Red Hat Knowledgebase

Red Hat Enterprise Linux now comes with two different implementations of Java™, IBM's 1.4.2 Java release and BEA's JRockit 1.4.2_04.

These new Java™ packages use the alternatives system to abstract the locations and "brands" of your Java™ runtimes and are designed to eliminate the need for environment tweaking.

For example, the Java™ runtimes are now put in:

  
    /usr/lib/jvm/java-[version]-[vendor]-[release]/bin/java
    ie:  /usr/lib/jvm/java-1.4.2-ibm-1.4.2.0/bin/java

However, instead of pointing to:

/usr/lib/jvm/java-1.4.2-ibm-1.4.2.0/bin/java

which could be out of date or replaced by a different Java™ implementations, there is a symbolic link from:

/usr/bin/java -> /etc/alternatives/java

Since java and javac are available in /usr/bin and the java plugin is installed in the proper location, there is no need to set up your $JAVA_HOME and add $JAVA_HOME/bin to the $PATH, like you had to in the past.

The alternatives directory contains a symbolic link to the actual location of the Java™ runtimes.

    /etc/alternatives/java ->
    /usr/lib/jvm/java-1.4.2-ibm-1.4.2.0/bin/java

The alternatives system automatically maintains the current links on a priority based system. If the default is not desirable, then you can manually set the symlinks to a lower-priority alternative.

This configuration adds a layer of abstraction so you can update, switch versions, and/or switch vendors with out breaking applications.

For more information on the alternatives system see the man page for alternatives, man alternatives from the command line.