Could not resolve hostname hadoop.master: Name or service not known

[root@localhost ~]# start-dfs.sh
16/08/15 00:19:20 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
16/08/15 00:19:20 WARN hdfs.DFSUtil: Namenode for null remains unresolved for ID null.  Check your hdfs-site.xml file to ensure namenodes are configured properly.
Starting namenodes on [Hadoop.Master]
Hadoop.Master: ssh: Could not resolve hostname hadoop.master: Name or service not known
localhost: starting datanode, logging to /usr/hadoop/logs/hadoop-root-datanode-hadoop.master.out
Starting secondary namenodes [0.0.0.0]
0.0.0.0: starting secondarynamenode, logging to /usr/hadoop/logs/hadoop-root-secondarynamenode-hadoop.master.out
16/08/15 00:19:32 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable

127.0.0.1 Hadoop.Master