danielrosehill/usb-keyboard-reconnection-fix.md

## usb-keyboard-reconnection-fix.md

      
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              usb-keyboard-reconnection-fix.md
            
          
    Fix: USB Keyboard Not Recognized After Reconnection on Linux

Problem

When disconnecting and reconnecting a USB keyboard on Linux, the system fails to recognize the device even though it's physically connected. The keyboard works fine initially but requires a system reboot or multiple reconnection attempts to be detected again.
Root Cause

USB hubs are configured with autosuspend enabled (power control set to "auto"). When a keyboard is disconnected, the parent USB hub may enter a suspended state. Upon reconnecting the keyboard, the suspended hub doesn't properly wake up, preventing the keyboard from being enumerated and recognized by the system.
Solution

This fix implements three layers of protection to ensure USB keyboards are always recognized upon reconnection:
1. Create Udev Rule

Create a udev rule to disable USB autosuspend for keyboards and hubs:
sudo nano /etc/udev/rules.d/99-usb-keyboard-power.rules
Add the following content:
# Disable USB autosuspend for keyboards to prevent reconnection issues
# This ensures keyboards are always recognized when reconnected

# Disable autosuspend for all USB keyboards
ACTION=="add", SUBSYSTEM=="usb", ATTR{bInterfaceClass}=="03", ATTR{bInterfaceSubClass}=="01", ATTR{bInterfaceProtocol}=="01", ATTR{power/control}="on"

# Disable autosuspend for USB hubs to prevent hub suspension issues
ACTION=="add", SUBSYSTEM=="usb", ATTR{bDeviceClass}=="09", ATTR{power/control}="on"

Reload udev rules:
sudo udevadm control --reload-rules
sudo udevadm trigger
2. Create Systemd Service

Create a systemd service to ensure USB hub power settings persist across reboots:
sudo nano /etc/systemd/system/usb-keyboard-power.service
Add the following content:
[Unit]
Description=Disable USB autosuspend for keyboards and hubs
After=multi-user.target

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'for hub in /sys/bus/usb/devices/*/power/control; do device=$(dirname $(dirname $hub)); if [ -f "$device/bDeviceClass" ]; then class=$(cat "$device/bDeviceClass"); if [ "$class" = "09" ]; then echo "on" > "$hub"; fi; fi; done'
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
Enable and start the service:
sudo systemctl daemon-reload
sudo systemctl enable usb-keyboard-power.service
sudo systemctl start usb-keyboard-power.service
3. Immediate Fix (Current Session)

Apply the fix immediately without rebooting:
# Disable autosuspend for all USB hubs
for device in /sys/bus/usb/devices/*/bDeviceClass; do
    dir=$(dirname $device)
    class=$(cat $device 2>/dev/null)
    if [ "$class" = "09" ]; then
        sudo bash -c "echo 'on' > $dir/power/control"
    fi
done
Verification

Check that USB hubs have autosuspend disabled:
for device in /sys/bus/usb/devices/*/bDeviceClass; do
    dir=$(dirname $device)
    class=$(cat $device 2>/dev/null)
    if [ "$class" = "09" ]; then
        control=$(cat $dir/power/control 2>/dev/null)
        echo "$(basename $dir): Power control: $control"
    fi
done
All hubs should show Power control: on.
Testing


Disconnect your USB keyboard
Wait 5-10 seconds
Reconnect the keyboard
The keyboard should be immediately recognized and functional

Troubleshooting

Check keyboard device path

lsusb | grep -i keyboard
View USB connection events

sudo dmesg | tail -50 | grep -i "usb\|keyboard"
Check specific device power settings

First, find your keyboard's device path:
udevadm info -q all -n /dev/input/by-id/*kbd* | grep DEVPATH
Then check its power control (replace X-X with your device path):
cat /sys/bus/usb/devices/X-X/power/control
Verify udev rule is active

sudo udevadm test /sys/bus/usb/devices/1-4.4.2 2>&1 | grep power
Alternative: Disable USB Autosuspend Globally

If the above solution doesn't work, you can disable USB autosuspend globally via kernel parameters:

Edit GRUB configuration:

sudo nano /etc/default/grub

Add usbcore.autosuspend=-1 to GRUB_CMDLINE_LINUX_DEFAULT:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash usbcore.autosuspend=-1"


Update GRUB and reboot:

sudo update-grub
sudo reboot
Technical Details


USB Device Class 09: USB Hub
USB Interface Class 03, SubClass 01, Protocol 01: HID Keyboard (Boot Protocol)
Power control "on": Device cannot be autosuspended
Power control "auto": Device can be autosuspended based on runtime PM

Tested On


Ubuntu 25.04 / 25.10
Kernel 6.17.0-6-generic
Should work on most modern Linux distributions with systemd and udev

Notes


This fix keeps USB hubs powered at all times, which may have a minimal impact on power consumption (typically negligible on desktop systems)
The solution is particularly useful for mechanical keyboards, KVM switches, or USB hubs that experience reconnection issues
Some USB devices (like wireless keyboard receivers) may also benefit from this fix


Generated with Claude Code
This gist provides a technical solution based on real-world troubleshooting. While these steps worked in our testing environment, always validate configurations in your specific setup and consult your distribution's documentation for system-specific considerations.
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