TTY(4) FreeBSD 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 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.
SEE ALSO
stty(1), ioctl(2), ng_tty(4), pty(4), termios(4), getty(8)
HISTORY
A console typewriter device /dev/tty and asynchronous communication
interfaces /dev/tty[0-5] first appeared in Version 1 AT&T UNIX.
FreeBSD 13.1-RELEASE-p6 April 3, 2022 FreeBSD 13.1-RELEASE-p6
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