After messing around for the longest time trying to get a simple cifs Nas mount at boot I stumbled on a fix. Be sure to set this systemd function 'sudo systemctl enable remote-fs.target' or systemd will ignore the fstab directions and you'll be having to manually mount every boot. Of course the usual systemd parameters need to be in the fstab as well ',_netdev,x-systemd.automount,' beween cifs and the credentials.
Cheers from the Cloakroom.
