Alpine Linux Root on ZFS

ZFSBootMenu

This tutorial is based on the GRUB bootloader. Due to its independent implementation of a read-only ZFS driver, GRUB only supports a subset of ZFS features on the boot pool. [In general, bootloader treat disks as read-only to minimize the risk of damaging on-disk data.]

ZFSBootMenu is an alternative bootloader free of such limitations and has support for boot environments. Do not follow instructions on this page if you plan to use ZBM, as the layouts are not compatible. Refer to their site for installation details.

Customization

Unless stated otherwise, it is not recommended to customize system configuration before reboot.

Only use well-tested pool features

You should only use well-tested pool features. Avoid using new features if data integrity is paramount. See, for example, this comment.

Preparation

  1. Disable Secure Boot. ZFS modules can not be loaded if Secure Boot is enabled.

  2. Download latest extended variant of Alpine Linux live image, verify checksum and boot from it.

    gpg --auto-key-retrieve --keyserver hkps://keyserver.ubuntu.com --verify alpine-extended-*.asc

dd if=input-file of=output-file bs=1M

  3. Login as root user. There is no password.

  4. Configure Internet

    setup-interfaces -r
# You must use "-r" option to start networking services properly
# example:
network interface: wlan0
WiFi name:         <ssid>
ip address:        dhcp
<enter done to finish network config>
manual netconfig:  n

  5. If you are using wireless network and it is not shown, see Alpine Linux wiki for further details. wpa_supplicant can be installed with apk add wpa_supplicant without internet connection.

  6. Configure SSH server

    setup-sshd
# example:
ssh server:        openssh
allow root:        "prohibit-password" or "yes"
ssh key:           "none" or "<public key>"

    Configurations set here will be copied verbatim to the installed system.

  7. Set root password or /root/.ssh/authorized_keys.

    Choose a strong root password, as it will be copied to the installed system. However, authorized_keys is not copied.

  8. Connect from another computer

    ssh root@192.168.1.91

  9. Configure NTP client for time synchronization

    setup-ntp busybox

  10. Set up apk-repo. A list of available mirrors is shown. Press space bar to continue

    setup-apkrepos

  11. Throughout this guide, we use predictable disk names generated by udev

    apk update
apk add eudev
setup-devd udev

    It can be removed after reboot with setup-devd mdev && apk del eudev.

  12. Target disk

    List available disks with

    find /dev/disk/by-id/

    If virtio is used as disk bus, power off the VM and set serial numbers for disk. For QEMU, use -drive format=raw,file=disk2.img,serial=AaBb. For libvirt, edit domain XML. See this page for examples.

    Declare disk array

    DISK='/dev/disk/by-id/ata-FOO /dev/disk/by-id/nvme-BAR'

    For single disk installation, use

    DISK='/dev/disk/by-id/disk1'

  13. Set a mount point

    MNT=$(mktemp -d)

  14. Set partition size:

    Set swap size in GB, set to 1 if you don’t want swap to take up too much space

    SWAPSIZE=4

    Set how much space should be left at the end of the disk, minimum 1GB

    RESERVE=1

  15. Install ZFS support from live media:

    apk add zfs

  16. Install bootloader programs and partition tool

    apk add grub-bios grub-efi parted e2fsprogs cryptsetup util-linux

System Installation

  1. Partition the disks.

    Note: you must clear all existing partition tables and data structures from target disks.

    For flash-based storage, this can be done by the blkdiscard command below:

    partition_disk () {
 local disk="${1}"
 blkdiscard -f "${disk}" || true

 parted --script --align=optimal  "${disk}" -- \
 mklabel gpt \
 mkpart EFI 2MiB 1GiB \
 mkpart bpool 1GiB 5GiB \
 mkpart rpool 5GiB -$((SWAPSIZE + RESERVE))GiB \
 mkpart swap  -$((SWAPSIZE + RESERVE))GiB -"${RESERVE}"GiB \
 mkpart BIOS 1MiB 2MiB \
 set 1 esp on \
 set 5 bios_grub on \
 set 5 legacy_boot on

 partprobe "${disk}"
}

for i in ${DISK}; do
   partition_disk "${i}"
done

  2. Setup encrypted swap. This is useful if the available memory is small:

    for i in ${DISK}; do
   cryptsetup open --type plain --key-file /dev/random "${i}"-part4 "${i##*/}"-part4
   mkswap /dev/mapper/"${i##*/}"-part4
   swapon /dev/mapper/"${i##*/}"-part4
done

  3. Load ZFS kernel module

    modprobe zfs

  4. Create boot pool

    # shellcheck disable=SC2046
zpool create -o compatibility=legacy  \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl \
    -O canmount=off \
    -O devices=off \
    -O normalization=formD \
    -O relatime=on \
    -O xattr=sa \
    -O mountpoint=/boot \
    -R "${MNT}" \
    bpool \
           mirror \
    $(for i in ${DISK}; do
       printf '%s ' "${i}-part2";
      done)

    If not using a multi-disk setup, remove mirror.

    You should not need to customize any of the options for the boot pool.

    GRUB does not support all of the zpool features. See spa_feature_names in grub-core/fs/zfs/zfs.c. This step creates a separate boot pool for /boot with the features limited to only those that GRUB supports, allowing the root pool to use any/all features.

  5. Create root pool

    # shellcheck disable=SC2046
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -R "${MNT}" \
    -O acltype=posixacl \
    -O canmount=off \
    -O compression=zstd \
    -O dnodesize=auto \
    -O normalization=formD \
    -O relatime=on \
    -O xattr=sa \
    -O mountpoint=/ \
    rpool \
    mirror \
   $(for i in ${DISK}; do
      printf '%s ' "${i}-part3";
     done)

    If not using a multi-disk setup, remove mirror.

  6. Create root system container:

    • Unencrypted

      zfs create \
 -o canmount=off \
 -o mountpoint=none \
rpool/alpinelinux

    • Encrypted:

      Avoid ZFS send/recv when using native encryption, see `a ZFS developer's comment on this issue`__ and `this spreadsheet of bugs`__. A LUKS-based guide has yet to be written. Once compromised, changing password will not keep your data safe. See zfs-change-key(8) for more info

      zfs create \
  -o canmount=off \
         -o mountpoint=none \
         -o encryption=on \
         -o keylocation=prompt \
         -o keyformat=passphrase \
rpool/alpinelinux

    You can automate this step (insecure) with: echo POOLPASS | zfs create ....

    Create system datasets, manage mountpoints with mountpoint=legacy

    zfs create -o canmount=noauto -o mountpoint=/  rpool/alpinelinux/root
zfs mount rpool/alpinelinux/root
zfs create -o mountpoint=legacy rpool/alpinelinux/home
mkdir "${MNT}"/home
mount -t zfs rpool/alpinelinux/home "${MNT}"/home
zfs create -o mountpoint=legacy  rpool/alpinelinux/var
zfs create -o mountpoint=legacy rpool/alpinelinux/var/lib
zfs create -o mountpoint=legacy rpool/alpinelinux/var/log
zfs create -o mountpoint=none bpool/alpinelinux
zfs create -o mountpoint=legacy bpool/alpinelinux/root
mkdir "${MNT}"/boot
mount -t zfs bpool/alpinelinux/root "${MNT}"/boot
mkdir -p "${MNT}"/var/log
mkdir -p "${MNT}"/var/lib
mount -t zfs rpool/alpinelinux/var/lib "${MNT}"/var/lib
mount -t zfs rpool/alpinelinux/var/log "${MNT}"/var/log

  7. Format and mount ESP

    for i in ${DISK}; do
 mkfs.vfat -n EFI "${i}"-part1
 mkdir -p "${MNT}"/boot/efis/"${i##*/}"-part1
 mount -t vfat -o iocharset=iso8859-1 "${i}"-part1 "${MNT}"/boot/efis/"${i##*/}"-part1
done

mkdir -p "${MNT}"/boot/efi
mount -t vfat -o iocharset=iso8859-1 "$(echo "${DISK}" | sed "s|^ *||"  | cut -f1 -d' '|| true)"-part1 "${MNT}"/boot/efi

System Configuration

  1. Workaround for GRUB to recognize predictable disk names:

    export ZPOOL_VDEV_NAME_PATH=YES

  2. Install system to disk

    BOOTLOADER=grub setup-disk -k lts -v "${MNT}"

    GRUB installation will fail and will be reinstalled later. The error message about ZFS kernel module can be ignored.

  3. Allow EFI system partition to fail at boot:

    sed -i "s|vfat.*rw|vfat rw,nofail|" "${MNT}"/etc/fstab

  4. Chroot

    for i in /dev /proc /sys; do mkdir -p "${MNT}"/"${i}"; mount --rbind "${i}" "${MNT}"/"${i}"; done
chroot "${MNT}" /usr/bin/env DISK="${DISK}" sh

  5. Apply GRUB workaround

    echo 'export ZPOOL_VDEV_NAME_PATH=YES' >> /etc/profile.d/zpool_vdev_name_path.sh
# shellcheck disable=SC1091
. /etc/profile.d/zpool_vdev_name_path.sh

# GRUB fails to detect rpool name, hard code as "rpool"
sed -i "s|rpool=.*|rpool=rpool|"  /etc/grub.d/10_linux

# BusyBox stat does not recognize zfs, replace fs detection with ZFS
sed -i 's|stat -f -c %T /|echo zfs|' /usr/sbin/grub-mkconfig

# grub-probe fails to identify fs mounted at /boot
BOOT_DEVICE=$(zpool status -P bpool | grep -- -part2 | head -n1 | sed  "s|.*/dev*|/dev|" | sed "s|part2.*|part2|")
sed -i "s|GRUB_DEVICE_BOOT=.*|GRUB_DEVICE_BOOT=${BOOT_DEVICE}|"  /usr/sbin/grub-mkconfig

    The sed workaround for grub-mkconfig needs to be applied for every GRUB update, as the update will overwrite the changes.

  6. Install GRUB:

    mkdir -p /boot/efi/alpine/grub-bootdir/i386-pc/
mkdir -p /boot/efi/alpine/grub-bootdir/x86_64-efi/
for i in ${DISK}; do
 grub-install --target=i386-pc --boot-directory \
     /boot/efi/alpine/grub-bootdir/i386-pc/  "${i}"
done
grub-install --target x86_64-efi --boot-directory \
  /boot/efi/alpine/grub-bootdir/x86_64-efi/ --efi-directory \
  /boot/efi --bootloader-id alpine --removable
if test -d /sys/firmware/efi/efivars/; then
  apk add efibootmgr
  grub-install --target x86_64-efi --boot-directory \
    /boot/efi/alpine/grub-bootdir/x86_64-efi/ --efi-directory \
    /boot/efi --bootloader-id alpine
fi

  7. Generate GRUB menu:

    mkdir -p /boot/grub
grub-mkconfig -o /boot/grub/grub.cfg
cp /boot/grub/grub.cfg \
 /boot/efi/alpine/grub-bootdir/x86_64-efi/grub/grub.cfg
cp /boot/grub/grub.cfg \
 /boot/efi/alpine/grub-bootdir/i386-pc/grub/grub.cfg

  8. For both legacy and EFI booting: mirror ESP content:

    espdir=$(mktemp -d)
find /boot/efi/ -maxdepth 1 -mindepth 1 -type d -print0 \
| xargs -t -0I '{}' cp -r '{}' "${espdir}"
find "${espdir}" -maxdepth 1 -mindepth 1 -type d -print0 \
| xargs -t -0I '{}' sh -vxc "find /boot/efis/ -maxdepth 1 -mindepth 1 -type d -print0 | xargs -t -0I '[]' cp -r '{}' '[]'"

  9. Exit chroot

    exit

  10. Unmount filesystems and create initial system snapshot You can later create a boot environment from this snapshot. See Root on ZFS maintenance page.

    umount -Rl "${MNT}"
zfs snapshot -r rpool@initial-installation
zfs snapshot -r bpool@initial-installation
zpool export -a

  11. Reboot

    reboot