如何实现Ctrl+Space等效于Ctrl+Shift，单独按空格按下即触发？

Alright, let's fix this exactly how you want it—you need Ctrl+Space to behave like Ctrl+Shift, have the spacebar spit out a space the moment you press it (not when you let go), and you want to skip X-based tools like xcape. Plus, you're cool with other key+Space combinations acting as key+Shift.

The perfect tool for this is keyd—a lightweight, user-space key remapper that works outside of X (so it works on Wayland, TTYs, everything) and handles keydown events exactly how we need it. Here's the step-by-step:

Step 1: Install keyd #

First, grab the package from your distro's repos. For Debian/Ubuntu-based systems:

sudo apt install keyd

For Fedora/RHEL:

sudo dnf install keyd

If it's not available, you can build it from source (it's a small, simple build process).

Step 2: Create the configuration file #

Create a new config file at /etc/keyd/default.conf (you'll need sudo privileges to edit this):

[ids]
# Apply this config to all input devices
*

[main]
# Set up spacebar as an overload: hold with other keys = modifier, press alone = instant space
space = overload(space_mod, space)

[space_mod]
# Map Ctrl+Space to Ctrl+Shift
C = C(Shift)

# Optional: Uncomment these lines to make other key+Space combinations act as key+Shift
# A = A(Shift)  # Alt+Space → Alt+Shift
# M = M(Shift)  # Super/Windows+Space → Super+Shift
# S = S(Shift)  # Shift+Space → Shift+Shift (useless, but just an example)

What this does: #

• The overload(space_mod, space) line is the magic: when you press space alone, it sends a normal space the moment you press down (no waiting for release, which fixes your fast-typing issue). When you hold space with another key, it switches to the space_mod layer.
• In the space_mod layer, C = C(Shift) tells keyd that holding Ctrl + Space should send Ctrl + Shift instead. The optional lines let you extend this behavior to other modifier keys if you want.

Step 3: Activate the config #

Enable keyd to start on boot, then start it immediately:

sudo systemctl enable --now keyd

Step 4: Test it out #

• Tap the spacebar: you should see a space appear instantly when you press it, not when you release.
• Hold Ctrl + Space: try using this for shortcuts that require Ctrl+Shift (like selecting text in a terminal or toggling uppercase in a text editor)—it should work exactly like pressing Ctrl+Shift.
• If you added the optional lines, test Alt+Space or Super+Space too—they'll behave as their respective +Shift combinations.

Why this beats at-home-modifier/xcape: #

• keyd doesn't rely on X, so it works across your entire system (TTYs, Wayland, X11, even login screens).
• It sends the space on keydown by default for single presses, so no annoying lag or waiting for release like you had with xcape.
• It's lightweight and runs in the background without fuss.

内容的提问来源于stack exchange，提问作者Oblitzitate