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Re: dotdee: a proposal for improving conffile management in Debian

On Wed, May 4, 2011 at 3:22 PM, Raphael Hertzog <hertzog@debian.org> wrote:
> Hi,
> On Fri, 29 Apr 2011, Dustin Kirkland wrote:
>> As Ubuntu Server Core Developer and Packager, I'm quite keen on
>> improving two problems we encounter frequently, with respect to
>> conffiles:
> I would also like to solve those problems.
>> Here, I'm proposing a tool called "dotdee" that I think would greatly
>> benefit Debian and Debian-derived distributions such as Ubuntu.  Its
>> stated goal is to turn any given flat file on your system to a
>> dynamically concatenated flat file generated from a unique ".d"
>> directory dedicated to that particular file.  With such a dedicated
>> and well-formed directory, system administrators, Debian packagers,
>> and distributions could conveniently place additional configuration
>> snippets in particular conffile's dedicated ".d" directory.
> I don't want to go into details but I also do not believe that dotdee is
> a complete answer to the problem. It just doesn't scale to all the
> configuration file format that we can encounter and it's not clean enough
> to be able to use it in other packages.

I totally agree with you on the scalability problem with dotdee
working with every configuration file format under the sun.  The
initial implementation was merely a prototype, but the more I think
about that problem, the less interested I am in having dotdee solve it

> Let me explain what I would suggest to solve the problem. The root problem
> is that dpkg is not flexible enough to manage the configuration files, and
> it probably never will be. It just doesn't have the required knowledge.
> However it knows when the package tries to upgrade the configuration file
> and it installs the file itself.
> I propose that we take out of dpkg the knowledge required to install a
> configuration file. dpkg would still provide the default configuration
> handler that implements the prompt that we know today but we should be
> able to replace it easily.

I really like where this is heading... :-)

> By default, dpkg would use a program named dpkg-conffile-handler to
> install new configuration files. That program would in fact be an
> alternatives pointing by default to the default configuration file handler
> provided by dpkg (the one we have now and that prompts us).  Other
> configuration handlers could be registered in the alternative... for
> example one using a VCS to manage the configuration files, etc.
> It would also be possible to override the choice of the default
> configuration file handler for specific configuration files using
> configuration snippets put in .d directories:
> - /lib/dpkg/conffile-handling.d/ could be used by packages that want
>  to generate their configuration files or use something more complicated
>  than what dpkg offers (for example with ucf, or a script using Config::Model)
> - /etc/dpkg/conffile-handling.d/ could be used by the local admin to
>  further override everything
> dotdee could be one tool that the administrator could use as configuration
> file handler but it doesn't need to be the only one. And you don't need to
> divert the original file, dpkg takes care of all that part implicitly. The
> admin would just do something like this:
> # echo "handler /etc/foo.conf dotdee" >/etc/dpkg/conffile-handling.d/foo
> # dotdee --setup /etc/foo.conf
> With this solution it's also easy for a package to setup a custom conffile
> handler to take over another conffile or to pre/post-process it.
> There's quite some work left to define the interface that the
> dpkg-conffile-handler programs must implement, and to the way the override
> would work but I think this would be a clean solution to all the problems
> that annoy you.
> What do you think ?

Sounds good to me.  I think that will give administrators and Debian
as a distro the flexibility that it needs to really start solving this

>> But in the mean time, what do you think?  Have you encountered similar
>> problems before?  What other approaches have been taken to try and
>> solve this?  What parts of this proposal do you think are reasonable?
>> Are any parts completely unreasonable?  Are there extensions or
>> changes you propose?
> While dotdee could be acceptable for local admins to use, I think it's far
> from being acceptable for official Debian packages. It really looks like
> taking over other files without any way for the local admin to keep
> control on his configuration files.

Fair enough.

Okay, as for dotdee, I'm just about finished with a 1.0 version, and
will upload it to Ubuntu's new queue by the end of this week.  (It
would be fabulous if someone could sponsor it for me into the Debian
new queue as well ;-).

> I think my proposal is way better in this regard.
> Up to now, all the people who have had those problems dealt with them with
> tools that overwrite entirely the configuration files and never took care
> to think about proper integration in packages.

Definitely.  It's a good approach.


Dustin Kirkland
Ubuntu Core Developer

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