[Solved] Install RHEL 8 always does UEFI

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lightman47
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[Solved] Install RHEL 8 always does UEFI

Post by lightman47 » 2021/05/12 14:55:32

Since the CentOS announcement, I'm now installing RHEL 8.3 on my machines. One of them is all new hardware due to a lost motherboard in a storm power incident. It is Ryzen 7 7300X on Amd B450 motherboard with MSI BIOS and WD 2TB SSD - two (1TB) partitions. Win 10 is successfully installed on the first partition as MBR, I believe. Every time (regardless of BIOS settings) I install RHEL 8, it installs as UEFI. This results in no access to Windows, and many updates on RHEL 3rd party repos don't update (VirtualBox, Nvidia drivers, etc.) - they seem to complain about Secure Boot, which is disabled!!

I need to force RHEL to install as MBR. Partition managers all seem to want to use GPT that I suspect is the cause of my problem.

If you want/need more info I'll happily supply it but I am just looking for how to install RHEL NOT in UEFI mode.

Thank you.
Last edited by lightman47 on 2021/05/13 17:57:48, edited 1 time in total.

organicchemistry_01
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Re: Install RHEL 8 always does UEFI

Post by organicchemistry_01 » 2021/05/12 19:51:16

When you installed your Windows 10, your bios should already be set in MBR mode prior. You cannot change to MBR midway if you want to dual boot.

lightman47
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Re: Install RHEL 8 always does UEFI

Post by lightman47 » 2021/05/12 20:01:31

How I wish that was the case.

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TrevorH
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Re: Install RHEL 8 always does UEFI

Post by TrevorH » 2021/05/12 22:24:10

Sounds like some sort of BIOS bug to me.
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jlehtone
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Re: Install RHEL 8 always does UEFI

Post by jlehtone » 2021/05/13 11:40:31

TrevorH wrote:
2021/05/12 22:24:10
Sounds like some sort of BIOS bug to me.
I've had one machine where UEFI/BIOS was case sensitive about content in EFI System Partition (ESP). An USB for MS Windows refused to boot in UEFI mode due to that. New USB with different case (on VFAT!!!) and all was well. Alas, OP must have a different problem.

Overall, "MBR" and "GPT" are different formats for partition table. GPT does not use sector 0 like MBR does, although it can put "protective MBR" in there. I had a dual-boot from GPT-drive, where Windows did start in UEFI mode and CentOS (5?) in legacy mode.

UEFI motherboards have the "UEFI" mode and "legacy" mode. The legacy mode acts like there were "BIOS". Both modes can be enabled simultaneously, at least on some boards. If the UEFI mode is disabled, then there is no way that Linux would boot in UEFI mode; drives are probed only by legacy routine.

Windows in legacy mode requires MBR on system drive. Other drives can have GPT.
Windows in UEFI mode requires GPT on system drive. Other drives can have MBR.
Linux is more flexible.

"Secure Boot" compares loaded binaries (e.g. kernel, kernel modules like NVidia's driver) to certificates that are stored on motherboard (flash).
Certificates can/must be added, for example for ELRepo's kmod-nvidia.
WD 2TB SSD - two (1TB) partitions. Win 10 is successfully installed on the first partition as MBR, I believe.
You should be able to check which partition table format the drive has.

Linux installer prefers to have more than one partition. So does Windows, even in legacy mode. The MBR can have at most 4 partitions (of which one can be "extended"; multiple "logical drives"). The GPT can have many more partitions (but no "extended"). Linux can use LVM for some filesystems; multiple "logical volumes" within one partition.

lightman47
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Re: Install RHEL 8 always does UEFI

Post by lightman47 » 2021/05/13 17:57:25

UPDATE:

I got it! Win 10 is now on the first 1TB partition of the SSD and RHEL 8.3 on the second, exactly as desired. While I did a lot of BIOS 'fiddling' and even had to do one 'reset to default' (heh), I believe what did it for me was Disabling the other 10 or so boot choices after the first 3 that I set. (There were 14 or more choices ???). Then there were all the overclocking settings, and a number of others that I tend to avoid touching. Additionally, I found the virtualization setting (has another name now) and enabled it - which solved my VirtualBox issue.

I performed my grub2-mkconfig -o /boot/grub2/grub.cfg and it found Windows, then set the default to RHEL with grub2-set-default 0. :D Happy guy!

I am very grateful for all your input - it helped with the thought process on this new and complicated BIOS and also my weak understanding of disk partitioning. I keep learning.

Thank you!!

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