Quick configuration about the hadoop-maxwell

　　Some problems I came across when I deployed hadoop.
　　Java:
　　1) Install jdk:
　　openjdk-7-jdk
　　2) To find the path of java:
　　You can use "file" command to track the position of java
　　e.g.
　　which javac                 -->     /usr/bin/javac
　　file /usr/bin/javac         -->     /etc/alternatives/javac
　　file /etc/alternatives/javac    -->     /usr/lib/jvm/java-7-openlink-amd64/bin/javac
　　file /usr/lib/jvm/java-7-openlink-amd64/bin/javac   --> Done
　　/usr/bin/jvm/java-7-openjdk-amd64/
　　3) Set the environment variable of java in /etc/profile
　　export JAVA_HOME=/usr/lib/jvm/java-1.7.0-openjdk-i386
　　export JRE_HOME=${JAVA_HOME}/jre

　　export>　　export PATH=${JAVA_HOME}/bin:$PATH
　　source /etc/profile   # to make it effective
　　SSH:
　　1) Install OpenSSH Server
　　2) To config logging without pwd
　　ssh-keygen -t rsa
　　Copy the public key into the file authorized_keys

　　cp>　　3) Restart the service of SSH
　　service sshd restart
　　Hostname:
　　Copy the file of map between ip address and hostname into each host:/etc/hosts
　　Download the most stable version of hadoop: 1.2.1
　　1) Config the configuration files in directories, e.g. hadoop-env.sh, mapred-site.xml, core-site.xml, hdfs-site.xml
　　!!!!You may need to set the property to avoid default port
　　
　　mapred.job.tracker.http.address
　　hostname:50030
　　
　　Set the directory of hadoop into environment variable(in .bashrc file):
　　export HADOOP_PREFIX=/home/hadoop/hadoop-dir
　　exoprt PATH=$PATH:$HADOOP_PREFIX/bin
　　Some problems when configing Hadoop:
　　1) To custumize the plug-in of hadoop in eclipse, refer to the following url:
　　https://docs.google.com/document/d/1yuZ4IjlquPkmC1zXtCeL4GUNKT1uY1xnS_SCBJHps6A/edit?pli=1
　　2) Plug-in error:
　　When create a new map/reduce project, it appears the error message as follows:

　　"The selected wizard could not be started. Plug-in org.apache.hadoop.eclipse was unable to load>　　That is because of the version of java, utilizing the right version of java will be okay, i.e., update-alternatives
　　3) iptables
　　See the following error in logfile
　　java.io.IOException: File /root/hadoop-data/tmp/mapred/system/jobtracker.info could only be replicated to 0 nodes, instead of 1
　　Solutions: stop iptables on all hosts
　　service iptables stop