Turning freenas server OFF from a Raspberry Pi.

On the pi server:

# copy the pi key to the freenas server
ssh-copy-id -i ~/.ssh/id_rsa.pub root@freenas

On the pi server:

# ssh into the nas server from the pi
ssh root@freenas

Now logged into the freenas server:

# edit the sudoers file
visudo

# go to the end, i to insert, add:
root ALL = (ALL) NOPASSWD: /sbin/shutdown -h now
# save and exit ( escape : w q )

Exit the freenas box:

exit

Back on the pi, tell the freenas server to shut down

ssh 'root@freenas' "shutdown -h now"

The box should shut down.