| 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.
INTRISIG 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.QUITISIG 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.ERASEICANON 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.KILLICANON 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.EOFICANON 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.NLICANON flag is set. It is the line delimiter
‘\n’.EOLICANON flag is set. Is an additional line
delimiter, like NL.SUSPISIG 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.STOPIXON (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.STARTIXON (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.CRICANON 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.
EOL2EOL character. Same function as
EOL.WERASEICANON 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.REPRINTICANON flag is set. Causes the current input edit
line to be retyped.DSUSPSUSP 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.LNEXTIEXTEN flag is set. Receipt of this character
causes the next character to be taken literally.DISCARDIEXTEN flag is set. Receipt of this character
toggles the flushing of terminal output.STATUSICANON 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.
IGNBRKBRKINTIGNPARPARMRKINPCKISTRIPINLCRIGNCRICRNLIXONIXOFFIXANYIMAXBELIn 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.
CSIZECS5CS6CS7CS8CSTOPBCREADPARENBPARODDHUPCLCLOCALCCTS_OFLOWCTS flow control of output */CRTSCTSCCTS_OFLOW |
CCTS_IFLOW */CRTS_IFLOWMDMBUFThe 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.
ECHOKEECHOEECHOECHONLNL even if ECHO is
off */ECHOPRTECHOCTLISIGINTR,
QUIT, [D]SUSP */ICANONALTWERASEWERASE algorithm */IEXTENDISCARD and
LNEXT */EXTPROCTOSTOPFLUSHONOKERNINFOVSTATUS */PENDINNOFLSHIf 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 |