一、异常现象
安装好hadoop之后，执行格式化namenode命令时，抛出以下异常：
18/03/21 21:02:10 WARN net.DNS: Unable to determine local hostname -falling back to "localhost"
java.net.UnknownHostException: rayner: rayner
at java.net.InetAddress.getLocalHost(InetAddress.java:1475)
at org.apache.hadoop.net.DNS.resolveLocalHostname(DNS.java:284)
at org.apache.hadoop.net.DNS.<clinit>(DNS.java:61)
at org.apache.hadoop.hdfs.server.namenode.NNStorage.newBlockPoolID(NNStorage.java:991)
at org.apache.hadoop.hdfs.server.namenode.NNStorage.newNamespaceInfo(NNStorage.java:600)
at org.apache.hadoop.hdfs.server.namenode.FSImage.format(FSImage.java:162)
at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:1125)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1567)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1694)
Caused by: java.net.UnknownHostException: rayner
at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901)
at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1295)
at java.net.InetAddress.getLocalHost(InetAddress.java:1471)
... 8 more
18/03/21 21:02:10 WARN net.DNS: Unable to determine address of the host-falling back to "localhost" address
java.net.UnknownHostException: rayner: rayner
at java.net.InetAddress.getLocalHost(InetAddress.java:1475)
at org.apache.hadoop.net.DNS.resolveLocalHostIPAddress(DNS.java:307)
at org.apache.hadoop.net.DNS.<clinit>(DNS.java:62)
at org.apache.hadoop.hdfs.server.namenode.NNStorage.newBlockPoolID(NNStorage.java:991)
at org.apache.hadoop.hdfs.server.namenode.NNStorage.newNamespaceInfo(NNStorage.java:600)
at org.apache.hadoop.hdfs.server.namenode.FSImage.format(FSImage.java:162)
at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:1125)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1567)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1694)
Caused by: java.net.UnknownHostException: rayner
at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901)
at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1295)
at java.net.InetAddress.getLocalHost(InetAddress.java:1471)
... 8 more
二、异常原因
是因为更改了虚拟机的hostname
vim /etc/sysconfig/network
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而/etc/hosts 下的文件没有修改
三、异常解决
（1）编辑 /etc/hosts 文件
（2）将 主机IP 和 对应的主机名称 进行映射
添加下图红框中内容
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三、参考资料
1.Unable to determine local hostname -falling back to "localhost"
