You may hit this error if you have had a failed attempt at deploying the UCP and there is still orphaned references to it on the Docker host. I forgot to remove the old UCP Docker volumes so when I tried to deploy the latest verion of UCP this happened.
"FATA[0001] unable to verify that no UCP components already exist: the following volumes appear to be from an existing UCP installation and must be removed before proceeding with a new in stallation: ucp-kv ucp-metrics-data ucp-auth-api-certs ucp-auth-store-certs ucp-client-root-c a ucp-cluster-root-ca ucp-controller-server-certs ucp-auth-worker-certs ucp-auth-worker-data
ucp-kv-certs ucp-auth-store-data ucp-controller-client-certs ucp-node-certs"
"FATA[0001] unable to verify that no UCP components already exist: the following volumes appear to be from an existing UCP installation and must be removed before proceeding with a new in stallation: ucp-kv ucp-metrics-data ucp-auth-api-certs ucp-auth-store-certs ucp-client-root-c a ucp-cluster-root-ca ucp-controller-server-certs ucp-auth-worker-certs ucp-auth-worker-data
ucp-kv-certs ucp-auth-store-data ucp-controller-client-certs ucp-node-certs"
Simply use the docker volume prune command to get rid of all the old volumes which are not associated to a running container. Tread with caution if you are using a production system.