termio(7I) termio(7I)
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);
This release supports a general interface for asynchronous communications ports that is hardware-independent. The user interface to this
functionality is using function calls (the preferred interface) described in termios(3C) or ioctl commands described in this section. This
section also discusses the common features of the terminal subsystem which are relevant with both user interfaces.
When a terminal file is opened, it normally causes the process to wait until a connection is established. In practice, user programs seldom
open terminal files; they are opened by the system and become a user's standard input, output, and error files. The first terminal file
opened by the session leader that is not already associated with a session becomes the controlling terminal for that session. The control-
ling 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() (see 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 out-
put is occurring, and are only lost when the character input buffers of the system become completely full, which is rare. For example, the
number of characters in the line discipline buffer may exceed {MAX_CANON} and IMAXBEL (see below) is not set, or the user may accumulate
{ MAX_INPUT} number of input characters that have not yet been read by some program. When the input limit is reached, all the characters
saved in the buffer up to that point are thrown away without notice.
Session Management (Job Control)
A control terminal will distinguish one of the process groups in the session associated with it to be the foreground process group. All
other process groups in the session are designated as background process groups. This foreground process group plays a special role in han-
dling signal-generating input characters, as discussed below. By default, when a controlling terminal is allocated, the controlling
process's process group is assigned as foreground process group.
Background process groups in the controlling process's session are subject to a job control line discipline when they attempt to access
their controlling terminal. Process groups can be sent signals that will cause them to stop, unless they have made other arrangements. An
exception is made for members of orphaned process groups.
An orphaned process group is one where the process group (see getpgid(2)) has no members with a parent in a different process group but
sharing the same controlling terminal. When a member of an orphaned process group attempts to access its controlling terminal, EIO is
returned because there would be no way to restart the process if it were stopped on one of these signals.
If a member of a background process group attempts to read its controlling terminal, its process group will be sent a SIGTTIN signal,
which will normally cause the members of that process group to stop. If, however, the process is ignoring or holding SIGTTIN, or is a mem-
ber of an orphaned process group, the read will fail with errno set to EIO, and no signal is sent.
If a member of a background process group attempts to write its controlling terminal and the TOSTOP bit is set in the c_lflag field, its
process group is sent a SIGTTOU signal, which will normally cause the members of that process group to stop. If, however, the process is
ignoring or holding SIGTTOU, the write will succeed. If the process is not ignoring or holding SIGTTOU and is a member of an orphaned
process group, the write will fail with errno set to EIO, and no signal will be sent.
If TOSTOP is set and a member of a background process group attempts to ioctl its controlling terminal, and that ioctl will modify termi-
nal parameters (for example, TCSETA, TCSETAW, TCSETAF, or TIOCSPGRP), its process group will be sent a SIGTTOU signal, which will normally
cause the members of that process group to stop. If, however, the process is ignoring or holding SIGTTOU, the ioctl will succeed. If the
process is not ignoring or holding SIGTTOU and is a member of an orphaned process group, the write will fail with errno set to EIO, and no
signal will be sent.
Canonical Mode Input Processing
Normally, terminal input is processed in units of lines. A line is delimited by a newline (ASCII LF) character, an end-of-file (ASCII EOT)
character, or an end-of-line character. This means that a program attempting to read will block until an entire line has been typed. Also,
no matter how many characters are requested in the read call, at most one line will be returned. It is not necessary, however, to read a
whole line at once; any number of characters may be requested in a read, even one, without losing information.
During input, erase and kill processing is normally done. The ERASE character (by default, the character DEL) erases the last character
typed. The WERASE character (the character Control-w) erases the last "word" typed in the current input line (but not any preceding spaces
or tabs). A "word" is defined as a sequence of non-blank characters, with tabs counted as blanks. Neither ERASE nor WERASE will erase
beyond the beginning of the line. The KILL character (by default, the character NAK) kills (deletes) the entire input line, and optionally
outputs a newline character. All these characters operate on a key stroke basis, independent of any backspacing or tabbing that may have
been done. The REPRINT character (the character Control-r) prints a newline followed by all characters that have not been read. Reprinting
also occurs automatically if characters that would normally be erased from the screen are fouled by program output. The characters are
reprinted as if they were being echoed; 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
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 acti-
vated 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 charac-
ters 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.
Comparing Different Cases of MIN, TIME Interaction
Some points to note about MIN and TIME :
o In the following explanations, note that the interactions of MIN and TIME are not symmetric. For example, when MIN > 0 and TIME =
0, TIME has no effect. However, in the opposite case, where MIN = 0 and TIME > 0, both MIN and TIME play a role in that MIN is
satisfied with the receipt of a single character.
o Also note that in case A (MIN > 0, TIME > 0), TIME represents an intercharacter timer, whereas in case C ( MIN = 0, TIME > 0), TIME
represents a read timer.
These two points highlight the dual purpose of the MIN/TIME feature. Cases A and B, where MIN > 0, exist to handle burst mode activity
(for example, file transfer programs), where a program would like to process at least MIN characters at a time. In case A, the intercharac-
ter 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 typ-
ing. 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 (Control-c or ASCII ETX) generates a SIGINT signal. SIGINT is sent to all foreground processes associated with the control-
ling terminal. Normally, each such process is forced to terminate, but arrangements may be made either to ignore the signal
or to receive a trap to an agreed upon location. (See signal.h(3HEAD)).
QUIT (Control-| or ASCII FS) generates a SIGQUIT signal. Its treatment is identical to the interrupt signal except that, unless
a receiving process has made other arrangements, it will not only be terminated but a core image file (called core) will
be created in the current working directory.
ERASE (DEL) erases the preceding character. It does not erase beyond the start of a line, as delimited by a NL, EOF, EOL, or EOL2
character.
WERASE (Control-w or ASCII ETX) erases the preceding "word". It does not erase beyond the start of a line, as delimited by a NL,
EOF, EOL, or EOL2 character.
KILL (Control-u or ASCII NAK) deletes the entire line, as delimited by a NL, EOF, EOL, or EOL2 character.
REPRINT (Control-r or ASCII DC2) reprints all characters, preceded by a newline, that have not been read.
EOF (Control-d or ASCII EOT) may be used to generate an end-of-file from a terminal. When received, all the characters waiting
to be read are immediately passed to the program, without waiting for a newline, and the EOF is discarded. Thus, if no
characters are waiting (that is, the EOF occurred at the beginning of a line) zero characters are passed back, which is the
standard end-of-file indication. Unless escaped, the EOF character is not echoed. Because EOT is the default EOF character,
this prevents terminals that respond to EOT from hanging up.
NL (ASCII LF) is the normal line delimiter. It cannot be changed or escaped.
EOL (ASCII NULL) is an additional line delimiter, like NL . It is not normally used.
EOL2 is another additional line delimiter.
SWTCH (Control-z or ASCII EM) Header file symbols related to this special character are present for compatibility purposes only
and the kernel takes no special action on matching SWTCH (except to discard the character).
SUSP (Control-z or ASCII SUB) generates a SIGTSTP signal. SIGTSTP stops all processes in the foreground process group for that
terminal.
DSUSP (Control-y or ASCII EM). It generates a SIGTSTP signal as SUSP does, but the signal is sent when a process in the fore-
ground process group attempts to read the DSUSP character, rather than when it is typed.
STOP (Control-s or ASCII DC3) can be used to suspend output temporarily. It is useful with CRT terminals to prevent output from
disappearing before it can be read.
While output is suspended, STOP characters are ignored and not read.
START (Control-q or ASCII DC1) is used to resume output. Output has been suspended by a STOP character. While output is not sus-
pended, START characters are ignored and not read.
DISCARD (Control-o or ASCII SI) causes subsequent output to be discarded. Output is discarded until another DISCARD character is
typed, more input arrives, or the condition is cleared by a program.
LNEXT (Control-v or ASCII SYN) causes the special meaning of the next character to be ignored. This works for all the special
characters mentioned above. It allows characters to be input that would otherwise be interpreted by the system (for example
KILL, QUIT). The character values for INTR, QUIT, ERASE, 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 backslash () character, in which case no special function is done. Any of the special characters
may be preceded by the LNEXT character, in which case no special function is done.
Modem Disconnect
When a modem disconnect is detected, a SIGHUP signal is sent to the terminal's controlling process.
Unless other arrangements have been made, these signals cause the process to terminate. If SIGHUP is ignored or caught, any subsequent
read returns with an end-of-file indication until the terminal is closed.
If the controlling process is not in the foreground process group of the terminal, a SIGTSTP is sent to the terminal's foreground process
group. Unless other arrangements have been made, these signals cause the processes to stop.
Processes in background process groups that attempt to access the controlling terminal after modem disconnect while the terminal is still
allocated to the session will receive appropriate SIGTTOU and SIGTTIN signals. Unless other arrangements have been made, this signal
causes the processes to stop.
The controlling terminal will remain in this state until it is reinitialized with a successful open by the controlling process, or deallo-
cated by the controlling process.
Terminal Parameters
The parameters that control the behavior of devices and modules providing the termios interface are specified by the termios structure
defined by termios.h. Several ioctl(2) system calls that fetch or change these parameters use this structure that contains the following
members:
tcflag_t c_iflag; /* input modes */
tcflag_t c_oflag; /* output modes */
tcflag_t c_cflag; /* control modes */
tcflag_t c_lflag; /* local modes */
cc_t c_cc[NCCS]; /* control chars */
The special control characters are defined by the array c_cc. The symbolic name NCCS is the size of the Control-character array and is also
defined by <termios.h>. The relative positions, subscript names, and typical default values for each function are as follows:
+--------------------+--------------------+-----------------------+
|Relative Position | Subscript Name | Typical Default Value |
+--------------------+--------------------+-----------------------+
|0 |VINTR | ETX |
+--------------------+--------------------+-----------------------+
|1 |VQUIT | FS |
+--------------------+--------------------+-----------------------+
|2 |VERASE | DEL |
+--------------------+--------------------+-----------------------+
|3 |VKILL | NAK |
+--------------------+--------------------+-----------------------+
|4 |VEOF | EOT |
+--------------------+--------------------+-----------------------+
|5 |VEOL | NUL |
+--------------------+--------------------+-----------------------+
|6 |VEOL2 | NUL |
+--------------------+--------------------+-----------------------+
|7 |VWSTCH | NUL |
+--------------------+--------------------+-----------------------+
|8 |VSTART | NUL |
+--------------------+--------------------+-----------------------+
|9 |VSTOP | DC3 |
+--------------------+--------------------+-----------------------+
|10 |VSUSP | SUB |
+--------------------+--------------------+-----------------------+
|11 |VDSUSP | EM |
+--------------------+--------------------+-----------------------+
|12 |VREPRINT | DC2 |
+--------------------+--------------------+-----------------------+
|13 |VDISCARD | SI |
+--------------------+--------------------+-----------------------+
|14 |VWERASE | ETB |
+--------------------+--------------------+-----------------------+
|15 |VLNEXT | SYN |
+--------------------+--------------------+-----------------------+
|16-19 |Reserved | |
+--------------------+--------------------+-----------------------+
Input Modes
The c_iflag field describes the basic terminal input control:
IGNBRK Ignore break condition.
BRKINT Signal interrupt on break.
IGNPAR Ignore characters with parity errors.
PARMRK Mark parity errors.
INPCK Enable input parity check.
ISTRIP Strip character.
INLCR Map NL to CR on input.
IGNCR Ignore CR.
ICRNL Map CR to NL on input.
IUCLC Map upper-case to lower-case on input.
IXON Enable start/stop output control.
IXANY Enable any character to restart output.
IXOFF Enable start/stop input control.
IMAXBEL Echo BEL on input line too long.
If IGNBRK is set, a break condition (a character framing error with data all zeros) detected on input is ignored, that is, not put on the
input queue and therefore not read by any process. If IGNBRK is not set and BRKINT is set, the break condition shall flush the input and
output queues and if the terminal is the controlling terminal of a foreground process group, the break condition generates a single SIGINT
signal to that foreground process group. If neither IGNBRK nor BRKINT is set, a break condition is read as a single ' ' (ASCII NULL) char-
acter, or if PARMRK is set, as '377', ' ', c, where '377' is a single character with value 377 octal (0xff hex, 255 decimal), ' ' is a
single character with value 0, and c is the errored character received.
If IGNPAR is set, a byte with framing or parity errors (other than break) is ignored.
If PARMRK is set, and IGNPAR is not set, a byte with a framing or parity error (other than break) is given to the application as the three-
character sequence: '377', ' ', c, where '377' is a single character with value 377 octal (0xff hex, 255 decimal), ' ' is a single
character with value 0, and c is the errored character received. To avoid ambiguity in this case, if ISTRIP is not set, a valid character
of '377' is given to the application as `377.' If neither IGNPAR nor PARMRK is set, a framing or parity error (other than break) is
given to the application as a single ' ' (ASCII NULL) character.
If INPCK is set, input parity checking is enabled. If INPCK is not set, input parity checking is disabled. This allows output parity gener-
ation without input parity errors. Note that whether input parity checking is enabled or disabled is independent of whether parity detec-
tion 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 charac-
ter restarts output that has been suspended.
If IXOFF is set, the system transmits a STOP character when the input queue is nearly full, and a START character when enough input has
been read so that the input queue is nearly empty again.
If IMAXBEL is set, the ASCII BEL character is echoed if the input stream overflows. Further input is not stored, but any input already
present in the input stream is not disturbed. If IMAXBEL is not set, no BEL character is echoed, and all input present in the input queue
is discarded if the input stream overflows.
Output Modes
The c_oflag field specifies the system treatment of output:
OPOST Post-process output.
OLCUC Map lower case to upper on output.
ONLCR Map NL to CR-NL on output.
OCRNL Map CR to NL on output.
ONOCR No CR output at column 0.
ONLRET NL performs CR function.
OFILL Use fill characters for delay.
OFDEL Fill is DEL, else NULL.
NLDLY Select newline delays:
NL0
NL1
CRDLY
Select carriage-return delays:
CR0
CR1
CR2
CR3
TABDLY
Select horizontal tab delays or tab expansion:
TAB0
TAB1
TAB2
TAB3 Expand tabs to spaces
XTABS Expand tabs to spaces
BSDLY
Select backspace delays:
BS0
BS1
VTDLY
Select vertical tab delays:
VT0
VT1
FFDLY
Select form feed delays:
FF0
FF1
If OPOST is set, output characters are post-processed as indicated by the remaining flags; otherwise, characters are transmitted without
change.
If OLCUC is set, a lower case alphabetic character is transmitted as the corresponding upper case character. This function is often used in
conjunction with IUCLC.
If ONLCR is set, the NL character is transmitted as the CR-NL character pair. If OCRNL is set, the CR character is transmitted as the NL
character. If ONOCR is set, no CR character is transmitted when at column 0 (first position). If ONRET is set, the NL character is
assumed to do the carriage-return function; the column pointer is set to 0 and the delays specified for CR are used. Otherwise, the NL
character is assumed to do just the line-feed function; the column pointer remains unchanged. The column pointer is also set to 0 if the CR
character is actually transmitted.
The delay bits specify how long transmission stops to allow for mechanical or other movement when certain characters are sent to the termi-
nal. In all cases, a value of 0 indicates no delay. If OFILL is set, fill characters are transmitted for delay instead of a timed delay.
This is useful for high baud rate terminals that need only a minimal delay. If OFDEL is set, the fill character is DEL ; otherwise it is
NULL.
If a form-feed or vertical-tab delay is specified, it lasts for about 2 seconds.
Newline delay lasts about 0.10 seconds. If ONLRET is set, the carriage-return delays are used instead of the newline delays. If OFILL is
set, two fill characters are transmitted.
Carriage-return delay type 1 is dependent on the current column position, type 2 is about 0.10 seconds, and type 3 is about 0.15 seconds.
If OFILL is set, delay type 1 transmits two fill characters, and type 2 transmits four fill characters.
Horizontal-tab delay type 1 is dependent on the current column position. Type 2 is about 0.10 seconds. Type 3 specifies that tabs are to be
expanded into spaces. If OFILL is set, two fill characters are transmitted for any delay.
Backspace delay lasts about 0.05 seconds. If OFILL is set, one fill character is transmitted.
The actual delays depend on line speed and system load.
Control Modes
The c_cflag field describes the hardware control of the terminal:
CBAUD Baud rate:
B0 Hang up
B50 50 baud
B75 75 baud
B110 110 baud
B134 134 baud
B150 150 baud
B200 200 baud
B300 300 baud
B600 600 baud
B1200 1200 baud
B1800 1800 baud
B2400 2400 baud
B4800 4800 baud
B9600 9600 baud
B19200 19200 baud
EXTA External A
B38400 38400 baud
EXTB External B
B57600 57600 baud
B76800 76800 baud
B115200 115200 baud
B153600 153600 baud
B230400 230400 baud
B307200 307200 baud
B460800 460800 baud
CSIZE Character size:
CS5 5 bits
CS6 6 bits
CS7 7 bits
CS8 8 bits
CSTOPB Send two stop bits, else one
CREAD Enable receiver
PARENB Parity enable
PARODD Odd parity, else even
HUPCL Hang up on last close
CLOCAL Local line, else dial-up
CIBAUD Input baud rate, if different from output rate
PAREXT Extended parity for mark and space parity
CRTSXOFF Enable inbound hardware flow control
CRTSCTS Enable outbound hardware flow control
CBAUDEXT Bit to indicate output speed > B38400
CIBAUDEXT Bit to indicate input speed > B38400
The CBAUD bits together with the CBAUDEXT bit specify the output baud rate. To retrieve the output speed from the termios structure pointed
to by termios_p see the following code segment.
speed_t ospeed;
if (termios_p->c_cflag & CBAUDEXT)
ospeed = (termios_p->c_cflag & CBAUD) + CBAUD + 1;
else
ospeed = termios_p->c_cflag & CBAUD;
To store the output speed in the termios structure pointed to by termios_p see the following code segment.
speed_t ospeed;
if (ospeed > CBAUD) {
termios_p->c_cflag |= CBAUDEXT;
ospeed -= (CBAUD + 1);
} else
termios_p->c_cflag &= ~CBAUDEXT;
termios_p->c_cflag =
(termios_p->c_cflag & ~CBAUD) | (ospeed & CBAUD);
The zero baud rate, B0, is used to hang up the connection. If B0 is specified, the data-terminal-ready signal is not asserted. Normally,
this disconnects the line.
If the CIBAUDEXT or CIBAUD bits are not zero, they specify the input baud rate, with the CBAUDEXT and CBAUD bits specifying the output baud
rate; otherwise, the output and input baud rates are both specified by the CBAUDEXT and CBAUD bits. The values for the CIBAUD bits are
the same as the values for the CBAUD bits, shifted left IBSHIFT bits. For any particular hardware, impossible speed changes are ignored.
To retrieve the input speed in the termios structure pointed to by termios_p see the following code segment.
speed_t ispeed;
if (termios_p->c_cflag & CIBAUDEXT)
ispeed = ((termios_p->c_cflag & CIBAUD) >> IBSHIFT)
+ (CIBAUD >> IBSHIFT) + 1;
else
ispeed = (termios_p->c_cflag & CIBAUD) >> IBSHIFT;
To store the input speed in the termios structure pointed to by termios_p see the following code segment.
speed_t ispeed;
if (ispeed == 0) {
ispeed = termios_p->c_cflag & CBAUD;
if (termios_p->c_cflag & CBAUDEXT)
ispeed += (CBAUD + 1);
}
if ((ispeed << IBSHIFT) > CIBAUD) {
termios_p->c_cflag |= CIBAUDEXT;
ispeed -= ((CIBAUD >> IBSHIFT) + 1);
} else
termios_p->c_cflag &= ~CIBAUDEXT;
termios_p->c_cflag =
(termios_p->c_cflag & ~CIBAUD) |
((ispeed << IBSHIFT) & CIBAUD);
The CSIZE bits specify the character size in bits for both transmission and reception. This size does not include the parity bit, if any.
If CSTOPB is set, two stop bits are used; otherwise, one stop bit is used. For example, at 110 baud, two stops bits are required.
If PARENB is set, parity generation and detection is enabled, and a parity bit is added to each character. If parity is enabled, the PARODD
flag specifies odd parity if set; otherwise, even parity is used.
If CREAD is set, the receiver is enabled. Otherwise, no characters are received.
If HUPCL is set, the line is disconnected when the last process with the line open closes it or terminates. That is, the data-terminal-
ready signal is not asserted.
If CLOCAL is set, the line is assumed to be a local, direct connection with no modem control; otherwise, modem control is assumed.
If CRTSXOFF is set, inbound hardware flow control is enabled.
If CRTSCTS is set, outbound hardware flow control is enabled.
The four possible combinations for the state of CRTSCTS and CRTSXOFF bits and their interactions are described below.
Case A: CRTSCTS off, CRTSXOFF off. In this case the hardware flow control is disabled.
Case B: CRTSCTS on, CRTSXOFF off. In this case only outbound hardware flow control is enabled. The state of CTS signal is used to
do outbound flow control. It is expected that output will be suspended if CTS is low and resumed when CTS is high.
Case C: CRTSCTS off, CRTSXOFF on. In this case only inbound hardware flow control is enabled. The state of RTS signal is used to do
inbound flow control. It is expected that input will be suspended if RTS is low and resumed when RTS is high.
Case D: CRTSCTS on, CRTSXOFF on. In this case both inbound and outbound hardware flow control are enabled. Uses the state of CTS
signal to do outbound flow control and RTS signal to do inbound flow control.
Local Modes
The c_lflag field of the argument structure is used by the line discipline to control terminal functions. The basic line discipline pro-
vides the following:
ISIG Enable signals.
ICANON Canonical input (erase and kill processing).
XCASE Canonical upper/lower presentation.
ECHO Enable echo.
ECHOE Echo erase character as BS-SP-BS &.
ECHOK Echo NL after kill character.
ECHONL Echo NL .
NOFLSH Disable flush after interrupt or quit.
TOSTOP Send SIGTTOU for background output.
ECHOCTL Echo control characters as char, delete as ^?.
ECHOPRT Echo erase character as character erased.
ECHOKE BS-SP-BS erase entire line on line kill.
FLUSHO Output is being flushed.
PENDIN Retype pending input at next read or input character.
IEXTEN Enable extended (implementation-defined) functions.
If ISIG is set, each input character is checked against the special control characters INTR, QUIT, SWTCH, SUSP, STATUS, and DSUSP. If an
input character matches one of these control characters, the function associated with that character is performed. (Note: If SWTCH is set
and the character matches, the character is simply discarded. No other action is taken.) If ISIG is not set, no checking is done. Thus,
these special input functions are possible only if ISIG is set.
If ICANON is set, canonical processing is enabled. This enables the erase and kill edit functions, and the assembly of input characters
into lines delimited by NL-c, EOF, EOL, and EOL . If ICANON is not set, read requests are satisfied directly from the input queue. A read
is not satisfied until at least MIN characters have been received or the timeout value TIME has expired between characters. This allows
fast bursts of input to be read efficiently while still allowing single character input. The time value represents tenths of seconds.
If XCASE is set and ICANON is set, an upper case letter is accepted on input if preceded by a backslash () character, and is output pre-
ceded by a backslash () character. In this mode, the following escape sequences are generated on output and accepted on input:
+-----------------------------+-----------------------------+
| FOR: | USE: |
+-----------------------------+-----------------------------+
|` |' |
+-----------------------------+-----------------------------+
|| |! |
+-----------------------------+-----------------------------+
|~ |^ |
+-----------------------------+-----------------------------+
|{ |( |
+-----------------------------+-----------------------------+
|} |) |
+-----------------------------+-----------------------------+
| |\ |
+-----------------------------+-----------------------------+
For example, input A as a,
as \n, and N as \
.
If ECHO is set, characters are echoed as received.
When ICANON is set, the following echo functions are possible.
o If ECHO and ECHOE are set, and ECHOPRT is not set, the ERASE and WERASE characters are echoed as one or more ASCII BS SP BS, which
clears the last character(s) from a CRT screen.
o If ECHO, ECHOPRT, and IEXTEN are set, the first ERASE and WERASE character in a sequence echoes as a backslash (), followed by the
characters being erased. Subsequent ERASE and WERASE characters echo the characters being erased, in reverse order. The next non-
erase character causes a `/' (slash) to be typed before it is echoed. ECHOPRT should be used for hard copy terminals.
o If ECHOKE and IEXTEN are set, the kill character is echoed by erasing each character on the line from the screen (using the mecha-
nism selected by ECHOE and ECHOPRa).
o If ECHOK is set, and ECHOKE is not set, the NL character is echoed after the kill character to emphasize that the line is deleted.
Note that a `' (escape) character or an LNEXT character preceding the erase or kill character removes any special function.
o If ECHONL is set, the NL character is echoed even if ECHO is not set. This is useful for terminals set to local echo (so called
half-duplex).
If ECHOCTL and IEXTEN are set, all control characters (characters with codes between 0 and 37 octal) other than ASCII TAB, ASCII NL, the
START character, and the STOP character, ASCII CR, and ASCII BS are echoed as ^ X, where X is the character given by adding 100 octal to
the code of the control character (so that the character with octal code 1 is echoed as ^ A), and the ASCII DEL character, with code 177
octal, is echoed as ^ ?.
If NOFLSH is set, the normal flush of the input and output queues associated with the INTR, QUIT, and SUSP characters is not done. This
bit should be set when restarting system calls that read from or write to a terminal (see sigaction(2)).
If TOSTOP and IEXTEN are set, the signal SIGTTOU is sent to a process that tries to write to its controlling terminal if it is not in the
foreground process group for that terminal. This signal normally stops the process. Otherwise, the output generated by that process is out-
put to the current output stream. Processes that are blocking or ignoring SIGTTOU signals are excepted and allowed to produce output, if
any.
If FLUSHO and IEXTEN are set, data written to the terminal is discarded. This bit is set when the FLUSH character is typed. A program can
cancel the effect of typing the FLUSH character by clearing FLUSHO.
If PENDIN and IEXTEN are set, any input that has not yet been read is reprinted when the next character arrives as input. PENDIN is then
automatically cleared.
If IEXTEN is set, the following implementation-defined functions are enabled: special characters ( WERASE, REPRINT, DISCARD, and LNEXT)
and local flags ( TOSTOP, ECHOCTL, ECHOPRT, ECHOKE, FLUSHO, and PENDIN).
Minimum and Timeout
The MIN and TIME values were described previously, in the subsection, Non-canonical Mode Input Processing. The initial value of MIN is 1,
and the initial value of TIME is 0.
Terminal Size
The number of lines and columns on the terminal's display is specified in the winsize structure defined by sys/termios.h and includes the
following members:
unsigned short ws_row; /* rows, in characters */
unsigned short ws_col; /* columns, in characters */
unsigned short ws_xpixel; /* horizontal size, in pixels */
unsigned short ws_ypixel; /* vertical size, in pixels */
Termio Structure
The SunOS/SVR4 termio structure is used by some 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:
+--------------------+--------------------+------------------------+
|Relative Positions | Subscript Names | Typical Default Values |
+--------------------+--------------------+------------------------+
|0 |VINTR | EXT |
+--------------------+--------------------+------------------------+
|1 |VQUIT | FS |
+--------------------+--------------------+------------------------+
|2 |VERASE | DEL |
+--------------------+--------------------+------------------------+
|3 |VKILL | NAK |
+--------------------+--------------------+------------------------+
|4 |VEOF | EOT |
+--------------------+--------------------+------------------------+
|5 |VEOL | NUL |
+--------------------+--------------------+------------------------+
|6 |VEOL2 | NUL |
+--------------------+--------------------+------------------------+
|7 |Reserved | |
+--------------------+--------------------+------------------------+
The MIN values is stored in the VMIN element of the c_cc array; the TIME value is stored in the VTIME element of the c_cc array. The
VMIN element is the same element as the VEOF element; the VTIME element is the same element as the VEOL element.
The calls that use the termio structure only affect the flags and control characters that can be stored in the termio structure; all other
flags and control characters are unaffected.
Modem Lines
On special files representing serial ports, modem control lines can be read. Control lines (if the underlying hardware supports it) may
also be changed. Status lines are read-only. The following modem control and status lines may be supported by a device; they are defined by
sys/termios.h:
TIOCM_LE line enable
TIOCM_DTR data terminal ready
TIOCM_RTS request to send
TIOCM_ST secondary transmit
TIOCM_SR secondary receive
TIOCM_CTS clear to send
TIOCM_CAR carrier detect
TIOCM_RNG ring
TIOCM_DSR data set ready
TIOCM_CD is a synonym for TIOCM_CAR, and TIOCM_RI is a synonym for TIOCM_RNG. Not all of these are necessarily supported by any particular
device; check the manual page for the device in question.
The software carrier mode can be enabled or disabled using the TIOCSSOFTCAR ioctl. If the software carrier flag for a line is off, the line
pays attention to the hardware carrier detect (DCD) signal. The tty device associated with the line cannot be opened until DCD is asserted.
If the software carrier flag is on, the line behaves as if DCD is always asserted.
The software carrier flag is usually turned on for locally connected terminals or other devices, and is off for lines with modems.
To be able to issue the TIOCGSOFTCAR and TIOCSSOFTCAR ioctl calls, the tty line should be opened with O_NDELAY so that the open(2) will not
wait for the carrier.
Default Values
The initial termios values upon driver open is configurable. This is accomplished by setting the "ttymodes" property in the file /ker-
nel/drv/options.conf. Since this property is assigned during system initialization, any change to the "ttymodes" property will not take
effect until the next reboot. The string value assigned to this property should be in the same format as the output of the stty(1) command
with the -g option.
If this property is undefined, the following termios modes are in effect. The initial input control value is BRKINT, ICRNL, IXON, IMAX-
BEL. The initial output control value is OPOST, ONLCR, TAB3. The initial hardware control value is B9600, CS8, CREAD. The initial line-dis-
cipline control value is ISIG, ICANON, IEXTEN, ECHO, ECHOK, ECHOE, ECHOKE, ECHOCTL.
The ioctls supported by devices and STREAMS modules providing the termios(3C) interface are listed below.
Some calls may not be supported by all devices or modules. The functionality provided by these calls is also available through the pre-
ferred function call interface specified on termios.
TCGETS The argument is a pointer to a termios structure. The current terminal parameters are fetched and stored into that struc-
ture.
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 transmit-
ted; all characters queued for input are discarded and then the change occurs.
TCSBRK The argument is an int value. Wait for the output to drain. If the argument is 0, then send a break (zero valued bits for
0.25 seconds).
TCXONC Start/stop control. The argument is an int value. If the argument is 0, suspend output; if 1, restart suspended output; if
2, suspend input; if 3, restart suspended input.
TCFLSH The argument is an int value. If the argument is 0, flush the input queue; if 1, flush the output queue; if 2, flush both
the input and output queues.
TIOCGPGRP The argument is a pointer to a pid_t. Set the value of that pid_t to the process group ID of the foreground process group
associated with the terminal. See termios(3C) for a description of TCGETPGRP.
TIOCSPGRP The argument is a pointer to a pid_t. Associate the process group whose process group ID is specified by the value of that
pid_t with the terminal. The new process group value must be in the range of valid process group ID values. Otherwise, the
error EPERM is returned.
TIOCGSID The argument is a pointer to a pid_t. The session ID of the terminal is fetched and stored in the pid_t.
TIOCGWINSZ The argument is a pointer to a winsize structure. The terminal driver's notion of the terminal size is stored into that
structure.
TIOCSWINSZ The argument is a pointer to a winsize structure. The terminal driver's notion of the terminal size is set from the values
specified in that structure. If the new sizes are different from the old sizes, a SIGWINCH signal is set to the process
group of the terminal.
TIOCMBIS The argument is a pointer to an int whose value is a mask containing modem control lines to be turned on. The control lines
whose bits are set in the argument are turned on; no other control lines are affected.
TIOCMBIC The argument is a pointer to an int whose value is a mask containing modem control lines to be turned off. The control
lines whose bits are set in the argument are turned off; no other control lines are affected.
TIOCMGET The argument is a pointer to an int. The current state of the modem status lines is fetched and stored in the int pointed
to by the argument.
TIOCMSET The argument is a pointer to an int containing a new set of modem control lines. The modem control lines are turned on or
off, depending on whether the bit for that mode is set or clear.
TIOCSPPS The argument is a pointer to an int that determines whether pulse-per-second event handling is to be enabled (non-zero) or
disabled (zero). If a one-pulse-per-second reference clock is attached to the serial line's data carrier detect input, the
local system clock will be calibrated to it. A clock with a high error, that is, a deviation of more than 25 microseconds
per tick, is ignored.
TIOCGPPS The argument is a pointer to an int, in which the state of the even handling is returned. The int is set to a non-zero
value if pulse-per-second (PPS) handling has been enabled. Otherwise, it is set to zero.
TIOCGSOFTCAR The argument is a pointer to an int whose value is 1 or 0, depending on whether the software carrier detect is turned on or
off.
TIOCSSOFTCAR The argument is a pointer to an int whose value is 1 or 0. The value of the integer should be 0 to turn off software car-
rier, or 1 to turn it on.
TIOCGPPSEV The argument is a pointer to a struct ppsclockev. This structure contains the following members:
struct timeval tv;
uint32_t serial;
"tv" is the system clock timestamp when the event (pulse on the DCD pin) occurred. "serial" is the ordinal of the event,
which each consecutive event being assigned the next ordinal. The first event registered gets a "serial" value of 1. The
TIOCGPPSEV returns the last event registered; multiple calls will persistently return the same event until a new one is
registered. In addition to time stamping and saving the event, if it is of one-second period and of consistently high accu-
racy, the local system clock will automatically calibrate to it.
Files in or under /dev
stty(1), fork(2), getpgid(2), getsid(2), ioctl(2), setsid(2), sigaction(2), signal(3C), tcsetpgrp(3C), termios(3C), signal.h(3HEAD),
streamio(7I)
14 Sep 2005 termio(7I)