查看Linux中自带的jdk ,设置JAVA_HOME

我用centos7是64位的, 发现本机有java ,就找了一下其位置

找到了jdk-1.7.0_75

which java

[root@host2 hadoop-1.1.2]# which java
/usr/bin/java
[root@host2 hadoop-1.1.2]# ls /usr/bin/java
/usr/bin/java
[root@host2 hadoop-1.1.2]# ls -l /usr/bin/java
lrwxrwxrwx. 1 root root 22 Jun 20 03:00 /usr/bin/java -> /etc/alternatives/java
[root@host2 hadoop-1.1.2]# ls -l /etc/alternatives/java
lrwxrwxrwx. 1 root root 39 Jun 20 03:00 /etc/alternatives/java -> /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java （可以看出文件是link ，是个链接）
[root@host2 hadoop-1.1.2]# ls -l /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java-rwxr-xr-x. 1 root root 36548 Oct 25 2011 /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
[root@host2 hadoop-1.1.2]# cd /usr/lib/jvm/jre-1.7.0-openjdk.x86_64
[root@host2 jre-1.7.0-openjdk.x86_64]# ls
bin lib

如此来，可以暂时的断定是 /usr/lib/jvm/jre-1.7.0-openjdk.x86_64

设置新版本的jdk

[root@test01]# ln -snf /usr/local/jdk1.8.0_144 /usr/local/jdk 

#更新jdk

update-alternatives --install /usr/bin/java java /usr/local/jdk/bin/java 300
update-alternatives --install /usr/bin/javac javac /usr/local/jdk/bin/javac 300
update-alternatives --install /usr/bin/jar jar /usr/local/jdk/bin/jar 300

update-alternatives --config java

ln -s /usr/local/jdk/jre /usr/lib/jvm/jre

ldconfig

选择带有jdk1.8.0_144 的选项

即可以了

java -version  

查看是否是新的版本