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. On machines that support it, the boot menu emits beeps when it is ready to receive keystrokes. It beeps once on BIOS systems, and beeps twice on UEFI systems. Some boot parameters can then be appended to enable accessibility features (see also Del 5.1.7, «The Boot Screen»). Note that on most architectures the boot loader interprets your keyboard as a QWERTY keyboard.
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 Del 5.3.2, «Debian Installer Parameters».
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
Serial braille displays cannot safely be automatically detected (since that may damage some of them). You thus need to append the
brltty= 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
Support for software speech synthesis is available on all installer images which have the graphical installer, i.e. all netinst, CD and DVD images, and the netboot gtk variant. It can be activated by selecting it in the boot menu by typing
s Enter. The textual version of the installer will then be automatically selected, and support for software speech synthesis will be automatically installed on the target system.
If several sound cards are detected, you will be prompted to press Enter when you hear speech from the desired sound card.
The first question (language) is spoken in english, and the remainder of installation is spoken in the selected language (if available in
The default speech rate is quite slow. To make it faster, press CapsLock+6. To make it slower, press CapsLock+5. The default volume should be medium. To make it louder, press CapsLock+2. To make it quieter, press CapsLock+1. To get more details on the browsing shortcuts, see the Speakup guide. To just accept the default answer for a question, simply press Enter at the prompt. To provide an empty answer for a question, type
! at the prompt. To get back to the previous question, type
< at the prompt.
Support for hardware speech synthesis devices is available on all installer images which have the graphical installer, i.e. all netinst, CD and DVD images, and the netboot gtk variant. You thus need to select a «Graphical install» entry in the boot menu.
Hardware speech synthesis devices cannot be automatically detected. You thus need to append the
speakup.synth= boot parameter to tell
speakup which driver it should use.
driver should be replaced by the driver code for your device (see driver code list). The textual version of the installer will then be automatically selected, and support for the speech synthesis device will be automatically installed on the target system.
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.
If desired a textual version of the bootloader can be activated before adding the boot parameter by typing
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
d shortcut, or append the
theme=dark boot parameter.
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.
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 Tillegg B, Automating the installation using preseeding.
Documentation on accessibility of the installed system is available on the Debian Accessibility wiki page.