Last night in #HomeLab :
* Dang it, this proxmox server isn't booting after I removed the GPU.
* & I don't have inputs on left on my monitor or display cables on other machines in convenient to move places.
* ... Oh right! My crowdfunded #JetKVM arrived last month, I should open one and try it out.
Success! That new little Ethernet connected h264 streaming https://jetkvm.com/ is literal magic. A joy to use. Also a potential Security Nightmare, so I'm treating it as a crash-cart and won't leave it attached, at least with USB connected.
Original problem: Motherboard BIOS device numbering combined with Linux stupidity. enp3s0 turned itself into enp2s0 upon removal of the PCIe GPU (why?!?) which didn't match the setup in /etc/network/interfaces.
This is partially systemd's fault. But also Linux's in general. A friend ironically pointed out that the https://systemd.io/PREDICTABLE_INTERFACE_NAMES/ is properly in YELLING CASE even though it is the wrong solution to this decades old problem in the face of non-server hardware UEFI BIOS that renumbers IO bus ports based on device presence. The rotten cheese was merely moved, not thrown out.
I'd call my (likely hand edits) to /etc/network/interfaces and the concept of that file listing actual interfaces the problem. None of the above configuration methods really do what we _want_ to express.
"The only network interface with the active Ethernet connection? yeah use that one."
"The interface that gets an address showing X as its default gateway"
"The faster interface"
"Don't believe this interface's lies - it's an untrusted network."
There are ways to express some configuration desires in a more robust to changes manner, but they tend to be hacks instead of the first thing you reach for. Thus problems.