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TERMIOS(4)	       FreeBSD Kernel Interfaces Manual		    TERMIOS(4)

NAME
     termios --	general	terminal line discipline

SYNOPSIS
     #include <termios.h>

DESCRIPTION
     This describes a general terminal line discipline that is supported on
     tty asynchronous communication ports.

   Opening a Terminal Device File
     When a terminal file is opened, it	normally causes	the process to wait
     until a connection	is established.	 For most hardware, the	presence of a
     connection	is indicated by	the assertion of the hardware CARRIER line.
     If	the termios structure associated with the terminal file	has the	CLOCAL
     flag set in the cflag, or if the O_NONBLOCK flag is set in	the open(2)
     call, then	the open will succeed even without a connection	being present.
     In	practice, applications seldom open these files;	they are opened	by
     special programs, such as getty(8)	or rlogind(8), and become an applica-
     tion's standard input, output, and	error files.

   Job Control in a Nutshell
     Every process is associated with a	particular process group and session.
     The grouping is hierarchical: every member	of a particular	process	group
     is	a member of the	same session.  This structuring	is used	in managing
     groups of related processes for purposes of job control; that is, the
     ability from the keyboard (or from	program	control) to simultaneously
     stop or restart a complex command (a command composed of one or more
     related processes).  The grouping into process groups allows delivering
     of	signals	that stop or start the group as	a whole, along with arbitrat-
     ing which process group has access	to the single controlling terminal.
     The grouping at a higher layer into sessions is to	restrict the job con-
     trol related signals and system calls to within processes resulting from
     a particular instance of a	``login''.  Typically, a session is created
     when a user logs in, and the login	terminal is setup to be	the control-
     ling terminal; all	processes spawned from that login shell	are in the
     same session, and inherit the controlling terminal.

     A job control shell operating interactively (that is, reading commands
     from a terminal) normally groups related processes	together by placing
     them into the same	process	group.	A set of processes in the same process
     group is collectively referred to as a ``job''.  When the foreground
     process group of the terminal is the same as the process group of a par-
     ticular job, that job is said to be in the	``foreground''.	 When the
     process group of the terminal is different	from the process group of a
     job (but is still the controlling terminal), that job is said to be in
     the ``background''.  Normally the shell reads a command and starts	the
     job that implements that command.	If the command is to be	started	in the
     foreground	(typical), it sets the process group of	the terminal to	the
     process group of the started job, waits for the job to complete, and then
     sets the process group of the terminal back to its	own process group (it
     puts itself into the foreground).	If the job is to be started in the
     background	(as denoted by the shell operator "&"),	it never changes the
     process group of the terminal and does not	wait for the job to complete
     (that is, it immediately attempts to read the next	command).  If the job
     is	started	in the foreground, the user may	type a key (usually `^Z')
     which generates the terminal stop signal (SIGTSTP)	and has	the effect of
     stopping the entire job.  The shell will notice that the job stopped, and
     will resume running after placing itself in the foreground.  The shell
     also has commands for placing stopped jobs	in the background, and for
     placing stopped or	background jobs	into the foreground.

   Orphaned Process Groups
     An	orphaned process group is a process group that has no process whose
     parent is in a different process group, yet is in the same	session.  Con-
     ceptually it means	a process group	that does not have a parent that could
     do	anything if it were to be stopped.  For	example, the initial login
     shell is typically	in an orphaned process group.  Orphaned	process	groups
     are immune	to keyboard generated stop signals and job control signals
     resulting from reads or writes to the controlling terminal.

   The Controlling Terminal
     A terminal	may belong to a	process	as its controlling terminal.  Each
     process of	a session that has a controlling terminal has the same con-
     trolling terminal.	 A terminal may	be the controlling terminal for	at
     most one session.	The controlling	terminal for a session is allocated by
     the session leader	by issuing the TIOCSCTTY ioctl.	 A controlling termi-
     nal is never acquired by merely opening a terminal	device file.  When a
     controlling terminal becomes associated with a session, its foreground
     process group is set to the process group of the session leader.

     The controlling terminal is inherited by a	child process during a fork(2)
     function call.  A process relinquishes its	controlling terminal when it
     creates a new session with	the setsid(2) function;	other processes
     remaining in the old session that had this	terminal as their controlling
     terminal continue to have it.  A process does not relinquish its control-
     ling terminal simply by closing all of its	file descriptors associated
     with the controlling terminal if other processes continue to have it
     open.

     When a controlling	process	terminates, the	controlling terminal is	disas-
     sociated from the current session,	allowing it to be acquired by a	new
     session leader.  Subsequent access	to the terminal	by other processes in
     the earlier session will be denied, with attempts to access the terminal
     treated as	if modem disconnect had	been sensed.

   Terminal Access Control
     If	a process is in	the foreground process group of	its controlling	termi-
     nal, read operations are allowed.	Any attempts by	a process in a back-
     ground process group to read from its controlling terminal	causes a
     SIGTTIN signal to be sent to the process's	group unless one of the	fol-
     lowing special cases apply: if the	reading	process	is ignoring or block-
     ing the SIGTTIN signal, or	if the process group of	the reading process is
     orphaned, the read(2) returns -1 with errno set to	EIO and	no signal is
     sent.  The	default	action of the SIGTTIN signal is	to stop	the process to
     which it is sent.

     If	a process is in	the foreground process group of	its controlling	termi-
     nal, write	operations are allowed.	 Attempts by a process in a background
     process group to write to its controlling terminal	will cause the process
     group to be sent a	SIGTTOU	signal unless one of the following special
     cases apply: if TOSTOP is not set,	or if TOSTOP is	set and	the process is
     ignoring or blocking the SIGTTOU signal, the process is allowed to	write
     to	the terminal and the SIGTTOU signal is not sent.  If TOSTOP is set,
     and the process group of the writing process is orphaned, and the writing
     process is	not ignoring or	blocking SIGTTOU, the write(2) returns -1 with
     errno set to EIO and no signal is sent.

     Certain calls that	set terminal parameters	are treated in the same	fash-
     ion as write, except that TOSTOP is ignored; that is, the effect is iden-
     tical to that of terminal writes when TOSTOP is set.

   Input Processing and	Reading	Data
     A terminal	device associated with a terminal device file may operate in
     full-duplex mode, so that data may	arrive even while output is occurring.
     Each terminal device file has associated with it an input queue, into
     which incoming data is stored by the system before	being read by a
     process.  The system imposes a limit, {MAX_INPUT},	on the number of bytes
     that may be stored	in the input queue.  The behavior of the system	when
     this limit	is exceeded depends on the setting of the IMAXBEL flag in the
     termios c_iflag.  If this flag is set, the	terminal is sent an ASCII BEL
     character each time a character is	received while the input queue is
     full.  Otherwise, the input queue is flushed upon receiving the charac-
     ter.

     Two general kinds of input	processing are available, determined by
     whether the terminal device file is in canonical mode or noncanonical
     mode.  Additionally, input	characters are processed according to the
     c_iflag and c_lflag fields.  Such processing can include echoing, which
     in	general	means transmitting input characters immediately	back to	the
     terminal when they	are received from the terminal.	 This is useful	for
     terminals that can	operate	in full-duplex mode.

     The manner	in which data is provided to a process reading from a terminal
     device file is dependent on whether the terminal device file is in	canon-
     ical or noncanonical mode.

     Another dependency	is whether the O_NONBLOCK flag is set by open(2) or
     fcntl(2).	If the O_NONBLOCK flag is clear, then the read request is
     blocked until data	is available or	a signal has been received.  If	the
     O_NONBLOCK	flag is	set, then the read request is completed, without
     blocking, in one of three ways:

	   1.	If there is enough data	available to satisfy the entire
		request, and the read completes	successfully the number	of
		bytes read is returned.

	   2.	If there is not	enough data available to satisfy the entire
		request, and the read completes	successfully, having read as
		much data as possible, the number of bytes read	is returned.

	   3.	If there is no data available, the read	returns	-1, with errno
		set to EAGAIN.

     When data is available depends on whether the input processing mode is
     canonical or noncanonical.

   Canonical Mode Input	Processing
     In	canonical mode input processing, terminal input	is processed in	units
     of	lines.	A line is delimited by a newline `\n' character, an end-of-
     file (EOF)	character, or an end-of-line (EOL) character.  See the Special
     Characters	section	for more information on	EOF and	EOL.  This means that
     a read request will not return until an entire line has been typed, or a
     signal has	been received.	Also, no matter	how many bytes are requested
     in	the read call, at most one line	is returned.  It is not, however, nec-
     essary to read a whole line at once; any number of	bytes, even one, may
     be	requested in a read without losing information.

     {MAX_CANON} is a limit on the number of bytes in a	line.  The behavior of
     the system	when this limit	is exceeded is the same	as when	the input
     queue limit {MAX_INPUT}, is exceeded.

     Erase and kill processing occur when either of two	special	characters,
     the ERASE and KILL	characters (see	the Special Characters section), is
     received.	This processing	affects	data in	the input queue	that has not
     yet been delimited	by a newline NL, EOF, or EOL character.	 This un-
     delimited data makes up the current line.	The ERASE character deletes
     the last character	in the current line, if	there is any.  The KILL	char-
     acter deletes all data in the current line, if there is any.  The ERASE
     and KILL characters have no effect	if there is no data in the current
     line.  The	ERASE and KILL characters themselves are not placed in the
     input queue.

   Noncanonical	Mode Input Processing
     In	noncanonical mode input	processing, input bytes	are not	assembled into
     lines, and	erase and kill processing does not occur.  The values of the
     VMIN and VTIME members of the c_cc	array are used to determine how	to
     process the bytes received.

     MIN represents the	minimum	number of bytes	that should be received	when
     the read(2) function successfully returns.	 TIME is a timer of 0.1	second
     granularity that is used to time out bursty and short term	data transmis-
     sions.  If	MIN is greater than { MAX_INPUT}, the response to the request
     is	undefined.  The	four possible values for MIN and TIME and their	inter-
     actions are described below.

   Case	A: MIN > 0, TIME > 0
     In	this case TIME serves as an inter-byte timer and is activated after
     the first byte is received.  Since	it is an inter-byte timer, it is reset
     after a byte is received.	The interaction	between	MIN and	TIME is	as
     follows: as soon as one byte is received, the inter-byte timer is
     started.  If MIN bytes are	received before	the inter-byte timer expires
     (remember that the	timer is reset upon receipt of each byte), the read is
     satisfied.	 If the	timer expires before MIN bytes are received, the char-
     acters received to	that point are returned	to the user.  Note that	if
     TIME expires at least one byte is returned	because	the timer would	not
     have been enabled unless a	byte was received.  In this case (MIN >	0,
     TIME > 0) the read	blocks until the MIN and TIME mechanisms are activated
     by	the receipt of the first byte, or a signal is received.	 If data is in
     the buffer	at the time of the read(), the result is as if data had	been
     received immediately after	the read().

   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
     bytes are received	(i.e., the pending read	blocks until MIN bytes are
     received),	or a signal is received.  A program that uses this case	to
     read record-based terminal	I/O may	block indefinitely in the read opera-
     tion.

   Case	C: MIN = 0, TIME > 0
     In	this case, since MIN = 0, TIME no longer represents an inter-byte
     timer.  It	now serves as a	read timer that	is activated as	soon as	the
     read function is processed.  A read is satisfied as soon as a single byte
     is	received or the	read timer expires.  Note that in this case if the
     timer expires, no bytes are returned.  If the timer does not expire, the
     only way the read can be satisfied	is if a	byte is	received.  In this
     case the read will	not block indefinitely waiting for a byte; if no byte
     is	received within	TIME*0.1 seconds after the read	is initiated, the read
     returns a value of	zero, having read no data.  If data is in the buffer
     at	the time of the	read, the timer	is started as if data had been
     received immediately after	the read.

   Case	D: MIN = 0, TIME = 0
     The minimum of either the number of bytes requested or the	number of
     bytes currently available is returned without waiting for more bytes to
     be	input.	If no characters are available,	read returns a value of	zero,
     having read no data.

   Writing Data	and Output Processing
     When a process writes one or more bytes to	a terminal device file,	they
     are processed according to	the c_oflag field (see the Output Modes	sec-
     tion).  The implementation	may provide a buffering	mechanism; as such,
     when a call to write() completes, all of the bytes	written	have been
     scheduled for transmission	to the device, but the transmission will not
     necessarily have been completed.

   Special Characters
     Certain characters	have special functions on input	or output or both.
     These functions are summarized as follows:

     INTR    Special character on input	and is recognized if the ISIG flag
	     (see the Local Modes section) is enabled.	Generates a SIGINT
	     signal which is sent to all processes in the foreground process
	     group for which the terminal is the controlling terminal.	If
	     ISIG is set, the INTR character is	discarded when processed.

     QUIT    Special character on input	and is recognized if the ISIG flag is
	     enabled.  Generates a SIGQUIT signal which	is sent	to all pro-
	     cesses in the foreground process group for	which the terminal is
	     the controlling terminal.	If ISIG	is set,	the QUIT character is
	     discarded when processed.

     ERASE   Special character on input	and is recognized if the ICANON	flag
	     is	set.  Erases the last character	in the current line; see
	     Canonical Mode Input Processing.  It does not erase beyond	the
	     start of a	line, as delimited by an NL, EOF, or EOL character.
	     If	ICANON is set, the ERASE character is discarded	when pro-
	     cessed.

     KILL    Special character on input	and is recognized if the ICANON	flag
	     is	set.  Deletes the entire line, as delimited by a NL, EOF, or
	     EOL character.  If	ICANON is set, the KILL	character is discarded
	     when processed.

     EOF     Special character on input	and is recognized if the ICANON	flag
	     is	set.  When received, all the bytes waiting to be read are
	     immediately passed	to the process,	without	waiting	for a newline,
	     and the EOF is discarded.	Thus, if there are no bytes waiting
	     (that is, the EOF occurred	at the beginning of a line), a byte
	     count of zero is returned from the	read(),	representing an	end-
	     of-file indication.  If ICANON is set, the	EOF character is dis-
	     carded when processed.

     NL	     Special character on input	and is recognized if the ICANON	flag
	     is	set.  It is the	line delimiter `\n'.

     EOL     Special character on input	and is recognized if the ICANON	flag
	     is	set.  Is an additional line delimiter, like NL.

     SUSP    If	the ISIG flag is enabled, receipt of the SUSP character	causes
	     a SIGTSTP signal to be sent to all	processes in the foreground
	     process group for which the terminal is the controlling terminal,
	     and the SUSP character is discarded when processed.

     STOP    Special character on both input and output	and is recognized if
	     the IXON (output control) or IXOFF	(input control)	flag is	set.
	     Can be used to temporarily	suspend	output.	 It is useful with
	     fast terminals to prevent output from disappearing	before it can
	     be	read.  If IXON is set, the STOP	character is discarded when
	     processed.

     START   Special character on both input and output	and is recognized if
	     the IXON (output control) or IXOFF	(input control)	flag is	set.
	     Can be used to resume output that has been	suspended by a STOP
	     character.	 If IXON is set, the START character is	discarded when
	     processed.

     CR	     Special character on input	and is recognized if the ICANON	flag
	     is	set; it	is the `\r', as	denoted	in the C Standard {2}.	When
	     ICANON and	ICRNL are set and IGNCR	is not set, this character is
	     translated	into a NL, and has the same effect as a	NL character.

     The following special characters are extensions defined by	this system
     and are not a part	of IEEE	Std 1003.1 (``POSIX.1'') termios.

     EOL2    Secondary EOL character.  Same function as	EOL.

     WERASE  Special character on input	and is recognized if the ICANON	flag
	     is	set.  Erases the last word in the current line according to
	     one of two	algorithms.  If	the ALTWERASE flag is not set, first
	     any preceding whitespace is erased, and then the maximal sequence
	     of	non-whitespace characters.  If ALTWERASE is set, first any
	     preceding whitespace is erased, and then the maximal sequence of
	     alphabetic/underscores or non alphabetic/underscores.  As a spe-
	     cial case in this second algorithm, the first previous non-white-
	     space character is	skipped	in determining whether the preceding
	     word is a sequence	of alphabetic/underscores.  This sounds	con-
	     fusing but	turns out to be	quite practical.

     REPRINT
	     Special character on input	and is recognized if the ICANON	flag
	     is	set.  Causes the current input edit line to be retyped.

     DSUSP   Has similar actions to the	SUSP character,	except that the
	     SIGTSTP signal is delivered when one of the processes in the
	     foreground	process	group issues a read() to the controlling ter-
	     minal.

     LNEXT   Special character on input	and is recognized if the IEXTEN	flag
	     is	set.  Receipt of this character	causes the next	character to
	     be	taken literally.

     DISCARD
	     Special character on input	and is recognized if the IEXTEN	flag
	     is	set.  Receipt of this character	toggles	the flushing of	termi-
	     nal output.

     STATUS  Special character on input	and is recognized if the ICANON	flag
	     is	set.  Receipt of this character	causes a SIGINFO signal	to be
	     sent to the foreground process group of the terminal.  Also, if
	     the NOKERNINFO flag is not	set, it	causes the kernel to write a
	     status message to the terminal that displays the current load
	     average, the name of the command in the foreground, its process
	     ID, the symbolic wait channel, the	number of user and system sec-
	     onds used,	the percentage of cpu the process is getting, and the
	     resident set size of the process.

     The NL and	CR characters cannot be	changed.  The values for all the
     remaining characters can be set and are described later in	the document
     under Special Control Characters.

     Special character functions associated with changeable special control
     characters	can be disabled	individually by	setting	their value to
     {_POSIX_VDISABLE};	see Special Control Characters.

     If	two or more special characters have the	same value, the	function per-
     formed when that character	is received is undefined.

   Modem Disconnect
     If	a modem	disconnect is detected by the terminal interface for a con-
     trolling terminal,	and if CLOCAL is not set in the	c_cflag	field for the
     terminal, the SIGHUP signal is sent to the	controlling process associated
     with the terminal.	 Unless	other arrangements have	been made, this	causes
     the controlling process to	terminate.  Any	subsequent call	to the read()
     function returns the value	zero, indicating end of	file.  Thus, processes
     that read a terminal file and test	for end-of-file	can terminate appro-
     priately after a disconnect.  Any subsequent write() to the terminal
     device returns -1,	with errno set to EIO, until the device	is closed.

General	Terminal Interface
   Closing a Terminal Device File
     The last process to close a terminal device file causes any output	to be
     sent to the device	and any	input to be discarded.	Then, if HUPCL is set
     in	the control modes, and the communications port supports	a disconnect
     function, the terminal device performs a disconnect.

   Parameters That Can Be Set
     Routines that need	to control certain terminal I/O	characteristics	do so
     by	using the termios structure as defined in the header <termios.h>.
     This structure contains minimally four scalar elements of bit flags and
     one array of special characters.  The scalar flag elements	are named:
     c_iflag, c_oflag, c_cflag,	and c_lflag.  The character array is named
     c_cc, and its maximum index is NCCS.

   Input Modes
     Values of the c_iflag field describe the basic terminal input control,
     and are composed of following masks:

	   IGNBRK   /* ignore BREAK condition */
	   BRKINT   /* map BREAK to SIGINTR */
	   IGNPAR   /* ignore (discard)	parity errors */
	   PARMRK   /* mark parity and framing errors */
	   INPCK    /* enable checking of parity errors	*/
	   ISTRIP   /* strip 8th bit off chars */
	   INLCR    /* map NL into CR */
	   IGNCR    /* ignore CR */
	   ICRNL    /* map CR to NL (ala CRMOD)	*/
	   IXON	    /* enable output flow control */
	   IXOFF    /* enable input flow control */
	   IXANY    /* any char	will restart after stop	*/
	   IMAXBEL  /* ring bell on input queue	full */

     In	the context of asynchronous serial data	transmission, a	break condi-
     tion is defined as	a sequence of zero-valued bits that continues for more
     than the time to send one byte.  The entire sequence of zero-valued bits
     is	interpreted as a single	break condition, even if it continues for a
     time equivalent to	more than one byte.  In	contexts other than asynchro-
     nous serial data transmission the definition of a break condition is
     implementation defined.

     If	IGNBRK is set, a break condition 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 flushes 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 `\0',	or if PARMRK
     is	set, as	`\377',	`\0', `\0'.

     If	IGNPAR is set, a byte with a framing or	parity error (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-charac-
     ter sequence `\377', `\0',	X, where `\377', `\0' is a two-character flag
     preceding each sequence and X is the data of the character	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 PARMRK nor	IGNPAR is set, a framing or parity error (other	than
     break) is given to	the application	as a single character `\0'.

     If	INPCK is set, input parity checking is enabled.	 If INPCK is not set,
     input parity checking is disabled,	allowing 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 (see Control Modes).  If parity detection is enabled but
     input parity checking is disabled,	the hardware to	which the terminal is
     connected recognizes the parity bit, but the terminal special file	does
     not check whether this bit	is set correctly or not.

     If	ISTRIP is set, valid input bytes 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 charac-
     ter.  If IGNCR is set, a received CR character is ignored (not read).  If
     IGNCR is not set and ICRNL	is set,	a received CR character	is translated
     into a NL character.

     If	IXON is	set, start/stop	output control is enabled.  A received STOP
     character suspends	output and a received START character restarts output.
     If	IXANY is also set, then	any character may restart output.  When	IXON
     is	set, START and STOP characters are not read, but merely	perform	flow
     control functions.	 When IXON is not set, the START and STOP characters
     are read.

     If	IXOFF is set, start/stop input control is enabled.  The	system shall
     transmit one or more STOP characters, which are intended to cause the
     terminal device to	stop transmitting data,	as needed to prevent the input
     queue from	overflowing and	causing	the undefined behavior described in
     Input Processing and Reading Data,	and shall transmit one or more START
     characters, which are intended to cause the terminal device to resume
     transmitting data,	as soon	as the device can continue transmitting	data
     without risk of overflowing the input queue.  The precise conditions
     under which STOP and START	characters are transmitted are implementation
     defined.

     If	IMAXBEL	is set and the input queue is full, subsequent input shall
     cause an ASCII BEL	character to be	transmitted to the output queue.

     The initial input control value after open() is implementation defined.

   Output Modes
     Values of the c_oflag field describe the basic terminal output control,
     and are composed of the following masks:

	   OPOST   /* enable following output processing */
	   ONLCR   /* map NL to	CR-NL (ala CRMOD) */
	   OCRNL   /* map CR to	NL */
	   OXTABS  /* expand tabs to spaces */
	   ONOEOT  /* discard EOT's `^D' on output) */
	   ONOCR   /* do not transmit CRs on column 0 */
	   ONLRET  /* on the terminal NL performs the CR function */

     If	OPOST is set, the remaining flag masks are interpreted as follows;
     otherwise characters are transmitted without change.

     If	ONLCR is set, newlines are translated to carriage return, linefeeds.

     If	OCRNL is set, carriage returns are translated to newlines.

     If	OXTABS is set, tabs are	expanded to the	appropriate number of spaces
     (assuming 8 column	tab stops).

     If	ONOEOT is set, ASCII EOT's are discarded on output.

     If	ONOCR is set, no CR character is transmitted when at column 0 (first
     position).

     If	ONLRET is set, the NL character	is assumed to do the carriage-return
     function; the column pointer will be set to 0.

   Control Modes
     Values of the c_cflag field describe the basic terminal hardware control,
     and are composed of the following masks.  Not all values specified	are
     supported by all hardware.

	   CSIZE       /* character size mask */
	   CS5	       /* 5 bits (pseudo) */
	   CS6	       /* 6 bits */
	   CS7	       /* 7 bits */
	   CS8	       /* 8 bits */
	   CSTOPB      /* send 2 stop bits */
	   CREAD       /* enable receiver */
	   PARENB      /* parity enable	*/
	   PARODD      /* odd parity, else even	*/
	   HUPCL       /* hang up on last close	*/
	   CLOCAL      /* ignore modem status lines */
	   CCTS_OFLOW  /* CTS flow control of output */
	   CRTSCTS     /* same as CCTS_OFLOW */
	   CRTS_IFLOW  /* RTS flow control of input */
	   MDMBUF      /* flow control output via Carrier */

     The CSIZE bits specify the	byte size in bits for both transmission	and
     reception.	 The c_cflag is	masked with CSIZE and compared with the	values
     CS5, CS6, CS7, or CS8.  This size does not	include	the parity bit,	if
     any.  If CSTOPB is	set, two stop bits are used, otherwise one stop	bit.
     For example, at 110 baud, two stop	bits are normally used.

     If	CREAD is set, the receiver is enabled.	Otherwise, no character	is
     received.	Not all	hardware supports this bit.  In	fact, this flag	is
     pretty silly and if it were not part of the termios specification it
     would be omitted.

     If	PARENB is set, parity generation and detection are enabled and a par-
     ity bit is	added to each character.  If parity is enabled,	PARODD speci-
     fies odd parity if	set, otherwise even parity is used.

     If	HUPCL is set, the modem	control	lines for the port are lowered when
     the last process with the port open closes	the port or the	process	termi-
     nates.  The modem connection is broken.

     If	CLOCAL is set, a connection does not depend on the state of the	modem
     status lines.  If CLOCAL is clear,	the modem status lines are monitored.

     Under normal circumstances, a call	to the open() function waits for the
     modem connection to complete.  However, if	the O_NONBLOCK flag is set or
     if	CLOCAL has been	set, the open()	function returns immediately without
     waiting for the connection.

     The CCTS_OFLOW (CRTSCTS) flag is currently	unused.

     If	MDMBUF is set then output flow control is controlled by	the state of
     Carrier Detect.

     If	the object for which the control modes are set is not an asynchronous
     serial connection,	some of	the modes may be ignored; for example, if an
     attempt is	made to	set the	baud rate on a network connection to a termi-
     nal on another host, the baud rate	may or may not be set on the connec-
     tion between that terminal	and the	machine	it is directly connected to.

   Local Modes
     Values of the c_lflag field describe the control of various functions,
     and are composed of the following masks.

	   ECHOKE      /* visual erase for line	kill */
	   ECHOE       /* visually erase chars */
	   ECHO	       /* enable echoing */
	   ECHONL      /* echo NL even if ECHO is off */
	   ECHOPRT     /* visual erase mode for	hardcopy */
	   ECHOCTL     /* echo control chars as	^(Char)	*/
	   ISIG	       /* enable signals INTR, QUIT, [D]SUSP */
	   ICANON      /* canonicalize input lines */
	   ALTWERASE   /* use alternate	WERASE algorithm */
	   IEXTEN      /* enable DISCARD and LNEXT */
	   EXTPROC     /* external processing */
	   TOSTOP      /* stop background jobs from output */
	   FLUSHO      /* output being flushed (state) */
	   NOKERNINFO  /* no kernel output from	VSTATUS	*/
	   PENDIN      /* XXX retype pending input (state) */
	   NOFLSH      /* don't	flush after interrupt */

     If	ECHO is	set, input characters are echoed back to the terminal.	If
     ECHO is not set, input characters are not echoed.

     If	ECHOE and ICANON are set, the ERASE character causes the terminal to
     erase the last character in the current line from the display, if possi-
     ble.  If there is no character to erase, an implementation	may echo an
     indication	that this was the case or do nothing.

     If	ECHOK and ICANON are set, the KILL character causes the	current	line
     to	be discarded and the system echoes the `\n' character after the	KILL
     character.

     If	ECHOKE and ICANON are set, the KILL character causes the current line
     to	be discarded and the system causes the terminal	to erase the line from
     the display.

     If	ECHOPRT	and ICANON are set, the	system assumes that the	display	is a
     printing device and prints	a backslash and	the erased characters when
     processing	ERASE characters, followed by a	forward	slash.

     If	ECHOCTL	is set,	the system echoes control characters in	a visible
     fashion using a caret followed by the control character.

     If	ALTWERASE is set, the system uses an alternative algorithm for deter-
     mining what constitutes a word when processing WERASE characters (see
     WERASE).

     If	ECHONL and ICANON are set, the `\n' character echoes even if ECHO is
     not 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, and EOL, as described in Canonical Mode Input
     Processing.

     If	ICANON is not set, read	requests are satisfied directly	from the input
     queue.  A read is not satisfied until at least MIN	bytes have been
     received or the timeout value TIME	expired	between	bytes.	The time value
     represents	tenths of seconds.  See	Noncanonical Mode Input	Processing for
     more details.

     If	ISIG is	set, each input	character is checked against the special con-
     trol characters INTR, QUIT, and SUSP (job control only).  If an input
     character matches one of these control characters,	the function associ-
     ated 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	IEXTEN is set, implementation-defined functions	are recognized from
     the input data.  How IEXTEN being set interacts with ICANON, ISIG,	IXON,
     or	IXOFF is implementation	defined.  If IEXTEN is not set,	then implemen-
     tation-defined functions are not recognized, and the corresponding	input
     characters	are not	processed as described for ICANON, ISIG, IXON, and
     IXOFF.

     If	NOFLSH is set, the normal flush	of the input and output	queues associ-
     ated with the INTR, QUIT, and SUSP	characters are not be done.

     If	TOSTOP is set, the signal SIGTTOU is sent to the process group of a
     process that tries	to write to its	controlling terminal if	it is not in
     the foreground process group for that terminal.  This signal, by default,
     stops the members of the process group.  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 pro-
     duce output and the SIGTTOU signal	is not sent.

     If	NOKERNINFO is set, the kernel does not produce a status	message	when
     processing	STATUS characters (see STATUS).

   Special Control Characters
     The special control characters values are defined by the array c_cc.
     This table	lists the array	index, the corresponding special character,
     and the system default value.  For	an accurate list of the	system
     defaults, consult the header file <ttydefaults.h>.

	   Index Name	 Special Character    Default Value
	   VEOF		 EOF		      ^D
	   VEOL		 EOL		      _POSIX_VDISABLE
	   VEOL2	 EOL2		      _POSIX_VDISABLE
	   VERASE	 ERASE		      ^? `\177'
	   VWERASE	 WERASE		      ^W
	   VKILL	 KILL		      ^U
	   VREPRINT	 REPRINT	      ^R
	   VINTR	 INTR		      ^C
	   VQUIT	 QUIT		      ^\\ `\34'
	   VSUSP	 SUSP		      ^Z
	   VDSUSP	 DSUSP		      ^Y
	   VSTART	 START		      ^Q
	   VSTOP	 STOP		      ^S
	   VLNEXT	 LNEXT		      ^V
	   VDISCARD	 DISCARD	      ^O
	   VMIN		 ---		      1
	   VTIME	 ---		      0
	   VSTATUS	 STATUS		      ^T

     If	the value of one of the	changeable special control characters (see
     Special Characters) is {_POSIX_VDISABLE}, that function is	disabled; that
     is, no input data is recognized as	the disabled special character.	 If
     ICANON is not set,	the value of {_POSIX_VDISABLE} has no special meaning
     for the VMIN and VTIME entries of the c_cc	array.

     The initial values	of the flags and control characters after open() is
     set according to the values in the	header <sys/ttydefaults.h>.

FreeBSD	9.3			April 19, 1994			   FreeBSD 9.3

NAME | SYNOPSIS | DESCRIPTION | General Terminal Interface

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