Window 8 in efi mode and Ubuntu in legacy bios mode
cjwatson at ubuntu.com
Tue Oct 22 14:38:53 UTC 2013
On Mon, Oct 21, 2013 at 08:16:32PM -0500, Jim Byrnes wrote:
> I am again trying to dual boot Win 8 and Ubuntu 13.10 on a Toshiba
> laptop, though a different one this time.
> The only way I can get the live DVD to boot to a usable desktop is
> to turn off the efi boot and put nomodeset in grub.
> I've done a lot of googling on dual booting and find many references
> that basically say that both OS's must use the same scheme, ie both
> efi or both bios. What I can't find is the consequences of not
> doing that. If it means to boot Win 8 I must enable efi and to boot
> to Ubuntu I must disable it, that would be ok, but I doubt it is
> that simple.
In principle this sort of scheme should be possible. The main gotchas I
can think of would be:
* Your BIOS needs to support the GPT partitioning scheme. Contrary to
popular belief, GPT isn't intrinsically UEFI-specific (though I'd
argue it's the best thing to have come out of the UEFI committee);
but some of them do more parsing of the partition table than they
need to and claim that no operating system is installed. I've been
meaning to incorporate a workaround for this into Ubuntu for a while
but haven't yet got round to it; in the meantime
http://mjg59.dreamwidth.org/8035.html suggests an fdisk-based
workaround which ought to help.
* In theory the BIOS calls that read data from disk ought to be able to
cope with offsets above the 2 terabyte limit (2^32 512-byte sectors).
In practice they often appear not to, so it's best not to install
Ubuntu above 2TiB if you plan to boot it in BIOS mode. This probably
isn't a problem on a laptop.
* If you install this way then you won't get a Windows entry in the
Ubuntu boot loader, or if you do then it won't work. They should
still both be bootable, in that Windows' initial boot code will
reside in the EFI System Partition while Ubuntu's will reside in the
MBR and the sectors immediately after it, but you might need to keep
a fairly clear head during partitioning and similar operations to
make sure you don't break this.
Colin Watson [cjwatson at ubuntu.com]
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