Introduction
This page is based on experience of setting up Java 8 on Ubuntu 14.04. Much of it may be applicable to other Java versions and distros.
Architecture
First we check which architecture we are running on.
Open a terminal and type the command :
arch
The output could be i686 or i386 for a 32 bits system or x86_64 for a 64 bits system.
Environment
No JVM
On a machine without any defined java, it will look like this. The update-alternatives doesn't display any defined alternatives:
user@machine:~$ update-alternatives --get-selections | grep java lucli auto /usr/lib/liblucene2-java/lucli
If you try to run java, it doesn't run successfully:
user@machine:~$ java -version The program 'java' can be found in the following packages: * default-jre * gcj-4.8-jre-headless * openjdk-7-jre-headless * gcj-4.6-jre-headless * openjdk-6-jre-headless Try: sudo apt-get install <selected package>
The next test will be to use the update-java-alternatives command, to check if we have some installed JVM:
user@machine:~$ sudo update-java-alternatives -l default-java 1073 /usr/lib/jvm/default-java java-1.8.0-openjdk-i386 1069 /usr/lib/jvm/java-1.8.0-openjdk-i386 java-8-openjdk-i386 1069 /usr/lib/jvm/java-8-openjdk-i386 java-8-oracle 1070 /usr/lib/jvm/java-8-oracle ramdisk-java-8-oracle 1073 /usr/lib/jvm/ramdisk-java-8-oracle
Hopefully in this example some existing JVM are installed however the JVM setup seems to be broken. Check your Java Environment then Install one.
If no existing JVM are installed, install Oracle JDK or Open JDK.
Current JVM
user@machine$ java -version java version "1.8.0_91" Java(TM) SE Runtime Environment (build 1.8.0_91-b14) Java HotSpot(TM) Server VM (build 25.91-b14, mixed mode)
The previous command shows us that we have a running java on our system.
user@machine$ which java /usr/bin/java
The previous command shows us that we are running a java command from /usr/bin.
Let's see where is the java command:
user@machine$ ls -al /usr/bin/java lrwxrwxrwx 1 root root 22 Mar 12 2013 /usr/bin/java -> /etc/alternatives/java
As you can see the java command from /usr/bin is a symlink and will be resolved against the java command contained in /etc/alternatives.
user@machine$ file /etc/alternatives/java /etc/alternatives/java: symbolic link to `/usr/lib/jvm/ramdisk-java-8-oracle/jre/bin/java'
The previous command shows us where lies the java command and hopefully the directory /usr/lib/jvm/ramdisk-java-8-oracle/jre/bin contains the real java command.
user@machine$ ls -al /usr/lib/jvm/ramdisk-java-8-oracle/jre/bin/java -rwxr-xr-x 1 root root 5730 May 4 10:54 /usr/lib/jvm/ramdisk-java-8-oracle/jre/bin/java
Update Alternatives
On Ubuntu 14.04 the Java commands are under the /usr/bin and /etc/alternatives directories.
Both directories expose all the Java commands and tools as symlinks and as such whem runned are resolved against the standard /usr/bin directory who usually populates the $PATH environment variable.
However in order to manage multiple version of Java the update-alternatives mechanism has been introduced. It allows multiple "providers" to be installed on the same machine, and configures which is the default.
This mechanism consists of two directories, /etc/alternatives who contains the symlinks and /var/lib/dpkg/alternatives who contains update-alternatives state information and a update-alternatives command.
Now take a look in the file /var/lib/dpkg/alternatives/java:
manual /usr/bin/java java.1.gz /usr/share/man/man1/java.1.gz /usr/lib/jvm/java-8-openjdk-i386/jre/bin/java 1069 /usr/lib/jvm/java-8-openjdk-i386/jre/man/man1/java.1.gz /usr/lib/jvm/java-8-oracle/jre/bin/java 1070 /usr/lib/jvm/java-8-oracle/man/man1/java.1.gz /usr/lib/jvm/ramdisk-java-8-oracle/jre/bin/java 1073
That file teaches us that there are several java command installed on this machine.
The following command shows the current alternatives configuration. This command helps to ensure that the default-java we defined will resolved the correct commands, tools and libraries.
user@machine:~$ update-alternatives --get-selections | grep java appletviewer manual /usr/lib/jvm/default-java/bin/appletviewer extcheck manual /usr/lib/jvm/default-java/bin/extcheck firefox-javaplugin.so auto /usr/lib/jvm/default-java/jre/lib/i386/libnpjp2.so idlj manual /usr/lib/jvm/default-java/bin/idlj itweb-settings auto /usr/lib/jvm/default-java/jre/bin/itweb-settings jar manual /usr/lib/jvm/default-java/bin/jar jarsigner manual /usr/lib/jvm/default-java/bin/jarsigner java manual /usr/lib/jvm/default-java/jre/bin/java javac manual /usr/lib/jvm/default-java/bin/javac javadoc manual /usr/lib/jvm/default-java/bin/javadoc javah manual /usr/lib/jvm/default-java/bin/javah javap manual /usr/lib/jvm/default-java/bin/javap javaws auto /usr/lib/jvm/java-6-openjdk-i386/jre/bin/javaws jcmd manual /usr/lib/jvm/default-java/bin/jcmd jconsole manual /usr/lib/jvm/default-java/bin/jconsole jdb manual /usr/lib/jvm/default-java/bin/jdb jdeps manual /usr/lib/jvm/default-java/bin/jdeps jexec manual /usr/lib/jvm/default-java/jre/lib/jexec jhat manual /usr/lib/jvm/default-java/bin/jhat jinfo manual /usr/lib/jvm/default-java/bin/jinfo jjs manual /usr/lib/jvm/default-java/jre/bin/jjs jmap manual /usr/lib/jvm/default-java/bin/jmap jps manual /usr/lib/jvm/default-java/bin/jps jrunscript manual /usr/lib/jvm/default-java/bin/jrunscript jsadebugd manual /usr/lib/jvm/default-java/bin/jsadebugd jstack manual /usr/lib/jvm/default-java/bin/jstack jstat manual /usr/lib/jvm/default-java/bin/jstat jstatd manual /usr/lib/jvm/default-java/bin/jstatd keytool manual /usr/lib/jvm/default-java/jre/bin/keytool lucli auto /usr/lib/liblucene2-java/lucli native2ascii manual /usr/lib/jvm/default-java/bin/native2ascii orbd manual /usr/lib/jvm/default-java/jre/bin/orbd pack200 manual /usr/lib/jvm/default-java/jre/bin/pack200 policytool manual /usr/lib/jvm/default-java/jre/bin/policytool rmic manual /usr/lib/jvm/default-java/bin/rmic rmid manual /usr/lib/jvm/default-java/jre/bin/rmid rmiregistry manual /usr/lib/jvm/default-java/jre/bin/rmiregistry schemagen manual /usr/lib/jvm/default-java/bin/schemagen serialver manual /usr/lib/jvm/default-java/bin/serialver servertool manual /usr/lib/jvm/default-java/jre/bin/servertool tnameserv manual /usr/lib/jvm/default-java/jre/bin/tnameserv unpack200 manual /usr/lib/jvm/default-java/jre/bin/unpack200 wsgen manual /usr/lib/jvm/default-java/bin/wsgen wsimport manual /usr/lib/jvm/default-java/bin/wsimport xjc manual /usr/lib/jvm/default-java/bin/xjc
Update Java Alternatives
Known JVMs
The update-alternatives command shows the installed JVM on a command name basis:
user@machine:~$ update-alternatives --list java /usr/lib/jvm/default-java/jre/bin/java
The update-java-alternatives command shows the installed JVMs and their respective priority number.
user@machine$ update-java-alternatives -l default-java 1073 /usr/lib/jvm/default-java java-1.8.0-openjdk-i386 1069 /usr/lib/jvm/java-1.8.0-openjdk-i386 java-8-openjdk-i386 1069 /usr/lib/jvm/java-8-openjdk-i386 java-8-oracle 1070 /usr/lib/jvm/java-8-oracle ramdisk-java-8-oracle 1073 /usr/lib/jvm/ramdisk-java-8-oracle
Java Layout
Java Installation Directory
Either the Open JDK or the Oracle JDK install their environment below /usr/lib/jvm:
user@machine:/usr/lib/jvm$ ls -al total 100 drwxr-xr-x 5 root root 4096 Jul 11 12:07 . drwxr-xr-x 205 root root 53248 Jul 7 09:33 .. lrwxrwxrwx 1 root root 34 Jul 7 15:33 default-java -> /usr/lib/jvm/ramdisk-java-8-oracle lrwxrwxrwx 1 root root 41 Jul 7 15:34 .default-java.jinfo -> /usr/lib/jvm/.ramdisk-java-8-oracle.jinfo lrwxrwxrwx 1 root root 19 Apr 22 19:41 java-1.8.0-openjdk-i386 -> java-8-openjdk-i386 -rw-r--r-- 1 root root 3083 Jul 11 11:49 .java-1.8.0-openjdk-i386.jinfo drwxr-xr-x 7 root root 4096 Apr 25 12:34 java-8-openjdk-i386 lrwxrwxrwx 1 root root 30 Apr 25 12:39 .java-8-openjdk-i386.jinfo -> .java-1.8.0-openjdk-i386.jinfo drwxr-xr-x 8 root root 4096 May 4 10:55 java-8-oracle -rw-r--r-- 1 root root 3135 Jul 11 11:48 .java-8-oracle.jinfo drwxr-xr-x 2 root root 4096 Apr 25 12:42 openjdk-8 lrwxrwxrwx 1 root root 20 Jul 7 11:46 ramdisk-java-8-oracle -> /media/java-8-oracle -rw-r--r-- 1 root root 3563 Jul 11 11:47 .ramdisk-java-8-oracle.jinfo
Beyond the various directories, files and links in the /usr/lib/jvm directory several remarks need to be done.
The default-java symlink
First of all we use the debian layout by setting up the default-java symlink. Tomcat or Eclipse are tools who use the default-java symlink.
We see in the previous output that the default-java point to a ramdisk-java-8-oracle who is a local symlink who points to another directory.
Then setup the default-java symlink to your default JVM
cd /usr/lib/jvm sudo ln -s ramdisk-java-8-oracle default-java
The .jinfo file
Second we see .jinfo files, one per JDK installed. In our example we have three different JVM and we see their respective .jinfo files.
Let's see the content of the .java-8-oracle.jinfo:
name=java-8-oracle alias=java-8-oracle priority=1070 section=main jre ControlPanel /usr/lib/jvm/java-8-oracle/jre/bin/ControlPanel jre java /usr/lib/jvm/java-8-oracle/jre/bin/java jre javaws /usr/lib/jvm/java-8-oracle/jre/bin/javaws jre jcontrol /usr/lib/jvm/java-8-oracle/jre/bin/jcontrol jre jjs /usr/lib/jvm/java-8-oracle/jre/bin/jjs jre keytool /usr/lib/jvm/java-8-oracle/jre/bin/keytool jre orbd /usr/lib/jvm/java-8-oracle/jre/bin/orbd jre pack200 /usr/lib/jvm/java-8-oracle/jre/bin/pack200 jre policytool /usr/lib/jvm/java-8-oracle/jre/bin/policytool jre rmid /usr/lib/jvm/java-8-oracle/jre/bin/rmid jre rmiregistry /usr/lib/jvm/java-8-oracle/jre/bin/rmiregistry jre servertool /usr/lib/jvm/java-8-oracle/jre/bin/servertool jre tnameserv /usr/lib/jvm/java-8-oracle/jre/bin/tnameserv jre unpack200 /usr/lib/jvm/java-8-oracle/jre/bin/unpack200 jre jexec /usr/lib/jvm/java-8-oracle/jre/lib/jexec jdk appletviewer /usr/lib/jvm/java-8-oracle/bin/appletviewer jdk extcheck /usr/lib/jvm/java-8-oracle/bin/extcheck jdk idlj /usr/lib/jvm/java-8-oracle/bin/idlj jdk jar /usr/lib/jvm/java-8-oracle/bin/jar jdk jarsigner /usr/lib/jvm/java-8-oracle/bin/jarsigner jdk javac /usr/lib/jvm/java-8-oracle/bin/javac jdk javadoc /usr/lib/jvm/java-8-oracle/bin/javadoc jdk javafxpackager /usr/lib/jvm/java-8-oracle/bin/javafxpackager jdk javah /usr/lib/jvm/java-8-oracle/bin/javah jdk javap /usr/lib/jvm/java-8-oracle/bin/javap jdk javapackager /usr/lib/jvm/java-8-oracle/bin/javapackager jdk jcmd /usr/lib/jvm/java-8-oracle/bin/jcmd jdk jconsole /usr/lib/jvm/java-8-oracle/bin/jconsole jdk jdb /usr/lib/jvm/java-8-oracle/bin/jdb jdk jdeps /usr/lib/jvm/java-8-oracle/bin/jdeps jdk jhat /usr/lib/jvm/java-8-oracle/bin/jhat jdk jinfo /usr/lib/jvm/java-8-oracle/bin/jinfo jdk jmap /usr/lib/jvm/java-8-oracle/bin/jmap jdk jmc /usr/lib/jvm/java-8-oracle/bin/jmc jdk jps /usr/lib/jvm/java-8-oracle/bin/jps jdk jrunscript /usr/lib/jvm/java-8-oracle/bin/jrunscript jdk jsadebugd /usr/lib/jvm/java-8-oracle/bin/jsadebugd jdk jstack /usr/lib/jvm/java-8-oracle/bin/jstack jdk jstat /usr/lib/jvm/java-8-oracle/bin/jstat jdk jstatd /usr/lib/jvm/java-8-oracle/bin/jstatd jdk jvisualvm /usr/lib/jvm/java-8-oracle/bin/jvisualvm jdk native2ascii /usr/lib/jvm/java-8-oracle/bin/native2ascii jdk rmic /usr/lib/jvm/java-8-oracle/bin/rmic jdk schemagen /usr/lib/jvm/java-8-oracle/bin/schemagen jdk serialver /usr/lib/jvm/java-8-oracle/bin/serialver jdk wsgen /usr/lib/jvm/java-8-oracle/bin/wsgen jdk wsimport /usr/lib/jvm/java-8-oracle/bin/wsimport jdk xjc /usr/lib/jvm/java-8-oracle/bin/xjc plugin xulrunner-1.9-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin firefox-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin iceape-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin iceweasel-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin mozilla-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin midbrowser-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so plugin xulrunner-javaplugin.so /usr/lib/jvm/java-8-oracle/jre/lib/i386/libnpjp2.so
As you can see this file contains the description of each java tools, either jre, jdk or plugin tools are associated with a particular command or library.
In case the jinfo file doesn't exist, create one with the previous content and adjust paths accordingly.
The priority value needs to be unique among the JVM installations. Choose a priority number who do not collapse an existing one.
Then setup the .default-java.jinfo symlink to your default JVM.
cd /usr/lib/jvm sudo ln -s .ramdisk-java-8-oracle.jinfo .default-java.jinfo