Fix missing Realtek NIC firmware in Proxmox 8.3 with kernel 6.11 on Lenovo ideacentre 300s

After installing Proxmox 8.3 onto a Lenovo ideacentre 300s and opting-in to Linux kernel 6.11, the error w: possible missing firmware /lib/firmware/rtl_nic/rtl8126a-3.fw for module r8169 was shown. The easiest way to fix it is by downloading the firmware file directly from the Linux source tree and updating the initramfs.

Download and copy firmware

Run the follow commands to download the file and copy it into place:

# Set the name of the firmware file as an environment variable.
# This is for future script reusability.
export NEEDED_FW=rtl8126a-3.fw

# Create a new firmware directory and change into it.
mkdir ${NEEDED_FW}_dir
cd ${NEEDED_FW}_dir

# Download the firmware file.
wget https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/rtl_nic/${NEEDED_FW}

# Copy the firmware file to the correct location.
sudo cp ${NEEDED_FW} /lib/firmware/rtl_nic/

# Change to the parent directory and delete the firmware file and directory.
cd ..
rm -R ${NEEDED_FW}_dir

# Unset the environment variable.
unset NEEDED_FW

If you have other Realtek add-in cards or USB adaptors that require additional firmware files, change the value of NEEDED_FW=rtl8126a-3.fw to the correct firmware file and rerun the commands.

Update initramfs

After you've downloaded all your required firmware files and copied them to /lib/firmware/rtl_nic/, regenerate all of your initramfs to use the new firmware by issuing the follow command:

update-initramfs -u -k all

Reboot the server for the new firmware to take effect.