Is it possible to change the default users/groups used by Ambari before installation. We have Linux servers that are tightly controlled and our admins do not allow any app creating users and groups. Another restriction is the length of the usernames cannot exceed 8 chars. One of the user ids (zookeeper) that Ambari creates by default is 9 chars. We are planning to create the default users and groups manually before installing Ambari. If we create an 8 character id for zookeeper, a) will it create problems during installation, and b) can we configure the zookeeper id for Ambari to be different from the default value.