I ran into an issue with being unable to apt-update because of grub-probe failing to determine my root filesystem type. This wasn’t a ZFS-root system, it had a separate /boot partition. The error was “grub-probe: error: failed to get canonical path of `tank/root’.” Most solutions suggest the use of the ZPOOL_VDEV_NAME_PATH environment variable, but this didn’t fix the problem for me.

I found out that the actual problem was that in my single-drive zpool, a networking hiccup caused it to be marked as degraded. Despite the fact that the pool still worked, the fact that there was no fully-online vdev caused some confusion for grub-probe. Upon clearing the errors with zpool clear, it worked fine.