FATAL: data directory "/usr/local/var/postgres" has group or world access
DETAIL: Permissions should be u=rwx (0700).
sudo chown -R <USERNAME> /usr/local/var/postgres
sudo chmod -R 700 /usr/local/var/postgres
FATAL: database files are incompatible with server
DETAIL: The data directory was initialized by PostgreSQL version 9.4, which is not compatible with this version 9.6.1.
rm -rf /usr/local/var/postgres && initdb /usr/local/var/postgres -E utf8
psql: FATAL: database "<USERNAME>" does not exist
createdb <USERNAME>