Installing Arch Linux on ZFS

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This article details the steps required to install Arch Linux onto a root ZFS filesystem. This article supplements the Beginners' Guide.

Installing archzfs

Using the archzfs repository is highly recommended for effortless updates.

Warning: The ZFS packages are tied to the kernel version they were built against. This means it will not be possible to perform kernel updates until new packages (or package sources) are released by the ZFS package maintainer.
Note: This guide uses the unofficial archzfs repository hosted at This repository is maintained by Jesus Alvarez and is signed with his PGP key: 0EE7A126.

Embedding archzfs into archiso

See ZFS#Embed_the_archzfs_packages_into_an_archiso.

Using the archzfs repository

Activate the required network connection and then edit /etc/pacman.d/mirrorlist and configure the mirrors for pacman to use. Once that is done, edit /etc/pacman.conf and add the archzfs repository:

# nano /etc/pacman.conf
Server =$repo/$arch
Note: You should change the repo name from 'demz-repo-core' to 'demz-repo-archiso' if you are using the standard Arch ISOs to install (didn't build your own, above)

Next, add the archzfs maintainer's PGP key to the local trust:

# pacman-key -r 0EE7A126
# pacman-key --lsign-key 0EE7A126

Finally, update the pacman databases and install archzfs:

# pacman -Syy

This is also the best time to install your favorite text editor, otherwise nano will have to be used.

# pacman -S archzfs dosfstools gptfdisk vim

Partition the destination drive

Review Beginners'_Guide#Prepare_the_storage_drive for information on determining the partition table type to use for ZFS. ZFS supports GPT and MBR partition tables.

ZFS manages its own partitions, so only a basic partition table scheme is required. The partition that will contain the ZFS filesystem should be of the type bf00, or "Solaris Root".

Partition scheme

Here is an example of a basic partition scheme that could be employed for your ZFS root setup:

Part     Size   Type
----     ----   -------------------
   1     512M   Ext4 (8300)
   2     XXXG   Solaris Root (bf00)
Note: It may be required to create an additional partition to contain a bootloader depending on your hardware and chosen bootloader. See Beginners'_Guide#Install_and_configure_a_bootloader for more information.
Note: ZFSonLinux supports a variety of bootloaders. See #Install and configure the bootloader for more details.

Format the destination disk

Setup the ZFS filesystem

First, make sure the ZFS modules are loaded,

# modprobe zfs

Create the root zpool

# zpool create zroot /dev/disk/by-id/<id-to-partition>
Warning: Always use id names when working with ZFS, otherwise import errors will occur.

Create necessary filesystems

If so desired, sub-filesystem mount points such as /home and /root can be created with the following commands:

# zfs create zroot/home
# zfs create zroot/root

Swap partition

ZFS does not allow the use swapfiles, but it is possible to use a ZFS volume as swap partition. It is important to set the ZVOL block size to match the system page size; for x86_64 systems that is 4k.

Create a 8gb (or whatever is required) ZFS volume:

# zfs create -V 8G -b 4K <pool>/swap

Initialize and enable the volume as a swap partition:

# mkswap /dev/zvol/<pool>/swap
# swapon /dev/zvol/<pool>/swap

After using pacstrap to install the base system, edit /mnt/etc/fstab to ensure the swap partition is mounted at boot:

/dev/zvol/<pool>/swap none swap defaults 0 0

Make sure to unmount all ZFS filesystems before rebooting the machine, otherwise any ZFS pools will refuse to be imported:

# zfs umount -a

Configure the root filesystem

Now it is time to set the mount point of the root filesystem:

# zfs set mountpoint=/ zroot

and optionally, any sub-filesystems:

# zfs set mountpoint=/home zroot/home
# zfs set mountpoint=/root zroot/root

Set the bootfs property on the descendant root filesystem so the boot loader knows where to find the operating system.

# zpool set bootfs=zroot zroot

Export the pool,

# zpool export zroot
Warning: Don't skip this, otherwise you will be required to use -f when importing your pools. This unloads the imported pool.
Note: This might fail if you added a swap partition above. Need to turn it off with the swapoff command.

Finally, re-import the pool,

# zpool import -d /dev/disk/by-id -R /mnt zroot
Note: "-d" is not the actual device id, but the /dev/by-id directory containing the symlinks.

If there is an error in this step, you can export the pool to redo the command. The ZFS filesystem is now ready to use.

Mount the boot partitions

UEFI systems

   # mkdir /mnt/boot
   # mount /dev/sda2 /mnt/boot
   # mkdir /mnt/boot/efi
   # mount /dev/sda1 /mnt/boot/efi

BIOS systems

   # mkdir /mnt/boot
   # mount /dev/sda1 /mnt/boot

Install and configure the Arch Linux installation

Install the base packages

   # pacstrap -i /mnt base base-devel
   The other packages will be installed in the chrooted environment

Generate the fstab,

   # genfstab -U -p /mnt | grep boot >> /mnt/etc/fstab
Note: ZFS auto mounts its own partitions, so we do not need ZFS partitions in fstab file.

If installing on a UEFI system, you will need to load the efivars kernel module before chrooting into the installation:

   # modprobe efivars

Chroot into the installation

   # arch-chroot /mnt /bin/bash

Next, follow the Beginners' Guide from the "Locale" section to the "Configure Pacman Section". Once done, edit pacman.conf, add the archzfs repo (change it to [demz-repo-core] now if you were using [demz-repo-archiso] earlier), and update the pacman database,

   # pacman -Syy
   # pacman -Su --ignore filesystem,bash
   # pacman -S bash
   # pacman -Su
   Now lets install the other needed packages.
   # pacman -S gnupg vim archzfs

Re-create the initramfs, edit /etc/mkinitcpio.conf and add zfs before filesystems. Also, move keyboard hook before zfs so you can type in console if something goes wrong. You may also remove fsck. Your HOOKS line should look something like this:

HOOKS="base udev autodetect modconf block keyboard zfs filesystems"

Regenerate the initramfs with the command:

   # mkinitcpio -p linux

Finally, set root password and add a regular user.

Install and configure the bootloader

For BIOS motherboards

Follow Grub2#BIOS_systems_2 to install grub onto your disk. grub-mkconfig does not properly detect the ZFS filesystem, so it is necessary to edit grub.cfg manually:

set timeout=2
set default=0

# (0) Arch Linux
menuentry "Arch Linux" {
    set root=(hd0,1)
    linux /vmlinuz-linux zfs=zroot
    initrd /initramfs-linux.img

For UEFI motherboards

Use EFISTUB and rEFInd for the UEFI boot loader. See Beginners' Guide#For UEFI motherboards. The kernel parameters in refind_linux.conf for ZFS should include zfs=bootfs or zfs=zroot so the system can boot from ZFS. The 'root' and 'rootfstype' parameters aren't needed.

Unmount and restart

This is it, we are done!

   # exit
   # umount /mnt/boot
   # zfs umount -a
   # zpool export zroot
   # reboot
Warning: If you do not properly export the zpool, the pool will refuse to import in the ramdisk environment and you will be stuck at the busybox terminal.


If the new installation does not boot because the zpool cannot be imported, you will need to chroot into the installation and properly export the zpool. See ZFS#Emergency chroot repair with archzfs.

Once inside the chroot environment, load the ZFS module and force import the zpool,

   # zpool import -a -f

now export the pool:

   # zpool export <pool>

To see your available pools, use,

   # zpool status

It is necessary to export a pool because of the way ZFS uses the hostid to track the system the zpool was created on. The hostid is generated partly based on your network setup. During the installation in the archiso your network configuration could be different generating a different hostid than the one contained in your new installation. Once the zfs filesystem is exported and then re-imported in the new installation, the hostid is reset. See Re: Howto zpool import/export automatically? - msg#00227.

If ZFS complains about "pool may be in use" after every reboot, you should properly export pool as described above, and then rebuild ramdisk in normally booted system:

   # mkinitcpio -p linux

See also