5.2. Accessibility

Some users may need specific support because of e.g. some visual impairment. USB braille displays are detected automatically (not serial displays connected via a serial-to-USB converter), but most other accessibility features have to be enabled manually. Some boot parameters can be appended to enable accessibility features. Note that on most architectures the boot loader interprets your keyboard as a QWERTY keyboard.

5.2.1. Installer front-end

The Debian installer supports several front-ends for asking questions, with varying convenience for accessibility: notably, text uses plain text while newt uses text-based dialog boxes. The choice can be made at the boot prompt, see the documentation for DEBIAN_FRONTEND in Section 5.3.2, “Debian Installer Parameters”.

5.2.2. USB Braille Displays

USB braille displays should be automatically detected. A textual version of the installer will then be automatically selected, and support for the braille display will be automatically installed on the target system. You can thus just press Enter at the boot menu. Once brltty is started, you can choose a braille table by entering the preference menu. Documentation on key bindings for braille devices is available on the brltty website.

5.2.3. Serial Braille Displays

Serial braille displays cannot safely be automatically detected (since that may damage some of them). You thus need to append the brltty=driver,port boot parameter to tell brltty which driver and port it should use. driver should be replaced by the two-letter driver code for your terminal (see the BRLTTY manual). port should be replaced by the name of the serial port the display is connected to, ttyS0 is the default, ttyUSB0 can be typically used when using a serial-to-USB converter. A third parameter can be provided, to choose the name of the braille table to be used (see the BRLTTY manual); the English table is the default. Note that the table can be changed later by entering the preference menu. A fourth parameter can be provided to pass parameters to the braille driver, such as protocol=foo which is needed for some rare models. Documentation on key bindings for braille devices is available on the brltty website.

5.2.4. Board Devices

Some accessibility devices are actual boards that are plugged inside the machine and that read text directly from the video memory. To get them to work framebuffer support must be disabled by using the fb=false boot parameter. This will however reduce the number of available languages.

5.2.5. High-Contrast Theme

For users with low vision, the installer can use a high-contrast color theme that makes it more readable. To enable it, you can use the Accessible high contrast entry from the boot screen with the c shortcut, or append the theme=dark boot parameter.

5.2.6. Zoom

For users with low vision, the graphical installer has a very basic zoom support: the Control++ and Control+- shortcuts increase and decrease the font size.

5.2.7. Expert install, rescue mode, automated install

Expert, Rescue, and Automated installation choices are also available with accessibility support. To access them, one has to first enter the Advanced options submenu from the boot menu by typing a. When using a BIOS system (the boot menu will have beeped only once), this has to be followed by Enter ; for UEFI systems (the boot menu will have beeped twice) that must not be done. Then, to enable speech synthesis, s can optionally be pressed (followed again by Enter on BIOS systems but not on UEFI systems). From there, various shortcuts can be used: x for expert installation, r for rescue mode, or a for automated installation. Again these need to be followed by Enter when using a BIOS system.

The automated install choice allows to install Debian completely automatically by using preseeding, whose source can be entered after accessibility features get started. Preseeding itself is documented in Appendix B, Automating the installation using preseeding.

5.2.8. Accessibility of the installed system

Documentation on accessibility of the installed system is available on the Debian Accessibility wiki page.