Arch Linux

SimonJ

Member

Registered: 2021-05-11

Posts: 119

[SOLVED] UEFI and dual boot

Hello and please be kind, I am a long time linux user but it has been a long time since I set up a dual boot machine.

I got a new machine with an nvme drive in it and I intended to only run Arch, so I have set up an encrypted LVM with an unecrypted boot and 500M EFI partition. This all boots fine and I have done this on a few machines now.

The problem is I then thought I could install windows, so like the old days I took out the drive and installed an SSD and installed Windows, this again all works, but then the boot menu only showed windows, no arch. So I booted the install ISO and arch-chrooted in and set up the uefi again, reboot and all is good, but to get to windows I have to go to the boot manager.

I realize my mistake was this should have all been planned ahead of time and now as I see it, the least I have to do is set up a windows efi partition that is 500M and then reinstall windows and then reinstall grub to that same partition. Windows has set a 100M partition, the wiki says this is too small.

My question is, Windows will use an existing EFI partition but would it use the one on the nvme? or does it have to be on the installation drive?

Given I have only done this all today I could also wipe everything and start again, I have backups and all the media for installation.

I am also considering leaving windows as a hidden option as it will rarely get used anyway.

Thanks for your time and wisdom.

Last edited by SimonJ (2022-09-25 20:43:40)

æyno

Member

Registered: 2022-09-25

Posts: 7

Re: [SOLVED] UEFI and dual boot

The EFI partition used by Windows probably doesn't matter, if you want to have an option to boot on Windows in your grub, you simply have to mount the EFI partition used by Windows on your system, then activate os-prober in /etc/default/grub, then run grub-mkconfig. This should allow you to have a Windows entry in your GRUB menu.

I hope this will help you.

SimonJ

Member

Registered: 2021-05-11

Posts: 119

Re: [SOLVED] UEFI and dual boot

The EFI partition used by Windows probably doesn't matter, if you want to have an option to boot on Windows in your grub, you simply have to mount the EFI partition used by Windows on your system, then activate os-prober in /etc/default/grub, then run grub-mkconfig. This should allow you to have a Windows entry in your GRUB menu.

I hope this will help you.

This works but I need to keep it mounted in fstab so updates do not remove it?

Thank you.

Scimmia

Fellow

Registered: 2012-09-01

Posts: 11,544

Re: [SOLVED] UEFI and dual boot

A 100M partition is only too small if you want to put your kernels/initramfs on it. For many uses, it would be just fine.

In general, though, you want one ESP per system. All OSs use it. You can have more than one, but it tends to make things a bit messier. If you're using your firmware's boot manager, you just have NVRAM entries for whatever you want. If you using another boot manager, you'd have to tell us what that is. (previous poster assumed grub for some reason)

SimonJ

Member

Registered: 2021-05-11

Posts: 119

Re: [SOLVED] UEFI and dual boot

A 100M partition is only too small if you want to put your kernels/initramfs on it. For many uses, it would be just fine.

In general, though, you want one ESP per system. All OSs use it. You can have more than one, but it tends to make things a bit messier. If you're using your firmware's boot manager, you just have NVRAM entries for whatever you want. If you using another boot manager, you'd have to tell us what that is. (previous poster assumed grub for some reason)

I am using grub so this is all OK for now. I will leave it as it is working, and may redo the partitions if I get time to do it.

Many thanks, I am always learning something. :-)