/usr/etc/transactional-update.conf
This is the reference configuration file for transactional-update, containing distribution default values. This file should not be changed by the administrator.
/etc/transactional-update.conf
To change the default configuration for transactional-update copy or create this file and change the options accordingly. See transactional-update.conf(5) for a description of the configuration options. Values from this file will overwride the distribution default values.
/var/lib/overlay/
See Section 4.3, “/etc” for an explanation of this directory's contents.