add a paragraph for "downgrading issue" in package management page

1 files changed, 21 insertions, 1 deletions

diff --git a/chapter08/pkgmgt.xml b/chapter08/pkgmgt.xml
index e898416d8..6c628c3d6 100644
--- a/chapter08/pkgmgt.xml
+++ b/chapter08/pkgmgt.xml
@@ -71,7 +71,27 @@
       against <filename class='libraryfile'>libfoo.so.2</filename> in order to
       use the new library version. You should not remove the previous
       libraries unless all the dependent packages are recompiled.</para>
-      </listitem> </itemizedlist>
+      </listitem>
+
+      <listitem> <para>If a package containing a shared library is updated,
+      and the name of library doesn't change, but the version number of the
+      library <emphasis role="bold">file</emphasis> decreases (for example,
+      the name of the library is kept named
+      <filename class='libraryfile'>libfoo.so.1</filename>,
+      but the name of library file is changed from
+      <filename class='libraryfile'>libfoo.so.1.25</filename> to
+      <filename class='libraryfile'>libfoo.so.1.24</filename>),
+      you should remove the library file from the previously installed version
+      (<filename class='libraryfile'>libfoo.so.1.25</filename> in the case).
+      Or, a <command>ldconfig</command> run (by yourself using a command
+      line, or by the installation of some package) will reset the symlink
+      <filename class='libraryfile'>libfoo.so.1</filename> to point to
+      the old library file because it seems having a <quote>newer</quote>
+      version, as its version number is larger.  This situation may happen if
+      you have to downgrade a package, or the package changes the versioning
+      scheme of library files suddenly.</para> </listitem>
+
+    </itemizedlist>
 
   </sect2>