Difference between revisions of "Installing Arch Linux on ZFS"

From ArchWiki
Jump to navigation Jump to search
m (Create the root zpool: typo)
m (avoid contractions to comply with Help:Style#Language_register)
Line 90: Line 90:
  # zfs set mountpoint=/root zroot/root
  # zfs set mountpoint=/root zroot/root
and if you have seperate datasets for system directories (ie {{ic|/var}} or {{ic|/usr}})
and if you have separate datasets for system directories (ie {{ic|/var}} or {{ic|/usr}})
  # zfs set mountpoint=legacy zroot/usr
  # zfs set mountpoint=legacy zroot/usr
Line 124: Line 124:
  # cp /etc/zfs/zpool.cache /mnt/etc/zfs/zpool.cache
  # cp /etc/zfs/zpool.cache /mnt/etc/zfs/zpool.cache
if you don't have /etc/zfs/zpool.cache, create it:
if you do not have /etc/zfs/zpool.cache, create it:
  # zpool set cachefile=/etc/zfs/zpool.cache zroot
  # zpool set cachefile=/etc/zfs/zpool.cache zroot

Revision as of 09:09, 28 April 2015

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


See ZFS#Installation for installing the ZFS packages. If installing Arch Linux onto ZFS from the archiso, it would be easier to use the demz-repo-archiso repository.

Embedding archzfs into archiso

See ZFS article.

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.
Warning: Several GRUB bugs (bug #42861, zfsonlinux/grub/issues/5) prevent or complicate installing it on ZFS partitions, use of a separate boot partition is recommended

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
  • Always use id names when working with ZFS, otherwise import errors will occur.
  • The zpool command will normally activate all features. See ZFS#GRUB-compatible_pool_creation when using GRUB.

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 -o mountpoint=/home
# zfs create zroot/root -o mountpoint=/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

See ZFS#Swap volume.

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

and if you have separate datasets for system directories (ie /var or /usr)

# zfs set mountpoint=legacy zroot/usr
# zfs set mountpoint=legacy zroot/var

and put them in /etc/fstab

# <file system>        <dir>         <type>    <options>             <dump> <pass>
zroot/usr              /usr          zfs       defaults,noatime      0      0
zroot/var              /var          zfs       defaults,noatime      0      0

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: Do not 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

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 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:
  • 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:

set timeout=2
set default=0

# (0) Arch Linux
menuentry "Arch Linux" {
    set root=(hd0,msdos1)
    linux /vmlinuz-linux zfs=zroot rw
    initrd /initramfs-linux.img

if you did not create a separate /boot participation, kernel and initrd paths have to be in the following format:



   linux /@/boot/vmlinuz-linux zfs=zroot rw
   initrd /@/boot/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 are 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.target to auto mount the pools and set the hostid.

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

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 do write the hostid file safely you need to use a small C program:

#include <stdio.h>
#include <errno.h>
#include <unistd.h>

int main() {
    int res;
    res = sethostid(gethostid());
    if (res != 0) {
        switch (errno) {
            case EACCES:
            fprintf(stderr, "Error! No permission to write the"
                         " file used to store the host ID.\n"
                         "Are you root?\n");
            case EPERM:
            fprintf(stderr, "Error! The calling process's effective"
                            " user or group ID is not the same as"
                            " its corresponding real ID.\n");
            fprintf(stderr, "Unknown error.\n");
        return 1;
    return 0;

Copy it, save it as writehostid.c and compile it with gcc -o writehostid writehostid.c, finally execute it and regenerate the initramfs image:

# ./writehostid
# mkinitcpio -p linux

You can now delete the two files writehostid.c and writehostid. Your system should work and reboot properly now.

See also