Create one mongo repliSet

mkdir -p /srv/mongodb/rs0-0 /srv/mongodb/rs0-1 /srv/mongodb/rs0-2

Run instances

mongod --port 27017 --dbpath /srv/mongodb/rs0-0 --replSet rs0 --smallfiles --oplogSize 128
mongod --port 27018 --dbpath /srv/mongodb/rs0-1 --replSet rs0 --smallfiles --oplogSize 128
mongod --port 27019 --dbpath /srv/mongodb/rs0-2 --replSet rs0 --smallfiles --oplogSize 128

Enable replicaSet

mongo --port 27017
rs.initiate()
rs.conf()
rs.status()

Add other instances as repliSet

* Login to 'primary' node by mongo client

rs.add("<hostname>:27018")
rs.add("<hostname>:27019")

Check ReplicatSet config

* Login to any replicaSet instance

rs.conf()
rs.status()