Arch Linux

jouissance

Member

Registered: 2015-07-15

Posts: 20

[Solved] Combining UEFI and BIOS boot modes on a USB drive install

I want to be able to use a pre-existing Arch installation on a USB drive to install Arch onto both UEFI and BIOS systems. That is to say, I want to be able to plug the USB drive into a BIOS laptop, install Arch on the laptop HDD, then plug the USB drive into a UEFI laptop, and install Arch onto it as well. After some reading, I'm still confused. If I understand correctly, the BIO laptop will need to support GPT schemes, otherwise this is impossible. Correct? And assuming it does, the procedure would be to create 3 partitions--a GPT root partition, a BIOS boot partition, and an EFI boot partition--then configure GRUB accordingly, correct? Then I would just use the CSM toggle in BIO setup to choose which mode to boot with, correct? But I've also read that it's not a good idea to combine both booting modes on the same system. Is this true?

Last edited by jouissance (2015-12-21 17:10:56)

Scimmia

Fellow

Registered: 2012-09-01

Posts: 11,605

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

I've done it, but not with GRUB. You can get around BIOS systems that don't like GPT by using a hybrid MBR. Kind of hacky, but it works. Other than that, you mostly just need to install both a BIOS and a UEFI bootloader. You can run into architecture issues with UEFI, so watch that.

Head_on_a_Stick

Member

From: London

Registered: 2014-02-20

Posts: 7,751

Website

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

I've also read that it's not a good idea to combine both booting modes on the same system. Is this true?

No.

It's the one mistake in the happyassasin article.

I always combine UEFI (with systemd-boot) and non-UEFI (with GRUB) on my Arch systems.

Use a GPT disk and include both an EFISYS partition (type ef00) and a BIOS boot partition (type ef02) then install systemd-boot *and* GRUB (using the non-UEFI command) to the drive.

Last edited by Head_on_a_Stick (2015-12-14 08:30:59)

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mouseman

Member

From: Outta nowhere

Registered: 2014-04-04

Posts: 291

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

I've also read that it's not a good idea to combine both booting modes on the same system. Is this true?

No.

It's the one mistake in the happyassasin article.

I always combine UEFI (with systemd-boot) and non-UEFI (with GRUB) on my Arch systems.

Use a GPT disk and include both an EFISYS partition (type ef00) and a BIOS boot partition (type ef02) then install systemd-boot *and* GRUB (using the non-UEFI command) to the drive.

Can I ask why you do that?

You reckon that would/should work with FreeBSD for instance?

Head_on_a_Stick

Member

From: London

Registered: 2014-02-20

Posts: 7,751

Website

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

Can I ask why you do that?

I like to try out live distributions and many do not support UEFI so it let me boot up Arch again afterwards without having to fiddle with the firmware options.

You reckon that would/should work with FreeBSD for instance?

I don't know about FreeBSD but my OpenBSD system will boot in either mode (with Secure Boot enabled)
http://daemonforums.org/showthread.php? … #post57379

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jouissance

Member

Registered: 2015-07-15

Posts: 20

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

I've also read that it's not a good idea to combine both booting modes on the same system. Is this true?

No.

It's the one mistake in the happyassasin article.

I always combine UEFI (with systemd-boot) and non-UEFI (with GRUB) on my Arch systems.

Use a GPT disk and include both an EFISYS partition (type ef00) and a BIOS boot partition (type ef02) then install systemd-boot *and* GRUB (using the non-UEFI command) to the drive.

Works great, thanks.

tom.ty89

Member

Registered: 2012-11-15

Posts: 897

Re: [Solved] Combining UEFI and BIOS boot modes on a USB drive install

You can even do it with grub only running grub-install with --target x86-64-efi and --target i386-pc (if you do not boot in UEFI mode then --removable is necessary for --target x86-64-efi).

FWIW MBR/MSDOS+ESP might actually have higher compatibility than GPT+ESP+EF02. Simple logic, since UEFI exists after MBR/MSDOS while BIOS exist before GPT