ubuntu 16.4下hadoop配置伪分布式时出现的坑

在ubuntu16.4下spark的单机/伪分布式配置我在此就不在一一赘述，详情请点击如下连接：

Hadoop安装教程_单机/伪分布式配置_Hadoop2.6.0/Ubuntu14.04

我出现问题是在配置好伪分布式的文件并且NameNode 的格式化正确我弄成后，在启动hdfs时出现如下错误：

hadoop@litao-virtual-machine:/usr/local/hadoop$ ./sbin/start-dfs.sh 
Starting namenodes on [localhost]
localhost: Error: JAVA_HOME is not set and could not be found.
localhost: Error: JAVA_HOME is not set and could not be found.
Starting secondary namenodes [0.0.0.0]
0.0.0.0: Error: JAVA_HOME is not set and could not be found.

此错误多出现于你的java环境没有配置正确的时候，关于如何正确配置ubuntu下的java请出门右转问百度。

当你的环境是ubuntu16.4 hadoop2.7.4 并且java已经确保正确配置时，（网上其它关于次报错的解决办法都尝试过时）或许下面我的解决办法会让你柳暗花明：

 vim ./etc/hadoop/hadoop-env.sh  #打开你hadoop安装路径下的hadoop环境配置脚本 

# The only required environment variable is JAVA_HOME.  All others are
# optional.  When running a distributed configuration it is best to
# set JAVA_HOME in this file, so that it is correctly defined on
# remote nodes.

# The java implementation to use.
JAVA_HOME=/usr/local/java/jdk1.8.0_151 #你的java路径
export JAVA_HOME   #添加这两行内容
export JAVA_HOME=${JAVA_HOME}

# The jsvc implementation to use. Jsvc is required to run secure datanodes

之后就可以重新执行:

./sbin/start-dfs.sh 

#由于我在写博客时已经运行过，所以会提示已经运行
1 hadoop@litao-virtual-machine:/usr/local/hadoop$ ./sbin/start-dfs.sh 
Starting namenodes on [localhost]
localhost: namenode running as process 5085. Stop it first.
localhost: datanode running as process 5239. Stop it first.
Starting secondary namenodes [0.0.0.0]
0.0.0.0: secondarynamenode running as process 5407. Stop it first.

问题原因：

　　根因未知，只是在检查机子各项配置没有问题之后，加上各种猜测性测试得到的解决办法。

希望本条微博可以给您带来帮助！