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·
    2 months 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.

    • The HobbyistOPEnglish
      1·
      2 months ago

      I’m very grateful for your extended help. I’ve made some progress. I’m able to get the prompt to appear asking me for my passphrase to unlock the right partition (sda3 in my case). Entering the passphrase, however, drops me in the Dracut emergency shell after ~3min of dracut logs, seemingly looping. (Edit: the reason for why it drops me in the shell is very unclear. It says Dropping to debug shell. /bin/sh: can't access tty: job control turned off. And if I try to exit the dracut shell, it says dracut Warning: could not boot.).

      In the Dracut emergency shell, checking /dev/mapper/ I see a luks-<sda3-uuid> listed. Running blkid I see it listed too with TYPE=crypto_LUKS. I also see a dev/dm-0 with a dedicated UUID, in ext4. I ran blkid which shows:

      /dev/mapper/luks-705fc477-573a-4ef6-81b6-a14c43cda1f5: UUID="57955343-922a-4918-9bc1-797ca8d13a9c" TYPE="ext4"
/dev/sda1: UUID="cc5e0b03-3544-4bef-ab8b-8b72dd236926" TYPE="ext4"
/dev/sda2: UUID="4df1af6c-3199-4bb2-bb12-bcf897cfc6fc" TYPE="swap"
/dev/sda3: UUID="705fc477-573a-4ef6-81b6-a14c43cda1f5" TYPE="crypto_LUKS"
/dev/dm-0: UUID="57955343-922a-4918-9bc1-797ca8d13a9c" TYPE="ext4"

      I checked the status of the filesystem running cryptsetup status /dev/mapper/luks-<sda3-uuid> and it says it is active, which I guess means it is unlocked?

      I checked the /root directory, and it is empty. So I tried to mount the partition myself: mount /dev/mapper/luks-<sda3-uuid> /root but it fails saying mount: mounting /dev/mapper/luks-<sda3-uuid> on /root failed: No such file or directory and that got me really puzzled? I’ve been searching far and wide but I can’t seem to find anyone with a similar situation. I feel like I’m close to getting this working.

      Below is my syslinux kernel config, and the 2nd and 3rd items are what I booted into (/boot/extlinux.conf)

      # Generated by update-extlinux 6.04_pre1-r15
DEFAULT menu.c32
PROMPT 0
MENU TITLE Alpine/Linux Boot Menu
MENU HIDDEN
MENU AUTOBOOT Alpine will be booted automatically in # seconds.
TIMEOUT 10
LABEL lts
  MENU DEFAULT
  MENU LABEL Linux lts
  LINUX vmlinuz-lts
  INITRD initramfs-lts
  APPEND root=/dev/mapper/root modules=sd-mod,usb-storage,ext4 cryptroot=UUID=705fc477-573a-4ef6-81b6-a14c43cda1f5 cryptdm=root rootfstype=ext4 rd.debug log_buf_len=1M rd.shell

LABEL lts
  MENU DEFAULT
  MENU LABEL Dracut Linux lts
  LINUX vmlinuz-lts
  INITRD /boot/initramfs-6.6.56-0-lts.img
  APPEND root=/dev/mapper/luks-705fc477-573a-4ef6-81b6-a14c43cda1f5 modules=sd-mod,usb-storage,ext4 rootfstype=ext4 rd.shell rd.debug log_buf_len=1M rd.luks.uuid=705fc477-573a-4ef6-81b6-a14c43cda1f5

LABEL lts
  MENU DEFAULT
  MENU LABEL Dracut Linux lts 2
  LINUX vmlinuz-lts
  INITRD /boot/initramfs-6.6.56-0-lts.img
  APPEND modules=sd-mod,usb-storage,ext4,dm,crypt,rootfs-block rootfstype=ext4 rootflags=rw,relatime rd.shell rd.debug log_buf_len=1M root=UUID=57955343-922a-4918-9bc1-797ca8d13a9c rd.luks.uuid=705fc477-573a-4ef6-81b6-a14c43cda1f5

      And here the /proc/cmdline of the booted partition:

      BOOT_IMAGE=vmlinuz-lts modules=sd-mod,usb-storage,ext4,dm,crypt,rootfs-block rootfstype=ext4 rootflags=rw,relatime rd.shell rd.debug log_buf_len=1M root=UUID=57955343-922a-4918-9bc1-797ca8d13a9c rd.luks.uuid=705fc477-573a-4ef6-81b6-a14c43cda1f5 initrd=/boot/initramfs-6.6.56-0-lts.img

      Here is my setup, when I boot in my regular initramfs (the one I’m trying to replicate using dracut):

      mytestalpine:~# lsblk -o NAME,FSTYPE,FSVER,LABEL,UUID,FSAVAIL,FSUSE%,MOUNTPOINTS
NAME     FSTYPE      FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
sda                                                                                  
├─sda1   ext4                    cc5e0b03-3544-4bef-ab8b-8b72dd236926  195.5M    21% /boot
├─sda2   swap                    4df1af6c-3199-4bb2-bb12-bcf897cfc6fc                [SWAP]
└─sda3   crypto_LUKS             705fc477-573a-4ef6-81b6-a14c43cda1f5                
  └─root ext4                    57955343-922a-4918-9bc1-797ca8d13a9c    2.3G     8% /

mytestalpine:~# lsblk -l -n /dev/sda3
sda3   8:3   0  2.8G 0 part  
root 253:0   0  2.8G 0 crypt /

      Note: No idea of the relevance, but I’m testing this setup in a VM, with a BIOS firmware.

      • chameleon@fedia.io
        2·
        2 months ago

        Sorry, I’ve had a (self-imposed) busy week, but I have to admit, that also has me rather stumped. As far as I can tell, your second entry should work. If the device is visible in /dev/mapper under a name, it should be able to mount under that name.

        The only thing I can think of is that some important module like the ext4 module might be missing somehow? You can get pretty confusing errors when that happens. Dracut is supposed to parse /etc/fstab for everything needed to boot, and maybe that’s not recognizing your root for some reason. dmesg might have some useful info at the end after you try to mount it. If that’s what’s happening, you could try to add add_drivers+=" ext4 " in your dracut.conf and regenerate it (the spaces are important!). But if that’s not it, then I’m probably out of ideas now.