Comment 29 for bug 1569925

Seeing a similar issue here with so called "diskless" clients. That is, all of their filesystems are network mounts including the root filesystem. These systems use iscsi targets for the root filesystem and during shutdown the network is turned off before the file I/O operations are completed which causes the system to hang with filesystem IO errors.

I'm currently looking to see if there is some way to make systemd keep the network up no matter what, all the way until the machine physically reboots or shuts down (ie. disable the network shutdown completely).

This worked in 14.04 and got broken in 16.04 apparently due to the switch to systemd as far as I can tell (great tool, isn't it?).