termio(7) UNIX System V 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.
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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's 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 #) 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
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termio(7) UNIX System V termio(7)
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 fouled 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.
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 values for MIN and
TIME should be set by the programmer in the termios or termio structure.
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
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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.
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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 frequent 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. The EOF character is not echoed unless it is
escaped or ECHOCTL is set. 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.
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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.
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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 VERASE #
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 VWERASE ETB
15 VLNEXT SYN
16-19 reserved
For the non-canonical mode the positions of VEOF and VEOL are shared by
VMIN and VTIME:
4 VMIN used to set the value of MIN
5 VTIME used to set the value of TIME
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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.
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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:
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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.
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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
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
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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, 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.
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.
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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).
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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.
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:
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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
For the non-canonical mode the positions VEOF and VEOL are shared by VMIN
and VTIME:
4 VMIN used to set the value of MIN
5 VTIME used to set the value of TIME
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
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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).
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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. On some controllers, if
the argument is 0, input flow control characters will be
flushed, causing the unflushed output queue to overflow a
busy output device.
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.
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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), termios(2), streamio(7).
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