Dockerfile to build on top of postgres, brittle and gross, but works by more or less reimplementing the entry point.

Dockerfile

FROM postgres:9.3
MAINTAINER krujos

ENV PGDATA /var/lib/postgresql/data #Why do I need this?
RUN chown -R postgres "$PGDATA"; gosu postgres initdb; sed -ri "s/^#(listen_addresses\s*=\s*)\S+/\1'*'/" "$PGDATA"/postgresql.conf ; { echo; echo 'host all all 0.0.0.0/0 trust'; } >> "$PGDATA"/pg_hba.conf
RUN ( chown -R postgres "$PGDATA"; gosu postgres postgres & sleep 2 ; psql -U postgres -c "create user schedule_user;"; psql -U postgres -c "alter user schedule_user password 'schedule_password';"; psql -U postgres -c "create database schedule with owner schedule_user;"; )

ENTRYPOINT ["/docker-entrypoint.sh"]

EXPOSE 5432
CMD ["postgres"]

#docker run -p 5432:5432 -d schedule-postgres

Did you figure out why the comment is necessary? It's really bizarre that it does not work without the comment, when all logic says that it should not work with the comment.