linux下jdk多版本切换

系统环境

1. 系统 almalinux 9

2. java Orcale jdk1.8 & jdk17

3. jdk 安装方式 yum localinstall rpm包 (注：安装jdk时未对/etc/profile进行更改)

如何切换

参考Linux下怎么切换使用两个版本的JDK

使用alternatives --config java更改jdk版本

[root@minato ~]# alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
   1           /usr/java/jdk1.8.0_351-amd64/bin/java
*+ 2           /usr/java/jdk-17.0.5/bin/java

Enter to keep the current selection[+], or type selection number: 1
[root@minato ~]# java -version
java version "1.8.0_351"
Java(TM) SE Runtime Environment (build 1.8.0_351-b10)
Java HotSpot(TM) 64-Bit Server VM (build 25.351-b10, mixed mode)

---

发现alternatives完全是巧合，是探究rpm安装未配置profile命令如何生效发现的。
先使用whereis查看java位置，发现它是在/usr/bin目录下。

[root@minato ~]# whereis java
java: /usr/bin/java /usr/share/man/man1/java.1

然后卸载，不论那个版本，都是在这个位置，然后查看/usr/bin目录

[root@minato ~]# cd /usr/bin/
[root@minato bin]# ll|grep java
lrwxrwxrwx  1 root root          22 Dec  5 08:18 java -> /etc/alternatives/java
lrwxrwxrwx  1 root root          23 Dec  5 08:18 javac -> /etc/alternatives/javac
lrwxrwxrwx  1 root root          25 Dec  5 08:18 javadoc -> /etc/alternatives/javadoc
lrwxrwxrwx  1 root root          32 Dec  5 08:18 javafxpackager -> /etc/alternatives/javafxpackager
lrwxrwxrwx  1 root root          23 Dec  5 08:18 javah -> /etc/alternatives/javah
lrwxrwxrwx  1 root root          23 Dec  5 08:18 javap -> /etc/alternatives/javap
lrwxrwxrwx  1 root root          30 Dec  5 08:18 javapackager -> /etc/alternatives/javapackager
lrwxrwxrwx  1 root root          30 Dec  5 08:18 java-rmi.cgi -> /etc/alternatives/java-rmi.cgi
lrwxrwxrwx  1 root root          24 Dec  5 08:18 javaws -> /etc/alternatives/javaws

发现，这里面的java是个链接，继续查下去

[root@minato bin]# cd /etc/alternatives/
[root@minato alternatives]# ll|grep java
lrwxrwxrwx  1 root root 45 Dec  5 08:18 appletviewer -> /usr/java/jdk1.8.0_351-amd64/bin/appletviewer
lrwxrwxrwx  1 root root 52 Dec  5 08:18 appletviewer.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/appletviewer.1
lrwxrwxrwx  1 root root 45 Dec  5 08:18 ControlPanel -> /usr/java/jdk1.8.0_351-amd64/bin/ControlPanel
lrwxrwxrwx  1 root root 41 Dec  5 08:18 extcheck -> /usr/java/jdk1.8.0_351-amd64/bin/extcheck
lrwxrwxrwx  1 root root 48 Dec  5 08:18 extcheck.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/extcheck.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 idlj -> /usr/java/jdk1.8.0_351-amd64/bin/idlj
lrwxrwxrwx  1 root root 44 Dec  5 08:18 idlj.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/idlj.1
lrwxrwxrwx  1 root root 36 Dec  5 08:18 jar -> /usr/java/jdk1.8.0_351-amd64/bin/jar
lrwxrwxrwx  1 root root 43 Dec  5 08:18 jar.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jar.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 jarsigner -> /usr/java/jdk1.8.0_351-amd64/bin/jarsigner
lrwxrwxrwx  1 root root 49 Dec  5 08:18 jarsigner.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jarsigner.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 java -> /usr/java/jdk1.8.0_351-amd64/bin/java
lrwxrwxrwx  1 root root 44 Dec  5 08:18 java.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/java.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 javac -> /usr/java/jdk1.8.0_351-amd64/bin/javac
lrwxrwxrwx  1 root root 45 Dec  5 08:18 javac.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javac.1
lrwxrwxrwx  1 root root 40 Dec  5 08:18 javadoc -> /usr/java/jdk1.8.0_351-amd64/bin/javadoc
lrwxrwxrwx  1 root root 47 Dec  5 08:18 javadoc.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javadoc.1
lrwxrwxrwx  1 root root 47 Dec  5 08:18 javafxpackager -> /usr/java/jdk1.8.0_351-amd64/bin/javafxpackager
lrwxrwxrwx  1 root root 54 Dec  5 08:18 javafxpackager.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javafxpackager.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 javah -> /usr/java/jdk1.8.0_351-amd64/bin/javah
lrwxrwxrwx  1 root root 45 Dec  5 08:18 javah.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javah.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 javap -> /usr/java/jdk1.8.0_351-amd64/bin/javap
lrwxrwxrwx  1 root root 45 Dec  5 08:18 javap.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javap.1
lrwxrwxrwx  1 root root 45 Dec  5 08:18 javapackager -> /usr/java/jdk1.8.0_351-amd64/bin/javapackager
lrwxrwxrwx  1 root root 52 Dec  5 08:18 javapackager.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javapackager.1
lrwxrwxrwx  1 root root 45 Dec  5 08:18 java-rmi.cgi -> /usr/java/jdk1.8.0_351-amd64/bin/java-rmi.cgi
lrwxrwxrwx  1 root root 39 Dec  5 08:18 javaws -> /usr/java/jdk1.8.0_351-amd64/bin/javaws
lrwxrwxrwx  1 root root 46 Dec  5 08:18 javaws.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/javaws.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 jcmd -> /usr/java/jdk1.8.0_351-amd64/bin/jcmd
lrwxrwxrwx  1 root root 44 Dec  5 08:18 jcmd.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jcmd.1
lrwxrwxrwx  1 root root 41 Dec  5 08:18 jconsole -> /usr/java/jdk1.8.0_351-amd64/bin/jconsole
lrwxrwxrwx  1 root root 48 Dec  5 08:18 jconsole.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jconsole.1
lrwxrwxrwx  1 root root 41 Dec  5 08:18 jcontrol -> /usr/java/jdk1.8.0_351-amd64/bin/jcontrol
lrwxrwxrwx  1 root root 36 Dec  5 08:18 jdb -> /usr/java/jdk1.8.0_351-amd64/bin/jdb
lrwxrwxrwx  1 root root 43 Dec  5 08:18 jdb.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jdb.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 jdeps -> /usr/java/jdk1.8.0_351-amd64/bin/jdeps
lrwxrwxrwx  1 root root 45 Dec  5 08:18 jdeps.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jdeps.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 jhat -> /usr/java/jdk1.8.0_351-amd64/bin/jhat
lrwxrwxrwx  1 root root 44 Dec  5 08:18 jhat.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jhat.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 jinfo -> /usr/java/jdk1.8.0_351-amd64/bin/jinfo
lrwxrwxrwx  1 root root 45 Dec  5 08:18 jinfo.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jinfo.1
lrwxrwxrwx  1 root root 36 Dec  5 08:18 jjs -> /usr/java/jdk1.8.0_351-amd64/bin/jjs
lrwxrwxrwx  1 root root 43 Dec  5 08:18 jjs.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jjs.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 jmap -> /usr/java/jdk1.8.0_351-amd64/bin/jmap
lrwxrwxrwx  1 root root 44 Dec  5 08:18 jmap.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jmap.1
lrwxrwxrwx  1 root root 36 Dec  5 08:18 jps -> /usr/java/jdk1.8.0_351-amd64/bin/jps
lrwxrwxrwx  1 root root 43 Dec  5 08:18 jps.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jps.1
lrwxrwxrwx  1 root root 43 Dec  5 08:18 jrunscript -> /usr/java/jdk1.8.0_351-amd64/bin/jrunscript
lrwxrwxrwx  1 root root 50 Dec  5 08:18 jrunscript.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jrunscript.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 jsadebugd -> /usr/java/jdk1.8.0_351-amd64/bin/jsadebugd
lrwxrwxrwx  1 root root 49 Dec  5 08:18 jsadebugd.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jsadebugd.1
lrwxrwxrwx  1 root root 39 Dec  5 08:18 jstack -> /usr/java/jdk1.8.0_351-amd64/bin/jstack
lrwxrwxrwx  1 root root 46 Dec  5 08:18 jstack.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jstack.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 jstat -> /usr/java/jdk1.8.0_351-amd64/bin/jstat
lrwxrwxrwx  1 root root 45 Dec  5 08:18 jstat.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jstat.1
lrwxrwxrwx  1 root root 39 Dec  5 08:18 jstatd -> /usr/java/jdk1.8.0_351-amd64/bin/jstatd
lrwxrwxrwx  1 root root 46 Dec  5 08:18 jstatd.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jstatd.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 jvisualvm -> /usr/java/jdk1.8.0_351-amd64/bin/jvisualvm
lrwxrwxrwx  1 root root 49 Dec  5 08:18 jvisualvm.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/jvisualvm.1
lrwxrwxrwx  1 root root 40 Dec  5 08:18 keytool -> /usr/java/jdk1.8.0_351-amd64/bin/keytool
lrwxrwxrwx  1 root root 47 Dec  5 08:18 keytool.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/keytool.1
lrwxrwxrwx  1 root root 45 Dec  5 08:18 native2ascii -> /usr/java/jdk1.8.0_351-amd64/bin/native2ascii
lrwxrwxrwx  1 root root 52 Dec  5 08:18 native2ascii.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/native2ascii.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 orbd -> /usr/java/jdk1.8.0_351-amd64/bin/orbd
lrwxrwxrwx  1 root root 44 Dec  5 08:18 orbd.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/orbd.1
lrwxrwxrwx  1 root root 40 Dec  5 08:18 pack200 -> /usr/java/jdk1.8.0_351-amd64/bin/pack200
lrwxrwxrwx  1 root root 47 Dec  5 08:18 pack200.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/pack200.1
lrwxrwxrwx  1 root root 43 Dec  5 08:18 policytool -> /usr/java/jdk1.8.0_351-amd64/bin/policytool
lrwxrwxrwx  1 root root 50 Dec  5 08:18 policytool.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/policytool.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 rmic -> /usr/java/jdk1.8.0_351-amd64/bin/rmic
lrwxrwxrwx  1 root root 44 Dec  5 08:18 rmic.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/rmic.1
lrwxrwxrwx  1 root root 37 Dec  5 08:18 rmid -> /usr/java/jdk1.8.0_351-amd64/bin/rmid
lrwxrwxrwx  1 root root 44 Dec  5 08:18 rmid.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/rmid.1
lrwxrwxrwx  1 root root 44 Dec  5 08:18 rmiregistry -> /usr/java/jdk1.8.0_351-amd64/bin/rmiregistry
lrwxrwxrwx  1 root root 51 Dec  5 08:18 rmiregistry.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/rmiregistry.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 schemagen -> /usr/java/jdk1.8.0_351-amd64/bin/schemagen
lrwxrwxrwx  1 root root 49 Dec  5 08:18 schemagen.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/schemagen.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 serialver -> /usr/java/jdk1.8.0_351-amd64/bin/serialver
lrwxrwxrwx  1 root root 49 Dec  5 08:18 serialver.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/serialver.1
lrwxrwxrwx  1 root root 43 Dec  5 08:18 servertool -> /usr/java/jdk1.8.0_351-amd64/bin/servertool
lrwxrwxrwx  1 root root 50 Dec  5 08:18 servertool.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/servertool.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 tnameserv -> /usr/java/jdk1.8.0_351-amd64/bin/tnameserv
lrwxrwxrwx  1 root root 49 Dec  5 08:18 tnameserv.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/tnameserv.1
lrwxrwxrwx  1 root root 42 Dec  5 08:18 unpack200 -> /usr/java/jdk1.8.0_351-amd64/bin/unpack200
lrwxrwxrwx  1 root root 49 Dec  5 08:18 unpack200.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/unpack200.1
lrwxrwxrwx  1 root root 38 Dec  5 08:18 wsgen -> /usr/java/jdk1.8.0_351-amd64/bin/wsgen
lrwxrwxrwx  1 root root 45 Dec  5 08:18 wsgen.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/wsgen.1
lrwxrwxrwx  1 root root 41 Dec  5 08:18 wsimport -> /usr/java/jdk1.8.0_351-amd64/bin/wsimport
lrwxrwxrwx  1 root root 48 Dec  5 08:18 wsimport.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/wsimport.1
lrwxrwxrwx  1 root root 36 Dec  5 08:18 xjc -> /usr/java/jdk1.8.0_351-amd64/bin/xjc
lrwxrwxrwx  1 root root 43 Dec  5 08:18 xjc.1 -> /usr/java/jdk1.8.0_351-amd64/man/man1/xjc.1

这个对应的就是jdk的安装地址了。
查找/etc/alternatives目录是做什么的，发现alternatives这个命令。