Chapter 12. Enabling accessibility for visually impaired users
Chapter 12. Enabling accessibility for visually impaired users As a system administrator, you can configure the desktop environment to support users with a visual impairment. To enable accessibility, perform the following procedures. 12.1. Components that provide accessibility features On the RHEL 9 desktop, the Orca screen reader ensures accessibility for users with a visual impairment. Orca is included in the default RHEL installation. Orca reads information from the screen and communicates it to you using the following components: Speech Dispatcher Orca uses Speech Dispatcher to communicate with the speech synthesizer. Speech Dispatcher supports various speech synthesis backends, ensures that messages from other applications do not to interrupt the messages from Orca, and provides other functionality. Speech synthesizer Provides a speech output. The default speech synthesizer is eSpeak-NG . Braille display Provides a tactile output. The BRLTTY service enables this functionality. Additional resources Orca help page 12.2. Enabling the Accessibility menu You can enable the Accessibility menu icon in the top panel, which provides a menu with several accessibility options. Procedure Open the Settings application. Select Accessibility . Enable the Always Show Accessibility Menu item. Enabling the Accessibility menu in Settings Verification Check that the Accessibility menu icon is displayed on the top bar even when all options from this menu are switched off. 12.3. Enabling the screen reader You can enable the Orca screen reader in your desktop environment. The screen reader then reads the text displayed on the screen to improve accessibility. Procedure Enable the screen reader using either of the following ways: Press the Super + Alt + S keyboard shortcut. If the top panel shows the Universal Access menu, select Screen Reader in the menu. Verification Open an application with text content. Check that the screen reader reads the text in the application. 12.4. Enabling a Braille display device 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. 12.4.1. Supported types of Braille display device The following types of Braille display devices are supported on RHEL 9. Table 12.1. Braille display device types and the corresponding syntax Braille device type Syntax of the type Note Serial device serial:path Relative paths are at /dev . USB device [serial-number] The brackets ( [] ) here indicate optionality. Bluetooth device bluetooth:address 12.4.2. 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 the brltty package is installed: Optionally, you can install speech synthesis support for brltty : Procedure Enable the brltty service to start on boot: Verification Reboot the system. Check that the brltty service is running: 12.4.3. Authorizing users of a Braille display device To use a Braille display device, you must set the users who are authorized to use the Braille display device. Procedure In the /etc/brltty.conf file, ensure that keyfile is set to /etc/brlapi.key : This is the default value. Your organization might have overridden it. Authorize the selected users by adding them to the brlapi group: Additional resources Editing user groups using the command line 12.4.4. Setting the driver for a Braille display device The brltty service automatically chooses a driver for your Braille display device. If the automatic detection fails or takes too long, you can set the driver manually. Prerequisites The automatic driver detection has failed or takes too long. Procedure Open the /etc/brltty.conf configuration file. Find the braille-driver directive, which specifies the driver for your Braille display device. 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, to use the XWindow driver: To set multiple drivers, list them separated by commas. Automatic detection then chooses from the listed drivers. 12.4.5. Connecting a Braille display device The brltty service automatically connects to your Braille display device. If the automatic detection fails, you can set the connection method manually. Prerequisites The Braille display device is physically connected to your system. The automatic connection has failed. Procedure If the device is connected by a serial-to-USB adapter, find the actual device name in the kernel messages on the device plug: Open the /etc/brltty.conf configuration file. Find the braille-device directive. In the braille-device directive, specify the connection. You can also set multiple devices, separated by commas, and each of them will be probed in turn. For example: Example 12.1. Settings for the first serial device Example 12.2. Settings for the first USB device matching Braille driver Example 12.3. Settings for a specific USB device by serial number Example 12.4. Settings for a serial-to-USB adapter Use the device name that you found earlier in the kernel messages: Note Setting braille-device to usb: does not work for a serial-to-USB adapter. Example 12.5. Settings for a specific Bluetooth device by address 12.4.6. Setting the text table The brltty service automatically selects a text table based on your system language. If your system language does not match the language of a document that you want to read, you can set the text table manually. Procedure Edit the /etc/brltty.conf file. Identify the code of your selected text table. You can find all available text tables in the /etc/brltty/Text/ directory. The code is the file name of the text table without its file suffix. Specify the code of the selected text table in the text-table directive. For example, to use the text table for American English: 12.4.7. Setting the contraction table You can select which table is used to encode the abbreviations with a Braille display device. Relative paths to particular contraction tables are stored within the /etc/brltty/Contraction/ directory. Warning If no table is specified, the brltty service does not use a contraction table. Procedure Choose a contraction table from the list in the /etc/brltty.conf file. For example, to use the contraction table for American English, grade 2:
dnf install brltty dnf install brltty-espeak-ng systemctl enable --now brltty 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 api-parameters Auth=keyfile:/etc/brlapi.key usermod --append -G brlapi user-name XWindow braille-driver xw journalctl --dmesg | fgrep ttyUSB braille-device serial:ttyS0 braille-device usb: braille-device usb:nnnnn braille-device serial:ttyUSB0 braille-device bluetooth:xx:xx:xx:xx:xx:xx text-table en_US # English (United States) contraction-table en-us-g2 # English (US, grade 2)