刚刚搭建了立一个namenode，一个datanode的集群，format节点成功，并且start-all成功，但是当我运行

$ bin/hadoop fs -mkdir input

$ bin/hadoop fs -put conf/core-site.xml input

命令后，出现了异常：error hdfs.DFSClient:Exception closing file  /user/root/input/core-site.xml:org.apache.hadoop.ipc.RemoteException:java.io.IOException:File /user

/root/input/core-site.xml could only be replicated to 0 nodes,instead of 1