I am installing Apache Solr on Linux Debian (Squeeze). I have been instructed to install sun-java jdk 1st. Then am told that I should use the command sudo update-alternatives --config java to make sure that a particular java (sun-java) is the default runtime. Yet when I run this command I get:

There are 3 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 auto mode 1 /usr/bin/gij-4.4 1044 manual mode 2 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 manual mode 3 /usr/lib/jvm/java-6-sun/jre/bin/java 63 manual mode Press enter to keep the current choice[*], or type selection number: 

So which number should I select to have sun-java as the default runtime? Also, what exactly do th auto and manual modes mean? If I select 3 above and run the update-alternative command I receive the same output as above, again nothing seems to have changed except that the * is now in front of the 3, though it still reads manual mode.

Is there a way to confirm that what I have done is correct?

10 Answers

You will notice a big change when selecting options if you type in "java -version" after doing so. So if you run update-alternatives --config java and select option 3, you will be using the Sun implementation.
Also, with regards to auto vs manual mode, making a selection should take it out of auto mode per this page stating:

When using the --config option, alternatives will list all of the choices for the link group of which given name is the master link. You will then be prompted for which of the choices to use for the link group. Once you make a change, the link group will no longer be in auto mode. You will need to use the --auto option in order to return to the automatic state.

And I believe auto mode is set when you install the first/only JRE/JDK.

Assuming one has installed a JDK in /opt/java/jdk1.8.0_144 then:

1. Install the alternative for javac

   $ sudo update-alternatives --install /usr/bin/javac javac /opt/java/jdk1.8.0_144/bin/javac 1 

2. Check / update the alternatives config:

   $ sudo update-alternatives --config javac 

If there is only a single alternative for javac you will get a message saying so, otherwise select the option for the new JDK.

To check everything is setup correctly then:

$ which javac /usr/bin/javac $ ls -l /usr/bin/javac lrwxrwxrwx 1 root root 23 Sep 4 17:10 /usr/bin/javac -> /etc/alternatives/javac $ ls -l /etc/alternatives/javac lrwxrwxrwx 1 root root 32 Sep 4 17:10 /etc/alternatives/javac -> /opt/java/jdk1.8.0_144/bin/javac 

And finally

$ javac -version javac 1.8.0_144 

Repeat for java, keytool, jar, etc as needed.

update-alternatives is problematic in this case as it forces you to update all the elements depending on the JDK.

For this specific purpose, the package java-common contains a tool called update-java-alternatives.

It's straightforward to use it. First list the JDK installs available on your machine:

root@mylaptop:~# update-java-alternatives -l java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64 java-1.8.0-openjdk-amd64 1069 /usr/lib/jvm/java-1.8.0-openjdk-amd64 

And then pick one up:

root@mylaptop:~# update-java-alternatives -s java-1.7.0-openjdk-amd64 

This is how I install jdk

#!/bin/bash cd /opt/ sudo mkdir java sudo tar -zxvf ~/Downloads/jdk-8u192-linux-x64.tar.gz sudo ln -s jdk1.8.0_192 current for file in /opt/java/current/bin/* do if [ -x $file ] then filename=`basename $file` sudo update-alternatives --install /usr/bin/$filename $filename $file 20000 sudo update-alternatives --set $filename $file #echo $file $filename fi done 

I'm using Ubuntu 18.04 LTS. Most of the time, when I change my java version, I also want to use the same javac version.
I use update-alternatives this way, using a java_home alternative instead :

Installation

Install every java version in /opt/java/<version>, for example

~$ ll /opt/java/ total 24 drwxr-xr-x 6 root root 4096 jan. 22 21:14 ./ drwxr-xr-x 9 root root 4096 feb. 7 13:40 ../ drwxr-xr-x 8 stephanecodes stephanecodes 4096 jan. 8 2019 jdk-11.0.2/ drwxr-xr-x 7 stephanecodes stephanecodes 4096 dec. 15 2018 jdk1.8.0_201/ 

Configure alternatives

~$ sudo update-alternatives --install /opt/java/current java_home /opt/java/jdk-11.0.2/ 100 ~$ sudo update-alternatives --install /opt/java/current java_home /opt/java/jdk1.8.0_201 200 

Declare JAVA_HOME (In this case, I use a global initialization script for this)

~$ sudo sh -c 'echo export JAVA_HOME=\"/opt/java/current\" >> environment.sh' 

Log Out or restart Ubuntu (this will reload /etc/profile.d/environment.sh)

Usage

Change java version

Choose the version you want to use

~$ sudo update-alternatives --config java_home There are 2 choices for the alternative java_home (providing /opt/java/current). Selection Path Priority Status ------------------------------------------------------------ 0 /opt/java/jdk-11.0.2 200 auto mode 1 /opt/java/jdk-11.0.2 200 manual mode * 2 /opt/java/jdk1.8.0_201 100 manual mode Press <enter> to keep the current choice[*], or type selection number: 

Check version

~$ java -version openjdk version "11.0.2" 2019-01-15 OpenJDK Runtime Environment 18.9 (build 11.0.2+9) OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode) ~$ javac -version javac 11.0.2 

Tip

Add the following line to ~/.bash_aliases file :

alias change-java-version="sudo update-alternatives --config java_home && java -version && javac -version" 

Now use the change-java-version command to change java version

There are many other binaries that need to be linked so I think it's much better to try something like sudo update-alternatives --all and choosing the right alternatives for everything else besides java and javac.

If you want to switch the jdk on a regular basis (or update to a new one once it is released), it's very conveniant to use sdkman.

You can additional tools like maven with sdkman, too.

Have a look at At the bottom of this page an other method is descibed using a command from the java-common package

I have 2 versions of java Installed on my AWS EC2 instance; java 8 & 11 but couponservice-0.0.1-SNAPSHOT.jar file needs java 11 to run because this .jar file was created using java 11.

[root@ip-172-31-94-132 ~]# alternatives --config java

There are 2 programs which provide 'java'.

Selection Command

• 1 java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.302.b08-0.amzn2.0.1.x86_64/jre/bin/java)

• 2 /usr/java/jdk-11.0.12/bin/java

Enter to keep the current selection[+], or type selection number: 2

[root@ip-172-31-94-132 ~]# java -version

java version "11.0.12" 2021-07-20 LTS Java(TM) SE Runtime Environment 18.9 (build 11.0.12+8-LTS-237) Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.12+8-LTS-237, mixed mode)

Now you can run .jar file specific to

[root@ip-172-31-94-132 ~]# java -jar couponservice-0.0.1-SNAPSHOT.jar

Reference:-

After installing any open jdk simply run and select your desired jdk:

sudo update-alternatives --config java