How do I get Ubuntu to figure out the interfaces available on my computer and generate a new /etc/network/interfaces file? It created it the first time so I know it can somehow.
Is there something like dpkg-reconfigure <what?> that would just recheck for me?
in ubuntu 14.04.1 THIS happens if you clone a system to other hardware as /etc/udev/rules.d/70-persistent-net.rules contains MAC address's of ethernet hardware on the source computer.
YES - just deleting /etc/udev/rules.d/70-persistent-net.rules allows things to be refreshed to a working state at reboot.
eth0 style network names. With the new 'predictable network interface names' introduced around ubuntu15.10 the 70-perisistent-net.rules trick no longer applies.
/etc/network/interfaces is generated by the actual installer, not any of the packages on your system:
opus:~ broder$ dpkg -S /etc/network/interfaces
dpkg: /etc/network/interfaces not found.
Because it's not managed by any particular package, no package is going to modify the file.
If you want to add new interfaces to /etc/network/interfaces, you have to do that manually. Alternatively, if you want your network interfaces to be managed automatically by your system, I believe the official answer at this point is to use NetworkManager. NetworkManager will handle configuration for any network interface that's not listed in /etc/network/interfaces.
Try run below command
dpkg-reconfigure ifupdown
possibly.
However, you are probably running into an issue with udev. If you have rebooted, and eth0 disappeared:
ifconfig -a
you can mv/rm the file in /etc/udev/rules.d/70-persistent-net.rules and reboot, and your primary ethernet card should become eth0 again.
This would happen if you switched motherboards/network cards.
