84 lines
3.2 KiB
Markdown
84 lines
3.2 KiB
Markdown
---
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title: Keyboard Mapping
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description: Changing keyboard mapping at the hwdb level
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published: true
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date: 2024-03-07T22:50:17.227Z
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tags:
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editor: markdown
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dateCreated: 2024-03-07T22:50:15.696Z
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---
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References:
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- https://wiki.archlinux.org/index.php/Map_scancodes_to_keycodes
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- https://github.com/Earnestly/pkgbuilds/blob/master/system-config/hwdb-capslock-as-control.hwdb
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Maping keys is pretty simple, and if it's done at the udev level, it's universal, so it doesn't require any X or Wayland specific configuration.
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As an example, I map my compose key (menu key) to right meta (aka super, logo, windows, apple, or command key), and CapsLock to left Control.
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## Get Scancode
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First, get the scancode(s) of the key(s) you wish to change. Easiest way is to use `evteest(1)`. For each keypress, you'll get information similar to the following:
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```
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Event: time 1496690003.603531, -------------- SYN_REPORT ------------
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Event: time 1496690003.723467, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70065
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Event: time 1496690003.723467, type 1 (EV_KEY), code 127 (KEY_COMPOSE), value 0
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```
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The code you will need to use in the udev hwdb config file is the `MSC_SCAN` value (in this case: 70065).
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## Get Hardware ID
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Next you will need the hardware Vendor and Product ids from `lsusb(1)`. These are two sets of four hexidecimal digits separated by a colon (:) printed right before the device name.
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```
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Bus 001 Device 005: ID 258a:1006 <keyboard name here>
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```
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In this example, the Vendor ID is `258a`, and the Product ID is `1006`.
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## Create udev hwdb Configuration
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Then create `/etc/udev/hwdb.d/61-custom-keyboard.hwdb` with the following contents:
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```
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evdev:input:b0003v258Ap1006*
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KEYBOARD_KEY_70065=rightmeta
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KEYBOARD_KEY_70039=leftctrl
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```
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A few notes on the format of this file:
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- The format for the device identifying line for usb devices is `evdev:input:b0003v<Vendor ID>p<ProductID>*`.
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- If `<Product ID>` and `<Vendor ID>` contain letters, they must be capitalized
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- These scancodes can be quite device-specific, so it is wise to be specific to *at least* the vendor and product IDs
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- There are methods for identifying atk keyboards as well. Check the Arch Wiki page listed in the references above for more info
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- Defining a key to change is done with `KEYBOARD_KEY_<scancode>=<new keycode>`
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- `<scancode>` is the code we pulled from evtest earlier
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- `<new keycode>` is the keycode we want to emit when the key is pressed. Names of keycodes are listed in `/usr/include/linux/input-event-codes.h`, and should be all lowercased in your udev config.
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- The filename `61-custom-keyboard.hwdb` is somewhat arbitrary, but make sure that you order your file *after* the existing `60-keyboard.hwdb`.
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## Update Hardware Database Index
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After changing the config files, the hwdb needs to be rebuilt:
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```
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# systemd-hwdb update
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```
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To start using this new hwdb, either reboot or tell udev to reload:
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```
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# udevadm trigger
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```
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Note that this will only work for adding or modifying existing key mappings. Deleted key mappings are kept in the kernel until a reboot.
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## Testing the New Mappings
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A simple test can be run before trying the keys directly:
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```
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# udevadm info /dev/input/by-path/*-usb-*-kbd | grep KEYBOARD_KEY
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```
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