<listitem>
<para>
- Update the local keyring with the keyring of Debian archive
- keys and removes from the keyring the archive keys which are no
- longer valid.
+ Update the local keyring with the archive keyring and remove from
+ the local keyring the archive keys which are no longer valid.
+ The archive keyring is shipped in the <literal>archive-keyring</literal> package of your
+ distribution, e.g. the <literal>debian-archive-keyring</literal> package in Debian.
+
+ </para>
+
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>net-update</term>
+ <listitem>
+ <para>
+
+ Work similar to the <command>update</command> command above, but get the
+ archive keyring from an URI instead and validate it against a master key.
+
+ This requires an installed &wget; and an APT build configured to have
+ a server to fetch from and a master keyring to validate.
+
+ APT in Debian does not support this command and relies on
+ <command>update</command> instead, but Ubuntu's APT does.
</para>