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Re: GRUB and the risk of block list corruption in extX

From: Bruce Dubbs
Subject: Re: GRUB and the risk of block list corruption in extX
Date: Fri, 08 Feb 2013 12:56:52 -0600
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Lennart Sorensen wrote:
On Fri, Feb 08, 2013 at 06:17:57PM +0100, Martin Wilck wrote:
In my case, the reason is a multiboot setup based on chainloading the
indiviual installed OS's bootloaders from a central, primary bootloader.
This is easily accomplished by installing the individual OS's
bootloaders in their respective "/" or "/boot" partitions. Linux
distributions have encouraged this kind of setup over several years -
"install boot loader in first sector of root/boot partition" used to be
a prominent option somewhere in the installation process (these
distributions were usually GRUB 0.9x based - GRUB 0.9x developers didn't
seem to have a big issue with stage1_5 being loaded via block lists).

Recent GRUB2-based distributions like Fedora have removed this option,
and some users are dissatisfied with that. I would like to understand
what the actual risk is. So I'd appreciate examples for the "pretty
serious problems" you mention.

grub 2 has a lot more features, is a lot bigger, and might not fit in
your embedding area of some filesystems.

Of course the block list breaks if the file in the filesystem is modified
or moved without updating the block list, which used to break lilo all the
time whenever one forgot to run the lilo command after making a change.
Sure grub 0.9x was a bit less fragile than lilo, but block lists for
files that could potentially be changed is fragile.

Embedding enough of grub in the first track or a boot partition (as EFI
systems support, as do a number of non x86 architectures) gives a much
more reliable system since it can read anything else it needs using the
filesystem and hence doesn't break if files are changed.

You don't need an EFI system to give GRUB enough space. You just need to partition the drive so the first partition starts at 1MB instead of sector 63. I think using a GPT partition scheme is quite preferred over the MSDOS scheme designed 30 years ago.

I will note that this causes problems for some systems, but I haven't seen it since I don't do windows.

  -- Bruce

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