[Bug 1483923] Re: dpkg-divert breaks nginx installation

[Thomas Ward]

I'm going to take the following actions on this bug, and the Server Team
is OK'd to say otherwise, since I'm slightly sleep deprived.

> Agreed, no need to patch this in Ubuntu. Should be done in Debian,
which I can see would have the same problem. -- Benjamin Bach, November
11, 2015, Comment 7

Given that there is no need to patch this in Ubuntu, and this should be
done in Debian, I am going to "Won't Fix" this bug here, and suggest
that you file a bug against the Debian package and have them fix it
there.  If they decide to make changes, they'll make it in when I next
merge the package from Debian Unstable.  This link is Debian's "How to
File a Bug" page and can help you get started with filing a bug in
Debian against the nginx package for this issue (since it should really
be fixed there): https://www.debian.org/Bugs/Reporting


> AIUI, it isn't appropriate for a package to modify another package's behaviour from under its feet in this way. Debian Policy Appendix G (not formally policy I don't think) says: "Do not attempt to divert a conffile, as dpkg does not handle it well.". -- Robie Basak, November 11, 2015, Comment #6

Idle hands are the Devil's Playthings, so I went and poked the Debian
IRC channels.  #debian-mentors also refers to 10.7.4 of the Debian
packaging policy - https://www.debian.org/doc/debian-policy/ch-
files.html - which states the same thing in its contents:

I'm just going to quote it here for simplicity, with a later point below
of what spots I'm specifically referring to:

---

10.7.4 Sharing configuration files

If two or more packages use the same configuration file and it is
reasonable for both to be installed at the same time, one of these
packages must be defined as owner of the configuration file, i.e., it
will be the package which handles that file as a configuration file.
Other packages that use the configuration file must depend on the owning
package if they require the configuration file to operate. If the other
package will use the configuration file if present, but is capable of
operating without it, no dependency need be declared.

If it is desirable for two or more related packages to share a
configuration file and for all of the related packages to be able to
modify that configuration file, then the following should be done:

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.)

Sometimes it's appropriate to create a new package which provides the
basic infrastructure for the other packages and which manages the shared
configuration files. (The sgml-base package is a good example.)

If the configuration file cannot be shared as described above, the
packages must be marked as conflicting with each other. Two packages
that specify the same file as a conffile must conflict. This is an
instance of the general rule about not sharing files. Neither
alternatives nor diversions are likely to be appropriate in this case;
in particular, dpkg does not handle diverted conffiles well.

When two packages both declare the same conffile, they may see left-over
configuration files from each other even though they conflict with each
other. If a user removes (without purging) one of the packages and
installs the other, the new package will take over the conffile from the
old package. If the file was modified by the user, it will be treated
the same as any other locally modified conffile during an upgrade.

The maintainer scripts must not alter a conffile of any package,
including the one the scripts belong to.

---

The specific points I read on this are as follows:

- Two packages that specify the same file as a conffile must conflict.
*This is an instance of the general rule about not sharing files.*
Neither alternatives nor diversions are likely to be appropriate in this
case; in particular, dpkg does not handle diverted conffiles well.

- The maintainer scripts must not alter a conffile of any package,
including the one the scripts belong to.

Because I see this, I believe the `dpkg-divert` approach is the wrong
way to do it, and therefore this is an invalid approach for this, and
not something we need to fix, at least if we stick to Debian packaging
policy.

But, I'll leave that decision to Debian, since that's outside the scope
of Ubuntu, in my opinion.

In either case, I am marking this bug down here in Ubuntu as "Won't
Fix", and I suggest you file a bug in Debian if you want Debian's nginx
packagers to look at the issue further.

** Changed in: nginx (Ubuntu)
       Status: New => Won't Fix

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https://bugs.launchpad.net/bugs/1483923

Title:
  dpkg-divert breaks nginx installation

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