title: Docker compose won't wait for Postgres to start
body: <p>I made a Dockerfile based on python3 image, here is the code:</p>
  
  <pre><code> FROM python:3
  
  ENV PYTHONUNBUFFERED 1
  RUN mkdir /code
  WORKDIR /code
  ADD requirements.txt /code/
  RUN pip install -r requirements.txt
  ADD . /code/
  </code></pre>
  
  <p>This is my docker-compose.yml file, that starts a simple Django app:</p>
  
  <pre><code>version: '2'
  
  services:
  
    web:
      build: .
      env_file: composeexample/.env
      command: python3 manage.py runserver 0.0.0.0:8000
      volumes:
        - .:/code
      ports:
        - "8000:8000"
      depends_on:
        - "db"
      command: ["./wait-for-postgres.sh", "db", "--", "python", "news/"]
    db:
     image: postgresql
     volumes:
       - /var/lib/postgresql/data
  </code></pre>
  
  <p>I'm trying to execute the ./wait-for-postgres.sh script from this page: <a href="https://docs.docker.com/compose/startup-order/" rel="nofollow noreferrer">https://docs.docker.com/compose/startup-order/</a></p>
  
  <p>And it have the following code:</p>
  
  <pre><code>#!/bin/bash
  # wait-for-postgres.sh
  
  set -e
  
  host="$1"
  shift
  cmd="$@"
  
  until psql -h "$host" -U "postgres" -c '\l'; do
    &gt;&amp;2 echo "Postgres is unavailable - sleeping"
    sleep 1
  done
  
  &gt;&amp;2 echo "Postgres is up - executing command"
  exec $cmd
  </code></pre>
  
  <p>However, my Postgres image on docker has its own Dockerfile, this is the PostgreSQL Dockerfile:</p>
  
  <pre><code>#
  # example Dockerfile for https://docs.docker.com/examples/postgresql_service/
  #
  FROM ubuntu
  
  # Add the PostgreSQL PGP key to verify their Debian packages.
  # It should be the same key as https://www.postgresql.org/media/keys/ACCC4CF8.asc
  RUN apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys B97B0AFCAA1A47F044F244A07FCC7D46ACCC4CF8
  
  # Add PostgreSQL's repository. It contains the most recent stable release
  #     of PostgreSQL, ``9.3``.
  RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main" &gt; /etc/apt/sources.list.d/pgdg.list
  
  # Install ``python-software-properties``, ``software-properties-common`` and PostgreSQL 9.3
  #  There are some warnings (in red) that show up during the build. You can hide
  #  them by prefixing each apt-get statement with DEBIAN_FRONTEND=noninteractive
  RUN apt-get update &amp;&amp; apt-get install -y python-software-properties software-properties-common postgresql-9.3 postgresql-client-9.3 postgresql-contrib-9.3
  
  # Note: The official Debian and Ubuntu images automatically ``apt-get clean``
  # after each ``apt-get``
  
  # Run the rest of the commands as the ``postgres`` user created by the ``postgres-9.3`` package when it was ``apt-get installed``
  USER postgres
  
  # Create a PostgreSQL role named ``docker`` with ``docker`` as the password and
  # then create a database `docker` owned by the ``docker`` role.
  # Note: here we use ``&amp;&amp;\`` to run commands one after the other - the ``\``
  #       allows the RUN command to span multiple lines.
  RUN    /etc/init.d/postgresql start &amp;&amp;\
      psql --command "CREATE USER docker WITH SUPERUSER PASSWORD 'docker';" &amp;&amp;\
      createdb -O docker docker
  
  # Adjust PostgreSQL configuration so that remote connections to the
  # database are possible.
  RUN echo "host all  all    0.0.0.0/0  md5" &gt;&gt; /etc/postgresql/9.3/main/pg_hba.conf
  
  # And add ``listen_addresses`` to ``/etc/postgresql/9.3/main/postgresql.conf``
  RUN echo "listen_addresses='*'" &gt;&gt; /etc/postgresql/9.3/main/postgresql.conf
  
  # Expose the PostgreSQL port
  EXPOSE 5432
  
  # Add VOLUMEs to allow backup of config, logs and databases
  VOLUME  ["/etc/postgresql", "/var/log/postgresql", "/var/lib/postgresql"]
  
  # Set the default command to run when starting the container
  # Set the default command to run when starting the container
  CMD ["/usr/lib/postgresql/9.3/bin/postgres", "-D", "/var/lib/postgresql/9.3/main", "-c", "config_file=/etc/postgresql/9.3/main/postgresql.conf"]
  </code></pre>
  
  <p>When I run docker-compose up, the first time the DB starts normally when I stop the service (with Ctrl+C) and try it once again the web service says that the DB service is starting.</p>
  
  <p>Then i try to run the script, in this line:</p>
  
  <pre><code>command: ["./wait-for-postgres.sh", "db", "--", "python", "news/"]
  </code></pre>
  
  <p>But postgres sleeps forever, saying:</p>
  
  <pre><code>Postgres is unavailable - sleeping
  ./wait-for-postgres.sh: line 10: psql: command not found
  </code></pre>
  
  <p>Can you help me solve the riddle?
  Thanks!</p>