Add hadoop datanode. This works, despite hadoop... For various hadoop network reasons, I've had to add in the /etc/nsswitch.conf file which to date I've managed to avoid (seems like hadoop namenode has to do a reverse lookup on the name the datanode gives it, and for some reason, even though it was defined in /etc/hosts, it looks like /etc/hosts wasn't being used for this purpose until nsswitch.conf got added). This gets a bit tricky as that particular file you could argue should be determined either by hosts or by network, or by something else.