Root on ZFS with native encryption

Setting up Alpine Linux using ZFS with a pool that uses ZFS' native encryption capabilities

Download

Download the extended release from https://www.alpinelinux.org/downloads/ as only it contains the zfs kernel mods at the time of this writing (2020.07.10)

Write it to a USB device and boot from it.

Initial setup

Run the following

   setup-alpine

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

OPTIONAL

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 into my terminal window from these instructions.

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 your resulting machine. You will be reminded again at the end of this doc.

Add needed packages

   apk add zfs sfdisk e2fsprogs syslinux

Create our partitions

We're assuming `/dev/sda` here and in the rest of the document but you can use whatever you need to. To see a list, 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

Create the root filesystem using zfs

   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.