this post was submitted on 19 Mar 2025
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Need help with setting up full disk encryption (FDE) where /home is on another drive. (lemmy.world)
submitted 13 hours ago* (last edited 13 hours ago) by mazzilius_marsti@lemmy.world to c/linux@lemmy.ml
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Any distro would do, but for my case, it is Arch because I have more control over the partitions. I would like the OS, so root, swap and others on 1 drive. The /home should be on a separate drive. The tricky thing is to have everything encrypted, except /boot and /efi of course.

Now, here is what I can do

  1. FDE on 1 drive. This is easy: you create /efi, /boot and then create a large LUKS partition. From there, you create LVM on that LUKS partition and get your: /, /home and swap. Then mount everything correctly and install.

In the grub config, you only need to set it so it knows the LUKS partitom and where the root is. For eg, if your LUKs partition is /dev/sda3, you do:

  • cryptdevice=UUID=<uuid of the /dev/sda3>: cryptlvm rootfs=/dev/vg/root.
  1. Unencrypted /home on another drive. This is like 1) but /home is mounted on a separate drive. Still need to do the grub config, but nothing is needed for /home. It is automatically mounted when you login.

Now for my case: Encrypt /home

The encryption and mount part is easy. But how to get the OS to recognize it? The Arch wiki has this weird thing where you create an encryption key, they called it home.key, using cryptsetup. You then store the key in /etc and then in your /etc/crypttab, you specifiy the drive with /home and location of the key. No need for any passphrase.

The problem I have with this is that keys are stored in root. So if my root system is corrupted, I cant even decrypt home....

Any advice is welcome..

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[–] mina86@lemmy.wtf 2 points 7 hours ago

If you go with adding a passphrase to the drive keep in mind that if it’s a unique one you may end up forgetting it since you won’t normally be using it. Even if you set it to the same passphrase as root partition, if you ever change passphrase for root you might forget to change home passphrase.

I would probably just make a physical copy of the key file. It’s just 32 bytes (no, larger key file doesn’t make things any more secure) so you can hexdump -C it and copy the key on a piece of paper.