This was a stubborn one.
Was trying to use Docker via Dusty for the first time.
docker-machine --debug start dusty
This would hang with the following.
Testing TCP connection to: localhost:64623
Testing TCP connection to: localhost:64623
Testing TCP connection to: localhost:64623
...
No problems connecting to localhost:64623 via ssh localhost -p 64623.
No issues navigating to https://localhost:64623. I would see a page with the SSH server version.
SSH-2.0-OpenSSH_6.4
The culprit was this entry in /etc/hosts, from some experimentation on blocking ads via a hosts file.
0 localhost
The fix was to properly define localhost.
127.0.0.1 localhost
::1 localhost
I opened docker-machine#1946 to improve the error message here.