Debian Stretch Root on ZFS


Newer release available


  • 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:

  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 two different encryption options: unencrypted and LUKS (full-disk encryption). ZFS native encryption has not yet been released. With either 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.

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. 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 Debian GNU/Linux Live CD. If prompted, login with the username user and password live. Connect your system to the Internet as appropriate (e.g. join your WiFi network).

1.2 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.

$ sudo apt update
$ sudo apt install --yes openssh-server
$ sudo systemctl restart ssh

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

1.3 Become root:

$ sudo -i

1.4 Setup and update the repositories:

# echo deb stretch contrib >> /etc/apt/sources.list
# echo deb stretch-backports main contrib >> /etc/apt/sources.list
# apt update

1.5 Install ZFS in the Live CD environment:

# apt install --yes debootstrap gdisk dkms dpkg-dev linux-headers-amd64
# apt install --yes -t stretch-backports zfs-dkms
# modprobe zfs
  • The dkms dependency is installed manually just so it comes from stretch and not stretch-backports. This is not critical.

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(s):

Run this if you need legacy (BIOS) booting:
# sgdisk -a1 -n1:24K:+1000K -t1:EF02 /dev/disk/by-id/scsi-SATA_disk1

Run this for UEFI booting (for use now or in the future):
# sgdisk     -n2:1M:+512M   -t2:EF00 /dev/disk/by-id/scsi-SATA_disk1

Run this for the boot pool:
# sgdisk     -n3:0:+1G      -t3:BF01 /dev/disk/by-id/scsi-SATA_disk1

Choose one of the following options:

2.2a Unencrypted:

# sgdisk     -n4:0:0        -t4:BF01 /dev/disk/by-id/scsi-SATA_disk1

2.2b LUKS:

# sgdisk     -n4:0:0        -t4:8300 /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.

  • If you are creating a mirror or raidz topology, repeat the partitioning commands for all the disks which will be part of the pool.

2.3 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@userobj_accounting=enabled \
      -O acltype=posixacl -O canmount=off -O compression=lz4 -O devices=off \
      -O normalization=formD -O relatime=on -O xattr=sa \
      -O mountpoint=/ -R /mnt \
      bpool /dev/disk/by-id/scsi-SATA_disk1-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. 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.


  • 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.

2.4 Create the root pool:

Choose one of the following options:

2.4a 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 /dev/disk/by-id/scsi-SATA_disk1-part4

2.4b LUKS:

# apt install --yes cryptsetup
# cryptsetup luksFormat -c aes-xts-plain64 -s 512 -h sha256 \
# cryptsetup luksOpen /dev/disk/by-id/scsi-SATA_disk1-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
  • 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 -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

  • 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.

  • 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.

  • 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.

  • 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).

  • 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.


  • 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

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 filesystem datasets for the root and boot filesystems:

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

# zfs create -o canmount=noauto -o mountpoint=/boot bpool/BOOT/debian
# zfs mount bpool/BOOT/debian

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                                 rpool/home
# zfs create -o mountpoint=/root             rpool/home/root
# zfs create -o canmount=off                 rpool/var
# zfs create -o canmount=off                 rpool/var/lib
# zfs create                                 rpool/var/log
# zfs create                                 rpool/var/spool

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

If you wish to exclude these from snapshots:
# zfs create -o com.sun:auto-snapshot=false  rpool/var/cache
# zfs create -o com.sun:auto-snapshot=false  rpool/var/tmp
# chmod 1777 /mnt/var/tmp

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

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

If you use /usr/local on this system:
# zfs create -o canmount=off                 rpool/usr
# zfs create                                 rpool/usr/local

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 Snap packages:
# zfs create                                 rpool/var/snap

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

If this system will use GNOME:
# zfs create                                 rpool/var/lib/AccountsService

If this system will use Docker (which manages its own datasets & snapshots):
# zfs create -o com.sun:auto-snapshot=false  rpool/var/lib/docker

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

A tmpfs is recommended later, but if you want a separate dataset for /tmp:
# zfs create -o com.sun:auto-snapshot=false  rpool/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 such as logs (in /var/log). This will be especially important if/when a beadm or similar utility is integrated. The setting is used by some ZFS snapshot utilities to exclude transient 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 stretch /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 stretch main contrib
deb-src stretch main contrib
deb stretch/updates main contrib
deb-src stretch/updates main contrib
deb stretch-updates main contrib
deb-src stretch-updates main contrib

# vi /mnt/etc/apt/sources.list.d/stretch-backports.list
deb stretch-backports main contrib
deb-src stretch-backports main contrib

# vi /mnt/etc/apt/preferences.d/90_zfs
Package: src:zfs-linux
Pin: release n=stretch-backports
Pin-Priority: 990

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:

# ln -s /proc/self/mounts /etc/mtab
# apt update

# apt install --yes locales
# dpkg-reconfigure locales

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

# dpkg-reconfigure tzdata

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

# apt install --yes dpkg-dev linux-headers-amd64 linux-image-amd64
# apt install --yes zfs-initramfs

4.7 For LUKS installs only, setup crypttab:

# apt install --yes cryptsetup

# echo luks1 UUID=$(blkid -s UUID -o value \
      /dev/disk/by-id/scsi-SATA_disk1-part4) none \
      luks,discard,initramfs > /etc/crypttab

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

4.8 Install GRUB

Choose one of the following options:

4.8a Install GRUB for legacy (BIOS) 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 -s 1 -n EFI /dev/disk/by-id/scsi-SATA_disk1-part2
# mkdir /boot/efi
# echo PARTUUID=$(blkid -s PARTUUID -o value \
      /dev/disk/by-id/scsi-SATA_disk1-part2) \
      /boot/efi vfat nofail,x-systemd.device-timeout=1 0 1 >> /etc/fstab
# mount /boot/efi
# apt install --yes grub-efi-amd64 shim
  • 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.

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

4.9 Set a root password

# passwd

4.10 Enable importing bpool

This ensures that bpool is always imported, regardless of whether /etc/zfs/zpool.cache exists, whether it is in the cachefile or not, or whether zfs-import-scan.service is enabled.

# vi /etc/systemd/system/zfs-import-bpool.service

ExecStart=/sbin/zpool import -N -o cachefile=none bpool


# systemctl enable zfs-import-bpool.service

4.11 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

4.12 Optional (but kindly requested): Install popcon

The popularity-contest package reports the list of packages install on your system. Showing that ZFS is popular may be helpful in terms of long-term attention from the distro.

# apt install --yes popularity-contest

Choose Yes at the prompt.

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 -u -k all
update-initramfs: Generating /boot/initrd.img-4.9.0-8-amd64

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 Workaround GRUB’s missing zpool-features support:

# vi /etc/default/grub
Set: GRUB_CMDLINE_LINUX="root=ZFS=rpool/ROOT/debian"

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

# vi /etc/default/grub
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
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.9.0-8-amd64
Found initrd image: /boot/initrd.img-4.9.0-8-amd64

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 /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 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=debian --recheck --no-floppy

5.7 Verify that the ZFS module is installed:

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

5.8 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 and services using the PrivateTmp feature of systemd automatically use After=var-tmp.mount.

Until there is support for mounting /boot in the initramfs, we also need to mount that, because it was marked canmount=noauto. Also, with UEFI, we need to ensure it is mounted before its child filesystem /boot/efi.

rpool is guaranteed to be imported by the initramfs, so there is no point in adding to those filesystems.

For UEFI booting, unmount /boot/efi first:
# umount /boot/efi

Everything else applies to both BIOS and UEFI booting:

# zfs set mountpoint=legacy bpool/BOOT/debian
# echo bpool/BOOT/debian /boot zfs \
      nodev,relatime,x-systemd.requires=zfs-import-bpool.service 0 0 >> /etc/fstab

# zfs set mountpoint=legacy rpool/var/log
# echo rpool/var/log /var/log zfs nodev,relatime 0 0 >> /etc/fstab

# zfs set mountpoint=legacy rpool/var/spool
# echo rpool/var/spool /var/spool zfs nodev,relatime 0 0 >> /etc/fstab

If you created a /var/tmp dataset:
# zfs set mountpoint=legacy rpool/var/tmp
# echo rpool/var/tmp /var/tmp zfs nodev,relatime 0 0 >> /etc/fstab

If you created a /tmp dataset:
# zfs set mountpoint=legacy rpool/tmp
# echo rpool/tmp /tmp zfs nodev,relatime 0 0 >> /etc/fstab

Step 6: First Boot

6.1 Snapshot the initial installation:

# zfs snapshot bpool/BOOT/debian@install
# zfs snapshot rpool/ROOT/debian@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 -a

6.4 Reboot:

# reboot

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

6.6 Create a user account:

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

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

# usermod -a -G audio,cdrom,dip,floppy,netdev,plugdev,sudo,video YOURUSERNAME

6.8 Mirror GRUB

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

6.8a For legacy (BIOS) 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 debian-2 to -3, etc.):
# dd if=/dev/disk/by-id/scsi-SATA_disk1-part2 \
# efibootmgr -c -g -d /dev/disk/by-id/scsi-SATA_disk2 \
      -p 2 -L "debian-2" -l '\EFI\debian\grubx64.efi'

# mount /boot/efi

Step 7: (Optional) Configure Swap

Caution: On systems with extremely high memory pressure, using a zvol for swap can result in lockup, regardless of how much swap is still available. This issue is currently being investigated in:

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:

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 discard 0 0 >> /etc/fstab
# echo RESUME=none > /etc/initramfs-tools/conf.d/resume

The RESUME=none is necessary to disable resuming from hibernation. This does not work, as the zvol is not present (because the pool has not yet been imported) at the time the resume script runs. If it is not disabled, the boot process hangs for 30 seconds waiting for the swap zvol to appear.

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:

# tasksel

Note: This will check “Debian desktop environment” and “print server” by default. If you want a server installation, unselect those.

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 snapshots of the initial installation:

$ sudo zfs destroy bpool/BOOT/debian@install
$ sudo zfs destroy rpool/ROOT/debian@install

9.3 Optional: Disable the root password

$ sudo usermod -p '*' root

9.4 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
Comment out GRUB_TERMINAL=console
Save and quit.

$ sudo update-grub

Note: Ignore errors from osprober, if present.

9.5 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.).


Rescuing using a Live CD

Go through Step 1: Prepare The Install Environment.

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

For LUKS, first unlock the disk(s):
# apt install --yes cryptsetup
# cryptsetup luksOpen /dev/disk/by-id/scsi-SATA_disk1-part4 luks1
Repeat for additional disks, if this is a mirror or raidz topology.

# zpool export -a
# zpool import -N -R /mnt rpool
# zpool import -N -R /mnt bpool
# zfs mount rpool/ROOT/debian
# 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/efi
# 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


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

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.


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