I tested with your single-file approach and that also fails. Note that bionic now has systemd 237, so maybe something is missing (or regressed) ?
$ apt-cache policy systemd systemd: Installed: 237-3ubuntu10.26 Candidate: 237-3ubuntu10.26 Version table: *** 237-3ubuntu10.26 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic-proposed/main amd64 Packages 100 /var/lib/dpkg/status 237-3ubuntu10.25 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages 237-3ubuntu10.19 500 500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages 237-3ubuntu10 500 500 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/main amd64 Packages -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1671951 Title: networkd should allow configuring IPV6 MTU To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cloud-init/+bug/1671951/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs