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The configuration is stored in a revision-managed database. Every time a new configuration is saved, it is ''commited'' to the database. The current (running) configuration is shown by ''checking out'' the latest configuration revision; called ''HEAD''. Each revision is associated with a revision number, which is a simple, increasing integer counter. When a user commits a configuration, it's first applied (made effective to the system). If the application was successful, it is saved.
Whenever a new configuration is applied, it's transformed into event keys, which may have an ID and several values. These new keys are compared to the old (running configuration) keys, comprising an event list. If a user commits a configuration which results in no events (differences in keys) an exception (error) is given. One example of this would be if a user added the line <
pre>media autoselect</ pre> to an < pre>interface</ pre>. Since autoselect is the default media type, no event would be generated by this configuration change (which is correct, since it doesn't not represent a change in the system state). If a list of events were generated, it's delivered to the [[backend]]'s routines responsible of updating the system state. The minimally necessary change in order to bring the system into the new requested state will be performed.
Upon boot (system startup) the latest revision (HEAD) is checked out by the [[backend]], and compared to the old list of keys, which is of course empty. Thus, a every change necessary to bring a reset system into the state requested by the configuration is performed.