infrastructure/docs/wip/KVM-SWITCH-MAC-NOBARA.md

One-Key KVM: Mac ↔ Nobara

Status: WIP - Scripts created, needs testing
Hardware: Dell U3821DW, MX Keys S, MX Master 3S
Updated: 2026-02-01

Overview

Software KVM solution to switch the Dell U3821DW ultrawide monitor and Logitech MX peripherals between Mac (MacBook Pro M3) and Nobara Linux using DDC/CI and HID++ commands.

Hardware Mapping

Monitor Inputs

Input	Code	Port	Computer
USB-C	27	USB-C	Mac
HDMI 2	18	HDMI 2	Nobara

Peripheral Channels

Channel	Code	Connection	Computer
1	0x00	Bluetooth	Mac
2	0x01	Logi Bolt USB	Nobara

Devices

• Monitor: Dell U3821DW (38" Ultrawide, DDC/CI enabled)
• Keyboard: Logitech MX Keys S (Easy-Switch capable)
• Mouse: Logitech MX Master 3S (Easy-Switch capable)
• Receiver: Logi Bolt USB (PID: 046d:c548)

Prerequisites

Mac

# Install m1ddc (DDC control for Apple Silicon)
brew install m1ddc

# Install hidapitester (HID control)
curl -sL https://github.com/todbot/hidapitester/releases/latest/download/hidapitester-macos-arm64.zip -o /tmp/hidapitester.zip
unzip -o /tmp/hidapitester.zip -d ~/bin/
chmod +x ~/bin/hidapitester

Nobara (Linux)

# Install ddcutil
sudo dnf install ddcutil

# Add user to i2c group (requires reboot)
sudo usermod -aG i2c $USER

# Install hidapitester
curl -sL https://github.com/todbot/hidapitester/releases/latest/download/hidapitester-linux-amd64.zip -o /tmp/hidapitester.zip
unzip -o /tmp/hidapitester.zip -d ~/bin/
chmod +x ~/bin/hidapitester

# Udev rule for non-root HID access
echo 'SUBSYSTEM=="usb", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c548", MODE="0666"' | \
  sudo tee /etc/udev/rules.d/99-logitech-bolt.rules
sudo udevadm control --reload-rules && sudo udevadm trigger

Scripts

Switch to Nobara (Run on Mac)

Location: ~/scripts/to_nobara.sh

#\!/bin/bash
# KVM Switch: Mac → Nobara
set -e

echo "Switching to Nobara..."

# Switch Monitor to HDMI 2
m1ddc set input 18

# Switch Mouse to Bolt (Channel 2)
~/bin/hidapitester --vid 046d --pid c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output "0x10,0x01,0x09,0x1b,0x01,0x00,0x00"

# Switch Keyboard to Bolt (Channel 2)
~/bin/hidapitester --vid 046d --pid c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output "0x10,0x02,0x09,0x1b,0x01,0x00,0x00"

echo "Done\!"

Switch to Mac (Run on Nobara)

Location: ~/scripts/to_mac.sh

#\!/bin/bash
# KVM Switch: Nobara → Mac
set -e

echo "Switching to Mac..."

# Switch Monitor to USB-C
ddcutil setvcp 60 27

# Switch Mouse to Bluetooth (Channel 1)
~/bin/hidapitester --vid 046d --pid c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output "0x10,0x01,0x09,0x1b,0x00,0x00,0x00"

# Switch Keyboard to Bluetooth (Channel 1)
~/bin/hidapitester --vid 046d --pid c548 --usage 0x0001 --usagePage 0xff00 \
    --open --length 7 --send-output "0x10,0x02,0x09,0x1b,0x00,0x00,0x00"

echo "Done\!"

Keyboard Shortcuts

Mac (Logi Options+)

1. Logi Options+ → MX Keys S → Smart Actions
2. Create "KVM Switch" action
3. Trigger: F12
4. Action: System → Open File → ~/scripts/to_nobara.sh

Nobara (GNOME)

1. Settings → Keyboard → Custom Shortcuts
2. Command: /home/USER/scripts/to_mac.sh
3. Shortcut: F12

Troubleshooting

Monitor doesn't switch

• DDC/CI disabled: Monitor Menu → Others → DDC/CI → On
• USB-C hub blocking DDC: Connect monitor directly to Mac USB-C port
• Linux permissions: Ensure user in i2c group, reboot after adding

Peripherals don't switch

• Wrong device index: The 0x01/0x02 values depend on Bolt pairing order

  # Find correct indices on machine with Bolt receiver
  hidapitester --vid 046d --pid c548 --list-detail
  

• Different Bolt PID: Some receivers have different product IDs

  hidapitester --list | grep 046d
  

HID++ Command Reference

Byte	Purpose	Values
0x10	Report ID (short)	Fixed
0x01/0x02	Device index	Mouse=0x01, Keyboard=0x02 (may vary)
0x09	Feature index	Change Host feature
0x1b	Function	Set host
0x00/0x01	Channel	0x00=Ch1, 0x01=Ch2, 0x02=Ch3

DDC Input Codes (Dell U3821DW)

Input	Code	Hex
DisplayPort 1	15	0x0F
DisplayPort 2	16	0x10
HDMI 1	17	0x11
HDMI 2	18	0x12
USB-C	27	0x1B

Files Location

Scripts are stored on Mac at ~/scripts/:

• to_nobara.sh - Switch to Nobara (run on Mac)
• to_mac.sh - Switch to Mac (copy to Nobara)
• debug_kvm.sh - Diagnostic script
• setup_nobara.sh - Nobara setup script

TODO

• Test monitor switching with DDC/CI enabled
• Verify Bolt receiver PID on Nobara
• Confirm device indices for keyboard/mouse
• Set up keyboard shortcuts on both machines
• Test bidirectional switching