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termio(7)


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(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: 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  

 +----------+------------+----------------+
 |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

 +----------+---------+--------------------------------+
 |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:

CRDLY
Select carriage-return delays:

TABDLY
Select horizontal tab delays: or tab expansion:

XTABS
Expand tabs to spaces.

BSDLY
Select backspace delays:

VTDLY
Select vertical tab delays:

FFDLY
Select form feed delays:
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.

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 ``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:     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 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  

 +----------+------------+----------------+
 |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

 +----------+---------+--------------------------------+
 |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_LE
line enable

TIOCMGET/TIOCMSET
get/set line status, see ``ioctl commands''

TIOCMBIC/TIOCMBIS
clear/set lines, see ``ioctl commands''

TIOCM_DTR
data terminal ready

TIOCM_RTS
request to send

TIOCM_ST
secondary transmit

TIOCM_SR
secondary receive

TIOCM_CTS
clear to send

TIOCM_CAR
carrier detect

TIOCM_RNG
ring

TIOCM_DSR
data set ready
TIOCM_CD is a synonym for TIOCM_CAR, and TIOCM_RI is a synonym for TIOCM_RNG. These are used by the TIOCMSET, TIOCMBIS, TIOCMGET and TIOCMBIC ioctls. 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


/dev/*

References

fork(2), ioctl(2), setsid(2), signal(2), streamio(7), termios(3C)
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004