Root on ZFS with native encryption

This is a guide for installing Alpine Linux with its root partition on an encrypted ZFS volume, using ZFS's own encryption capabilities. The system will be encrypted when powered off and will need to be unlocked by typing a passphrase at boot. To be able to boot the system, the `/boot` partition remains unencrypted.

Downloading Alpine

Download the extended release from https://www.alpinelinux.org/downloads/ as only it contains the zfs kernel modules at the time of writing (2022-02-12).

Write it to a USB device and boot from it.

Initial Setup

Run the following to start the installation procedure:

   setup-alpine

Answer all the questions, and hit ctrl-c when promted for which disk you'd like to use.

Optional: SSH access

This section is optional and it assumes internet connectivity. You may enable sshd so you can ssh into the box and copy and paste the rest of the commands from these instructions into a terminal window.

Edit `/etc/ssh/sshd_config` and search for `Permit`. Change the value after `PermitRootLogin` to read `yes`

save and exit to shell. Run `service sshd restart`

Now you can ssh in as root. Do not forget to go back and comment this line out when you're done since it will be enabled on the resulting machine. You will be reminded again at the end of this doc.

Add required packages

   apk add zfs sfdisk e2fsprogs syslinux

Partition setup

We're assuming that `/dev/sda` is the target storage device here and in the rest of the document, but the name of the storage device you wish to install to may be different. To see a list of storage devices and determine the correct one, type `sfdisk -l`.

   echo -e "/dev/sda1: start=1M,size=100M,bootable\n/dev/sda2: start=101M" | sfdisk --quiet --label dos /dev/sda

Create device nodes

   mdev -s

Create the /boot filesystem

   mkfs.ext4 /dev/sda1

ZFS setup

Create the root zpool

   modprobe zfs
   zpool create -f -o ashift=12 \
       -O acltype=posixacl -O canmount=off -O compression=lz4 \
       -O dnodesize=auto -O normalization=formD -O relatime=on -O xattr=sa \
       -O encryption=aes-256-gcm -O keylocation=prompt -O keyformat=passphrase \
       -O mountpoint=/ -R /mnt \
       rpool /dev/sda2

You will have to enter your passphrase at this point. Choose wisely, as your passphrase is most likely the weakest link in this setup.

A few notes on the options supplied to zpool:

- `ashift=12` is recommended here because many drives today have 4KiB (or larger) physical sectors, even though they present 512B logical sectors

- `acltype=posixacl` enables POSIX ACLs globally

- `normalization=formD` eliminates some corner cases relating to UTF-8 filename normalization. It also enables `utf8only=on`, meaning that only files with valid UTF-8 filenames will be accepted.

- `xattr=sa` vastly improves the performance of extended attributes, but is Linux-only. If you care about using this pool on other OpenZFS implementation don't specify this option.

After completing this, confirm that the pool has been created:

   # zpool status

Should return something like:

     pool: rpool
    state: ONLINE
     scan: none requested
   config:

       NAME        STATE     READ WRITE CKSUM
       rpool       ONLINE       0     0     0
         sda2      ONLINE       0     0     0

   errors: No known data errors

Create the required datasets and mount root

   zfs create -o mountpoint=none -o canmount=off rpool/ROOT
   zfs create -o mountpoint=legacy rpool/ROOT/alpine
   mount -t zfs rpool/ROOT/alpine /mnt/

Mount the `/boot` filesystem

   mkdir /mnt/boot/
   mount -t ext4 /dev/sda1 /mnt/boot/

Enable ZFS' services

   rc-update add zfs-import sysinit
   rc-update add zfs-mount sysinit

Install Alpine Linux

   setup-disk /mnt
   dd if=/usr/share/syslinux/mbr.bin of=/dev/sda # write mbr so we can boot

Reboot and enjoy!

😉

NOTE: If you went with the optional step, be sure to disable root login after you reboot.