ZFS on Ubuntu error: Failed to load ZFS module stack

  If you see the above error in a fresh installation of ZFS on Ubuntu one cause may be that the package build-essentials wasn’t installed prior to installing the ubuntu-zfs package; run:  
sudo apt-get purge ubuntu-zfs
  then check for the remaining packages with the following:  
dpkg –list | grep zfs
  …and apt-get purge any remaining relevant ZFS packages.   Then:  
sudo apt-get install build-essential
  …then install ubuntu-zfs as you did originally:  
sudo apt-get install ubuntu-zfs
  This time it should take properly. This isn’t the only cause of that error but on a fresh install with a new OS it’s one possibility.