Alpine Linux Root on ZFS

Customization

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

Preparation

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

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

Login as root user. There is no password.

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

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.

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.

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.
Connect from another computer
```
ssh root@192.168.1.91
```
Configure NTP client for time synchronization
```
setup-ntp busybox
```
Set up apk-repo. A list of available mirrors is shown. Press space bar to continue
```
setup-apkrepos
```
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.
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'
```
Set a mount point
```
MNT=$(mktemp -d)
```
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
```
Install ZFS support from live media:
```
apk add zfs
```

Install bootloader programs and partition tool

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

System Installation

Partition the disks.

Note: you must clear all existing partition tables and data structures from the disks, especially those with existing ZFS pools or mdraid and those that have been used as live media. Those data structures may interfere with boot process.

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

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

Load ZFS kernel module
```
modprobe zfs
```

Create boot pool

# shellcheck disable=SC2046
zpool create -d \
    -o feature@async_destroy=enabled \
    -o feature@bookmarks=enabled \
    -o feature@embedded_data=enabled \
    -o feature@empty_bpobj=enabled \
    -o feature@enabled_txg=enabled \
    -o feature@extensible_dataset=enabled \
    -o feature@filesystem_limits=enabled \
    -o feature@hole_birth=enabled \
    -o feature@large_blocks=enabled \
    -o feature@lz4_compress=enabled \
    -o feature@spacemap_histogram=enabled \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl \
    -O canmount=off \
    -O compression=lz4 \
    -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.

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.

Create root system container:

Unencrypted

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

Encrypted:

Pick a strong password. 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

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

Workaround for GRUB to recognize predictable disk names:
```
export ZPOOL_VDEV_NAME_PATH=YES
```
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.

Allow EFI system partition to fail at boot:

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

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

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.

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

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

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 '{}' '[]'"

Exit chroot
```
exit
```
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
```
Reboot
```
reboot
```