One of my servers crashed because of a motherboard problem, but, as
luck had it, there was something on the HD I was working on and I
hadn't fully backed up.

I stuck another motherboard in and started up the machine again, up it
came, after fsck'ing the HD and everything worked, apart from the
network. Checked lspci etc and as far as I could see, there was nothing
wrong, but I just couldn't get eth0 to work (did I say there was only 1
network card?)

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 ????????

Rowland