Ok. I grabbed a coffee and started to feel human again. I dug deeper and here is what I found:
This is stupid but reasonable.
Obviously there is a block entry for my desktop IP in iptables, which includes http and https.
So where does it come from?
I remembered that I activated fail2ban for preventing brute force attacks.
I found an entry in /var/log/fail2ban.log
Ok. So I checked fail2ban
There it is. Obviously my Desktop simply gets blocked on http and https.
This is the reason why there is no error message anywhere and everything looks fine. It is because everything IS fine and behaving as intended.
So I removed my IP from the fail2ban jail with:
and switched the omv webgui ports back to 80 and 443 again with omv-firstaid.
I tried accessing the webgui on 443 and.... Tadaaaa it works.
IT is amazing ... just do it the correct way, and it works.
So how did this happen?
- My root disk was 100% full. The shares started, but nginx and the php webgui had an issue with that and did not start properly.
- I tried to connect to the webgui during this, but it failed. Anyhow there were log entries about my failed connection attempts in /var/log/auth.log
- These failed connection attempts have been recognized by fail2ban, as intended, and my IP has been jailed.
- After I emptied the disk, updated omv and everything was fine again, the fail2ban entry persisted.
When starting my investigation I got mislead by some posts having a similar issue, but having unintended port conflicts. That was why I first started looking there.
My issue is solved now, and I hope my description will help others in the future