Keyboard issues in GRUB bootloader on a Mac Mini booting Mac OS, Windows and Ubuntu Linux

The Mac Mini, my main machine for daily work, has the following partition configuration for triple-booting Windows, Mac and Ubuntu Linux: 

• Partition 1: Mac OS X (HFS+)
• Partition 2: Windows 8 (NTFS)
• Partition 3: Ubuntu Linux (Ext4) 
• Partition 4: DATA (NTFS)

rEFIt is used as the boot manager to allow me to select which partition to boot from at startup. GRUB2 is installed on partition #2 and configured to select between Windows 8 and Linux. This configuration has been working well for a few years.

However, recently after the old USB keyboard (a Microsoft Wired Keyboard 600) failed and had to be replaced with a Prolink PKCS-1002 keyboard, I could no longer select between Windows and Linux at the GRUB2 boot menu, and the system booted to Windows by default. The selection of the Mac OS X partition from the rEFIt menu still worked fine. Once booted to Mac OS, Windows or Linux (by changing the GRUB default entry), I could use the keyboard without hassle. The keyboard issue would still remain even when the Windows 7 BCD bootloader was used, suggesting that the issue was not specific to the GRUB bootloader.

You would probably tell me to go to BIOS and enable USB legacy support, but hey, this is a Mac that uses EFI and boots Windows via BIOS emulation, which most likely would already have legacy USB support, otherwise the old keyboard could not have worked.

Adding keyboard support to GRUB menu

After some research, I decided to follow the advice in this forum thread, which basically told me to add the following lines to /etc/default/grub:

GRUB_PRELOAD_MODULES=”usb usb_keyboard ehci ohci uhci”
GRUB_TERMINAL_INPUT=”usb_keyboard”

and run:

grub-mkconfig -o /boot/grub/grub.cfg
update-grub2

Well, I tried that, which turned out to be a big mistake. The USB keyboard now indeed worked fine in the GRUB menu but selecting any entry would only return error grub error: disk (hd0,msdos5) not found. A simple ls in the GRUB rescue console resulted in the same error. I guess the preloading of keyboard modules at the GRUB menu disrupted the initialization of other system driver packages and the system failed to recognize the hard disk partition to boot from.

I stupidly did not backup my grub.cfg file and the only recourse was to boot from a Ubuntu Live CD, revert the above change to /etc/default/grub and follow this guide to restore the GRUB default configuration. Fortunately this worked and I was back to square one, with a non-working keyboard at GRUB menu.

Keyboard compatibilities

At this point I decided to buy another keyboard, a Logitech K120, and see if the same issues still persist. Surprisingly everything worked and I was able to use the new keyboard to select either Windows or Linux to boot to.

So what is the issue causing only the Prolink keyboard not to work? I checked the hardware ID of all three keyboards from Windows Device Manager:

Logitech K120: VID_046D&PID_C31C [working at GRUB menu]
Microsoft Wire Keyboard 600: VID_045E&PID_0750  [working at GRUB menu]
Prolink PKCS-1002: VID_1A2C&PID_0027 [not working at GRUB menu]

All 3 keyboards are recognized as HID Keyboard Device by Windows:

Despite much effort, I could not find anything from the Device Properties page of the Prolink keyboard that could provide any hint why it could not work. I can only hazard a guess that its implementation of USB Human Interface Device is flawed causing it to fail to work with the emulated BIOS at the GRUB menu while Windows, which presumably has more sophisticated error handling, is able to detect the keyboard without issues.