[root@MongoDB1 bin]# ./mongodump -h 172.17.1.20:27030 -uxxxx -pxxxx  --db=guandb_online -o /data/backup/ 
2018-08-24T11:27:40.206+0800    Failed: error connecting to db server: server returned error on SASL authentication step: Authentication failed.

./mongodump -h 172.17.1.20:27030 -uxxxx -pxxxx  --db=guandb_online -o /data/backup/ --authenticationDatabase admin

        "_id" : "admin.xxxx",
        "user" : "xxxx",
        "db" : "admin",
        "roles" : [
                {
                        "role" : "userAdminAnyDatabase",
                        "db" : "admin"
                },
                {
                        "role" : "readWriteAnyDatabase",
                        "db" : "admin"
                }
        ]
}