termios - general terminal line discipline
#include <termios.h>
This describes a general terminal line discipline that is
supported on
tty asynchronous communication ports.
Opening a Terminal Device File [Toc] [Back]
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) or sshd(8), and become an
application's
standard input, output, and error files.
Job Control in a Nutshell [Toc] [Back]
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 set up 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
than 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
doesn't 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.
Orphaned Process Groups [Toc] [Back]
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 doesn't 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.
The Controlling Terminal [Toc] [Back]
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.
Terminal Access Control [Toc] [Back]
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.
Input Processing and Reading Data [Toc] [Back]
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() or
fcntl(). 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:
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 processing mode is
canonical or noncanonical.
Canonical Mode Input Processing [Toc] [Back]
In canonical mode input processing, terminal input is processed 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 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.
Noncanonical Mode Input Processing [Toc] [Back]
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.
VMIN represents the minimum number of bytes that should be
received when
the read(2) function successfully returns. VTIME is a timer
of 0.1 second
granularity that is used to time out bursty and short
term data
transmissions. If VMIN is greater than {MAX_INPUT}, the response to the
request is undefined. The four possible values for VMIN and
VTIME and
their interactions are described below.
Case A: VMIN > 0, VTIME > 0
In this case VTIME 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 VMIN and
VTIME is as
follows: as soon as one byte is received, the inter-byte
timer is started.
If VMIN 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 VMIN bytes are received, the
characters received to that point are returned to the user.
Note that if
VTIME expires at least one byte is returned because the
timer would not
have been enabled unless a byte was received. In this case
(VMIN > 0,
VTIME > 0) the read blocks until the VMIN and VTIME 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: VMIN > 0, VTIME = 0
In this case, since the value of VTIME is zero, the timer
plays no role
and only VMIN is significant. A pending read is not satisfied until VMIN
bytes are received (i.e., the pending read blocks until VMIN
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: VMIN = 0, VTIME > 0
In this case, since VMIN = 0, VTIME 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 VTIME*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.
Case D: VMIN = 0, VTIME = 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 [Toc] [Back]
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.
Special Characters [Toc] [Back]
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 a 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 endof-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
`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 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 ', 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 1003.1 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 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 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.
Modem Disconnect [Toc] [Back]
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.
General Terminal Interface [Toc] [Back] 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 [Toc] [Back]
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.
Input Modes [Toc] [Back]
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 */
IUCLC /* translate upper case to lower case */
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 ` ', 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 framing or parity
error (other than break) is given to the application as the
three-character
sequence `377', ` ', X, where `377', ` ' 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
` '.
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.
If IUCLC is set, characters will be translated from upper to
lower case
on input.
The initial input control value after open() is implementation defined.
Output Modes [Toc] [Back]
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) */
OXTABS /* expand tabs to spaces */
ONOEOT /* discard EOT's (^D) on output */
OCRNL /* map CR to NL */
OLCUC /* translate lower case to upper case */
ONOCR /* No CR output at column 0 */
ONLRET /* 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 OXTABS 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 OCRNL is set, carriage returns are translated to newlines.
If OLCUC is set, lower case is translated to upper case on
output.
If ONOCR is set, no CR character is output when at column 0.
If ONLRET is set, NL also performs CR on output, and reset
current column
to 0.
Control Modes [Toc] [Back]
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.
Local Modes [Toc] [Back]
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 */
XCASE /* canonical upper/lower case */
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 `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 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 `0 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 VMIN bytes
have been received
or the timeout value VTIME 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 is not done.
If XCASE and ICANON is set, an upper case character is preserved on input
if prefixed by a character. In addition, this prefix is
added to upper
case characters on output.
In addition, the following special character translations
are in effect:
for: use:
` '
|
~
{
}
\
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).
Special Control Characters [Toc] [Back]
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 <ttydefaults.h>.
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 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>.
tcgetattr(3), tcsetattr(3)
OpenBSD 3.6 April 19, 1994
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