I upgraded the server from 14.04 to 16.04 and slowly discovered everything was not working perfectly with the ZFS functionality. Researching it appears zfsonlinux doesn’t support 16.04 since ZFS is a part of 16.04. However I couldn’t get the Ubuntu version to load and got this error. It gave me the pointer that the old trusty (14.04) version was the issue.
The following packages have unmet dependencies: zfsutils-linux : Depends: zfs-doc (= 0.6.5.6-0ubuntu15) but 0.6.5.7-1~trusty is to be installed Depends: libnvpair1linux but it is not going to be installed Depends: libuutil1linux but it is not going to be installed Depends: libzfs2linux but it is not going to be installed Depends: libzpool2linux but it is not going to be installed Recommends: zfs-zed but it is not going to be installed E: Unable to correct problems, you have held broken packages.
So had to purge the non Ubuntu trusty packages and start over. This will find the old installed zfs packages:
dpkg -l|grep zfs
Then you can purge the packages old trusty (14.04) to remove them:
sudo apt-get purge zfs-doc
Make sure nothing odd is in /etc/apt. Then install the native Ubuntu version with the normal:
sudo apt install zfsutils-linux