Update role user: not authorized on admin to execu

When I try to get info about replica I get the following error:

rep0:PRIMARY> rs.printReplicationInfo()
2015-05-19T13:30:29.231+0200 error: {
        "$err" : "not authorized for query on local.system.namespaces",
        "code" : 13
} at src/mongo/shell/query.js:131

I have tried to execute the command with the two following users:

    [
        {
                "_id" : "admin.siteRootAdmin",
                "user" : "siteRootAdmin",
                "db" : "admin",
                "roles" : [
                        {
                                "role" : "root",
                                "db" : "admin"
                        }
                ]
        },
        {
                "_id" : "admin.mongoadmin",
                "user" : "mongoadmin",
                "db" : "admin",
                "roles" : [
                        {
                                "role" : "userAdminAnyDatabase",
                                "db" : "admin"
                        },
                        {
                                "role" : "dbOwner",
                                "db" : "admin"
                        },
                        {
                                "role" : "clusterAdmin",
                                "db" : "admin"
                        }
                ]
        }
]

Althought I have clusterAdmin role to work with replicas, I have tried to update roles of mongoadmin to read local database (as all roles are granted on admin db) but I get the following error:

rep0:PRIMARY> db.system.users.update({"user":"mongoadmin"},{$addToSet:{"roles":"readAnyDatabase"}})
WriteResult({
        "writeError" : {
                "code" : 13,
                "errmsg" : "not authorized on admin to execute command { update: \"system.users\", updates: [ { q: { user: \"mongoadmin\" }, u: { $addToSet: { roles: \"readAnyDatabase\" } }, multi: false, upsert: false } ], ordered: true }"
        }
})

What is supposed I need to have in order to get full access to all replica commands in addition to clusterAdmin role?
If any of both users have permissions in admin db (mongoadmin is dbOwner), why I don't have permissions for update command?

I was updating roles with the wrong command here is the right one:

db.grantRolesToUser( "mongoadmin", [{ role: "read", db: "local"}])

Now I can check the 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)