Shift=true with a ZFS-pool doesn't work, says not supported?

LXD Support
1

I used to use Btrfs as my filesystem, but I recently moved my servers over to ZFS and now many of my containers will not work. lxc info does say I have idmapping enabled and the documentation for LXD does seem to say that that should be enough, but alas, I only get the following:

Error: Failed to setup device mount "test": idmapping abilities are required but aren't supported on system
Try `lxc info --show-log instance` for more info

lxc info|grep idmap
    idmapped_mounts: "true"
    idmapped_mounts_v2: "true"

This is on Ubuntu 23.04 with kernel 6.2.0-32-generic and ZFS 2.1.9-2ubuntu1.1

I have tried googling for a while now, but all the results I get seem to be talking about something different or about using raw.idmap and I don’t understand what am I doing wrong. Could someone more knowledgeable please explain why shift=true doesn’t work with ZFS, when it worked just fine with Btrfs and how do I fix this? I am new to ZFS, so I wouldn’t be surprised if it was something I am missing, but that error message isn’t very useful in solving it.

2

ZFS does not yet support idmapped mounts in the Ubuntu kernel. It has been very recently added to the, as yet unreleased, 2.2 release of ZFS (https://www.phoronix.com/news/OpenZFS-2.2-rc1).

So in the meantime you can use shiftfs which is in the Ubuntu kernel (for now) by enabling it in the LXD snap:

sudo snap set lxd shiftfs.enable=true
sudo systemctl reload snap.lxd.daemon
3

I feel like openZFS < 2.2.0 not supporting idmapping should be mentioned in the documentation for the LXD ZFS-driver’s limitations. I fully thought it’d support idmapping just the same as Btrfs does.

Such a nuisance, but I guess I’ll use shiftfs, then. Thanks.

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