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。