Well, the 18.04 LTS has been release for the Odroid C1, so guess what I've done.... that's right, I've upgraded...
This time, the board has not come back online...

I got my remote hands to shutdown the power of the observatory, I shall fix it when I'm over there in December.
Shame, I had everything almost tip-top, I was just fixing one tiny issue that cropped up lately about my udev rules and the mount USB cable.

Tooo bad !
What went wrong ? Doesn't boot ?

And how did you perform the upgrade? Did you use the do-release-upgrade command or edit the apt sources.list files by hand? Or something different all together?

I used the do-release-upgrade command. Oh well, not the end of the world, I backed up everything I needed onto the USB drive anyway.

Strange that the do-release-upgrade script didn’t do its job. Glad to read that you’ve got a backup of the essential stuff though!

This may be due to the change of network devices naming in 18.04 - if you have /etc/network/interfaces with explicit device names and do not have udev rules to rename devices to your names it will fail. I'm just guessing here but it seems plausible to me. Maybe your remote hands can edit the names ?
That is why I never use ubuntu on remote servers without remote console - it is designed for the desktop and bites you in the behind in the worse possible moment.
I would humbly suggest moving to debian - it is a bit harder to set up (no PPA, older packages etc.) but it is worth it at the end - just my HO.

Hello,

Thanks, that's some good info there, I shall check the file first before going for a full re-install.
Only me can work on the observatory, nobody else.

I choose Ubuntu for the PPA, had Debian to start off on that board.

Been there, done that... Had to migrate several systems back. That is the punishment for going for shiny objects!
Regarding interface names. You can get it back by adding to kernel command line following args:
net.ifnames=0 biosdevname=0
You can add it in cmdline.txt. Actually if you can get the boot card out and fix it on different machine your board should come right up.
Hope it helps.

Maybe Mr. Remote hands could ship the Odroid back to you? At least then you can fix it ahead of your next trip and reinstall it in December. Or send it back to Mr. Remote hands to reinstall it for you?

Remote hand will not be able to do this.
When I designed the new observatory box, I wanted to put the electronics on the outside within a external sealed box for easy access. Sadly, I wasn't able to think about something good and went with the original design, ie: all inside.
Well, now I'm kind of suffering for it in a way. So, maybe this is the wake up call I need and design that external box after all. Or buy a ready made cabinet for it.

Actually you need the sdcard only. But I guess it is not accessible as well.
I used to have this type of problem in different context and I solved it by having some kind of serial interface or console accessible for "remote hands" which can be connected to with dedicated cheap device (like pre-configured pi-zero-w or something) which can forward this to the network (in my case it was - pre-configured old laptop with configured vpn). In your case: maybe redesign it in the way the boot card is accessible? Or just configure odroid to boot from usb stick if it is present and make rescue-usb-socket accessible to remote hands + leave the "rescue stick" with them.

I do not use the SdCard, I use the eMMC card which is located at the back of the board...
Shall look into this boot from usb, not sure if you can do it with an oDroid C1.