#dpkg -S /etc/network/if-down.d/*
postfix: /etc/network/if-down.d/postfix resolvconf: /etc/network/if-down.d/resolvconf ifupdown: /etc/network/if-down.d/upstart
#dpkg -S /etc/network/ if-down. d/*
postfix: /etc/network/ if-down. d/postfix if-down. d/resolvconf if-down. d/upstart
resolvconf: /etc/network/
ifupdown: /etc/network/