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I've got a laptop here that came with a Windows 8 installation. What I did: Removed the harddisk, put in an SSD, and now I've (unsuccessfully) tried to install Debian. I've used all the default options of the Graphical Installer and chose not to force UEFI. However, it doesn't boot, but hangs in PXE trying to start via IPV4.

Now, I'm revisiting the installer and wondering: If I choose "force UEFI", does that only affect the installation on the SSD?

Can I swap back the harddisk and will my Windows 8 installation automagically work, or will "force UEFI" do other things I don't know about that will make it impossible to swap back my harddisk at a later time?

  • Please enter the BIOS and check the boot options, if you have not done so. Disable PXE if you do not need it, and check whether you find (U)EFI entries. You may also experiment with trying to enable Legacy Boot. – Ned64 Aug 28 '15 at 16:03
  • That doesn't answer the question: what "force UEFI" actually means. I can think of several options: (A) It's a misnomer for a message cautioning that some poorly programmed firmware might get confused by the presence of 2 types of boot record, (B) the installer will inactivate all legacy BIOS boot records, (C) it'll destroy all non-UEFI partitions, (D/E) it'll do B or C even on disks that are removed, such as OP's. Option D/E is clearly not possible. Of the others, I'm going to assume the truth is (A)... so I'm installing UEFI Debian 8/Jessie alongside BIOS Windows 7 & we'll see what happens – underscore_d Oct 4 '15 at 10:13
  • Anyhow, a machine that came preinstalled with Windows 8 is almost certainly in UEFI mode already. – underscore_d Oct 4 '15 at 10:20
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You're in luck because as part of my own adventures, I had a similar question to you. Forging ahead, I just did the following:

  • took a machine with Windows 7 installed in legacy BIOS compatibility mode on HDD0 and an unused data drive on HDD1 - leaving these drives connected
  • toggled its firmware to UEFI mode
  • installed Debian 8/Jessie in UEFI mode on an mSATA SSD
  • chose "Force UEFI", again assuming the option A outlined in my comment above
  • hoped for the best

Everything was fine. To boot Debian, I leave my BIOS in UEFI mode. To boot Windows 7, I toggle back into legacy mode.

Thus, I have to assume my option A above was correct: "Force UEFI" seems like a poor way of wording the proposition 'Some firmwares might get horribly confused if you install a UEFI/GPT bootloader on one disk, while having BIOS/MBR bootloaders elsewhere on the system. Would you like to give up, just in case?'

Having said that, for anyone thinking my setup is a tad confusing, you're right - and this experience has shown my firmware might well be one of those poorly programmed ones - to say the least. But I don't believe that specific anecdote is relevant here, so I'll stop myself. The key thing is that it works - for now!

  • Sure. I was passing and needed to try it anyway! The installer is very informative about what it'll do to disks - and very cautious - so I imagine this is an exaggerated example of that: a hypothetical caveat against badly coded firmwares. I think any firmware that allowed UEFI to break bootability of preexisting BIOS disks would be very broken - and offline disks especially so. (Even mine isn't that bad!) And again, a laptop shipped with Win 8 probably used UEFI already. usual DISCLAIMER: this is purely anecdotal and I take no responsibility for anyone exploding – underscore_d Oct 9 '15 at 20:12
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I've installed successfully both ways and it doesn't pose an issue as I do not dual boot; I use other alternatives for running win on a machine.

I did notice the UEFI swap partition size is significantly smaller than legacy install... I don't know why that is...

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