TIOCSBRK void

Set terminal hardware into BREAK condition.

TIOCCBRK void

Clear terminal hardware BREAK condition.

TIOCSDTR void

Assert data terminal ready (DTR).

TIOCCDTR void

Clear data terminal ready (DTR).

TIOCSRTS void

Assert request to send (RTS).

TIOCCRTS void

Clear request to send (RTS).

TIOCGPGRP int *tpgrp

Return current process group associated with the terminal in the integer pointed to by tpgrp.

TIOCSPGRP int *tpgrp

Associate terminal with process group number in the integer pointed to by tpgrp.

TIOCGETA struct termios *term

Place current value of termios state associated with device in the structure pointed to by term.

TIOSGETA struct termios *term

Immediately set termios state associated with device, using data in the structure pointed to by term.

TIOSGETAW struct termios *term

Wait for output to complete, then set termios state associated with device, using data in the structure pointed to by term.

TIOSGETAF struct termios *term

Wait for output to complete, clear pending input, then set termios state associated with device, using data in the structure pointed to by term.

TIOSGETAR struct termios *term

Clear pending input, then set termios state associated with device, using data in the structure pointed to by term.

TIOCOUTQ int *num

Place current number of bytes in the output queue in the integer pointed to by num.

TIOCSTI char *cp

Simulate typed input. Pretend the terminal received the character pointed to by cp.

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 should 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.

TIOCNXCL void

Clear exclusive use on the terminal.

TIOCFLUSH int *what

Clear input or output queue, depending on value of integer pointed to by what. If the integer contains the FREAD bit defined in sys/file.h, the input queue is cleared. If it contains the FWRITE bit, the output queue is clear. If it is zero, both queues are cleared.

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

Redirect kernel console output depending on the value of the integer pointed to by on. If it is non-zero, redirect kernel console output to this terminal; if it is zero, redirect kernel console output back to the normal console.

TIOCMSET int *state

The integer pointed to by state contains bits that correspond to modem states. this call sets the terminal modem state to that represented by state. The defined variables and modem states are:

CM_DTR	Data Terminal Ready
TIOCM_RTS	Request To Send
TIOCM_CTS	Clear To Send
TIOCM_CAR	Carrier Detect
TIOCM_CD	Carrier Detect
TIOCM_RNG	Ring Indication
TIOCM_RI	Ring Indication
TIOCM_DSR	Data Set Ready

TIOCMGET int *state

Return current state of the terminal modem lines; see TIOCMSET for a description of bits that can be set in state.

TIOCMBIS int *state

The bits in the integer pointed to by state represent modem state, but they are OR-ed with the current state.

TIOCMBIC int *state

The bits in the integer pointed to by state represent modem state, but each bit that is on in state is cleared in the terminal.

SEE ALSO

stty(1)

fcntl(2)

ioctl(2)

tcgetattr(2)

tcsetattr(2)

pty(4)

termios(4)