[Bug 1393832] Re: Modules fail to enable when configured after apache2 is configured

[Colin Watson]

It took me a while to figure out how to reproduce this reliably; at
first I could reproduce it only in the context of autopkgtest, but not
in a minimal schroot.  It took some strace analysis to figure it out.
This is not a dpkg bug after all.

What's happening here is that apache2 in Ubuntu ships ufw profiles,
which means that it fires the ufw trigger, but only if ufw is installed
(so in order to reproduce this in a minimal schroot you first need to
install ufw).  This causes apache2 to have "Status: install ok triggers-
awaited" rather than the more usual "Status: install ok installed".

I've uploaded apache2 to tolerate the "triggers-awaited" and "triggers-
pending" states here.  I expect this to clear these autopkgtest
failures.

** No longer affects: dpkg (Ubuntu)

** Changed in: apache2 (Ubuntu)
       Status: New => Fix Committed

** Changed in: apache2 (Ubuntu)
     Assignee: (unassigned) => Colin Watson (cjwatson)

** Changed in: apache2 (Ubuntu)
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/1393832

Title:
  Modules fail to enable when configured after apache2 is configured

Status in “apache2” package in Ubuntu:
  Fix Committed

Bug description:
  This is related to Debian bug 745834 and Launchpad bug 1312854, which
  Stefan kindly fixed in http://anonscm.debian.org/cgit/pkg-
  apache/apache2.git/commit/?id=804b53b7d5901e47c2751cdf78908ccd9c594c5b
  that went into 2.4.10-3 that I merged in 2.4.10-7ubuntu1 that is now
  stuck in vivid-proposed.

  The fix seems to work fine in Debian, but not in Ubuntu, though I
  haven't been able to figure out why. It seems to be a difference in
  behaviour between dpkg 1.17.21 in Debian and dpkg 1.17.21ubuntu1 in
  Ubuntu.

  The code:

      if ! dpkg-query -f '${Status}' -W apache2|grep -q installed; then

  is inside apache2-maintscript-helper, which is called from libapache2
  -mod-passenger's postinst.

  I thought this was a bit dubious as I seem to recall something about
  dpkg reentrancy within a maintainer script to be unreliable and not
  recommended, though I can't find any reference to that right now.

  I can reproduce this on Ubuntu (with vivid-proposed in sources.list)
  by running "apt-get install apache2 libapache2-mod-passenger", but
  also again by running "dpkg -P apache2 libapache2-mod-passenger" and
  then (from /var/cache/apt/archives) "dpkg -i
  apache2_2.4.10-7ubuntu1_amd64.deb libapache2-mod-
  passenger_4.0.53-1_amd64.deb".

  In both these cases apache2 is configured first, and then libapache2
  -mod-passenger. However, on Ubuntu, I get the output "Package apache2
  is not configured yet. Will defer actions by package libapache2-mod-
  passenger." during configuration of libapache2-mod-passenger, even
  though apache2 was configured. As a consequence, the module never gets
  enabled as expected, and the puppet dep8 test fails.

  On Debian, I cannot reproduce this. The result of "if ! dpkg-query -f
  '${Status}' -W apache2|grep -q installed" seems to be the opposite in
  exactly the same scenario.

  So I'm not sure whether I can file this as a bug in Debian since I
  don't know whether the dpkg-query is defined to work, or in fact why
  Debian and Ubuntu behave differently on this.

  Adding a dpkg task, since it'd be nice to have a definitive answer
  (that applies to Debian too) as to whether this call is defined to
  work as expected, or if it is documented to not be permitted to be
  used.

  If we cannot do it this way, then maybe touching a file in
  apache2.postinst (and removing it in prerm or wherever) would be
  another way to test to see if apache2 is configured yet, that would
  work for us in this case.

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