--- title: Keyboard Mapping description: Changing keyboard mapping at the hwdb level published: true date: 2024-03-09T03:27:27.730Z tags: editor: markdown dateCreated: 2024-03-07T22:50:15.696Z --- References: - https://wiki.archlinux.org/index.php/Map_scancodes_to_keycodes - https://github.com/Earnestly/pkgbuilds/blob/master/system-config/hwdb-capslock-as-control.hwdb 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. 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. ## Get Scancode 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: ``` Event: time 1496690003.603531, -------------- SYN_REPORT ------------ Event: time 1496690003.723467, type 4 (EV_MSC), code 4 (MSC_SCAN), value 70065 Event: time 1496690003.723467, type 1 (EV_KEY), code 127 (KEY_COMPOSE), value 0 ``` The code you will need to use in the udev hwdb config file is the `MSC_SCAN` value (in this case: 70065). ## Get Hardware ID 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. ``` Bus 001 Device 005: ID 258a:1006 ``` In this example, the Vendor ID is `258a`, and the Product ID is `1006`. ## Create udev hwdb Configuration Then create `/etc/udev/hwdb.d/61-custom-keyboard.hwdb` with the following contents: ``` evdev:input:b0003v258Ap1006* KEYBOARD_KEY_70065=rightmeta KEYBOARD_KEY_70039=leftctrl ``` A few notes on the format of this file: - The format for the device identifying line for usb devices is `evdev:input:b0003vp*`. - If `` and `` contain letters, they must be capitalized - These scancodes can be quite device-specific, so it is wise to be specific to *at least* the vendor and product IDs - There are methods for identifying atk keyboards as well. Check the Arch Wiki page listed in the references above for more info - Defining a key to change is done with `KEYBOARD_KEY_=` - `` is the code we pulled from evtest earlier - `` 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. - The filename `61-custom-keyboard.hwdb` is somewhat arbitrary, but make sure that you order your file *after* the existing `60-keyboard.hwdb`. ## Update Hardware Database Index After changing the config files, the hwdb needs to be rebuilt: ``` # systemd-hwdb update ``` To start using this new hwdb, either reboot or tell udev to reload: ``` # udevadm trigger ``` Note that this will only work for adding or modifying existing key mappings. Deleted key mappings are kept in the kernel until a reboot. ## Testing the New Mappings A simple test can be run before trying the keys directly: ``` # udevadm info /dev/input/by-path/*-usb-*-kbd | grep KEYBOARD_KEY ```