| 1 |
On Tue, Apr 15, 2014 at 8:38 AM, Nikos Chantziaras <realnc@×××××.com> wrote: |
| 2 |
> As an old fart with MBR hardwired into my brain, I'm not sure I understand |
| 3 |
> how booting from a GPT partitioned disk works now. |
| 4 |
> |
| 5 |
> So, I had to (note: "had to", not "wanted to") install Windows 8.1 on my |
| 6 |
> machine. I had a dual boot Gentoo/Windows7 before that. So I did a backup, |
| 7 |
> wiped the Windows7 partition, and then ran the W8.1 install (from a USB |
| 8 |
> flash drive.) |
| 9 |
> |
| 10 |
> Windows complained that it can't install into MBR partitioned disks on EFI |
| 11 |
> systems. So I booted Gentoo again, and converted my disk to GPT (with |
| 12 |
> sys-apps/gptfdisk.) I backed up my MBR partition table before of course |
| 13 |
> (with dd). I wasn't sure whether I needed an EFI BIOS boot partition (ID |
| 14 |
> ef02), so I created one just to be safe by shrinking my swap partition by |
| 15 |
> 100MB and giving that space to a new ef02 partition. This new partition |
| 16 |
> ended up as /dev/sda5 and I formatted it with a FAT32 filesystem. |
| 17 |
> |
| 18 |
> So far so good. Now what happens with grub-install? I wasn't sure whether I |
| 19 |
> needed to do: |
| 20 |
> |
| 21 |
> grub-install /dev/sda5 |
| 22 |
> |
| 23 |
> or: |
| 24 |
> |
| 25 |
> grub-install /dev/sda |
| 26 |
> |
| 27 |
> So I did both. Note: I'm using grub-0.97-r13 and Gentoo ships it with GPT |
| 28 |
> support. |
| 29 |
> |
| 30 |
> I tested it, and it booted OK. So far so good. |
| 31 |
> |
| 32 |
> Now I installed Windows 8.1. It took the free space of the Windows 7 |
| 33 |
> partition I had wiped, and created a bunch of new ones, including an EFI |
| 34 |
> boot partition (ID ef00). |
| 35 |
> |
| 36 |
> After that, grub didn't show up anymore. So I booted from a sysrescuecd USB |
| 37 |
> stick into my Gentoo, and ran this again: |
| 38 |
> |
| 39 |
> grub-install /dev/sda5 |
| 40 |
> grub-install /dev/sda |
| 41 |
> |
| 42 |
> Now the system boots into grub again, unless I press F11 at the POST screen |
| 43 |
> and tell my EFI firmware to load the "Windows Boot Loader" instead. |
| 44 |
> |
| 45 |
> I'm very, very confused by all this. The EFI boot partition (ef00) created |
| 46 |
> by Windows is not empty; it contains the Windows EFI boot loader. The EFI |
| 47 |
> BIOS boot partition I created myself (ef02) is still empty; grub-install |
| 48 |
> /dev/sda5 didn't seem to put anything in it. |
| 49 |
> |
| 50 |
> So what the hell does grub-install do? How is my system able to boot into |
| 51 |
> grub at all? And, most importantly, how do I boot Windows 8 from grub now? |
| 52 |
> |
| 53 |
> |
| 54 |
|
| 55 |
So you have a few things going on here. |
| 56 |
|
| 57 |
1. You are booting using EFI. grub-0.97 does not support EFI, so it |
| 58 |
must have auto-switched to BIOS compatibility mode when you tried to |
| 59 |
boot using GRUB. |
| 60 |
|
| 61 |
2. It is probably not possible to load the Windows EFI loader from a |
| 62 |
BIOS boot loader. You would need to chainload the Windows BIOS boot |
| 63 |
sector, which probably does not exist on an EFI installation. |
| 64 |
|
| 65 |
3. I am not sure if Gentoo's grub-0.97 actually knows about the BIOS |
| 66 |
boot partition (ef02). I'm actually not sure where it copies the stage |
| 67 |
1.5 loader on a GPT disk. |
| 68 |
|
| 69 |
If you really want to use grub-0.97, I think you will need to force |
| 70 |
BIOS compatibility mode on and install Windows in BIOS mode. |
| 71 |
|
| 72 |
Alternatively, you could convert to GRUB 2, which supports EFI |
| 73 |
natively and should be able to load the Windows boot loader. Note that |
| 74 |
I have not personally set up a dual-boot system in a very long time, |
| 75 |
and never with GRUB 2, so I cannot vouch for how this works in |
| 76 |
practice. |
Archives