模拟namenode崩溃，使用secondarynamenode恢复
方法一、使用namespaceID
1、在namenode节点上，将dfs.name.dir指定的目录中(这里是name目录)的内容情况，以此来模拟故障发生。
[hadoop@node1 name]$ ls
current image in_use.lock
[hadoop@node1 name]$ rm -rf *
2、将集群关闭后，再重启我们看到namenode守护进程消失。
[hadoop@node1 name]$ stop-all.sh
stopping jobtracker
192.168.1.152: stopping tasktracker
192.168.1.153: stopping tasktracker
stopping namenode
192.168.1.152: stopping datanode
192.168.1.153: stopping datanode
192.168.1.152: stopping secondarynamenode
[hadoop@node1 name]$ start-all.sh
starting namenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-namenode-node1.out
192.168.1.152: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node2.out
192.168.1.153: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node3.out
192.168.1.152: starting secondarynamenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-secondarynamenode-node2.out
starting jobtracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-jobtracker-node1.out
192.168.1.152: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node2.out
192.168.1.153: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node3.out
[hadoop@node1 name]$ jps
31942 Jps
31872 JobTracker
而且namenode的日志中有报错：
2013-11-14 06:19:59,172 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = node1/192.168.1.151
STARTUP_MSG: args = []
STARTUP_MSG: version = 0.20.2
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010
************************************************************/
2013-11-14 06:19:59,395 INFO org.apache.hadoop.ipc.metrics.RpcMetrics: Initializing RPC Metrics with hostName=NameNode, port=9000
2013-11-14 06:19:59,400 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: Namenode up at: node1.com/192.168.1.151:9000
2013-11-14 06:19:59,403 INFO org.apache.hadoop.metrics.jvm.JvmMetrics: Initializing JVM Metrics with processName=NameNode, sessionId=null
2013-11-14 06:19:59,407 INFO org.apache.hadoop.hdfs.server.namenode.metrics.NameNodeMetrics: Initializing NameNodeMeterics using context object:org.apache.hadoop.metrics.spi.NullContext
2013-11-14 06:19:59,557 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: fsOwner=hadoop,hadoop
2013-11-14 06:19:59,558 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: supergroup=supergroup
2013-11-14 06:19:59,558 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: isPermissionEnabled=true
2013-11-14 06:19:59,568 INFO org.apache.hadoop.hdfs.server.namenode.metrics.FSNamesystemMetrics: Initializing FSNamesystemMetrics using context object:org.apache.hadoop.metrics.spi.NullContext
2013-11-14 06:19:59,569 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Registered FSNamesystemStatusMBean
2013-11-14 06:19:59,654 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:317)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:87)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:311)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:292)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:201)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:279)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:956)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:965)
2013-11-14 06:19:59,658 INFO org.apache.hadoop.ipc.Server: Stopping server on 9000
2013-11-14 06:19:59,663 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:317)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:87)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:311)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:292)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:201)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:279)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:956)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:965) 2013-11-14 06:19:59,664 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at node1/192.168.1.151
************************************************************/
3、查看HDFS的文件失败：
[hadoop@node1 name]$ hadoop dfs -ls /user/hive/warehouse
13/11/14 06:21:06 INFO ipc.Client: Retrying connect to server: node1/192.168.1.151:9000. Already tried 0 time(s).
13/11/14 06:21:07 INFO ipc.Client: Retrying connect to server: node1/192.168.1.151:9000. Already tried 1 time(s).
13/11/14 06:21:08 INFO ipc.Client: Retrying connect to server: node1/192.168.1.151:9000. Already tried 2 time(s).
13/11/14 06:21:09 INFO ipc.Client: Retrying connect to server: node1/192.168.1.151:9000. Already tried 3 time(s).
4、关闭集群，格式化namenode：
[hadoop@node1 name]$ stop-all.sh
stopping jobtracker
192.168.1.152: stopping tasktracker
192.168.1.153: stopping tasktracker
no namenode to stop
192.168.1.152: stopping datanode
192.168.1.153: stopping datanode
192.168.1.152: stopping secondarynamenode
[hadoop@node1 name]$ hadoop namenode -format
13/11/14 06:21:37 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = node1/192.168.1.151
STARTUP_MSG: args = [-format]
STARTUP_MSG: version = 0.20.2
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010
************************************************************/
Re-format filesystem in /app/user/hdfs/name ? (Y or N) Y
13/11/14 06:21:39 INFO namenode.FSNamesystem: fsOwner=hadoop,hadoop
13/11/14 06:21:39 INFO namenode.FSNamesystem: supergroup=supergroup
13/11/14 06:21:39 INFO namenode.FSNamesystem: isPermissionEnabled=true
13/11/14 06:21:39 INFO common.Storage: Image file of size 96 saved in 0 seconds.
13/11/14 06:21:39 INFO common.Storage: Storage directory /app/user/hdfs/name has been successfully formatted.
13/11/14 06:21:39 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at node1/192.168.1.151
************************************************************/
5、从任意datanode中获取namenode格式化之前namespaceID并修改namenode的namespaceID跟datanode一致：
[hadoop@node2 current]$ cat VERSION
#Thu Nov 14 02:27:10 CST 2013
namespaceID=2062292356
storageID=DS-107813142-192.168.1.152-50010-1379339943465
cTime=0
storageType=DATA_NODE
layoutVersion=-18
[hadoop@node2 current]$ pwd
/app/user/hdfs/data/current
----修改namenode的namespaceID----
[hadoop@node1 current]$ cat VERSION
#Thu Nov 14 06:29:31 CST 2013
namespaceID=2062292356
cTime=0
storageType=NAME_NODE
layoutVersion=-18
6、删除新的namenode的fsimage文件：
[hadoop@node1 current]$ ll
total 16
-rw-rw-r-- 1 hadoop hadoop 4 Nov 14 06:21 edits
-rw-rw-r-- 1 hadoop hadoop 96 Nov 14 06:21 fsimage
-rw-rw-r-- 1 hadoop hadoop 8 Nov 14 06:21 fstime
-rw-rw-r-- 1 hadoop hadoop 101 Nov 14 06:22 VERSION
[hadoop@node1 current]$ rm fsimage
7、从Secondarynamenode拷贝fsimage到Namenode的current目录下：
[hadoop@node2 current]$ ll
total 16
-rw-rw-r-- 1 hadoop hadoop 4 Nov 14 05:38 edits
-rw-rw-r-- 1 hadoop hadoop 2410 Nov 14 05:38 fsimage
-rw-rw-r-- 1 hadoop hadoop 8 Nov 14 05:38 fstime
-rw-rw-r-- 1 hadoop hadoop 101 Nov 14 05:38 VERSION
[hadoop@node2 current]$ scp fsimage node1:/app/user/hdfs/name/current
The authenticity of host 'node1 (192.168.1.151)' can't be established.
RSA key fingerprint is ca:9a:7e:19:ee:a1:35:44:7e:9d:d4:09:5c:fc:c5:0a.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'node1,192.168.1.151' (RSA) to the list of known hosts.
fsimage 100% 2410 2.4KB/s 00:00
8、重启集群：
[hadoop@node1 current]$ start-all.sh
starting namenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-namenode-node1.out
192.168.1.152: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node2.out
192.168.1.153: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node3.out
192.168.1.152: starting secondarynamenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-secondarynamenode-node2.out
starting jobtracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-jobtracker-node1.out
192.168.1.152: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node2.out
192.168.1.153: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node3.out
[hadoop@node1 current]$ jps
32486 Jps
32419 JobTracker
32271 NameNode
9、验证数据的完整性：
[hadoop@node1 current]$ hadoop dfs -ls /user/hive/warehouse
Found 8 items
drwxr-xr-x - hadoop supergroup 0 2013-10-17 16:18 /user/hive/warehouse/echo
drwxr-xr-x - hadoop supergroup 0 2013-10-28 13:48 /user/hive/warehouse/jack
drwxr-xr-x - hadoop supergroup 0 2013-09-18 15:54 /user/hive/warehouse/table4
drwxr-xr-x - hadoop supergroup 0 2013-09-18 15:53 /user/hive/warehouse/table5
drwxr-xr-x - hadoop supergroup 0 2013-09-18 15:48 /user/hive/warehouse/test
drwxr-xr-x - hadoop supergroup 0 2013-10-25 14:50 /user/hive/warehouse/test1
drwxr-xr-x - hadoop supergroup 0 2013-10-25 14:52 /user/hive/warehouse/test2
drwxr-xr-x - hadoop supergroup 0 2013-10-25 14:30 /user/hive/warehouse/test3 [hadoop@node3 conf]$ hive Logging initialized using configuration in jar:file:/app/hive/lib/hive-common-0.11.0.jar!/hive-log4j.properties
Hive history file=/tmp/hadoop/hive_job_log_hadoop_7451@node3_201311111325_424288589.txt
hive> show tables;
OK
echo
jack
table4
table5
test
test1
test2
test3
Time taken: 27.589 seconds, Fetched: 8 row(s)
hive> select * from table4;
OK
NULL NULL NULL
1 1 5
2 4 5
3 4 5
4 5 6
5 6 7
6 1 5
7 5 6
8 3 6
NULL NULL NULL
Time taken: 2.124 seconds, Fetched: 10 row(s)
之前里面的数据没有丢失。
方法二：使用hadoop namenode -importCheckpoint
1、删除name目录：
[hadoop@node1 hdfs]$ rm -rf name
2、关闭集群，从secondarynamenode拷贝namesecondary目录到dfs.name.dir：
[hadoop@node2 hdfs]$ scp -r namesecondary node1:/app/user/hdfs/
fsimage 100% 157 0.2KB/s 00:00
fstime 100% 8 0.0KB/s 00:00
fsimage 100% 2410 2.4KB/s 00:00
VERSION 100% 101 0.1KB/s 00:00
edits 100% 4 0.0KB/s 00:00
fstime 100% 8 0.0KB/s 00:00
fsimage 100% 2410 2.4KB/s 00:00
VERSION 100% 101 0.1KB/s 00:00
edits 100% 4 0.0KB/s 00:00
3、在namenode节点上执行hadoop namenode -importCheckpoint
[hadoop@node1 hdfs]$ hadoop namenode -importCheckpoint
13/11/14 07:24:20 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = node1/192.168.1.151
STARTUP_MSG: args = [-importCheckpoint]
STARTUP_MSG: version = 0.20.2
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010
************************************************************/
13/11/14 07:24:20 INFO metrics.RpcMetrics: Initializing RPC Metrics with hostName=NameNode, port=9000
13/11/14 07:24:20 INFO namenode.NameNode: Namenode up at: node1.com/192.168.1.151:9000
13/11/14 07:24:20 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=NameNode, sessionId=null
13/11/14 07:24:20 INFO metrics.NameNodeMetrics: Initializing NameNodeMeterics using context object:org.apache.hadoop.metrics.spi.NullContext
13/11/14 07:24:21 INFO namenode.FSNamesystem: fsOwner=hadoop,hadoop
13/11/14 07:24:21 INFO namenode.FSNamesystem: supergroup=supergroup
13/11/14 07:24:21 INFO namenode.FSNamesystem: isPermissionEnabled=true
13/11/14 07:24:21 INFO metrics.FSNamesystemMetrics: Initializing FSNamesystemMetrics using context object:org.apache.hadoop.metrics.spi.NullContext
13/11/14 07:24:21 INFO namenode.FSNamesystem: Registered FSNamesystemStatusMBean
13/11/14 07:24:21 INFO common.Storage: Storage directory /app/user/hdfs/name is not formatted.
13/11/14 07:24:21 INFO common.Storage: Formatting ...
13/11/14 07:24:21 INFO common.Storage: Number of files = 26
13/11/14 07:24:21 INFO common.Storage: Number of files under construction = 0
13/11/14 07:24:21 INFO common.Storage: Image file of size 2410 loaded in 0 seconds.
13/11/14 07:24:21 INFO common.Storage: Edits file /app/user/hdfs/namesecondary/current/edits of size 4 edits # 0 loaded in 0 seconds.
13/11/14 07:24:21 INFO common.Storage: Image file of size 2410 saved in 0 seconds.
13/11/14 07:24:21 INFO common.Storage: Image file of size 2410 saved in 0 seconds.
13/11/14 07:24:21 INFO namenode.FSNamesystem: Number of transactions: 0 Total time for transactions(ms): 0Number of transactions batched in Syncs: 0 Number of syncs: 0 SyncTimes(ms): 0
13/11/14 07:24:21 INFO namenode.FSNamesystem: Finished loading FSImage in 252 msecs
13/11/14 07:24:21 INFO hdfs.StateChange: STATE* Safe mode ON.
The ratio of reported blocks 0.0000 has not reached the threshold 0.9990. Safe mode will be turned off automatically.
13/11/14 07:24:21 INFO mortbay.log: Logging to org.slf4j.impl.Log4jLoggerAdapter(org.mortbay.log) via org.mortbay.log.Slf4jLog
13/11/14 07:24:21 INFO http.HttpServer: Port returned by webServer.getConnectors()[].getLocalPort() before open() is -1. Opening the listener on 50070
13/11/14 07:24:21 INFO http.HttpServer: listener.getLocalPort() returned 50070 webServer.getConnectors()[].getLocalPort() returned 50070
13/11/14 07:24:21 INFO http.HttpServer: Jetty bound to port 50070
13/11/14 07:24:21 INFO mortbay.log: jetty-6.1.14
13/11/14 07:24:21 INFO mortbay.log: Started SelectChannelConnector@node1.com:50070
13/11/14 07:24:21 INFO namenode.NameNode: Web-server up at: node1.com:50070
13/11/14 07:24:21 INFO ipc.Server: IPC Server Responder: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server listener on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 0 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 1 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 2 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 3 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 4 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 5 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 6 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 9 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 7 on 9000: starting
13/11/14 07:24:21 INFO ipc.Server: IPC Server handler 8 on 9000: starting
13/11/14 07:37:05 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at node1/192.168.1.151
************************************************************/
[hadoop@node1 current]$ start-all.sh
starting namenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-namenode-node1.out
192.168.1.152: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node2.out
192.168.1.153: starting datanode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-datanode-node3.out
192.168.1.152: starting secondarynamenode, logging to /app/hadoop/bin/../logs/hadoop-hadoop-secondarynamenode-node2.out
starting jobtracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-jobtracker-node1.out
192.168.1.152: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node2.out
192.168.1.153: starting tasktracker, logging to /app/hadoop/bin/../logs/hadoop-hadoop-tasktracker-node3.out
[hadoop@node1 current]$ jps
1027 JobTracker
1121 Jps
879 NameNode
4、验证数据的完整性：
[hadoop@node3 conf]$ hive Logging initialized using configuration in jar:file:/app/hive/lib/hive-common-0.11.0.jar!/hive-log4j.properties
Hive history file=/tmp/hadoop/hive_job_log_hadoop_8383@node3_201311111443_2018635710.txt
hive> select * from table4;
OK
NULL NULL NULL
1 1 5
2 4 5
3 4 5
4 5 6
5 6 7
6 1 5
7 5 6
8 3 6
NULL NULL NULL
Time taken: 3.081 seconds, Fetched: 10 row(s)
总结：
注意：恢复的namenode中secondarynamenode的最近一次check到故障发生这段时间的内容将丢失，所以fs.checkpoint.period参数值在实际设定中要尽可能的权衡。并且也时常备份secondarynamenode节点中的内容，因为scondarynamenode也是单点的，以防发生故障。
补充说明：如果是用新的节点来恢复namenode，则要注意
1、新节点的Linux环境，目录结构，环境变量等等配置需要跟原来的namenode一模一样，包括conf目录下的所有文件配置。
2、新namenode的主机名要与原namenode保持一致，如果是重新命名主机名的话，则需要批量替换datanode和secondarynamenode的hosts文件，并且重新配置以下文件的部分core-site.xml文件中的fs.default.name
hdfs-site.xml文件中的dfs.http.address(secondarynamenode节点上)
mapred-site.xml文件中的mapred.job.tracker(如果jobtracker与namenode在同一个机器上，一般都是同一台机器上)。
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