title: permission with volume docker and wordpress
body: <p>I've created a docker-composer.yml file to run a container for wordpress mysql and phpmyadmin. It starts well bt i have a permission problem.  All my files have www-data:www-data for user and group and when i want to create a new theme in wp-content i have a permission denied. Im in ubuntu 18.04. </p>
  
  <p>here is my docker-compose.yml file :</p>
  
  <pre><code>version: '3'
  
  services:
    # Database
    db:
      image: mysql:5.7
      volumes:
        - db_data:/var/lib/mysql
      restart: always
      environment:
        MYSQL_ROOT_PASSWORD: password
       MYSQL_DATABASE: wordpress
        MYSQL_USER: wordpress
        MYSQL_PASSWORD: wordpress
      networks:
        - wpsite
    # phpmyadmin
    phpmyadmin:
      depends_on:
        - db
      image: phpmyadmin/phpmyadmin
      restart: always
      ports:
        - '8080:80'
      environment:
        PMA_HOST: db
        MYSQL_ROOT_PASSWORD: password 
      networks:
        - wpsite
    # Wordpress
    wordpress:
      depends_on:
        - db
      image: wordpress:latest
      ports:
       - '8000:80'
      restart: always
      volumes: ['./:/var/www/html']
      environment:
        WORDPRESS_DB_HOST: db:3306
        WORDPRESS_DB_USER: wordpress
        WORDPRESS_DB_PASSWORD: wordpress
      networks:
        - wpsite
  networks:
    wpsite:
  volumes:
    db_data:
  </code></pre>
  
  <p>i tried to change to "chown -Rf myname:myname ." so there i can create a file but upload for files in wordpress doesn't work now. So i wonder how to set properly permissons with a docker mounted volume in ubuntu.</p>