Eu estava atualizando funções com o comando errado aqui está o correto:
db.grantRolesToUser( "mongoadmin", [{ role: "read", db: "local"}])
Agora posso verificar o replicainfo:
rep0:PRIMARY> rs.printReplicationInfo()
configured oplog size: 990MB
log length start to end: 617347secs (171.49hrs)
oplog first event time: Thu May 14 2015 14:25:04 GMT+0200 (CEST)
oplog last event time: Thu May 21 2015 17:54:11 GMT+0200 (CEST)
now: Thu May 21 2015 17:54:24 GMT+0200 (CEST)
