Comment 2 for bug 1536335

I tried to reproduce this with a 14.04 → 16.04 upgrade in several scenarios, but I can't yet. Nicolas, do you actually use ifupdown on this system, i. e. can you please attach your /etc/network/interfaces and /etc/network/interfaces.d/* ?

Even if I remove "eth0" from /etc/network/interfaces, 14.04's resolvconf still creates /run/resolvconf/interfaces/ (it will be empty then). This happens both in the upstart job (/etc/init/resolvconf.conf) and in the systemd service (/lib/systemd/system/resolvconf.service). So it appears to me that resolvconf was never started before you started the upgrade even.

Did you do anything to disable resolvconf in 14.04?

I suppose we could guard against this by teaching resolvconf to mkdir the runtime directory on resolvconf --enable-updates, instead of in the init scripts. But that doesn't help to understand what went wrong on your system.

Thanks!