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tty(7)
NAME
tty - General terminal interface
SYNOPSIS
#include <sys/termios.h>
DESCRIPTION
This section describes both a particular special file /dev/tty and the
terminal drivers used for conversational computing. Much of the terminal
interface performance is governed by the settings of a terminal's termios
structure. This structure provides definitions for terminal input and
output processing, control and local modes, and so on. These definitions
are found in the termios.h header file.
Line Disciplines
The operating system supports STREAMS-based and clist-based line
disciplines, which allows for both STREAMS- and clist-based terminal
drivers. Both line disciplines are POSIX compliant.
The STREAMS-based line discipline is implemented as the STREAMS module
ldterm. This line discipline performs most of the functions defined by the
termios interface for session management and character processing but not
some low level device control. In order to determine if a terminal device
is implemented as a STREAMS device, use the libc function isastream on the
open file descriptor. See the isastream(3) reference page.
Users can switch line disciplines by using the command strchg or the I_POP
or I_PUSH STREAMS ioctls. The ldterm line discipline is the only STREAMS-
based line discipline provided by the base operating system for use with
terminals. However, additional STREAMS modules to support features needed
in countries other than the United States can be pushed above and below the
ldterm module.
The operating system supports several clist-based line disciplines for
controlling communication lines. By default, the Standard line discipline,
which supports full POSIX terminal semantics, is the only line discipline
available for terminals. However, after the installation of worldwide
portability subsets, two additional line disciplines are available for
processing the multibyte and single-byte coded character sets used for
Asian languages. The atty(7) and ttty(7) reference pages, which are also
available after the worldwide portability subsets are installed, describe
these additional line disciplines.
Line discipline switching is done with the TIOCSETD ioctl for clist-based
terminal drivers. The following example illustrates how to switch line
disciplines:
int ldisc = LDISC;
ioctl(fd,TIOCSETD,&ldisc);
In this example, LDISC is the index into the linesw table. (See the
/sys/bsd/tty_conf.c file.)
Other clist disciplines exist for special purposes, such as communication
lines for network devices. The current line discipline can be obtained
with the TIOCGETD ioctl for clist-based terminal drivers. Pending output is
discarded when the line discipline is changed. When the Standard line
discipline is used, NTTYDISC (value 2) is returned by default for BSD
compatibility. TTYDISC (value 0) is returned only when you compile the
application with the -D_USE_NEW_TTY switch. When the atty or ttty line
discipline is used, ASYDISC (value 9) or TSBDISC (value 10) is returned,
respectively.
The Controlling Terminal
The operating system supports the concept of a controlling terminal. Any
process in the system can have a controlling terminal associated with it.
Certain events, such as the delivery of keyboard generated signals (for
example, interrupt, quit, suspend), affect all the processes in the process
group associated with the controlling terminal. The controlling terminal
also determines the physical device that is accessed when the indirect
device /dev/tty is opened.
In earlier versions of UNIX systems, a controlling terminal was implicitly
assigned to a process if, at the time an open was done on the terminal, the
terminal was not the controlling terminal for any process, and if the
process doing the open did not have a controlling terminal. In this
version of UNIX, in accordance with POSIX 1003.1, a process must be a
session leader to allocate a controlling terminal. In addition, the
allocation is now done explicitly with a call to ioctl(). (This implies
that the O_NOCTTY flag to the open() function is ignored.) The following
example illustrates the correct sequence for obtaining a controlling tty
(no error checking is shown). This code fragment calls the setsid()
function to make the current process the group and session leader, and to
remove any controlling tty that the process may already have. It then
opens the console device and attaches it to the current session as the
controlling terminal. Note that the process must not already be a session
or process group leader, and the console must not already be the
controlling tty of any other session.
(void)setsid(); /* become session leader and */
/* lose controlling tty */
fd = open("/dev/console", O_RDWR);
(void)ioctl(fd,TIOCSCTTY,0);
A process can remove the association it has with its controlling terminal
by opening the /dev/tty file and issuing the following call:
ioctl(fd, TIOCNOTTY, 0);
For example:
fd = open("/dev/tty", O_RDWR);
if (fd > = 0) {
ioctl(fd,TIOCNOTTY,0);
close(fd);
}
If the calling process is not the session leader, the process group of the
calling process is set to 0.
When a control terminal file is closed, pending input is removed, and
pending output is sent to the receiving device.
When a terminal file is opened, the process blocks until a carrier signal
is detected. If the open() function is called with the O_NONBLOCK flag
set, however, the process does not wait. Instead, the first read() or
write() call will wait for carrier to be established. If the CLOCAL mode
is set in the termios structure, the driver assumes that modem control is
not in effect, and open(), read(), and write() therefore proceed without
waiting for a carrier signal to be established.
Process Groups
Each process belongs to a process group with a specific process group ID.
Each process belongs to the process group of its creating process. This
enables related processes to be signaled. Process group IDs are unique
identifiers that cannot be used for other system process groups until the
original process group is disbanded. Each process group also has a group
leader process. A process group leader has the same process ID as its
process group.
Each process group belongs to a session. Each process in the process group
also belongs to the process group's session. A process which is not the
process group leader can create its own session and process group with a
call to the setsid() function. That calling process then becomes the
session leader of the new session and of the new process group. The new
session has no controlling terminal until the session leader assigns one to
it. The calling process's ID is assigned to the new process group. With
the setpgid() function, other processes can be added to a process group.
A controlling terminal can have a distinguished process group associated
with it known as the foreground process group. The terminal's foreground
process group is the one that receives signals generated by the INTR, QUIT,
and SUSP special control characters. Certain operations on the terminal
are also restricted to processes in the terminal's foreground process group
(see "Terminal Access Control"). A terminal's foreground process group may
be changed by calling the tcsetpgrp() function. A terminal's current
foreground process group may be obtained by calling the tcgetpgrp()
function.
Input Processing Modes
The terminal drivers have two major modes, characterized by the kind of
processing that takes place on the input characters:
Canonical If a terminal is in canonical mode, input is collected and
processed one line at a time. Lines are terminated by a newline
(\n), End-of-File (EOF), or End-of-Line (EOL) character. A read
request is not returned until the line has been terminated, or a
signal has been received. The maximum number of bytes of unread
input allowed on an input terminal is MAX_INPUT bytes. If the
maximum number of unread bytes exceeds MAX_INPUT bytes, the
behavior of the driver depends on the setting of the IMAXBEL
input flag (see "Input Editing").
Erase and kill processing is performed on input that has not been
terminated by one of the line termination characters. Erase
processing removes the last character in the line, kill
processing removes the whole line.
Noncanonical
This mode eliminates erase and kill processing, making input
characters available to the user program as they are typed. Input
is not processed into lines. The received bytes are processed
according to the values at the VMIN and VTIME indexes of the c_cc
array in the termios structure.
MIN MIN is the minimum number of bytes the terminal can
receive in noncanonical mode before a read is
considered successful.
TIME TIME, measured in 0.1 second granularity, times out
sporadic input.
These cases are summarized as follows:
MIN>0, TIME>0
In this case, TIME is an interbyte timer that is
activated after the first byte of the input line is
received, and reset after each byte is received. The
read operation is a success if MIN bytes are read
before TIME runs out. If TIME runs out before MIN
bytes have been received, the characters that were
received are returned.
MIN>0, TIME=0
In this case, only MIN is used. A queued read() waits
until MIN bytes are received, or a signal is received.
MIN=0, TIME>0
In this case, TIME is used as a read timer that starts
when a read() call is made. The read() call is
finished when one byte is read, or when TIME runs out.
MIN=0, TIME=0
In this case, either the number of requested bytes or
the number of currently available bytes is returned,
depending on which is the lesser number. The read()
function returns a zero if no data was read.
Canonical mode is entered by setting the ICANON flag of the c_lflag field
in the in the terminal's termios structure. Other input processing is
performed according to the other flags set in the c_iflag and c_lflag
fields.
Input Editing
A terminal ordinarily operates in full-duplex mode. Characters may be
typed at any time, even while output is occurring. Characters are only
lost when:
· The system's character input buffers become completely choked, which
is rare.
· The user has accumulated the maximum allowed number of input
characters (MAX_INPUT) that have not yet been read by some program.
The MAX_INPUT limit is 512 characters. When this limit is reached,
the terminal driver refuses to accept any further input and rings the
terminal bell if IMAXBEL is set in the c_iflag field, or throws away
all input and output without notice if this flag is not set.
Input characters are normally accepted in either even or odd parity with
the parity bit being stripped off before the character is given to the
program. The ISTRIP mask of the c_iflag field controls whether the parity
bit is stripped (ISTRIP set) or not stripped (ISTRIP not set). By setting
the PARENB flag in the c_cflag field, and either setting (not setting) the
PARODD flag, it is possible to have input characters with EVEN (ODD) parity
discarded or marked (see "Input Modes").
In all of the line disciplines, it is possible to simulate terminal input
using the TIOCSTI ioctl, which takes, as its third argument, the address of
a character. The system pretends that this character was typed on the
argument terminal, which must be the control terminal for the process,
unless the process has superuser privileges.
Input characters are normally echoed by putting them in an output queue as
they arrive. This may be disabled by clearing the ECHO bit in the c_lflag
word using the tcsetattr() call or the TIOCSETA, TIOCSETAW, or TIOCSETAF
ioctls.
In canonical mode, terminal input is processed in units of lines. A
program attempting to read will normally be suspended until an entire line
has been received (but see the description of SIGTTIN in "Terminal Access
Control"). No matter how many characters are requested in the read call,
at most one line will be returned. It is not, however, necessary to read a
whole line at once; any number of characters may be requested in a read,
even one, without losing information. In read() requests, the O_NONBLOCK
flag affects the read() operation behavior.
If O_NONBLOCK is not set, a read() request is blocked until data or a
signal has been received. If the O_NONBLOCK flag is set, the read()
request is not blocked, and one of the following situations holds:
· Some data may have been typed, but there may or may not be enough data
to satisfy the entire read request. In either case, the read()
function returns the data available, returning the number of bytes of
data it read.
· If there is no data for the read operation, the read() returns a -1
with an error of EAGAIN.
During input, line editing is normally done with the erase special control
character (VERASE) logically erasing the last character typed and the kill
special control character (VKILL) logically erasing the entire current
input line. These characters never erase beyond the beginning of the
current input line or an EOF (End-of-File). These characters, along with
the other special control characters, may be entered literally by preceding
them with the literal-next character (VLNEXT - default ^V).
The drivers normally treat either a newline character (`\n'), End-of-File
character (EOF), or End-of-Line character (EOL) as terminating an input
line, echoing a return and a line feed. If the ICRNL character bit is set
in the c_iflag word then carriage returns are translated to newline
characters on input, and are normally echoed as carriage return-linefeed
sequences. If ICRNL is not set, this processing for carriage return is
disabled, and it is simply echoed as a return, and does not terminate
cooked mode input.
The POSIX terminal driver also provides two other editing characters in
normal mode. The word-erase character, normally <Ctrl-W>, is a c_cc
structure special control character VWERASE. This character erases the
preceding word, but not any spaces before it. For the purposes of <Ctrl-
W>, a word is defined as a sequence of nonblank characters, with tabs
counted as blanks. However, if the ALTWERASE flag is set in the c_lflag
word, then a word is considered to be any sequence of alphanumerics or
underscores bounded by characters that are not alphanumerics or
underscores. Finally, the reprint character, normally <Ctrl-R>, is a c_cc
structure special control character VREPRINT. This character retypes the
pending input beginning on a new line. Retyping occurs automatically in
canonical mode if characters which would normally be erased from the screen
are fouled by program output.
Input Modes
The termios structure has an input mode field c_iflag, which controls basic
terminal input characteristics. These characteristics are masks that can
be bitwise inclusive ORed. The masks include:
BRKINT An interrupt is signaled on a break condition.
ICRNL All carriage returns are mapped to newline characters when input.
IGNBRK Break conditions are ignored.
IGNCR Carriage returns are ignored.
IGNPAR Characters with parity errors are ignored.
INLCR Newline characters are mapped to carriage returns when input.
INPCK Parity checks are enabled on input.
ISTRIP The eighth bit (parity bit) is stripped on input characters.
IXOFF Stop/start characters are sent for input flow control enabled.
IXON Stop/start characters are recognized for output flow control.
IXANY Any char will restart output after stop.
IUCLC Map upper case to lower case on input.
PARMRK Parity errors are marked with a three character sequence.
IMAXBEL The bell is rung when the input queue fills.
The input mode mask bits can be combined for the following results:
The setting of IGNBRK causes input break conditions to be ignored. If
IGNBRK is not set, but BRKINT is set, the break condition has the same
effect as if the VINTR control character had been typed. If neither IGNBRK
nor BRKINT are set, then the break condition is input as a single character
'\0'. If the PARMRK flag is set, then the input is read as three
characters, '\377', '\0', and '\0'.
The setting of IGNPAR causes a byte with a parity or framing error, except
for breaks, to be ignored (that is, discarded). If IGNPAR is not set, but
PARMRK is set, a byte with parity or framing error, except for breaks, is
passed as the three characters '\377', '\0', and X, where X is the
character data received in error. If the ISTRIP flag is not set, the valid
character '\377' is passed as '\377', '377'. If both PARMRK and IGNPAR are
not set, framing or parity errors, including breaks, are passed as the
single character '\0'.
The setting of INPCK enables input parity checking. If input parity
checking is not enabled (INPCK not set), then characters with parity errors
are simply passed through as is. The enabling/disabling of input parity
checking is independent of the generation of parity on output.
Setting ISTRIP causes the eighth bit of the eight valid input bits to be
stripped before processing. If this mask is not set, all eight bits are
processed.
Setting INLCR causes a newline character to be read as a carriage return
character. If the IGNCR flag is also set, the carriage return is ignored.
If the IGNCR flag is not set, INLCR works as described earlier.
The STOP character (normally <Ctrl-S>) suspends output and the START
character (normally <Ctrl-Q>) restarts output. Setting IXON enables
stop/start output control, in which the START and STOP characters are not
read, but rather perform flow control functions. Extra stop characters
typed when output is already stopped have no effect, unless the start and
stop characters are made the same, in which case output resumes. Disabling
IXON causes the START and STOP characters to be read.
Setting IXOFF enables stop/start input control. When this flag is set, the
terminal device will be sent STOP characters to halt the transmission of
data when the input queue is in danger of overflowing (exceed MAX_INPUT).
When enough characters have been read to reduce the amount of data queued
to an acceptable level, a START character is sent to the device to allow it
to continue transmitting data. This mode is useful when the terminal is
actually another machine that obeys those conventions.
Input Echoing and Redisplay
The terminal driver has several modes for handling the echoing of terminal
input, controlled by bits in the c_lflag field of the termios structure.
Hardcopy Terminals
When a hardcopy terminal is in use, the ECHOPRT bit is normally set in the
local flags word. Characters which are logically erased are then printed
out backwards preceded by \ (backslash) and followed by a / (slash) in this
mode.
Erasing Characters from a CRT
When a CRT terminal is in use, the ECHOE bit may be set to cause input to
be erased from the screen with a "backspace-space-backspace" sequence when
character or word deleting sequences are used. The ECHOKE bit may be set
as well, causing the input to be erased in this manner on line kill
sequences as well.
Echoing of Control Characters
If the ECHOCTL bit is set in the local flags word, then nonprinting
(control) characters are normally echoed as ^X (for some X) rather than
being echoed unmodified; DELETE is echoed as ^?.
Output Processing
When one or more characters are written, they are actually transmitted to
the terminal as soon as previously written characters have finished typing.
(As noted above, input characters are normally echoed by putting them in
the output queue as they arrive.) When a process produces characters more
rapidly than the terminal can accept them, it will be suspended when its
output queue exceeds some limit. When the queue has drained down to some
threshold the program is resumed. Even parity is normally generated on
output. If the NOEOT bit is set in the c_oflag word of the termios
structure, the EOT character (<Ctrl-D>) is not transmitted, to prevent
terminals that respond to it from hanging up.
The terminal drivers provide necessary processing for canonical and
noncanonical mode output including delay generation for certain special
characters and parity generation. Delays are available after backspaces
(BSDLY), formfeeds (FFDLY), carriage returns (CRDLY), tabs (TABDLY) and
newlines (NLDLY). The driver will also optionally expand tabs into spaces,
where the tab stops are assumed to be set every eight columns, and
optionally convert newlines to carriage returns followed by newline.
Output process is controlled by bits in the c_oflag field of the termios
structure. Refer to the write(2) reference page for a description of the
O_NONBLOCK flag.
The terminal drivers provide for mapping from lowercase to uppercase
(OLCUC) for terminals lacking lower case, and for other special processing
on deficient terminals.
Finally, the terminal driver, supports an output flush character, normally
<Ctrl-O>, which sets the FLUSHO bit in the local mode word, causing
subsequent output to be flushed until it is cleared by a program or more
input is typed. This character has effect in both canonical and
noncanonical modes and causes any pending input to be retyped. An ioctl to
flush the characters in the input or output queues, TIOCFLUSH, is also
available.
Uppercase Terminals
If the IUCLC bit in the c_iflag field is set in the tty flags, then all
uppercase letters are mapped into the corresponding lowercase letter. The
uppercase letter may be generated by preceding it by \ (backslash).
Uppercase letters are preceded by a \ (backslash) when output. In
addition, the following escape sequences will be generated on output and
accepted on input if the XCASE bit is set in the c_lflag word:
For: ` | ~ { }
Use: \' \! \^ \( \)
Line Control and Breaks
There are several ioctl calls available to control the state of the
terminal line. The TIOCSBRK ioctl will set the break bit in the hardware
interface causing a break condition to exist; this can be cleared (usually
after a delay with sleep(3)) by TIOCCBRK. The tcsendbreak() can also be
used to cause a break condition for a specified amount of time. Break
conditions in the input are handled according to the c_iflag field settings
for the termios structure. Refer to the section Input Modes" for a
complete listing of the c_iflag field settings. The TIOCCDTR ioctl will
clear the data terminal ready condition; it can be set again by TIOCSDTR.
When the carrier signal from the dataset drops (usually because the user
has hung up his terminal) a SIGHUP hangup signal is sent to the processes
in the distinguished process group of the terminal; this usually causes
them to terminate. The sending of SIGHUP does not take place if the CLOCAL
bit is set in c_cflag field of the driver. Access to the terminal by other
processes is then normally revoked, so any further reads will fail, and
programs that read a terminal and test for End-of-File on their input will
terminate appropriately.
Interrupt Characters
When the ISIG bit is set in the c_lflag word, there are several characters
that generate signals in both canonical and noncanonical mode; all are sent
to the processes in the foreground process group of the terminal. If the
NOFLSH bit is not set in c_lflag, these characters also flush pending input
and output when typed at a terminal. The characters shown here are the
defaults; the symbolic names of the indices of these characters in the c_cc
array of the termios structure are also shown. The characters may be
changed.
^C VINTR (in c_cc) generates a SIGINT signal. This is the normal
way to stop a process which is no longer interesting, or to
regain control in an interactive program.
^\ VQUIT (in c_cc) generates a SIGQUIT signal. This is used to
cause a program to terminate and produce a core image, if
possible, in the file core in the current directory.
^Z VSUSP (in c_cc) generates a SIGTSTP signal, which is used to
suspend the current process group.
^Y VDSUSP (in c_cc) generates a SIGTSTP signal as <Ctrl-Z> does, but
the signal is sent when a program attempts to read the <Ctrl-Y>,
rather than when it is typed.
Terminal Access Control
If a process attempts to read from its controlling terminal when the
process is not in the foreground process group of the terminal, that
background process group is sent a SIGTTIN signal. This signal normally
causes the members of that process group to stop. If, however, the process
is ignoring SIGTTIN, has SIGTTIN blocked, or if the reading process'
process group is orphaned, the read will return -1 and set errno to [EIO].
The operation will then not send a signal.
If a process attempts to write to its controlling terminal when the process
is not in the foreground process group of the terminal, and the TOSTOP bit
is set in the c_lflag word of the termios structure, that background
process group is sent a SIGTTOU signal and the process is prohibited from
writing. If TOSTOP is not set, or if TOSTOP is set and the process is
blocking or ignoring the SIGTTOU signal, process writes to the terminal are
allowed, and the SIGTTOU signal is not sent. If TOSTOP is set, if the
writing process' process group is orphaned, and if SIGTTOU is not blocked
by the writing process, the write operation returns a -1 with errno set to
[EIO], and does not a send a signal.
Terminal/Window Sizes
To accommodate terminals and workstations with variable-sized windows, the
terminal driver provides a mechanism for obtaining and setting the current
terminal size. The driver does not use this information internally, but
only stores it and provides a uniform access mechanism. When the size is
changed, a SIGWINCH signal is sent to the terminal's process group so that
knowledgeable programs may detect size changes.
tty Parameters
In contrast to earlier versions of the tty driver, the POSIX terminal
parameters and structures are contained in a single structure, the termios
structure defined in the sys/termios.h file. Refer to the termios(4)
reference page for a complete summary of this file.
Basic ioctl Calls
A large number of ioctl(2) calls apply to terminals. Some have the general
form:
#include <sys/termios.h>
ioctl(fildes, code, arg)
struct termios *arg;
The applicable codes are:
TIOCGETA Gets the termios structure and all its associated parameters.
The interface delays until output is quiescent, then throws away
any unread characters.
TIOCSETA Sets the parameters according to the termios structure.
TIOCSETAW Drains the output before setting the parameters according to the
termios structure. Sets the parameters like TIOCSETA.
TIOCSETAF Drains the output and flushes the input before setting the
parameters according to the termios structure. Sets the
parameters like TIOCSETA.
With the following codes arg is ignored:
TIOCEXCL Set "exclusive-use" mode: no further opens are permitted until
the file has been closed.
TIOCNXCL Turn off "exclusive-use" mode.
With the following codes arg is a pointer to an int:
TIOCFLUSH If the int pointed to by arg has a zero value, all characters
waiting in input or output queues are flushed. Otherwise, the
value of the int is for the FREAD and FWRITE bits defined in the
sys/file.h file; if the FREAD bit is set, all characters waiting
in input queues are flushed, and if the FWRITE bit is set, all
characters waiting in output queues are flushed.
ioctls for Controlling Terminals
TIOCSCTTY Sets the terminal as the controlling terminal for the calling
process.
TIOCNOTTY Voids the terminal as a controlling terminal for the calling
process. If the calling process is not the session leader, the
process group of the calling process is seet to 0.
With the following codes, arg is a pointer to an int:
TIOCGPGRP The arg parameter is a pointer to the value representing the
process group ID of the process group, and is returned by the
controlling terminal specified by the filedes parameter. See
tcgetpgrp(3) for more information on error codes that can occur
if this ioctl fails.
TIOCSPGRP The arg parameter is a pointer to the value to which the process
group ID for the terminal specified by the filedes parameter will
be set. This terminal must be the controlling terminal and must
be associated with the calling process's session. The process
group value must match a process group ID of a process in the
same session as the calling process. See tcsetpgrp for more
information on error codes that can occur if this ioctl fails.
Miscellaneous tty ioctl Codes
The following are miscellaneous ioctl terminal commands. In cases where
arguments are required, they are described; arg should otherwise be given
as 0.
TIOCSTI The argument points to a character that the system pretends had
been typed on the terminal.
TIOCSBRK The break bit is set in the terminal.
TIOCCBRK The break bit is cleared.
TIOCSDTR Data terminal ready is set.
TIOCCDTR Data terminal ready is cleared.
TIOCSTOP Output is stopped as if the ``stop'' character had been typed.
TIOCSTART Output is restarted as if the ``start'' character had been typed.
TIOCOUTQ Returns in the int pointed to by arg the number of characters
queued for output to the terminal.
TIOCREMOTE
Sets the terminal for remote input editing.
TIOCCONS Sets or clears the virtual console. The arg parameter is a
pointer to an integer. A non zero value sets the virtual console
to the requesting tty. A zero value clears the virtual console.
Set this to write console messages to the virtual console rather
than /dev/console. Clearing a virtual console causes console
messages to resume being sent to /dev/console. Only one virtual
console may be in effect at a time. This ioctl requires
superuser privilege.
FIONREAD Returns in the int pointed to by arg the number of characters
immediately readable from the argument descriptor. This works
for files, pipes, and terminals.
Controlling Terminal Modems
The following ioctls apply to modems:
TIOCMODG The arg parameter is a pointer to an int, which is the value of
the modem control state.
TIOCMODS The arg parameter is a pointer to an int, which is the value to
which the modem control state is to be set.
TIOCMSET Sets all modem bits.
TIOCMBIS The arg parameter is a pointer to an int, which specifies the
modem bits to be set.
TIOCMBIC arg is a pointer to an int, which specifies the modem bits to be
cleared.
TIOCMGET Gets all the modem bits and returns them in the int point to by
arg.
Window/Terminal Sizes
Each terminal has provision for storage of the current terminal or window
size in a winsize structure, which has the following format:
struct winsize {
unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, pixels */
unsigned short ws_ypixel; /* vertical size, pixels */
};
A value of 0 (zero) in any field is interpreted as ``undefined;'' the
entire structure is zeroed on final close.
The applicable ioctl functions are:
TIOCGWINSZ
The arg parameter is a pointer to a struct winsize into which
will be placed the current terminal or window size information.
TIOCSWINSZ
The arg parameter is a pointer to a struct winsize, which will be
used to set the current terminal or window size information. If
the new information is different than the old information, a
SIGWINCH signal will be sent to the terminal's process group.
NOTES
The following System V and BSD ioctls are currently supported as a
compatibility interface for System V and older BSD system programs. They
should not be used in new applications. The ioctl call has the following
format:
ioctl (fdes, cmd, arg)
The System V termio ioctls use a pointer to a termio structure for the arg
parameter. The following include is required for the System V termio
ioctls:
#include <sys/termio>
The parameters of the tty driver are set/returned by translating the termio
structure to/from a termios structure.
TCGETA Gets termio structure.
TCSETA Sets termio structure.
TCSETAW Drains output and then sets termio structure.
TCSETAF Drains output, flushes input, and then sets termio structure.
The following group of System V ioctls take an integer value for the arg
parameter.
TCSBREAK Sends break.
TCSBRK Sends break.
TCXONC Sets flow control. The arg parameter uses same values as the
POSIX function tcflow() (must include <sys/termios.h>)
TCFLSH Flushes queue(s). You must include <sys/fcntl.h> for valid arg
parameters (for example, FREAD for flushing input side).
The following group of BSD compatibility ioctls use a pointer to a sgttyb
structure for the arg parameter. The tty parameters of the tty driver are
set/returned by translating the sgttyb structure to/from a termios
structure.
TIOCGETP Returns tty parameters.
TIOCSETP Sets tty parameters.
TIOCSETN Sets tty parameter without flushing.
The next group uses a pointer to the local mode bits (an integer value) as
their arg parameter. The local mode bits are converted to the appropriate
POSIX termios flag settings.
TIOCLBIS The arg value is used as a mask to set the local mode bits.
TIOCLBIC The arg value is used as a mask to clear the local mode bits.
TIOCLSET The arg value is used to replace the current setting of the local
mode bits.
TIOCLGET The arg parameter is used to return the current value of the
local mode bits.
The following group uses a pointer to a ltchars structure as their arg
parameter. The local special characters are translated to POSIX termios
control characters.
TIOCSLTC Set local control characters.
TIOCGLTC Get local control characters.
The following group of BSD compatibility ioctls sets/clears the POSIX
CLOCAL and HUPCL flags. The CLOCAL flag turns modem control on/off in the
tty driver. If the arg parameter (a pointer to an integer) for
TIOCMODEM/TIOCNMODEM is nonzero and the requesting process has super user
privileges the change is made permanent. Otherwise after the last close,
the tty line reverts back to the default value. The HUPCL flag determines
if the terminal line should be disconnected (that is, DTR is non asserted)
after the last close. The TIOCHPCL ioctl ignores the arg parameter.
TIOCMODEM Clears CLOCAL.
TIOCNMODEM
Sets CLOCAL.
TIOCHPCL Sets HUPCL.
FILES
/dev/tty Special file for tty.
/dev/tty* Special files for ttys, where the * (asterisk) sign represents
the tty number.
/dev/console
Device special file for console.
RELATED INFORMATION
Functions: ioctl(2), sigvec(2), tcsetattr(3), tcgetattr(3), tcdrain(3),
tcflush(3), tcsendbreak(3), tcgetpgrp(3), tcsetpgrp(3).
Commands: csh(1), strchg(1), tset(1), getty(8).
Files: termios(4)
Interfaces: atty(7), ldterm(7), modem(7), ttty(7).
IEEE Std POSIX 1003.1-1988
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