Chapter 23. Configuring the desktop environment for accessibility

As a system administrator, you can configure the desktop environment to support users with a visual impairment.

To enable accessibility, perform the following procedures.

23.1. Components that provide accessibility features

Accessibility for users with a visual impairment is ensured by the Orca screen reader on the Red Hat Enterprise Linux 8 desktop. Orca is included in the default RHEL installation.

Orca reads information from the screen and communicates it to you using the following components:

Speech synthesizer
Provides a speech output. The default speech synthesizer on RHEL 8 is eSpeak-NG.
Braille display
Provides a tactile output. The BRLTTY service enables this functionality.

Additional resources

23.2. Configuring the brltty service

The Braille display is a device that uses the brltty service to provide tactile output for visually impaired users.

In order for the Braille display to work correctly, perform the following procedures.

23.2.1. Enabling the brltty service

To enable the Braille display, enable the brltty service to start automatically on boot. By default, brltty is disabled.

Prerequisites

  • Ensure that brltty and speech synthesis for brltty are installed:

    # yum install brltty brltty-espeak-ng

Procedure

  • Enable the brltty service to start on boot:

    # systemctl enable --now brltty

Verification steps

  1. Reboot the system.
  2. Check that the brltty service is running:

    # systemctl status brltty
    ● brltty.service - Braille display driver for Linux/Unix
       Loaded: loaded (/usr/lib/systemd/system/brltty.service; enabled; vendor pres>
       Active: active (running) since Tue 2019-09-10 14:13:02 CEST; 39s ago
      Process: 905 ExecStart=/usr/bin/brltty (code=exited, status=0/SUCCESS)
     Main PID: 914 (brltty)
        Tasks: 3 (limit: 11360)
       Memory: 4.6M
       CGroup: /system.slice/brltty.service
               └─914 /usr/bin/brltty

23.2.2. Authorizing users of a Braille display device

To set the users who are authorized to use a Braille display device, you can choose one of the following methods, which have an equal effect:

Authorization using the /etc/brlapi.key file is suitable only for the file systems where users or groups can be assigned to a file.

Authorization using the /etc/brltty.conf file is suitable even for the file systems where users or groups cannot be assigned to a file.

23.2.2.1. Authorizing users of a Braille display device with brltty.conf

Procedure

  1. Open the /etc/brltty.conf file, and find the section called Application Programming Interface Parameters.
  2. Specify the users.

    • To specify one or more individual users, list the users on the following line:

      api-parameters Auth=user:user_1, user_2, ...    # Allow some local user
    • To specify a user group, enter its name on the following line:

      api-parameters Auth=group:group    # Allow some local group

23.2.2.2. Authorizing users of a Braille display device with brlapi.key

Authorization using the /etc/brlapi.key file is suitable only for the file systems where users or groups can be assigned to a file.

Prerequisites

  • Your system must use a file system where users or groups can be assigned to a file.

Procedure

  1. Create the /etc/brlapi.key file.

    # mcookie > /etc/brlapi.key
  2. Change ownership of the /etc/brlapi.key to particular user or group.

    • To specify an individual user:

      # chown user_1 /etc/brlapi.key
    • To specify a group:

      # chown group_1 /etc/brlapi.key
  3. Adjust the content of /etc/brltty.conf by including the following line:

    api-parameters Auth=keyfile:/etc/brlapi.key

23.2.3. Setting the driver for a Braille display device

The braille-driver directive in /etc/brltty.conf file specifies a two-letter driver identification code of the driver for the Braille display device.

Procedure

  • Decide whether you want to use the autodetection for finding the appropriate driver for your Braille display device.

    • To use autodetection, use the default option as follows:

      braille-driver	auto	 # autodetect
      Warning

      Autodetection tries all drivers. Therefore, it might take a long time or even fail. For this reason, setting up a particular driver is recommended.

    • If you do not want to use the autodetection, specify the identification code of the required driver in the braille-driver directive.

      Choose the identification code of required driver from the list provided in /etc/brltty.conf, for example:

      braille-driver	xw	 # XWindow

      You can also set multiple drivers, separated by commas, and autodetection is then performed among them.

23.2.4. Configuring a Braille display device

The braille-device directive in the /etc/brltty.conf file specifies the device to which the Braille display device is connected.

23.2.4.1. Supported types of Braille display device

This section describes which types of Braille display devices are supported.

Table 23.1. Braille display device types and the corresponding syntax

Braille device typeSyntax of the typeNote

Serial device

serial:path

Relative paths are at /dev.

USB device

[serial-number]

The brackets ([]) here indicate optionality.

Bluetooth device

bluetooth:address

 

Example 23.1. Settings for particular Braille display devices

# First serial device
braille-device	serial:ttyS0
# First USB device matching braille driver
braille-device	usb:
# Specific USB device by serial number
braille-device	usb:nnnnn
# Specific Bluetooth device by address
braille-device	bluetooth:xx:xx:xx:xx:xx:xx

You can also set multiple devices, separated by commas, and each of them will be probed in turn.

Important

If the device is connected by a serial-to-USB adapter, setting braille-device to usb: does not work. In this case, identify the virtual serial device that the kernel has created for the adapter. The virtual serial device can look like this:

serial:ttyUSB0

You can find the actual device name in the kernel messages on the device plug with the following command:

# dmesg | fgrep ttyUSB0

23.2.4.2. Setting specific parameters for Braille display devices

To set specific parameters for particular Braille display devices, use the braille-parameters directive in /etc/brltty.conf file. The braille-parameters directive passes non-generic parameters through to the braille driver. Choose the required parameters from the list in /etc/brltty.conf.

23.2.4.2.1. Setting the text table

The text-table directive in /etc/brltty.conf specifies which text table is used to encode the symbols. Relative paths to text tables are stored within the /etc/brltty/Text/ directory.

Procedure

  1. Decide whether you want to use the autoselection for finding the appropriate text table.
  2. If you want to use the autoselection, leave text-table specified to auto, which is the default option.

    text-table	auto	 # locale-based autoselection

    This ensures that local-based autoselection with fallback to en-nabcc is performed.

    For example, to use the text table for American English:

    text-table	en_US	 # English (United States)
23.2.4.2.2. Setting the contraction table

The contraction-table directive in the /etc/brltty.conf file specifies which table is used to encode the abbreviations. Relative paths to particular contraction tables are stored within the /etc/brltty/Contraction/ directory.

Procedure

  • Choose the required contraction-table from the list in /etc/brltty.conf.

    For example, to use the contraction table for American English, grade 2:

    contraction-table	en-us-g2	 # English (US, grade 2)
Warning

If not specified, no contraction table is used.

23.3. Switching on Always Show Universal Access Menu

To activate the Orca screen reader, enable the Always Show Universal Access Menu option as described in the following procedure.

Procedure

  1. Open the Gnome Settings menu.
  2. Select Universal Access.
  3. Enable the Always Show Universal Access Menu item.

    Enabling the Always Show Universal Access Menu option in GNOME Settings

    always show univ acces menu new

Verification steps

  • Check that the Universal Access Menu icon is displayed on the top bar even when all options from this menu are switched off.

    universal access menu

Alternatively, you can enable the Orca screen reader by pressing the Super+Alt+S keyboard shortcut. As a result, the Universal Access Menu icon is displayed on the top bar.

Warning

If you activate Orca by pressing the keyboard shortcut, the icon disappears in case that the user disables all of the provided options from the Universal Access Menu. The missing icon might cause difficulties to users with a visual impairment.

You can prevent the inaccessibility of the icon by switching on the Always Show Universal Access Menu option as described in the above procedure. When the Always Show Universal Access Menu option is enabled, the icon is displayed on the top bar even when all options from this menu are disabled.