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AIX Version 4 Files Reference

lft Special File


Provides character-based terminal support for the local graphics display and keyboard.


The lft file is the application interface to the "Low Function Terminal (LFT) Subsystem". It provides support for a VT100-like terminal which is associated with the local graphics display and keyboard. It provides only character operations and is designed to be used during system installation, startup, shutdown, and stand-alone diagnostics.

The terminal supports a single logical screen size of 80 characters and 25 lines and a single color. Dynamic reconfiguration is not supported, configuration changes take effect at the next system startup. In the cases when multiple fonts may be used to achieve the 80x25 screen size, the user may set which font is used with the next system restart. See "LFT User Commands" for details of the available commands.

When multiple displays are available, the LFT Subsystem initially uses the default display. The user may change to another display and set the default display. See "LFT User Commands" for details of the available commands.

Usage Considerations

The LFT device driver supports the lft special file. The device driver is a streams based driver. It handles only the system attached keyboard and graphics displays.

Sharing Displays with Graphic Subsystem

Certain LFT ioctl commands allow graphics subsystems, such as AIXwindows, to obtain exclusive use of the displays, a right initially held by the LFT. However, this is done by the Rendering Context Manager (RCM) on behalf of the graphics subsystem. See "Rendering Context Manager" for details of the procedure for becoming a graphics process.

Subroutine Support

The lft special file supports the open, close, read, write, and ioctl subroutines.

ioctl system call

The functions performed by the ioctl commands fall into three categories:

Sharing devices
IOCINFO The IOCINFO ioctl operation is defined for all device drivers that use the ioctl subroutine. The IOCINFO operation returns a devinfo structure, which is defined in the devinfo.h file.
LFT_SET_DEFLT_DISP Sets the default display.
LFT_ACQ_DISP Acquire display for exclusive use.
LFT_REL_DISP Release display.
LFT_DIAG_OWNER Acquire display for diagnostics.
Query information about configured displays and keyboard devices
LFT_QUERY_LFT Query common LFT information.
LFT_QUERY_DISP Query display information.
Compatibility with the common tty ioctl commands










Implementation Specifics

The lft special file is part of Base Operating System (BOS) Runtime.

Related Information

Low Function Terminal (LFT) Subsystem Overview in AIX Version 4.3 Kernel Extensions and Device Support Programming Concepts.

rcm and kbd Special Files.

Special Files Overview.

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