Chapter 11. Configuring a System for Accessibility

Accessibility in Red Hat Enterprise Linux 7 is ensured by the Orca screen reader, which is included in the default installation of the operating system. This chapter explains how a system administrator can configure a system to support users with a visual impairment.
Orca reads information from the screen and communicates it to the user using:
  • a speech synthesizer, which provides a speech output
  • a braille display, which provides a tactile output
For more information on Orca settings, see its help page.
In order that Orca's communication outputs function properly, the system administrator needs to:

11.1. Configuring the brltty Service

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

Enable the brltty Service

The braille display cannot work unless brltty is running. By default, brltty is disabled. Enable brltty to be started on boot: 
~]# systemctl enable brltty.service

Authorize Users to Use the Braille Display

To set the users who are authorized to use the braille display, choose one of the following procedures, which have an equal effect. The procedure using the /etc/brltty.conf file is suitable even for the file systems where users or groups cannot be assigned to a file. The procedure using the /etc/brlapi.key file is suitable only for the file systems where users or groups can be assigned to a file.

Procedure 11.1. Setting Access to Braille Display by Using /etc/brltty.conf

  1. Open the /etc/brltty.conf file, and find the section called Application Programming Interface Parameters.
  2. Specify the users.
    1. 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
    2. To specify a user group, enter its name on the following line: 
      api-parameters Auth=group:group		# Allow some local group

Procedure 11.2. Setting Access to Braille Display by Using /etc/brlapi.key

  1. Create the /etc/brlapi.key file. 
    ~]# mcookie > /etc/brlapi.key
  2. Change ownership of the /etc/brlapi.key to particular user or group.
    1. To specify an individual user: 
      ~]# chown user_1 /etc/brlapi.key
    2. To specify a group: 
      ~]# chown group_1 /etc/brlapi.key
  3. Adjust the content of /etc/brltty.conf to include this: 
    api-parameters Auth=keyfile:/etc/brlapi.key

Set the Braille Driver

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

Procedure 11.3. Setting the Braille Driver

  • Decide whether you want to use the autodetection for finding the appropriate braille driver.
    1. If you want to use autodetection, leave braille driver specified to auto, which is the default option. 
      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 braille driver is recommended.
    2. If you do not want to use the autodetection, specify the identification code of the required braille driver in the braille-driver directive.
      Choose the identification code of required braille 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.

Set the Braille Device

The braille-device directive in /etc/brltty.conf specifies the device to which the braille display is connected. The following device types are supported (see Table 11.1, “Braille Device Types and the Corresponding Syntax”):

Table 11.1. Braille Device Types and the Corresponding Syntax

Braille Device TypeSyntax of the Type
serial deviceserial:path [a]
USB device[serial-number] [b]
Bluetooth devicebluetooth:address
[a] Relative paths are at /dev.
[b] The brackets ([]) here indicate optionality.
Examples of settings for particular devices: 
braille-device	serial:ttyS0	                # First serial device
braille-device	usb:	                        # First USB device matching braille driver
braille-device	usb:nnnnn	                # Specific USB device by serial number
braille-device	bluetooth:xx:xx:xx:xx:xx:xx	# Specific Bluetooth device by address
You can also set multiple devices, separated by commas, and each of them will be probed in turn.

Warning

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

Set Specific Parameters for Particular Braille Displays

If you need to set specific parameters for particular braille displays, use the braille-parameters directive in /etc/brltty.conf. The braille-parameters directive passes non-generic parameters through to the braille driver. Choose the required parameters from the list in /etc/brltty.conf.

Set 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 in the /etc/brltty/Text/ directory.

Procedure 11.4. Setting the Text Table

  1. Decide whether you want to use the autoselection for finding the appropriate text table.
    1. 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.
    2. If you do not want to use the autoselection, choose the required text-table from the list in /etc/brltty.conf.
      For example, to use the text table for American English: 
      text-table	en_US	 # English (United States)

Set the Contraction Table

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