Ubuntu下Hadoop单机部署及分布式集群部署
设置root用户密码
打开终端 ctrl+Alt+T
修改root 密码 sudo passwd root
输入密码
用户root用户登录 su root
Ubuntu 8.10 默认没有安装ssh服务 ,需要手动安装以后才能实现
sudo apt-get install ssh
或sudo apt-get install openssh-server //安装openssh-server
用ifconfig查看ip地址
远程用crt连接
ubuntu 10.2.128.46
ubuntu1 10.2.128.20
ubuntu2 10.2.128.120
安装vim
sudo apt-get install vim
1、安装JDK
1.1、到官网下载相关的JDK
这里下载的是 jdk-6u23-linux-i586.bin。
下载地址：http://www.oracle.com/technetwork/java/javase/downloads/index.html
找jdk6
放置在/home/linuxidc
sudo sh jdk-6u23-linux-i586.bin
cp -rf jdk1.6.0_33/ /usr/lib/
sudo gedit /etc/environment
export JAVA_HOME=/usr/lib/jdk1.6.0_33
export JRE_HOME=/usr/lib/jdk1.6.0_33/jre
export CLASSPATH=$CLASSPATH:$JAVA_HOME/lib:$JAVA_HOME/jre/lib
vim /etc/profile
export JAVA_HOME=/usr/lib/jdk1.6.0_33
export JRE_HOME=/usr/lib/jdk1.6.0_33/jre
export CLASSPATH=$CLASSPATH:$JAVA_HOME/lib:$JAVA_HOME/jre/lib
export PATH=$JAVA_HOME/bin:$JAVA_HOME/jre/bin:$PATH:$JAVA_HOME/bin
加在umak前即可
reboot
root@linuxidc-virtual-machine:/etc# java -version
java version "1.6.0_33"
Java(TM) SE Runtime Environment (build 1.6.0_33-b03)
Java HotSpot(TM) Client VM (build 20.8-b03, mixed mode)
JDK环境的操作需要在所有的namenode和datanode上面进行操作。
2、增加一个用户组用户，用于Hadoop运行及访问。
sudo addgroup hadoop
sudo adduser --ingroup hadoop hadoop
删除用户
在root用户下：userdel -r newuser
在普通用户下：sudo userdel -r newuser
先退出 再删除
3、生成SSH证书，配置SSH加密key
su - hadoop //切换到hadoop用户
ssh-keygen -t rsa -P "" //生成ssh key
cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys //设置允许ssh访问
设置完成后通过ssh localhost测试一下。
4、下载hadoop发行版，地址：
http://hadoop.apache.org/common/releases.html#Download
http://mirror.bit.edu.cn/apache/hadoop/common/hadoop-0.20.2/
已拷贝到opt
tar -zxvf hadoop-0.20.2.tar.gz
5、修改主机名 linuxidc-virtual-machine
root@linuxidc-virtual-machine:/opt# hostname
linuxidc-virtual-machine
假定我们发现我们的机器的主机名不是我们想要的，通过对"/etc/sysconfig/network"文件修改其中"HOSTNAME"后面的值，改成我们规划的名称。
vim /etc/hostname
Master.Hadoop
reboot后变为
root@Master:~# hostname
Master.Hadoop
vim /etc/hosts
127.0.1.1 Master.Hadoop
4.关掉ipv6
修改hadoop根目录下conf/hadoop-env.sh文件(还没下载hadoop的下载解压先～)
export HADOOP_OPTS=-Djava.net.preferIPv4Stack=true
cat /proc/sys/net/ipv6/conf/all/disable_ipv6
为0
备选情况：为1是成功，应使用以下方式
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1、
5、将hadoop目录所有者更改为hadoop
chown -R hadoop:hadoop /opt/hadoop-0.20.2/
mv hadoop-0.20.2 hadoop
6.安装hadoop
下面说说如何配置和启动：
基本思路
a、配置JDK
b 配置core-site.xml
c mapred-site.xml
d hdfs-site.xml
创建存放数据的目录
mkdir /opt/hadoop-datastore
打开conf/core-site.xml,配置如下
<configuration>
<property>
<name>hadoop.tmp.dir</name>
<value>/opt/hadoop-datastore/</value>
<description>A base for other temporary directories.</description>
</property>
<property>
<name>fs.default.name</name>
<value>hdfs://localhost:54310</value>
<description>The name of the default file system. A URI whose
scheme and authority determine the FileSystem implementation. The
uri's scheme determines the config property (fs.SCHEME.impl) naming
the FileSystem implementation class. The uri's authority is used to
determine the host, port, etc. for a filesystem.</description>
</property>
</configuration>
mapred-site.xml如下：
<configuration>
<property>
<name>mapred.job.tracker</name>
<value>localhost:54311</value>
<description>The host and port that the MapReduce job tracker runs
at. If "local", then jobs are run in-process as a single map
and reduce task.
</description>
</property>
</configuration>
hdfs-site.xml如下：
<configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
<description>Default block replication.
The actual number of replications can be specified when the file is created.
The default is used if replication is not specified in create time.
</description>
</property>
</configuration>
vim hadoop-env.sh
export JAVA_HOME=/usr/lib/jdk1.6.0_33
ok，配置完毕
格式化HDFS：
/opt/hadoop/bin/hadoop namenode -format
输出
root@Master:/opt/hadoop# /opt/hadoop/bin/hadoop namenode -format
12/07/13 14:27:29 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = Master.Hadoop/127.0.1.1
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 /opt/hadoop-datastore/dfs/name ? (Y or N) y
Format aborted in /opt/hadoop-datastore/dfs/name
12/07/13 14:27:35 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at Master.Hadoop/127.0.1.1
************************************************************/
启动HDFS和MapReduce
改为hadoop用户
/opt/hadoop/bin/start-all.sh
输出
starting namenode, logging to /opt/hadoop/bin/../logs/hadoop-root-namenode-Master.Hadoop.out
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is 3e:55:d8:be:47:46:21:95:29:9b:9e:c5:fb:02:f4:d2.
Are you sure you want to continue connecting (yes/no)? yes
localhost: Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
root@localhost's password:
localhost: starting datanode, logging to /opt/hadoop/bin/../logs/hadoop-root-datanode-Master.Hadoop.out
root@localhost's password:
localhost: starting secondarynamenode, logging to /opt/hadoop/bin/../logs/hadoop-root-secondarynamenode-Master.Hadoop.out
starting jobtracker, logging to /opt/hadoop/bin/../logs/hadoop-root-jobtracker-Master.Hadoop.out
root@localhost's password:
localhost: starting tasktracker, logging to /opt/hadoop/bin/../logs/hadoop-root-tasktracker-Master.Hadoop.out
9、停止服务的脚本是：
/opt/hadoop/bin/stop-all.sh
10.启动成功后，用jps查看下。
5.运行wordcount.java
在Hadoop所在目录里有几个jar文件，其中hadoop-examples-0.20.203.0.jar就是我们需要的，它里面含有wordcount，咱们使用命令建立测试的文件
(1)先在本地磁盘建立两个输入文件file01 和file02:
$ echo “Hello World Bye World” > file01
$ echo “Hello Hadoop Goodbye Hadoop” > file02
./hadoop fs -ls /
(2)在hdfs 中建立一个input 目录：./hadoop fs -mkdir input
删除./hadoop dfs -rmr input
(3)将file01 和file02 拷贝到hdfs 中：
./hadoop fs -copyFromLocal /home/linuxidc/file0* input
./hadoop fs -ls /user/root/input
Found 2 items
-rw-r--r-- 1 root supergroup 22 2012-07-13 15:07 /user/root/input/file01
-rw-r--r-- 1 root supergroup 28 2012-07-13 15:07 /user/root/input/file02
root@Master:/opt/hadoop/bin# ./hadoop fs -cat /user/root/input/file01/
Hello World Bye World
(4)执行wordcount：
$ Hadoop jar hadoop-0.20.1-examples.jar wordcount input output
$ bin/hadoop jar hadoop-0.20.1-examples.jar wordcount input output
Exceptioninthread"m
ain" java.io.IOException: Error openingjobjar: hadoop-0.20.2-examples.jar
at org.apache.hadoop.util.RunJar.main(RunJar.java:90)
Caused by: java.util.zip.ZipException: error in opening zip file
at java.util.zip.ZipFile.open(Native Method)
at java.util.zip.ZipFile.<init>(ZipFile.java:114)
at java.util.jar.JarFile.<init>(JarFile.java:135)
at java.util.jar.JarFile.<init>(JarFile.java:72)
at org.apache.hadoop.util.RunJar.main(RunJar.java:88)
解决办法：
注意路径：
./hadoop jar /opt/hadoop/hadoop-0.20.2-examples.jar wordcount input output
输出
12/07/13 15:20:22 INFO input.FileInputFormat: Total input paths to process : 2
12/07/13 15:20:22 INFO mapred.JobClient: Running job: job_201207131429_0001
12/07/13 15:20:23 INFO mapred.JobClient: map 0% reduce 0%
12/07/13 15:20:32 INFO mapred.JobClient: map 100% reduce 0%
12/07/13 15:20:44 INFO mapred.JobClient: map 100% reduce 100%
12/07/13 15:20:46 INFO mapred.JobClient: Job complete: job_201207131429_0001
12/07/13 15:20:46 INFO mapred.JobClient: Counters: 17
12/07/13 15:20:46 INFO mapred.JobClient: Job Counters
12/07/13 15:20:46 INFO mapred.JobClient: Launched reduce tasks=1
12/07/13 15:20:46 INFO mapred.JobClient: Launched map tasks=2
12/07/13 15:20:46 INFO mapred.JobClient: Data-local map tasks=2
12/07/13 15:20:46 INFO mapred.JobClient: FileSystemCounters
12/07/13 15:20:46 INFO mapred.JobClient: FILE_BYTES_READ=79
12/07/13 15:20:46 INFO mapred.JobClient: HDFS_BYTES_READ=50
12/07/13 15:20:46 INFO mapred.JobClient: FILE_BYTES_WRITTEN=228
12/07/13 15:20:46 INFO mapred.JobClient: HDFS_BYTES_WRITTEN=41
12/07/13 15:20:46 INFO mapred.JobClient: Map-Reduce Framework
12/07/13 15:20:46 INFO mapred.JobClient: Reduce input groups=5
12/07/13 15:20:46 INFO mapred.JobClient: Combine output records=6
12/07/13 15:20:46 INFO mapred.JobClient: Map input records=2
12/07/13 15:20:46 INFO mapred.JobClient: Reduce shuffle bytes=45
12/07/13 15:20:46 INFO mapred.JobClient: Reduce output records=5
12/07/13 15:20:46 INFO mapred.JobClient: Spilled Records=12
12/07/13 15:20:46 INFO mapred.JobClient: Map output bytes=82
12/07/13 15:20:46 INFO mapred.JobClient: Combine input records=8
12/07/13 15:20:46 INFO mapred.JobClient: Map output records=8
12/07/13 15:20:46 INFO mapred.JobClient: Reduce input records=6
(5)完成之后，查看结果：
root@Master:/opt/hadoop/bin# ./hadoop fs -cat /user/root/output/part-r-00000
Bye 1
GoodBye 1
Hadoop 2
Hello 2
World 2
root@Master:/opt/hadoop/bin# jps
3049 TaskTracker
2582 DataNode
2849 JobTracker
10386 Jps
2361 NameNode
2785 SecondaryNameNode
OK 以上部分，已完成了 ubuntu下单机hadoop的搭建。
--------------------------------------------------------
下面我们进行集群的搭建（3台ubuntu服务器）
1、三台机器：已安装jdk，添加hadoop用户
ubuntu 10.2.128.46 master
ubuntu1 10.2.128.20 slave1
ubuntu2 10.2.128.120 slave2
修改三台机器所有的/etc/hosts文件如下：
127.0.0.1 localhost
10.2.128.46 master.Hadoop
10.2.128.20 slave1.Hadoop
10.2.128.120 slave2.Hadoop
以下操作均在Hadoop用户下操作
2、生成SSH证书，配置SSH加密key
su - hadoop //切换到hadoop用户
ssh-keygen -t rsa -P "" //生成ssh key
cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys //设置允许ssh访问
在namenode（Master）上
hadoop@Master:~/.ssh$ scp authorized_keys Slave1.Hadoop:/home/hadoop/.ssh/
hadoop@Master:~/.ssh$ scp authorized_keys Slave2.Hadoop:/home/hadoop/.ssh/
测试：ssh node2或者ssh node3（第一次需要输入yes）。
如果不须要输入密码则配置成功，如果还须要请检查上面的配置能不能正确。
hadoop@Master:~/.ssh$ ssh Slave1.Hadoop
Welcome to Ubuntu precise (development branch)
hadoop@Master:~/.ssh$ ssh Slave2.Hadoop
Welcome to Ubuntu precise (development branch)
2、hadoop-0.20.2.tar.gz 拷贝到/home/linuxidc/install_Hadoop目录下
可采用的方法
1 ) 安装Hadoop集群通常要将安装软件解压到集群内的所有机器上。并且安装路径要一致，如果我们用HADOOP_HOME指代安装的根路径，通常，集群里的所有机器的
HADOOP_HOME路径相同。
2 ) 如果集群内机器的环境完全一样，可以在一台机器上配置好，然后把配置好的软件即hadoop-0.20.203整个文件夹拷贝到其他机器的相同位置即可。
3 ) 可以将Master上的Hadoop通过scp拷贝到每一个Slave相同的目录下，同时根据每一个Slave的Java_HOME 的不同修改其hadoop-env.sh 。
3,相关配置
4) 为了方便，使用hadoop命令或者start-all.sh等命令，修改Master上/etc/profile 新增以下内容：
export JAVA_HOME=/usr/lib/jdk1.6.0_33
export JRE_HOME=/usr/lib/jdk1.6.0_33/jre
export CLASSPATH=$CLASSPATH:$JAVA_HOME/lib:$JAVA_HOME/jre/lib
export HADOOP_HOME=/opt/hadoop
export PATH=$JAVA_HOME/bin:$JAVA_HOME/jre/bin:$PATH:$JAVA_HOME/bin:$HADOOP_HOME/bin
修改完毕后，执行source /etc/profile 来使其生效。
配置conf下的文件：
vim hadoop-env.sh
export JAVA_HOME=/usr/lib/jdk1.6.0_33
vim core-site.xml
----------------------------------
<configuration>
<property>
<name>hadoop.tmp.dir</name>
<value>/opt/hadoop-datastore/</value>
<description>A base for other temporary directories.</description>
</property>
<property>
<name>fs.default.name</name>
<value>hdfs://Master.Hadoop:54310</value>
<description>The name of the default file system. A URI whose
scheme and authority determine the FileSystem implementation. The
uri's scheme determines the config property (fs.SCHEME.impl) naming
the FileSystem implementation class. The uri's authority is used to
determine the host, port, etc. for a filesystem.</description>
</property>
</configuration>
-----------------------------------------
vim hdfs-site.xml
------------------------------------------
<configuration>
<property>
<name>dfs.replication</name>
<value>3</value>
<description>Default block replication.
The actual number of replications can be specified when the file is created.
The default is used if replication is not specified in create time.
</description>
</property>
</configuration>
-------------------------------------
vim mapred-site.xml
------------------------------------
<configuration>
<property>
<name>mapred.job.tracker</name>
<value>Master.Hadoop:54311</value>
<description>The host and port that the MapReduce job tracker runs
at. If "local", then jobs are run in-process as a single map
and reduce task.
</description>
</property>
</configuration>
-------------------------------------
vim masters
Master.Hadoop
root@Master:/opt/hadoop/conf# vim slaves
Slave1.Hadoop
Slave2.Hadoop
采用方法3，将Master上的Hadoop拷贝到每个Slave下
切换为root用户
su root
执行 scp -r hadoop Slave1.Hadoop:/opt/
在Slave1.Hadoop上
su root
chown -R hadoop:hadoop /opt/hadoop/
创建目录
mkdir /opt/hadoop-datastore/
chown -R hadoop:hadoop /opt/hadoop-datastore/
同理 其他Slave
在namenode执行 格式化hadoop
root@Master:/opt/hadoop/bin# hadoop namenode -format
输出：
12/07/23 18:54:36 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = Master.Hadoop/10.2.128.46
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 /opt/hadoop-datastore/dfs/name ? (Y or N) y
Format aborted in /opt/hadoop-datastore/dfs/name
12/07/23 18:54:45 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at Master.Hadoop/10.2.128.46
************************************************************/
启动hadoop
./start-all.sh
root@Master:/opt# chown -R hadoop:hadoop /opt/hadoop/
root@Master:/opt# chown -R hadoop:hadoop /opt/hadoop-datastore/
root@Master:/opt# su hadoop
hadoop@Master:/opt$ cd hadoop/bin/
hadoop@Master:/opt/hadoop/bin$ ./start-all.sh
遇到的问题：
starting namenode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-namenode-Master.Hadoop.out
Slave1.Hadoop: datanode running as process 7309. Stop it first.
Slave2.Hadoop: datanode running as process 4920. Stop it first.
Master.Hadoop: starting secondarynamenode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-secondarynamenode-Master.Hadoop.out
starting jobtracker, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-jobtracker-Master.Hadoop.out
Slave1.Hadoop: tasktracker running as process 7477. Stop it first.
Slave2.Hadoop: tasktracker running as process 5088. Stop it first.
网上参考：
可能是楼主启动集群后，又重复格式化namenode导致的。
如果只是测试学习，可以使用如下解决方法：
1、首先kill掉26755、21863和26654几个进程。如果kill 26755不行，可以kill -kill 26755。
2、手动删除conf/hdfs-site.xml文件中配置的dfs.data.dir目录下的内容。
3、执行$HADOOP_HOME/bin/hadoop namenode -format
4、启动集群$HADOOP_HOME/bin/start-all.sh
后果：
HDFS中内容会全部丢失。
解决方案：重新进行了格式化
su hadoop
hadoop@Master:/opt/hadoop/bin$ ./hadoop namenode -format
12/07/24 10:43:29 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = Master.Hadoop/10.2.128.46
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 /opt/hadoop-datastore/dfs/name ? (Y or N) y
Format aborted in /opt/hadoop-datastore/dfs/name
12/07/24 10:43:32 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at Master.Hadoop/10.2.128.46
************************************************************/
hadoop@Master:/opt/hadoop/bin$ ./start-all.sh
starting namenode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-namenode-Master.Hadoop.out
Slave1.Hadoop: starting datanode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-datanode-Slave1.Hadoop.out
Slave2.Hadoop: starting datanode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-datanode-Slave2.Hadoop.out
Master.Hadoop: starting secondarynamenode, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-secondarynamenode-Master.Hadoop.out
starting jobtracker, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-jobtracker-Master.Hadoop.out
Slave2.Hadoop: starting tasktracker, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-tasktracker-Slave2.Hadoop.out
Slave1.Hadoop: starting tasktracker, logging to /opt/hadoop/bin/../logs/hadoop-hadoop-tasktracker-Slave1.Hadoop.out
hadoop@Master:/opt/hadoop/bin$
--------------------------------------------------------------------------------------------------------------------------
以下为验证部分：
hadoop@Master:/opt/hadoop/bin$ ./hadoop dfsadmin -report
Safe mode is ON
Configured Capacity: 41137831936 (38.31 GB)
Present Capacity: 31127531520 (28.99 GB)
DFS Remaining: 31127482368 (28.99 GB)
DFS Used: 49152 (48 KB)
DFS Used%: 0%
Under replicated blocks: 0
Blocks with corrupt replicas: 0
Missing blocks: 0
-------------------------------------------------
Datanodes available: 2 (2 total, 0 dead)
Name: 10.2.128.120:50010
Decommission Status : Normal
Configured Capacity: 20568915968 (19.16 GB)
DFS Used: 24576 (24 KB)
Non DFS Used: 4913000448 (4.58 GB)
DFS Remaining: 15655890944(14.58 GB)
DFS Used%: 0%
DFS Remaining%: 76.11%
Last contact: Tue Jul 24 10:50:43 CST 2012
Name: 10.2.128.20:50010
Decommission Status : Normal
Configured Capacity: 20568915968 (19.16 GB)
DFS Used: 24576 (24 KB)
Non DFS Used: 5097299968 (4.75 GB)
DFS Remaining: 15471591424(14.41 GB)
DFS Used%: 0%
DFS Remaining%: 75.22%
Last contact: Tue Jul 24 10:50:41 CST 2012
web查看方式：http://10.2.128.46:50070/
查看job信息
http://10.2.128.46:50030/jobtracker.jsp
要想检查守护进程是否正在运行，可以使用 jps 命令（这是用于 JVM 进程的ps 实用程序）。这个命令列出 5 个守护进程及其进程标识符。
hadoop@Master:/opt/hadoop/conf$ jps
2823 Jps
2508 JobTracker
2221 NameNode
2455 SecondaryNameNode
netstat -nat
tcp 0 0 10.2.128.46:54311 0.0.0.0:* LISTEN
tcp 0 0 10.2.128.46:54310 10.2.128.46:44150 ESTABLISHED
tcp 267 0 10.2.128.46:54311 10.2.128.120:48958 ESTABLISHED
tcp 0 0 10.2.128.46:54310 10.2.128.20:41230 ESTABLISHED
./hadoop dfs -ls /
hadoop@Master:/opt/hadoop/bin$ ./hadoop dfs -ls /
Found 2 items
drwxr-xr-x - root supergroup 0 2012-07-13 15:20 /opt
drwxr-xr-x - root supergroup 0 2012-07-13 15:20 /user
hadoop@Master:/opt/hadoop$ bin/hadoop fs -mkdir input
遇到问题：
mkdir: org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot create directory /user/hadoop/input. Name node is in safe mode.
那什么是Hadoop的安全模式呢？
在分布式文件系统启动的时候，开始的时候会有安全模式，当分布式文件系统处于安全模式的情况下，文件系统中的内容不允许修改也不允许删除，直到安全 模式结束。
安全模式主要是为了系统启动的时候检查各个DataNode上数据块的有效性，同时根据策略必要的复制或者删除部分数据块。
运行期通过命令也可以进入安全模式。在实践过程中，系统启动的时候去修改和删除文件也会有安全模式不允许修改的出错提示，只需要等待一会儿即可。
现在就清楚了，那现在要解决这个问题，我想让Hadoop不处在safe mode 模��下，能不能不用等，直接解决呢？
答案是可以的，只要在Hadoop的目录下输入：
hadoop@Master:/opt/hadoop/bin$ ./hadoop dfsadmin -safemode leave
hadoop@Master:/opt/hadoop$ bin/hadoop fs -mkdir input
hadoop@Master:/opt/hadoop/bin$ cd ..
hadoop@Master:/opt/hadoop$ bin/hadoop fs -mkdir input
hadoop@Master:/opt/hadoop$ bin/hadoop fs -put conf/core-site.xml input
hadoop@Master:/opt/hadoop$ bin/hadoop jar hadoop-0.20.2-examples.jar grep input output 'dfs[a-z.]+'
6.补充
Q: bin/hadoop jar hadoop-0.20.2-examples.jar grep input output 'dfs[a-z.]+' 什么意思啊？
A: bin/hadoop jar（使用hadoop运行jar包） hadoop-0.20.2_examples.jar（jar包的名字） grep （要使用的类，后边的是参数）input output 'dfs[a-z.]+'
整个就是运行hadoop示例程序中的grep，对应的hdfs上的输入目录为input、输出目录为output。
Q: 什么是grep?
A: A map/reduce program that counts the matches of a regex in the input.
查看结果：
hadoop@Master:/opt/hadoop$ bin/hadoop fs -ls /user/hadoop/output
Found 2 items
drwxr-xr-x - hadoop supergroup 0 2012-07-24 11:29 /user/hadoop/output/_logs
-rw-r--r-- 3 hadoop supergroup 0 2012-07-24 11:30 /user/hadoop/output/part-00000
hadoop@Master:/opt/hadoop$ bin/hadoop fs -rmr /user/hadoop/outputtest
Deleted hdfs://Master.Hadoop:54310/user/hadoop/outputtest
hadoop@Master:/opt/hadoop$ bin/hadoop fs -rmr /user/hadoop/output
Deleted hdfs://Master.Hadoop:54310/user/hadoop/output
改用其他例子
hadoop@Master:/opt/hadoop$ bin/hadoop jar /opt/hadoop/hadoop-0.20.2-examples.jar wordcount input output
hadoop@Master:/opt/hadoop$ bin/hadoop fs -ls /user/hadoop/output
Found 2 items
drwxr-xr-x - hadoop supergroup 0 2012-07-24 11:43 /user/hadoop/output/_logs
-rw-r--r-- 3 hadoop supergroup 772 2012-07-24 11:43 /user/hadoop/output/part-r-00000
hadoop@Master:/opt/hadoop$ bin/hadoop fs -cat /user/hadoop/output/part-r-00000
(fs.SCHEME.impl) 1
--> 1
<!-- 1
</configuration> 1
</property> 2
<?xml 1
<?xml-stylesheet 1
测试成功!
重启遇到的错误
INFO ipc.Client: Retrying connect to server: master/192.168.0.45:54310. Already tried 0 time
./hadoop dfsadmin -report
cd /opt/hadoop-datastore/
/opt/hadoop/bin/stop-all.sh
rm -rf *
/opt/hadoop/bin/hadoop namenode -format
/opt/hadoop/bin/start-all.sh
./hadoop dfsadmin -report