boot on LUKS encrypted drive ( initramfs Vs initrd ) ? (programming.dev)

submitted 5 months ago* (last edited 5 months ago) by [email protected] to c/[email protected]

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Hi,

I'm trying to encrypt the root filesystem / of a raspberry pi 4 device running under Devuan rpi ( custom kernel )

I'm following LUKS on Raspberry Pi 2021 guide

That explain step by step how achieve this.

But the guide use initramfs and my distro seem to use initrd

So the question, is: should I migrate to initramfs ? and how check whats is inside my current initrd

or keep-up with initrd but then how insert the necessary to enable LUKS drive to be mounted by it ( initrd ) ?

Thanks.

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[-] [email protected] 2 points 5 months ago* (last edited 5 months ago)

Edit: You are right. I looked it up:

There seems to be an actual technical difference, in the kernel, between an initrd and an initramfs. An initrd is apparently mounted like a normal file system, it's just in RAM instead of a backed by a block device. An initramfs is a tmpfs into which a (usually cpio) archive is extracted into. The initramfs apparently would be preferable generally, because the kernel understands that it's a ramdisk, whereas with an initrd it would go through the block device layer, which would mean it would use more ram: If you read a file from an initrd, the kernel would copy the file to ram (unnecessarily, since it's already in ram) like it would for a filesystem on disk, but for a tmpfs/initramfs, it understands it doesn't need to do that.

From a user's perspective there is no significant functional difference I don't think, and I don't think this relevant to OP's question, that probably has more to do with the userspace tools.

[-] [email protected] 2 points 5 months ago

https://en.m.wikipedia.org/wiki/Initial_ramdisk

In Linux systems, initrd (initial ramdisk) is a scheme for loading a temporary root file system into memory, to be used as part of the Linux startup process. initrd and initramfs (from INITial RAM File System) refer to two different methods of achieving this. Both are commonly used to make preparations before the real root file system can be mounted.

As i said 2 different things, initrd was used to create a ramdisk, a block device. Initramfs basically directly offers a filesystem instead of a block device.

systemd has now a interface called systemd-initrd: https://github.com/systemd/systemd/blob/main/docs/INITRD_INTERFACE.md

initrd was deprecated see here: https://lkml.org/lkml/2020/7/14/1508

[-] [email protected] 2 points 5 months ago* (last edited 5 months ago)

Yes, sorry, you are correct. I've edited my other comments.

this post was submitted on 11 Jan 2025

23 points (96.0% liked)

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