Chapter 13. 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.
13.1. Components that provide accessibility features
On the Red Hat Enterprise Linux 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
13.3. 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.
13.4. 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.
13.4.1. Supported types of Braille display device
The following types of Braille display devices are supported on Red Hat Enterprise Linux 9.
Braille device type | Syntax of the type | Note |
---|---|---|
Serial device |
|
Relative paths are at |
USB device |
|
The brackets ( |
Bluetooth device |
|
13.4.2. 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:# dnf install brltty
Optionally, you can install speech synthesis support for
brltty
:# dnf install brltty-espeak-ng
Procedure
Enable the
brltty
service to start on boot:# systemctl enable --now brltty
Verification steps
- Reboot the system.
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
13.4.3. 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 thatkeyfile
is set to/etc/brlapi.key
:api-parameters Auth=keyfile:/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:# usermod --append -G brlapi user-name
Additional resources
13.4.4. 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:# XWindow braille-driver xw
To set multiple drivers, list them separated by commas. Automatic detection then chooses from the listed drivers.
13.4.5. 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:
# journalctl --dmesg | fgrep ttyUSB
-
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 13.1. Settings for the first serial device
braille-device serial:ttyS0
Example 13.2. Settings for the first USB device matching Braille driver
braille-device usb:
Example 13.3. Settings for a specific USB device by serial number
braille-device usb:nnnnn
Example 13.4. Settings for a serial-to-USB adapter
Use the device name that you found earlier in the kernel messages:
braille-device serial:ttyUSB0
NoteSetting
braille-device
tousb:
does not work for a serial-to-USB adapter.Example 13.5. Settings for a specific Bluetooth device by address
braille-device bluetooth:xx:xx:xx:xx:xx:xx
13.4.6. 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:
text-table en_US # English (United States)
13.4.7. 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.
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:
contraction-table en-us-g2 # English (US, grade 2)