[CentOS] rescue - UEFI revert to BIOS boot - how?

Wed Nov 21 07:25:38 UTC 2018
Michel van Deventer <michel at van.deventer.cx>


I had the same sort of issue. My workstation with a Asrock motherboard 
suddenly decided to reset UEFI to defaults which caused my Fedora 
installation not to boot. I could boot with a Live USB stick and use 
efibootmgr to set the UEFI boot for Fedora but next time I powered on my 
machine the same issue happened (I remove AC power from my workstation 
when it is not in use). Turned out to be a flat battery for the BIOS 
(coin cell). I replaced the coin cell and set the UEFI boot with the 
Live USB stick and all was well.
The efibootmgr command was something like :
efibootmgr -c --part 2 --loader /EFI/Fedora/grubx64.efi --label Fedora

Please check the manpage of efibootmgr,  the process of how to setup the 
UEFI boot is described very well.



On 2018-11-21 05:00, Steven Tardy wrote:
> On Tue, Nov 20, 2018 at 7:40 AM lejeczek via CentOS <centos at centos.org>
> wrote:
>> hi guys
>> I have a box on which UEFI boot has gone haywire and instead
>> of boot it power the box down, that is before even going to
>> grub2. (displays some error message)
>> I if change to BIOS boot then I can start Centos' rescue -
>> my question is: how can I rescue, re-build grub so it would
>> boot from tradition BIOS?
> If the OS was installed with UEFI enabled I would go back to UEFI mode.
> Then re-add your OS boot configuration within the BIOS setup screen.
> Most motherboard manufacturers detail this process on their website 
> where
> you browse the disk to select somefilename.efi and give it a label 
> “CentOS”.
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