blog/Circular_package_dependencies_harms_apt_recovery.html

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   6     <title>Petter Reinholdtsen: Circular package dependencies harms apt recovery</title>
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  12  <h1>
  13      <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  14
  15  </h1>
  16
  17 </div>
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  19
  20     <div class="entry">
  21       <div class="title">Circular package dependencies harms apt recovery</div>
  22       <div class="date">27th July 2010</div>
  23       <div class="body"><p>I discovered this while doing
  24 <a href="http://people.skolelinux.org/pere/blog/Automatic_upgrade_testing_from_Lenny_to_Squeeze.html">automated
  25 testing of upgrades from Debian Lenny to Squeeze</a>.  A few packages
  26 in Debian still got circular dependencies, and it is often claimed
  27 that apt and aptitude should be able to handle this just fine, but
  28 some times these dependency loops causes apt to fail.</p>
  29
  30 <p>An example is from todays
  31 <a href="http://people.skolelinux.org/~pere/debian-upgrade-testing//test-20100727-lenny-squeeze-kde-aptitude.txt">upgrade
  32 of KDE using aptitude</a>.  In it, a bug in kdebase-workspace-data
  33 causes perl-modules to fail to upgrade.  The cause is simple.  If a
  34 package fail to unpack, then only part of packages with the circular
  35 dependency might end up being unpacked when unpacking aborts, and the
  36 ones already unpacked will fail to configure in the recovery phase
  37 because its dependencies are unavailable.</p>
  38
  39 <p>In this log, the problem manifest itself with this error:</p>
  40
  41 <blockquote><pre>
  42 dpkg: dependency problems prevent configuration of perl-modules:
  43  perl-modules depends on perl (>= 5.10.1-1); however:
  44   Version of perl on system is 5.10.0-19lenny2.
  45 dpkg: error processing perl-modules (--configure):
  46  dependency problems - leaving unconfigured
  47 </pre></blockquote>
  48
  49 <p>The perl/perl-modules circular dependency is already
  50 <a href="http://bugs.debian.org/527917">reported as a bug</a>, and will
  51 hopefully be solved as soon as possible, but it is not the only one,
  52 and each one of these loops in the dependency tree can cause similar
  53 failures.  Of course, they only occur when there are bugs in other
  54 packages causing the unpacking to fail, but it is rather nasty when
  55 the failure of one package causes the problem to become worse because
  56 of dependency loops.</p>
  57
  58 <p>Thanks to
  59 <a href="http://lists.debian.org/debian-devel/2010/06/msg00116.html">the
  60 tireless effort by Bill Allombert</a>, the number of circular
  61 dependencies
  62 <a href="http://debian.semistable.com/debgraph.out.html">left in Debian
  63 is dropping</a>, and perhaps it will reach zero one day. :)</p>
  64
  65 <p>Todays testing also exposed a bug in
  66 <a href="http://bugs.debian.org/590605">update-notifier</a> and
  67 <a href="http://bugs.debian.org/590604">different behaviour</a> between
  68 apt-get and aptitude, the latter possibly caused by some circular
  69 dependency.  Reported both to BTS to try to get someone to look at
  70 it.</p>
  71 </div>
  72
  73       <div class="tags">Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian">debian</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/nuug">nuug</a>.</div>
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