Linux @lemmy.ml SpongeB0B @programming.dev 2mo ago

boot on LUKS encrypted drive ( initramfs Vs initrd ) ?

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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14 comments

AFAIK initramfs is the same thing as initrd. But do you have update-initramfs command available?
- Nope, both do the same thing but they are not the same thing.
  
  If so what is the difference?
  
  That they are 2 different tools. Here
  
  Based on first result
  
  We can use initrd for Linux kernels 2.4 and lower. Conversely, initramfs is for kernels 2.6 and above.
  
  Since on all modern system initial filesystem is tmpfs sometimes it is confused and initramfs is called initrd (for example: in grub to load initramfs you use initrd command).
  
  Also systemd says I am using initrd (on my Fedora machine)
  
  systemd[1]: Running in initrd.
  
  But I have initramfs packed with dracut in /boot folder
  
  /boot/initramfs-6.12.8-200.fc41.x86_64.img
  
  Initramfs and initrd are 2 different things, the problem where the confusion happens is that initrd is deprecated since a few years.
  
  Now, systemd has implemented an interface called systemd-initrd which basically is initramfs.
  
  I guess here is were the confusion lies. Nowadays everything is initramfs even if it called initrd.
  
  The original initrd differs from initramfs, but it is no longer a thing.
  
  Sorry if i came across a little bit snappy have not had a great week so far.
  
  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.
  
  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
  
  Yes, sorry, you are correct. I've edited my other comments.
  
  Everything is fine. It's always nice to learn something new. Hope you will have better week!

14 comments