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Re: How to restore BIOS-based backup on a UEFI machine



On 2021-01-14 at 10:41, Jesper Dybdal wrote:

> I backup my Buster server simply as a (compressed, encrypted) cpio 
> archive.
> 
> Restoring it to a BIOS-based machine is simple: boot a rescue cd, 
> partition the disk, restore all files, fix fstab if necessary, run 
> update-grub and grub-install in a chroot environment.  That works.
> 
> But if the machine should some day die and I can only find/buy a 
> UEFI-only machine to restore it to, how do I do that?  And are there 
> any precautions I should take in advance (on the BIOS system, before 
> creating backups that may be needed on a future UEFI system) in order
> to make it easier to restore to a UEFI machine?
> 
> (My knowledge of UEFI is almost non-existent, and my knowledge of 
> grub is very limited.)

If my understanding is correct, a lot will depend on whether the machine
you're trying to restore it on is using a motherboard with a newer Intel
chipset or something else (an older one or, at least as far as I've been
able to determine to date, any AMD chipset).

Newer-model Intel chipsets specifically prohibit booting to internal
hard drives in "legacy boot" mode, i.e. (at least as far as I can
determine) to drives whose boot information is specified in the MBR
rather than with EFI partitions on GPT[1]. Older ones, and AMD chipsets
as a whole as far as I can determine, don't.

If you're trying to restore on a machine with that restriction attached,
you're probably going to need to convert the install which is being
restored from backup from MBR-style partitioning to GPT-style
partitioning - which is likely to include making changes to the
boot-configuration settings that are present in the backup (files under
/boot, if nothing else). I don't have enough experience with that to
give good guidance, unfortunately.

If you're trying to restore on a machine without that restriction, then
as long as you set the UEFI to boot the computer in "legacy" mode, I'd
expect things should be as straightforward as always.


[1] Yes, this is vague and probably not entirely accurate. My browser
just crashed and will take a while to bring back up, so I don't care to
do the research to resolve that fuzziness before sending this.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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