[Oneiric-Topic] Augeas Integration

Scott Kitterman ubuntu at kitterman.com
Fri Apr 1 15:03:33 UTC 2011


On Friday, April 01, 2011 07:05:23 AM Raphaël Pinson wrote:
> Hello,
> 
> 
> In a (more or less) related subject to the Puppet integration thread,
> I would like to raise the idea of integrating Augeas [0] deeper in
> Ubuntu.
> 
> Augeas is a unified configuration API which allows to parse and modify
> configuration files using XPath expressions. It features a C API,
> bindings for many languages (Python, Ruby, Perl, Haskell, Java, PHP,
> etc.) and a command line utility called augtool. The Ruby bindings
> have been used to provide a native Augeas Puppet type since Puppet
> 0.24.7.
> 
> Augeas works by using bidirectional pieces of code called lenses. A
> lens is a grammar file which allows to parse a configuration file
> format and turn it into a tree, and then take a modified tree and
> write it back to the configuration files. Lenses ensure that only
> proper trees are written back to files, i.e. the syntax of the file
> written by Augeas is ensured by the lens.
> 
> Currently, 90+ lenses are provided by Augeas. On a rather standard
> Lucid machine I have at work, Augeas is able to parse 141 files and
> produces 8054 nodes:
> 
> rpinson at rpinson:~$ augtool match /augeas/files//path | wc -l
> 141
> rpinson at rpinson:~$ augtool print /files | wc -l
> 8054
> 
> 
> On the long run, Augeas is not meant to provide all these lenses, but
> instead we would like lenses to be shipped with each project, as a
> standard parsing and writing facility for configuration files across
> Unix systems. This would allow for example to bind the lenses with the
> version of the program providing the configuration files, ensuring
> that the lens parses and writes the proper configuration stanzas for
> the given version.
> 
> This journey of sending lenses upstream and making Augeas a standard
> has to begin somewhere, and I'm suggesting to make it begin in Ubuntu,
> by including the lenses in each package they are related to.
> 
> For example, the mysql.aug lens would be provided by the mysql-common
> package, and the httpd.aug package would be provided by
> apache2.2-common, etc. I would be happy to train package maintainers
> willing to take that step so they can maintain the lenses and make
> them evolve with time, or even send them to their upstream if they
> can.
> 
> I would like to go even a step further in Ubuntu (and Debian if
> possible). Debian Policy, which Ubuntu developers follow, states
> (section 10.7.4, "Sharing configuration files" [1]):
> 
> ``One of the related packages (the "owning" package) will manage the
> configuration file with maintainer scripts as described in the
> previous section.
> 
> The owning package should also provide a program that the other
> packages may use to modify the configuration file.
> 
> The related packages must use the provided program to make any desired
> modifications to the configuration file. They should either depend on
> the core package to guarantee that the configuration modifier program
> is available or accept gracefully that they cannot modify the
> configuration file if it is not. (This is in addition to the fact that
> the configuration file may not even be present in the latter
> scenario.)''
> 
> 
> There are few packages currently that provide a program to manage
> their configuration files, making it hard for other packages to tune
> system configuration. One of the workarounds that are implemented in
> quite a few packages is to allow 'foo.d'  kind of directories (e.g.
> sudoers.d, xinetd.d, pam.d, etc.). This allows packages to drop their
> configuration file without affecting other files, but it doesn't allow
> them to modify generic parameters.
> 
> 
> Once packages are shipped with their own Augeas lens, I suggest that
> policy could be adapted to allow the use of Augeas lenses provided by
> the owning packages as an alternative to using a program. This would
> allow for much more freedom to safely manipulate configuration files
> in package maintainer scripts.
> 
> 
> What are your thoughts on the subject?
> 
> 
> Cheers,
> 
> 
> Raphaël
> 
> 
> [0] http://www.augeas.net
> [1] http://www.debian.org/doc/debian-policy/ch-files.html#s10.7.4

I don't think any policy changes are needed.  I think providing a lense and 
Recommending or Depending on Augeas is sufficient.  I don't read "provide a 
program" as meaning the actual code is required to live in the relevant 
package.  

I agree with the concept.  I think that we need to move forward on something 
like this in coordination with Debian (at leasts on the goals and technology).  
Ubuntu may choose to implement aspects of this before Debian does, but no 
matter which distro is ahead at any given time, I think it's essential that 
both be on the same road.

Scott K




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