Linux7查看默认jdk安装目录（默认只有jre环境，无jdk开发环境。附：安装jdk并配置JAVA_HOME）_linux的jdk安装在哪个目录

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1、检测默认jre运行环境

（1） 查看linux7默认运行环境jre

# cd /etc/alternatives
# ll
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如下图：

java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64/jre/bin/java

或者 使用以下命令输出：

# ls -lrt /etc/alternatives/java
lrwxrwxrwx. 1 root root 71 Apr 30 09:45 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64/jre/bin/java


# rpm -qa|grep openjdk -i
java-1.8.0-openjdk-headless-1.8.0.262.b10-1.el7.x86_64
java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
# 
# find / -name java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm-exports/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
/usr/lib/jvm-private/java-1.8.0-openjdk-1.8.0.262.b10-1.el7.x86_64
#
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（2） 检测开发环境jdk

[root@localhost lib]# javac
bash: javac: command not found...
Similar command is: 'java'
[root@localhost lib]# 
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（3） 联网安装开发环境jdk（无网建议卸载自带jdk和jre，安装统一版本的离线jdk）

3.1）检测yum源存在的jdk版本

[root@localhost lib]# yum search java|grep jdk
ldapjdk-javadoc.noarch : Javadoc for ldapjdk
......
......
java-1.8.0-openjdk.i686 : OpenJDK Runtime Environment 8
java-1.8.0-openjdk.x86_64 : OpenJDK 8 Runtime Environment
java-1.8.0-openjdk-accessibility.i686 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility.x86_64 : OpenJDK accessibility connector
java-1.8.0-openjdk-demo.i686 : OpenJDK Demos 8
java-1.8.0-openjdk-demo.x86_64 : OpenJDK 8 Demos
java-1.8.0-openjdk-devel.i686 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel.x86_64 : OpenJDK 8 Development Environment
java-1.8.0-openjdk-headless.i686 : OpenJDK Headless Runtime Environment 8
java-1.8.0-openjdk-headless.x86_64 : OpenJDK 8 Headless Runtime Environment
java-1.8.0-openjdk-javadoc.noarch : OpenJDK 8 API documentation
java-1.8.0-openjdk-javadoc-zip.noarch : OpenJDK 8 API documentation compressed
java-1.8.0-openjdk-src.i686 : OpenJDK Source Bundle 8
java-1.8.0-openjdk-src.x86_64 : OpenJDK 8 Source Bundle
......
......
ldapjdk.noarch : The Mozilla LDAP Java SDK
[root@localhost lib]# 
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附（参考）：
（1）单独安装jre命令：yum install java-1.8.0-openjdk
（2）单独安装jdk命令：yum install java-1.8.0-openjdk-devel.x86_64

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3.2）yum方式安装jdk

执行以下命令可安装或升级默认jre：

# yum install java-1.8.0-openjdk
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3.3）yum方式安装jdk（建议版本与jre版本保持一致）

# yum install java-1.8.0-openjdk-devel.x86_64
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查看安装软件，如下图：

# rpm -qa|grep java-1.8.0-openjdk -i
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jdk安装目录如下：

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3、配置JAVA_HOME

# vim /etc/profile
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（1）配置/etc/profile文件，在最后添加jdk配置信息

# jdk config
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.322.b06-1.el7_9.x86_64
export JRE_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.322.b06-1.el7_9.x86_64/jre
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$JAVA_HOME/bin:$JAVA_HOME/jre/bin:$PATH:$HOME/bin
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重启加载环境变量配置，测试javac命令

[root@localhost jvm]# source /etc/profile
[root@localhost jvm]# 
[root@localhost jvm]# javac
...
...

[root@localhost jvm]# 
[root@localhost jvm]# javac -version
javac 1.8.0_322
[root@localhost jvm]# 
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