I have Ubuntu 20.10 on zfs root (upgraded from 20.04) I tried to restore 20.04 using zsys features at boot, which was unsuccessful. I have a backup (created using syncoid). Using zfs send/receive. I created a new pool in a separated disk called spool. It has a restored 20.04 before the upgrade.

I'd like to be able to choose at boot time between the two rpools. How to I set it up with grub.

1 Answer 1


The root is selected using the kernel boot parameter root=ZFS=pool/fsname. Simply add another grub entry with a different entry for different root.

  • Is there a way to make "update-grub" do it for me. The file /etc/grub.d/10_linux_zfs might be a good candidate for modification. I just do not know enough to make the changes.
    – user63726
    Oct 25, 2020 at 23:03
  • I tried to make the change manually. It fails to mount spool (the new rpool). It tied to mount it the root from spool on /root/spool/ROOT.. instead of /
    – user63726
    Oct 29, 2020 at 1:04
  • I suspect you forgot to set mount point=legacy on spool/ROOT. Oct 29, 2020 at 6:20
  • If I do that. I do not think that all the subpools and the user pools will be mounted.
    – user63726
    Oct 31, 2020 at 0:18
  • They aren't directly related. The root file system gets mounted by the initramfs under /sysroot during the initramfs stage. The other file systems get mounted after switchroot by systems via the zfs-import-cache and zfs-import-scan services. Oct 31, 2020 at 6:09

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