Ny post.

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+Title: Circular package dependencies harms apt recovery
+Tags: english, nuug, debian
+Date: 2010-07-27 23:50
+
+<p>I discovered this while doing
+<a href="http://people.skolelinux.org/pere/blog/Automatic_upgrade_testing_from_Lenny_to_Squeeze.html">automated
+testing of upgrades from Debian Lenny to Squeeze</a>.  A few packages
+in Debian still got circular dependencies, and it is often claimed
+that apt and aptitude should be able to handle this just fine, but
+some times these dependency loops causes apt to fail.</p>
+
+<p>An example is from todays
+<a href="http://people.skolelinux.org/~pere/debian-upgrade-testing//test-20100727-lenny-squeeze-kde-aptitude.txt">upgrade
+of KDE using aptitude</a>.  In it, a bug in kdebase-workspace-data
+causes perl-modules to fail to upgrade.  The cause is simple.  If a
+package fail to unpack, then only part of packages with the circular
+dependency might end up being unpacked when unpacking aborts, and the
+ones already unpacked will fail to configure in the recovery phase
+because its dependencies are unavailable.</p>
+
+<p>In this log, the problem manifest itself with this error:</p>
+
+<blockquote><pre>
+dpkg: dependency problems prevent configuration of perl-modules:
+ perl-modules depends on perl (>= 5.10.1-1); however:
+  Version of perl on system is 5.10.0-19lenny2.
+dpkg: error processing perl-modules (--configure):
+ dependency problems - leaving unconfigured
+</pre></blockquote>
+
+<p>The perl/perl-modules circular dependency is already
+<a href="http://bugs.debian.org/527917">reported as a bug</a>, and will
+hopefully be solved as soon as possible, but it is not the only one,
+and each one of these loops in the dependency tree can cause similar
+failures.  Of course, they only occur when there are bugs in other
+packages causing the unpacking to fail, but it is rather nasty when
+the failure of one package causes the problem to become worse because
+of dependency loops.</p>
+
+<p>Thanks to
+<a href="http://lists.debian.org/debian-devel/2010/06/msg00116.html">the
+tireless effort by Bill Allombert</a>, the number of circular
+dependencies
+<a href="http://debian.semistable.com/debgraph.out.html">left in Debian
+is dropping</a>, and perhaps it will reach zero one day. :)</p>
+
+<p>Todays testing also exposed a bug in
+<a href="http://bugs.debian.org/590605">update-notifier</a> and
+<a href="http://bugs.debian.org/590604">different behaviour</a> between
+apt-get and aptitude, the latter possibly caused by some circular
+dependency.  Reported both to BTS to try to get someone to look at
+it.</p>