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Change Gentoo Handbook to recommend GPT partition tables?
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srs5694
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PostPosted: Wed Oct 23, 2013 6:42 pm    Post subject: Reply with quote

1clue wrote:
Could you make a post which could be used as a portion of the handbook, as a modification of the official docs, aimed at a potentially new user? I'll append it with your name on the bug report. Or, you could go to bugs.gentoo.org and post to bug 488844.


I've already cut-and-pasted my above post to the bug report. Actually modifying the installation guide will take considerably more effort, and the authors and editors of that guide need to decide whether to do anything about it. If they decide to do something, I could probably help, but I don't want to put a lot of effort into re-writing something if that effort will be wasted.
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1clue
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PostPosted: Wed Oct 23, 2013 7:46 pm    Post subject: Reply with quote

Good enough. I saw your post on the bug report, and I'll say good enough at this point and let the machine do its thing.

Thank you for your time.
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1clue
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PostPosted: Wed Oct 23, 2013 7:49 pm    Post subject: Reply with quote

I have to say, for me personally the decision has been consistently in the GPT side your decision tree for quite a few years. My hardware has exactly one OS on the bare metal, whatever that OS is.
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NeddySeagoon
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PostPosted: Wed Oct 23, 2013 8:14 pm    Post subject: Reply with quote

Team,

GPT and grub legacy can be a bit fragile as grub cannot install its stage1.5 due to lack cf space.
Instead, stage1 uses a block list to load stage2 directly. This means that every time grub is updated, it must be reinstalled to the MBR to update the block list.

Further, a brain dead BIOS will look for the bootable flag in the protective MSDOS partition table, so new users still need fdisk to set this partition bootable.
Setting the bootable flag in the GPT table doesn't work - but I did try it :)
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NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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srs5694
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PostPosted: Thu Oct 24, 2013 1:25 am    Post subject: Reply with quote

NeddySeagoon wrote:
Further, a brain dead BIOS will look for the bootable flag in the protective MSDOS partition table, so new users still need fdisk to set this partition bootable.


Unfortunately, using fdisk to fix this won't work for much longer; versions of fdisk that support GPT make it impossible to adjust the boot/active flag on the protective MBR's 0xEE partition. Fortunately, the latest (git-accessible) versions of parted make it possible to adjust it by setting a disk-wide flag (whose name I don't recall offhand), but if you happen to have the new fdisk and the old parted, you're pretty much out of luck. In the medium term, of course, using parted for this will be the solution; and in the long term the solution will be to use EFI-mode booting. This is yet another complication to revising the handbook to recommend using GPT.

Quote:
Setting the bootable flag in the GPT table doesn't work - but I did try it :)


Note that the term "bootable flag" is ambiguous at best under GPT. This phrase could mean either of two things:


  • The "boot flag" under parted, GParted, and similar tools. This flag actually sets the GPT type code for an EFI System Partition (ESP). This has only the vaguest conceptual similarity to a "boot flag" on MBR, so it's really quite unfortunate that the parted developers chose to overload this "flag." Under gdisk, an ESP is identified as having a type code of EF00, which is a better conceptual representation of what's going on, even though the true GUID value is C12A7328-F81F-11D2-BA4B-00A0C93EC93B. (gdisk uses its own unique 2-byte hexadecimal type codes as shorthand for the true GUID values.)
  • The "legacy BIOS bootable" attribute. Conceptually, this is much closer to the "boot flag" under MBR, but under parted and GParted, it's called the "legacy_boot" flag. Under gdisk, you manage attributes using the "a" option on the experts' menu. Several other attributes are available under GPT, but they're all fairly obscure.


In practice, most Linux users mean the first of these things when they refer to a "boot flag" on a GPT disk. Neither of these settings has any effect on the protective MBR. AFAIK no BIOS or EFI uses the legacy BIOS bootable attribute in determining how to boot a computer. I have heard of EFIs that look for an ESP to help determine the boot mode, but its presence would signal an attempt to boot in EFI mode, not in BIOS mode. Thus, setting the parted "boot flag" on a partition you intend to boot in BIOS mode would have no effect at best and would be counterproductive at worst.
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