Frequently Asked Question (FAQ)

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XKB

What is XKB?

See: ./introduction-to-xkb.md "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?
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 do my keyboard shortcuts not work properly?

• 🚧 TODO: Setups with multiple layout and/or non-Latin keyboard layouts may have some issues.
• 🚧 TODO: #420

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

There are currently some issue with modifier-only shortcuts. See this issue.

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.md "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.md "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.md "debugging tools" to ensure that it is specific to the application.

Your keyboard layout uses features not supported by libxkbcommon

See: ./compatibility.md "compatibility"

None of the previous

If none of the previous is conclusive, then this may an issue with libxkbcommon. Please use our ./debugging.md "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.md "User-configuration".
• If you want to modify the standard keyboard layout database, please first try it locally (see our ./debugging.md "debugging tools") and then file an issue or a merge request at the xkeyboard-config project.

See also the ./keymap-text-format-v1-v2.md "keymap text format" documentation for the syntax and the ./compatibility.md "compatibility" page for the supported features.

How do I test my custom layout without installing it?

Use our ./debugging.md "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:

``c // Find the real modifier mapping of the virtual modifierLevelThree` #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;
}