add failcheck on startup

Dockerfile

@@ -9,4 +9,5 @@ ADD htdocs /var/www/html
 RUN mkdir /var/www/data
 RUN chown www-data:www-data /var/www/ -R
 EXPOSE 80
-CMD apachectl -D FOREGROUND
+ADD start.sh /usr/local/bin/start.sh
+CMD /usr/local/bin/start.sh

start.sh

@@ -0,0 +1,7 @@
+ #!/usr/bin/env bash
+ set -e
+ find /var/www -not -user www-data | grep -q /var && {
+      echo "ERROR: /var/www or one or more of it's children is not owned by www-data:www-data"
+      exit 1
+ }
+ apachectl -D FOREGROUND