Installing Arch Linux on ZFS

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 http://demizerone.com/demz-repo-core. This repository is maintained by Jesus Alvarez and is signed with his PGP key: 0EE7A126.

Embedding archzfs into archiso

See ZFS article.

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:

[demz-repo-core]
Server = http://demizerone.com/$repo/$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 (did not 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 archzfs

Tip: This is also the best time to install your favorite text editor (otherwise nano or vi will have to be used) and the proper partition tools: for UEFI and GPT install dosfstools and gptfdisk.

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, using MBR, of a basic partition scheme that could be employed for your ZFS root setup:

Part     Size   Type
----     ----   -------------------------
   1     512M   Ext boot partition (8300)
   2     XXXG   Solaris Root (bf00)

Here is an example using GPT. The BIOS boot partition contains the bootloader.

Part     Size   Type
----     ----   -------------------------
   1       2M   BIOS boot partition (ef02)
   1     512M   Ext boot partition (8300)
   2     XXXG   Solaris Root (bf00)

An additional partition may be required depending on your hardware and chosen bootloader. Consult Beginners'_Guide#Install_and_configure_a_bootloader for more info.

Tip: Bootloaders with support for ZFS are described in #Install and configure the bootloader.

Format the destination disk

Format the boot partition as well as any other system partitions. Do not do anything to the Solaris partition nor to the BIOS boot partition. ZFS will manage the first, and your bootloader the second.

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

Note that if you want to use other datasets for system directories (/var or /etc included) your system will not boot unless they are listed in /etc/fstab! We will address that at the appropriate time in this tutorial.

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 8 GB (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 /root/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

First, 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 symbolic links.

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.

Be sure to bring the zpool.cache file into your new system. This is required later for the ZFS daemon to start.

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

Install and configure Arch Linux

Follow the following steps using the Beginners' Guide. It will be noted where special consideration must be taken for ZFSonLinux.

• First mount any boot or system partitions using the mount command.

• Install the base system.

• The procedure described in Beginners' Guide#Generate an fstab is usually overkill for ZFS. ZFS usually auto mounts its own partitions, so we do not need ZFS partitions in fstab file, unless the user made datasets of system directories. To generate the fstab for filesystems, use:

# genfstab -U -p /mnt | grep boot >> /mnt/etc/fstab

• Edit the /etc/fstab:

Note:

• If you chose to create datasets for system directories, keep them in this fstab! Comment out the lines for the '/, /root, and /home mountpoints, rather than deleting them. You may need those UUIDs later if something goes wrong.
• Anyone who just stuck with the guide's directions can delete everything except for the swap file and the boot/EFI partition. It seems convention to replace the swap's uuid with /dev/zvol/zroot/swap.

• When creating the initial ramdisk, first 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 (if you are not using Ext3 or Ext4). 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

Install and configure the bootloader

For BIOS motherboards

Follow GRUB#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:

/boot/grub/grub.cfg

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 are not needed.

Unmount and restart

We're almost done!

# exit
# umount /mnt/boot
# zfs umount -a
# zpool export zroot

Now 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.

After the first boot

If everything went fine up to this point, your system will boot. Once. For your system to be able to reboot without issues, you need to enable the zfs service and set the hostid.

When running ZFS on root, the machine's hostid will not be available at the time of mounting the root filesystem. There are two solutions to this. You can either place your spl hostid in the kernel parameters in your boot loader. For example, adding spl.spl_hostid=0x00bab10c.

The other solution is to make sure that there is a hostid in /etc/hostid, and then regenerate the initramfs image. Which will copy the hostid into the initramfs image.

# hostid > /etc/hostid
# mkinitcpio -p linux

Your system should work and reboot properly now.

See also

• HOWTO install Ubuntu to a Native ZFS Root
• ZFS cheatsheet
• Funtoo ZFS install guide