docker-entrypoint.sh

#!/bin/bash
set -e

if [ "$1" = 'postgres' ]; then
	chown -R postgres "$PGDATA"
	
	if [ -z "$(ls -A "$PGDATA")" ]; then
		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
	fi
	
	exec gosu postgres "$@"
fi

exec "$@"

Dockerfile

FROM debian:wheezy

# add our user and group first to make sure their IDs get assigned consistently, regardless of whatever dependencies get added
RUN groupadd -r postgres && useradd -r -g postgres postgres

RUN apt-get update && apt-get install -y curl

RUN echo 'deb http://apt.postgresql.org/pub/repos/apt/ wheezy-pgdg main' > /etc/apt/sources.list.d/pgdg.list

RUN curl -sSL https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
RUN apt-get update && apt-get install -y postgresql-9.3

RUN curl -o /usr/local/bin/gosu -SL 'https://github.com/tianon/gosu/releases/download/1.0/gosu' \
	&& chmod +x /usr/local/bin/gosu

ENV PATH /usr/lib/postgresql/9.3/bin:$PATH
ENV PGDATA /var/lib/postgresql/data
VOLUME /var/lib/postgresql/data

ADD ./docker-entrypoint.sh /

ENTRYPOINT ["/docker-entrypoint.sh"]

EXPOSE 5432
CMD ["postgres"]