Updating configuration files

[Steve Langasek]

On Wed, Feb 09, 2011 at 09:22:16AM -0500, Barry Warsaw wrote:
> There's one thing I miss from my days running Gentoo, and no, it's not the
> unholy number of hours it takes to upgrade due to recompiles. :)

> When a system configuration file gets updated, emerge gives you a richer set
> of options for dealing with changes.  I'm reminded of this with the just
> upgraded ntp package, which modifies /etc/ntp.conf.

> Debian/Ubuntu gives you the option to:

> * Keep your version
> * Install the new maintainers version
> * See the diff
> * Drop into a shell to "deal with" the situation

> I think these are insufficient.  What I really want to do is merge my
> local changes with the new package version, and I'd like the tool to help
> me do it.

> emerge gives me several other options.  It's been ages since I ran Gentoo so I
> don't remember all the details, but one other option was extremely helpful:

> * Interactively merge local changes with the new version of the config
> * file

So these days, there are three major paradigms used for configuration file
management within Debian packages.

 - conffiles - this is the built-in dpkg prompt you refer to, with the
   incomplete set of choices.  Really, this is only a suitable mechanism for
   configuration files that will rarely, *if ever*, need to be changed by
   either the local admin or the package maintainer.

 - templates spit out by maintainer scripts - this avoids the annoying
   prompts, but also generally doesn't give the admin very much support for
   updating to new package defaults because the maintainer doesn't go to the
   effort of manually merging the changes in.

 - ucf.  This option *does* store the original version of the file on disk
   in order to support a three-way merge, which makes it possible to offer
   better options on upgrade.  Not quite the same as an interactive merge,
   but an interactive merge option could be added here without too much
   extra work.

This last is the one is the way to go, but it really should be pulled into
dpkg itself.  I don't recall if Sean's patches were based on ucf or not.  In
the meantime, use of ucf requires explicit action by the package maintainer,
so it's generally only the real problem children that get converted over to
its use.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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