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