Not-so-predictable network names

[Alexander Thomas]

There was a discussion titled “example network script will misname
interface if installing stretch” just a few weeks ago. It ended with:

Thomas Lange wrote:
> > Using jessie as the base os to install stretch.
> > 30-interface will setup /etc/network/interfaces with
> > something like eth0, and if you upgrade to stretch,
> > it will reboot and eth0 is now named something like
> > enp3s0f1.
> This is already fixed in FAI 5.1.

I now have the same problem while installing xenial from a jessie
NFSroot. It defines an interface eth0 in /etc/network/interfaces, but
when the installed system boots, the interface is named ‘ens3’.

I installed FAI 5.1.2 and ensured I have the latest config scripts
from the FAI git repository, but it makes no difference. I tried the
following workaround inspired by the same discussion thread, by
renaming $NIC1 in scripts/DEBIAN/30-interface as follows:

NIC1="$(udevadm test /sys/class/net/$NIC1 2>/dev/null | fgrep
ID_NET_NAME_SLOT | cut -d= -f2)"

Although it feels dirty and unreliable and I don't know why I need to
use SLOT here instead of PATH, it worked fine, at first. When I try to
install a VM with a virtio network interface, it breaks. In that case,
ID_NET_NAME_SLOT is no longer in the udevadm output, only
ID_NET_NAME_MAC is. Still, the interface eventually becomes ‘ens3’,
but that name is nowhere to be found in the udevadm output.

How do I ensure /etc/network/interfaces is always written with the
correct names? Or how do I end up with a truly predictable network
device?


Regards,
Alexander