Unix/Linux Go Back    


OpenDarwin 7.2.1 - man page for termios (opendarwin section 4)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


TERMIOS(4)			   BSD 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 com-
     munication 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(2) or
     rlogind(2), and become an application'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 arbitrating which process group has access to the single controlling
     terminal.	The grouping at a higher layer into sessions is to restrict the job control
     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 controlling terminal; all processes spawned from that login shell are in the
     same session, and inherit the controlling terminal.  A job control shell operating interac-
     tively (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 particular job, that job is said to be in
     the "foreground".	When the process group of the terminal is different than the process
     group of a job (but is still the controlling terminal), that job is said to be in the "back-
     ground".  Normally the shell reads a command and starts the job that implements that com-
     mand.  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 com-
     plete, 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 doesn't
     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 gener-
     ates the terminal stop signal (SIGTSTP) and has the affect 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 dif-
     ferent process group, yet is in the same session.	Conceptually it means a process group
     that doesn't 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 controlling 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 terminal 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 disassociated 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 terminal, read operations
     are allowed.  Any attempts by a process in a background process group to read from its con-
     trolling terminal causes a SIGTTIN signal to be sent to the process's group unless one of
     the following special cases apply:  If the reading process is ignoring or blocking 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 terminal, write opera-
     tions are allowed.  Attempts by a process in a background process group to write to its con-
     trolling 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
     returns -1 with errno set to EIO and no signal is sent.

     Certain calls that set terminal parameters are treated in the same fashion as write, except
     that TOSTOP is ignored; that is, the effect is identical 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 associ-
     ated 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 character.

     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 canonical or noncanonical mode.

     Another dependency is whether the O_NONBLOCK flag is set by open() or fcntl().  If the
     O_NONBLOCK flag is clear, then the read request is blocked until data is available or a sig-
     nal 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 non-
     canonical.

   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, necessary 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 character 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 MIN and TIME 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 function
     successfully returns.  TIME is a timer of 0.1 second granularity that is used to time out
     bursty and short term data transmissions.	If MIN is greater than { MAX_INPUT}, the response
     to the request is undefined.  The four possible values for MIN and TIME and their interac-
     tions 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 characters 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 sig-
     nificant.	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 operation.

   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 sat-
     isfied 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 imme-
     diately after the read.

   Case D: MIN = 0, TIME = 0
     The minimum of either the number of bytes requested or the number of bytes currently avail-
     able is returned without waiting for more bytes to be input.  If no characters are avail-
     able, 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 section).  The implementation may pro-
     vide 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 processes 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 processed.

     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 discarded 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 addi-
	     tional 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 dis-
	     carded 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
     1003.1 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 special case in this second algorithm, the first pre-
	     vious non-whitespace character is skipped in determining whether the preceding word
	     is a sequence of alphabetic/undercores.  This sounds confusing 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 deliv-
	     ered when one of the processes in the foreground process group issues a read() to
	     the controlling terminal.

     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 terminal 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 seconds 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 performed when that
     character is received is undefined.

   Modem Disconnect
     If a modem disconnect is detected by the terminal interface for a controlling 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() func-
     tion returns the value zero, indicating end of file.  Thus, processes that read a terminal
     file and test for end-of-file can terminate appropriately after a disconnect.  Any subse-
     quent 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 communi-
     cations 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 ele-
     ments 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 */
	   IUCLC    /* translate upper case to lower case */

     In the context of asynchronous serial data transmission, a break condition 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 asynchronous
     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 control-
     ling 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 con-
     dition 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-character sequence '\377', '\0', X, where
     '\377', '\0' is a two-character flag preceding each sequence and X is the data of the char-
     acter 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 check-
     ing 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 detec-
     tion 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 character.  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 char-
     acter 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 charac-
     ters, 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 implementa-
     tion 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.

     If IUCLC is set, characters will be translated from upper to lower case on input.

     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) */
	   OXTABS  /* expand tabs to spaces */
	   ONOEOT  /* discard EOT's '^D' on output) */
	   OCRNL   /* map CR to NL */
	   OLCUC   /* translate lower case to upper case */
	   ONOCR   /* No CR output at column 0 */
	   ONLRET  /* NL performs 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 OXTABS is set, tabs are expanded to the appropriate number of spaces (assuming 8 column
     tab stops).

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

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

     If OLCUC is set, lower case is translated to upper case on output.

     If ONOCR is set, no CR character is output when at column 0.

     If ONLRET is set, NL also performs CR on output, and reset current column 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, other-
     wise 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 parity bit is added to
     each character.  If parity is enabled, PARODD specifies 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 terminates.  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 terminal on another host, the baud rate may or may not be set on
     the connection 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 char-
     acter in the current line from the display, if possible.  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 determining what consti-
     tutes 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 control characters INTR,
     QUIT, and SUSP (job control only).  If an input character matches one of these control char-
     acters, 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 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 implementation-defined functions are not recognized, and the corre-
     sponding 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 associated with the INTR,
     QUIT, and SUSP characters are not be done.

     If ICANON is set, an upper case character is preserved on input if prefixed by a \ charac-
     ter.  In addition, this prefix is added to upper case characters on output.

     In addition, the following special character translations are in effect:

	   for:    use:
	   `	   \'
	   |	   \!
	   ~	   \^
	   {	   \(
	   }	   \)
	   \	   \\

     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 ter-
     minal.  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 produce 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>.

SEE ALSO
     tcgetattr(3), tcsetattr(3)

4th Berkeley Distribution		  April 19, 1994		4th Berkeley Distribution
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 06:57 PM.