输入#start-all.sh后，启动完后输入#jps发现没有namenode，立马去看日志，显示如下：
2017-07-11 14:18:47,407 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: STARTUP_MSG: /************************************************************ STARTUP_MSG: Starting NameNode STARTUP_MSG: host = localhost.localdomain/127.0.0.1 STARTUP_MSG: args = [] STARTUP_MSG: version = 1.0.4 STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.0 -r 1393290; compiled by 'hortonfo' on Wed Oct 3 05:13:58 UTC 2012 ************************************************************/ 2017-07-11 14:18:47,670 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties 2017-07-11 14:18:47,682 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered. 2017-07-11 14:18:47,683 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s). 2017-07-11 14:18:47,683 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: NameNode metrics system started 2017-07-11 14:18:48,070 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source ugi registered. 2017-07-11 14:18:48,074 WARN org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Source name ugi already exists! 2017-07-11 14:18:48,109 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source jvm registered. 2017-07-11 14:18:48,110 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source NameNode registered. 2017-07-11 14:18:48,152 INFO org.apache.hadoop.hdfs.util.GSet: VM type = 64-bit 2017-07-11 14:18:48,152 INFO org.apache.hadoop.hdfs.util.GSet: 2% max memory = 19.33375 MB 2017-07-11 14:18:48,152 INFO org.apache.hadoop.hdfs.util.GSet: capacity = 2^21 = 2097152 entries 2017-07-11 14:18:48,152 INFO org.apache.hadoop.hdfs.util.GSet: recommended=2097152, actual=2097152 2017-07-11 14:18:48,274 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: fsOwner=root 2017-07-11 14:18:48,274 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: supergroup=supergroup 2017-07-11 14:18:48,274 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: isPermissionEnabled=true 2017-07-11 14:18:48,279 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: dfs.block.invalidate.limit=100 2017-07-11 14:18:48,279 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: isAccessTokenEnabled=false accessKeyUpdateInterval=0 min(s), accessTokenLifetime=0 min(s) 2017-07-11 14:18:48,799 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Registered FSNamesystemStateMBean and NameNodeMXBean 2017-07-11 14:18:48,823 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: Caching file names occuring more than 10 times 2017-07-11 14:18:48,839 ERROR org.apache.hadoop.hdfs.server.namenode.FSNamesystem: FSNamesystem initialization failed. java.io.IOException: NameNode is not formatted. at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:330) at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:388) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:362) at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:276) at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:496) at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1279) at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1288) 2017-07-11 14:18:48,840 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.io.IOException: NameNode is not formatted. at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:330) at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:388) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:362) at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:276) at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:496) at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1279) at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1288) 就是java.io.IOException: NameNode is not formatted.这个错误。但是我明明有执行format命令啊，在网上搜了各种方法（例如终止hadoop进程，删除namenode和tmp文件夹下的所有文件，再重新格式化都不行），后来有一篇博客提到权限的问题，我不知道是不是没有为hadoop专门创建用户，所以即使在hdfs-site.xml里面配置了namenode的路径，他也没有权限读写，所以格式化失败，难道root用户执行hadoop的格式化命令，权限也不够吗，是不是用root执行还要做些什么配置啊，后来他博客还提到一句话-------
dfs.name.dir和dfs.data.dir这两个路径不需要手动建，hadoop初始化会自动建立，我刚开始是手动建的，后来删了，让他自己建就成功了，再也不抱错了，namenode成功出现在进程中
附上他博客地址http://buguoruci.blog.51cto.com/4104173/1278610
