Ubuntu 22.04 Root on ZFS

Overview 

Ubuntu Installer 

The Ubuntu installer still has ZFS support, but it was almost removed for 22.04 and it no longer installs zsys. At the moment, this HOWTO still uses zsys, but that will be probably be removed in the near future.

Raspberry Pi 

If you are looking to install on a Raspberry Pi, see Ubuntu 20.04 Root on ZFS for Raspberry Pi.

Caution 

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 

Ubuntu 22.04.1 (“jammy”) Desktop CD (not any server images)
Installing on a drive which presents 4 KiB logical sectors (a “4Kn” drive) only works with UEFI booting. This not unique to ZFS. GRUB does not and will not work on 4Kn with legacy (BIOS) booting.

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.

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 

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

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

Make your changes.

Test:

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

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

Encryption 

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.

Step 1: Prepare The Install Environment 

Boot the Ubuntu Live CD. From the GRUB boot menu, select Try or Install Ubuntu. On the Welcome page, select your preferred language and Try Ubuntu. Connect your system to the Internet as appropriate (e.g. join your WiFi network). Open a terminal (press Ctrl-Alt-T).
Setup and update the repositories:
```
sudo apt update
```
Optional: Install and 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.
sudo apt install --yes openssh-server vim
```
Installing the full vim package fixes terminal problems that occur when using the vim-tiny package (that ships in the Live CD environment) over SSH.

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.
Disable automounting:

If the disk has been used before (with partitions at the same offsets), previous filesystems (e.g. the ESP) will automount if not disabled:
```
gsettings set org.gnome.desktop.media-handling automount false
```
Become root:
```
sudo -i
```

Install ZFS in the Live CD environment:

apt install --yes debootstrap gdisk zfsutils-linux

systemctl stop zed

Step 2: Disk Formatting 

Set a variable with the disk name:
```
DISK=/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.

Hints:
- 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.
- For a mirror or raidz topology, use DISK1, DISK2, etc.
- When choosing a boot pool size, consider how you will use the space. A kernel and initrd may consume around 100M. If you have multiple kernels and take snapshots, you may find yourself low on boot pool space, especially if you need to regenerate your initramfs images, which may be around 85M each. Size your boot pool appropriately for your needs.
If you are re-using a disk, clear it as necessary:

Ensure swap partitions are not in use:
```
swapoff --all
```
If the disk was previously used in an MD array:
```
apt install --yes mdadm

# See if one or more MD arrays are active:
cat /proc/mdstat
# If so, stop them (replace ``md0`` as required):
mdadm --stop /dev/md0

# For an array using the whole disk:
mdadm --zero-superblock --force $DISK
# For an array using a partition (e.g. a swap partition per this HOWTO):
mdadm --zero-superblock --force ${DISK}-part2
```
If the disk was previously used with zfs:
```
wipefs -a $DISK
```
For flash-based storage, if the disk was previously used, you may wish to do a full-disk discard (TRIM/UNMAP), which can improve performance:
```
blkdiscard -f $DISK
```
Clear the partition table:
```
sgdisk --zap-all $DISK
```
If you get a message about the kernel still using the old partition table, reboot and start over (except that you can skip this step).
Create bootloader partition(s):
```
sgdisk     -n1:1M:+512M   -t1:EF00 $DISK

# For legacy (BIOS) booting:
sgdisk -a1 -n5:24K:+1000K -t5:EF02 $DISK
```
Note: While the Ubuntu installer uses an MBR label for legacy (BIOS) booting, this HOWTO uses GPT partition labels for both UEFI and legacy (BIOS) booting. This is simpler than having two options. It is also provides forward compatibility (future proofing). In other words, for legacy (BIOS) booting, this will allow you to move the disk(s) to a new system/motherboard in the future without having to rebuild the pool (and restore your data from a backup). The ESP is created in both cases for similar reasons. Additionally, the ESP is used for /boot/grub in single-disk installs, as discussed below.
Create a partition for swap:

Previous versions of this HOWTO put swap on a zvol. Ubuntu recommends against this configuration due to deadlocks. There is a bug report upstream.

Putting swap on a partition gives up the benefit of ZFS checksums (for your swap). That is probably the right trade-off given the reports of ZFS deadlocks with swap. If you are bothered by this, simply do not enable swap.

Choose one of the following options if you want swap:
- For a single-disk install:
```
sgdisk     -n2:0:+500M    -t2:8200 $DISK
```
- For a mirror or raidz topology:
```
sgdisk     -n2:0:+500M    -t2:FD00 $DISK
```
Adjust the swap swize to your needs. If you wish to enable hiberation (which only works for unencrypted installs), the swap partition must be at least as large as the system’s RAM.
Create a boot pool partition:
```
sgdisk     -n3:0:+2G      -t3:BE00 $DISK
```
The Ubuntu installer uses 5% of the disk space constrained to a minimum of 500 MiB and a maximum of 2 GiB. Making this too small (and 500 MiB might be too small) can result in an inability to upgrade the kernel.
Create a root pool partition:

Choose one of the following options:
- Unencrypted or ZFS native encryption:
```
sgdisk     -n4:0:0        -t4:BF00 $DISK
```
- LUKS:
```
sgdisk     -n4:0:0        -t4:8309 $DISK
```
If you are creating a mirror or raidz topology, repeat the partitioning commands for all the disks which will be part of the pool.
Create the boot pool:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -o cachefile=/etc/zfs/zpool.cache \
    -o compatibility=grub2 \
    -o feature@livelist=enabled \
    -o feature@zpool_checkpoint=enabled \
    -O devices=off \
    -O acltype=posixacl -O xattr=sa \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/boot -R /mnt \
    bpool ${DISK}-part3
```
You should not need to customize any of the options for the boot pool.

Ignore the warnings about the features “not in specified ‘compatibility’ feature set.”

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. Note that GRUB opens the pool read-only, so all read-only compatible features are “supported” by GRUB.

Hints:
- If you are creating a mirror topology, create the pool using:
```
zpool create \
    ... \
    bpool mirror \
    /dev/disk/by-id/scsi-SATA_disk1-part3 \
    /dev/disk/by-id/scsi-SATA_disk2-part3
```
- For raidz topologies, replace mirror in the above command with raidz, raidz2, or raidz3 and list the partitions from the additional disks.
- The boot pool name is no longer arbitrary. It _must_ be bpool. If you really want to rename it, edit /etc/grub.d/10_linux_zfs later, after GRUB is installed (and run update-grub).
Feature Notes:
- The allocation_classes feature should be safe to use. However, unless one is using it (i.e. a special vdev), there is no point to enabling it. It is extremely unlikely that someone would use this feature for a boot pool. If one cares about speeding up the boot pool, it would make more sense to put the whole pool on the faster disk rather than using it as a special vdev.
- The device_rebuild feature should be safe to use (except on raidz, which it is incompatible with), but the boot pool is small, so this does not matter in practice.
- The log_spacemap and spacemap_v2 features have been tested and are safe to use. The boot pool is small, so these do not matter in practice.
- The project_quota feature has been tested and is safe to use. This feature is extremely unlikely to matter for the boot pool.
- The resilver_defer should be safe but the boot pool is small enough that it is unlikely to be necessary.
- As a read-only compatible feature, the userobj_accounting feature should be compatible in theory, but in practice, GRUB can fail with an “invalid dnode type” error. This feature does not matter for /boot anyway.
Create the root pool:

Choose one of the following options:
- Unencrypted:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool ${DISK}-part4
```
- ZFS native encryption:
```
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O encryption=on -O keylocation=prompt -O keyformat=passphrase \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool ${DISK}-part4
```
- LUKS:
```
cryptsetup luksFormat -c aes-xts-plain64 -s 512 -h sha256 ${DISK}-part4
cryptsetup luksOpen ${DISK}-part4 luks1
zpool create \
    -o ashift=12 \
    -o autotrim=on \
    -O acltype=posixacl -O xattr=sa -O dnodesize=auto \
    -O compression=lz4 \
    -O normalization=formD \
    -O relatime=on \
    -O canmount=off -O mountpoint=/ -R /mnt \
    rpool /dev/mapper/luks1
```
Notes:
- The use of ashift=12 is recommended here because many drives today have 4 KiB (or larger) physical sectors, even though they present 512 B logical sectors. Also, a future replacement drive may have 4 KiB physical sectors (in which case ashift=12 is desirable) or 4 KiB logical sectors (in which case ashift=12 is required).
- Setting -O acltype=posixacl enables POSIX ACLs globally. If you do not want this, remove that option, but later add -o acltype=posixacl (note: lowercase “o”) to the zfs create for /var/log, as journald requires ACLs Also, disabling ACLs apparently breaks umask handling with NFSv4.
- Setting xattr=sa vastly improves the performance of extended attributes. Inside ZFS, extended attributes are used to implement POSIX ACLs. Extended attributes can also be used by user-space applications. They are used by some desktop GUI applications. They can be used by Samba to store Windows ACLs and DOS attributes; they are required for a Samba Active Directory domain controller. Note that xattr=sa is Linux-specific. If you move your xattr=sa pool to another OpenZFS implementation besides ZFS-on-Linux, extended attributes will not be readable (though your data will be). If portability of extended attributes is important to you, omit the -O xattr=sa above. Even if you do not want xattr=sa for the whole pool, it is probably fine to use it for /var/log.
- 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.
- recordsize is unset (leaving it at the default of 128 KiB). If you want to tune it (e.g. -O recordsize=1M), see these various blog posts.
- Setting relatime=on is a middle ground between classic POSIX atime behavior (with its significant performance impact) and atime=off (which provides the best performance by completely disabling atime updates). Since Linux 2.6.30, relatime has been the default for other filesystems. See RedHat’s documentation for further information.
- Make sure to include the -part4 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).
- ZFS native encryption now defaults to aes-256-gcm.
- For LUKS, the key size chosen is 512 bits. However, XTS mode requires two keys, so the LUKS key is split in half. Thus, -s 512 means AES-256.
- Your passphrase will likely be the weakest link. Choose wisely. See section 5 of the cryptsetup FAQ for guidance.
Hints:
- If you are creating a mirror topology, create the pool using:
```
zpool create \
    ... \
    rpool mirror \
    /dev/disk/by-id/scsi-SATA_disk1-part4 \
    /dev/disk/by-id/scsi-SATA_disk2-part4
```
- For raidz topologies, replace mirror in the above command with raidz, raidz2, or raidz3 and list the partitions from the additional disks.
- When using LUKS with mirror or raidz topologies, use /dev/mapper/luks1, /dev/mapper/luks2, etc., which you will have to create using cryptsetup.
- The pool name is arbitrary. If changed, the new name must be used consistently. On systems that can automatically install to ZFS, the root pool is named rpool by default.

Step 3: System Installation 

Create filesystem datasets to act as containers:

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

Create filesystem datasets for the root and boot filesystems:

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

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

zfs create -o mountpoint=/boot bpool/BOOT/ubuntu_$UUID

Create datasets:

zfs create -o com.ubuntu.zsys:bootfs=no -o canmount=off \
    rpool/ROOT/ubuntu_$UUID/usr
zfs create -o com.ubuntu.zsys:bootfs=no -o canmount=off \
    rpool/ROOT/ubuntu_$UUID/var
zfs create rpool/ROOT/ubuntu_$UUID/var/lib
zfs create rpool/ROOT/ubuntu_$UUID/var/log
zfs create rpool/ROOT/ubuntu_$UUID/var/spool

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
chmod 700 /mnt/root

The datasets below are optional, depending on your preferences and/or software choices.

If you wish to separate these to exclude them from snapshots:

zfs create rpool/ROOT/ubuntu_$UUID/var/cache
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/nfs
zfs create rpool/ROOT/ubuntu_$UUID/var/tmp
chmod 1777 /mnt/var/tmp

If desired (the Ubuntu installer creates these):

zfs create rpool/ROOT/ubuntu_$UUID/var/lib/apt
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/dpkg

If you use /srv on this system:

zfs create -o com.ubuntu.zsys:bootfs=no \
    rpool/ROOT/ubuntu_$UUID/srv

If you use /usr/local on this system:

zfs create rpool/ROOT/ubuntu_$UUID/usr/local

If this system will have games installed:

zfs create rpool/ROOT/ubuntu_$UUID/var/games

If this system will have a GUI:

zfs create rpool/ROOT/ubuntu_$UUID/var/lib/AccountsService
zfs create rpool/ROOT/ubuntu_$UUID/var/lib/NetworkManager

If this system will use Docker (which manages its own datasets & snapshots):

zfs create rpool/ROOT/ubuntu_$UUID/var/lib/docker

If this system will store local email in /var/mail:

zfs create rpool/ROOT/ubuntu_$UUID/var/mail

If this system will use Snap packages:

zfs create rpool/ROOT/ubuntu_$UUID/var/snap

If you use /var/www on this system:

zfs create rpool/ROOT/ubuntu_$UUID/var/www

For a mirror or raidz topology, create a dataset for /boot/grub:

zfs create -o com.ubuntu.zsys:bootfs=no bpool/grub

A tmpfs is recommended later, but 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.

Note: If you separate a directory required for booting (e.g. /etc) into its own dataset, you must add it to ZFS_INITRD_ADDITIONAL_DATASETS in /etc/default/zfs. Datasets with canmount=off (like rpool/usr above) do not matter for this.

Mount a tmpfs at /run:

mkdir /mnt/run
mount -t tmpfs tmpfs /mnt/run
mkdir /mnt/run/lock

Install the minimal system:
```
debootstrap jammy /mnt
```
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.

Copy in zpool.cache:

mkdir /mnt/etc/zfs
cp /etc/zfs/zpool.cache /mnt/etc/zfs/

Step 4: System Configuration 

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.

Configure the network interface:

Find the interface name:
```
ip addr show
```
Adjust NAME below to match your interface name:
```
vi /mnt/etc/netplan/01-netcfg.yaml
```
```
network:
  version: 2
  ethernets:
    NAME:
      dhcp4: true
```
Customize this file if the system is not a DHCP client.

Configure the package sources:

vi /mnt/etc/apt/sources.list

deb http://archive.ubuntu.com/ubuntu jammy main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu jammy-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu jammy-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu jammy-security main restricted universe multiverse

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

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

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

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 tzdata keyboard-configuration console-setup
```
Install your preferred text editor:
```
apt install --yes nano

apt install --yes vim
```
Installing the full vim package fixes terminal problems that occur when using the vim-tiny package (that is installed by debootstrap) over SSH.
For LUKS installs only, setup /etc/crypttab:
```
apt install --yes cryptsetup

echo luks1 /dev/disk/by-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.

Hint: If you are creating a mirror or raidz topology, repeat the /etc/crypttab entries for luks2, etc. adjusting for each disk.
Create the EFI filesystem:

Perform these steps for both UEFI and legacy (BIOS) booting:
```
apt install --yes dosfstools

mkdosfs -F 32 -s 1 -n EFI ${DISK}-part1
mkdir /boot/efi
echo /dev/disk/by-uuid/$(blkid -s UUID -o value ${DISK}-part1) \
    /boot/efi vfat defaults 0 0 >> /etc/fstab
mount /boot/efi
```
For a mirror or raidz topology, repeat the mkdosfs for the additional disks, but do not repeat the other commands.

Note: The -s 1 for mkdosfs is only necessary for drives which present 4 KiB logical sectors (“4Kn” drives) to meet the minimum cluster size (given the partition size of 512 MiB) for FAT32. It also works fine on drives which present 512 B sectors.
Put /boot/grub on the EFI System Partition:

For a single-disk install only:
```
mkdir /boot/efi/grub /boot/grub
echo /boot/efi/grub /boot/grub none defaults,bind 0 0 >> /etc/fstab
mount /boot/grub
```
This allows GRUB to write to /boot/grub (since it is on a FAT-formatted ESP instead of on ZFS), which means that /boot/grub/grubenv and the recordfail feature works as expected: if the boot fails, the normally hidden GRUB menu will be shown on the next boot. For a mirror or raidz topology, we do not want GRUB writing to the EFI System Partition. This is because we duplicate it at install without a mechanism to update the copies when the GRUB configuration changes (e.g. as the kernel is upgraded). Thus, we keep /boot/grub on the boot pool for the mirror or raidz topologies. This preserves correct mirroring/raidz behavior, at the expense of being able to write to /boot/grub/grubenv and thus the recordfail behavior.
Install GRUB/Linux/ZFS in the chroot environment for the new system:

Choose one of the following options:
- Install GRUB/Linux/ZFS for legacy (BIOS) booting:
```
apt install --yes grub-pc linux-image-generic zfs-initramfs zsys
```
  Select (using the space bar) all of the disks (not partitions) in your pool.
- Install GRUB/Linux/ZFS for UEFI booting:
```
apt install --yes \
    grub-efi-amd64 grub-efi-amd64-signed linux-image-generic \
    shim-signed zfs-initramfs zsys
```
  Notes:
  - Ignore any error messages saying ERROR: Couldn't resolve device and WARNING: Couldn't determine root device. cryptsetup does not support ZFS.
  - Ignore any error messages saying Module zfs not found and couldn't connect to zsys daemon. The first seems to occur due to a version mismatch between the Live CD kernel and the chroot environment, but this is irrelevant since the module is already loaded. The second may be caused by the first but either way is irrelevant since zed is started manually later.
  - For a mirror or raidz topology, this step only installs GRUB on the first disk. The other disk(s) will be handled later. For some reason, grub-efi-amd64 does not prompt for install_devices here, but does after a reboot.
Optional: Remove os-prober:
```
apt purge --yes os-prober
```
This avoids error messages from update-grub. os-prober is only necessary in dual-boot configurations.
Set a root password:
```
passwd
```

Configure swap:

Choose one of the following options if you want swap:

For an unencrypted single-disk install:

mkswap -f ${DISK}-part2
echo /dev/disk/by-uuid/$(blkid -s UUID -o value ${DISK}-part2) \
    none swap discard 0 0 >> /etc/fstab
swapon -a

For an unencrypted mirror or raidz topology:

apt install --yes mdadm

# Adjust the level (ZFS raidz = MD raid5, raidz2 = raid6) and
# raid-devices if necessary and specify the actual devices.
mdadm --create /dev/md0 --metadata=1.2 --level=mirror \
    --raid-devices=2 ${DISK1}-part2 ${DISK2}-part2
mkswap -f /dev/md0
echo /dev/disk/by-uuid/$(blkid -s UUID -o value /dev/md0) \
    none swap discard 0 0 >> /etc/fstab

For an encrypted (LUKS or ZFS native encryption) single-disk install:

apt install --yes cryptsetup

echo swap ${DISK}-part2 /dev/urandom \
      swap,cipher=aes-xts-plain64:sha256,size=512 >> /etc/crypttab
echo /dev/mapper/swap none swap defaults 0 0 >> /etc/fstab

For an encrypted (LUKS or ZFS native encryption) mirror or raidz topology:

apt install --yes cryptsetup mdadm

# Adjust the level (ZFS raidz = MD raid5, raidz2 = raid6) and
# raid-devices if necessary and specify the actual devices.
mdadm --create /dev/md0 --metadata=1.2 --level=mirror \
    --raid-devices=2 ${DISK1}-part2 ${DISK2}-part2
echo swap /dev/md0 /dev/urandom \
      swap,cipher=aes-xts-plain64:sha256,size=512 >> /etc/crypttab
echo /dev/mapper/swap none swap defaults 0 0 >> /etc/fstab

Optional (but recommended): 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
```

Setup system groups:

addgroup --system lpadmin
addgroup --system lxd
addgroup --system sambashare

Optional: Install SSH:

apt install --yes openssh-server

vi /etc/ssh/sshd_config
# Set: PermitRootLogin yes

Step 5: GRUB Installation 

Verify that the ZFS boot filesystem is recognized:
```
grub-probe /boot
```
Refresh the initrd files:
```
update-initramfs -c -k all
```
Note: Ignore any error messages saying ERROR: Couldn't resolve device and WARNING: Couldn't determine root device. cryptsetup does not support ZFS.

Disable memory zeroing:

vi /etc/default/grub
# Add init_on_alloc=0 to: GRUB_CMDLINE_LINUX_DEFAULT
# Save and quit (or see the next step).

This is to address performance regressions.

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

vi /etc/default/grub
# Comment out: GRUB_TIMEOUT_STYLE=hidden
# Set: GRUB_TIMEOUT=5
# Below GRUB_TIMEOUT, add: GRUB_RECORDFAIL_TIMEOUT=5
# 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.

Update the boot configuration:
```
update-grub
```
Note: Ignore errors from osprober, if present.
Install the boot loader:

Choose one of the following options:
- For legacy (BIOS) booting, install GRUB to the MBR:
```
grub-install $DISK
```
  Note that you are installing GRUB to the whole disk, not a partition.
  
  If you are creating a mirror or raidz topology, repeat the grub-install command for each disk in the pool.
- For UEFI booting, install GRUB to the ESP:
```
grub-install --target=x86_64-efi --efi-directory=/boot/efi \
    --bootloader-id=ubuntu --recheck --no-floppy
```
Disable grub-initrd-fallback.service

For a mirror or raidz topology:
```
systemctl mask grub-initrd-fallback.service
```
This is the service for /boot/grub/grubenv which does not work on mirrored or raidz topologies. Disabling this keeps it from blocking subsequent mounts of /boot/grub if that mount ever fails.

Another option would be to set RequiresMountsFor=/boot/grub via a drop-in unit, but that is more work to do here for no reason. Hopefully this bug will be fixed upstream.
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/bpool
touch /etc/zfs/zfs-list.cache/rpool
zed -F &
```
Verify that zed updated the cache by making sure these are not empty:
```
cat /etc/zfs/zfs-list.cache/bpool
cat /etc/zfs/zfs-list.cache/rpool
```
If either is empty, force a cache update and check again:
```
zfs set canmount=on bpool/BOOT/ubuntu_$UUID
zfs set canmount=on rpool/ROOT/ubuntu_$UUID
```
If they are still empty, stop zed (as below), start zed (as above) and try again.

Once the files have data, stop zed:
```
fg
Press Ctrl-C.
```
Fix the paths to eliminate /mnt:
```
sed -Ei "s|/mnt/?|/|" /etc/zfs/zfs-list.cache/*
```
Exit from the chroot environment back to the LiveCD environment:
```
exit
```

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 -a

Reboot:
```
reboot
```
Wait for the newly installed system to boot normally. Login as root.

Step 6: First Boot 

Install GRUB to additional disks:

For a UEFI mirror or raidz topology only:

dpkg-reconfigure grub-efi-amd64

Select (using the space bar) all of the ESP partitions (partition 1 on
each of the pool disks).

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

Step 7: Full Software Installation 

Upgrade the minimal system:
```
apt dist-upgrade --yes
```
Install a regular set of software:

Choose one of the following options:
- Install a command-line environment only:
```
apt install --yes ubuntu-standard
```
- 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:
```
rm /etc/netplan/01-netcfg.yaml
vi /etc/netplan/01-network-manager-all.yaml
```
```
network:
  version: 2
  renderer: NetworkManager
```
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"
    fi
done
```
Reboot:
```
reboot
```

Step 8: Final Cleanup 

Wait for the system to boot normally. Login using the account you created. Ensure the system (including networking) works normally.
Optional: Disable the root password:
```
sudo usermod -p '*' root
```
Optional (but highly recommended): Disable root SSH logins:

If you installed SSH earlier, revert the temporary change:
```
sudo vi /etc/ssh/sshd_config
# Remove: PermitRootLogin yes

sudo systemctl restart ssh
```
Optional: Re-enable the graphical boot process:

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
# Uncomment: GRUB_TIMEOUT_STYLE=hidden
# Add quiet and splash to: GRUB_CMDLINE_LINUX_DEFAULT
# Comment out: GRUB_TERMINAL=console
# Save and quit.

sudo update-grub
```
Note: Ignore errors from osprober, if present.
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.).

Troubleshooting 

Rescuing using a Live CD 

Go through Step 1: Prepare The Install Environment.

For LUKS, first unlock the disk(s):

cryptsetup luksOpen /dev/disk/by-id/scsi-SATA_disk1-part4 luks1
# Repeat for additional disks, if this is a mirror or raidz topology.

Mount everything correctly:

zpool export -a
zpool import -N -R /mnt rpool
zpool import -N -R /mnt bpool
zfs load-key -a
# Replace “UUID” as appropriate; use zfs list to find it:
zfs mount rpool/ROOT/ubuntu_UUID
zfs mount bpool/BOOT/ubuntu_UUID
zfs mount -a

If needed, you can chroot into your installed environment:

mount --make-private --rbind /dev  /mnt/dev
mount --make-private --rbind /proc /mnt/proc
mount --make-private --rbind /sys  /mnt/sys
mount -t tmpfs tmpfs /mnt/run
mkdir /mnt/run/lock
chroot /mnt /bin/bash --login
mount -a

Do whatever you need to do to fix your system.

When done, cleanup:

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

Areca 

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.

MPT2SAS 

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 ZFS_INITRD_PRE_MOUNTROOT_SLEEP=X in /etc/default/zfs. The system will wait X seconds for all drives to appear before importing the pool.

QEMU/KVM/XEN 

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 = [
   "/usr/share/OVMF/OVMF_CODE.fd:/usr/share/OVMF/OVMF_VARS.fd",
   "/usr/share/OVMF/OVMF_CODE.secboot.fd:/usr/share/OVMF/OVMF_VARS.fd",
   "/usr/share/AAVMF/AAVMF_CODE.fd:/usr/share/AAVMF/AAVMF_VARS.fd",
   "/usr/share/AAVMF/AAVMF32_CODE.fd:/usr/share/AAVMF/AAVMF32_VARS.fd",
   "/usr/share/OVMF/OVMF_CODE.ms.fd:/usr/share/OVMF/OVMF_VARS.ms.fd"
]

sudo systemctl restart libvirtd.service

VMware 

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