Der Eintrag dns-nameservers in der /etc/network/interfaces hat keinen Effekt.

bisherige "Notlösung"

post-up echo 'nameserver <IP-HERE>' > /etc/resolv.conf

Der Eintrag wird beim Speichern mit Hilfe der libgfanet entfernt.

HOOK SCRIPTS

https://manpages.debian.org/testing/ifupdown/interfaces.5.en.html#HOOK_SCRIPTS

Evtl. könnte ein script im order /etc/network/if-up.d/ helfen

/etc/network/if-pre-up.d/

Scripts in this directory are run before bringing the interface up.

/etc/network/if-up.d/

Scripts in this directory are run after bringing the interface up.

/etc/network/if-down.d/

Scripts in this directory are run before bringing the interface down.

/etc/network/if-post-down.d/

Scripts in this directory are run after bringing the interface down.

Beispiel für /etc/network/if-up.d/nameserver

#!/bin/sh
beep
grep -e "dns-nameservers"  /etc/network/interfaces | sed -e 's/dns-nameservers/nameserver/g' | awk '!x[$0]++' > /etc/resolv.conf