bionic (4) tty.4freebsd.gz

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NAME

     tty — general terminal interface

SYNOPSIS

     #include <sys/ioctl.h>

DESCRIPTION

     This section describes the interface to the terminal drivers in the system.

   Terminal Special Files
     Each hardware terminal port on the system usually has a terminal special device file associated with it in
     the directory ``/dev/'' (for example, ``/dev/tty03'').  When a user logs into the system on one of these
     hardware terminal ports, the system has already opened the associated device and prepared the line for
     normal interactive use (see getty(8).)  There is also a special case of a terminal file that connects not
     to a hardware terminal port, but to another program on the other side.  These special terminal devices are
     called ptys and provide the mechanism necessary to give users the same interface to the system when logging
     in over a network (using rlogin(1), or telnet(1) for example).  Even in these cases the details of how the
     terminal file was opened and set up is already handled by special software in the system.  Thus, users do
     not normally need to worry about the details of how these lines are opened or used.  Also, these lines are
     often used for dialing out of a system (through an out-calling modem), but again the system provides
     programs that hide the details of accessing these terminal special files (see tip(1)).

     When an interactive user logs in, the system prepares the line to behave in a certain way (called a line
     discipline), the particular details of which is described in stty(1) at the command level, and in
     termios(4) at the programming level.  A user may be concerned with changing settings associated with his
     particular login terminal and should refer to the preceding man pages for the common cases.  The remainder
     of this man page is concerned with describing details of using and controlling terminal devices at a low
     level, such as that possibly required by a program wishing to provide features similar to those provided by
     the system.

   Terminal File Operations
     All of the following operations are invoked using the ioctl(2) system call.  Refer to that man page for a
     description of the request and argp parameters.  In addition to the ioctl requests defined here, the
     specific line discipline in effect will define other requests specific to it (actually termios(4) defines
     them as function calls, not ioctl requests.)  The following section lists the available ioctl requests.
     The name of the request, a description of its purpose, and the typed argp parameter (if any) are listed.
     For example, the first entry says

           TIOCSPGRP int *tpgrp

     and would be called on the terminal associated with file descriptor zero by the following code fragment:

             int pgrp;

             pgrp = getpgrp();
             ioctl(0, TIOCSPGRP, &pgrp);

   Terminal File Request Descriptions
     TIOCSETD int *ldisc
                 This call is obsolete but left for compatibility.  Before FreeBSD 8.0, it would change to the
                 new line discipline pointed to by ldisc.

     TIOCGETD int *ldisc
                 Return the current line discipline in the integer pointed to by ldisc.

     TIOCSBRK void
                 Set the terminal hardware into BREAK condition.

     TIOCCBRK void
                 Clear the terminal hardware BREAK condition.

     TIOCSDTR void
                 Assert data terminal ready (DTR).

     TIOCCDTR void
                 Clear data terminal ready (DTR).

     TIOCGPGRP int *tpgrp
                 Return the current process group with which the terminal is associated in the integer pointed
                 to by tpgrp.  This is the underlying call that implements the termios(4) tcgetattr() call.

     TIOCSPGRP int *tpgrp
                 Associate the terminal with the process group (as an integer) pointed to by tpgrp.  This is the
                 underlying call that implements the termios(4) tcsetattr() call.

     TIOCGETA struct termios *term
                 Place the current value of the termios state associated with the device in the termios
                 structure pointed to by term.  This is the underlying call that implements the termios(4)
                 tcgetattr() call.

     TIOCSETA struct termios *term
                 Set the termios state associated with the device immediately.  This is the underlying call that
                 implements the termios(4) tcsetattr() call with the TCSANOW option.

     TIOCSETAW struct termios *term
                 First wait for any output to complete, then set the termios state associated with the device.
                 This is the underlying call that implements the termios(4) tcsetattr() call with the TCSADRAIN
                 option.

     TIOCSETAF struct termios *term
                 First wait for any output to complete, clear any pending input, then set the termios state
                 associated with the device.  This is the underlying call that implements the termios(4)
                 tcsetattr() call with the TCSAFLUSH option.

     TIOCOUTQ int *num
                 Place the current number of characters in the output queue in the integer pointed to by num.

     TIOCSTI char *cp
                 Simulate typed input.  Pretend as if the terminal received the character pointed to by cp.

     TIOCNOTTY void
                 This call is obsolete but left for compatibility.  In the past, when a process that did not
                 have a controlling terminal (see The Controlling Terminal in termios(4)) first opened a
                 terminal device, it acquired that terminal as its controlling terminal.  For some programs this
                 was a hazard as they did not want a controlling terminal in the first place, and this provided
                 a mechanism to disassociate the controlling terminal from the calling process.  It must be
                 called by opening the file /dev/tty and calling TIOCNOTTY on that file descriptor.

                 The current system does not allocate a controlling terminal to a process on an open() call:
                 there is a specific ioctl called TIOCSCTTY to make a terminal the controlling terminal.  In
                 addition, a program can fork() and call the setsid() system call which will place the process
                 into its own session - which has the effect of disassociating it from the controlling terminal.
                 This is the new and preferred method for programs to lose their controlling terminal.

     TIOCSTOP void
                 Stop output on the terminal (like typing ^S at the keyboard).

     TIOCSTART void
                 Start output on the terminal (like typing ^Q at the keyboard).

     TIOCSCTTY void
                 Make the terminal the controlling terminal for the process (the process must not currently have
                 a controlling terminal).

     TIOCDRAIN void
                 Wait until all output is drained, or until the drain wait timeout expires.

     TIOCGDRAINWAIT int *timeout
                 Return the current drain wait timeout in seconds.

     TIOCSDRAINWAIT int *timeout
                 Set the drain wait timeout in seconds.  A value of zero disables timeouts.  The default drain
                 wait timeout is controlled by the tunable sysctl(8) OID kern.tty_drainwait.

     TIOCEXCL void
                 Set exclusive use on the terminal.  No further opens are permitted except by root.  Of course,
                 this means that programs that are run by root (or setuid) will not obey the exclusive setting -
                 which limits the usefulness of this feature.

     TIOCNXCL void
                 Clear exclusive use of the terminal.  Further opens are permitted.

     TIOCFLUSH int *what
                 If the value of the int pointed to by what contains the FREAD bit as defined in <sys/file.h>,
                 then all characters in the input queue are cleared.  If it contains the FWRITE bit, then all
                 characters in the output queue are cleared.  If the value of the integer is zero, then it
                 behaves as if both the FREAD and FWRITE bits were set (i.e., clears both queues).

     TIOCGWINSZ struct winsize *ws
                 Put the window size information associated with the terminal in the winsize structure pointed
                 to by ws.  The window size structure contains the number of rows and columns (and pixels if
                 appropriate) of the devices attached to the terminal.  It is set by user software and is the
                 means by which most full-screen oriented programs determine the screen size.  The winsize
                 structure is defined in <sys/ioctl.h>.

     TIOCSWINSZ struct winsize *ws
                 Set the window size associated with the terminal to be the value in the winsize structure
                 pointed to by ws (see above).

     TIOCCONS int *on
                 If on points to a non-zero integer, redirect kernel console output (kernel printf's) to this
                 terminal.  If on points to a zero integer, redirect kernel console output back to the normal
                 console.  This is usually used on workstations to redirect kernel messages to a particular
                 window.

     TIOCMSET int *state
                 The integer pointed to by state contains bits that correspond to modem state.  Following is a
                 list of defined variables and the modem state they represent:

                 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_CD   Carrier Detect (synonym).
                 TIOCM_RNG  Ring Indication.
                 TIOCM_RI   Ring Indication (synonym).
                 TIOCM_DSR  Data Set Ready.

                 This call sets the terminal modem state to that represented by state.  Not all terminals may
                 support this.

     TIOCMGET int *state
                 Return the current state of the terminal modem lines as represented above in the integer
                 pointed to by state.

     TIOCMBIS int *state
                 The bits in the integer pointed to by state represent modem state as described above, however
                 the state is OR-ed in with the current state.

     TIOCMBIC int *state
                 The bits in the integer pointed to by state represent modem state as described above, however
                 each bit which is on in state is cleared in the terminal.

IMPLEMENTATION NOTES

     The total number of input and output bytes through all terminal devices are available via the kern.tk_nin
     and kern.tk_nout read-only sysctl(8) variables.

SEE ALSO

     stty(1), ioctl(2), ng_tty(4), pty(4), termios(4), getty(8)