Make Windows 7 UEFI bootable

Question

I recently installed Linux intending to be able to double boot, however, I had to install it in UEFI mode because of some weird BIOS settings, although Windows 7 is not installed in UEFI mode. After this I haven't been able to boot Windows at all. What I want to do is to make Windows 7 UEFI bootable so that I can add it to my UEFI GRUB. Unfortunately, I am unable to boot Windows, and I don't have access to an installation CD or anything like that for Windows. Are there any way to enable UEFI booting of Windows from Linux? A program or package or something like that?

---

Edit:

I read this guide on how to convert a Windows installation to UEFI mode, and from what I understand, the necessary steps is to convert the hard disk from MBR to GPT and then use a Windows system repair disc to create a partition with an UEFI boot loader.

So my question boils down to this: can I use gptgen on Linux to safely convert my hard disk to GPT and then use a system repair disc created with a different Windows computer?

Answer 1

You have several options:

• Re-install Ubuntu in BIOS/CSM/legacy mode -- This is almost certainly possible, but will require preparing your boot medium correctly and/or controlling your computer's CSM, which can be a confusing challenge. See this page of mine for more on the CSM.
• Install a BIOS-mode boot loader for Linux -- You can install a BIOS-mode version of GRUB 2 (or some other BIOS-mode boot loader) from your current installation. This should get things working in BIOS mode. Installing the grub-pc package and then running sudo grub-install /dev/sda will probably do the trick; however, a lot depends on configuration details, such as how many disks you've got and how they're partitioned.
• Convert Windows to boot in EFI mode -- This can be done, but is a bit of a pain. See this page for one procedure. I'm vaguely familiar with the gptgen utility to which you refer, but I'm much more familiar with GPT fdisk (gdisk), which can also do the job, since I wrote GPT fdisk. Note that converting from MBR to GPT is only part of the job; the more important task is installing an EFI-mode boot loader for Windows.
• Use rEFInd -- rEFInd can switch from its native EFI-mode boot to a BIOS-mode boot on most (but not all) EFIs. This feature is disabled by default on UEFI-based PCs, though, because it's more likely to cause problems than solve them on most systems. In your case, though, it may be a desirable option. See this question and my answer to it for details on this approach.
• Re-install Windows in EFI mode -- This option may be a reasonable one, particularly if you've accidentally wiped out your Windows installation when you installed Ubuntu.

It's hard for me to say which approach is best for you because I have inadequate information. Critically, I don't know how your disk is partitioned. Some people who find themselves in your situation discover, to their horror, that they've accidentally wiped out their Windows installations. If you're in this situation, re-installing Windows in EFI mode is likely the easiest solution -- but you may need to take extreme recovery steps if you had important personal data on the disk. If you've already done an MBR-to-GPT conversion but have left the Windows partitions otherwise intact, then converting Windows to boot in EFI mode is almost certainly the best approach. If you have two disks (a GPT disk for Ubuntu and an MBR disk for Windows), then using rEFInd to boot Windows in BIOS mode or installing a BIOS-mode boot loader for Linux are likely the best options. If you've got one MBR disk that's still in MBR mode, then installing a BIOS-mode boot loader for Linux is likely the best approach. (Note that re-installing Ubuntu in BIOS mode is simply an "overkill" way to install a BIOS-mode boot loader for Linux. Despite being overkill, it may be easier than doing a technically simpler installation of the BIOS-mode boot loader only, since the installer is designed for newbies to use whereas manual GRUB installation is not.)