Hello, as there were some follow up emails let me explain the problem.
The standard Debian tor@default.service has "After=network.target nss-lookup.target" in it, so one would think network should be fully functional when the services starts, but it was not in my case. At the time when tor started the eno0 did not yet have a IPv6, so it complained that it could not bind to some port in the config, because the IP supplied with the port was not ready yet.
The after that 5 retries to start tor it gets stuck, systemd status tells it is running, but nyx can says it is not running.
After the 5 restarts I saw that ifup had some issue too, which was caused by some config in /etc/network/interfaces, which was working ok and the IPv6 was also reachable, but still the ifup@eno0.service was not working well. I have no idea about how and where to find that service.
However, I changed the "network" parameter in the interfaces config to be supplied with the IPv6, so like 2001:0DB8:0001::0002/64 instead of "network 64" in a separate line. This satisfied ifup it seems, but still it was too slow to be up and running before Tor was started.
Then I searched again and found a quick and dirty (aka lazy) solution for that, in "tor@default.service" I added this line:
ExecStartPre=/bin/sh -c 'until ping -c1 google.com; do sleep 1; done;'
in the "[Service]" section.
I also tried to add "network-online.target" and some "ifup@eno0.service" in the "After=" line above, but I guess it must be somehow different, maybe has to be some target instead.
So with this line a ping of google.com has to work at least once for the service to be started. In combination with the standard "TimeoutStartSec=300" that should work well.
I am sure there is nicer solutions, but why bother.
yours yl