Merge pull request #1560 from nextcloud/redis-permissions

note on the redis socket file permissions

admin_manual/configuration_server/caching_configuration.rst

@@ -116,6 +116,16 @@ recommended if Redis is running on the same system as Nextcloud) use this exampl
 
 Only "host" and "port" variables are required, the other ones are optional.
 
+Be sure to set the right permissions on redis.sock so that your webserver can
+read and write to it. For this you typically have to add the webserver user
+to the redis group::
+
+  usermod -a -G redis www-data
+
+You might need to restart apache for the changes to take effect::
+
+ systemctl restart apache2
+
 Redis is very configurable; consult `the Redis documentation 
 <http://redis.io/documentation>`_ to learn more.