termios —
general terminal line discipline
#include
<termios.h>
This describes a general terminal line discipline that is supported on tty
asynchronous communication ports.
When a terminal file is opened, it normally causes the process to wait until a
connection is established. For most hardware, the presence of a connection is
indicated by the assertion of the hardware
CARRIER line. If the termios structure
associated with the terminal file has the
CLOCAL flag set in the cflag, or if the
O_NONBLOCK flag is set in the
open(2) call, then the open will succeed even
without a connection being present. In practice, applications seldom open
these files; they are opened by special programs, such as
getty(8), and become an application's standard
input, output, and error files.
Every process is associated with a particular process group and session. The
grouping is hierarchical: every member of a particular process group is a
member of the same session. This structuring is used in managing groups of
related processes for purposes of
job control;
that is, the ability from the keyboard (or from program control) to
simultaneously stop or restart a complex command (a command composed of one or
more related processes). The grouping into process groups allows delivering of
signals that stop or start the group as a whole, along with arbitrating which
process group has access to the single controlling terminal. The grouping at a
higher layer into sessions is to restrict the job control related signals and
system calls to within processes resulting from a particular instance of a
“login”. Typically, a session is created when a user logs in,
and the login terminal is setup to be the controlling terminal; all processes
spawned from that login shell are in the same session, and inherit the
controlling terminal.
A job control shell operating interactively (that is, reading commands from a
terminal) normally groups related processes together by placing them into the
same process group. A set of processes in the same process group is
collectively referred to as a “job”. When the foreground process
group of the terminal is the same as the process group of a particular job,
that job is said to be in the “foreground”. When the process
group of the terminal is different from the process group of a job (but is
still the controlling terminal), that job is said to be in the
“background”. Normally the shell reads a command and starts the
job that implements that command. If the command is to be started in the
foreground (typical), it sets the process group of the terminal to the process
group of the started job, waits for the job to complete, and then sets the
process group of the terminal back to its own process group (it puts itself
into the foreground). If the job is to be started in the background (as
denoted by the shell operator "&"), it never changes the process
group of the terminal and does not wait for the job to complete (that is, it
immediately attempts to read the next command). If the job is started in the
foreground, the user may type a key (usually
‘
^Z’) which generates the terminal stop
signal (
SIGTSTP) and has the effect of
stopping the entire job. The shell will notice that the job stopped, and will
resume running after placing itself in the foreground. The shell also has
commands for placing stopped jobs in the background, and for placing stopped
or background jobs into the foreground.
An orphaned process group is a process group that has no process whose parent is
in a different process group, yet is in the same session. Conceptually it
means a process group that does not have a parent that could do anything if it
were to be stopped. For example, the initial login shell is typically in an
orphaned process group. Orphaned process groups are immune to keyboard
generated stop signals and job control signals resulting from reads or writes
to the controlling terminal.
A terminal may belong to a process as its controlling terminal. Each process of
a session that has a controlling terminal has the same controlling terminal. A
terminal may be the controlling terminal for at most one session. The
controlling terminal for a session is allocated by the session leader by
issuing the
TIOCSCTTY ioctl. A controlling
terminal is never acquired by merely opening a terminal device file. When a
controlling terminal becomes associated with a session, its foreground process
group is set to the process group of the session leader.
The controlling terminal is inherited by a child process during a
fork(2) function call. A process relinquishes its
controlling terminal when it creates a new session with the
setsid(2) function; other processes remaining in
the old session that had this terminal as their controlling terminal continue
to have it. A process does not relinquish its controlling terminal simply by
closing all of its file descriptors associated with the controlling terminal
if other processes continue to have it open.
When a controlling process terminates, the controlling terminal is disassociated
from the current session, allowing it to be acquired by a new session leader.
Subsequent access to the terminal by other processes in the earlier session
will be denied, with attempts to access the terminal treated as if modem
disconnect had been sensed.
If a process is in the foreground process group of its controlling terminal,
read operations are allowed. Any attempts by a process in a background process
group to read from its controlling terminal causes a
SIGTTIN signal to be sent to the process's
group unless one of the following special cases apply: if the reading process
is ignoring or blocking the
SIGTTIN signal,
or if the process group of the reading process is orphaned, the
read(2) returns -1 with
errno set to
EIO and no signal is sent. The default
action of the
SIGTTIN signal is to stop the
process to which it is sent.
If a process is in the foreground process group of its controlling terminal,
write operations are allowed. Attempts by a process in a background process
group to write to its controlling terminal will cause the process group to be
sent a
SIGTTOU signal unless one of the
following special cases apply: if
TOSTOP is
not set, or if
TOSTOP is set and the
process is ignoring or blocking the
SIGTTOU
signal, the process is allowed to write to the terminal and the
SIGTTOU signal is not sent. If
TOSTOP is set, and the process group of the
writing process is orphaned, and the writing process is not ignoring or
blocking
SIGTTOU, the
write(2) returns -1 with errno set to
EIO and no signal is sent.
Certain calls that set terminal parameters are treated in the same fashion as
write, except that
TOSTOP is ignored; that
is, the effect is identical to that of terminal writes when
TOSTOP is set.
A terminal device associated with a terminal device file may operate in
full-duplex mode, so that data may arrive even while output is occurring. Each
terminal device file has associated with it an input queue, into which
incoming data is stored by the system before being read by a process. The
system imposes a limit, {
MAX_INPUT}, on the
number of bytes that may be stored in the input queue. The behavior of the
system when this limit is exceeded depends on the setting of the
IMAXBEL flag in the termios
c_iflag. If this flag is set, the terminal is
sent an ASCII
BEL character each time a
character is received while the input queue is full. Otherwise, the input
queue is flushed upon receiving the character.
Two general kinds of input processing are available, determined by whether the
terminal device file is in canonical mode or noncanonical mode. Additionally,
input characters are processed according to the
c_iflag and
c_lflag fields. Such processing can include
echoing, which in general means transmitting input characters immediately back
to the terminal when they are received from the terminal. This is useful for
terminals that can operate in full-duplex mode.
The manner in which data is provided to a process reading from a terminal device
file is dependent on whether the terminal device file is in canonical or
noncanonical mode.
Another dependency is whether the
O_NONBLOCK
flag is set by
open(2) or
fcntl(2). If the
O_NONBLOCK flag is clear, then the read
request is blocked until data is available or a signal has been received. If
the
O_NONBLOCK flag is set, then the read
request is completed, without blocking, in one of three ways:
- If there is enough data available to satisfy the entire
request, and the read completes successfully the number of bytes read is
returned.
- If there is not enough data available to satisfy the
entire request, and the read completes successfully, having read as much
data as possible, the number of bytes read is returned.
- If there is no data available, the read returns -1, with
errno set to
EAGAIN.
When data is available depends on whether the input processing mode is canonical
or noncanonical.
In canonical mode input processing, terminal input is processed in units of
lines. A line is delimited by a newline
‘
\n’ character, an end-of-file
(
EOF) character, or an end-of-line
(
EOL) character. See the
Special Characters
section for more information on
EOF and
EOL. This means that a read request will
not return until an entire line has been typed, or a signal has been received.
Also, no matter how many bytes are requested in the read call, at most one
line is returned. It is not, however, necessary to read a whole line at once;
any number of bytes, even one, may be requested in a read without losing
information.
{
MAX_CANON} is a limit on the number of bytes
in a line. The behavior of the system when this limit is exceeded is the same
as when the input queue limit {
MAX_INPUT},
is exceeded.
Erase and kill processing occur when either of two special characters, the
ERASE and
KILL characters (see the
Special Characters
section), is received. This processing affects data in the input queue that
has not yet been delimited by a newline
NL,
EOF, or
EOL character. This un-delimited data makes
up the current line. The
ERASE character
deletes the last character in the current line, if there is any. The
KILL character deletes all data in the
current line, if there is any. The
ERASE
and
KILL characters have no effect if there
is no data in the current line. The
ERASE
and
KILL characters themselves are not
placed in the input queue.
In noncanonical mode input processing, input bytes are not assembled into lines,
and erase and kill processing does not occur. The values of the
VMIN and
VTIME members of the
c_cc array are used to determine how to
process the bytes received.
MIN represents the minimum number of bytes
that should be received when the
read(2) function
successfully returns.
TIME is a timer of
0.1 second granularity that is used to time out bursty and short term data
transmissions. If
MIN is greater than
{
MAX_INPUT}, the response to the request is
undefined. The four possible values for
MIN
and
TIME and their interactions are
described below.
In this case
TIME serves as an inter-byte
timer and is activated after the first byte is received. Since it is an
inter-byte timer, it is reset after a byte is received. The interaction
between
MIN and
TIME is as follows: as soon as one byte is
received, the inter-byte timer is started. If
MIN bytes are received before the
inter-byte timer expires (remember that the timer is reset upon receipt of
each byte), the read is satisfied. If the timer expires before
MIN bytes are received, the characters
received to that point are returned to the user. Note that if
TIME expires at least one byte is returned
because the timer would not have been enabled unless a byte was received. In
this case (
MIN > 0,
TIME > 0) the read blocks until the
MIN and
TIME mechanisms are activated by the
receipt of the first byte, or a signal is received. If data is in the buffer
at the time of the
read(), the result is as if
data had been received immediately after the
read().
In this case, since the value of
TIME is
zero, the timer plays no role and only
MIN
is significant. A pending read is not satisfied until
MIN bytes are received (i.e., the pending
read blocks until
MIN bytes are received),
or a signal is received. A program that uses this case to read record-based
terminal
I/O may block indefinitely in the
read operation.
In this case, since
MIN = 0,
TIME no longer represents an inter-byte
timer. It now serves as a read timer that is activated as soon as the read
function is processed. A read is satisfied as soon as a single byte is
received or the read timer expires. Note that in this case if the timer
expires, no bytes are returned. If the timer does not expire, the only way the
read can be satisfied is if a byte is received. In this case the read will not
block indefinitely waiting for a byte; if no byte is received within
TIME*0.1 seconds after the read is
initiated, the read returns a value of zero, having read no data. If data is
in the buffer at the time of the read, the timer is started as if data had
been received immediately after the read.
The minimum of either the number of bytes requested or the number of bytes
currently available is returned without waiting for more bytes to be input. If
no characters are available, read returns a value of zero, having read no
data.
When a process writes one or more bytes to a terminal device file, they are
processed according to the
c_oflag field (see
the
Output Modes section).
The implementation may provide a buffering mechanism; as such, when a call to
write() completes, all of the bytes written have
been scheduled for transmission to the device, but the transmission will not
necessarily have been completed.
Certain characters have special functions on input or output or both. These
functions are summarized as follows:
INTR- Special character on input and is recognized if the
ISIG flag (see the
Local Modes section) is
enabled. Generates a SIGINT signal
which is sent to all processes in the foreground process group for which
the terminal is the controlling terminal. If
ISIG is set, the
INTR character is discarded when
processed.
QUIT- Special character on input and is recognized if the
ISIG flag is enabled. Generates a
SIGQUIT signal which is sent to all
processes in the foreground process group for which the terminal is the
controlling terminal. If ISIG is set,
the QUIT character is discarded when
processed.
ERASE- Special character on input and is recognized if the
ICANON flag is set. Erases the last
character in the current line; see
Canonical
Mode Input Processing. It does not erase beyond the start of a line,
as delimited by an NL,
EOF, or
EOL character. If
ICANON is set, the
ERASE character is discarded when
processed.
KILL- Special character on input and is recognized if the
ICANON flag is set. Deletes the entire
line, as delimited by a NL,
EOF, or
EOL character. If
ICANON is set, the
KILL character is discarded when
processed.
EOF- Special character on input and is recognized if the
ICANON flag is set. When received, all
the bytes waiting to be read are immediately passed to the process,
without waiting for a newline, and the
EOF is discarded. Thus, if there are no
bytes waiting (that is, the EOF
occurred at the beginning of a line), a byte count of zero is returned
from the read(), representing an end-of-file
indication. If ICANON is set, the
EOF character is discarded when
processed.
NL- Special character on input and is recognized if the
ICANON flag is set. It is the line
delimiter ‘\n’.
EOL- Special character on input and is recognized if the
ICANON flag is set. Is an additional
line delimiter, like NL.
SUSP- If the
ISIG flag is
enabled, receipt of the SUSP character
causes a SIGTSTP signal to be sent to
all processes in the foreground process group for which the terminal is
the controlling terminal, and the SUSP
character is discarded when processed.
STOP- Special character on both input and output and is
recognized if the
IXON (output control)
or IXOFF (input control) flag is set.
Can be used to temporarily suspend output. It is useful with fast
terminals to prevent output from disappearing before it can be read. If
IXON is set, the
STOP character is discarded when
processed.
START- Special character on both input and output and is
recognized if the
IXON (output control)
or IXOFF (input control) flag is set.
Can be used to resume output that has been suspended by a
STOP character. If
IXON is set, the
START character is discarded when
processed.
CR- Special character on input and is recognized if the
ICANON flag is set; it is the
‘\r’, as denoted in the C Standard
{2}. When ICANON and
ICRNL are set and
IGNCR is not set, this character is
translated into a NL, and has the same
effect as a NL character.
The following special characters are extensions defined by this system and are
not a part of
IEEE Std 1003.1
(“POSIX.1”) termios.
EOL2- Secondary
EOL character.
Same function as EOL.
WERASE- Special character on input and is recognized if the
ICANON flag is set. Erases the last
word in the current line according to one of two algorithms. If the
ALTWERASE flag is not set, first any
preceding whitespace is erased, and then the maximal sequence of
non-whitespace characters. If ALTWERASE
is set, first any preceding whitespace is erased, and then the maximal
sequence of alphabetic/underscores or non alphabetic/underscores. As a
special case in this second algorithm, the first previous non-whitespace
character is skipped in determining whether the preceding word is a
sequence of alphabetic/underscores. This sounds confusing but turns out to
be quite practical.
REPRINT- Special character on input and is recognized if the
ICANON flag is set. Causes the current
input edit line to be retyped.
DSUSP- Has similar actions to the
SUSP character, except that the
SIGTSTP signal is delivered when one of
the processes in the foreground process group issues a
read() to the controlling terminal.
LNEXT- Special character on input and is recognized if the
IEXTEN flag is set. Receipt of this
character causes the next character to be taken literally.
DISCARD- Special character on input and is recognized if the
IEXTEN flag is set. Receipt of this
character toggles the flushing of terminal output.
STATUS- Special character on input and is recognized if the
ICANON flag is set. Receipt of this
character causes a SIGINFO signal to be
sent to the foreground process group of the terminal. Also, if the
NOKERNINFO flag is not set, it causes
the kernel to write a status message to the terminal that displays the
current load average, the name of the command in the foreground, its
process ID, the symbolic wait channel, the number of user and system
seconds used, the percentage of cpu the process is getting, and the
resident set size of the process.
The
NL and
CR characters cannot be changed. The values
for all the remaining characters can be set and are described later in the
document under Special Control Characters.
Special character functions associated with changeable special control
characters can be disabled individually by setting their value to
{_POSIX_VDISABLE}; see
Special Control
Characters.
If two or more special characters have the same value, the function performed
when that character is received is undefined.
If a modem disconnect is detected by the terminal interface for a controlling
terminal, and if
CLOCAL is not set in the
c_cflag field for the terminal, the
SIGHUP signal is sent to the controlling
process associated with the terminal. Unless other arrangements have been
made, this causes the controlling process to terminate. Any subsequent call to
the
read() function returns the value zero,
indicating end of file. Thus, processes that read a terminal file and test for
end-of-file can terminate appropriately after a disconnect. Any subsequent
write() to the terminal device returns -1, with
errno set to
EIO, until the device is closed.
The last process to close a terminal device file causes any output to be sent to
the device and any input to be discarded. Then, if
HUPCL is set in the control modes, and the
communications port supports a disconnect function, the terminal device
performs a disconnect.
Routines that need to control certain terminal I/O characteristics do so by
using the termios structure as defined in the header
<termios.h>.
This structure contains minimally four scalar elements of bit flags and one
array of special characters. The scalar flag elements are named:
c_iflag,
c_oflag,
c_cflag, and
c_lflag. The character array is named
c_cc, and its maximum index is
NCCS.
Values of the
c_iflag field describe the basic
terminal input control, and are composed of following masks:
IGNBRK- /* ignore BREAK condition */
BRKINT- /* map BREAK to SIGINTR */
IGNPAR- /* ignore (discard) parity errors */
PARMRK- /* mark parity and framing errors */
INPCK- /* enable checking of parity errors */
ISTRIP- /* strip 8th bit off chars */
INLCR- /* map NL into CR */
IGNCR- /* ignore CR */
ICRNL- /* map CR to NL (ala CRMOD) */
IXON- /* enable output flow control */
IXOFF- /* enable input flow control */
IXANY- /* any char will restart after stop */
IMAXBEL- /* ring bell on input queue full */
In the context of asynchronous serial data transmission, a break condition is
defined as a sequence of zero-valued bits that continues for more than the
time to send one byte. The entire sequence of zero-valued bits is interpreted
as a single break condition, even if it continues for a time equivalent to
more than one byte. In contexts other than asynchronous serial data
transmission the definition of a break condition is implementation defined.
If
IGNBRK is set, a break condition detected
on input is ignored, that is, not put on the input queue and therefore not
read by any process. If
IGNBRK is not set
and
BRKINT is set, the break condition
flushes the input and output queues and if the terminal is the controlling
terminal of a foreground process group, the break condition generates a single
SIGINT signal to that foreground process
group. If neither
IGNBRK nor
BRKINT is set, a break condition is read as
a single ‘
\0’, or if
PARMRK is set, as
‘
\377’,
‘
\0’,
‘
\0’.
If
IGNPAR is set, a byte with a framing or
parity error (other than break) is ignored.
If
PARMRK is set, and
IGNPAR is not set, a byte with a framing or
parity error (other than break) is given to the application as the
three-character sequence ‘
\377’,
‘
\0’, X, where
‘
\377’,
‘
\0’ is a two-character flag preceding
each sequence and X is the data of the character received in error. To avoid
ambiguity in this case, if
ISTRIP is not
set, a valid character of ‘
\377’ is
given to the application as ‘
\377’,
‘
\377’. If neither
PARMRK nor
IGNPAR is set, a framing or parity error
(other than break) is given to the application as a single character
‘
\0’.
If
INPCK is set, input parity checking is
enabled. If
INPCK is not set, input parity
checking is disabled, allowing output parity generation without input parity
errors. Note that whether input parity checking is enabled or disabled is
independent of whether parity detection is enabled or disabled (see
Control Modes). If parity
detection is enabled but input parity checking is disabled, the hardware to
which the terminal is connected recognizes the parity bit, but the terminal
special file does not check whether this bit is set correctly or not.
If
ISTRIP is set, valid input bytes are first
stripped to seven bits, otherwise all eight bits are processed.
If
INLCR is set, a received
NL character is translated into a
CR character. If
IGNCR is set, a received
CR character is ignored (not read). If
IGNCR is not set and
ICRNL is set, a received
CR character is translated into a
NL character.
If
IXON is set, start/stop output control is
enabled. A received
STOP character suspends
output and a received
START character
restarts output. If
IXANY is also set, then
any character may restart output. When
IXON
is set,
START and
STOP characters are not read, but merely
perform flow control functions. When
IXON
is not set, the
START and
STOP characters are read.
If
IXOFF is set, start/stop input control is
enabled. The system shall transmit one or more
STOP characters, which are intended to
cause the terminal device to stop transmitting data, as needed to prevent the
input queue from overflowing and causing the undefined behavior described in
Input
Processing and Reading Data, and shall transmit one or more
START characters, which are intended to
cause the terminal device to resume transmitting data, as soon as the device
can continue transmitting data without risk of overflowing the input queue.
The precise conditions under which
STOP and
START characters are transmitted are
implementation defined.
If
IMAXBEL is set and the input queue is
full, subsequent input shall cause an ASCII
BEL character to be transmitted to the
output queue.
The initial input control value after
open() is
implementation defined.
Values of the
c_oflag field describe the basic
terminal output control, and are composed of the following masks:
OPOST- /* enable following output processing */
ONLCR- /* map NL to CR-NL (ala
CRMOD) */
OCRNL- /* map CR to NL */
TABDLY- /* tab delay mask */
TAB0- /* no tab delay and expansion */
TAB3- /* expand tabs to spaces */
ONOEOT- /* discard
EOT's
‘^D’ on output) */
ONOCR- /* do not transmit CRs on column 0 */
ONLRET- /* on the terminal NL performs the CR function */
If
OPOST is set, the remaining flag masks are
interpreted as follows; otherwise characters are transmitted without change.
If
ONLCR is set, newlines are translated to
carriage return, linefeeds.
If
OCRNL is set, carriage returns are
translated to newlines.
The
TABDLY bits specify the tab delay. The
c_oflag is masked with
TABDLY and compared with the values
TAB0 or
TAB3. If
TAB3 is set, tabs are expanded to the
appropriate number of spaces (assuming 8 column tab stops).
If
ONOEOT is set, ASCII
EOT's are discarded on output.
If
ONOCR is set, no CR character is
transmitted when at column 0 (first position).
If
ONLRET is set, the NL character is assumed
to do the carriage-return function; the column pointer will be set to 0.
Values of the
c_cflag field describe the basic
terminal hardware control, and are composed of the following masks. Not all
values specified are supported by all hardware.
CSIZE- /* character size mask */
CS5- /* 5 bits (pseudo) */
CS6- /* 6 bits */
CS7- /* 7 bits */
CS8- /* 8 bits */
CSTOPB- /* send 2 stop bits */
CREAD- /* enable receiver */
PARENB- /* parity enable */
PARODD- /* odd parity, else even */
HUPCL- /* hang up on last close */
CLOCAL- /* ignore modem status lines */
CCTS_OFLOW- /*
CTS flow control of
output */
CRTSCTS- /* same as
CCTS_OFLOW
*/
CRTS_IFLOW- /* RTS flow control of input */
MDMBUF- /* flow control output via Carrier */
The
CSIZE bits specify the byte size in bits
for both transmission and reception. The
c_cflag is masked with
CSIZE and compared with the values
CS5,
CS6,
CS7, or
CS8. This size does not include the parity
bit, if any. If
CSTOPB is set, two stop
bits are used, otherwise one stop bit. For example, at 110 baud, two stop bits
are normally used.
If
CREAD is set, the receiver is enabled.
Otherwise, no character is received. Not all hardware supports this bit. In
fact, this flag is pretty silly and if it were not part of the
termios specification it would be omitted.
If
PARENB is set, parity generation and
detection are enabled and a parity bit is added to each character. If parity
is enabled,
PARODD specifies odd parity if
set, otherwise even parity is used.
If
HUPCL is set, the modem control lines for
the port are lowered when the last process with the port open closes the port
or the process terminates. The modem connection is broken.
If
CLOCAL is set, a connection does not
depend on the state of the modem status lines. If
CLOCAL is clear, the modem status lines are
monitored.
Under normal circumstances, a call to the
open()
function waits for the modem connection to complete. However, if the
O_NONBLOCK flag is set or if
CLOCAL has been set, the
open() function returns immediately without
waiting for the connection.
The
CCTS_OFLOW
(
CRTSCTS) flag is currently unused.
If
MDMBUF is set then output flow control is
controlled by the state of Carrier Detect.
If the object for which the control modes are set is not an asynchronous serial
connection, some of the modes may be ignored; for example, if an attempt is
made to set the baud rate on a network connection to a terminal on another
host, the baud rate may or may not be set on the connection between that
terminal and the machine it is directly connected to.
Values of the
c_lflag field describe the
control of various functions, and are composed of the following masks.
ECHOKE- /* visual erase for line kill */
ECHOE- /* visually erase chars */
ECHO- /* enable echoing */
ECHONL- /* echo
NL even if
ECHO is off */
ECHOPRT- /* visual erase mode for hardcopy */
ECHOCTL- /* echo control chars as ^(Char) */
ISIG- /* enable signals
INTR,
QUIT,
[D]SUSP */
ICANON- /* canonicalize input lines */
ALTWERASE- /* use alternate
WERASE
algorithm */
IEXTEN- /* enable
DISCARD and
LNEXT */
EXTPROC- /* external processing */
TOSTOP- /* stop background jobs from output */
FLUSHO- /* output being flushed (state) */
NOKERNINFO- /* no kernel output from
VSTATUS */
PENDIN- /* XXX retype pending input (state) */
NOFLSH- /* don't flush after interrupt */
If
ECHO is set, input characters are echoed
back to the terminal. If
ECHO is not set,
input characters are not echoed.
If
ECHOE and
ICANON are set, the
ERASE character causes the terminal to
erase the last character in the current line from the display, if possible. If
there is no character to erase, an implementation may echo an indication that
this was the case or do nothing.
If
ECHOK and
ICANON are set, the
KILL character causes the current line to
be discarded and the system echoes the
‘
\n’ character after the
KILL character.
If
ECHOKE and
ICANON are set, the
KILL character causes the current line to
be discarded and the system causes the terminal to erase the line from the
display.
If
ECHOPRT and
ICANON are set, the system assumes that the
display is a printing device and prints a backslash and the erased characters
when processing
ERASE characters, followed
by a forward slash.
If
ECHOCTL is set, the system echoes control
characters in a visible fashion using a caret followed by the control
character.
If
ALTWERASE is set, the system uses an
alternative algorithm for determining what constitutes a word when processing
WERASE characters (see
WERASE).
If
ECHONL and
ICANON are set, the
‘
\n’ character echoes even if
ECHO is not set.
If
ICANON is set, canonical processing is
enabled. This enables the erase and kill edit functions, and the assembly of
input characters into lines delimited by
NL,
EOF,
and
EOL, as described in
Canonical
Mode Input Processing.
If
ICANON is not set, read requests are
satisfied directly from the input queue. A read is not satisfied until at
least
MIN bytes have been received or the
timeout value
TIME expired between bytes.
The time value represents tenths of seconds. See
Noncanonical
Mode Input Processing for more details.
If
ISIG is set, each input character is
checked against the special control characters
INTR,
QUIT, and
SUSP (job control only). If an input
character matches one of these control characters, the function associated
with that character is performed. If
ISIG
is not set, no checking is done. Thus these special input functions are
possible only if
ISIG is set.
If
IEXTEN is set, implementation-defined
functions are recognized from the input data. How
IEXTEN being set interacts with
ICANON,
ISIG,
IXON, or
IXOFF is implementation defined. If
IEXTEN is not set, then
implementation-defined functions are not recognized, and the corresponding
input characters are not processed as described for
ICANON,
ISIG,
IXON, and
IXOFF.
If
NOFLSH is set, the normal flush of the
input and output queues associated with the
INTR,
QUIT, and
SUSP characters are not be done.
If
TOSTOP is set, the signal
SIGTTOU is sent to the process group of a
process that tries to write to its controlling terminal if it is not in the
foreground process group for that terminal. This signal, by default, stops the
members of the process group. Otherwise, the output generated by that process
is output to the current output stream. Processes that are blocking or
ignoring
SIGTTOU signals are excepted and
allowed to produce output and the
SIGTTOU
signal is not sent.
If
NOKERNINFO is set, the kernel does not
produce a status message when processing
STATUS characters (see
STATUS).
The special control characters values are defined by the array
c_cc. This table lists the array index, the
corresponding special character, and the system default value. For an accurate
list of the system defaults, consult the header file
<sys/ttydefaults.h>.
If the value of one of the changeable special control characters (see
Special Characters) is
{_POSIX_VDISABLE}, that function is
disabled; that is, no input data is recognized as the disabled special
character. If
ICANON is not set, the value
of
{_POSIX_VDISABLE} has no special meaning
for the
VMIN and
VTIME entries of the
c_cc array.
The initial values of the flags and control characters after
open() is set according to the values in the
header
<sys/ttydefaults.h>.
stty(1),
tcgetsid(3),
tcsendbreak(3),
tcsetattr(3),
tcsetsid(3),
tty(4)