TERMIO(4I) Ioctl Requests TERMIO(4I)

NAME

termio - general terminal interface

SYNOPSIS

#include <termio.h>

ioctl(int fildes, int request, struct termio *arg);

ioctl(int fildes, int request, int arg);

#include <termios.h>

ioctl(int fildes, int request, struct termios *arg);

DESCRIPTION

This release supports a general interface for asynchronous
communications ports that is hardware-independent. The user interface
to this functionality is using function calls (the preferred interface)
described in termios(3C) or ioctl() commands described in this section.
This section also discusses the common features of the terminal
subsystem which are relevant with both user interfaces.

When a terminal file is opened, it normally causes the process to wait
until a connection is established. In practice, user programs seldom
open terminal files; they are opened by the system and become a user's
standard input, output, and error files. The first terminal file
opened by the session leader that is not already associated with a
session becomes the controlling terminal for that session. The
controlling terminal plays a special role in handling quit and
interrupt signals, as discussed below. The controlling terminal is
inherited by a child process during a fork(2). A process can break
this association by changing its session using setsid(2).

A terminal associated with one of these files ordinarily operates in
full-duplex mode. Characters may be typed at any time, even while
output is occurring, and are only lost when the character input buffers
of the system become completely full, which is rare. For example, the
number of characters in the line discipline buffer may exceed
{MAX_CANON} and IMAXBEL (see below) is not set, or the user may
accumulate {MAX_INPUT} number of input characters that have not yet
been read by some program. When the input limit is reached, all the
characters saved in the buffer up to that point are thrown away without
notice.

Session Management (Job Control)
A control terminal will distinguish one of the process groups in the
session associated with it to be the foreground process group. All
other process groups in the session are designated as background
process groups. This foreground process group plays a special role in
handling signal-generating input characters, as discussed below. By
default, when a controlling terminal is allocated, the controlling
process's process group is assigned as foreground process group.

Background process groups in the controlling process's session are
subject to a job control line discipline when they attempt to access
their controlling terminal. Process groups can be sent signals that
will cause them to stop, unless they have made other arrangements. An
exception is made for members of orphaned process groups.

An orphaned process group is one where the process group (see
getpgid(2)) has no members with a parent in a different process group
but sharing the same controlling terminal. When a member of an
orphaned process group attempts to access its controlling terminal, EIO
is returned because there would be no way to restart the process if it
were stopped on one of these signals.

If a member of a background process group attempts to read its
controlling terminal, its process group will be sent a SIGTTIN signal,
which will normally cause the members of that process group to stop.
If, however, the process is ignoring or holding SIGTTIN, or is a member
of an orphaned process group, the read will fail with errno set to EIO,
and no signal is sent.

If a member of a background process group attempts to write its
controlling terminal and the TOSTOP bit is set in the c_lflag field,
its process group is sent a SIGTTOU signal, which will normally cause
the members of that process group to stop. If, however, the process is
ignoring or holding SIGTTOU, the write will succeed. If the process is
not ignoring or holding SIGTTOU and is a member of an orphaned process
group, the write will fail with errno set to EIO, and no signal will be
sent.

If TOSTOP is set and a member of a background process group attempts to
ioctl() its controlling terminal, and that ioctl() will modify terminal
parameters (for example, TCSETA, TCSETAW, TCSETAF, or TIOCSPGRP), its
process group will be sent a SIGTTOU signal, which will normally cause
the members of that process group to stop. If, however, the process is
ignoring or holding SIGTTOU, the ioctl will succeed. If the process is
not ignoring or holding SIGTTOU and is a member of an orphaned process
group, the write will fail with errno set to EIO, and no signal will be
sent.

Canonical Mode Input Processing

Normally, terminal input is processed in units of lines. A line is
delimited by a newline (ASCII LF) character, an end-of-file (ASCII EOT)
character, or an end-of-line character. This means that a program
attempting to read will block until an entire line has been typed.
Also, no matter how many characters are requested in the read call, at
most one line will be returned. It is not necessary, however, to read
a whole line at once; any number of characters may be requested in a
read, even one, without losing information.

During input, erase, erase2, and kill processing is normally done. The
ERASE and ERASE2 character (by default, the character DEL for ERASE and
Control-h for ERASE2) erases the last character typed. The WERASE
character (the character Control-w) erases the last "word" typed in the
current input line (but not any preceding spaces or tabs). A "word" is
defined as a sequence of non-blank characters, with tabs counted as
blanks. None of ERASE or ERASE2 or WERASE will erase beyond the
beginning of the line. The KILL character (by default, the character
NAK) kills (deletes) the entire input line, and optionally outputs a
newline character. All these characters operate on a key stroke basis,
independent of any backspacing or tabbing that may have been done. The
REPRINT character (the character Control-r) prints a newline followed
by all characters that have not been read. Reprinting also occurs
automatically if characters that would normally be erased from the
screen are fouled by program output. The characters are reprinted as
if they were being echoed; consequently, if ECHO is not set, they are
not printed.

The ERASE, ERASE2, and KILL characters may be entered literally by
preceding them with the escape character. In this case, the escape
character is not read. The erase, erase2, and kill characters may be
changed.

Non-canonical Mode Input Processing
In non-canonical mode input processing, input characters are not
assembled into lines, and erase and kill processing does not occur.
The MIN and TIME values are used to determine how to process the
characters received.

MIN represents the minimum number of characters that should be received
when the read is satisfied (that is, when the characters are returned
to the user). TIME is a timer of 0.10-second granularity that is used
to timeout bursty and short-term data transmissions. 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
intercharacter timer and is activated after
the first character is received. Since it
is an intercharacter timer, it is reset
after a character is received. The
interaction between MIN and TIME is as
follows: as soon as one character is
received, the intercharacter timer is
started. If MIN characters are received
before the intercharacter timer expires
(note that the timer is reset upon receipt
of each character), the read is satisfied.
If the timer expires before MIN characters
are received, the characters received to
that point are returned to the user. Note
that if TIME expires, at least one character
will be returned because the timer would not
have been enabled unless a character was
received. In this case (MIN > 0, TIME > 0),
the read sleeps until the MIN and TIME
mechanisms are activated by the receipt of
the first character. If the number of
characters read is less than the number of
characters available, the timer is not
reactivated and the subsequent read is
satisfied immediately.

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
satisfied until MIN characters are received
(the pending read sleeps until MIN
characters are 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 intercharacter timer: it now
serves as a read timer that is activated as
soon as a read(2) is done. A read is
satisfied as soon as a single character is
received or the read timer expires. Note
that, in this case, if the timer expires, no
character is returned. If the timer does
not expire, the only way the read can be
satisfied is if a character is received. In
this case, the read will not block
indefinitely waiting for a character; if no
character is received within TIME *.10
seconds after the read is initiated, the
read returns with zero characters.

Case D: MIN = 0, TIME = 0 In this case, return is immediate. The
minimum of either the number of characters
requested or the number of characters
currently available is returned without
waiting for more characters to be input.

Comparing Different Cases of MIN, TIME Interaction
Some points to note about MIN and TIME:

+o In the following explanations, note that the interactions of MIN
and TIME are not symmetric. For example, when MIN > 0 and TIME =
0, TIME has no effect. However, in the opposite case, where MIN
= 0 and TIME > 0, both MIN and TIME play a role in that MIN is
satisfied with the receipt of a single character.

+o Also note that in case A (MIN > 0, TIME > 0), TIME represents an
intercharacter timer, whereas in case C (MIN = 0, TIME > 0), TIME
represents a read timer.

These two points highlight the dual purpose of the MIN/TIME feature.
Cases A and B, where MIN > 0, exist to handle burst mode activity (for
example, file transfer programs), where a program would like to process
at least MIN characters at a time. In case A, the intercharacter timer
is activated by a user as a safety measure; in case B, the timer is
turned off.

Cases C and D exist to handle single character, timed transfers. These
cases are readily adaptable to screen-based applications that need to
know if a character is present in the input queue before refreshing the
screen. In case C, the read is timed, whereas in case D, it is not.

Another important note is that MIN is always just a minimum. It does
not denote a record length. For example, if a program does a read of
20 bytes, MIN is 10, and 25 characters are present, then 20 characters
will be returned to the user.

Writing Characters

When one or more characters are written, they are transmitted to the
terminal as soon as previously written characters have finished typing.
nputt characters are echoed as they are typed if echoing has been
enabled. If a process produces characters more rapidly than they can
be typed, it will be suspended when its output queue exceeds some
limit. When the queue is drained down to some threshold, the program
is resumed.

Special Characters

Certain characters have special functions on input. These functions
and their default character values are summarized as follows:

INTR (Control-c or ASCII ETX) generates a SIGINT signal. SIGINT is
sent to all foreground processes associated with the
controlling terminal. Normally, each such process is forced
to terminate, but arrangements may be made either to ignore
the signal or to receive a trap to an agreed upon location.
(See signal.h(3HEAD)).

QUIT (Control-| or ASCII FS) generates a SIGQUIT signal. Its
treatment is identical to the interrupt signal except that,
unless a receiving process has made other arrangements, it
will not only be terminated but a core image file (called
core) will be created in the current working directory.

ERASE (DEL) erases the preceding character. It does not erase
beyond the start of a line, as delimited by a NL, EOF, EOL, or
EOL2 character.

ERASE2 (Control-h or ASCII BS) erases the preceding character, with
behaviour identical to that of ERASE.

WERASE (Control-w or ASCII ETX) erases the preceding "word". It does
not erase beyond the start of a line, as delimited by a NL,
EOF, EOL, or EOL2 character.

KILL (Control-u or ASCII NAK) deletes the entire line, as delimited
by a NL, EOF, EOL, or EOL2 character.

REPRINT (Control-r or ASCII DC2) reprints all characters, preceded by
a newline, that have not been read.

EOF (Control-d or ASCII EOT) may be used to generate an end-of-
file from a terminal. When received, all the characters
waiting to be read are immediately passed to the program,
without waiting for a newline, and the EOF is discarded.
Thus, if no characters are waiting (that is, the EOF occurred
at the beginning of a line) zero characters are passed back,
which is the standard end-of-file indication. Unless escaped,
the EOF character is not echoed. Because EOT is the default
EOF character, this prevents terminals that respond to EOT
from hanging up.

NL (ASCII LF) is the normal line delimiter. It cannot be changed
or escaped.

EOL (ASCII NULL) is an additional line delimiter, like NL. It is
not normally used.

EOL2 is another additional line delimiter.

SWTCH (Control-z or ASCII EM) Header file symbols related to this
special character are present for compatibility purposes only
and the kernel takes no special action on matching SWTCH
(except to discard the character).

SUSP (Control-z or ASCII SUB) generates a SIGTSTP signal. SIGTSTP
stops all processes in the foreground process group for that
terminal.

DSUSP (Control-y or ASCII EM). It generates a SIGTSTP signal as
SUSP does, but the signal is sent when a process in the
foreground process group attempts to read the DSUSP character,
rather than when it is typed.

STOP (Control-s or ASCII DC3) can be used to suspend output
temporarily. It is useful with CRT terminals to prevent
output from disappearing before it can be read. While output
is suspended, STOP characters are ignored and not read.

START (Control-q or ASCII DC1) is used to resume output. Output has
been suspended by a STOP character. While output is not
suspended, START characters are ignored and not read.

DISCARD (Control-o or ASCII SI) causes subsequent output to be
discarded. Output is discarded until another DISCARD
character is typed, more input arrives, or the condition is
cleared by a program.

STATUS (Control-t or ASCII DC4) generates a SIGINFO signal.
Processes with a handler will output status information when
they receive SIGINFO, for example, dd(8). If a process does
not have a SIGINFO handler, the signal will be ignored.

LNEXT (Control-v or ASCII SYN) causes the special meaning of the
next character to be ignored. This works for all the special
characters mentioned above. It allows characters to be input
that would otherwise be interpreted by the system (for example
KILL, QUIT). The character values for INTR, QUIT, ERASE,
ERASE2, WERASE, KILL, REPRINT, EOF, EOL, EOL2, SWTCH, SUSP,
DSUSP, STOP, START, DISCARD, STATUS, and LNEXT may be changed
to suit individual tastes. If the value of a special control
character is _POSIX_VDISABLE (0), the function of that special
control character is disabled. The ERASE, ERASE2, KILL, and
EOF characters may be escaped by a preceding backslash (\)
character, in which case no special function is done. Any of
the special characters may be preceded by the LNEXT character,
in which case no special function is done.

Modem Disconnect

When a modem disconnect is detected, a SIGHUP signal is sent to the
terminal's controlling process. Unless other arrangements have been
made, these signals cause the process to terminate. If SIGHUP is
ignored or caught, any subsequent read returns with an end-of-file
indication until the terminal is closed.

If the controlling process is not in the foreground process group of
the terminal, a SIGTSTP is sent to the terminal's foreground process
group. Unless other arrangements have been made, these signals cause
the processes to stop.

Processes in background process groups that attempt to access the
controlling terminal after modem disconnect while the terminal is still
allocated to the session will receive appropriate SIGTTOU and SIGTTIN
signals. Unless other arrangements have been made, this signal causes
the processes to stop.

The controlling terminal will remain in this state until it is
reinitialized ithh a successful open by the controlling process, or
deallocated by the controlling process.

Terminal Parameters

The parameters that control the behavior of devices and modules
providing the termios interface are specified by the termios structure
defined by <termios.h>. Several ioctl(2) system calls that fetch or
change these parameters use this structure that contains the following
members:

tcflag_t c_iflag; /* input modes */
tcflag_t c_oflag; /* output modes */
tcflag_t c_cflag; /* control modes */
tcflag_t c_lflag; /* local modes */
cc_t c_cc[NCCS]; /* control chars */

The special control characters are defined by the array c_cc. The
symbolic name NCCS is the size of the Control-character array and is
also defined by <termios.h>. The relative positions, subscript names,
and typical default values for each function are as follows:

Relative Position Subscript Name Typical Default Value
0 VINTR ETX
1 VQUIT FS
2 VERASE DEL
3 VKILL NAK
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 VWSTCH NUL
8 VSTART NUL
9 VSTOP DC3
10 VSUSP SUB
11 VDSUSP EM
12 VREPRINT DC2
13 VDISCARD SI
14 VWERASE ETB
15 VLNEXT SYN
16 VSTATUS DC4
17 VERASE2 BS
18-19 Reserved

Input Modes

The c_iflag field describes the basic terminal input control:

IGNBRK Ignore break condition.
BRKINT Signal interrupt on break.
IGNPAR Ignore characters with parity errors.
PARMRK Mark parity errors.
INPCK Enable input parity check.
ISTRIP Strip character.
INLCR Map NL to CR on input.
IGNCR Ignore CR.
ICRNL Map CR to NL on input.
IUCLC Map upper-case to lower-case on input.
IXON Enable start/stop output control.
IXANY Enable any character to restart output.
IXOFF Enable start/stop input control.
IMAXBEL Echo BEL on input line too long.

If IGNBRK is set, a break condition (a character framing error with
data all zeros) 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 shall flush 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' (ASCII NULL)
character, or if PARMRK is set, as `\377', `\0', c, where `\377' is a
single character with value 377 octal (0xff hex, 255 decimal), `\0' is
a single character with value 0, and c is the errored character
received.

If IGNPAR is set, a byte with framing or parity errors (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', c, where `\377' is a single
character with value 377 octal (0xff hex, 255 decimal), `\0' is a
single character with value 0, and c is the errored character received.
To avoid ambiguity in this case, if ISTRIP is not set, a valid
character of `\377' is given to the application as `\377'. If neither
IGNPAR nor PARMRK is set, a framing or parity error (other than break)
is given to the application as a single `\0' (ASCII NULL) character.

If INPCK is set, input parity checking is enabled. If INPCK is not
set, input parity checking is disabled. This allows 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. If parity detection is enabled but
input parity checking is disabled, the hardware to which the terminal
is connected will recognize the parity bit, but the terminal special
file will not check whether this is set correctly or not.

If ISTRIP is set, valid input characters 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). Otherwise, if ICRNL is set, a received CR character is
translated into a NL character.

If IUCLC is set, a received upper case, alphabetic character is
translated into the corresponding lower case character.

If IXON is set, start/stop output control is enabled. A received STOP
character suspends output and a received START character restarts
output. The STOP and START characters will not be read, but will
merely perform flow control functions. If IXANY is set, any input
character restarts output that has been suspended.

If IXOFF is set, the system transmits a STOP character when the input
queue is nearly full, and a START character when enough input has been
read so that the input queue is nearly empty again.

If IMAXBEL is set, the ASCII BEL character is echoed if the input
stream overflows. Further input is not stored, but any input already
present in the input stream is not disturbed. If IMAXBEL is not set,
no BEL character is echoed, and all input present in the input queue is
discarded if the input stream overflows.

Output Modes

The c_oflag field specifies the system treatment of output:

OPOST Post-process output.
OLCUC Map lower case to upper on output.
ONLCR Map NL to CR-NL on output.
OCRNL Map CR to NL on output.
ONOCR No CR output at column 0.
ONLRET NL performs CR function.
OFILL Use fill characters for delay.
OFDEL Fill is DEL, else INULL.
NLDLY Select newline delays:
NL0
NL1
CRDLY Select carriage-return delays:
CR0
CR1
CR2
CR3
TABDLY Select horizontal tab delays or tab expansion:
TAB0
TAB1
TAB2
TAB3 Expand tabs to spaces
XTABS Expand tabs to spaces
BSDLY Select backspace delays:
BS0
BS1
VTDLY Select vertical tab delays:
VT0
VT1
FFDLY Select form feed delays:
FF0
FF1

If OPOST is set, output characters are post-processed as indicated by
the remaining flags; otherwise, characters are transmitted without
change.

If OLCUC is set, a lower case alphabetic character is transmitted as
the corresponding upper case character. This function is often used in
conjunction with IUCLC.

If ONLCR is set, the NL character is transmitted as the CR-NL character
pair. If OCRNL is set, the CR character is transmitted as the NL
character. If ONOCR is set, no CR character is transmitted when at
column 0 (first position). If ONRET is set, the NL character is
assumed to do the carriage-return function; the column pointer is set
to 0 and the delays specified for CR are used. Otherwise, the NL
character is assumed to do just the line-feed function; the column
pointer remains unchanged. The column pointer is also set to 0 if the
CR character is actually transmitted.

The delay bits specify how long transmission stops to allow for
mechanical or other movement when certain characters are sent to the
terminal. In all cases, a value of 0 indicates no delay. If OFILL is
set, fill characters are transmitted for delay instead of a timed
delay. This is useful for high baud rate terminals that need only a
minimal delay. If OFDEL is set, the fill character is DEL; otherwise
it is NULL.

If a form-feed or vertical-tab delay is specified, it lasts for about 2
seconds.

Newline delay lasts about 0.10 seconds. If ONLRET is set, the
carriage-return delays are used instead of the newline delays. If
OFILL is set, two fill characters are transmitted.

Carriage-return delay type 1 is dependent on the current column
position, type 2 is about 0.10 seconds, and type 3 is about 0.15
seconds. If OFILL is set, delay type 1 transmits two fill characters,
and type 2 transmits four fill characters.

Horizontal-tab delay type 1 is dependent on the current column
position. Type 2 is about 0.10 seconds. Type 3 specifies that tabs
are to be expanded into spaces. If OFILL is set, two fill characters
are transmitted for any delay.

Backspace delay lasts about 0.05 seconds. If OFILL is set, one fill
character is transmitted.

The actual delays depend on line speed and system load.

Control Modes

The c_cflag field describes the hardware control of the terminal:

CBAUD Baud rate:
B0 Hang up
B50 50 baud
B75 75 baud
B110 110 baud
B134 134 baud
B150 150 baud
B200 200 baud
B300 300 baud
B600 600 baud
B1200 1200 baud
B1800 1800 baud
B2400 2400 baud
B4800 4800 baud
B9600 9600 baud
B19200 19200 baud
B38400 38400 baud
B57600 57600 baud
B76800 76800 baud
B115200 115200 baud
B153600 153600 baud
B230400 230400 baud
B307200 307200 baud
B460800 460800 baud
B921600 921600 baud
B1000000 1000000 baud
B1152000 1152000 baud
B1500000 1500000 baud
B2000000 2000000 baud
B2500000 2500000 baud
B3000000 3000000 baud
B3500000 3500000 baud
B4000000 4000000 baud

CSIZE Character size:
CS5 5 bits
CS6 6 bits
CS7 7 bits
CS8 8 bits
CSTOPB Send two stop bits, else one
CREAD Enable receiver
PARENB Parity enable
PARODD Odd parity, else even
HUPCL Hang up on last close
CLOCAL Local line, else dial-up
CIBAUD Input baud rate, if different from output rate
PAREXT Extended parity for mark and space parity
CRTSXOFF Enable inbound hardware flow control
CRTSCTS Enable outbound hardware flow control
CBAUDEXT Bit to indicate output speed > B38400
CIBAUDEXT Bit to indicate input speed > B38400

The CBAUD bits together with the CBAUDEXT bit specify the output baud
rate. To retrieve the output speed from the termios structure pointed
to by termios_p see the following code segment.

speed_t ospeed;
if (termios_p->c_cflag & CBAUDEXT)
ospeed = (termios_p->c_cflag & CBAUD) + CBAUD + 1;
else
ospeed = termios_p->c_cflag & CBAUD;

To store the output speed in the termios structure pointed to by
termios_p see the following code segment.

speed_t ospeed;
if (ospeed > CBAUD) {
termios_p->c_cflag |= CBAUDEXT;
ospeed -= (CBAUD + 1);
} else {
termios_p->c_cflag &= ~CBAUDEXT;
}
termios_p->c_cflag =
(termios_p->c_cflag & ~CBAUD) | (ospeed & CBAUD);

The zero baud rate, B0, is used to hang up the connection. If B0 is
specified, the data-terminal-ready signal is not asserted. Normally,
this disconnects the line.

If the CIBAUDEXT or CIBAUD bits are not zero, they specify the input
baud rate, with the CBAUDEXT and CBAUD bits specifying the output baud
rate; otherwise, the output and input baud rates are both specified by
the CBAUDEXT and CBAUD bits. The values for the CIBAUD bits are the
same as the values for the CBAUD bits, shifted left IBSHIFT bits. For
any particular hardware, impossible speed changes are ignored. To
retrieve the input speed in the termios structure pointed to by
termios_p see the following code segment.

speed_t ispeed;
if (termios_p->c_cflag & CIBAUDEXT) {
ispeed = ((termios_p->c_cflag & CIBAUD) >> IBSHIFT)
+ (CIBAUD >> IBSHIFT) + 1;
} else {
ispeed = (termios_p->c_cflag & CIBAUD) >> IBSHIFT;
}

To store the input speed in the termios structure pointed to by
termios_p see the following code segment.

speed_t ispeed;
if (ispeed == 0) {
ispeed = termios_p->c_cflag & CBAUD;
if (termios_p->c_cflag & CBAUDEXT)
ispeed += (CBAUD + 1);
}
if ((ispeed << IBSHIFT) > CIBAUD) {
termios_p->c_cflag |= CIBAUDEXT;
ispeed -= ((CIBAUD >> IBSHIFT) + 1);
} else {
termios_p->c_cflag &= ~CIBAUDEXT;
}
termios_p->c_cflag =
(termios_p->c_cflag & ~CIBAUD) | ((ispeed << IBSHIFT) & CIBAUD);

The CSIZE bits specify the character size in bits for both transmission
and reception. This size does not include the parity bit, if any. If
CSTOPB is set, two stop bits are used; otherwise, one stop bit is used.
For example, at 110 baud, two stops bits are required.

If PARENB is set, parity generation and detection is enabled, and a
parity bit is added to each character. If parity is enabled, the
PARODD flag specifies odd parity if set; otherwise, even parity is
used.

If CREAD is set, the receiver is enabled. Otherwise, no characters are
received.

If HUPCL is set, the line is disconnected when the last process with
the line open closes it or terminates. That is, the data-terminal-
ready signal is not asserted.

If CLOCAL is set, the line is assumed to be a local, direct connection
with no modem control; otherwise, modem control is assumed.

If CRTSXOFF is set, inbound hardware flow control is enabled.

If CRTSCTS is set, outbound hardware flow control is enabled.

The four possible combinations for the state of CRTSCTS and CRTSXOFF
bits and their interactions are described below.

Case A: CRTSCTS off, CRTSXOFF off. In this case the hardware flow
control is disabled.

Case B: CRTSCTS on, CRTSXOFF off. In this case only outbound hardware
flow control is enabled. The state of CTS signal is used to
do outbound flow control. It is expected that output will be
suspended if CTS is low and resumed when CTS is high.

Case C: CRTSCTS off, CRTSXOFF on. In this case only inbound hardware
flow control is enabled. The state of RTS signal is used to
do inbound flow control. It is expected that input will be
suspended if RTS is low and resumed when RTS is high.

Case D: CRTSCTS on, CRTSXOFF on. In this case both inbound and
outbound hardware flow control are enabled. Uses the state of
CTS signal to do outbound flow control and RTS signal to do
inbound flow control.

Local Modes

The c_lflag field of the argument structure is used by the line
discipline to control terminal functions. The basic line discipline
provides the following:

ISIG Enable signals.
ICANON Canonical input (erase and kill processing).
XCASE Canonical upper/lower presentation.
ECHO Enable echo.
ECHOE Echo erase character as BS-SP-BS &.
ECHOK Echo NL after kill character.
ECHONL Echo NL.
NOFLSH Disable flush after interrupt or quit.
TOSTOP Send
SIGTTOU for background output.
ECHOCTL Echo control characters as char, delete as ^?.
ECHOPRT Echo erase character as character erased.
ECHOKE BS-SP-BS erase entire line on line kill.
FLUSHO Output is being flushed.
PENDIN Retype pending input at next read or input character.
IEXTEN Enable extended (implementation-defined) functions.

If ISIG is set, each input character is checked against the special
control characters INTR, QUIT, SWTCH, SUSP, STATUS, and DSUSP. If an
input character matches one of these control characters, the function
associated with that character is performed. (Note: If SWTCH is set
and the character matches, the character is simply discarded. No other
action is taken.) If ISIG is not set, no checking is done. Thus, these
special input functions are possible only if ISIG is 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-c, EOF, EOL, and EOL. If ICANON is not set,
read requests are satisfied directly from the input queue. A read is
not satisfied until at least MIN characters have been received or the
timeout value TIME has expired between characters. This allows fast
bursts of input to be read efficiently while still allowing single
character input. The time value represents tenths of seconds.

If XCASE is set and ICANON is set, an upper case letter is accepted on
input if preceded by a backslash `\' character, and is output preceded
by a backslash `\' character. In this mode, the following escape
sequences are generated on output and accepted on input:

FOR: USE:
` \'
| \!
~ \^
{ \(
} \)
\ \\

For example, input A as \a, \n as \\n, and \N as \\\n.

If ECHO is set, characters are echoed as received.

When ICANON is set, the following echo functions are possible.

+o If ECHO and ECHOE are set, and ECHOPRT is not set, the ERASE,
ERASE2, and WERASE characters are echoed as one or more ASCII
BS SP BS, which clears the last character(s) from a CRT
screen.

+o If ECHO, ECHOPRT, and IEXTEN are set, the first ERASE,
ERASE2, and WERASE character in a sequence echoes as a
backslash `\', followed by the characters being erased.
Subsequent ERASE and WERASE characters echo the characters
being erased, in reverse order. The next non-erase character
causes a `/' (slash) to be typed before it is echoed.
ECHOPRT should be used for hard copy terminals.

+o If ECHOKE and IEXTEN are set, the kill character is echoed by
erasing each character on the line from the screen (using the
mechanism selected by ECHOE and ECHOPR).

+o If ECHOK is set, and ECHOKE is not set, the NL character is
echoed after the kill character to emphasize that the line is
deleted. Note that a `\' (escape) character or an LNEXT
character preceding the erase or kill character removes any
special function.

+o If ECHONL is set, the NL character is echoed even if ECHO is
not set. This is useful for terminals set to local echo (so
called half-duplex).

If ECHOCTL and IEXTEN are set, all control characters (characters with
codes between 0 and 37 octal) other than ASCII TAB, ASCII NL, the START
character, and the STOP character, ASCII CR, and ASCII BS are echoed as
^X, where X is the character given by adding `100' octal to the code of
the control character (so that the character with octal code `1' is
echoed as ^A), and the ASCII DEL character, with code `177' octal, is
echoed as ^?.

If NOFLSH is set, the normal flush of the input and output queues
associated with the INTR, QUIT, STATUS, and SUSP characters is not
done. This bit should be set when restarting system calls that read
from or write to a terminal (see sigaction(2)).

If TOSTOP and IEXTEN are set, the signal SIGTTOU is sent to a process
that tries to write to its controlling terminal if it is not in the
foreground process group for that terminal. This signal normally stops
the process. 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, if any.

If FLUSHO and IEXTEN are set, data written to the terminal is
discarded. This bit is set when the FLUSH character is typed. A
program can cancel the effect of typing the FLUSH character by clearing
FLUSHO.

If PENDIN and IEXTEN are set, any input that has not yet been read is
reprinted when the next character arrives as input. PENDIN is then
automatically cleared.

If IEXTEN is set, the following implementation-defined functions are
enabled: special characters ( WERASE, REPRINT, DISCARD, and LNEXT) and
local flags ( TOSTOP, ECHOCTL, ECHOPRT, ECHOKE, FLUSHO, and PENDIN).

Minimum and Timeout

The MIN and TIME values were described previously, in the subsection,
Non-canonical Mode Input Processing. The initial value of MIN is 1,
and the initial value of TIME is 0.

Terminal Size

The number of lines and columns on the terminal's display is specified
in the winsize structure defined by <sys/termios.h> and includes the
following members:

unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, in pixels */
unsigned short ws_ypixel; /* vertical size, in pixels */

Termio Structure

The SunOS/SVR4 termio structure is used by some ioctl()s; it is defined
by <sys/termio.h> and includes the following members:

unsigned short c_iflag; /* input modes */
unsigned short c_oflag; /* output modes */
unsigned short c_cflag; /* control modes */
unsigned short c_lflag; /* local modes */
char c_line; /* line discipline */
unsigned char c_cc[NCC]; /* control chars */

The special control characters are defined by the array c_cc. The
symbolic name NCC is the size of the Control-character array and is
also defined by <termio.h>. The relative positions, subscript names,
and typical default values for each function are as follows:

Relative Positions Subscript Names Typical Default Values
0 VINTR EXT
1 VQUIT FS
2 VERASE DEL
3 VKILL NAK
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 Reserved

The MIN values is stored in the VMIN element of the c_cc array; the
TIME value is stored in the VTIME element of the c_cc array. The VMIN
element is the same element as the VEOF element; the VTIME element is
the same element as the VEOL element.

The calls that use the termio structure only affect the flags and
control characters that can be stored in the termio structure; all
other flags and control characters are unaffected.

Modem Lines

On special files representing serial ports, modem control lines can be
read. Control lines (if the underlying hardware supports it) may also
be changed. Status lines are read-only. The following modem control
and status lines may be supported by a device; they are defined by
<sys/termios.h>:

TIOCM_LE line enable
TIOCM_DTR data terminal ready
TIOCM_RTS request to send
TIOCM_ST secondary transmit
TIOCM_SR secondary receive
TIOCM_CTS clear to send
TIOCM_CAR carrier detect
TIOCM_RNG ring
TIOCM_DSR data set ready

TIOCM_CD is a synonym for TIOCM_CAR, and TIOCM_RI is a synonym for
TIOCM_RNG. Not all of these are necessarily supported by any
particular device; check the manual page for the device in question.

The software carrier mode can be enabled or disabled using the
TIOCSSOFTCAR ioctl(). If the software carrier flag for a line is off,
the line pays attention to the hardware carrier detect (DCD) signal.
The tty device associated with the line cannot be opened until DCD is
asserted. If the software carrier flag is on, the line behaves as if
DCD is always asserted.

The software carrier flag is usually turned on for locally connected
terminals or other devices, and is off for lines with modems.

To be able to issue the TIOCGSOFTCAR and TIOCSSOFTCAR ioctl() calls,
the tty line should be opened with O_NDELAY so that the open(2) will
not wait for the carrier.

Default Values

The initial termios values upon driver open is configurable. This is
accomplished by setting the "ttymodes" property in the file
/kernel/drv/options.conf. Since this property is assigned during
system initialization, any change to the "ttymodes" property will not
take effect until the next reboot. The string value assigned to this
property should be in the same format as the output of the stty(1)
command with the -g option.

If this property is undefined, the following termios modes are in
effect. The initial input control value is BRKINT, ICRNL, IXON,
IMAXBEL. The initial output control value is OPOST, ONLCR, TAB3. The
initial hardware control value is B9600, CS8, CREAD. The initial line-
discipline control value is ISIG, ICANON, IEXTEN, ECHO, ECHOK, ECHOE,
ECHOKE, ECHOCTL.

IOCTLS

The ioctl()s supported by devices and STREAMS modules providing the
termios(3C) interface are listed below. Some calls may not be
supported by all devices or modules. The functionality provided by
these calls is also available through the preferred function call
interface specified on termios.

TCGETS The argument is a pointer to a termios structure. The
current terminal parameters are fetched and stored into
that structure.

TCSETS The argument is a pointer to a termios structure. The
current terminal parameters are set from the values
stored in that structure. The change is immediate.

TCSETSW The argument is a pointer to a termios structure. The
current terminal parameters are set from the values
stored in that structure. The change occurs after all
characters queued for output have been transmitted. This
form should be used when changing parameters that affect
output.

TCSETSF The argument is a pointer to a termios structure. The
current terminal parameters are set from the values
stored in that structure. The change occurs after all
characters queued for output have been transmitted; all
characters queued for input are discarded and then the
change occurs.

TCGETA The argument is a pointer to a termio structure. The
current terminal parameters are fetched, and those
parameters that can be stored in a termio structure are
stored into that structure.

TCSETA The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio
structure are set from the values stored in that
structure. The change is immediate.

TCSETAW The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio
structure are set from the values stored in that
structure. The change occurs after all characters queued
for output have been transmitted. This form should be
used when changing parameters that affect output.

TCSETAF The argument is a pointer to a termio structure. Those
terminal parameters that can be stored in a termio
structure are set from the values stored in that
structure. The change occurs after all characters queued
for output have been transmitted; all characters queued
for input are discarded and then the change occurs.

TCSBRK The argument is an int value. Wait for the output to
drain. If the argument is 0, then send a break (zero
valued bits for 0.25 seconds).

TCXONC Start/stop control. The argument is an int value. If
the argument is 0, suspend output; if 1, restart
suspended output; if 2, suspend input; if 3, restart
suspended input.

TCFLSH The argument is an int value. If the argument is 0,
flush the input queue; if 1, flush the output queue; if
2, flush both the input and output queues.

TIOCGPGRP The argument is a pointer to a pid_t. Set the value of
that pid_t to the process group ID of the foreground
process group associated with the terminal. See
termios(3C) for a description of TCGETPGRP.

TIOCSPGRP The argument is a pointer to a pid_t. Associate the
process group whose process group ID is specified by the
value of that pid_t with the terminal. The new process
group value must be in the range of valid process group
ID values. Otherwise, the error EPERM is returned.

TIOCGSID The argument is a pointer to a pid_t. The session ID of
the terminal is fetched and stored in the pid_t.

TIOCGWINSZ The argument is a pointer to a winsize structure. The
terminal driver's notion of the terminal size is stored
into that structure.

TIOCSWINSZ The argument is a pointer to a winsize structure. The
terminal driver's notion of the terminal size is set from
the values specified in that structure. If the new sizes
are different from the old sizes, a SIGWINCH signal is
set to the process group of the terminal.

TIOCMBIS The argument is a pointer to an int whose value is a mask
containing modem control lines to be turned on. The
control lines whose bits are set in the argument are
turned on; no other control lines are affected.

TIOCMBIC The argument is a pointer to an int whose value is a mask
containing modem control lines to be turned off. The
control lines whose bits are set in the argument are
turned off; no other control lines are affected.

TIOCMGET The argument is a pointer to an int. The current state
of the modem status lines is fetched and stored in the
int pointed to by the argument.

TIOCMSET The argument is a pointer to an int containing a new set
of modem control lines. The modem control lines are
turned on or off, depending on whether the bit for that
mode is set or clear.

TIOCSPPS The argument is a pointer to an int that determines
whether pulse-per-second event handling is to be enabled
(non-zero) or disabled (zero). If a one-pulse-per-second
reference clock is attached to the serial line's data
carrier detect input, the local system clock will be
calibrated to it. A clock with a high error, that is, a
deviation of more than 25 microseconds per tick, is
ignored.

TIOCGPPS The argument is a pointer to an int, in which the state
of the even handling is returned. The int is set to a
non-zero value if pulse-per-second (PPS) handling has
been enabled. Otherwise, it is set to zero.

TIOCGSOFTCAR The argument is a pointer to an int whose value is 1 or
0, depending on whether the software carrier detect is
turned on or off.

TIOCSSOFTCAR The argument is a pointer to an int whose value is 1 or
0. The value of the integer should be 0 to turn off
software carrier, or 1 to turn it on.

TIOCGPPSEV The argument is a pointer to a struct ppsclockev. This
structure contains the following members:

struct timeval tv;
uint32_t serial;

tv is the system clock timestamp when the event (pulse on
the DCD pin) occurred. serial is the ordinal of the
event, which each consecutive event being assigned the
next ordinal. The first event registered gets a serial
value of 1. The TIOCGPPSEV returns the last event
registered; multiple calls will persistently return the
same event until a new one is registered. In addition to
time stamping and saving the event, if it is of one-
second period and of consistently high accuracy, the
local system clock will automatically calibrate to it.

FILES

Files in or under /dev

SEE ALSO

stty(1), fork(2), getpgid(2), getsid(2), ioctl(2), setsid(2),
sigaction(2), signal(3C), tcsetpgrp(3C), termios(3C), signal.h(3HEAD),
streamio(4I)

illumos March 13, 2022 illumos