Ubuntu 20.04 Root on ZFS for Raspberry Pi

Overview

Newer release available

Caution

  • This HOWTO uses a whole physical disk.

  • Backup your data. Any existing data will be lost.

System Requirements

4 GiB of memory is recommended. Do not use deduplication, as it needs massive amounts of RAM. Enabling deduplication is a permanent change that cannot be easily reverted.

A Raspberry Pi 3 B/B+ would probably work (as the Pi 3 is 64-bit, though it has less RAM), but has not been tested. Please report your results (good or bad) using the issue link below.

Support

If you need help, reach out to the community using the Mailing Lists or IRC at #zfsonlinux on Libera Chat. If you have a bug report or feature request related to this HOWTO, please file a new issue and mention @rlaager.

Contributing

  1. Fork and clone: https://github.com/openzfs/openzfs-docs

  2. Install the tools:

    sudo apt install python3-pip

pip3 install -r docs/requirements.txt

# Add ~/.local/bin to your $PATH, e.g. by adding this to ~/.bashrc:
PATH=$HOME/.local/bin:$PATH

  3. Make your changes.

  4. Test:

    cd docs
make html
sensible-browser _build/html/index.html

  5. git commit --signoff to a branch, git push, and create a pull request. Mention @rlaager.

Encryption

WARNING: Encryption has not yet been tested on the Raspberry Pi.

This guide supports three different encryption options: unencrypted, ZFS native encryption, and LUKS. With any option, all ZFS features are fully available.

Unencrypted does not encrypt anything, of course. With no encryption happening, this option naturally has the best performance.

ZFS native encryption encrypts the data and most metadata in the root pool. It does not encrypt dataset or snapshot names or properties. The boot pool is not encrypted at all, but it only contains the bootloader, kernel, and initrd. (Unless you put a password in /etc/fstab, the initrd is unlikely to contain sensitive data.) The system cannot boot without the passphrase being entered at the console. Performance is good. As the encryption happens in ZFS, even if multiple disks (mirror or raidz topologies) are used, the data only has to be encrypted once.

LUKS encrypts almost everything. The only unencrypted data is the bootloader, kernel, and initrd. The system cannot boot without the passphrase being entered at the console. Performance is good, but LUKS sits underneath ZFS, so if multiple disks (mirror or raidz topologies) are used, the data has to be encrypted once per disk.

USB Disks

The Raspberry Pi 4 runs much faster using a USB Solid State Drive (SSD) than a microSD card. These instructions can also be used to install Ubuntu on a USB-connected SSD or other USB disk. USB disks have three requirements that do not apply to microSD cards:

  1. The Raspberry Pi’s Bootloader EEPROM must be dated 2020-09-03 or later.

    To check the bootloader version, power up the Raspberry Pi without an SD card inserted or a USB boot device attached; the date will be on the bootloader line. (If you do not see the bootloader line, the bootloader is too old.) Alternatively, run sudo rpi-eeprom-update on an existing OS on the Raspberry Pi (which on Ubuntu requires apt install rpi-eeprom).

    If needed, the bootloader can be updated from an existing OS on the Raspberry Pi using rpi-eeprom-update -a and rebooting. For other options, see Updating the Bootloader.

  2. The Raspberry Pi must configured for USB boot. The bootloader will show a boot line; if order includes 4, USB boot is enabled.

    If not already enabled, it can be enabled from an existing OS on the Raspberry Pi using rpi-eeprom-config -e: set BOOT_ORDER=0xf41 and reboot to apply the change. On subsequent reboots, USB boot will be enabled.

    Otherwise, it can be enabled without an existing OS as follows:

    • Download the Raspberry Pi Imager Utility.

    • Flash the USB Boot image to a microSD card. The USB Boot image is listed under Bootload in the Misc utility images folder.

    • Boot the Raspberry Pi from the microSD card. USB Boot should be enabled automatically.

  3. U-Boot on Ubuntu 20.04 does not seem to support the Raspberry Pi USB. Ubuntu 20.10 may work. As a work-around, the Raspberry Pi bootloader is configured to directly boot Linux. For this to work, the Linux kernel must not be compressed. These instructions decompress the kernel and add a script to /etc/kernel/postinst.d to handle kernel upgrades.

Step 1: Disk Formatting

The commands in this step are run on the system other than the Raspberry Pi.

This guide has you go to some extra work so that the stock ext4 partition can be deleted.

  1. Download and unpack the official image:

    curl -O https://cdimage.ubuntu.com/releases/20.04.4/release/ubuntu-20.04.4-preinstalled-server-arm64+raspi.img.xz
xz -d ubuntu-20.04.4-preinstalled-server-arm64+raspi.img.xz

# or combine them to decompress as you download:
curl https://cdimage.ubuntu.com/releases/20.04.4/release/ubuntu-20.04.4-preinstalled-server-arm64+raspi.img.xz | \
    xz -d > ubuntu-20.04.4-preinstalled-server-arm64+raspi.img

  2. Dump the partition table for the image:

    sfdisk -d ubuntu-20.04.4-preinstalled-server-arm64+raspi.img

    That will output this:

    label: dos
label-id: 0xddbefb06
device: ubuntu-20.04.4-preinstalled-server-arm64+raspi.img
unit: sectors

<name>.img1 : start=        2048, size=      524288, type=c, bootable
<name>.img2 : start=      526336, size=     6285628, type=83

    The important numbers are 524288 and 6285628. Store those in variables:

    BOOT=524288
ROOT=6285628

  3. Create a partition script:

    cat > partitions << EOF
label: dos
unit: sectors

1 : start=  2048,  size=$BOOT,  type=c, bootable
2 : start=$((2048+BOOT)),  size=$ROOT, type=83
3 : start=$((2048+BOOT+ROOT)), size=$ROOT, type=83
EOF

  4. Connect the disk:

    Connect the disk to a machine other than the target Raspberry Pi. If any filesystems are automatically mounted (e.g. by GNOME) unmount them. Determine the device name. For SD, the device name is almost certainly /dev/mmcblk0. For USB SSDs, the device name is /dev/sdX, where X is a lowercase letter. lsblk can help determine the device name. Set the DISK environment variable to the device name:

    DISK=/dev/mmcblk0    # microSD card
DISK=/dev/sdX        # USB disk

    Because partitions are named differently for /dev/mmcblk0 and /dev/sdX devices, set a second variable used when working with partitions:

    export DISKP=${DISK}p # microSD card
export DISKP=${DISK}  # USB disk ($DISKP == $DISK for /dev/sdX devices)

    Hint: microSD cards connected using a USB reader also have /dev/sdX names.

    WARNING: The following steps destroy the existing data on the disk. Ensure DISK and DISKP are correct before proceeding.

  5. Ensure swap partitions are not in use:

    swapon -v
# If a partition is in use from the disk, disable it:
sudo swapoff THAT_PARTITION

  6. Clear old ZFS labels:

    sudo zpool labelclear -f ${DISK}

    If a ZFS label still exists from a previous system/attempt, expanding the pool will result in an unbootable system.

    Hint: If you do not already have the ZFS utilities installed, you can install them with: sudo apt install zfsutils-linux Alternatively, you can zero the entire disk with: sudo dd if=/dev/zero of=${DISK} bs=1M status=progress

  7. Delete existing partitions:

    echo "label: dos" | sudo sfdisk ${DISK}
sudo partprobe
ls ${DISKP}*

    Make sure there are no partitions, just the file for the disk itself. This step is not strictly necessary; it exists to catch problems.

  8. Create the partitions:

    sudo sfdisk $DISK < partitions

  9. Loopback mount the image:

    IMG=$(sudo losetup -fP --show \
          ubuntu-20.04.4-preinstalled-server-arm64+raspi.img)

  10. Copy the bootloader data:

    sudo dd if=${IMG}p1 of=${DISKP}1 bs=1M

  11. Clear old label(s) from partition 2:

    sudo wipefs -a ${DISKP}2

    If a filesystem with the writable label from the Ubuntu image is still present in partition 2, the system will not boot initially.

  12. Copy the root filesystem data:

    # NOTE: the destination is p3, not p2.
sudo dd if=${IMG}p2 of=${DISKP}3 bs=1M status=progress conv=fsync

  13. Unmount the image:

    sudo losetup -d $IMG

  14. If setting up a USB disk:

    Decompress the kernel:

    sudo -sE

MNT=$(mktemp -d /mnt/XXXXXXXX)
mkdir -p $MNT/boot $MNT/root
mount ${DISKP}1 $MNT/boot
mount ${DISKP}3 $MNT/root

zcat -qf $MNT/boot/vmlinuz >$MNT/boot/vmlinux

    Modify boot config:

    cat >> $MNT/boot/usercfg.txt << EOF
kernel=vmlinux
initramfs initrd.img followkernel
boot_delay
EOF

    Create a script to automatically decompress the kernel after an upgrade:

    cat >$MNT/root/etc/kernel/postinst.d/zz-decompress-kernel << 'EOF'
#!/bin/sh

set -eu

echo "Updating decompressed kernel..."
[ -e /boot/firmware/vmlinux ] && \
    cp /boot/firmware/vmlinux /boot/firmware/vmlinux.bak
vmlinuxtmp=$(mktemp /boot/firmware/vmlinux.XXXXXXXX)
zcat -qf /boot/vmlinuz > "$vmlinuxtmp"
mv "$vmlinuxtmp" /boot/firmware/vmlinux
EOF

chmod +x $MNT/root/etc/kernel/postinst.d/zz-decompress-kernel

    Cleanup:

    umount $MNT/*
rm -rf $MNT
exit

  15. Boot the Raspberry Pi.

    Move the SD/USB disk to the Raspberry Pi. Boot it and login (e.g. via SSH) with ubuntu as the username and password. If you are using SSH, note that it takes a little bit for cloud-init to enable password logins on the first boot. Set a new password when prompted and login again using that password. If you have your local SSH configured to use ControlPersist, you will have to kill the existing SSH process before logging in the second time.

Step 2: Setup ZFS

  1. Become root:

    sudo -i

  2. Set the DISK and DISKP variables again:

    DISK=/dev/mmcblk0    # microSD card
DISKP=${DISK}p       # microSD card

DISK=/dev/sdX        # USB disk
DISKP=${DISK}        # USB disk

    WARNING: Device names can change when moving a device to a different computer or switching the microSD card from a USB reader to a built-in slot. Double check the device name before continuing.

  3. Install ZFS:

    apt update

apt install pv zfs-initramfs

    Note: Since this is the first boot, you may get Waiting for cache lock because unattended-upgrades is running in the background. Wait for it to finish.

  4. Create the root pool:

    Choose one of the following options:

    • Unencrypted:

      zpool create \
    -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 mountpoint=/ -R /mnt \
    rpool ${DISKP}2

    WARNING: Encryption has not yet been tested on the Raspberry Pi.

    • ZFS native encryption:

      zpool create \
    -o ashift=12 \
    -O encryption=aes-256-gcm \
    -O keylocation=prompt -O keyformat=passphrase \
    -O acltype=posixacl -O canmount=off -O compression=lz4 \
    -O dnodesize=auto -O normalization=formD -O relatime=on \
    -O xattr=sa -O mountpoint=/ -R /mnt \
    rpool ${DISKP}2

    • LUKS:

      cryptsetup luksFormat -c aes-xts-plain64 -s 512 -h sha256 ${DISKP}2
cryptsetup luksOpen ${DISK}-part4 luks1
zpool create \
    -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 mountpoint=/ -R /mnt \
    rpool /dev/mapper/luks1

    Notes:

Step 3: System Installation

  1. Create a filesystem dataset to act as a container:

    zfs create -o canmount=off -o mountpoint=none rpool/ROOT

  2. Create a filesystem dataset for the root filesystem:

    UUID=$(dd if=/dev/urandom bs=1 count=100 2>/dev/null |
    tr -dc 'a-z0-9' | cut -c-6)

zfs create -o canmount=noauto -o mountpoint=/ \
    -o com.ubuntu.zsys:bootfs=yes \
    -o com.ubuntu.zsys:last-used=$(date +%s) rpool/ROOT/ubuntu_$UUID
zfs mount rpool/ROOT/ubuntu_$UUID

    With ZFS, it is not normally necessary to use a mount command (either mount or zfs mount). This situation is an exception because of canmount=noauto.

  3. Create datasets:

    zfs create -o com.ubuntu.zsys:bootfs=no \
    rpool/ROOT/ubuntu_$UUID/srv
zfs create -o com.ubuntu.zsys:bootfs=no -o canmount=off \
    rpool/ROOT/ubuntu_$UUID/usr
zfs create rpool/ROOT/ubuntu_$UUID/usr/local
zfs create -o com.ubuntu.zsys:bootfs=no -o canmount=off \
    rpool/ROOT/ubuntu_$UUID/var
zfs create rpool/ROOT/ubuntu_$UUID/var/games
zfs create rpool/ROOT/ubuntu_$UUID/var/lib
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/AccountsService
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/apt
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/dpkg
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/NetworkManager
zfs create rpool/ROOT/ubuntu_$UUID/var/log
zfs create rpool/ROOT/ubuntu_$UUID/var/mail
zfs create rpool/ROOT/ubuntu_$UUID/var/snap
zfs create rpool/ROOT/ubuntu_$UUID/var/spool
zfs create rpool/ROOT/ubuntu_$UUID/var/www

zfs create -o canmount=off -o mountpoint=/ \
    rpool/USERDATA
zfs create -o com.ubuntu.zsys:bootfs-datasets=rpool/ROOT/ubuntu_$UUID \
    -o canmount=on -o mountpoint=/root \
    rpool/USERDATA/root_$UUID

    If you want a separate dataset for /tmp:

    zfs create -o com.ubuntu.zsys:bootfs=no \
    rpool/ROOT/ubuntu_$UUID/tmp
chmod 1777 /mnt/tmp

    The primary goal of this dataset layout is to separate the OS from user data. This allows the root filesystem to be rolled back without rolling back user data.

    If you do nothing extra, /tmp will be stored as part of the root filesystem. Alternatively, you can create a separate dataset for /tmp, as shown above. This keeps the /tmp data out of snapshots of your root filesystem. It also allows you to set a quota on rpool/tmp, if you want to limit the maximum space used. Otherwise, you can use a tmpfs (RAM filesystem) later.

  4. Optional: Ignore synchronous requests:

    microSD cards are relatively slow. If you want to increase performance (especially when installing packages) at the cost of some safety, you can disable flushing of synchronous requests (e.g. fsync(), O_[D]SYNC):

    Choose one of the following options:

    • For the root filesystem, but not user data:

      zfs set sync=disabled rpool/ROOT

    • For everything:

      zfs set sync=disabled rpool

    ZFS is transactional, so it will still be crash consistent. However, you should leave sync at its default of standard if this system needs to guarantee persistence (e.g. if it is a database or NFS server).

  5. Copy the system into the ZFS filesystems:

    (cd /; tar -cf - --one-file-system --warning=no-file-ignored .) | \
    pv -p -bs $(du -sxm --apparent-size / | cut -f1)m | \
    (cd /mnt ; tar -x)

Step 4: System Configuration

  1. Configure the hostname:

    Replace HOSTNAME with the desired hostname:

    hostname HOSTNAME
hostname > /mnt/etc/hostname
vi /mnt/etc/hosts

    Add a line:
127.0.1.1       HOSTNAME
or if the system has a real name in DNS:
127.0.1.1       FQDN HOSTNAME

    Hint: Use nano if you find vi confusing.

  2. Stop zed:

    systemctl stop zed

  3. Bind the virtual filesystems from the running environment to the new ZFS environment and chroot into it:

    mount --make-private --rbind /boot/firmware /mnt/boot/firmware
mount --make-private --rbind /dev  /mnt/dev
mount --make-private --rbind /proc /mnt/proc
mount --make-private --rbind /run  /mnt/run
mount --make-private --rbind /sys  /mnt/sys
chroot /mnt /usr/bin/env DISK=$DISK UUID=$UUID bash --login

  4. Configure a basic system environment:

    apt update

    Even if you prefer a non-English system language, always ensure that en_US.UTF-8 is available:

    dpkg-reconfigure locales
dpkg-reconfigure tzdata

  5. For LUKS installs only, setup /etc/crypttab:

    # cryptsetup is already installed, but this marks it as manually
# installed so it is not automatically removed.
apt install --yes cryptsetup

echo luks1 UUID=$(blkid -s UUID -o value ${DISK}-part4) none \
    luks,discard,initramfs > /etc/crypttab

    The use of initramfs is a work-around for cryptsetup does not support ZFS.

  6. Optional: Mount a tmpfs to /tmp

    If you chose to create a /tmp dataset above, skip this step, as they are mutually exclusive choices. Otherwise, you can put /tmp on a tmpfs (RAM filesystem) by enabling the tmp.mount unit.

    cp /usr/share/systemd/tmp.mount /etc/systemd/system/
systemctl enable tmp.mount

  7. Setup system groups:

    addgroup --system lpadmin
addgroup --system sambashare

  8. Patch a dependency loop:

    For ZFS native encryption or LUKS:

    apt install --yes curl patch

curl https://launchpadlibrarian.net/478315221/2150-fix-systemd-dependency-loops.patch | \
    sed "s|/etc|/lib|;s|\.in$||" | (cd / ; patch -p1)

    Ignore the failure in Hunk #2 (say n twice).

    This patch is from Bug #1875577 Encrypted swap won’t load on 20.04 with zfs root.

  9. Fix filesystem mount ordering:

    We need to activate zfs-mount-generator. This makes systemd aware of the separate mountpoints, which is important for things like /var/log and /var/tmp. In turn, rsyslog.service depends on var-log.mount by way of local-fs.target and services using the PrivateTmp feature of systemd automatically use After=var-tmp.mount.

    mkdir /etc/zfs/zfs-list.cache
touch /etc/zfs/zfs-list.cache/rpool
ln -s /usr/lib/zfs-linux/zed.d/history_event-zfs-list-cacher.sh /etc/zfs/zed.d
zed -F &

    Force a cache update:

    zfs set canmount=noauto rpool/ROOT/ubuntu_$UUID

    Verify that zed updated the cache by making sure this is not empty, which will take a few seconds:

    cat /etc/zfs/zfs-list.cache/rpool

    Stop zed:

    fg
Press Ctrl-C.

    Fix the paths to eliminate /mnt:

    sed -Ei "s|/mnt/?|/|" /etc/zfs/zfs-list.cache/*

  10. Remove old filesystem from /etc/fstab:

    vi /etc/fstab
# Remove the old root filesystem line:
#   LABEL=writable / ext4 ...

  11. Configure kernel command line:

    cp /boot/firmware/cmdline.txt /boot/firmware/cmdline.txt.bak
sed -i "s|root=LABEL=writable rootfstype=ext4|root=ZFS=rpool/ROOT/ubuntu_$UUID|" \
    /boot/firmware/cmdline.txt
sed -i "s| fixrtc||" /boot/firmware/cmdline.txt
sed -i "s|$| init_on_alloc=0|" /boot/firmware/cmdline.txt

    The fixrtc script is not compatible with ZFS and will cause the boot to hang for 180 seconds.

    The init_on_alloc=0 is to address performance regressions.

  12. Optional (but highly recommended): Make debugging booting easier:

    sed -i "s|$| nosplash|" /boot/firmware/cmdline.txt

  13. Reboot:

    exit
reboot

    Wait for the newly installed system to boot normally. Login as ubuntu.

Step 5: First Boot

  1. Become root:

    sudo -i

  2. Set the DISK variable again:

    DISK=/dev/mmcblk0    # microSD card

DISK=/dev/sdX        # USB disk

  3. Delete the ext4 partition and expand the ZFS partition:

    sfdisk $DISK --delete 3
echo ", +" | sfdisk --no-reread -N 2 $DISK

    Note: This does not automatically expand the pool. That will be happen on reboot.

  4. Create a user account:

    Replace YOUR_USERNAME with your desired username:

    username=YOUR_USERNAME

UUID=$(dd if=/dev/urandom bs=1 count=100 2>/dev/null |
    tr -dc 'a-z0-9' | cut -c-6)
ROOT_DS=$(zfs list -o name | awk '/ROOT\/ubuntu_/{print $1;exit}')
zfs create -o com.ubuntu.zsys:bootfs-datasets=$ROOT_DS \
    -o canmount=on -o mountpoint=/home/$username \
    rpool/USERDATA/${username}_$UUID
adduser $username

cp -a /etc/skel/. /home/$username
chown -R $username:$username /home/$username
usermod -a -G adm,cdrom,dip,lpadmin,lxd,plugdev,sambashare,sudo $username

  5. Reboot:

    reboot

    Wait for the system to boot normally. Login using the account you created.

  6. Become root:

    sudo -i

  7. Expand the ZFS pool:

    Verify the pool expanded:

    zfs list rpool

    If it did not automatically expand, try to expand it manually:

    DISK=/dev/mmcblk0    # microSD card
DISKP=${DISK}p       # microSD card

DISK=/dev/sdX        # USB disk
DISKP=${DISK}        # USB disk

zpool online -e rpool ${DISKP}2

  8. Delete the ubuntu user:

    deluser --remove-home ubuntu

Step 6: Full Software Installation

  1. Optional: Remove cloud-init:

    vi /etc/netplan/01-netcfg.yaml

    network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true

    rm /etc/netplan/50-cloud-init.yaml
apt purge --autoremove ^cloud-init
rm -rf /etc/cloud

  2. Optional: Remove other storage packages:

    apt purge --autoremove bcache-tools btrfs-progs cloud-guest-utils lvm2 \
    mdadm multipath-tools open-iscsi overlayroot xfsprogs

  3. Upgrade the minimal system:

    apt dist-upgrade --yes

  4. Optional: Install a full GUI environment:

    apt install --yes ubuntu-desktop
echo dtoverlay=vc4-fkms-v3d >> /boot/firmware/usercfg.txt

    Hint: If you are installing a full GUI environment, you will likely want to remove cloud-init as discussed above but manage your network with NetworkManager:

    rm /etc/netplan/*.yaml
vi /etc/netplan/01-network-manager-all.yaml

    network:
  version: 2
  renderer: NetworkManager

  5. Optional (but recommended): Disable log compression:

    As /var/log is already compressed by ZFS, logrotate’s compression is going to burn CPU and disk I/O for (in most cases) very little gain. Also, if you are making snapshots of /var/log, logrotate’s compression will actually waste space, as the uncompressed data will live on in the snapshot. You can edit the files in /etc/logrotate.d by hand to comment out compress, or use this loop (copy-and-paste highly recommended):

    for file in /etc/logrotate.d/* ; do
    if grep -Eq "(^|[^#y])compress" "$file" ; then
        sed -i -r "s/(^|[^#y])(compress)/\1#\2/" "$file"
    fi
done

  6. Reboot:

    reboot

Step 7: Final Cleanup

  1. Wait for the system to boot normally. Login using the account you created. Ensure the system (including networking) works normally.

  2. Optional: For LUKS installs only, backup the LUKS header:

    sudo cryptsetup luksHeaderBackup /dev/disk/by-id/scsi-SATA_disk1-part4 \
    --header-backup-file luks1-header.dat

    Store that backup somewhere safe (e.g. cloud storage). It is protected by your LUKS passphrase, but you may wish to use additional encryption.

    Hint: If you created a mirror or raidz topology, repeat this for each LUKS volume (luks2, etc.).