Hi folks,

I have Alpine Linux installed in an encrypted LUKS partition. I came across this tutorial which shows how to setup a key in a USB drive and when the drive is inserted and the computer booted, the LUKS partition auto-unlocks with the key on the USB drive.

https://askubuntu.com/questions/1414617/configure-ubuntu-22-04-zfs-for-automatic-luks-unlock-on-boot-via-usb-drive

I would like to setup the same thing but I do not have Alpine linux installed on ZFS, so I’m looking for ways to adapt the instructions.

So far, what I’ve done is:

  1. I’ve setup the key on the usb stick and I can unlock the LUKS partition with that key.
  2. create a /etc/mkinitfs/features.d/usb-unlock.sh script with the following content:

(the echo to /dev/kmesg was to check whether the script did indeed run at boot by trying to print to the kernel messages but I can’t find anything in the kernel messages).

#!/bin/sh

echo "usb-unlock script starting..." > /dev/kmsg

USB_MOUNT="/mnt/my-usb-key" # The USB stick mounting point
LUKS_KEY_FILE="awesome.key"  # The name of your keyfile on the USB stick

# Search for the USB stick with the key
for device in $(ls /dev/disk/by-uuid/*); do
    mount $device $USB_MOUNT 2>/dev/null
    if [ -f "$USB_MOUNT/$LUKS_KEY_FILE" ]; then
        # Unlock the LUKS partition
        cryptsetup luksOpen /dev/sda3 cryptroot \
            --key-file "$USB_MOUNT/$LUKS_KEY_FILE" && exit 0
    fi
    umount $USB_MOUNT
done
echo "No USB key found, falling back to password prompt." # this message never appears, despite not having found the key on the usb stick

echo "usb-unlock script ending." > /dev/kmsg
  1. I added usb-unlock to the features in mkinitfs.conf:
mytestalpine:~# cat /etc/mkinitfs/mkinitfs.conf 
features="ata base ide scsi usb virtio ext4 cryptsetup keymap usb-unlock"
  1. run mkinitfs to rebuild the initramfs. Then reboot to test the implementation, which was unsuccessful.

What am I missing / doing wrong? Thank you for your help!

Edit: forgot to add step 4

  • chameleon@fedia.io
    2·
    27 days ago

    I think you should check your root= line and add a rd.luks.uuid= to make it open it. Dracut will by default open the root FS as /dev/mapper/luks-abcdef... based on the LUKS container UUID. You can get that with cryptsetup luksUUID. /dev/mapper/root is just never going to show up unless you’ve assigned a custom name to that with the barely documented rd.luks.name, and I don’t see that in your setup. The cryptroot and cryptdm parameters aren’t used by Dracut either.

    With all of that missing it’s just gonna wait for that /dev/mapper/root to magically show up out of nowhere, without ever trying to open it.

    A correct cmdline will probably look something along the lines of root=/dev/mapper/luks-<uuid> modules=sd-mod,usb-storage,ext4 rootfstype=ext4 rootflags=rw,relatime rd.luks.uuid=<uuid> and once opening with passphrase works, you can start to mess with rd.luks.key=/awesome.key (and readd quiet when done debugging, if you want it that way).

    ldconfig errors and the missing modules should be fine. musl’s ldconfig is just a bit different but also isn’t required in quite the same way. I don’t think you should need to mess with modules manually. I don’t think you’re using LVM’s userland for your setup, just all the device-mapper kernel modules. Dracut will pull all the necessary bits in for you if you’re setting it up for LUKS.