Ubuntu 16.04 Root on ZFS



  • This HOWTO uses a whole physical disk.

  • Do not use these instructions for dual-booting.

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

System Requirements

Computers that have less than 2 GiB of memory run ZFS slowly. 4 GiB of memory is recommended for normal performance in basic workloads. If you wish to use deduplication, you will need massive amounts of RAM. Enabling deduplication is a permanent change that cannot be easily reverted.


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.


  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:
  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.


This guide supports the three different Ubuntu encryption options: unencrypted, LUKS (full-disk encryption), and eCryptfs (home directory encryption).

Unencrypted does not encrypt anything, of course. All ZFS features are fully available. With no encryption happening, this option naturally has the best performance.

LUKS encrypts almost everything: the OS, swap, home directories, and anything else. The only unencrypted data is the bootloader, kernel, and initrd. The system cannot boot without the passphrase being entered at the console. All ZFS features are fully available. Performance is good, but LUKS sits underneath ZFS, so if multiple disks (mirror or raidz configurations) are used, the data has to be encrypted once per disk.

eCryptfs protects the contents of the specified home directories. This guide also recommends encrypted swap when using eCryptfs. Other operating system directories, which may contain sensitive data, logs, and/or configuration information, are not encrypted. ZFS compression is useless on the encrypted home directories. ZFS snapshots are not automatically and transparently mounted when using eCryptfs, and manually mounting them requires serious knowledge of eCryptfs administrative commands. eCryptfs sits above ZFS, so the encryption only happens once, regardless of the number of disks in the pool. The performance of eCryptfs may be lower than LUKS in single-disk scenarios.

If you want encryption, LUKS is recommended.

Step 1: Prepare The Install Environment

1.1 Boot the Ubuntu Live CD. Select Try Ubuntu. Connect your system to the Internet as appropriate (e.g. join your WiFi network). Open a terminal (press Ctrl-Alt-T).

1.2 Setup and update the repositories:

$ sudo apt-add-repository universe
$ sudo apt update

1.3 Optional: Start the OpenSSH server in the Live CD environment:

If you have a second system, using SSH to access the target system can be convenient.

$ passwd
  There is no current password; hit enter at that prompt.
$ sudo apt --yes install openssh-server

Hint: You can find your IP address with ip addr show scope global | grep inet. Then, from your main machine, connect with ssh ubuntu@IP.

1.4 Become root:

$ sudo -i

1.5 Install ZFS in the Live CD environment:

# apt install --yes debootstrap gdisk zfs-initramfs

Note: You can ignore the two error lines about “AppStream”. They are harmless.

Step 2: Disk Formatting

2.1 If you are re-using a disk, clear it as necessary:

If the disk was previously used in an MD array, zero the superblock:
# apt install --yes mdadm
# mdadm --zero-superblock --force /dev/disk/by-id/scsi-SATA_disk1

Clear the partition table:
# sgdisk --zap-all /dev/disk/by-id/scsi-SATA_disk1

2.2 Partition your disk:

Run this if you need legacy (BIOS) booting:
# sgdisk -a1 -n2:34:2047  -t2:EF02 /dev/disk/by-id/scsi-SATA_disk1

Run this for UEFI booting (for use now or in the future):
# sgdisk     -n3:1M:+512M -t3:EF00 /dev/disk/by-id/scsi-SATA_disk1

Choose one of the following options:

2.2a Unencrypted or eCryptfs:

# sgdisk     -n1:0:0      -t1:BF01 /dev/disk/by-id/scsi-SATA_disk1

2.2b LUKS:

# sgdisk     -n4:0:+512M  -t4:8300 /dev/disk/by-id/scsi-SATA_disk1
# sgdisk     -n1:0:0      -t1:8300 /dev/disk/by-id/scsi-SATA_disk1

Always use the long /dev/disk/by-id/* aliases with ZFS. Using the /dev/sd* device nodes directly can cause sporadic import failures, especially on systems that have more than one storage pool.


  • ls -la /dev/disk/by-id will list the aliases.

  • Are you doing this in a virtual machine? If your virtual disk is missing from /dev/disk/by-id, use /dev/vda if you are using KVM with virtio; otherwise, read the troubleshooting section.

2.3 Create the root pool:

Choose one of the following options:

2.3a Unencrypted or eCryptfs:

# zpool create -o ashift=12 \
      -O atime=off -O canmount=off -O compression=lz4 -O normalization=formD \
      -O mountpoint=/ -R /mnt \
      rpool /dev/disk/by-id/scsi-SATA_disk1-part1

2.3b LUKS:

# cryptsetup luksFormat -c aes-xts-plain64 -s 256 -h sha256 \
# cryptsetup luksOpen /dev/disk/by-id/scsi-SATA_disk1-part1 luks1
# zpool create -o ashift=12 \
      -O atime=off -O canmount=off -O compression=lz4 -O normalization=formD \
      -O mountpoint=/ -R /mnt \
      rpool /dev/mapper/luks1


  • The use of ashift=12 is recommended here because many drives today have 4KiB (or larger) physical sectors, even though they present 512B logical sectors. Also, a future replacement drive may have 4KiB physical sectors (in which case ashift=12 is desirable) or 4KiB logical sectors (in which case ashift=12 is required).

  • Setting normalization=formD eliminates some corner cases relating to UTF-8 filename normalization. It also implies utf8only=on, which means that only UTF-8 filenames are allowed. If you care to support non-UTF-8 filenames, do not use this option. For a discussion of why requiring UTF-8 filenames may be a bad idea, see The problems with enforced UTF-8 only filenames.

  • Make sure to include the -part1 portion of the drive path. If you forget that, you are specifying the whole disk, which ZFS will then re-partition, and you will lose the bootloader partition(s).

  • For LUKS, the key size chosen is 256 bits. However, XTS mode requires two keys, so the LUKS key is split in half. Thus, -s 256 means AES-128, which is the LUKS and Ubuntu default.

  • Your passphrase will likely be the weakest link. Choose wisely. See section 5 of the cryptsetup FAQ for guidance.


  • The root pool does not have to be a single disk; it can have a mirror or raidz topology. In that case, repeat the partitioning commands for all the disks which will be part of the pool. Then, create the pool using zpool create ... rpool mirror /dev/disk/by-id/scsi-SATA_disk1-part1 /dev/disk/by-id/scsi-SATA_disk2-part1 (or replace mirror with raidz, raidz2, or raidz3 and list the partitions from additional disks).

  • The pool name is arbitrary. On systems that can automatically install to ZFS, the root pool is named rpool by default. If you work with multiple systems, it might be wise to use hostname, hostname0, or hostname-1 instead.

Step 3: System Installation

3.1 Create a filesystem dataset to act as a container:

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

On Solaris systems, the root filesystem is cloned and the suffix is incremented for major system changes through pkg image-update or beadm. Similar functionality for APT is possible but currently unimplemented. Even without such a tool, it can still be used for manually created clones.

3.2 Create a filesystem dataset for the root filesystem of the Ubuntu system:

# zfs create -o canmount=noauto -o mountpoint=/ rpool/ROOT/ubuntu
# zfs mount rpool/ROOT/ubuntu

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.

3.3 Create datasets:

# zfs create                 -o setuid=off              rpool/home
# zfs create -o mountpoint=/root                        rpool/home/root
# zfs create -o canmount=off -o setuid=off  -o exec=off rpool/var
# zfs create -o com.sun:auto-snapshot=false             rpool/var/cache
# zfs create                                            rpool/var/log
# zfs create                                            rpool/var/spool
# zfs create -o com.sun:auto-snapshot=false -o exec=on  rpool/var/tmp

If you use /srv on this system:
# zfs create                                            rpool/srv

If this system will have games installed:
# zfs create                                            rpool/var/games

If this system will store local email in /var/mail:
# zfs create                                            rpool/var/mail

If this system will use NFS (locking):
# zfs create -o com.sun:auto-snapshot=false \
             -o mountpoint=/var/lib/nfs                 rpool/var/nfs

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 such as logs (in /var/log). This will be especially important if/when a beadm or similar utility is integrated. Since we are creating multiple datasets anyway, it is trivial to add some restrictions (for extra security) at the same time. The com.sun.auto-snapshot setting is used by some ZFS snapshot utilities to exclude transient data.

3.4 For LUKS installs only:

# mke2fs -t ext2 /dev/disk/by-id/scsi-SATA_disk1-part4
# mkdir /mnt/boot
# mount /dev/disk/by-id/scsi-SATA_disk1-part4 /mnt/boot

3.5 Install the minimal system:

# chmod 1777 /mnt/var/tmp
# debootstrap xenial /mnt
# zfs set devices=off rpool

The debootstrap command leaves the new system in an unconfigured state. An alternative to using debootstrap is to copy the entirety of a working system into the new ZFS root.

Step 4: System Configuration

4.1 Configure the hostname (change HOSTNAME to the desired hostname).

# echo HOSTNAME > /mnt/etc/hostname

# vi /mnt/etc/hosts
Add a line:       HOSTNAME
or if the system has a real name in DNS:       FQDN HOSTNAME

Hint: Use nano if you find vi confusing.

4.2 Configure the network interface:

Find the interface name:
# ip addr show

# vi /mnt/etc/network/interfaces.d/NAME
auto NAME
iface NAME inet dhcp

Customize this file if the system is not a DHCP client.

4.3 Configure the package sources:

# vi /mnt/etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu xenial main universe
deb-src http://archive.ubuntu.com/ubuntu xenial main universe

deb http://security.ubuntu.com/ubuntu xenial-security main universe
deb-src http://security.ubuntu.com/ubuntu xenial-security main universe

deb http://archive.ubuntu.com/ubuntu xenial-updates main universe
deb-src http://archive.ubuntu.com/ubuntu xenial-updates main universe

4.4 Bind the virtual filesystems from the LiveCD environment to the new system and chroot into it:

# mount --rbind /dev  /mnt/dev
# mount --rbind /proc /mnt/proc
# mount --rbind /sys  /mnt/sys
# chroot /mnt /bin/bash --login

Note: This is using --rbind, not --bind.

4.5 Configure a basic system environment:

# locale-gen en_US.UTF-8

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

# echo LANG=en_US.UTF-8 > /etc/default/locale

# dpkg-reconfigure tzdata

# ln -s /proc/self/mounts /etc/mtab
# apt update
# apt install --yes ubuntu-minimal

If you prefer nano over vi, install it:
# apt install --yes nano

4.6 Install ZFS in the chroot environment for the new system:

# apt install --yes --no-install-recommends linux-image-generic
# apt install --yes zfs-initramfs

4.7 For LUKS installs only:

# echo UUID=$(blkid -s UUID -o value \
      /dev/disk/by-id/scsi-SATA_disk1-part4) \
      /boot ext2 defaults 0 2 >> /etc/fstab

# apt install --yes cryptsetup

# echo luks1 UUID=$(blkid -s UUID -o value \
      /dev/disk/by-id/scsi-SATA_disk1-part1) none \
      luks,discard,initramfs > /etc/crypttab

# vi /etc/udev/rules.d/99-local-crypt.rules
ENV{DM_NAME}!="", SYMLINK+="dm-name-$env{DM_NAME}"

# ln -s /dev/mapper/luks1 /dev/luks1


4.8 Install GRUB

Choose one of the following options:

4.8a Install GRUB for legacy (MBR) booting

# apt install --yes grub-pc

Install GRUB to the disk(s), not the partition(s).

4.8b Install GRUB for UEFI booting

# apt install dosfstools
# mkdosfs -F 32 -n EFI /dev/disk/by-id/scsi-SATA_disk1-part3
# mkdir /boot/efi
# echo PARTUUID=$(blkid -s PARTUUID -o value \
      /dev/disk/by-id/scsi-SATA_disk1-part3) \
      /boot/efi vfat nofail,x-systemd.device-timeout=1 0 1 >> /etc/fstab
# mount /boot/efi
# apt install --yes grub-efi-amd64

4.9 Setup system groups:

# addgroup --system lpadmin
# addgroup --system sambashare

4.10 Set a root password

# passwd

4.11 Fix filesystem mount ordering

Until ZFS gains a systemd mount generator, there are races between mounting filesystems and starting certain daemons. In practice, the issues (e.g. #5754) seem to be with certain filesystems in /var, specifically /var/log and /var/tmp. Setting these to use legacy mounting, and listing them in /etc/fstab makes systemd aware that these are separate mountpoints. 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.

# zfs set mountpoint=legacy rpool/var/log
# zfs set mountpoint=legacy rpool/var/tmp
# cat >> /etc/fstab << EOF
rpool/var/log /var/log zfs defaults 0 0
rpool/var/tmp /var/tmp zfs defaults 0 0

Step 5: GRUB Installation

5.1 Verify that the ZFS root filesystem is recognized:

# grub-probe /

Note: GRUB uses zpool status in order to determine the location of devices. grub-probe assumes all devices are in /dev. The zfs-initramfs package ships udev rules that create symlinks to work around the problem, but there have still been reports of problems. If this happens, you will get an error saying grub-probe: error: failed to get canonical path and should run the following:


5.2 Refresh the initrd files:

# update-initramfs -c -k all
update-initramfs: Generating /boot/initrd.img-4.4.0-21-generic

Note: When using LUKS, this will print “WARNING could not determine root device from /etc/fstab”. This is because cryptsetup does not support ZFS.

5.3 Optional (but highly recommended): Make debugging GRUB easier:

# vi /etc/default/grub
Remove quiet and splash from: GRUB_CMDLINE_LINUX_DEFAULT
Uncomment: GRUB_TERMINAL=console
Save and quit.

Later, once the system has rebooted twice and you are sure everything is working, you can undo these changes, if desired.

5.4 Update the boot configuration:

# update-grub
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.4.0-21-generic
Found initrd image: /boot/initrd.img-4.4.0-21-generic

5.5 Install the boot loader

5.5a For legacy (MBR) booting, install GRUB to the MBR:

# grub-install /dev/disk/by-id/scsi-SATA_disk1
Installing for i386-pc platform.
Installation finished. No error reported.

Do not reboot the computer until you get exactly that result message. Note that you are installing GRUB to the whole disk, not a partition.

If you are creating a mirror, repeat the grub-install command for each disk in the pool.

5.5b For UEFI booting, install GRUB:

# grub-install --target=x86_64-efi --efi-directory=/boot/efi \
      --bootloader-id=ubuntu --recheck --no-floppy

5.6 Verify that the ZFS module is installed:

# ls /boot/grub/*/zfs.mod

Step 6: First Boot

6.1 Snapshot the initial installation:

# zfs snapshot rpool/ROOT/ubuntu@install

In the future, you will likely want to take snapshots before each upgrade, and remove old snapshots (including this one) at some point to save space.

6.2 Exit from the chroot environment back to the LiveCD environment:

# exit

6.3 Run these commands in the LiveCD environment to unmount all filesystems:

# mount | grep -v zfs | tac | awk '/\/mnt/ {print $3}' | xargs -i{} umount -lf {}
# zpool export rpool

6.4 Reboot:

# reboot

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

6.6 Create a user account:

Choose one of the following options:

6.6a Unencrypted or LUKS:

# zfs create rpool/home/YOURUSERNAME
# cp -a /etc/skel/.[!.]* /home/YOURUSERNAME

6.6b eCryptfs:

# apt install ecryptfs-utils

# zfs create -o compression=off -o mountpoint=/home/.ecryptfs/YOURUSERNAME \
# adduser --encrypt-home YOURUSERNAME
# zfs rename rpool/home/temp-YOURUSERNAME rpool/home/YOURUSERNAME

The temporary name for the dataset is required to work-around a bug in ecryptfs-setup-private. Otherwise, it will fail with an error saying the home directory is already mounted; that check is not specific enough in the pattern it uses.

Note: Automatically mounted snapshots (i.e. the .zfs/snapshots directory) will not work through eCryptfs. You can do another eCryptfs mount manually if you need to access files in a snapshot. A script to automate the mounting should be possible, but has not yet been implemented.

6.7 Add your user account to the default set of groups for an administrator:

# usermod -a -G adm,cdrom,dip,lpadmin,plugdev,sambashare,sudo YOURUSERNAME

6.8 Mirror GRUB

If you installed to multiple disks, install GRUB on the additional disks:

6.8a For legacy (MBR) booting:

# dpkg-reconfigure grub-pc
Hit enter until you get to the device selection screen.
Select (using the space bar) all of the disks (not partitions) in your pool.

6.8b UEFI

# umount /boot/efi

For the second and subsequent disks (increment ubuntu-2 to -3, etc.):
# dd if=/dev/disk/by-id/scsi-SATA_disk1-part3 \
# efibootmgr -c -g -d /dev/disk/by-id/scsi-SATA_disk2 \
      -p 3 -L "ubuntu-2" -l '\EFI\Ubuntu\grubx64.efi'

# mount /boot/efi

Step 7: Configure Swap

7.1 Create a volume dataset (zvol) for use as a swap device:

# zfs create -V 4G -b $(getconf PAGESIZE) -o compression=zle \
      -o logbias=throughput -o sync=always \
      -o primarycache=metadata -o secondarycache=none \
      -o com.sun:auto-snapshot=false rpool/swap

You can adjust the size (the 4G part) to your needs.

The compression algorithm is set to zle because it is the cheapest available algorithm. As this guide recommends ashift=12 (4 kiB blocks on disk), the common case of a 4 kiB page size means that no compression algorithm can reduce I/O. The exception is all-zero pages, which are dropped by ZFS; but some form of compression has to be enabled to get this behavior.

7.2 Configure the swap device:

Choose one of the following options:

7.2a Unencrypted or LUKS:

Caution: Always use long /dev/zvol aliases in configuration files. Never use a short /dev/zdX device name.

# mkswap -f /dev/zvol/rpool/swap
# echo /dev/zvol/rpool/swap none swap defaults 0 0 >> /etc/fstab

7.2b eCryptfs:

# apt install cryptsetup
# echo cryptswap1 /dev/zvol/rpool/swap /dev/urandom \
      swap,cipher=aes-xts-plain64:sha256,size=256 >> /etc/crypttab
# systemctl daemon-reload
# systemctl start systemd-cryptsetup@cryptswap1.service
# echo /dev/mapper/cryptswap1 none swap defaults 0 0 >> /etc/fstab

7.3 Enable the swap device:

# swapon -av

Step 8: Full Software Installation

8.1 Upgrade the minimal system:

# apt dist-upgrade --yes

8.2 Install a regular set of software:

Choose one of the following options:

8.2a Install a command-line environment only:

# apt install --yes ubuntu-standard

8.2b Install a full GUI environment:

# apt install --yes ubuntu-desktop

Hint: If you are installing a full GUI environment, you will likely want to manage your network with NetworkManager. In that case, rm /etc/network/interfaces.d/eth0.

8.3 Optional: 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"

8.4 Reboot:

# reboot

Step 9: Final Cleanup

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

9.2 Optional: Delete the snapshot of the initial installation:

$ sudo zfs destroy rpool/ROOT/ubuntu@install

9.3 Optional: Disable the root password

$ sudo usermod -p '*' root

9.4 Optional:

If you prefer the graphical boot process, you can re-enable it now. If you are using LUKS, it makes the prompt look nicer.

$ sudo vi /etc/default/grub
Add quiet and splash to GRUB_CMDLINE_LINUX_DEFAULT
Comment out GRUB_TERMINAL=console
Save and quit.

$ sudo update-grub


Rescuing using a Live CD

Boot the Live CD and open a terminal.

Become root and install the ZFS utilities:

$ sudo -i
# apt update
# apt install --yes zfsutils-linux

This will automatically import your pool. Export it and re-import it to get the mounts right:

# zpool export -a
# zpool import -N -R /mnt rpool
# zfs mount rpool/ROOT/ubuntu
# zfs mount -a

If needed, you can chroot into your installed environment:

# mount --rbind /dev  /mnt/dev
# mount --rbind /proc /mnt/proc
# mount --rbind /sys  /mnt/sys
# chroot /mnt /bin/bash --login

Do whatever you need to do to fix your system.

When done, cleanup:

# mount | grep -v zfs | tac | awk '/\/mnt/ {print $3}' | xargs -i{} umount -lf {}
# zpool export rpool
# reboot


Most problem reports for this tutorial involve mpt2sas hardware that does slow asynchronous drive initialization, like some IBM M1015 or OEM-branded cards that have been flashed to the reference LSI firmware.

The basic problem is that disks on these controllers are not visible to the Linux kernel until after the regular system is started, and ZoL does not hotplug pool members. See https://github.com/zfsonlinux/zfs/issues/330.

Most LSI cards are perfectly compatible with ZoL. If your card has this glitch, try setting rootdelay=X in GRUB_CMDLINE_LINUX. The system will wait up to X seconds for all drives to appear before importing the pool.


Systems that require the arcsas blob driver should add it to the /etc/initramfs-tools/modules file and run update-initramfs -c -k all.

Upgrade or downgrade the Areca driver if something like RIP: 0010:[<ffffffff8101b316>]  [<ffffffff8101b316>] native_read_tsc+0x6/0x20 appears anywhere in kernel log. ZoL is unstable on systems that emit this error message.


  • Set disk.EnableUUID = "TRUE" in the vmx file or vsphere configuration. Doing this ensures that /dev/disk aliases are created in the guest.


Set a unique serial number on each virtual disk using libvirt or qemu (e.g. -drive if=none,id=disk1,file=disk1.qcow2,serial=1234567890).

To be able to use UEFI in guests (instead of only BIOS booting), run this on the host:

$ sudo apt install ovmf
$ sudo vi /etc/libvirt/qemu.conf
Uncomment these lines:
nvram = [
$ sudo service libvirt-bin restart