Hadoop出现namenode running as process 18472. Stop it first.等等，类似的出现了好几个。
namenode running as process 32972. Stop it first.
127.0.0.1: ssh: connect to host 127.0.0.1 port 22: No error
127.0.0.1: ssh: connect to host 127.0.0.1 port 22: No error
jobtracker running as process 81312. Stop it first.
127.0.0.1: ssh: connect to host 127.0.0.1 port 22: No error
解决办法：说明你没有启动起来，所以在启动之前你需要 在重新启动hadoop之前要先stop掉所有的hadoop服务。
然后恢复正常启动。
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Ubuntu 13.04上搭建Hadoop环境 http://www.linuxidc.com/Linux/2013-06/86106.htm
Ubuntu 12.10 +Hadoop 1.2.1版本集群配置 http://www.linuxidc.com/Linux/2013-09/90600.htm
Ubuntu上搭建Hadoop环境（单机模式+伪分布模式） http://www.linuxidc.com/Linux/2013-01/77681.htm
Ubuntu下Hadoop环境的配置 http://www.linuxidc.com/Linux/2012-11/74539.htm
单机版搭建Hadoop环境图文教程详解 http://www.linuxidc.com/Linux/2012-02/53927.htm
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