Hadoop-0.19.0的代码可以到Apache上下载,链接为http://archive.apache.org/dist/hadoop/core/hadoop-0.19.0/,我使用的Linux机器是RHEL 5,Linux上安装的Java版本为1.6.0_16,并且JAVA_HOME=/usr/java/jdk1.6.0_16。
实践过程
1、ssh无密码验证登陆localhost
保证Linux系统的ssh服务已经启动,并保证能够通过无密码验证登陆本机Linux系统。如果不能保证,可以按照如下的步骤去做:
(1)启动命令行窗口,执行命令行:
$ ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa $ cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys
(2)ssh登陆localhost,执行命令行:
$ ssh localhost
第一次登录,会提示你无法建立到127.0.0.1的连接,是否要建立,输入yes即可,下面是能够通过无密码验证登陆的信息:
[root@localhost hadoop-0.19.0]# ssh localhost
Last login: Sun Aug 1 18:35:37 2010 from 192.168.0.104
[root@localhost ~]#
2、Hadoop-0.19.0配置
下载hadoop-0.19.0.tar.gz,大约是40.3M,解压缩到Linux系统指定目录,这里我的是/root/hadoop-0.19.0目录下。
下面按照有序的步骤来说明配置过程:
(1)修改hadoop-env.sh配置
将Java环境的配置进行修改后,并取消注释“#”,修改后的行为:
export JAVA_HOME=/usr/java/jdk1.6.0_16
(2)修改hadoop-site.xml配置
在<configuration>与</configuration>加上3个属性的配置,修改后的配置文件内容为:
<!-- Put site-specific property overrides in this file. -->
<configuration>
<property>
<name>fs.default.name</name>
<value>hdfs://localhost:9000</value>
</property>
<property>
<name>mapred.job.tracker</name>
<value>localhost:9001</value>
</property>
<property>
<name>dfs.replication</name>
<value>1</value>
</property>
</configuration>
3、运行wordcount实例
wordcount例子是hadoop发行包中自带的实例,通过运行实例可以感受并尝试理解hadoop在执行MapReduce任务时的执行过程。按照官方的“Hadoop Quick Start”教程基本可以容易地实现,下面简单说一下我的练习过程。
导航到hadoop目录下面,我的是/root/hadoop-0.19.0。
(1)格式化HDFS
执行格式化HDFS的命令行:
[root@localhost hadoop-0.19.0]# bin/hadoop namenode -format
格式化执行信息如下所示:
10/08/01 19:04:02 INFO namenode.NameNode: STARTUP_MSG: /************************************************************ STARTUP_MSG: Starting NameNode STARTUP_MSG: host = localhost/127.0.0.1 STARTUP_MSG: args = [-format] STARTUP_MSG: version = 0.19.0 STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.19 -r 713890; compiled by 'ndaley' on Fri Nov 14 03:12:29 UTC 2008 ************************************************************/ Re-format filesystem in /tmp/hadoop-root/dfs/name ? (Y or N) y Format aborted in /tmp/hadoop-root/dfs/name 10/08/01 19:04:05 INFO namenode.NameNode: SHUTDOWN_MSG: /************************************************************ SHUTDOWN_MSG: Shutting down NameNode at localhost/127.0.0.1 ************************************************************/
(2)启动Hadoop相关后台进程
执行命令行:
[root@localhost hadoop-0.19.0]# bin/start-all.sh
启动执行信息如下所示:
starting namenode, logging to /root/hadoop-0.19.0/bin/../logs/hadoop-root-namenode-localhost.out localhost: starting datanode, logging to /root/hadoop-0.19.0/bin/../logs/hadoop-root-datanode-localhost.out localhost: starting secondarynamenode, logging to /root/hadoop-0.19.0/bin/../logs/hadoop-root-secondarynamenode-localhost.out starting jobtracker, logging to /root/hadoop-0.19.0/bin/../logs/hadoop-root-jobtracker-localhost.out localhost: starting tasktracker, logging to /root/hadoop-0.19.0/bin/../logs/hadoop-root-tasktracker-localhost.out
(3)准备执行wordcount任务的数据
首先,这里在本地创建了一个数据目录input,并拷贝一些文件到该目录下面,如下所示:
[root@localhost hadoop-0.19.0]# mkdir input
[root@localhost hadoop-0.19.0]# cp CHANGES.txt LICENSE.txt NOTICE.txt README.txt input/
然后,将本地目录input上传到HDFS文件系统上,执行如下命令:
[root@localhost hadoop-0.19.0]# bin/hadoop fs -put input/ input
(4)启动wordcount任务
执行如下命令行:
[root@localhost hadoop-0.19.0]# bin/hadoop jar hadoop-0.19.0-examples.jar wordcount input output
元数据目录为input,输出数据目录为output。
任务执行信息如下所示:
10/08/01 19:06:15 INFO mapred.FileInputFormat: Total input paths to process : 4 10/08/01 19:06:15 INFO mapred.JobClient: Running job: job_201008011904_0002 10/08/01 19:06:16 INFO mapred.JobClient: map 0% reduce 0% 10/08/01 19:06:22 INFO mapred.JobClient: map 20% reduce 0% 10/08/01 19:06:24 INFO mapred.JobClient: map 40% reduce 0% 10/08/01 19:06:25 INFO mapred.JobClient: map 60% reduce 0% 10/08/01 19:06:27 INFO mapred.JobClient: map 80% reduce 0% 10/08/01 19:06:28 INFO mapred.JobClient: map 100% reduce 0% 10/08/01 19:06:38 INFO mapred.JobClient: map 100% reduce 26% 10/08/01 19:06:40 INFO mapred.JobClient: map 100% reduce 100% 10/08/01 19:06:41 INFO mapred.JobClient: Job complete: job_201008011904_0002 10/08/01 19:06:41 INFO mapred.JobClient: Counters: 16 10/08/01 19:06:41 INFO mapred.JobClient: File Systems 10/08/01 19:06:41 INFO mapred.JobClient: HDFS bytes read=301489 10/08/01 19:06:41 INFO mapred.JobClient: HDFS bytes written=113098 10/08/01 19:06:41 INFO mapred.JobClient: Local bytes read=174004 10/08/01 19:06:41 INFO mapred.JobClient: Local bytes written=348172 10/08/01 19:06:41 INFO mapred.JobClient: Job Counters 10/08/01 19:06:41 INFO mapred.JobClient: Launched reduce tasks=1 10/08/01 19:06:41 INFO mapred.JobClient: Launched map tasks=5 10/08/01 19:06:41 INFO mapred.JobClient: Data-local map tasks=5 10/08/01 19:06:41 INFO mapred.JobClient: Map-Reduce Framework 10/08/01 19:06:41 INFO mapred.JobClient: Reduce input groups=8997 10/08/01 19:06:41 INFO mapred.JobClient: Combine output records=10860 10/08/01 19:06:41 INFO mapred.JobClient: Map input records=7363 10/08/01 19:06:41 INFO mapred.JobClient: Reduce output records=8997 10/08/01 19:06:41 INFO mapred.JobClient: Map output bytes=434077 10/08/01 19:06:41 INFO mapred.JobClient: Map input bytes=299871 10/08/01 19:06:41 INFO mapred.JobClient: Combine input records=39193 10/08/01 19:06:41 INFO mapred.JobClient: Map output records=39193 10/08/01 19:06:41 INFO mapred.JobClient: Reduce input records=10860
(5)查看任务执行结果
可以通过如下命令行:
bin/hadoop fs -cat output/*
执行结果,截取部分显示如下所示:
vijayarenu 20 violations. 1 virtual 3 vis-a-vis 1 visible 1 visit 1 volume 1 volume, 1 volumes 2 volumes. 1 w.r.t 2 wait 9 waiting 6 waiting. 1 waits 3 want 1 warning 7 warning, 1 warnings 12 warnings. 3 warranties 1 warranty 1 warranty, 1
(6)终止Hadoop相关后台进程
执行如下命令行:
[root@localhost hadoop-0.19.0]# bin/stop-all.sh
执行信息如下所示:
stopping jobtracker
localhost: stopping tasktracker
stopping namenode
localhost: stopping datanode
localhost: stopping secondarynamenode
已经将上面列出的5个进程jobtracker、tasktracker、namenode、datanode、secondarynamenode终止。
异常分析
在进行上述实践过程中,可能会遇到某种异常情况,大致分析如下:
1、Call to localhost/127.0.0.1:9000 failed on local exception异常
(1)异常描述
可能你会在执行如下命令行的时候出现:
[root@localhost hadoop-0.19.0]# bin/hadoop jar hadoop-0.19.0-examples.jar wordcount input output
出错异常信息如下所示:
10/08/01 19:50:55 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 0 time(s). 10/08/01 19:50:56 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 1 time(s). 10/08/01 19:50:57 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 2 time(s). 10/08/01 19:50:58 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 3 time(s). 10/08/01 19:50:59 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 4 time(s). 10/08/01 19:51:00 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 5 time(s). 10/08/01 19:51:01 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 6 time(s). 10/08/01 19:51:02 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 7 time(s). 10/08/01 19:51:03 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 8 time(s). 10/08/01 19:51:04 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 9 time(s). java.lang.RuntimeException: java.io.IOException: Call to localhost/127.0.0.1:9000 failed on local exception: Connection refused at org.apache.hadoop.mapred.JobConf.getWorkingDirectory(JobConf.java:323) at org.apache.hadoop.mapred.FileInputFormat.setInputPaths(FileInputFormat.java:295) at org.apache.hadoop.mapred.FileInputFormat.setInputPaths(FileInputFormat.java:268) at org.apache.hadoop.examples.WordCount.run(WordCount.java:146) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65) at org.apache.hadoop.examples.WordCount.main(WordCount.java:155) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:68) at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:141) at org.apache.hadoop.examples.ExampleDriver.main(ExampleDriver.java:61) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.util.RunJar.main(RunJar.java:165) at org.apache.hadoop.mapred.JobShell.run(JobShell.java:54) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:79) at org.apache.hadoop.mapred.JobShell.main(JobShell.java:68) Caused by: java.io.IOException: Call to localhost/127.0.0.1:9000 failed on local exception: Connection refused at org.apache.hadoop.ipc.Client.call(Client.java:699) at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:216) at $Proxy0.getProtocolVersion(Unknown Source) at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:319) at org.apache.hadoop.hdfs.DFSClient.createRPCNamenode(DFSClient.java:104) at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:177) at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:74) at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1367) at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:56) at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1379) at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:215) at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:120) at org.apache.hadoop.mapred.JobConf.getWorkingDirectory(JobConf.java:319) ... 21 more Caused by: java.net.ConnectException: Connection refused at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:574) at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:100) at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:299) at org.apache.hadoop.ipc.Client$Connection.access$1700(Client.java:176) at org.apache.hadoop.ipc.Client.getConnection(Client.java:772) at org.apache.hadoop.ipc.Client.call(Client.java:685) ... 33 more
(2)异常分析
从上述异常信息分析,这句是关键:
Retrying connect to server: localhost/127.0.0.1:9000.
是说在尝试10次连接到“server”时都无法成功,这就说明到server的通信链路是不通的。我们已经在hadoop-site.xml中配置了namenode结点的值,如下所示:
所以,敢肯定是无法连接到server,也就是很可能namenode进程根本就没有启动,更不必谈要执行任务了。
上述异常,我模拟的过程是:
格式化了HDFS,但是没有执行bin/start-all.sh,直接启动wordcount任务,就出现上述异常。
所以,应该执行bin/start-all.sh以后再启动wordcount任务。
2、Input path does not exist异常
(1)异常描述
当你在当前hadoop目录下面创建一个input目录,并cp某些文件到里面,开始执行:
[root@localhost hadoop-0.19.0]# bin/hadoop namenode -format
[root@localhost hadoop-0.19.0]# bin/start-all.sh
这时候,你认为input已经存在,应该可以执行wordcount任务了:
[root@localhost hadoop-0.19.0]# bin/hadoop jar hadoop-0.19.0-examples.jar wordcount input output
结果抛出一堆异常,信息如下:
org.apache.hadoop.mapred.InvalidInputException: Input path does not exist: hdfs://localhost:9000/user/root/input at org.apache.hadoop.mapred.FileInputFormat.listStatus(FileInputFormat.java:179) at org.apache.hadoop.mapred.FileInputFormat.getSplits(FileInputFormat.java:190) at org.apache.hadoop.mapred.JobClient.submitJob(JobClient.java:782) at org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:1127) at org.apache.hadoop.examples.WordCount.run(WordCount.java:149) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65) at org.apache.hadoop.examples.WordCount.main(WordCount.java:155) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:68) at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:141) at org.apache.hadoop.examples.ExampleDriver.main(ExampleDriver.java:61) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.util.RunJar.main(RunJar.java:165) at org.apache.hadoop.mapred.JobShell.run(JobShell.java:54) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:79) at org.apache.hadoop.mapred.JobShell.main(JobShell.java:68)
上述异常,我模拟的过程是:
[root@localhost hadoop-0.19.0]# bin/hadoop fs -rmr input
Deleted hdfs://localhost:9000/user/root/input
[root@localhost hadoop-0.19.0]# bin/hadoop fs -rmr output
Deleted hdfs://localhost:9000/user/root/output
因为之前我已经成功执行过一次。
(2)异常分析
应该不用多说了,是因为本地的input目录并没有上传到HDFS上,所出现org.apache.hadoop.mapred.InvalidInputException: Input path does not exist: hdfs://localhost:9000/user/root/input
在我的印象中,好像使用hadoop-0.16.4的时候,只要input目录存在,是不用执行上传命令,就可以运行的,后期的版本是不行的。
只需要执行上传的命令即可:
[root@localhost hadoop-0.19.0]# bin/hadoop fs -put input/ input