Frequently Asked Question (FAQ)

Table of Contents

• XKB
  • What is XKB?
  • What does … mean?
  • What are the differences with the Xorg/X11 implementation?
• Keyboard layouts
  • Where are the standard keyboard layouts designed?<br/>How to report an issue or propose a patch?
  • Where are the system keyboard layouts located?
  • Why does my key combination to switch between layouts not work?
  • Why do my keyboard shortcuts not work properly?
  • Why does my keyboard layout not work as expected?
  • How do I customize my layout?
  • How do I test my custom layout without installing it?
  • How do I swap some keys?
  • How do I define multiple groups per key?
  • How do I break a latch before triggering another latch or lock?
• Legacy X tools replacement
  • xmodmap
  • setxkbmap
  • xkbcomp
  • xev
• API
  • Modifiers
  • Keys

XKB

What is XKB?

See: Introduction to XKB.

What does … mean?

See: terminology.

What are the differences with the Xorg/X11 implementation?

Features

See XKB Compatibility.

Tools

See Legacy X tools replacement.

Keyboard layouts

Where are the standard keyboard layouts designed?<br/>How to report an issue or propose a patch?

The xkbcommon project does not provide keyboard layouts. Standard keyboard layouts are provided by the xkeyboard-config project. See contributing to xkeyboard-config for further information.

Where are the system keyboard layouts located?

They are usually located at /usr/share/xkeyboard-config-2, or /usr/share/X11/xkb on older setups.

Note

Do not modify system files! See How do I customize my layout? for further instructions.

Why does my key combination to switch between layouts not work?

There are some issues with modifier-only shortcuts: see this bug report.

This can be fixed by using the new parameter lockOnRelease in LockGroup(), available since libxkbcommon 1.11. This will be done at some point in xkeyboard-config.

 xkb_compatibility {
     interpret ISO_Next_Group {
         useModMapMods= level1;
         virtualModifier= AltGr;
-        action= LockGroup(group=+1);
+        action= LockGroup(group=+1, lockOnRelease);
     };
 };

Why do my keyboard shortcuts not work properly?

Users have different expectations when it comes to keyboard shortcuts. However, the reference use case is usually a single Latin keyboard layout, with fallbacks for other configurations. These fallbacks may not match users’ expectations nor even be consistent across applications. See The keyboard shortcuts mess for some examples.

Since version 1.14, libxkbcommon offers a dedicated API for Wayland compositors, which enables to customize the layouts to use for keyboard shortcuts.

Issue specific to a single application

File a bug report to the corresponding project. Possible reasons:

• Shortcuts handled with keycodes, not keysyms.
• Shortcuts handled using only the first layout.
• Shortcuts do not handle non-Latin keyboard layouts.

Issue specific to multiple applications

First, check if your desktop environment enables to customize shortcuts handling globally, e.g. by selecting specific layouts when some modifiers are active. If it does not, consider filing a bug report to your Wayland compositor project to encourage developers to implement the relevant API.

Why does my keyboard layout not work as expected?

There could be many reasons!

There is an issue with your keyboard layout database

libxkbcommon may not be able to load your configuration due to an issue (file not found, syntax error, unsupported keysym, etc.). Please use our debugging tools to get further information.

Note that the xkbcommon project does not provide keyboard layouts. See the xkeyboard-config project for further information.

Diacritics/accents do not work

This is most probably an issue with your Compose configuration. If you customized it, do not forget to restart your session before trying it.

Please use our debugging tools with the option --enable-compose to get further information.

Multiple groups per key do not work

See How do I define multiple groups per key?.

The application you use does not handle the keyboard properly

Please use our debugging tools to ensure that it is specific to the application.

Your keyboard layout uses features not supported by libxkbcommon

See: compatibility

None of the previous

If none of the previous is conclusive, then this may an issue with libxkbcommon. Please use our debugging tools to provide the maximum information (setup, log, expected/got results) and file a bug report!

How do I customize my layout?

This project does not provide any keyboard layout database:

• If you want to modify only your local keyboard configuration, see: User-configuration.
• If you want to modify the standard keyboard layout database, please first try it locally (see our debugging tools) and then file an issue or a merge request at the xkeyboard-config project.

See also the keymap text format documentation for the syntax and the compatibility page for the supported features.

How do I test my custom layout without installing it?

Use our debugging tools.

How do I swap some keys?

🚧 TODO

How do I define multiple groups per key?

Since version 1.8 the RMLVO API does not support parsing multiple groups per key anymore, because it may break the expectation of most desktop environments and tools that the number of groups should be equal to the number of configured layouts. See #262 and #518 for further details.

The following explain how to migrate for some common use cases:

Multiple layouts

If you define multiple layouts in a single xkb_symbols section, you should instead split them into individual sections and update your keyboard settings to use each such layout.

E.g. if you have a single layout variant1_variant2 defined as:

xkb_symbols "variant1_variant2" {
    key <AD01> {
        symbols[Group1] = [U13AA, U13C6],
        symbols[Group2] = [    q,     Q],
    };
    // …
};

then you should split it into:

xkb_symbols "variant1" {
    key <AD01> { [U13AA, U13C6] };
    // …
};
 
xkb_symbols "variant2" {
    key <AD01> { [    q,     Q] };
    // …
};

See also User-configuration to make the layouts discoverable for easy configuration in your keyboard settings app.

Option for multiple layouts

If you define an option that affect multiple groups at once in a single xkb_symbols section, you should split that section and update the corresponding rules for each layout index.

E.g. if one has the following group switcher on CapsLock key:

// File: ~/.config/xkb/symbols/group
partial xkb_symbols "caps_pairs" {
    replace key <CAPS> {
        repeat=No,
        symbols[Group1] = [ISO_Group_Lock, ISO_Group_Lock],
        symbols[Group2] = [ISO_Group_Lock, ISO_Group_Lock],
        symbols[Group3] = [ISO_Group_Lock, ISO_Group_Lock],
        symbols[Group4] = [ISO_Group_Lock, ISO_Group_Lock],
        actions[Group1] = [LockGroup(group=2), LockGroup(group=3) ],
        actions[Group2] = [LockGroup(group=1), LockGroup(group=4) ],
        actions[Group3] = [LockGroup(group=4), LockGroup(group=1) ],
        actions[Group4] = [LockGroup(group=3), LockGroup(group=2) ]
    };
};

and the corresponding custom rules:

// File: ~/.config/xkb/rules/evdev
include %S/evdev
 
! option         = symbols
  grp:caps_pairs = +group(caps_pairs)

then it should be migrated to:

// File: ~/.config/xkb/symbols/group
partial xkb_symbols "caps_pairs_1" {
    replace key <CAPS> {
        repeat=No,
        symbols[Group1] = [ISO_Group_Lock, ISO_Group_Lock],
        actions[Group1] = [LockGroup(group=2), LockGroup(group=3) ]
    };
};
partial xkb_symbols "caps_pairs_2" {
    replace key <CAPS> {
        symbols[Group1] = [ISO_Group_Lock, ISO_Group_Lock],
        actions[Group1] = [LockGroup(group=1), LockGroup(group=4) ]
    };
};
partial xkb_symbols "caps_pairs_3" {
    replace key <CAPS> {
        symbols[Group1] = [ISO_Group_Lock, ISO_Group_Lock],
        actions[Group1] = [LockGroup(group=4), LockGroup(group=1) ]
    };
};
partial xkb_symbols "caps_pairs_4" {
    replace key <CAPS> {
        symbols[Group1] = [ISO_Group_Lock, ISO_Group_Lock],
        actions[Group1] = [LockGroup(group=3), LockGroup(group=2) ]
    };
};

with the corresponding custom rules:

// File: ~/.config/xkb/rules/evdev
include %S/evdev
 
! layout[1]   option         = symbols
  *           grp:caps_pairs = +group(caps_pairs_1):1
 
! layout[2]   option         = symbols
  *           grp:caps_pairs = +group(caps_pairs_2):2
 
! layout[3]   option         = symbols
  *           grp:caps_pairs = +group(caps_pairs_3):3
 
! layout[4]   option         = symbols
  *           grp:caps_pairs = +group(caps_pairs_4):4

How do I break a latch before triggering another latch or lock?

Consider the following use cases:

1. If Caps_Lock is on the second level of some key, and Shift is latched, pressing the key locks Caps while also breaking the Shift latch, ensuring that the next character is properly uppercase.
2. On the German E1 layout, ISO_Level5_Latch is on the third level of <AC04>. So if a level 3 latch (typically on <RALT>) is used to access it, the level 5 must break the previous level 3 latch, else both latches would be active: the effective level would be 7 instead of the intended 5.

Both uses cases can be implemented using the following features:

• explicit action;
• multiple actions per level;
• VoidAction(): to break latches.

Patch that fixes the first use case:

--- old
+++ new
  key <LFSH> {
      [ISO_Level2_Latch, Caps_Lock],
+     [LatchMods(modifiers=Shift,latchToLock,clearLocks),
+      {VoidAction(), LockMods(modifiers=Lock)}],
      type=\"ALPHABETIC\"
  };

Legacy X tools replacement

xmodmap

xmodmap -pm

There is no strict equivalent. Since 1.10 xkbcli compile-keymap has the option --modmaps to print the modifiers maps from a keymap, but it does not print keysyms. In order to get the output for the current keymap, use it with xkbcli dump-keymap-*:

Automatic session type detection

xkbcli dump-keymap | xkbcli compile-keymap --modmaps

Wayland session

xkbcli dump-keymap-wayland | xkbcli compile-keymap --modmaps

X11 session / XWayland

xkbcli dump-keymap-x11 | xkbcli compile-keymap --modmaps

xmodmap -e "…"

xmodmap /path/to/file

No equivalent: xkbcli does not modify the display server keymap.

setxkbmap

setxkbmap -print -layout …

Since 1.9 one can use the --kccgst option:

xkbcli compile-keymap --kccgst --layout …

setxkbmap -query

No equivalent: xkbcli only query raw keymaps and has no access to the original RMLVO settings.

setxkbmap -layout …

No equivalent: xkbcli does not modify the display server keymap. One must use the tools specific to each display server in order order to achieve it.

If you use a custom layout, please have a look at User-configuration, which enables making custom layouts discoverable by keyboard configuration GUI.

xkbcomp

xkbcomp -xkb /path/to/keymap/file -

xkbcli compile-keymap --keymap /path/to/keymap/file

xkbcomp -xkb $DISPLAY -

Automatic session type detection

xkbcli dump-keymap

Wayland session

xkbcli dump-keymap-wayland

X11 session

xkbcli dump-keymap-x11

xkbcomp - $DISPLAY

xkbcomp /path/to/keymap/file $DISPLAY

No equivalent: xkbcli does not modify the display server keymap. One must use the tools specific to each display server in order order to achieve it. Please have a look at User-configuration, which enables making custom layouts discoverable by keyboard configuration GUI.

xev

xev -event keyboard

Automatic session type detection

xkbcli interactive

Wayland session

xkbcli interactive-wayland

X11 session

xkbcli interactive-x11

API

Modifiers

How to get the virtual modifier encoding?

The virtual modifiers encoding, (also: mappings to real modifiers in X11 jargon) is an implementation detail. However, some applications may require it in order to interface with legacy code.

libxkbcommon ≥ 1.10

Use the dedicated functions xkb_keymap::xkb_keymap_mod_get_mask() (since 1.10) and xkb_keymap::xkb_keymap_mod_get_mask2() (since 1.11).

libxkbcommon ≤ 1.9

Use the following snippet:

// Find the real modifier mapping of the virtual modifier `LevelThree`
#include <xkbcommon/xkbcommon.h>
#include <xkbcommon/xkbcommon-names.h>
const xkb_mod_index_t levelThree_idx = xkb_keymap_mod_get_index(keymap, XKB_VMOD_NAME_LEVEL3);
const xkb_mod_mask_t levelThree = UINT32_C(1) << levelThree_idx;
struct xkb_state* state = xkb_state_new(keymap);
assert(state); // Please handle error properly
xkb_state_update_mask(state, levelThree, 0, 0, 0, 0, 0);
const xkb_mod_mask_t levelThree_mapping = xkb_state_serialize_mods(state, XKB_STATE_MODS_EFFECTIVE);
xkb_state_unref(state);

How to get the keys that trigger modifiers?

There is no dedicated API, since the use cases are too diverse or niche. Nevertheless, the following snippet provide a minimal example to achieve it.

#include <xkbcommon/xkbcommon.h>
static ssize_t
xkb_keymap_mod_get_codes(struct xkb_keymap *keymap, xkb_mod_index_t mod,
                         xkb_keycode_t *codes_out, size_t codes_size)
{
    if (mod >= xkb_keymap_num_mods(keymap))
        return -1;
 
    ssize_t idx = 0;
    for (xkb_keycode_t k = xkb_keymap_min_keycode(keymap);
         k <= xkb_keymap_max_keycode(keymap) && idx >= 0; k++) {
        /*
         * We only test the first level of the first group.
         *
         * Since there is currently no way to reset the state, use a new one to
         * avoid side effects (latches, etc.)
         */
        struct xkb_state * const state = xkb_state_new(keymap);
        assert(state);
 
        static const enum xkb_key_direction directions[] = {
            XKB_KEY_DOWN,
            XKB_KEY_UP
        };
 
        for (size_t d = 0; d < ARRAY_SIZE(directions); d++) {
            if (xkb_state_update_key(state, k, directions[d]) &&
                xkb_state_mod_index_is_active(state, mod,
                                              XKB_STATE_MODS_EFFECTIVE)) {
                if ((size_t) idx < codes_size) {
                    assert(idx < (ssize_t) (SIZE_MAX / 2));
                    codes_out[idx++] = k;
                } else {
                    idx = -2;
                }
                break;
            }
        }
 
        xkb_state_unref(state);
    }
    return idx;
}

How to use keyboard shortcuts from a different layout?

The keyboard shortcuts mess

Keyboard shortcuts in applications are usually using Latin letters. In order to make them work on non-Latin keyboard layouts, each toolkit (Gtk, Qt, etc.) implements its strategy.

However there are some edge cases where this does not work:

• Strategies may differ slightly, resulting in different shortcuts behavior depending on the app used.
• Punctuation is usually not remapped. E.g. the standard Israeli layout cannot remap its key <AD01> “slash” to the US layout “q”.
• If one have multiple Latin layouts, shortcuts may be positioned differently. E.g. US Qwerty and French Azerty have different positions for Ctrl+Q, while the user might want all shortcuts to be positioned independently of the layout.

XKB limitations

Some users want explicitly to use keyboard shortcuts as if they were typing on another keyboard layout, e.g. using Qwerty shortcuts with a Dvorak layout. While achievable with modern XKB features (e.g. multiple actions per level), this is non-trivial and it does not scale well, thus preventing support in the standard keyboard database, xkeyboard-config.

Custom and consistent shortcuts behavior using libxkbcommon

Since libxkbcommon 1.14, tweaking the keyboard shortcuts can be achieved by using the following functions from the [state event API]:

xkb_state_machine_options::xkb_state_machine_options_shortcuts_update_mods()

Set the modifiers that will trigger the shortcuts tweak, typically Control+Alt+Super.

const xkb_mod_mask_t ctrl = xkb_keymap_mod_get_mask(keymap, XKB_MOD_NAME_CTRL);
const xkb_mod_mask_t alt = xkb_keymap_mod_get_mask(keymap, XKB_VMOD_NAME_ALT);
const xkb_mod_mask_t super = xkb_keymap_mod_get_mask(keymap, XKB_VMOD_NAME_SUPER);
const xkb_mod_mask_t shortcuts_mask = ctrl | alt | super;
if (xkb_state_machine_options_shortcuts_update_mods(options, shortcuts_mask, shortcuts_mask)) {
    /* handle error */
    …
}

xkb_state_machine_options::xkb_state_machine_options_shortcuts_set_mapping()

Set the layout to use for shortcuts for each relevant layout. There are 2 typical use cases:

Single layout

The user types with a single layout, but want the shortcuts to act as if using another layout: e.g. Qwerty shortcuts for the Arabic layout. The keymap would be configured with 2 layouts: the user layout then the shortcut layout (e.g. ara,us).

if (xkb_state_machine_options_shortcuts_set_mapping(options, 0, 1)) {
    /* handle error */
    …
}

Multiple layouts

The user types with multiples layouts but wants shortcuts consistency accross all the layouts, typically using the first layout as the reference.

// When using shortcuts, all layouts will behave as if using the *first* layout.
const xkb_layout_index_t num_layouts = xkb_keymap_num_layouts(keymap);
for (xkb_layout_index_t source = 1; source < num_layouts; source++) {
    if (xkb_state_machine_options_shortcuts_set_mapping(options, source, 0)) {
        /* handle error */
        …
    }
}

Keys

How to check if a keymap defines/binds a keycode?

Check if a keymaps defines a keycode

xkb_keymap::xkb_keymap_key_get_name() returns NULL if the keycode is not defined in the corresponding keymap:

if (xkb_keymap_key_get_name(keymap, keycode) != NULL)
    // use existing key ...

Check if a keymaps binds a keycode

xkb_keymap::xkb_keymap_num_layouts_for_key() returns 0 if the keycode is either not defined or unbound:

if (xkb_keymap_num_layouts_for_key(keymap, keycode))
    // use bound key ...