In Ubuntu 16.04, you could place into /etc/NetworkManager/dispatcher.d/pre-down.d a script to run something like "killall -s USR1 automount && sleep 1". This should help to timeout non-busy automounts before the network interface goes down.
In Ubuntu 16.04, you could place into /etc/NetworkMan ager/dispatcher .d/pre- down.d a script to run something like "killall -s USR1 automount && sleep 1". This should help to timeout non-busy automounts before the network interface goes down.