If you’re seeing an error like this in your postgresql.log:
LOG: could not connect socket for statistics collector: Invalid argument
LOG: disabling statistics collector for lack of working socket
WARNING: autovacuum not started because of misconfiguration
HINT: Enable the “track_counts” option.

There’s a good chance that your localhost entry in /etc/hosts is broken. In my case, there was a typo in the IP address, which should have been 127.0.0.1:
27.0.0.1 localhost

Once that was fixed, then the PostgreSQL database started up normally and Autovacuum was running.