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[Solved] Questions about Arch and Gentoo on same partition
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crossroads1112
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PostPosted: Mon Sep 01, 2014 12:37 am    Post subject: [Solved] Questions about Arch and Gentoo on same partition Reply with quote

Hello everyone. I'm a long time Arch Linux user and I've recently began the process of installing gentoo (I have just entered the chroot). Before I continue I have a few questions.

Currently this is my partition layout

/dev/sda1 is 512M formatted as ext4
/dev/sda2 is 16G formatted as swap
/dev/sda3 is 931.5G LUKS encrypted container containing btrfs.

Within btrfs I have four subvolumes:

rootvol which contains my Arch Linux root filesystem
homevol which contains my Arch Linux home directory
genroot which currently contains my gentoo root file system
genhome which will have my gentoo home folder

My question is, when it comes time to to install the linux kernel, will I have to use the same kernel for both Arch and Gentoo? If not, which should I shoose to use. I'd imagine they use the same intramfs image right?

Thanks.


Last edited by crossroads1112 on Tue Sep 02, 2014 1:50 pm; edited 1 time in total
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The Doctor
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PostPosted: Mon Sep 01, 2014 12:56 am    Post subject: Reply with quote

Quote:
/dev/sda1 is 512M formatted as ext4
A boot partition shouldn't need a Journal. I also shouldn't need to be so big, but no harm either way.
Quote:
My question is, when it comes time to to install the linux kernel, will I have to use the same kernel for both Arch and Gentoo?
You don't have to, but you could choose to. A kernel is pretty much a kernel. Catch 22 is that the modules would have to be installed on both root partitions.
Quote:
I'd imagine they use the same intramfs image right?
That depends on the initramfs. If it is tied to your Arch install via either a non-shared kernel or the root volume then you can't. If it isn't you may be able to. Although, again, there is no reason why you couldn't maintain two competently separate kernels and initramfs for each OS.

In theory, booting your new gentoo install might be as easy as adding a boot entry in your current bootloader but modifying the root= option.
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crossroads1112
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PostPosted: Mon Sep 01, 2014 2:04 am    Post subject: Reply with quote

The Doctor wrote:
That depends on the initramfs. If it is tied to your Arch install via either a non-shared kernel or the root volume then you can't. If it isn't you may be able to. Although, again, there is no reason why you couldn't maintain two competently separate kernels and initramfs for each OS.


Currently my intramfs image and kernel are in the ext4 /boot partition (I know that It doesn't need to be that big but my hard drive is 1TB so I figured I'd rather go too big than too small) :) ) I would rather use a separate kernel (so I can compile and optimize it myself. It would need to be in the boot partition because that is the only thing that is unencrypted. So would I just compile another kernel (name it like vmlinuz-linux-gentoo or something), copy the entry for Arch and change rootflages=subvol=genroot. Could I use the same intramfs image with two kernels or would I have to have two sepearte intramfs images?

Thank you so much for your help.
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The Doctor
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PostPosted: Mon Sep 01, 2014 2:22 am    Post subject: Reply with quote

Quote:
It would need to be in the boot partition because that is the only thing that is unencrypted.
This would be good practice anyway since duplicating partitions would just complicate your life and waste space.
Quote:
Could I use the same intramfs image with two kernels or would I have to have two sepearte intramfs images?
This kind of depends on what the Arch one does. If it has bits like kernel modules built in then the answer is no. If I remember correctly this is the case.

If you really want to dive into the optimization bit, you can roll your own It shouldn't be too difficult since all it should need is your crypt tools and maybe some btrfs tools. If everything required is simply built into the kernel then you have it easy. This can actually be a much better approach since you won't have to update it when you update the kernel.
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