jps命令的真相
[hadoop@hadoop001 ~]$ jps
13397 NameNode
13718 SecondaryNameNode
13530 DataNode
13887 Jps
[hadoop@hadoop001 ~]$
位置哪里的
[hadoop@hadoop001 ~]$ which jps
/usr/java/jdk1.8.0_144/bin/jps
[hadoop@hadoop001 ~]$
对应的进程的标识文件在哪 /tmp/hsperfdata_username
[hadoop@hadoop001 /]$ ll /tmp/ | grep hsperfdata
drwxr-xr-x. 2 hadoop hadoop 4096 Mar 16 06:02 hsperfdata_hadoop
drwxr-xr-x. 2 root root 4096 Mar 16 06:01 hsperfdata_root
[hadoop@hadoop001 /]$
[hadoop@hadoop001 hsperfdata_hadoop]$ pwd
/tmp/hsperfdata_hadoop
[hadoop@hadoop001 hsperfdata_hadoop]$ ll
total 96
-rw-------. 1 hadoop hadoop 32768 Mar 16 06:09 13397
-rw-------. 1 hadoop hadoop 32768 Mar 16 06:09 13530
-rw-------. 1 hadoop hadoop 32768 Mar 16 06:09 13718
[hadoop@hadoop001 hsperfdata_hadoop]$
root用户看所有用户的jps结果，普通用户只能看自己的
[root@hadoop001 ~]# jps
13397 NameNode
13718 SecondaryNameNode
13530 DataNode
14028 Jps
[root@hadoop001 home]# su - haha
[haha@hadoop001 ~]$ jps
14005 Jps
[haha@hadoop001 ~]$
process information unavailable
真假判断: ps -ef|grep namenode 真正判断进程是否可用
当出现process information unavailable ,不一定表示不可以用
[root@hadoop001 ~]# jps
1520 Jps
1378 -- process information unavailable
1210 -- process information unavailable
1086 -- process information unavailable
kill: 可能是人为的，也可能是某个进程在Linux系统中出现(OOM)自动给你kill
[root@hadoop001 tmp]# rm -rf hsperfdata_hadoop
[root@hadoop001 tmp]#
[root@hadoop001 tmp]# jps
1906 Jps
[root@hadoop001 tmp]#
**pid文件 集群进程启动和停止要的文件**
-rw-rw-r-- 1 hadoop hadoop 5 Feb 16 20:56 hadoop-hadoop-datanode.pid
-rw-rw-r-- 1 hadoop hadoop 5 Feb 16 20:56 hadoop-hadoop-namenode.pid
-rw-rw-r-- 1 hadoop hadoop 5 Feb 16 20:57 hadoop-hadoop-secondarynamenode.pid
Linux在tmp目录中会定期删除一些文件和文件夹，此周期为30天
[hadoop@hadoop001 hadoop]$ tail -10 hadoop-env.sh
# The directory where pid files are stored. /tmp by default.
# NOTE: this should be set to a directory that can only be written to by
# the user that will run the hadoop daemons. Otherwise there is the
# potential for a symlink attack.
export HADOOP_PID_DIR=${HADOOP_PID_DIR}
export HADOOP_SECURE_DN_PID_DIR=${HADOOP_PID_DIR}
# A string representing this instance of hadoop. $USER by default.
export HADOOP_IDENT_STRING=$USER
#比如自己修改PID文件路径为如下的方式
[hadoop@hadoop001 hadoop]$
mkdir /data/tmp
chmod -R 777 /data/tmp
export HADOOP_PID_DIR=/data/tmp
在生产中，我们需要修改PID的存放路径，因为默认放在/tmp下，如果删除了PID文件，会造成进程无法启动关闭。
[hadoop@hadoop001 tmp]$ rm -rf hadoop-hadoop-datanode.pid
[hadoop@hadoop001 tmp]$ stop-dfs.sh
19/03/16 06:43:23 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Stopping namenodes on [localhost]
localhost: stopping namenode
hadoop001: no datanode to stop
Stopping secondary namenodes [hadoop001]
hadoop001: stopping secondarynamenode
19/03/16 06:43:37 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
[hadoop@hadoop001 tmp]$ jps
14581 Jps
13530 DataNode
[hadoop@hadoop001 tmp]$ #删除了PID文件，发现无法关闭进程
