问题：hadoop启动后 jps 查不到namenode

start-dfs.sh

[root@master ~]# start-dfs.sh
Starting namenodes on [master]
master: starting namenode, logging to /usr/local/export/soft/hadoop-2.7.7/logs/hadoop-root-namenode-master.out
master: starting datanode, logging to /usr/local/export/soft/hadoop-2.7.7/logs/hadoop-root-datanode-master.out
slave02: starting datanode, logging to /usr/local/export/soft/hadoop-2.7.7/logs/hadoop-root-datanode-slave02.out
slave01: starting datanode, logging to /usr/local/export/soft/hadoop-2.7.7/logs/hadoop-root-datanode-slave01.out
Starting secondary namenodes [0.0.0.0]
0.0.0.0: starting secondarynamenode, logging to /usr/local/export/soft/hadoop-2.7.7/logs/hadoop-root-secondarynamenode-master.out
[root@master ~]# jps
3295 Jps
3170 SecondaryNameNode
3029 DataNode

jps查不到 namenode , 查看日志，报了这个 错误， 

我的基本配置，其实基本啥都没配置。

core-site.xml

<configuration>
 <property>
   <name>fs.defaultFS</name>
   <value>hdfs://master:9000/</value>
 </property>
  <property>
   <name>hadoop.tmp.dir</name>
   <value>/usr/local/export/soft/hadoop-2.7.7/tmp/</value>
 </property>
</configuration> 

hdfs-site.xml

<configuration>
 <property>
   <name>dfs.replication</name>
   <value>1</value>
</property>
</configuration>

解决方案： 重新格式化namenode，然后启动hadoop，jps存在namenode。

[root@master hadoop-2.7.7]# ./bin/hdfs namenode -format

然后我们再重新启动服务，就愉快的有了