[lfs-dev] Missing option for grub-install?

Bruce Dubbs bruce.dubbs at gmail.com
Mon Jan 21 09:21:16 PST 2019

On 01/21/2019 09:05 AM, Pierre Labastie via lfs-dev wrote:
> On 21/01/2019 11:09, Xi Ruoyao via lfs-dev wrote:
>> On 2019-01-21 10:44 +0100, Pierre Labastie via lfs-dev wrote:
>>> Hi,
>>> My machine has an UEFI BIOS, so that I rarely run grub-install. But yesterday,
>>> I built a new qemu VM, with a non-UEFI (virtual) BIOS. When running
>>> grub-install, it failed with a message (sorry, I haven't saved it) telling
>>> that it could not find /usr/lib/grub/x86_64-efi. Running "grub-install --help"
>>> returned:
>>> ---------
>>> [...]
>>> --target TARGET    install GRUB for TARGET platform [default=x86_64-efi]
>>> [...]
>>> ---------
>>> so I had to run "grub-install --target i386-pc /dev/sda". But now that I have
>>> done that, "grub-install --help" returns:
>>> ---------
>>> [...]
>>> --target TARGET    install GRUB for TARGET platform [default=i386-pc]
>>> [...]
>>> ---------
>>> So the default seems to be what is already installed. Checking the source for
>>> grub-install confirms that. I must have taken a virtual disk used for a former
>>> VM with UEFI BIOS.
>> No.  Grub 2.02 is detecting the target dynamically at runtime by checking if
>> /sys/firmware/efi is empty.  At first time your system was booted via UEFI so
>> this is not empty.  But at the second time your system was booted via Legacy
>> BIOS so this is empty.
> You are right about the process, but what amazes me is that the first boot was
> not particularly EFI. I had a DOS partitioning (not GPT), and no /boot/EFI
> dir, and yet it must have found something in /sys/firmware/efi since it
> proposed x86_64 as the default (I do have the EFI switches on in the kernel).
> Well, looks like it will be hard to reproduce.
>>> Should we add this switch (--target i386-pc) to the grub-install command in
>>> the book?
>> If the host is booted via UEFI we'll need that to install a non-UEFI Grub.
>> But I think it's dangerous (may break the booting process of the host).  We
>> should explain this option more seriously (maybe in a "NOTE" or even
>> "CAUTION").
> Yes, that may break machines with only UEFI boot. I think the command should
> be written without "--target", as it is now, but a note should be added to
> explain that the --target option may be used if the wrong if the application
> default is wrong

Agree.  Please do that when you get a chance.

   -- Bruce

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