centos7 yum安装java运行环境，初识hadoop-smile
安装java运行环境1.实验机相关信息：
#cat /etc/redhat-release
CentOS Linux> # uname -r
3.10.0-327.el7.x86_6
2.配置epel源，以yum方式安装openjdk
yum search java | grep -iJDK
yum install java-1.8.0-openjdkjava-1.8.0-openjdk-devel
3.设置JAVA_HOME环境变量
# cat/etc/profile.d/java_home.sh
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.161-0.b14.el7_4.x86_64
export PATH=$PATH:$JAVA_HOME/bin
使配置生效
source /etc/profile.d/java_home.sh或 ./etc/profile.d/java_home.sh
4.测试java是否安装配置成功
# java -version
openjdk version "1.8.0_161"
OpenJDK Runtime Environment (build 1.8.0_161-b14)
OpenJDK 64-Bit Server VM (build 25.161-b14, mixed mode)
5.创建java小程序，编译打印hello world
# cat helloworld.java
public> publicstatic voidmain(String[] args){
System.out.println("hello wolrd!");
}
}
# javac helloworld.java #编译后会出现helloworld.class 这个类文件
# java helloworld #运行
hello wolrd!
[*]如何运行 .jar.war这些java应用？ java-jar/path/to/*.jar
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接下来认识hadoop官网：http://hadoop.apache.org/
什么是Apache Hadoop？
Apache™Hadoop®项目为可靠的，可扩展的分布式计算开发开源软件。
Apache Hadoop软件库是一个框架，它允许使用简单的编程模型跨计算机群集分布式处理大型数据集。
旨在从单个服务器扩展到数千台机器，每台机器提供本地计算和存储。
该库本身不是依靠硬件来提供高可用性，而是设计用于在应用层检测并处理故障，从而在一组计算机之上提供高可用性服务，每个计算机都可能出现故障。
hadoop单机模式运行
官网下载二进制包，解压到/usr/locl目录，创建软连接同目录下hadoop，配置PATH变量，使生效
$ cat /etc/profile.d/hadoop.sh
export PATH=$PATH:/usr/local/hadoop/bin:/usr/local/hadoop/sbin
# hadoop
Usage: hadoop SUBCOMMAND
or hadoop >
where>
OPTIONS is none or any of:
buildpaths attempt to add>
--config dir Hadoop config directory
--debug turn on shell script debug mode
--help usage information
hostnames list[,of,host,names] hosts to use in slave mode
hosts filename list of hosts to use in slave mode
loglevel level set the log4j level for this command
workers turn on worker mode
SUBCOMMAND is one of:
Admin Commands:
daemonlog get/set the log level for each daemon
Client Commands:
archive create a Hadoop archive
checknative check native Hadoop and compression libraries availability
classpath prints the>
conftest validate configuration XML files
credential interact with credential providers
distch distributed metadata changer
distcp copy file or directories recursively
dtutil operations>
envvars display computed Hadoop environment variables
fs run a generic filesystem user client
gridmix submit a mix of synthetic job, modeling a profiled from production load
jar run a jar file. NOTE: please use "yarn jar" to launch YARN applications, not this command.
jnipath prints the java.library.path
kdiag Diagnose Kerberos Problems
kerbname show auth_to_local principal conversion
key manage keys via the KeyProvider
rumenfolder scale a rumen input trace
rumentrace convert logs into a rumen trace
s3guard manage metadata on S3
trace view and modify Hadoop tracing settings
version print the version
Daemon Commands:
kms run KMS, the Key Management Server
SUBCOMMAND may print help when invoked w/o parameters or with -h.
Hadoop 默认配置是以非分布式模式运行，即单 Java 进程，方便进行调试。可以执行附带的例子 WordCount 来感受下 Hadoop 的运行。将 input 文件夹中的文件作为输入，统计当中符合正则表达式 wo+ 的单词出现的次数，并输出结果到 output 文件夹中。
如果需要再次运行，需要删除output文件夹（因为Hadoop 默认不会覆盖结果文件）：
# cd /usr/local/hadoop/ # mkdir input
# cp etc/hadoop/*.xml input
# bin/hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.0.jar grep input output 'dfs+'
# cat output/*
1work
# hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.0.jar grep /etc/passwd output 'root'
# cat output/*
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