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TTY(4) |
FreeBSD Kernel Interfaces Manual |
TTY(4) |
tty —
general terminal interface
This section describes the interface to the terminal drivers in the system.
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.
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);
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.
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.
A console typewriter device /dev/tty and asynchronous
communication interfaces /dev/tty[0-5] first appeared
in Version 1 AT&T UNIX.
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