termios(4)

NAME

termios - general terminal line discipline

SYNOPSIS

#include <termios.h>

DESCRIPTION

This describes a general terminal line discipline that is
supported on
tty asynchronous communication ports.
Opening a Terminal Device File
When a terminal file is opened, it normally causes the pro
cess 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) or rlogind(8), and become
an application's standard input, output, and error files.
Job Control in a Nutshell
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 si
multaneously
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, read
ing 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 ter
minal to the
process group of the started job, waits for the job to com
plete, and then
sets the process group of the terminal back to its own pro
cess 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 (usu
ally `^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 back
ground, and for
placing stopped or background jobs into the foreground.
Orphaned Process Groups
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 par
ent that could
do anything if it were to be stopped. For example, the ini
tial login
shell is typically in an orphaned process group. Orphaned
process groups
are immune to keyboard generated stop signals and job con
trol signals
resulting from reads or writes to the controlling terminal.
The Controlling Terminal
A terminal may belong to a process as its controlling termi
nal. Each
process of a session that has a controlling terminal has the
same controlling terminal. A terminal may be the controlling termi
nal for at
most one session. The controlling terminal for a session is
allocated by
the session leader by issuing the TIOCSCTTY ioctl. A con
trolling 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 ter
minal 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 ter
minal is disassociated from the current session, allowing it to be ac
quired 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.
Terminal Access Control
If a process is in the foreground process group of its con
trolling 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 ignor
ing or blocking the SIGTTIN signal, or if the process group of the read
ing 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 con
trolling 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 follow
ing 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 al
lowed 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.
Input Processing and Reading Data
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 num
ber 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, deter
mined by
whether the terminal device file is in canonical mode or
noncanonical
mode. Additionally, input characters are processed accord
ing 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 re
ceived. If the
O_NONBLOCK flag is set, then the read request is completed,
without
blocking, in one of three ways:

1. If there is enough data available to satisfy the
entire
request, and the read completes successfully the
number of
bytes read is returned.
2. 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.
3. If there is no data available, the read returns
-1, with errno
set to EAGAIN.
When data is available depends on whether the input process
ing mode is
canonical or noncanonical.
Canonical Mode Input Processing In canonical mode input processing, terminal input is pro
cessed in units
of lines. A line is delimited by a newline `0 character, an
end-offile (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 undelimited data makes up the current line. The ERASE charac
ter 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.
Noncanonical Mode Input Processing 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 deter
mine 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.
Case A: MIN > 0, TIME > 0
In this case TIME serves as an inter-byte timer and is acti
vated 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 re
ceived, 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().
Case B: MIN > 0, TIME = 0
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 satis
fied 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.
Case C: MIN = 0, TIME > 0
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 initi
ated, 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.
Case D: MIN = 0, TIME = 0
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.
Writing Data and Output Processing 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 mecha
nism; as such,
when a call to write() completes, all of the bytes written
have been
scheduled for transmission to the device, but the transmis
sion will not
necessarily have been completed.
Special Characters
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 fore
ground process
group for which the terminal is the controlling ter
minal. 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(), repre
senting an endof-file indication. If ICANON is set, the EOF char
acter is discarded when processed.
NL Special character on input and is recognized if the
ICANON flag
is set. It is the line delimiter `0.
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 control
ling 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 dis
carded 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 ', as denoted in the C Standard
is set; it is the ` {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/under
scores. As a special case in this second algorithm, the first previ
ous nonwhitespace 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 process
es in the
foreground process group issues a read() to the con
trolling 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 termi
nal. 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 get
ting, 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 spe
cial 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.
Modem Disconnect
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 pro
cess 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 ter
minate appropriately after a disconnect. Any subsequent write() to the
terminal
device returns -1, with errno set to EIO, until the device
is closed.

General Terminal Interface

Closing a Terminal Device File
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.
Parameters That Can Be Set
Routines that need to control certain terminal I/O charac
teristics do so
by using the termios structure as defined in the header 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.
Input Modes
Values of the c_iflag field describe the basic terminal in
put 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 con
tinues for more
than the time to send one byte. The entire sequence of ze
ro-valued bits
is interpreted as a single break condition, even if it con
tinues 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 ig
nored, 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 control
ling 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 ` ', or
if PARMRK
is set, as `377', ` ', ` '.
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 fram
ing or parity
error (other than break) is given to the application as the
three-character sequence `377', ` ', X, where `377', ` ' is a two-char
acter 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
` '.
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 detec
tion is enabled
or disabled (see Control Modes). If parity detection is en
abled but
input parity checking is disabled, the hardware to which the
terminal is
connected recognizes the parity bit, but the terminal spe
cial 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 re
ceived 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 pre
vent 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 trans
mitting 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 implementa
tion defined.
Output Modes
Values of the c_oflag field describe the basic terminal out
put 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 */
OXTABS /* 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 new
lines.
If OXTABS is set, tabs are expanded to the appropriate num
ber 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 col
umn 0 (first
position).
If ONLRET is set, the NL character is assumed to do the car
riage-return
function; the column pointer will be set to 0.
Control Modes
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 trans
mission 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 pari
ty 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 specifi
cation it
would be omitted.
If PARENB is set, parity generation and detection are en
abled 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 immedi
ately 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 ex
ample, 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.
Local Modes
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 ter
minal. 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 dis
play, 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 `0 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 char
acters 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 algo
rithm for determining what constitutes a word when processing WERASE char
acters (see
WERASE).
If ECHONL and ICANON are set, the `0 character echoes even
if ECHO is
not set.
If ICANON is set, canonical processing is enabled. This en
ables 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 func
tion 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 rec
ognized 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 corre
sponding 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 sig
nal, by default,
stops the members of the process group. Otherwise, the out
put 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).
Special Control Characters The special control characters values are defined by the ar
ray 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

Index Name Special Character Default Value VEOF EOF ^D
VEOL EOL _POSIX_VDISABLE
VEOL2 EOL2 _POSIX_VDISABLE
VERASE ERASE ^? `177'
VWERASE WERASE ^W
VKILL KILL ^U
VREPRINT REPRINT ^R
VINTR INTR ^C
VQUIT QUIT ^ `34'
VSUSP SUSP ^Z
VDSUSP DSUSP ^Y
VSTART START ^Q
VSTOP STOP ^S
VLNEXT LNEXT ^V
VDISCARD DISCARD ^O
VMIN --- 1
VTIME --- 0
VSTATUS STATUS ^T
If the value of one of the changeable special control char
acters (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
BSD April 19, 1994

BSD

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