Indeed "ifquery -l --allow=hotplug" doesn't mention any interface, but eth0 comes up just fine anyway. When I comment out above file, it does not come up, so that file and ifup is definitively being used here.
But running "sudo ifup --verbose --allow=hotplug eth0" manually confirms that the stanza is being ignored. So the most probable explanation is that /etc/init.d/networking is being run during boot which takes care of the "auto" stanzas? Why isn't that being run for you? Can you please show "systemctl status networking"?
I have some trouble reproducing this. I installed systemd-sysv into a minimal VM without NetworkManager, and /etc/network/ interfaces. d/eth0. cfg has
# The primary network interface
auth eth0
iface eth0 inet dhcp
Indeed "ifquery -l --allow=hotplug" doesn't mention any interface, but eth0 comes up just fine anyway. When I comment out above file, it does not come up, so that file and ifup is definitively being used here.
But running "sudo ifup --verbose --allow=hotplug eth0" manually confirms that the stanza is being ignored. So the most probable explanation is that /etc/init. d/networking is being run during boot which takes care of the "auto" stanzas? Why isn't that being run for you? Can you please show "systemctl status networking"?