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(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, 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 (for example, if the number of characters
in the line discipline buffer exceeds MAX_CANON and IMAXBEL (see
below) is not set), or when the user has accumulated 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. 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 c_lflag 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 (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 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 BS) erases the last character typed.
The WERASE character (<Ctrl>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 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
(<Ctrl>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 (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 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 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:
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.
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 (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. 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(2)).
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
(<Ctrl>H) 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
(<Ctrl>U) 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 (that is, 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.
EOL
is an additional line delimiter, like NL. It is not normally used.
EOL2
is another line delimiter.
SWTCH
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 (for example, 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, 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.
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:
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:
Position
Name
Default value
0
VINTR
DEL
1
VQUIT
FS
2
VERASE
BS
3
VKILL
NAK
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:
Position
Name
Default value
4
VMIN
used to set the value of MIN
5
VTIME
used to set the value of TIME
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 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 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 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 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.
The initial output control value is OPOST, ONLCR, TAB3.
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
EXTA
External A
B38400
38400 baud
EXTB
External B
E
Character size:
CS5
5 bits
CS6
6 bits
CS7
7 bits
CS8
8 bits
PB
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 NBAUD 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, 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 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.
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 ``e'' character, and is output preceded
by a ``e'' 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:
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.
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.
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).
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.
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 octal code 177, 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 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 System V termio structure is used by some
ioctls; 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:
Position
Name
Default value
0
VINTR
DEL
1
VQUIT
FS
2
VERASE
BS
3
VKILL
NAK
4
VEOF
EOT
5
VEOL
NUL
6
VEOL2
NUL
7
reserved
For the non-canonical mode the positions of VEOF and
NEOL are shared by VMIN and VTIME:
Position
Name
Default value
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:
TIOCM_CD is a synonym for TIOCM_CAR,
and TIOCM_RI is a synonym for TIOCM_RNG. These are used by the
TIOCMSET, TIOCMBIS, TIOCMGET and TIOCMBICioctls. Not all of these are necessarily supported by any particular
device; check the manual page for the device in question.
ioctl commands
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(3C).
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. 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 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. See termios(3C)
for a description of TCSETPGRP.
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/TIOCMBIC
Set/clear modem control lines (set to TRUE/FALSE state).
This is a pointer to an int which contains the modem line identifier
for the modem lines to be set to TRUE/FALSE (from the
TIOCM_ definitions.
TIOCMGET
Get the state of all the modem control lines in the int pointed to
be the argument (in the TIOCM_ definitions). If the bit is 0, then the
line is disasserted; if 1, the line is asserted.
TIOCMSET
Set modem control line status. This is a pointer to an int. All
modem control lines are set to the value held in the int's bit which
represents the line (in the TIOCM_ definitions. For example, to set the DTR
line to FALSE, set the TIOCM_DTR bit to 0; set the bit to 1 for
TRUE.
.files/lowast.gif)
definitions.