# Installing Arch Linux on ZFS

Related articles

- ZFS
- Playing with ZFS
- ZFS on FUSE

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

## Installation

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.

## 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 -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 seperate 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`

    /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 don't 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`:

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,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:

     /dataset/@/actual/path

Example:

       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");
                break;
                case EPERM:
                fprintf(stderr, "Error! The calling process's effective"
                                " user or group ID is not the same as"
                                " its corresponding real ID.\n");
                break;
                default:
                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

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

Category:

- Getting and installing Arch