openzfs-docs/docs/Getting Started/Ubuntu/Ubuntu 20.04 Root on ZFS.rst

.. highlight:: sh

Ubuntu 20.04 Root on ZFS
========================

.. contents:: Table of Contents
  :local:

Overview
--------

Ubuntu Installer
~~~~~~~~~~~~~~~~

The Ubuntu installer has `support for root-on-ZFS
<https://arstechnica.com/gadgets/2020/03/ubuntu-20-04s-zsys-adds-zfs-snapshots-to-package-management/>`__.
This HOWTO produces nearly identical results as the Ubuntu installer because of
`bidirectional collaboration
<https://ubuntu.com/blog/enhancing-our-zfs-support-on-ubuntu-19-10-an-introduction>`__.

If you want a single-disk, unencrypted, desktop install, use the installer. It
is far easier and faster than doing everything by hand.

If you want a ZFS native encrypted, desktop install, you can `trivially edit
the installer
<https://linsomniac.gitlab.io/post/2020-04-09-ubuntu-2004-encrypted-zfs/>`__.
The ``-o recordsize=1M`` there is unrelated to encryption; omit that unless you
understand it. `Hopefully the installer will gain encryption support in the
future <https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1857398>`__.

If you want to setup a mirror or raidz topology, use LUKS encryption, and/or
install a server (no desktop GUI), use this HOWTO.

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 20.04 (“Focal”) Desktop CD
  <http://releases.ubuntu.com/18.04.3/ubuntu-18.04.3-desktop-amd64.iso>`__
  (*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. <http://savannah.gnu.org/bugs/?46700>`__

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 <http://wiki.freebsd.org/ZFSTuningGuide#Deduplication>`__. Enabling
deduplication is a permanent change that cannot be easily reverted.

Support
~~~~~~~

If you need help, reach out to the community using the :doc:`zfs-discuss
mailing list <../../Project and Community/Mailing Lists>` or IRC at
`#zfsonlinux <irc://irc.freenode.net/#zfsonlinux>`__ on `freenode
<https://freenode.net/>`__. If you have a bug report or feature request
related to this HOWTO, please `file a new issue and mention @rlaager
<https://github.com/openzfs/openzfs-docs/issues/new?body=@rlaager,%20I%20have%20the%20following%20issue%20with%20the%20Ubuntu%2020.04%20Root%20on%20ZFS%20HOWTO:>`__.

Contributing
~~~~~~~~~~~~

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

#. Install the tools::

    # On Debian 11 / Ubuntu 20.04 or later:
    sudo apt install python3-sphinx python3-sphinx-issues python3-sphinx-rtd-theme

    # On earlier releases:
    sudo apt install pip3
    pip3 install -r 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
---------------------------------------

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: 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; hit enter at that prompt.
  sudo apt install --yes 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
  systemctl stop zed

Step 2: Disk Formatting
-----------------------

2.1 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 <#troubleshooting>`__ section.

2.2 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 $DISK

Clear the partition table::

  sgdisk --zap-all $DISK

2.3 Create bootloader partition(s)::

  sgdisk     -n1:1M:+512M   -t1:EF00 $DISK

**Note:** This partition is setup for UEFI support. 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). Additionally, this is used for `/boot/grub` in single-disk scenarios,
as discussed below.

For legacy (BIOS) booting::

  sgdisk -a1 -n5:24K:+1000K -t5:EF02 $DISK

**Note:** For simplicity and forward compatibility, this HOWTO uses GPT
partition labels for both UEFI and legacy (BIOS) booting. The Ubuntu installer
uses an MBR label for legacy (BIOS) booting.

2.4 Create a partition for swap:

Previous versions of this HOWTO put swap on a zvol. `Ubuntu recommends against
this configuration due to deadlocks.
<https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1847628>`__ There is
`a bug report upstream <https://github.com/zfsonlinux/zfs/issues/7734>`__.

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:

2.4a For a single-disk install::

  sgdisk     -n2:0:+500M    -t2:8200 $DISK

2.4b For a mirror or raidz topology::

  sgdisk     -n2:0:+500M    -t2:FD00 $DISK

2.5 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.
<https://medium.com/@andaag/how-i-moved-a-ext4-ubuntu-install-to-encrypted-zfs-62af1170d46c>`__

2.6 Create a root pool partition:

Choose one of the following options:

2.6a Unencrypted or ZFS native encryption::

  sgdisk     -n4:0:0        -t4:BF00 $DISK

2.6b 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.

2.7 Create the boot pool::

  zpool create -o ashift=12 -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 feature@zpool_checkpoint=enabled \
      -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 ${DISK}-part3

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 <http://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/fs/zfs/zfs.c#n276>`__.
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 or raidz 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``
  (or replace ``mirror`` with ``raidz``, ``raidz2``, or ``raidz3`` and
  list the partitions from additional disks).
- The pool name is arbitrary. If changed, the new name must be used
  consistently. The ``bpool`` convention originated in this HOWTO.

**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 ``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.
- The ``spacemap_v2`` feature has been tested and is safe to use. The boot
  pool is small, so this does not matter in practice.
- 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.
- The ``zpool_checkpoint`` feature has been tested and is safe to use. The
  Ubuntu installer does not use it. This HOWTO does, as the feature may be
  desirable for the boot pool.

2.8 Create the root pool:

Choose one of the following options:

2.8a 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 ${DISK}-part4

2.8b ZFS native encryption::

  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 encryption=aes-256-gcm -O keylocation=prompt -O keyformat=passphrase \
      -O mountpoint=/ -R /mnt rpool ${DISK}-part4

2.8c LUKS::

  cryptsetup luksFormat -c aes-xts-plain64 -s 512 -h sha256 ${DISK}-part4
  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:**

- 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 <https://askubuntu.com/questions/970886/journalctl-says-failed-to-search-journal-acl-operation-not-supported>`__
- 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 <http://utcc.utoronto.ca/~cks/space/blog/linux/ForcedUTF8Filenames>`__.
- ``recordsize`` is unset (leaving it at the default of 128 KiB). If you want to
  tune it (e.g. ``-o recordsize=1M``), see `these
  <https://jrs-s.net/2019/04/03/on-zfs-recordsize/>`__ `various
  <http://blog.programster.org/zfs-record-size>`__ `blog
  <https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSFileRecordsizeGrowth>`__
  `posts
  <https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSRecordsizeAndCompression>`__.
- 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 <https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/power_management_guide/relatime>`__
  for further information.
- Setting ``xattr=sa`` `vastly improves the performance of extended
  attributes <https://github.com/zfsonlinux/zfs/commit/82a37189aac955c81a59a5ecc3400475adb56355>`__.
  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. <https://en.wikipedia.org/wiki/Extended_file_attributes#Linux>`__
  `They can be used by Samba to store Windows ACLs and DOS attributes;
  they are required for a Samba Active Directory domain
  controller. <https://wiki.samba.org/index.php/Setting_up_a_Share_Using_Windows_ACLs>`__
  Note that ``xattr=sa`` is
  `Linux-specific <http://open-zfs.org/wiki/Platform_code_differences>`__.
  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``.
- 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 defaults to ``aes-256-ccm``, but `the default has
  changed upstream <https://github.com/openzfs/zfs/commit/31b160f0a6c673c8f926233af2ed6d5354808393>`__
  to ``aes-256-gcm``. `AES-GCM seems to be generally preferred over AES-CCM
  <https://crypto.stackexchange.com/questions/6842/how-to-choose-between-aes-ccm-and-aes-gcm-for-storage-volume-encryption>`__,
  `is faster now
  <https://github.com/zfsonlinux/zfs/pull/9749#issuecomment-569132997>`__, and
  `will be even faster in the future
  <https://github.com/zfsonlinux/zfs/pull/9749>`__.
- 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 <https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions#5-security-aspects>`__
  for guidance.

**Hints:**

- If you are creating a mirror or raidz 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``
  (or replace ``mirror`` with ``raidz``, ``raidz2``, or ``raidz3`` and
  list the partitions from additional disks). For LUKS, 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
---------------------------

3.1 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

3.2 Create filesystem datasets for the root and boot filesystems::

  UUID=$(dd if=/dev/urandom of=/dev/stdout 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

  zfs create -o canmount=noauto -o mountpoint=/boot \
      bpool/BOOT/ubuntu_$UUID
  zfs mount bpool/BOOT/ubuntu_$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``.

3.3 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_$UUID/var/lib/AccountServices
  zfs create rpool/ROOT/ubuntu_$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

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.

3.4 Install the minimal system::

  debootstrap focal /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.

Step 4: System Configuration
----------------------------

4.1 Configure the hostname:

Replace ``HOSTNAME`` with the desired hostname::

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

.. code-block:: text

  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.

4.2 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

.. code-block:: yaml

  network:
    version: 2
    ethernets:
      NAME:
        dhcp4: true

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

4.3 Configure the package sources::

  vi /mnt/etc/apt/sources.list

.. code-block:: sourceslist

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

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 /usr/bin/env DISK=$DISK UUID=$UUID bash --login

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

4.5 Configure a basic system environment::

  apt update

  dpkg-reconfigure locales

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

  dpkg-reconfigure tzdata

If you prefer ``nano`` over ``vi``, install it::

  apt install --yes nano

4.6 For LUKS installs only, setup ``/etc/crypttab``::

  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
<https://bugs.launchpad.net/ubuntu/+source/cryptsetup/+bug/1612906>`__.

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

4.7 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 ${DISK}-part1
  mkdir /boot/efi
  echo UUID=$(blkid -s UUID -o value ${DISK}-part1) \
      /boot/efi vfat umask=0022,fmask=0022,dmask=0022 0 1 >> /etc/fstab
  mount /boot/efi

For a mirror or raidz topology, repeat these steps for the additional disks,
using ``/boot/efi2``, ``/boot/efi3``, etc.

**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.

4.8 Install GRUB/Linux/ZFS in the chroot environment for the new system:

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

**Note:** This puts `/boot/grub` on the EFI System Partition. This allows GRUB
to write to it, 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 becase 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.

Choose one of the following options:

4.8a 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.

4.8b 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

**Note:** For a mirror or raidz topology, this step only installs GRUB on the
first disk. The other disk(s) will be handled later.

4.9 (Optional): Remove os-prober::

    dpkg --purge os-prober

This avoids error messages from `update-grub`.  `os-prober` is only necessary
in dual-boot configurations.

4.10 Set a root password::

  passwd

4.11 Configure swap:

Choose one of the following options if you want swap:

4.11a For an unencrypted single-disk install::

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

4.11b 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 ${DISK2}-part2
  mkswap -f /dev/md0
  echo UUID=$(blkid -s UUID -o value /dev/md0) \
      none swap discard 0 0 >> /etc/fstab
  swapon -a

4.11c 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

4.11d 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

4.12 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

4.13 Setup system groups::

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

Step 5: GRUB Installation
-------------------------

5.1 Verify that the ZFS boot filesystem is recognized::

  grub-probe /boot

5.2 Refresh the initrd files::

  update-initramfs -c -k all

**Note:** When using LUKS, this will print “WARNING could not determine
root device from /etc/fstab”. This is because `cryptsetup does not
support ZFS
<https://bugs.launchpad.net/ubuntu/+source/cryptsetup/+bug/1612906>`__.

5.3 Disable memory zeroing::

    vi /etc/default/grub
    # Add init_on_alloc=0 to: GRUB_CMDLINE_LINUX_DEFAULT
    # Save and quit.

This is to address `performance regressions
<https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1862822>`__.

5.4 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.

5.5 Update the boot configuration::

  update-grub

**Note:** Ignore errors from ``osprober``, if present.

5.6 Install the boot loader:

5.6a 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.

5.6b For UEFI booting, install GRUB::

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

For a mirror or raidz topology, run this for the additional disk(s),
incrementing the “2” to “3” and so on for both ``/boot/efi2`` and
``ubuntu-2``::

  cp -a /boot/efi/EFI /boot/efi2
  grub-install --target=x86_64-efi --efi-directory=/boot/efi2 \
      --bootloader-id=ubuntu-2 --recheck --no-floppy

5.7 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
  ln -s /usr/lib/zfs-linux/zed.d/history_event-zfs-list-cacher.sh /etc/zfs/zed.d
  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=noauto bpool/BOOT/ubuntu_$UUID
  zfs set canmount=noauto rpool/ROOT/ubuntu_$UUID

Stop ``zed``::

  fg
  Press Ctrl-C.

Fix the paths to eliminate ``/mnt``::

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

Step 6: First Boot
------------------

6.1 (Optional): Install SSH::

  apt install --yes openssh-server

If you want to login as root via SSH, set ``PermitRootLogin yes`` in
``/etc/ssh/sshd_config``.  For security, undo this as soon as possible (i.e.
once you have your regular user account setup).

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 -a

6.4 Reboot::

  reboot

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

6.5 Create a user account:

Replace ``username`` with your desired username::

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

7.1 Upgrade the minimal system::

  apt dist-upgrade --yes

7.2 Install a regular set of software:

Choose one of the following options:

7.2a Install a command-line environment only::

  apt install --yes ubuntu-standard

7.2b Install a full GUI environment::

  apt install --yes ubuntu-desktop
  vi /etc/gdm3/custom.conf
  # In the [daemon] section, add: InitialSetupEnable=false

**Hint**: If you are installing a full GUI environment, you will likely
want to manage your network with NetworkManager::

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

.. code-block:: yaml

  network:
    version: 2
    renderer: NetworkManager

7.3 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"
      fi
  done

7.4 Reboot::

  reboot

Step 8: Final Cleanup
---------------------

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

8.2 Optional: Disable the root password::

  sudo usermod -p '*' root

8.3 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.

8.4 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 <#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
  # Replace “UUID” as appropriate; use zfs list to find it:
  zfs mount rpool/ROOT/ubuntu_UUID
  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
  mount /boot
  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

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 <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.

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.

VMware
~~~~~~

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

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:

.. code-block:: text

  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