--force-confdef? When is it different?

[bob@proulx.com (Bob Proulx)]

I am setting up a scripted update for a pool of machines and trying to
understand the ramifications.

In the dpkg man page:

              confnew: If a conffile  has  been  modified  always
              install  the  new version without prompting, unless
              the --force-confdef is  also  specified,  in  which
              case the default action is preferred.

              confold:  If  a  conffile  has been modified always
              keep the old version without prompting, unless  the
              --force-confdef  is  also  specified, in which case
              the default action is preferred.

              confdef: If a conffile  has  been  modified  always
              choose  the  default action. If there is no default
              action it will stop to ask the user unless --force-
              confnew  or  --force-confold is also been given, in
              which case it will use that  to  decide  the  final
              action.


When would confdef ever not be the same as confold?  How is the
default action determined?  I thought the default action was always
simply 'N'.  No?

I am thinking that --force-confmiss --force-confold are the
appropriate options for my case.  But if there is a time when the
default is determined to be different then should I specify
--force-confdef as well?

Thanks
Bob

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