https://github.com/mongodb/docs/blob/v2.6/source/tutorial/deploy-replica-set-with-auth.txt

Per sharad.aggarwal:

if I start the node as replica set, I cannot add user w/o doing an rs.initiate() which in these instructions is step 8.

If I start the node as standalone, then the user I created in step 2 will not be replicated to other nodes

What I ended up doing was do rs.initiate() and then create user