I have a PS/2 keyboard that is showing symptoms of cable failure. From time to time I need to access my BIOS with an F2 press very early in the boot process. Almost all wired keyboards I see (Amazon) are now USB. Will I lose access to the BIOS if the keyboard is active only when the USB drivers are started?

My BIOS allows USB keyboard access to change BIOS settings, after that the OS takes over and loads the necessary drivers for it. My BIOS is dated 2011.

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Any relatively modern BIOS should work with a USB keyboard, as long as the USB keyboard support isn't disabled in BIOS somehow. You could have problems with some USB keyboards though if you use grub. I had to replace my PS2 keyboard with a USB one and the BIOS works fine with it, Linux works fine with it, but grub just refuses to work with it even after trying all the legacy keyboard settings in the BIOS and all the grub settings I could find on google.

This doesn't really cause much of a problem for me though since I just need to wait for the grub countdown until it boots the default OS

And also look onto BIOS settings might be helpful. Even if they don't provide boot options from USB-HDs or -DVDs, there are sometimes items like "Enable USB legacy support", indicating BIOS adressing of USB bus. I checked boot menu access with such a PC by inserting an USB RF stick for a wireless keyboard successfully.

One only might encounter inaccessibility during chainloading some non-UNIX-OSes until switchover to their own USB-drivers is done.

I've never had a problem with a keyboard, USB or otherwise, being able to access the BIOS.

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I had a board once that set usb-legacy "off" by default, and when the battery ended it cleared CMOS so I had to plug a PS2 keyboard to access it again.

There's technically 3 stages where the usb keyboard will become available. When the bios / uefi does its thing. When the bootloader does its thing. And when the linux kernel gets around to the usb-hid part plus turning on usb. You can disable usb in the bios / uefi. And you can not include the usb modules in the kernel, so it's not foolproof. Plus the bootloader has to load the usb module (usb.mod), which it does by default most of the time.

GRUB> insmod usb

Not really needed these days, more of a thing when you had to choose between UHCI and OHCI as the usb type. It just kind of works out of the box these days. Although you might need to load part_gpt if dealing with newer drives. Mostly handled by default with update-grub.

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Mine works as soon as I switch on. As per what Shadow 7 says.

Thanks everyone! Turns out my BIOS has a setting to use USB at boot. I think I'm gonna be OK.

You should be OK with most modern wireless usb keyboards also. I use a logitech K400. So far on many machines it hasn't failed.