****************

Directory layout

****************

Cloud-init's directory structure is somewhat different from a regular

application::

  /var/lib/cloud/

      - data/

         - instance-id

         - previous-instance-id

         - datasource

         - previous-datasource

         - previous-hostname

      - handlers/

      - instance

      - instances/

          i-00000XYZ/

            - boot-finished

            - cloud-config.txt

            - datasource

            - handlers/

            - obj.pkl

            - scripts/

            - sem/

            - user-data.txt

            - user-data.txt.i

      - scripts/

         - per-boot/

         - per-instance/

         - per-once/

      - seed/

      - sem/

``/var/lib/cloud``

  The main directory containing the cloud-init specific subdirectories.

  It is typically located at ``/var/lib`` but there are certain configuration

  scenarios where this can be altered.

  TBD, describe this overriding more.

``data/``

  Contains information related to instance ids, datasources and hostnames of

  the previous and current instance if they are different. These can be

  examined as needed to determine any information related to a previous boot

  (if applicable).

``handlers/``

  Custom ``part-handlers`` code is written out here. Files that end up here are

  written out with in the scheme of ``part-handler-XYZ`` where ``XYZ`` is the

  handler number (the first handler found starts at 0).

``instance``

  A symlink to the current ``instances/`` subdirectory that points to the

  currently active instance (which is active is dependent on the datasource

  loaded).

``instances/``

  All instances that were created using this image end up with instance

  identifier subdirectories (and corresponding data for each instance). The

  currently active instance will be symlinked the ``instance`` symlink file

  defined previously.

``scripts/``

  Scripts that are downloaded/created by the corresponding ``part-handler``

  will end up in one of these subdirectories.

``seed/``

  TBD

``sem/``

  Cloud-init has a concept of a module semaphore, which basically consists

  of the module name and its frequency. These files are used to ensure a module

  is only ran `per-once`, `per-instance`, `per-always`. This folder contains

  semaphore `files` which are only supposed to run `per-once` (not tied to the

  instance id).

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