Ubuntu Manpage: tty — general terminal interface

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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 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 hardware 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 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. 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 wishing 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 implements 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
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 provides 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() 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.

However, environmental restrictions may prohibit the process from being able to fork() and
call the setsid() system call to disassociate it from the controlling terminal. In this
case, it must use TIOCNOTTY.

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, or until the drain wait timeout expires.

TIOCGDRAINWAIT int *timeout
Return the current drain wait timeout in seconds.

TIOCSDRAINWAIT int *timeout
Set the drain wait timeout in seconds. A value of zero disables timeouts. The default drain
wait timeout is controlled by the tunable sysctl(8) OID kern.tty_drainwait.

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/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 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.

IMPLEMENTATION NOTES

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

NAME

SYNOPSIS

DESCRIPTION

IMPLEMENTATION NOTES

SEE ALSO