Setting up the host file for all nodes

Now that the first slave (Slv1) node is set up, you need to update the hosts file on both the master (Mst0) and slave (Slv1) nodes to reflect all the remaining six or sixteen nodes in the super cluster. First, you will copy (using win32 Disk Imager) the image of the Slv1 SD card to your desktop. This image file will then be copied to the other six or fourteen slave SD cards, and then return them to the slave Pis. Finally, you will make additional minor modifications to the data on each card.

So, let's now edit again the hosts file on the master node. Enter exit to return to the pi@Mst0:~$ prompt, and then enter sudo vim/etc/hosts. Add the rest of the IP addresses and host names. Repeat this procedure for the slave (Slv1) node (see highlighted text in the following screenshot):

Do the same for the master node, (see the following screenshot): 

Note that those six additional records are place holders as the IP addresses for the remaining six slave nodes...