Install Arch Linux on ZFS
This article details the steps required to install Arch Linux onto a ZFS root filesystem.
Installation
To install Archlinux on ZFS, you need to boot archiso system with ZFS module.
Get ZFS module on archiso system
A script to easily install and load the ZFS module on running archiso system. It should work on any archiso version.
See eoli3n/archiso-zfs.
Embedding ZFS module into custom archiso
To build a custom archiso, see ZFS article.
An unofficial weekly build is available here.
Partition the destination drive
Review Partitioning 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".
Drives larger than 2TB require a GPT partition table. GRUB on BIOS/GPT configurations require a small (1~2MiB) BIOS boot partition to embed its image of boot code.
Depending upon your machine's firmware or your choice of boot mode, booting may or may not require an EFI partition. On a BIOS machine (or a UEFI machine booting in legacy mode) EFI partition is not required. Consult Arch boot process#Boot loader for more information.
Partition scheme
Here is an example of a basic partition scheme that could be employed for your ZFS root install on a BIOS/MBR installation using GRUB:
Part Size Type ---- ---- ------------------------- 1 XXXG Solaris Root (bf00)
Using GRUB on a BIOS (or UEFI machine in legacy boot mode) machine but using a GPT partition table:
Part Size Type ---- ---- ------------------------- 1 2M BIOS boot partition (ef02) 2 XXXG Solaris Root (bf00)
Another example, this time using a UEFI-specific bootloader (such as rEFInd) with an GPT partition table:
Part Size Type ---- ---- ------------------------- 1 100M EFI boot partition (ef00) 2 XXXG Solaris Root (bf00)
ZFS does not support swap files. If you require a swap partition, see ZFS#Swap volume for creating a swap ZVOL.
Example parted commands
Here are some example commands to partition a drive for the second scenario above ie using BIOS/legacy boot mode with a GPT partition table and a (slighty more than) 1MB BIOS boot partition for GRUB:
# parted /dev/sdx (parted)mklabel gpt (parted)mkpart non-fs 0% 2 (parted)mkpart primary 2 100% (parted)set 1 bios_grub on (parted)set 2 boot on (parted)quit
You can achieve the above in a single command like so:
# parted --script /dev/sdx mklabel gpt mkpart non-fs 0% 2 mkpart primary 2 100% set 1 bios_grub on set 2 boot on
If you are creating an EFI partition then that should have the boot flag set instead of the root partition.
Format the destination disk
If you have opted for a boot partition as well as any other non-ZFS system partitions then format them. 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
Create your pool and set all default dataset options. All dataset created on the zpool will inherit of each -O set at the zpool creation. Default options are detailed in Debian Buster Root on ZFS. Step 2: Disk Formatting.
-o ashift=9 for disks with a 512 byte physical sector size or -o ashift=12 for disks with a 4096 byte physical sector size. See lsblk -S -o NAME,PHY-SEC to get the physical sector size of each SCSI/SATA disk. Remove -S if you want the same value from all devices.ashift=9 on a 4096 byte sector size (even if it reports 512) will incur a performance penalty. Selecting ashift=12 on a 512 byte sector size may incur in a capacity penalty, but no performance penalty. If in doubt, for a modern drive, err on the side of ashift=12, or research your particular device for the appropriate value. Refer to OpenZFS issue #967 for a related discussion, and OpenZFS issue #2497 for a consequence of a higher ashift value.
# zpool create -f -o ashift=12 \
-O acltype=posixacl \
-O relatime=on \
-O xattr=sa \
-O dnodesize=legacy \
-O normalization=formD \
-O mountpoint=none \
-O canmount=off \
-O devices=off \
-R /mnt \
zroot /dev/disk/by-id/id-to-partition-partx
Compression and native encryption
This will enable compression and native encryption by default on all datasets:
# zpool create -f -o ashift=12 \
-O acltype=posixacl \
-O relatime=on \
-O xattr=sa \
-O dnodesize=legacy \
-O normalization=formD \
-O mountpoint=none \
-O canmount=off \
-O devices=off \
-R /mnt \
-O compression=lz4 \
-O encryption=aes-256-gcm \
-O keyformat=passphrase \
-O keylocation=prompt \
zroot /dev/disk/by-id/id-to-partition-partx
- Always use id names when working with ZFS, otherwise import errors will occur.
- GRUB users should keep in mind that the zpool-create command normally enables all features, some of which may not be supported by GRUB. See: ZFS#GRUB-compatible pool creation.
Create your datasets
Instead of using conventional disk partitions, ZFS has the concept of datasets to manage your storage. Unlike disk partitions, datasets have no fixed size and allow for different attributes, such as compression, to be applied per dataset. Normal ZFS datasets are mounted automatically by ZFS whilst legacy datasets are required to be mounted using fstab or with the traditional mount command.
One of the most useful features of ZFS is boot environments. Boot environments allow you to create a bootable snapshot of your system that you can revert to at any time instantly by simply rebooting and booting from that boot environment. This can make doing system updates much safer and is also incredibly useful for developing and testing software. In order to be able to use a boot environment manager such as beadm, zectlAUR (systemd-boot), or zedenvAUR (GRUB) to manage boot environments, your datasets must be configured properly. Key to this are that you split your data directories (such as /home) into datasets that are distinct from your system datasets and that you do not place data in the root of the pool as this cannot be moved afterwards.
You should always create a dataset for at least your root filesystem and in nearly all cases you will also want /home to be in a separate dataset. You may decide you want your logs to persist over boot environments. If you are a running any software that stores data outside of /home (such as is the case for database servers) you should structure your datasets so that the data directories of the software you want to run are separated out from the root dataset.
With these example commands, we will create a basic boot environment compatible configuration comprising of just root and /home datasets. It inherits default options from zpool creation.
# zfs create -o mountpoint=none zroot/data # zfs create -o mountpoint=none zroot/ROOT # zfs create -o mountpoint=/ -o canmount=noauto zroot/ROOT/default # zfs create -o mountpoint=/home zroot/data/home
You can also create your ROOT dataset without having to specify mountpoint to / since GRUB will mount it to / anyway. That gives you possibility to boot into some old versions of root just by cloning it and putting as menuentry of GRUB. In such, you can create ROOT with the following command:
# zfs create -o mountpoint=/roots/default zroot/ROOT/default
You can store /root in your zroot/data/home dataset.
# zfs create -o mountpoint=/root zroot/data/home/root
You will need to enable some options for datasets which hold specific directories:
| Directory | Dataset option | Details |
|---|---|---|
| / | canmount=noauto | |
| /var/log/journal | acltype=posixacl | Systemd#systemd-tmpfiles-setup.service fails to start at boot |
System datasets
To create datasets for system directories, use canmount=off.
For some examples, please read Debian-Buster-Root-on-ZFS#step-3-system-installation
# zfs create -o mountpoint=/var -o canmount=off zroot/var # zfs create zroot/var/log # zfs create -o mountpoint=/var/lib -o canmount=off zroot/var/lib # zfs create zroot/var/lib/libvirt # zfs create zroot/var/lib/docker
Export/Import your datasets
To validate your configurations, export then reimport all your zpools.
-f when importing your pools. This unloads the imported pool.# zpool export zroot # zpool import -d /dev/disk/by-id -R /mnt zroot -N
-d is not the actual device ID, but the /dev/by-id directory containing the symbolic links.
If this command fails and you are asked to import your pool via its numeric ID, run zpool import to find out the ID of your pool then use a command such as:
# zpool import 9876543212345678910 -R /mnt zroot
If you used native encryption, load zfs key.
# zfs load-key zroot
Manually mount your rootfs dataset because it uses canmount=noauto, then mount all others datasets.
# zfs mount zroot/ROOT/default # zfs mount -a
The ZFS filesystem is now ready to use.
Configure the root filesystem
If you used legacy datasets, it must be listed in /etc/fstab.
Set the bootfs property on the descendant root filesystem so the boot loader knows where to find the operating system.
# zpool set bootfs=zroot/ROOT/default zroot
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
if you do not have /etc/zfs/zpool.cache, create it:
# zpool set cachefile=/etc/zfs/zpool.cache zroot
Install and configure Arch Linux
Follow the following steps using the Installation guide. It will be noted where special consideration must be taken for ZFSonLinux.
- First mount any legacy or non-ZFS boot or system partitions using the mount command.
- Install the base system.
- The procedure described in Installation guide#Fstab is usually overkill for ZFS. ZFS usually auto mounts its own partitions, so we do not need ZFS partitions in
fstabfile, unless the user made legacy datasets of system directories. To generate thefstabfor filesystems, use:
# genfstab -U -p /mnt >> /mnt/etc/fstab
- Change root into the new system, per Installation guide#Chroot:
# arch-chroot /mnt
- Edit the
/etc/fstab:
- If you chose to create legacy datasets for system directories, keep them in this
fstab! - Comment out all non-legacy datasets apart from the swap file and the boot/EFI partition. It is a convention to replace the swap's uuid with
/dev/zvol/zroot/swap.
- You need to add the Arch ZFS repository to
/etc/pacman.conf, sign its key and install zfs-linux (or zfs-linux-lts if you are running the LTS kernel) within the arch-chroot before you can update the ramdisk with ZFS support.
- When creating the initial ramdisk, first edit
/etc/mkinitcpio.confand addzfsbefore filesystems. Also, movekeyboardhook beforezfsso you can type in console if something goes wrong. You may also remove fsck (if you are not using Ext3 or Ext4). YourHOOKSline should look something like this:
HOOKS=(base udev autodetect modconf block keyboard zfs filesystems)
When using systemd in the initrd, you need to install mkinitcpio-sd-zfsAUR and add the sd-zfs hook after the systemd hook instead of the zfs hook. Keep in mind that this hook uses different kernel parameters than the default zfs hook, more information can be found at the project page.
sd-zfs does not support native encryption yet dasJ/sd-zfs/issues/4.- If you are using a separate dataset for
/usrand have followed the instructions below, you must make sure you have theusrhook enabled afterzfs, or your system will not boot. - When you generate the initramfs, the
zpool.cacheis copied into the initrd. If you did not generate it before, or needed to regenerate it, remember to regenerate the initramfs again. - You can also use
legacymountpoint to let fstab mount it
Install and configure the bootloader
Using GRUB for EFI/BIOS
If you use GRUB, you can store your /boot on a zpool. Please read Debian-Buster-Root-on-ZFS#step-3-system-installation.
Install GRUB onto your disk as instructed here: GRUB#BIOS systems or GRUB#UEFI systems. The GRUB manual provides detailed information on manually configuring the software which you can supplement with GRUB and GRUB/Tips and tricks.
bug: broken root pool detection
Because of a known bug, grub-mkconfig will fail to detect the root pool and omit in /boot/grub/grub.cfg. Until this is fixed, there are two possible workarounds:
- Workaround A: Modify code for rpool detection in
/etc/grub.d/10_linux. Replace
rpool=`${grub_probe} --device ${GRUB_DEVICE} --target=fs_label 2>/dev/null || true`- with
rpool=`zdb -l \$\{GRUB_DEVICE\} | grep " name:" | cut -d\' -f2`- This will detect the correct root pool name and write working path to
/boot/grub/grub.cfgany time grub-mkconfig is used.
- Workaround B: Hardcoded path to root dataset in the kernel command line via
/etc/default/grub:
GRUB_CMDLINE_LINUX="root=ZFS=zroot/ROOT/default"
- Because
GRUB_CMDLINE_LINUXis added at the end of the kernel command line, this path will overwrite the wrong, auto-generated one. Even though this is the less intrusive option to fix the issue, you will have to make sure the path is correct yourself.
error: failed to get canonical path of
grub-mkconfig fails to properly generate entries for systems hosted on ZFS.
# grub-mkconfig -o /boot/grub/grub.cfg /usr/bin/grub-probe: error: failed to get canonical path of `/dev/bus-Your_Disk_ID-part#'
grub-install: error: failed to get canonical path of `/dev/bus-Your_Disk_ID-part#'
To work around this you must set this environment variable: ZPOOL_VDEV_NAME_PATH=1. For example:
# ZPOOL_VDEV_NAME_PATH=1 grub-mkconfig -o /boot/grub/grub.cfg
error: unknown filesystem
GRUB tools like grub-probe or grub-install may fail with the error unknown filesystem when filesystem detection fails. This may happen due to the filesystem not being supported by GRUB, or in the case of ZFS, unsupported features may be present (refer to ZFS#GRUB-compatible pool creation for appropriate features to include in a boot zpool.)
In order to troubleshoot the error, understand which filesystem it is failing to identify (e.g. run grub-probe on the suspects, like grub-probe / or grub-probe /boot). An example interaction follows:
# grub-probe /boot zfs # grub-probe / grub-probe: error: unknown filesystem.
After identifying the problem filesystem, run grub-probe -vvvv / and scan the output for the filesystem it was expected to identify. In this case, ZFS was expected, but the following output was generated:
grub-probe -vvvv /
(...) grub-core/kern/fs.c:56: Detecting zfs... grub-core/osdep/hostdisk.c:420: opening the device `/dev/sda4' in open_device() grub-core/fs/zfs/zfs.c:1199: label ok 0 grub-core/osdep/hostdisk.c:399: reusing open device `/dev/sda4' grub-core/fs/zfs/zfs.c:1014: check 2 passed grub-core/fs/zfs/zfs.c:1025: check 3 passed grub-core/fs/zfs/zfs.c:1032: check 4 passed grub-core/fs/zfs/zfs.c:1042: check 6 passed grub-core/fs/zfs/zfs.c:1050: check 7 passed grub-core/fs/zfs/zfs.c:1061: check 8 passed grub-core/fs/zfs/zfs.c:1071: check 9 passed grub-core/fs/zfs/zfs.c:1093: check 11 passed grub-core/fs/zfs/zfs.c:1119: check 10 passed grub-core/fs/zfs/zfs.c:1135: str=com.delphix:hole_birth grub-core/fs/zfs/zfs.c:1135: str=com.delphix:embedded_data grub-core/fs/zfs/zfs.c:1144: check 12 passed (feature flags) grub-core/fs/zfs/zfs.c:1884: zio_read: E 0: size 4096/4096 (...) grub-core/osdep/hostdisk.c:399: reusing open device `/dev/sda4' grub-core/fs/zfs/zfs.c:2117: zap: name = com.delphix:extensible_dataset, value = 18, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = com.datto:bookmark_v2, value = 0, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = com.datto:encryption, value = c, cd = 0 # <------------------ grub-core/kern/fs.c:78: zfs detection failed. # <---------------------------------------------------- grub-core/kern/fs.c:56: Detecting xfs... grub-core/fs/xfs.c:931: Reading sb grub-core/fs/xfs.c:270: Validating superblock grub-core/kern/fs.c:78: xfs detection failed. grub-core/kern/fs.c:56: Detecting ufs2... (...) grub-core/kern/fs.c:56: Detecting affs... grub-core/kern/fs.c:78: affs detection failed. grub-probe: error: unknown filesystem.
This shows that ZFS detection went well until the com.datto:encryption feature was detected. Since ZFS Native Encryption is not supported by GRUB (as of August 2021), detection of ZFS failed. A second, GRUB-compatible zpool may be appropriate to boot into an encrypted system - as of August 2021, this is the recommended approach (refer to the relevant OpenZFS project page).
A successful execution of grub-probe on a GRUB-compatible zpool looks like this:
grub-probe -vvvv /boot
(...) grub-core/osdep/hostdisk.c:399: reusing open device `/dev/sda3' grub-core/fs/zfs/zfs.c:2117: zap: name = com.delphix:extensible_dataset, value = 0, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = com.delphix:embedded_data, value = 1, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = com.delphix:hole_birth, value = 1, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = org.open-zfs:large_blocks, value = 0, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = org.illumos:lz4_compress, value = 1, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = , value = 0, cd = 0 grub-core/fs/zfs/zfs.c:2117: zap: name = , value = 0, cd = 0 grub-core/fs/zfs/zfs.c:3285: alive (...) grub-core/fs/zfs/zfs.c:1906: endian = 1 grub-core/fs/zfs/zfs.c:597: dva=8, 20008 grub-core/fs/zfs/zfs.c:2697: alive zfs
Booting your kernel and initrd from ZFS
You may skip this section if you have your kernel and initrd on a separate /boot partition using something like ext4 or vfat.
Otherwise grub needs to load your kernel and initrd are from a ZFS dataset the kernel and initrd paths have to be in the following format:
/dataset/@/actual/path
Example with Arch installed on the root dataset:
/boot/grub/grub.cfg
set timeout=5
set default=0
menuentry "Arch Linux" {
search -u UUID
linux /@/boot/vmlinuz-linux zfs=zroot rw
initrd /@/boot/initramfs-linux.img
}
Example with Arch installed on a nested dataset:
/boot/grub/grub.cfg
set timeout=5
set default=0
menuentry "Arch Linux" {
search -u UUID
linux /ROOT/default/@/boot/vmlinuz-linux zfs=zroot/ROOT/default rw
initrd /ROOT/default/@/boot/initramfs-linux.img
}
Booting your kernel and initrd from separate boot partition
Example with a separate non-ZFS /boot partition and Arch installed on a nested dataset:
/boot/grub/grub.cfg
set timeout=5
set default=0
menuentry "Arch Linux" {
search -u UUID
linux /vmlinuz-linux zfs=zroot/ROOT/default rw
initrd /initramfs-linux.img
}
Using systemd-boot for EFI only
Systemd-boot cannot open ZFS zpools, you must store your /boot on a separated VFAT or ext4 partition.
Install bootloader on your esp, following Systemd-boot#Installing the EFI boot manager.
Create a boot entry:
/efi/loader/entries/archlinux.conf
title Arch Linux linux vmlinuz-linux initrd intel-ucode.img initrd initramfs-linux.img options zfs=zroot/ROOT/default rw
Using rEFInd for UEFI
Use EFISTUB and rEFInd for the UEFI boot loader. 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.
Configure systemd ZFS mounts
For your system to be able to reboot without issues, you need to enable the zfs.target to auto mount the pools and set the hostid.
arch-chroot
For each pool you want automatically mounted execute:
# zpool set cachefile=/etc/zfs/zpool.cache <pool>
Enable the target with systemd:
# systemctl enable zfs.target
In order to mount zfs pools automatically on boot you need to enable the following services and targets:
# systemctl enable zfs-import-cache # systemctl enable zfs-mount # systemctl enable zfs-import.target
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, to get your number use the hostid command.
The other, and suggested, 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. To write the hostid file safely you need to use the zgenhostid command.
To use the libc-generated hostid (recommended):
# zgenhostid $(hostid)
To use a custom hostid (must be hexadecimal and 8 characters long):
# zgenhostid deadbeef
To let the tool generate a hostid:
# zgenhostid
Do not forget to regenerate your image using mkinitcpio.
Unmount and restart
We are almost done!
# umount /mnt/boot (if you have a legacy boot partition) # zfs umount -a # zpool export zroot
Now reboot.
Loading password from USB-Stick
It is possible to store password on usb-stick and load it when booting:
Save password on first bytes of usb-stick:
# dd if=your_password_file bs=32 count=1 of=/dev/disk/by-id/usb_stick
To create partition zfs partition you can either use previous described method with password prompt or pipe with dd:
# dd if=/dev/disk/by-id/usb_stick bs=32 count=1 | zfs create -o encryption=on -o keyformat=passphrase zroot/ROOT
Next step is modyfing zfs hook. By default zfs prompts for password. You have to change it to have it piped with dd from your pendrive. In order to do so modify /usr/lib/initcpio/hooks/zfs and change line:
# ! eval zfs load-key "${encryptionroot}"; do
to:
# ! eval dd if=/dev/disk/by-id/usb_stick bs=32 count=1 | zfs load-key "${encryptionroot}"; do
You are modifying your zfs hook so do not forget to regenerate your image using mkinitcpio. Now zfs should load password from your usb-stick on boot.
Troubleshooting
System fails to boot due to: cannot import zroot: no such pool available
You can try the following steps and see if they can help.
- Use the kernel modules from the archzfs repo instead of the dkms version. You can go back to the dkms version after a sucessfull boot.
- Remove the
/etc/zfs/zpool.cacheand run:
# zpool set cachefile=none zroot
- Remove the
/etc/hostid. - Rebuild your initramfs.