最近基于CentOS 7下安装hadoop集群，碰到了java环境变量的问题，同时也出现了jps命令无法找到的情况。简要描述一下基于CentOS 7下Java环境的配置及jps命令未找到的处理。
一、Java环境配置
在安装好了CentOS 7之后，Java环境已经安装好(如没有，则选择的安装类型不包括)
如下，我们可以查看Java的版本
[root@namenode ~]# java -version
openjdk version "1.8.0_65"
OpenJDK Runtime Environment (build 1.8.0_65-b17)
OpenJDK 64-Bit Server VM (build 25.65-b01, mixed mode)
[root@namenode ~]# which java
/usr/bin/java
如下Java的环境变量并没有配置，因此我们需要设定环境变量
那JAVA_HOME到底该设置哪个路径呢？
[root@namenode ~]# env |grep JAVA
[root@namenode ~]# ls -hltr /usr/bin/java
lrwxrwxrwx. 1 root root 22 Nov 16 17:17 /usr/bin/java -> /etc/alternatives/java
[root@namenode ~]# cd /etc/alternatives
[root@namenode alternatives]# ls -hltr java
lrwxrwxrwx. 1 root root 73 Nov 16 17:17 java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64/jre/bin/java
从上面可只java命令又是一个软链，指向了另外一个地方
[root@namenode bin]# ls -hltr /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64/jre/bin/
total 184K
-rwxr-xr-x. 1 root root 101K Oct 20 22:27 unpack200
-rwxr-xr-x. 1 root root 7.3K Oct 20 22:27 tnameserv
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 servertool
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 rmiregistry
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 rmid
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 policytool
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 pack200
-rwxr-xr-x. 1 root root 7.3K Oct 20 22:27 orbd
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 keytool
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 jjs
-rwxr-xr-x. 1 root root 7.2K Oct 20 22:27 java
上面的位置包含了一些文件，不过命令数量不多
下面我们切换到/usr/lib/jvm
[root@namenode alternatives]# cd /usr/lib/jvm
[root@namenode jvm]# ls
java jre-1.7.0
java-1.7.0-openjdk-1.7.0.91-2.6.2.3.el7.x86_64 jre-1.7.0-openjdk
java-1.8.0 jre-1.7.0-openjdk-1.7.0.91-2.6.2.3.el7.x86_64
java-1.8.0-openjdk jre-1.8.0
java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64 jre-1.8.0-openjdk
java-openjdk jre-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64
jre jre-openjdk
[root@namenode jvm]# ls -hltr java-1.8.0-openjdk
lrwxrwxrwx. 1 root root 40 Nov 16 17:17 java-1.8.0-openjdk -> /etc/alternatives/java_sdk_1.8.0_openjdk
上面又是一个软链，头都绕晕了。
[root@namenode bin]# cd /etc/alternatives/java_sdk_1.8.0_openjdk
[root@namenode java_sdk_1.8.0_openjdk]# ls
bin include jre lib tapset
[root@namenode java_sdk_1.8.0_openjdk]# cd bin
[root@namenode bin]# ls |wc -l
41
通过上面的排查，我们可以设定JAVA_HOME为/etc/alternatives/java_sdk_1.8.0_openjdk
[root@namenode bin]# vim /etc/profile.d/java.sh
export JAVA_HOME=/etc/alternatives/java_sdk_1.8.0_openjdk
export PATH=$PATH:$JAVA_HOME
[root@namenode bin]# env |grep JAVA_HOME
JAVA_HOME=/etc/alternatives/java_sdk_1.8.0_openjdk二、jps命令无法找到
[root@namenode ~]# jps
bash: jps: command not found...
[root@namenode ~]# find / -name jps
find: ‘/run/user/1001/gvfs’: Permission denied
[root@namenode ~]# rpm -qa |grep -i jdk
java-1.8.0-openjdk-headless-1.8.0.65-3.b17.el7.x86_64
java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64
java-1.7.0-openjdk-1.7.0.91-2.6.2.3.el7.x86_64
java-1.7.0-openjdk-headless-1.7.0.91-2.6.2.3.el7.x86_64
[root@namenode ~]# yum list *openjdk-devel*
需要安装openjdk-devel包
[root@namenode ~]# yum install java-1.8.0-openjdk-devel.x86_64
[root@namenode ~]# which jps
/usr/bin/jps
[root@namenode ~]# jps
12995 Jps
10985 ResourceManager
11179 NodeManager
10061 NameNode
10301 DataNode
10655 SecondaryNameNode
