Keyboard Listener (kl)

Description

kl is a lightweight, command-line global keystroke monitoring and echoing tool for GNU/Linux systems.

This tool is compiled directly to native binary with zero runtime dependencies. No Node.js, No Electron, No Python, written in pure C.

Install

You can install it with the AUR.

paru -S kl

or build from source

git clone https://github.com/yingyu5658/keyboard-listener.git
cd keyboard-listener
sudo make install

Usage

kl is desiged to interact with low-level kernel input events directly via /dev/input/eventx. We need to find the keyboard event file.

λ ~/ ls /dev/input/by-path
pci-0000:00:14.0-usb-0:1:1.0-event-mouse  pci-0000:00:14.0-usb-0:9:1.1-event
pci-0000:00:14.0-usb-0:1:1.0-mouse        pci-0000:00:14.0-usb-0:9:1.1-event-kbd
pci-0000:00:14.0-usb-0:9:1.0-event-kbd    platform-pcspkr-event-spkr

Find a file which includes words like "keyboard", "kbd" and so on. For the first time of running kl, it will create a config file: ~/.klrc, here is an example:

# kl config file (v0.0.1)
#
# Please see your README for details.
#
# This file was auto-generated because it was missing.

device = /dev/input/by-path/pci-0000:00:14.0-usb-0:9:1.0-event-kbd

time = true

then run sudo kl:

λ ~/ sudo kl
Device: /dev/input/by-path/pci-0000:00:14.0-usb-0:9:1.0-event-kbd
2026-05-17 21:54:22.210831: P
2026-05-17 21:54:22.330827: R
2026-05-17 21:54:22.602797: O
2026-05-17 21:54:22.866822: G
2026-05-17 21:54:22.954814: R
2026-05-17 21:54:23.026817: A
2026-05-17 21:54:23.146814: M
2026-05-17 21:54:23.378821: M
2026-05-17 21:54:23.546794: I
2026-05-17 21:54:23.626831: N
2026-05-17 21:54:23.802818: G
2026-05-17 21:54:23.898808: <SPACE>
2026-05-17 21:54:24.082826: I
2026-05-17 21:54:24.554789: N
2026-05-17 21:54:24.746833: <SPACE>
2026-05-17 21:54:24.890809: P
2026-05-17 21:54:25.066811: U
2026-05-17 21:54:25.170807: R
2026-05-17 21:54:25.210811: E
2026-05-17 21:54:25.570792: <SPACE>
2026-05-17 21:54:25.762816: C

You can also disable time echo with time = false:

λ ~/dev/key-catcher/ main* sudo kl    
Device: /dev/input/by-path/pci-0000:00:14.0-usb-0:9:1.0-event-kbd
L
E
S
S
<SPACE>
I
S
<SPACE>
M
O
R
E
.

---

SECURITY & PERMISSIONS

Due to the security model of modern Linux distributions (especially on Wayland/systemd-logind), direct access to these device nodes from an unprivileged GUI session is blocked to prevent unauthorized key logging.

If it can't work properly, add your user to the input group, and reboot your computer.

sudo usermod -aG input $USER

Report Bug

Feel free to create an issue or a pull request :)