termio(7) DG/UX R4.11 termio(7)
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
System V supports a general interface for asynchronous communications
ports that is hardware-independent. The user interface to this
functionality is via function calls (the preferred interface)
described in termios(2) 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, users' programs
seldom open terminal files; they are opened by the system and become
a user's standard input, output, and error files. The very first
terminal file opened by the session leader, which 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 (e.g., if
the number of characters in the line discipline buffer exceeds
{MAXCANON} and IMAXBEL [see below] is not set), or when the user has
accumulated {MAXINPUT} 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. These
are process groups which do not have a member with a parent in
another process group that is in the same session and therefore
shares the same controlling terminal. When a member of an orphaned
process group attempts to access its controlling terminal, errors
will be returned, since there is no process to continue it if it
should stop.
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 will be sent.
If a member of a background process group attempts to write its
controlling terminal and the TOSTOP bit is set in the clflag field,
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 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 (e.g., 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 be suspended 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 and kill processing is normally done. The ERASE
character (by default, the character number #) 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. Neither ERASE nor
WERASE will erase beyond the beginning of the line. The KILL
character (by default, the character @) 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 hampered by program output. The characters are reprinted
as if they were being echoed; consequencely, if ECHO is not set, they
are not printed.
The ERASE 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 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. Note that the blocking characteristics
associated with the MIN and TIME values will not apply to terminal
files opened with the ONDELAY or ONONBLOCK flags.
MIN represents the minimum number of characters that should be
received when the read is satisfied (i.e., 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 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.
Comparison of the different cases of MIN, TIME interaction
Some points to note about MIN and TIME:
1. 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.
2. Also note that in case A (MIN > 0, TIME > 0), TIME represents an
intercharacter timer, whereas in case C (TIME = 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
(e.g., 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. Input 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 (Rubout or ASCII DEL) 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(5)].
QUIT (CTRL-| 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 (#) erases the preceding character. It does not erase
beyond the start of a line, as delimited by a NL, EOF, EOL,
or EOL2 character.
WERASE (CTRL-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 (@) deletes the entire line, as delimited by a NL, EOF,
EOL, or EOL2 character.
REPRINT (CTRL-R or ASCII DC2) reprints all characters, preceded by
a newline, that have not been read.
EOF (CTRL-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 (i.e., 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 (CTRL-Z or ASCII EM) is used only when shl layers is
invoked.
SUSP (CTRL-Z or ASCII SUB) generates a SIGTSTP signal. SIGTSTP
stops all processes in the foreground process group for
that terminal.
DSUSP (CTRL-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 (CTRL-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 (CTRL-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 (CTRL-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.
LNEXT (CTRL-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 (e.g. KILL, QUIT).
The character values for INTR, QUIT, ERASE, WERASE, KILL, REPRINT,
EOF, EOL, EOL2, SWTCH, SUSP, DSUSP, STOP, START, DISCARD, 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, KILL, and EOF
characters may be escaped by a preceding \ 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 with 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:
tcflagt ciflag; /* input modes */
tcflagt coflag; /* output modes */
tcflagt ccflag; /* control modes */
tcflagt clflag; /* local modes */
cct ccc[NCCS]; /* control chars */
The special control characters are defined by the array ccc. 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:
0 VINTR DEL
1 VQUIT FS
2 VERSE #
3 VKILL @
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 VSWTCH NUL
8 VSTRT DC1
9 VSTOP DC3
10 VSUSP SUB
11 VDSUSP EM
12 VREPRINT DC2
13 VDISCRD SI
14 VWERSE ETB
15 VLNEXT SYN
16-19 reserved
Note that the VMIN and VTIME control characters used in non-canonical
mode input processing are stored in the same positions as the VEOF
and VEOL characters respectively.
Input modes
The ciflag 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 ASCII NULL
character (´\0´), or if PARMRK is set, as ´\377´, ´\0´, ´\0´.
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´, X, where X is the data of the
byte 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 IGNPAR nor PARMRK is set, a framing or
parity error (other than break) is given to the application as a
single ASCII NULL character (´\0´).
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.
The initial input control value is BRKINT, ICRNL, IXON, ISTRIP.
Output modes
The coflag 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 NULL.
NLDLY Select newline delays:
NL0
NL1
CRDLY Select carriage-return delays:
CR0
CR1
CR2
CR3
TABDLY Select horizontal tab delays:
TAB0 or tab expansion:
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 ONLRET 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.
The initial output control value is OPOST, ONLCR, TAB3.
Control Modes
The ccflag 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
EXTA External A
B38400 38400 baud
EXTB External B
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 (mark parity, else space, if PAREXT set)
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.
The CBAUD bits specify the baud rate. 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 CIBAUD bits are not zero, they specify the input
baud rate, with the CBAUD bits specifying the output baud rate;
otherwise, the output and input baud rates are both specified by the
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.
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 and
PAREXT is not set, the PARODD flag specifies odd parity if set;
otherwise, even parity is used. If parity is enabled and PAREXT is
set, the PARODD flag specifies mark parity if set; otherwise, space
parity is used. Note that PAREXT should only be used with termios
(not termio) structs, and that currently no hardware support is
available for this option.
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.
The initial hardware control value after open is B300, CS8, CREAD,
HUPCL.
Local modes
The clflag 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. 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, EOF, EOL, and EOL2. 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 if ICANON is set, an upper case letter is
accepted on input by preceding it with a \ character, and is output
preceded by a \ character. In this mode, the following escape
sequences are generated on output and accepted on input:
for: use:
` \´
| \!
~ \^
{ \(
} \)
\ \\
For example, A is input 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.
1. If ECHO and ECHOE are set, and ECHOPRT is not set, the ERASE
and WERASE characters are echoed as one or more ASCII BS SP
BS, which clears the last character(s) from a CRT screen.
2. If ECHO and ECHOPRT are set, the first ERASE 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.
3. If ECHOKE is set, the kill character is echoed by erasing each
character on the line from the screen (using the mechanism
selected by ECHOE and ECHOPRT).
4. 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 an escape character (\) or an LNEXT
character preceding the erase or kill character removes any
special function.
5. 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 is 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, 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 is 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 is 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 is set, any input that has not yet been read is reprinted
when the next character arrives as input.
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).
The initial line-discipline control value is ISIG, ICANON, ECHO,
ECHOK.
Minimum and Timeout
The MIN and TIME values are described above under 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 wsrow; /* rows, in characters */
unsigned short wscol; /* columns, in characters */
unsigned short wsxpixel; /* horizontal size, in pixels */
unsigned short wsypixel; /* vertical size, in pixels */
Termio structure
The System V termio structure is used by some ioctls; it is defined
by <sys/termio.h> and includes the following members:
unsigned short ciflag; /* input modes */
unsigned short coflag; /* output modes */
unsigned short ccflag; /* control modes */
unsigned short clflag; /* local modes */
char cline; /* line discipline */
unsigned char ccc[NCC]; /* control chars */
The special control characters are defined by the array ccc. 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:
0 VINTR DEL
1 VQUIT FS
2 VERASE #
3 VKILL @
4 VEOF EOT
5 VEOL NUL
6 VEOL2 NUL
7 reserved
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, the modem control lines
supported by the hardware can be read, and the modem status lines
supported by the hardware can be changed. The following modem
control and status lines may be supported by a device; they are
defined by <sys/termios.h>:
TIOCMLE line enable
TIOCMDTR data terminal ready
TIOCMRTS request to send
TIOCMST secondary transmit
TIOCMSR secondary receive
TIOCMCTS clear to send
TIOCMCAR carrier detect
TIOCMRNG ring
TIOCMDSR data set ready
TIOCMCD is a synonym for TIOCMCAR, and TIOCMRI is a synonym for
TIOCMRNG. Not all of these are necessarily supported by any
particular device; check the manual page for the device in question.
IOCTLS
The ioctls supported by devices and STREAMS modules providing the
termios 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(2).
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 pidt. Set the value
of that pidt to the process group ID of the
foreground process group associated with the terminal.
See termios(2) for a description or TCGETPGRP.
TIOCSPGRP The argument is a pointer to a pidt. Associate the
process group whose process group ID is specified by
the value of that pidt 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. See termios(2) for a description of
TCSETPGRP.
TIOCGSID The argument is a pointer to a pidt. The session ID
of the terminal is fetched and stored in the pidt.
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.
FILES
files in or under /dev
SEE ALSO
fork(2), ioctl(2), setsid(2), signal(2), open(2), termios(3C),
streamio(7).
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