The XKB Configuration Guide

Abstract

This document describes how to configure X11R7.5 XKB from a user's point of view. It covers basic configuration syntax and gives also a few examples.

Table of Contents
Overview
Selecting XKB Configuration
Direct XKB Configuration
Keymap XKB Configuration

Overview

The XKB configuration is decomposed into a number of components. Selecting proper parts and combining them back you can achieve most of the configurations you might need. Unless you have a completely atypical keyboard you really don't need to touch any of the xkb configuration files.

Selecting XKB Configuration

The easiest and the most natural way to specify a keyboard mapping is to use the rules component. As its name suggests it describes a number of general rules to combine all bits and pieces into a valid and useful keyboard mapping. All you need to do is to select a suitable rules file and then to feed it with a few parameters that will adjust the keyboard behaviour to fulfill your needs.

The parameters are:

XkbRules - files of rules to be used for keyboard mapping composition
XkbModel - name of the model of your keyboard type
XkbLayout - layout(s) you intend to use
XkbVariant - variant(s) of the layout you intend to use
XkbOptions - extra xkb configuration options

The proper rules file depends on your vendor. In reality, the commonest file of rules is xorg. For each rules file there is a description file named <vendor-rules>.lst, for instance xorg.lst which is located in the xkb configuration subdirectory rules (for example /etc/X11/xkb/rules).

Basic Configuration

Let's say you want to configure a PC-style American keyboard with 104 keys as described in xorg.lst. This can be done by simply writing several lines from below to your xorg.conf configuration file (previously known as /etc/X11/XF86Config-4 or /etc/X11/XF86Config):

Section "InputDevice"
    Identifier "Keyboard1"
    Driver "kbd"

    Option "XkbModel" "pc104"
    Option "XkbLayout" "us"
    Option "XKbOptions" ""
EndSection

The values of XkbModel and XkbLayout are really not surprising. The XkbOptions has been explicitly set to the empty set of parameters. The XkbVariant option has been left out. That means the default variant named basic is loaded.

Of course, this can be also done at runtime using the utility setxkbmap. The shell command loading the same keyboard mapping would look like:

setxkbmap -rules xorg -model pc104 -layout us -option ""

The configuration and the shell command would be very analogous for most other layouts (internationalized mappings).

Advanced Configuration

You can use multi-layouts xkb configuration. What does it mean? Basically it allows to load up to four different keyboard layouts at a time. Each such layout would reside in its own group. The groups (unlike complete keyboard remapping) can be switched very fast from one to another by a combination of keys.

Let's say you want to configure your new Logitech cordless desktop keyboard, you intend to use three different layouts at the same time - us, czech and german (in this order), and that you are used to Alt-Shift combination for switching among them.

Then the configuration snippet could look like this:

Section "InputDevice"
    Identifier "Keyboard1"
    Driver "kbd"

    Option "XkbModel" "logicordless"
    Option "XkbLayout" "us,cz,de"
    Option "XKbOptions" "grp:alt_shift_toggle"
EndSection

Of course, this can be also done at runtime using the utility setxkbmap. The shell command loading the same keyboard mapping would look like:

setxkbmap -rules xorg -model logicordless -layout "us,cz,de" \
         -option "grp:alt_shift_toggle"

Even More Advanced Configuration

Okay, let's say you are more demanding. You do like the example above but you want it to change a bit. Let's imagine you want the czech keyboard mapping to use another variant but basic. The configuration snippet then changes into:

Section "InputDevice"
    Identifier "Keyboard1"
    Driver "kbd"

    Option "XkbModel" "logicordless"
    Option "XkbLayout" "us,cz,de"
    Option "XkbVariant" ",bksl,"
    Option "XKbOptions" "grp:alt_shift_toggle"
EndSection

That seems tricky but it is not. The logic for settings of variants is the same as for layouts, that means the first and the third variant settings are left out (set to basic), the second is set to bksl (a special variant with an enhanced definition of the backslash key).

Analogously, the loading runtime will change to:

setxkbmap -rules xorg -model logicordless -layout "us,cz,de" \
         -variant ",bksl," -option "grp:alt_shift_toggle"

Basic Global Options

See rules/*.lst files.

Direct XKB Configuration

Generally, you can directly prescribe what configuration of each of basic xkb components should be used to form the resulting keyboard mapping. This method is rather "brute force". You precisely need to know the structure and the meaning of all of used configuration components.

This method also exposes all xkb configuration details directly into xorg.conf configuration file which is a not very fortunate fact. In rare occasions it may be needed, though. So how does it work?

Basic Components

There are five basic components used to form a keyboard mapping:

key codes - a translation of the scan codes produced by the keyboard into a suitable symbolic form
types - a specification of what various combinations of modifiers produce
key symbols - a translation of symbolic key codes into actual symbols
geometry - a description of physical keyboard geometry
compatibility maps - a specification of what action should each key produce in order to preserve compatibility with XKB-unware clients

Example Configuration

Look at the following example:

Section "InputDevice"
    Identifier "Keyboard0"
    Driver "kbd"

    Option "XkbKeycodes" "xorg"
    Option "XkbTypes"    "default"
    Option "XkbSymbols"  "en_US(pc104)+de+swapcaps"
    Option "XkbGeometry" "pc(pc104)"
    Option "XkbCompat"   "basic+pc+iso9995"
EndSection

This configuration sets the standard X server default interpretation of keyboard keycodes, and sets the default modifier types. The symbol table is composed of extended US keyboard layout in its variant for pc keyboards with 104 keys plus all keys for german layout are redefined respectively. Also the logical meaning of Caps-lock and Control keys is swapped. The standard keyboard geometry (physical look) is set to pc style keyboard with 104 keys. The compatibility map is set to allow basic shifting, to allow Alt keys to be interpreted and also to allow iso9995 group shifting.

Keymap XKB Configuration

Keymap configuration is the way formerly used to configure xkb. The user included a special keymap file which specified the direct xkb configuration. This method has been obsoleted by previously described rules files which are far more flexible and allow simpler and more intuitive syntax. It is preserved merely for compatibility reasons and should be avoided if possible.