Rowland Penny <rpenny241155@???> wrote:

> I stuck another motherboard in and started up the machine again

...

> Finally, in desperation, I ran 'dmesg | grep eth0' and found my problem:
>

> root@server:~# dmesg | grep eth0
> [    0.921998] r8169 0000:02:00.0 eth0: RTL8168b/8111b at 0xffffc90000006000, 00:1d:60:fc:29:e6, XID 18000000 IRQ 41
> [    0.922001] r8169 0000:02:00.0 eth0: jumbo features [frames: 4080 bytes, tx checksumming: ko]
> [    7.620169] systemd-udevd[362]: renamed network interface eth0 to eth1

>
> Why, oh why, did systemd-udevd rename eth0 to eth1 ????????

Is this an on-board ethernet ? If so, then udev has done this for "a long time". The different board will have a different MAC and udev will therefore give it a new name. You can edit /etc/udev/rules.d/70-persistent-net-rules.

Newer Systemd is far worse though - they've done away with usable names entirely and instead you are stuck with stupid long names based on bus address. Far easier to edit udev rules than to find everywhere the interface name is used and edit that.