服务器是一个云服务器，内存为1G，CPU为1核。
然后执行一个Hadoop本身自带的example报错的。报错信息如下：
There is insufficient memory for the Java Runtime Environment to continue.
Native memory allocation (mmap) failed to map 12288 bytes for committing reserved memory.
执行的命令是：
hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.6.5.jar grep /input/hadoop/core-site.xml /user/test1 'dfs[a-z.]+'
