- Update the local keyring with the keyring of Debian archive
- keys and removes from the keyring the archive keys which are no
- longer valid.
+ Perform an update working similarly to the <command>update</command> command above,
+ but get the archive keyring from a 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, relying on
+ <command>update</command> instead, but Ubuntu's APT does.