fedora-macbook-dialog

On Jul 27, 2013, at 7:58 PM, Pete Travis <me@petetravis.com> wrote:

> Hey Chris,
>
> As you've probably noticed, a lot of users are fairly confused about
> various multiboot permutations. To help, Chris Roberts, a new docs
> contributor, has begun work on a "Fedora Multiboot Guide". He's been
> working on copy for dual booting with Windows8, and I'm just now sitting
> down to work on general grub and efibootmgr use.
>
> My mental files on dual booting with Apple systems have a single entry,
> "Search the mailing list bucket for relevant threads from Chris Murphy."
> Would you be able to contribute something to the guide?  Anything from
> stream-of-consiousness notes and up would be useful. I would be willing
> to handle markup and polish if you don't have the cycles; your insight
> in any form would be a great addition.

Sure. I'm happy to contribute.

Because the support is in flux, I'm inclined to keep it concise so it's easier to translate and keep up to date. I think few details of how mactel-boot installs differ from (U)EFI installs is that useful. Curious users can just look at the code.

So perhaps early on, a brief overview in the documentation could describe various layout options: Fedora only; OS X + Fedora; OS X + Windows + Fedora; Windows + Fedora. So broadly, four layout possibilities, and explain the basic things the user will need to do, need to know, including consequences (possibly being "not recommended"), for each of those layout types.

Probably the biggest single thing to document is what the installer doesn't do, and non-obvious behaviors post-install:

a. Before running the installer, how to resize the existing JHFS+ volume, to make room for an eventual Fedora volume. Main text probably should recommend shrinking JHFS+ and leaving free space behind, which enables either a Guided or Manual Partitioning method. A side bar should proscribe using Boot Camp Assistant, which will create a hybrid MBR; and also in Disk Utility setting the extra partition as MS-DOS (FAT32 actually) will do the same thing. Hybrid MBRs aren't supported by parted, anaconda, or mactel-boot so there's a high risk of immediate or future data loss if the user installs Fedora (or anything else for that matter).

b. How to switch between OS X and Fedora, post-install. The way the Mac works sorta obviates needing to know anything about efibootmgr. 

c. Also post-install, the purpose of the disk icon that appears in OS X titled "Untitled" and that it's OK to rename it Fedora (or anything else for that matter.)


An open question is what to do about the case of Windows on a Mac, as this can take several forms. The most common, by far, will be OS X and Windows, which has been installed via Boot Camp Assistant, which creates a hybrid MBR, and thus documentation also ought to not recommend installing Fedora. 

The lesser likely cases: 
Windows BIOS install only (no OS X), might be worth testing but I'm pretty sure anaconda booted EFI mode wants the disk formatted GPT, even though Mac EFI firmware can boot from either GPT or MBR disks. 

Windows EFI, with or without OS X, is quite rare, but it would be possible for Fedora to install in this case (either into free space, or with installer supported NTFS shrink).






Chris Murphy


On Jul 29, 2013, at 11:07 AM, Pete Travis <me@petetravis.com> wrote:
> Thanks, this should get me started. I'll surely have some follow up questions later.
>
> No Fedora after BootCamp installs of windows?! That sucks.

Difficult.

With recent (last two years) OS X versions, after a BCA install of Windows, there are four partitions: EFI System, OS X, Recovery HD, and Windows. The MBR can only hold four primary partitions, and Apple doesn't support extended partitions.

So right away it's a problem, because there is no ideal layout for a hybrid MBR for a disk with a 5+ partition GPT. Only the GPT can tell the truth, and the MBR can only lie about the true on disk layout. And considering Windows only honors the MBR when BIOS booted (with the Apple EFI CSM), the MBR really does need to be correct or the user is in a high data loss risk situation. Lots of users do this anyway, and Apple's forums are littered with data loss stories.

In fact there is a long standing bug in Disk Utility whereby if the user creates a 5th partition, the hybrid MBR is replaced with a protective MBR, rendering Windows unbootable. The user isn't warned of this in advance. And it's not possible to regress, because when Apple's diskutil recreates the hybrid MBR (after deleting the 5th partition) it sets the MBR type code for Windows to 0C (for FAT32) instead of 07 (for NTFS) and is not flagged as bootable. So it still won't boot. These bugs have been reported to Apple long ago and they have done nothing, so in my opinion they don't care.

Also, there's some evidence that Apple's installer, when doing major version upgrades, is "repairing" hybrid MBRs, which in the case of a 5+ partition GPT, would also mean data loss in that Windows would become unbootable. So I think broadly speaking it's a bad idea to recommend it, and if anything is a good idea in a sidebar or warning to disclose that which Apple does not in any of their documentation or in the applications that cause the data loss itself.


Chris