I've seen a number of people on the forum receiving the error:

"Failed to connect to backend db, error: Access denied for user 'green'@'localhost' (using password: YES)"

I ran into this issue and spent a good bit of time trying to figure out what the problem was. Unfortunately none of the topics about this result in a solution. What ended up causing my problem was the use of a special character in the password for the green user account. To fix the issue, I ran '/usr/sbin/greensql-create-db' and entered a password without special characters in it for the green user.