+Make sure the data folder is writable by the web server user::
+
+ chown -R www-data:www-data /pithos/pithos/data
+
+If using an SQLite database, the same goes for the database file and the containing folder::
+
+ chown www-data:www-data /pithos/pithos/
+ chown www-data:www-data /pithos/pithos/backend.db
+