Command should be adduser, not aduser (page 281)

Christian Einfeldt, MadPenguin: Charles Darwin would “get” the beauty Debian if he were alive today. Martin Krafft certainly “gets” the beauty of Debian, and he wants you to get it too, so he has written a very detailed exposition of the Debian code and community. [...] If there was one word that I would use to describe Martin's book, that word would be “meticulous.”