I am posting this so it can help someone else, someday.
I have a DragonFly-5.4 system. I installed mysql56-server, and started it up. By default, it listens on “*”, which meant it listens on a local socket and IPv6 ::1 – not 127.0.0.1.
2019-06-04 13:35:03 15833 [Note] IPv6 is available.
2019-06-04 13:35:03 15833 [Warning] Failed to reset IPV6_V6ONLY flag (error: 45). The server will listen to IPv6 addresses only.
I put bind_address=127.0.0.1 into my.cnf to get IPv4 loopback to work. Local socket connections still worked either way. I’m not using IPv6 on this machine, so this solution works in this situation. I’m not sure my mysql decides to go only IPv6 based on a strange flag, but mysql is reliably unreliable.