How to remap network interfaces on boot time?

Question

It turns out that I'm trying to create a portable distro while getting prepared for any kind of hardware failure.

I'm creating (or restoring) a Debian distro by multistrap (or from my backups) and requiring the resulting disk to be bootable on a new (mostly compatible) hardware, including a VirtualBox machine.

As I asked before, one of the few required things for a "portable distro" is handling the network interfaces' names.

For example, on the real machine, first ethernet device is named as enp2s0 and in VirtualBox, it's named as enp0s3. How am I supposed to generate a /etc/network/interfaces file on boot?

Is there a more generic way to remap the network interface names (by symbolic links, maybe) and let every application use those names (the role names) without the necessity to know the real network interface names of the underlying hardware?

Answer 1

There are several ways you could solve this.

The most familiar way would probably be to disable the new network interface naming scheme by using the boot option net.ifnames=0, or by overriding /lib/systemd/network/99-default.link with ln -s /dev/null /etc/systemd/network/99-default.link, or by masking the udev rule file that actually implements the new-style names with ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules... see the Debian Wiki for more info on various ways to revert to the classic naming scheme. Then you could rewrite your /etc/network/interfaces to just use eth0.

The most flexible way would probably be to stop using static /etc/network/interfaces and switch to NetworkManager. It will automatically default to using DHCP on a network interface that has an active link, if there is no further configuration. That would automatically handle even cases when you have multiple NICs but only one (not necessarily the first one) is actually plugged in.

Or you could do your own thing, by writing a custom script that will read ip link show output (or the links in /sys/class/network) and rewrite /etc/network/interfaces (or whatever your actual network configuration file is) to suit. Then you could add the script as a systemd service with Wants=network-pre.target, Before=network-pre.target, After=module-init-tools.service and probably DefaultDependencies=no. This should allow the script to run as part of the early system set-up, after all modules have been loaded but before the network configuration begins.