学习环境： ubuntu
概要：
Nutch 是一个开源Java 实现的搜索引擎。它提供了我们运行自己的搜索引擎所需的全部工具。包括全文搜索和Web爬虫。
通过nutch，诞生了hadoop、tika、gora。
先安装SVN和Ant环境。(通过编译源码方式来使用nutch)
apt-get install ant
apt-get install subversion
hu@hu-VirtualBox:~/data/nutch$ svn co https://svn.apache.org/repos/asf/nutch/tags/release-1.6/
hu@hu-VirtualBox:~/data/nutch$ cd release-1.6/
hu@hu-VirtualBox:~/data/nutch/release-1.6$ ant
hu@hu-VirtualBox:~/data/nutch/release-1.6$ cd runtime/
备注runtime目录下有两个目录，分别代表了nutch两种不同运行方式。deploy依赖hadoop。
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime$ ls
deploy local
那nutch和hadoop是通过什么连接起来的？
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime$ ls deploy/
apache-nutch-1.6.job bin
是通过nutch脚本。通过hadoop命令吧apache-nutch-1.6.job提交给hadoop的JobTracker。
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime$ cd local/
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ mkdir urls
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ touch urls/url.txt
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ vi urls/url.txt
备注：urls/url.txt中输入爬取地址 http://blog.tianya.cn
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ ./bin/nutch crawl
Usage: Crawl <urlDir> -solr <solrURL> [-dir d] [-threads n] [-depth i] [-topN N]
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ nohup ./bin/nutch crawl urls -dir data -threads 100 -depth 3 &
备注：查看运行概要 hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ cat nohup.out
查看运行详情 通过logs/hadoop.log文件
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ ls logs/
hadoop.log
通过查看nohup.out发现出现异常
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ cat nohup.out
solrUrl is not set, indexing will be skipped...
crawl started in: data
rootUrlDir = urls
threads = 100
depth = 3
solrUrl=null
Injector: starting at 2013-12-08 21:10:30
Injector: crawlDb: data/crawldb
Injector: urlDir: urls
Injector: Converting injected urls to crawl db entries.
solrUrl is not set, indexing will be skipped...
crawl started in: data
rootUrlDir = urls
threads = 100
depth = 3
solrUrl=null
Injector: starting at 2013-12-08 21:10:38
Injector: crawlDb: data/crawldb
Injector: urlDir: urls
Injector: Converting injected urls to crawl db entries.
Injector: total number of urls rejected by filters: 0
Injector: total number of urls injected after normalization and filtering: 1
Injector: Merging injected urls into crawl db.
Injector: finished at 2013-12-08 21:10:53, elapsed: 00:00:14
Generator: starting at 2013-12-08 21:10:53
Generator: Selecting best-scoring urls due for fetch.
Generator: filtering: true
Generator: normalizing: true
Generator: jobtracker is 'local', generating exactly one partition.
Generator: Partitioning selected urls for politeness.
Generator: segment: data/segments/20131208211101
Generator: finished at 2013-12-08 21:11:08, elapsed: 00:00:15
Fetcher: No agents listed in 'http.agent.name' property.
Exception in thread "main" java.lang.IllegalArgumentException: Fetcher: No agents listed in 'http.agent.name' property.
at org.apache.nutch.fetcher.Fetcher.checkConfiguration(Fetcher.java:1389)
at org.apache.nutch.fetcher.Fetcher.fetch(Fetcher.java:1274)
at org.apache.nutch.crawl.Crawl.run(Crawl.java:136)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65)
at org.apache.nutch.crawl.Crawl.main(Crawl.java:55)
【解决方案】
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ vi conf/nutch-site.xml
打开 conf/nutch-site.xml. 在nutch-site.xml中添加"http.agent.name"信息。 （conf/nutch-default.xml有默认配置信息）
<configuration>
<property>
<name>http.agent.name</name>
<value>Mozilla/5.0 (Windows NT 6.1; WOW64; rv:20.0; WUID=11ec69f3ac129124d5a2480d127648e0; WTB=2938) Gecko/20100101 Firefox/20.0</value>
<description>HTTP 'User-Agent' request header. MUST NOT be empty -
please set this to a single word uniquely related to your organization.
NOTE: You should also check other related properties:
http.robots.agents
http.agent.description
http.agent.url
http.agent.email
http.agent.version
and set their values appropriately.
</description>
</property>
</configuration>
(如果修改源文件中配置文件，即/release-1.6/conf/nutch-site.xml，在更改nutch配置文件之后，需要重新进行ant编译)
hu@hu-VirtualBox:~/data/nutch/release-1.6/runtime/local$ ls data/
crawldb linkdb segments
下回再学关于查看抓取数据详细信息。
总结：nutch的入门重点在于分析nutch脚本文件
参考：