TERMIOS(4) | Device Drivers Manual | TERMIOS(4) |
termios
—
#include <termios.h>
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.
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
character (usually ‘^Z
’) which
generates the terminal stop signal (SIGTSTP
) and has
the affect of stopping the entire job. The shell will notice that the job
stopped (see wait(2)), 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.
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.
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.
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:
EAGAIN
.When data is available depends on whether the input processing mode is canonical or noncanonical.
\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.
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) system call 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.
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(2), the result is as if data
had been received immediately after the
read(2).
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.
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.
INTR
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
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
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
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
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(2), representing
an end-of-file indication. If ICANON
is set, the
EOF
character is discarded when processed.NL
ICANON
flag is set. It is the line delimiter
‘\n
’.EOL
ICANON
flag is set. Is an additional line
delimiter, like NL
.SUSP
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
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
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
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
EOL
character. Same function as
EOL
.WERASE
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
ICANON
flag is set. Causes the current input edit
line to be retyped.DSUSP
SUSP
character, except
that the SIGTSTP
signal is delivered when one of
the processes in the foreground process group issues a
read(2) to the controlling
terminal.LNEXT
IEXTEN
flag is set. Receipt of this character
causes the next character to be taken literally.DISCARD
IEXTEN
flag is set. Receipt of this character
toggles the flushing of terminal output.STATUS
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.
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(2) 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(2) to the
terminal device returns -1, with errno set to
EIO
, until the device is closed.
HUPCL
is set in the control modes, and the
communications port supports a disconnect function, the terminal device
performs a disconnect.
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
.
IGNBRK
BRKINT
IGNPAR
PARMRK
INPCK
ISTRIP
INLCR
IGNCR
ICRNL
IXON
IXOFF
IXANY
IMAXBEL
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(2) is implementation defined.
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.
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 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.
CSIZE
CS5
CS6
CS7
CS8
CSTOPB
CREAD
PARENB
PARODD
HUPCL
CLOCAL
CCTS_OFLOW
CTS
flow control of output */CRTSCTS
CCTS_OFLOW |
CCTS_IFLOW
*/CRTS_IFLOW
MDMBUF
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(2) function waits for the
modem connection to complete. However, if the
O_NONBLOCK
flag is set or if
CLOCAL
has been set, the
open(2) function returns
immediately without waiting for the connection.
If the tty(4)
TIOCFLAG_CLOCAL
flag has been set on the port then
the CLOCAL
flag will automatically be set on every
open.
The CCTS_OFLOW
and
CRTS_IFLOW
flags are currently unused. Only
CRTSCTS
, which has the combined effect, is
implemented. Note that CRTSCTS
support is hardware
and driver dependent. Check the specific port driver manual page to see if
hardware flow control is supported on the port you are using.
If the tty(4)
TIOCFLAG_CRTSCTS
flag has been set on the port then
the CRTSCTS
flag will automatically be set on every
open.
If MDMBUF
is set then output flow control
is controlled by the state of Carrier Detect.
If the tty(4)
TIOCFLAG_MDMBUF
flag has been set on the port then
the MDMBUF
flag will automatically be set on every
open.
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.
ECHOKE
ECHOE
ECHO
ECHONL
NL
even if ECHO
is
off */ECHOPRT
ECHOCTL
ISIG
INTR
,
QUIT
, [D]SUSP
*/ICANON
ALTWERASE
WERASE
algorithm */IEXTEN
DISCARD
and
LNEXT
*/EXTPROC
TOSTOP
FLUSHO
NOKERNINFO
VSTATUS
*/PENDIN
NOFLSH
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 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
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
).
<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(2) is set according to the
values in the header
<sys/ttydefaults.h>
.
October 7, 2006 | NetBSD 9.4 |