Config replicate in configuarge file
file: /etc/mongod.conf Add:

replication:
   replSetName: rs9

Restart mongod:

$ service mongod restart

Access mongo shell
On mongo master:
Initiate replicate master and add member slave

> rs.initiate( {
   _id : "rs9",
   members: [ { _id : 0, host : "IP_MASTER:27017" } ]
})
> rs.add("IP_SLAVE:27017")

Done