Bootstrapping hangs with 'SocksPort 0'
Debian uses a minimal torrc on onion.debian.org (our onionbalance node) and tor from Debian backports. We recently upgraded from 0.3.3.9-1~bpo9+1 to 0.3.4.8-1~bpo9+1 and discovered that our onionbalance services were no longer working, but the backend onion services and our normal onion services were still working. The issue was that the tor daemon on onion.debian.org could not achieve bootstrap. tor 0.3.3.9 worked with the existing config, but 0.3.4.8 did not. Changing the SocksPort parameter from 0 to 6666 allowed tor 0.3.4.8 to achieve bootstrap.
The config does not contain any onion services, because those are setup by onionbalance via the tor control port.
So the issue appears to be that tor is not trying to contact the tor network unless it has a socks port or an onion service or other tor network requiring thing configured.
SocksPort 0 Log notice syslog #HiddenServiceSingleHopMode 1 #HiddenServiceNonAnonymousMode 1 ControlPort 9051