1.jps命令位置

[hadoop@Hadoop001 tmp]$ which jps
/usr/java/jdk1.8.0_45/bin/jps
[hadoop@Hadoop001 tmp]$ which java
/usr/java/jdk1.8.0_45/bin/java

2.查看java进程

[hadoop@Hadoop001 tmp]$ jps
4882 NameNode
4982 DataNode
5177 SecondaryNameNode
5371 Jps

3.存储进程pid （hsperfdata_用户名称）

[hadoop@Hadoop001 tmp]$ ll
drwxr-xr-x  2 hadoop hadoop 4096 Jul  4 04:33 hsperfdata_hadoop
[hadoop@Hadoop001 tmp]$ cd hsperfdata_hadoop/
[hadoop@Hadoop001 hsperfdata_hadoop]$ ll
total 96
-rw------- 1 hadoop hadoop 32768 Jul  4 04:33 4882
-rw------- 1 hadoop hadoop 32768 Jul  4 04:33 4982
-rw------- 1 hadoop hadoop 32768 Jul  4 04:33 5177

4.process information unavailable

[root@Hadoop001 dfs]# jps
4882 -- process information unavailable
5397 Jps
4982 -- process information unavailable
5177 -- process information unavailable
[alvin@Hadoop001 ~]$ jps
5452 Jps

进程所在的用户jps查看显示进程信息，
非root用户没有，
root显示process information unavailable。如果进程被kill了，有可能jps 还是显示xxxx -- process information unavailable，需要用ps -ef | grep pid 确认。