jtuple

Assuming there are 2 nodes called riak@host1 and riak@host2. 

Attach to riak console for riak@host1. Either 'riak-admin console' if the node is down, or 'riak-admin attach' if the node is already up and running.

Update the first line below with the right "other node" name, then copy/paste:

Other = 'riak@host2'.
net_adm:ping(Other).
riak_kv_console:join([atom_to_list(Other)]).
riak:join(Other).