Any idea how to convert from UEFI back to Legacy Grub?

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Any idea how to convert from UEFI back to Legacy Grub?

The kernel wants to do EFI boot and looks for grub.efi
and the article below fails to cover that issue.

(How to convert RHEL system from UEFI & GPT to legacy BIOS & MBR
https://access.redhat.com/solutions/767293)

Responses

Jereme,

UPDATE - anyone landing here, the link mentioned above by Jereme Hall has been retired (see post below by Jamie Bainbridge).

UPDATE: for existing servers, see Jamie Bainbridge's update below

When loading a fresh new system, the BIOS can be changed so the system is not set for EFI. For physical hardware, the procedure varies and depends on the vendor's hardware. I've had to do this at the BIOS or other BIOS-like interface on a mixture of physical servers.

While I may not necessarily be able to respond, what hardware are you using? Make, Model... This will help hunt down the procedure for your specific hardware. What BIOS level is your system at?

If it is a workstation, some workstations we are receiving come with a seeming inability use anything but UEFI, but there are ways around it, just not highly documented, and again, in this case, in this paragraph, it the procedure was specific to that hardware in question.

I keep finding this page, but the link posted results in "Access Denied" for me. Can we post the answer in this thread?

Would running these two commands work for a drive with MBR?

grub2-install /dev/sda
grub2-mkconfig -o /boot/grub2/grub.cfg

did this ever get resolved for you?

I am looking for the same solution on changing a number of VMware-hosted VMs that are currently using UEFI/GPT that I need to convert to traditional BIOS/MBR boot. They are a mixture of both Red-Hat 7 and Red-Hat 8 servers.

Like you, I get Access Denied when trying to open the suggested link.

Chris,

UPDATE: (thanks Jamie Bainbridge) -- the link from the original poster at solution 767293 was retired, see Jamie Bainbridge's comments below. He also mentions that it is possible to convert some EFI systems back to MBR boot, but not all (see below). It would not be simple and there are quite a lot of factors to consider.

To separate some issues...

When I originally saw this discussion, I immediately thought of a physical non-virtual system that someone at the BIOS level would change prior to loading the operating system.

To convert an existing system that was built under UEFI to non-UEFI is another matter entirely. I'm not sure if that can be done in an easy way, and I've personally not heard of someone taking a Red Hat system built under UEFI (physical or virtual) and converting it to non-UEFI.

I'd open a case and ask Red Hat if it was possible. I can perhaps look into this later today, however, I have never heard of anyone converting an existing UEFI system (phy/virt) to non-UEFI.

Regards,
RJ

Thanks, RJ. I do have a Red-Hat support account but still received the access denial when trying to look at the originally quoted message.

I have never tackled a similar conversion either but am challenged with doing so as a means to enable Azure Site Recovery as a hot-backup solution for the VMs.

Thanks for the quick follow-up

The OP's link at solution 767293 has been retired, as we found those steps don't actually work in all situations. We don't want to provide steps which ruin systems and make them unrecoverable.

There are things which weren't considered in the steps like MBR doesn't support disks over 2 TiB in capacity, GPT can have more partitions than MBR, disks can have different sector sizes (512,512e,2k), it appears gdisk has changed its interactive commands between major releases, partition alignment can make things difficult, the list goes on.

It's definitely possible to convert some EFI systems back to MBR boot, but not all.

I'd actually be surprised if we support such a conversion. I doubt we are testing for this sort of thing and there are a lot of variables to consider. The answer might be to reinstall. You can automate installs with Kickstart to make that process a lot quicker.

Thanks much Jamie

Regards,
RJ